www.advmat.de www.MaterialsViews.com
Zheyi Meng, Han Bao, Jingtao Wang, Chendi Jiang, Minghui Zhang, Jin Zhai,* and Lei Jiang In living organisms, biological ion channels open and close in response to various stimuli from surroundings to regulate ionic exchange through the cell membrane.[1] But natural ion channels can only function in a fragile environment (the lipid bilayer), which limits their applications. Inspired by nature, many abiotic nanogating devices, which are called artificial ion channels, have been synthesized, such as mesostructured silica,[2] alumina,[3] or titania[4] nanochannel arrays, track-etching polymer films,[5] quartz nanopipettes,[6] colloidal composite films,[7] carbon nanotubes,[8] ion- or electron-beametched silicon nitride and oxide films,[9] etc. They control fluids through them in nanoconfined geometries. The polyethylene terephthalate (PET) nanoporous membrane is a kind of artificial polymeric ion channels. Due to the regular shape of the nanochannel, the narrow distribution of the channel size and the available surface group for modification,[10] the PET nanochannel has applied to fabricate various nanogating devices to respond to a single stimulus, such as pH,[11] temperature,[12] specific ions[13] or biomolecules,[14] or to dual stimuli, such as pH and light.[15] In recent years, single or multiple PET nanochannels have been applied in energy conversion systems. In these systems, PET nanochannels regulate the process of the conversion from mechanical energy,[16] light,[17] concentration gradient,[18] etc., towards electricity, with their specific ionic transportation properties. On the chloroplast thylakoid membrane (or photosynthesis membrane) of green plant leaves, ion channel proteins[19] control the photoelectrical conversion of the photosynthesis according to the ever-changing environment by regulating ion transports across the membrane.[20] Here, inspired by the function of natural ion channels on the photosynthesis membrane, we introduce the PET membrane with conical nanochannel arrays into a photoelectrical conversion system to regulate the light-induced ionic current (Figure 1). In this system, photosystem II (PSII) complexes were applied as the ‘pump’ to convert light into ionic currents. The PSII complex is a kind of natural photoelectrical conversion materials extracted from Prof. J. Zhai, Prof. L. Jiang, Z. Meng, J. Wang, C. Jiang, M. Zhang Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education School of Chemistry and Environment Beihang University Beijing 100191, P. R. China E-mail: [email protected] Dr. H. Bao College of Arts and Science Oklahoma State University Stillwater, OK, 74078, USA
DOI: 10.1002/adma.201304755
Adv. Mater. 2014, 26, 2329–2334
green plants and some certain bacteria. In recent several decades, extensive research efforts were directed to the application of the native PSII in photovoltaic devices,[21] or to the development of artificial photosynthesis devices mimicking the mechanism of PSII.[22] As an important component in the photosynthesis, PSII could absorb visible light and split water to generate oxygen[23] and drive concerted proton-electron transfers,[24] which lead to the separate ionic and electron flows in the photosynthesis membrane. But in previous PSII photoelectrical conversion devices, the photocurrents were often controlled by external factors, like the illumination intensity[25] or wavelength.[26] With the charged inner surface and the asymmetry in shape, PET conical nanochannels could selectively handle molecular or ion species in fluid.[27] PET conical nanochannel arrays could perform the ionic current rectification equivalently with the single channel and conduct larger transmembrane ionic currents than the single one could. So, the PET membrane with conical nanochannel arrays was chosen as the ‘valve’ to regulate the ionic current produced in the system. The PSII complex applied in the experiments is extracted from the chloroplast thylakoid membranes of spinach leaves (details in Supporting Information 1). Its function of oxygen evolution has been studied in previous researches.[28] PET multiporous membranes were fabricated by the asymmetric tracketching method. The diameters of the base (the larger opening of the channel) are in the hundred nanometer scale, and the diameters of the tip (the smaller opening) are 20–30 nm or smaller (Supporting Information 2, Figure S2). The size of the tip is smaller than that of PSII complex particles,[29] so ions can permeate the PET membrane, but PSII particles cannot. For the single conical nanochannel, the size of the tip is a geometric parameter to reflect the conductance of the channel in electrolyte solutions. For conical nanochannel arrays, the conductance mainly depends on both the number and the tip size of open channels after etching.[27b] In order to reflect the two factors by a single geometric parameter, the permeability area (PA) of the membrane was defined to evaluate the conductance of the membrane. The PA means the actual area per square centimeter on the membrane for ions to permeate. It depends on the number and the size of open channels and can be calculated by the ionic conductance in 1 M KCl (pH = 7) under 1 V voltage (see the Experimental Section). The light-induced ionic current (or photocurrent) of the PECS was measured in a custom-designed conductivity cell. The conductivity cell was composed of two chambers, and the PET membrane was located between them (Figure 1). The measurement electrodes were both Ag/AgCl electrodes. The anode and cathode were placed in the two chambers separately. Both chambers were filled with the same 2-mercaptoethane sulfonic acid (MES) – NaOH buffer solution (pH = 6.5),
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
COMMUNICATION
Artificial Ion Channels Regulating Light-Induced Ionic Currents in Photoelectrical Conversion Systems
2329
www.advmat.de
COMMUNICATION
www.MaterialsViews.com
Figure 1. The natural ion channel on the thylakoid membrane of green plant leaves (top) and the artificial ion channel in the photoelectrical conversion system (PECS; bottom). The function of the PET multiporous membrane in the PECS is regulating the photocurrent by regulating ion transport, the same with that in the natural counterpart. PSII complexes act as the ionic flow resource in both of the two systems.
and in the anode chamber, the solution was containing PSII complexes (32 μg Chl mL−1). The concentration of PSII also affects the photocurrent responses (details in Supporting Information 3), and we choose this concentration to supply ample light-responsible reaction centers. The illumination applied in the experiments was white light (100 mW cm−2) to mimic the natural sunlight. Figure 2a illustrates the typical photocurrent response of the PECS upon a cyclic ‘ON-OFF’ illumination, and the PA of the PET membrane applied here is 2.07 μm2 cm−2. The illumination cycle was set to last 30 s and repetitive to testify whether the photocurrent of the PECS is stable and repeatable. In Figure 2a, the photocurrent produced by the system is ca. 0.20 nA and keeps stable under irradiation. The positive photocurrent indicates that the direction of the anion flow is from the cathode chamber to the anode chamber and the cations move in the opposite direction. After the irradiation was shut down, the photocurrent returned to zero. And when PSII particles were removed from the system, no photocurrent was generated. It reveals that the PSII is the resource of the lightinduced ionic current. In Figure 2b, when the multiporous membrane was removed from the system, the current in the ‘ON–OFF’ illumination circles fluctuated violently and performs irregular. It indicates the PET nanochannel arrays regulate the light-induce ionic transport directly. The photocurrent response could also be performed by the current–voltage (I–V) curve in the ‘ON–OFF’ illumination (Supporting Information 4), but the response was not obvious. Thus, we choose the current–time (I–t) curve to reflect the generation and regulation of photocurrents.
2330
wileyonlinelibrary.com
The generation of the photocurrents could be explained by the light-induced concerted proton–electron transfer in PSII and the ionic transportation characters of the nanochannels. In the anode chamber (Figure 2c), light drives the splitting of water to molecular oxygen, protons and reductive equivalents in PSII[25] Equation 1: 2H2 O → 4H+ + O2 + 4e −
(1)
Electrons may transfer from PSII to the electrode by a certain process,[21a] and protons are accepted instantly by the basic components of MES (MES—) in the buffer solution.[24b,30] It results in the depletion of anions and the accumulation of excessive cations in the anode chamber. While in the cathode chamber, the oxidation of molecular oxygen or protons will happen to consume reductive equivalents in response to the anode reaction Equation 2: O2 + 2H2 O + 4e− → 4OH− or 2H+ + 2e− → H2
(2)
Whichever reaction happens, the result is the same: the depletion of cations and the accumulation of excessive anions in the cathode chamber. So, the light-induced ionic potential across the multiporous membrane is generated (the potential is about –0.35 mV, measuring details in Supporting Information 5). It drives the cationic migration from the anode to the cathode and the anionic migration in the opposite direction. That is the generation of the light-induce ionic current. As the nanochannel array confines the ionic flows, the generated protons
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2014, 26, 2329–2334
www.advmat.de www.MaterialsViews.com
COMMUNICATION Figure 2. a) The photocurrent of the PECS with (solid line)/without (dotted line) PSII in cyclic ‘ON–OFF’ illumination. b) The photocurrent of the PECS without the PET membrane in ‘ON–OFF’ illumination circles. c) The light-driven ionic potential produced by PSII particles and the anode chamber is at the higher potential upon illumination. d) The PA regulates the magnitude of the photocurrent. The photocurrent gets larger with the increasing of PA.
may not remove from PSII instantly and it would inhibit PSII from producing more protons.[31] So the ionic potential could be maintained on a certain level and keep the ionic current stable. Without PET nanochannels, PSII and ions diffused freely in the electrolyte cell, and generated unordered ionic currents. In the PECS, the nanochannels confines the ionic flows, thus the regulation of the photocurrent will depend on the ionic conductance through the conical nanochannel array. And for the PET membrane, the ionic conductance is governed by PA, channel direction and surface charge. Then, we focus on the influence of the three factors to the regulation of photocurrent. The PA of the membrane reflects the conductance of the nanochannels in electrolyte solutions directly. So we could change the PA to control the magnitude of the photocurrent. The photocurrents with PET membranes in four different PAs (0.237, 2.07, 38.1, and 3920 μm2 cm−2) were also measured in ‘ON–OFF’ illumination circles (Figure 2d). The photocurrents were ca. 0.065 (Figure 2d1), 0.20 (Figure 2d2), 0.83 (Figure 2d3), and 3.5 nA (Figure 2d4). From Figure 2d, we can see that the intensity of the photocurrent is dependent on the PA of the membrane. When the permeability area is small, the photocurrent is remarkably influenced by noisy signals or even inundated in them (Supporting Information 6, Figure S6a). With the increasing of the PA, the current got steady and the fluctuations of the current disappeared. There is one thing should be noted that the photocurrent produced by this system
Adv. Mater. 2014, 26, 2329–2334
will not rise endlessly with the increasing of the PA. When the PA reached the magnitude of 104 μm2 cm−2, sizes of some nanochannel tips would get very large, and PSII particles would leak out of the anode chamber through the membrane, which leaded to the drastic fluctuation of the photocurrent (Supporting Information 6, Figure S6b). For the geometric asymmetry, the PET conical nanochannels perform the ionic current rectification, which can conduct ion current preferentially in one direction and inhibits the current flow in the opposite direction. So, in the PECS, the photocurrent could also be regulated by switching of the channel direction. The photocurrents with the multiporous membrane (PA: 38.13 μm2 cm−2) in two opposite directions were measured in ‘ON/ OFF’ illumination circles (Figure 3a). When the tips of the channels were towards the anode chamber (we could call it the OPEN direction), the photocurrent (ca. 0.7 nA) was generated obviously and regularly (Figure 3a, solid line). When the tips oriented to the cathode chamber (we could call it the CLOSE direction), there were no significant photocurrent and only some weak fluctuations on the current-time curve (Figure 3a, dot line). The absolute values of the currents with the two directions under the same bias in the same buffer solution manifest the difference in the ionic conductance (Figure 3b). In the OPEN direction, the conductance was much higher than the one in the CLOSE direction. The Poisson/Nernst–Planck (PNP) model[27,32] was adopted to explain the relationship between the
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
2331
www.advmat.de
COMMUNICATION
www.MaterialsViews.com
Figure 3. a) The direction of the channels regulates the photocurrent in the PECS. The PA of the membrane is 38.1 μm2 cm−2. When channel tips oriented to the anode, remarkable photocurrents were generated (solid line). And when channel tips directed to the cathode, no obvious phenomenon was induced (dot line). b) The I–V curves of the unmodified channels in the buffer solution reflect the conductance in different directions. When the tips were placed at the anode, the conductance is higher than the one in the opposite direction. c) The theoretical calculated cation (solid line) and anion (dotted line) distribution curves under the bias of 1 V in the conical channel in two directions: the upper one, the tip was placed towards the anode; the lower one, the tip was placed towards the cathode. The tip side was considered as the zero point along the pore axis and it was the same in Figure 3f. d) The influence of the surface charge to the photocurrent. The PA of the membrane is 10.2 μm2. The photocurrents turned from ca. 0.23 (solid line) to 0.04 nA (dot line). e) The I–V curves of the channels before (solid line) and after (dot line) modification in the buffer solution. When the negative groups on the channel surface were replaced by neutral ones, the conductance in the conical channel decreased under negative voltages. f) The theoretical calculated cation (solid line) and anion (dot line) distribution curves under the bias of 1 V in the conical channel with two surface charge densities: the upper one, 1 e nm−2; the lower one, 0.5 e nm−2.
ionic current and the channel direction (Supporting Information 7). Theoretical ion distributions in the conical nanochannel along the pore axis were calculated to explain the ionic conductance change quantitatively (Figure 3c). In the OPEN direction, the concentrations of anions and cations in the channel were higher than the ones in the bulk. While in the CLOSE direction, the ionic concentrations in the channel were lower than the ones in the bulk. The ion distribution difference in the two directions means the significant conductance difference, which led to the change of the photocurrent. For membranes with various PA, the regulation of the channel array may result in the ON–OFF or the magnitude change of the photocurrent (Supporting Information 8). Surface charge of conical nanochannels induce electrostatic screening and electrokinetic effects that may also have large effects on the channel conductance and the photocurrent.[27a,32] The track-etched PET nanochannels have carboxyls (–COOH) on the surface. When exposed to solutions whose pH are
2332
wileyonlinelibrary.com
larger than 3, these carboxyls are deprotonated to carboxylate ions (–COO−).[5a] So the surface of these nanochannels is negative in the MES–NaOH buffer (pH = 6.5). To change surface charges, PET membranes were modified with ethylenediamine by a classical EDC–NHSS cross-linking reaction,[11b,14f ] and the modification could be verified by the corresponding I–V curve measured in the acid condition (Supporting Information 9, Figure S9). Before and after the modification, photocurrents were measured in the same condition (with the same membrane and the PA is 10.3 μm2 cm−2 before modification) to see the influence of the surface charge. The photocurrent dropped down from ca. 0.23 to 0.04 nA (Figure 3d), decreased by about 83 % after modification. Ethylenediamine is a small molecule, so the influence of the modification to the PA could be neglected. After modification, as the carboxy groups on the surface were replace by the amino groups, the negative surface would turn to neutral at pH 6.5, and the negative charge density of the channel surface declined. Coupled with that, the channel
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2014, 26, 2329–2334
www.advmat.de www.MaterialsViews.com Photocurrent Measuring: The light-responsive ion transport properties of the PECS were evaluated by measuring the ionic current through the nanochannel under exposure to cyclic ‘ON–OFF’ illumination at 30 s intervals and in an ice-water bath to preserve the activity of PSII articles. All the ionic currents in this work were measured by a Keithley 6487 picoammeter (Keithley Instruments, Cleveland, OH). Measurements of the light-induced ionic current (photocurrent) were carried out in a customdesigned conductivity cell composed of two chambers, the cathode chamber filled with the 2-mercaptoethane sulfonic acid (MES) and NaOH buffer solution (pH = 6.5) and the anode chamber filled with the same solution but containing PSII particles (PSII concentration is 32 μg Chl mL−1), separated by the PET nanochannel membrane. The effective area of the membrane contacting with solutions was 0.5 cm2. The measurement electrodes were both Ag/AgCl electrodes. Unlike previous researches, no redox mediators were applied in the photoelectrical conversion system. Current–Voltage Measuring: The ionic transportation properties of the PET membrane were studied by measuring the ionic current through unmodified and modified channels. The ionic current was measured also by the Keithley 6487 picoammeter). The PET multiporous membrane was mounted between the two chambers of the conductivity cell, and both halves of the cell were filled with the buffer solution for PSII or 0.1 M KCl. The main transmembrane potential applied in this work was a scanning voltage from –2 to +2 V, and the voltage was applied by Ag/ AgCl electrodes. Each test was repeated at least four times to obtain the average current value at different voltages.
COMMUNICATION
conductance decreased after modification under the negative bias (in Figure 3f, the tip side of the channel was set to be the negative pole of the bias). The theoretical ion distribution curves calculated by the PNP model (Supporting Information 7) with different surface charge densities (here we choose 1 and 0.5 e nm−2) could explain the effect of the surface charge on the conducting states of the nanochannels. Under the negative bias, the decrease of the negative charge density on the channel surface results in the decline of the local ionic concentrations within the channel, which inhibits the ionic transport. It should be emphasized that in all experiments of the present case, no redox mediators were applied in the photoelectrical conversion system. The system with/without a classical mediator for PSII, phenyl p-benzoquinone,[28,33] was tested under illumination, and it showed no obvious difference (Supporting Information 10, Figure S10). In summary, inspired by the structure and the function of the photosynthetic membrane in green plants, we applied the PET multiporous membrane in the PECS to functionalize as the valve of the light-induced ionic current. The artificial ion channels realize the regulation of photocurrents in the device design and the magnitude of the photocurrent is dependent on the membrane permeability area, the channel direction and the channel surface charge. Due to the controllable conductance of the channels, the PET multiporous membrane shows great potential in light-responsive sensors and photovoltaic devices with PSII, photosystem I,[34] bacteriorhodopsin,[35] and other light-responsive materials.[17]
Supporting Information Supporting Information is available from the Wiley Online Library or from the author.
Acknowledgements Experimental Section Nanochannel Fabrication: The multiporous PET membrane was fabricated by the track-etching method.[5a] PET membranes (12 μm in thickness) were purchased and had been irradiated with rapid heavy ions of intensity 1 × 108 cm−2 (GSI, Darmstadt, Germany). The asymmetry chemical etching was performed to produce conical nanochannels. The PET membrane was located between the two chambers of a conductivity cell at 35 °C, one chamber was filled with etching solution (9 M NaOH), while stopping solution (1 M KCl + 1 M HCOOH) was added in the other cell to neutralize the etchant as soon as pores opened, thus slowing down the further etching process. A voltage of 1 V was applied across the membrane to monitor the etching process. Longer time for etching leads to more open channels and larger size of channels.[36] After etching, the membrane was soaked in MilliQ water (18.2 MΩ) to remove residual salts. Permeability Area Calculating: The conductance of the PET multiporous membrane mainly depends on the number of open nanopores on it after etching and the tip radius of these open pores, and the permeability area (PA) of the membrane was defined to measure them. It means the real area per square centimeter on the membrane for ions to permeate, and can be calculated by measuring the ionic current in 1 M KCl (pH = 7) under 1 V bias with Equation 3: PA =
IL 0.5Uk (c)
(3)
This formula is derived by Ohm's law and the formula of the conductivity. I is the intensity of the light-induced ionic current, L is the length of the nanochannel, 0.5 means in this device the effective area of the membrane contacting with solutions is 0.5 cm2, U is the applied bias and it is 1 V in this condition, k(c) is the conductivity of the electrolyte, and for 1 M KCl solution at 25 °C k(c) is 0.1119 Ω−1 cm−1.
Adv. Mater. 2014, 26, 2329–2334
We thank Kefeng Wang (BUAA), Jianwei Nai (BUAA), and Dafeng Wang (PKU) for beneficial discussions. This work is supported by the National Research Fund for Fundamental Key Projects (2011CB935704, 2012CB720904), National Natural Science Foundation (21271016), Program for New Century Excellent Talents in University and Ph.D. Programs Foundation of Ministry of Education of China (30400002011127001). Received: September 22, 2013 Revised: November 18, 2013 Published online: December 17, 2013
[1] a) A. de la Escosura-Muniz, A. Merkoci, ACS Nano 2012, 6, 7556; b) E. Gouaux, R. MacKinnon, Science 2005, 310, 1461. [2] a) J. Pang, J. N. Stuecker, Y. Jiang, A. J. Bhakta, E. D. Branson, P. Li, J. Cesarano, D. Sutton, P. Calvert, C. J. Brinker, Small 2008, 4, 982; b) K. Yu, B. Smarsly, C. J. Brinker, Adv. Funct. Mater. 2003, 13, 47; c) L.-J. Cheng, L. J. Guo, Nano Lett. 2007, 7, 3165. [3] a) W. Chen, Z. Q. Wu, X. H. Xia, J. J. Xu, H. Y. Chen, Angew. Chem. Int. Ed. 2010, 49, 7943; b) N. Liu, Z. Chen, D. R. Dunphy, Y. B. Jiang, R. A. Assink, C. J. Brinker, Angew. Chem. Int. Ed. 2003, 42, 1731; c) L.-J. Cheng, L. J. Guo, ACS Nano 2009, 3, 575. [4] a) Q. Zhang, Z. Liu, X. Hou, X. Fan, J. Zhai, L. Jiang, Chem. Commun. 2012, 48, 5901; b) Y. G. Guo, J. S. Hu, H. P. Liang, L. J. Wan, C. L. Bai, Adv. Funct. Mater. 2005, 15, 196. [5] a) X. Hou, H. Zhang, L. Jiang, Angew. Chem. Int. Ed. 2012, 51, 5296; b) A. Abou Chaaya, M. Le Poitevin, S. Cabello-Aguilar, S. Balme, M. Bechelany, S. Kraszewski, F. Picaud, J. Cambedouzou, E. Balanzat, J.-M. Janot, T. Thami, P. Miele, P. Dejardin, J. Phys. Chem. C 2013, 117, 15306; c) S. b. Balme, J.-M. Janot, L. Berardo,
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
2333
www.advmat.de
COMMUNICATION
www.MaterialsViews.com
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
2334
F. o. Henn, D. Bonhenry, S. Kraszewski, F. Picaud, C. Ramseyer, Nano Lett. 2010, 11, 712; d) D. Fink, P. S. Alegaonkar, A. V. Petrov, M. Wilhelm, P. Szimkowiak, M. Behar, D. Sinha, W. R. Fahrner, K. Hoppe, L. T. Chadderton, Nucl. Instrum. Methods Phys. Res., Sect. B 2005, 236, 11. a) J. Liu, M. Kvetny, J. Feng, D. Wang, B. Wu, W. Brown, G. Wang, Langmuir 2011, 28, 1588; b) C. Wei, A. J. Bard, S. W. Feldberg, Anal. Chem. 1997, 69, 4627; c) B. Vilozny, P. Actis, R. A. Seger, Q. Vallmajo-Martin, N. Pourmand, Anal. Chem. 2011, 83, 6121; d) L.-X. Zhang, S.-L. Cai, Y.-B. Zheng, X.-H. Cao, Y.-Q. Li, Adv . Func . Mater. 2011, 21, 2103; e) N. Sa, Y. Fu, L. A. Baker, Anal . Chem . 2010, 82, 9963. a) O. Schepelina, N. Poth, I. Zharov, Adv. Funct. Mater. 2010, 20, 1962; b) R. Schmuhl, J. Sekulic, S. Roy Chowdhury, C. J. M. van Rijn, K. Keizer, A. van den Berg, J. E. ten Elshof, D. H. A. Blank, Adv. Mater. 2004, 16, 900. a) G. Pilatos, E. C. Vermisoglou, G. E. Romanos, G. N. Karanikolos, N. Boukos, V. Likodimos, N. K. Kanellopoulos, Adv. Func. Mater. 2010, 20, 2500; b) F. Fornasiero, H. G. Park, J. K. Holt, M. Stadermann, C. P. Grigoropoulos, A. Noy, O. Bakajin, Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 17250; c) J. Wu, K. Gerstandt, H. Zhang, J. Liu, B. J. Hinds, Nat. Nano. 2012, 7, 133. a) Y. H. Lanyon, G. De Marzi, Y. E. Watson, A. J. Quinn, J. P. Gleeson, G. Redmond, D. W. M. Arrigan, Anal. Chem. 2007, 79, 3048; b) U. F. Keyser, B. N. Koeleman, S. van Dorp, D. Krapf, R. M. M. Smeets, S. G. Lemay, N. H. Dekker, C. Dekker, Nat . Phys . 2006, 2, 473; c) J. Li, D. Stein, C. McMullan, D. Branton, M. J. Aziz, J. A. Golovchenko, Nature 2001, 412, 166. a) X. Hou, H. Zhang, L. Jiang, Angew. Chem. Int. Ed. 2012, 51, 5296; b) A. Kocer, L. Tauk, P. Déjardin, Biosens. Bioelectron. 2012, 38, 1; c) Z. Siwy, E. Heins, C. C. Harrell, P. Kohli, C. R. Martin, J. Am. Chem. Soc. 2004, 126, 10850. a) X. Hou, Y. Liu, H. Dong, F. Yang, L. Li, L. Jiang, Adv. Mater. 2010, 22, 2440; b) M. Ali, P. Ramirez, S. Mafé, R. Neumann, W. Ensinger, ACS Nano 2009, 3, 603. a) W. Guo, H. Xia, F. Xia, X. Hou, L. Cao, L. Wang, J. Xue, G. Zhang, Y. Song, D. Zhu, Y. Wang, L. Jiang, ChemPhysChem 2010, 11, 859; b) B. Yameen, M. Ali, R. Neumann, W. Ensinger, W. Knoll, O. Azzaroni, Small 2009, 5, 1287; c) S. Nasir, M. Ali, W. Ensinger, Nanotechnology 2012, 23, 225502. a) X. Hou, W. Guo, F. Xia, F. Q. Nie, H. Dong, Y. Tian, L. Wen, L. Wang, L. Cao, Y. Yang, J. Xue, Y. Song, Y. Wang, D. Liu, L. Jiang, J. Am. Chem. Soc. 2009, 131, 7800; b) Y. He, D. Gillespie, D. Boda, I. Vlassiouk, R. S. Eisenberg, Z. S. Siwy, J. Am. Chem. Soc. 2009, 131, 5194; c) M. Ali, S. Nasir, P. Ramirez, J. Cervera, S. Mafe, W. Ensinger, ACS Nano 2012, 6, 9247. a) N. Liu, Y. Jiang, Y. Zhou, F. Xia, W. Guo, L. Jiang, Angew. Chem. Int. Ed. 2013, 52, 2007.; b) I. Vlassiouk, T. R. Kozel, Z. S. Siwy, J. Am. Chem. Soc. 2009, 131, 8211; c) M. Ali, S. Nasir, Q. H. Nguyen, J. K. Sahoo, M. N. Tahir, W. Tremel, W. Ensinger, J. Am. Chem. Soc. 2011, 133, 17307; d) D. Fink, I. Klinkovich, O. Bukelman, R. S. Marks, A. Kiv, D. Fuks, W. R. Fahrner, L. Alfonta, Biosens. Bioelectron. 2009, 24, 2702; e) Q. H. Nguyen, M. Ali, V. Bayer, R. Neumann, W. Ensinger, Nanotechnology 2010, 21, 365701.
wileyonlinelibrary.com
[15] a) M. Zhang, X. Hou, J. Wang, Y. Tian, X. Fan, J. Zhai, L. Jiang, Adv. Mater. 2012, 24, 2424; b) L. Wen, Q. Liu, J. Ma, Y. Tian, C. Li, Z. Bo, L. Jiang, Adv. Mater. 2012, 24, 6193. [16] Y. Xie, X. Wang, J. Xue, K. Jin, L. Chen, Y. Wang, Appl. Phys. Lett. 2008, 93. [17] L. Wen, X. Hou, Y. Tian, J. Zhai, L. Jiang, Adv. Funct. Mater. 2010, 20, 2636. [18] W. Guo, L. Cao, J. Xia, F.-Q. Nie, W. Ma, J. Xue, Y. Song, D. Zhu, Y. Wang, L. Jiang, Adv. Funct. Mater. 2010, 20, 1339. [19] R. Nevo, D. Charuvi, O. Tsabari, Z. Reich, The Plant Journal 2012, 70, 157. [20] a) C. Spetea, B. Schoefs, Commun. Integr. Biol. 2010, 3, 122; b) S. Zimmermann, T. Ehrhardt, G. Plesch, B. Müller-Röber, CMLS, Cell. Mol. Life Sci. 1999, 55, 183. [21] a) M. Kato, T. Cardona, A. W. Rutherford, E. Reisner, J. Am. Chem. Soc. 2012, 134, 8332; b) F. Kopnov, I. Cohen-Ofri, D. Noy, Angew. Chem. Int. Ed. 2011, 50, 12347; c) V. Bhalla, X. Zhao, V. Zazubovich, J. Electroanal. Chem. 2011, 657, 84. [22] M. Hambourger, G. F. Moore, D. M. Kramer, D. Gust, A. L. Moore, T. A. Moore, Chem. Soc. Rev. 2009, 38, 25. [23] M. T. Giardi, E. Pace, Trends Biotechnol. 2005, 23, 257. [24] a) M. Sjödin, S. Styring, B. Åkermark, L. Sun, L. Hammarström, J. Am. Chem. Soc. 2000, 122, 3932; b) B. A. Diner, D. A. Force, D. W. Randall, R. D. Britt, Biochemistry 1998, 37, 17931. [25] O. Yehezkeli, R. Tel-Vered, J. Wasserman, A. Trifonov, D. Michaeli, R. Nechushtai, I. Willner, Nat. Commun. 2012, 3, 742. [26] M. Nagata, M. Amano, T. Joke, K. Fujii, A. Okuda, M. Kondo, S. Ishigure, T. Dewa, K. Iida, F. Secundo, Y. Amao, H. Hashimoto, M. Nango, ACS Macro Lett. 2012, 1, 296; [27] a) Z. S. Siwy, Adv. Funct. Mater. 2006, 16, 735; b) J. Cervera, B. Schiedt, R. Neumann, S. Mafe, P. Ramirez, J. Chem. Phys. 2006, 124, 104706. [28] a) H. Bao, C. Zhang, Y. Ren, J. Zhao, Biochim. Biophys. Acta, Bioenerg. 2010, 1797, 339; b) H. Bao, C. Zhang, K. Kawakami, Y. Ren, J. R. Shen, J. Zhao, Biochim. Biophys. Acta, Bioenerg. 2008, 1777, 1109. [29] J.-R. Shen, N. Kamiya, Biochemistry 2000, 39, 14739. [30] C. Costentin, M. Robert, J.-M. Savéant, J. Am. Chem. Soc. 2007, 129, 5870. [31] a) T. Shutova, H. Kenneweg, J. Buchta, J. Nikitina, V. Terentyev, S. Chernyshov, B. Andersson, S. I. Allakhverdiev, V. V. Klimov, H. Dau, W. Junge, G. Samuelsson, EMBO J 2008, 27, 782; b) H. Ishikita, A. V. Soudackov, S. Hammes-Schiffer, J. Am. Chem. Soc. 2007, 129, 11146. [32] L.-J. Cheng, L. J. Guo, Chem. Soc. Rev. 2010, 39, 923. [33] F. Müh, C. Glöckner, J. Hellmich, A. Zouni, Biochim. Biophys. Acta, Bioenerg. 2012, 1817, 44. [34] S. C. Tan, L. I. Crouch, M. R. Jones, M. Welland, Angew. Chem. Int. Ed. 2012, 51, 6667. [35] a) N. K. Allam, C.-W. Yen, R. D. Near, M. A. El-Sayed, Energy Environ. Sci. 2011, 4, 2909; b) C. W. Yen, L. K. Chu, M. A. El-Sayed, J. Am. Chem. Soc. 2010, 132, 7250. [36] O. L. Orelovich, B. A. Sartowska, A. Presz, P. Y. Apel, J. Microsc. 2010, 237, 404.
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2014, 26, 2329–2334
Zheyi Meng, Han Bao, Jingtao Wang, Chendi Jiang, Minghui Zhang, Jin Zhai,* and Lei Jiang In living organisms, biological ion channels open and close in response to various stimuli from surroundings to regulate ionic exchange through the cell membrane.[1] But natural ion channels can only function in a fragile environment (the lipid bilayer), which limits their applications. Inspired by nature, many abiotic nanogating devices, which are called artificial ion channels, have been synthesized, such as mesostructured silica,[2] alumina,[3] or titania[4] nanochannel arrays, track-etching polymer films,[5] quartz nanopipettes,[6] colloidal composite films,[7] carbon nanotubes,[8] ion- or electron-beametched silicon nitride and oxide films,[9] etc. They control fluids through them in nanoconfined geometries. The polyethylene terephthalate (PET) nanoporous membrane is a kind of artificial polymeric ion channels. Due to the regular shape of the nanochannel, the narrow distribution of the channel size and the available surface group for modification,[10] the PET nanochannel has applied to fabricate various nanogating devices to respond to a single stimulus, such as pH,[11] temperature,[12] specific ions[13] or biomolecules,[14] or to dual stimuli, such as pH and light.[15] In recent years, single or multiple PET nanochannels have been applied in energy conversion systems. In these systems, PET nanochannels regulate the process of the conversion from mechanical energy,[16] light,[17] concentration gradient,[18] etc., towards electricity, with their specific ionic transportation properties. On the chloroplast thylakoid membrane (or photosynthesis membrane) of green plant leaves, ion channel proteins[19] control the photoelectrical conversion of the photosynthesis according to the ever-changing environment by regulating ion transports across the membrane.[20] Here, inspired by the function of natural ion channels on the photosynthesis membrane, we introduce the PET membrane with conical nanochannel arrays into a photoelectrical conversion system to regulate the light-induced ionic current (Figure 1). In this system, photosystem II (PSII) complexes were applied as the ‘pump’ to convert light into ionic currents. The PSII complex is a kind of natural photoelectrical conversion materials extracted from Prof. J. Zhai, Prof. L. Jiang, Z. Meng, J. Wang, C. Jiang, M. Zhang Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education School of Chemistry and Environment Beihang University Beijing 100191, P. R. China E-mail: [email protected] Dr. H. Bao College of Arts and Science Oklahoma State University Stillwater, OK, 74078, USA
DOI: 10.1002/adma.201304755
Adv. Mater. 2014, 26, 2329–2334
green plants and some certain bacteria. In recent several decades, extensive research efforts were directed to the application of the native PSII in photovoltaic devices,[21] or to the development of artificial photosynthesis devices mimicking the mechanism of PSII.[22] As an important component in the photosynthesis, PSII could absorb visible light and split water to generate oxygen[23] and drive concerted proton-electron transfers,[24] which lead to the separate ionic and electron flows in the photosynthesis membrane. But in previous PSII photoelectrical conversion devices, the photocurrents were often controlled by external factors, like the illumination intensity[25] or wavelength.[26] With the charged inner surface and the asymmetry in shape, PET conical nanochannels could selectively handle molecular or ion species in fluid.[27] PET conical nanochannel arrays could perform the ionic current rectification equivalently with the single channel and conduct larger transmembrane ionic currents than the single one could. So, the PET membrane with conical nanochannel arrays was chosen as the ‘valve’ to regulate the ionic current produced in the system. The PSII complex applied in the experiments is extracted from the chloroplast thylakoid membranes of spinach leaves (details in Supporting Information 1). Its function of oxygen evolution has been studied in previous researches.[28] PET multiporous membranes were fabricated by the asymmetric tracketching method. The diameters of the base (the larger opening of the channel) are in the hundred nanometer scale, and the diameters of the tip (the smaller opening) are 20–30 nm or smaller (Supporting Information 2, Figure S2). The size of the tip is smaller than that of PSII complex particles,[29] so ions can permeate the PET membrane, but PSII particles cannot. For the single conical nanochannel, the size of the tip is a geometric parameter to reflect the conductance of the channel in electrolyte solutions. For conical nanochannel arrays, the conductance mainly depends on both the number and the tip size of open channels after etching.[27b] In order to reflect the two factors by a single geometric parameter, the permeability area (PA) of the membrane was defined to evaluate the conductance of the membrane. The PA means the actual area per square centimeter on the membrane for ions to permeate. It depends on the number and the size of open channels and can be calculated by the ionic conductance in 1 M KCl (pH = 7) under 1 V voltage (see the Experimental Section). The light-induced ionic current (or photocurrent) of the PECS was measured in a custom-designed conductivity cell. The conductivity cell was composed of two chambers, and the PET membrane was located between them (Figure 1). The measurement electrodes were both Ag/AgCl electrodes. The anode and cathode were placed in the two chambers separately. Both chambers were filled with the same 2-mercaptoethane sulfonic acid (MES) – NaOH buffer solution (pH = 6.5),
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
COMMUNICATION
Artificial Ion Channels Regulating Light-Induced Ionic Currents in Photoelectrical Conversion Systems
2329
www.advmat.de
COMMUNICATION
www.MaterialsViews.com
Figure 1. The natural ion channel on the thylakoid membrane of green plant leaves (top) and the artificial ion channel in the photoelectrical conversion system (PECS; bottom). The function of the PET multiporous membrane in the PECS is regulating the photocurrent by regulating ion transport, the same with that in the natural counterpart. PSII complexes act as the ionic flow resource in both of the two systems.
and in the anode chamber, the solution was containing PSII complexes (32 μg Chl mL−1). The concentration of PSII also affects the photocurrent responses (details in Supporting Information 3), and we choose this concentration to supply ample light-responsible reaction centers. The illumination applied in the experiments was white light (100 mW cm−2) to mimic the natural sunlight. Figure 2a illustrates the typical photocurrent response of the PECS upon a cyclic ‘ON-OFF’ illumination, and the PA of the PET membrane applied here is 2.07 μm2 cm−2. The illumination cycle was set to last 30 s and repetitive to testify whether the photocurrent of the PECS is stable and repeatable. In Figure 2a, the photocurrent produced by the system is ca. 0.20 nA and keeps stable under irradiation. The positive photocurrent indicates that the direction of the anion flow is from the cathode chamber to the anode chamber and the cations move in the opposite direction. After the irradiation was shut down, the photocurrent returned to zero. And when PSII particles were removed from the system, no photocurrent was generated. It reveals that the PSII is the resource of the lightinduced ionic current. In Figure 2b, when the multiporous membrane was removed from the system, the current in the ‘ON–OFF’ illumination circles fluctuated violently and performs irregular. It indicates the PET nanochannel arrays regulate the light-induce ionic transport directly. The photocurrent response could also be performed by the current–voltage (I–V) curve in the ‘ON–OFF’ illumination (Supporting Information 4), but the response was not obvious. Thus, we choose the current–time (I–t) curve to reflect the generation and regulation of photocurrents.
2330
wileyonlinelibrary.com
The generation of the photocurrents could be explained by the light-induced concerted proton–electron transfer in PSII and the ionic transportation characters of the nanochannels. In the anode chamber (Figure 2c), light drives the splitting of water to molecular oxygen, protons and reductive equivalents in PSII[25] Equation 1: 2H2 O → 4H+ + O2 + 4e −
(1)
Electrons may transfer from PSII to the electrode by a certain process,[21a] and protons are accepted instantly by the basic components of MES (MES—) in the buffer solution.[24b,30] It results in the depletion of anions and the accumulation of excessive cations in the anode chamber. While in the cathode chamber, the oxidation of molecular oxygen or protons will happen to consume reductive equivalents in response to the anode reaction Equation 2: O2 + 2H2 O + 4e− → 4OH− or 2H+ + 2e− → H2
(2)
Whichever reaction happens, the result is the same: the depletion of cations and the accumulation of excessive anions in the cathode chamber. So, the light-induced ionic potential across the multiporous membrane is generated (the potential is about –0.35 mV, measuring details in Supporting Information 5). It drives the cationic migration from the anode to the cathode and the anionic migration in the opposite direction. That is the generation of the light-induce ionic current. As the nanochannel array confines the ionic flows, the generated protons
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2014, 26, 2329–2334
www.advmat.de www.MaterialsViews.com
COMMUNICATION Figure 2. a) The photocurrent of the PECS with (solid line)/without (dotted line) PSII in cyclic ‘ON–OFF’ illumination. b) The photocurrent of the PECS without the PET membrane in ‘ON–OFF’ illumination circles. c) The light-driven ionic potential produced by PSII particles and the anode chamber is at the higher potential upon illumination. d) The PA regulates the magnitude of the photocurrent. The photocurrent gets larger with the increasing of PA.
may not remove from PSII instantly and it would inhibit PSII from producing more protons.[31] So the ionic potential could be maintained on a certain level and keep the ionic current stable. Without PET nanochannels, PSII and ions diffused freely in the electrolyte cell, and generated unordered ionic currents. In the PECS, the nanochannels confines the ionic flows, thus the regulation of the photocurrent will depend on the ionic conductance through the conical nanochannel array. And for the PET membrane, the ionic conductance is governed by PA, channel direction and surface charge. Then, we focus on the influence of the three factors to the regulation of photocurrent. The PA of the membrane reflects the conductance of the nanochannels in electrolyte solutions directly. So we could change the PA to control the magnitude of the photocurrent. The photocurrents with PET membranes in four different PAs (0.237, 2.07, 38.1, and 3920 μm2 cm−2) were also measured in ‘ON–OFF’ illumination circles (Figure 2d). The photocurrents were ca. 0.065 (Figure 2d1), 0.20 (Figure 2d2), 0.83 (Figure 2d3), and 3.5 nA (Figure 2d4). From Figure 2d, we can see that the intensity of the photocurrent is dependent on the PA of the membrane. When the permeability area is small, the photocurrent is remarkably influenced by noisy signals or even inundated in them (Supporting Information 6, Figure S6a). With the increasing of the PA, the current got steady and the fluctuations of the current disappeared. There is one thing should be noted that the photocurrent produced by this system
Adv. Mater. 2014, 26, 2329–2334
will not rise endlessly with the increasing of the PA. When the PA reached the magnitude of 104 μm2 cm−2, sizes of some nanochannel tips would get very large, and PSII particles would leak out of the anode chamber through the membrane, which leaded to the drastic fluctuation of the photocurrent (Supporting Information 6, Figure S6b). For the geometric asymmetry, the PET conical nanochannels perform the ionic current rectification, which can conduct ion current preferentially in one direction and inhibits the current flow in the opposite direction. So, in the PECS, the photocurrent could also be regulated by switching of the channel direction. The photocurrents with the multiporous membrane (PA: 38.13 μm2 cm−2) in two opposite directions were measured in ‘ON/ OFF’ illumination circles (Figure 3a). When the tips of the channels were towards the anode chamber (we could call it the OPEN direction), the photocurrent (ca. 0.7 nA) was generated obviously and regularly (Figure 3a, solid line). When the tips oriented to the cathode chamber (we could call it the CLOSE direction), there were no significant photocurrent and only some weak fluctuations on the current-time curve (Figure 3a, dot line). The absolute values of the currents with the two directions under the same bias in the same buffer solution manifest the difference in the ionic conductance (Figure 3b). In the OPEN direction, the conductance was much higher than the one in the CLOSE direction. The Poisson/Nernst–Planck (PNP) model[27,32] was adopted to explain the relationship between the
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
2331
www.advmat.de
COMMUNICATION
www.MaterialsViews.com
Figure 3. a) The direction of the channels regulates the photocurrent in the PECS. The PA of the membrane is 38.1 μm2 cm−2. When channel tips oriented to the anode, remarkable photocurrents were generated (solid line). And when channel tips directed to the cathode, no obvious phenomenon was induced (dot line). b) The I–V curves of the unmodified channels in the buffer solution reflect the conductance in different directions. When the tips were placed at the anode, the conductance is higher than the one in the opposite direction. c) The theoretical calculated cation (solid line) and anion (dotted line) distribution curves under the bias of 1 V in the conical channel in two directions: the upper one, the tip was placed towards the anode; the lower one, the tip was placed towards the cathode. The tip side was considered as the zero point along the pore axis and it was the same in Figure 3f. d) The influence of the surface charge to the photocurrent. The PA of the membrane is 10.2 μm2. The photocurrents turned from ca. 0.23 (solid line) to 0.04 nA (dot line). e) The I–V curves of the channels before (solid line) and after (dot line) modification in the buffer solution. When the negative groups on the channel surface were replaced by neutral ones, the conductance in the conical channel decreased under negative voltages. f) The theoretical calculated cation (solid line) and anion (dot line) distribution curves under the bias of 1 V in the conical channel with two surface charge densities: the upper one, 1 e nm−2; the lower one, 0.5 e nm−2.
ionic current and the channel direction (Supporting Information 7). Theoretical ion distributions in the conical nanochannel along the pore axis were calculated to explain the ionic conductance change quantitatively (Figure 3c). In the OPEN direction, the concentrations of anions and cations in the channel were higher than the ones in the bulk. While in the CLOSE direction, the ionic concentrations in the channel were lower than the ones in the bulk. The ion distribution difference in the two directions means the significant conductance difference, which led to the change of the photocurrent. For membranes with various PA, the regulation of the channel array may result in the ON–OFF or the magnitude change of the photocurrent (Supporting Information 8). Surface charge of conical nanochannels induce electrostatic screening and electrokinetic effects that may also have large effects on the channel conductance and the photocurrent.[27a,32] The track-etched PET nanochannels have carboxyls (–COOH) on the surface. When exposed to solutions whose pH are
2332
wileyonlinelibrary.com
larger than 3, these carboxyls are deprotonated to carboxylate ions (–COO−).[5a] So the surface of these nanochannels is negative in the MES–NaOH buffer (pH = 6.5). To change surface charges, PET membranes were modified with ethylenediamine by a classical EDC–NHSS cross-linking reaction,[11b,14f ] and the modification could be verified by the corresponding I–V curve measured in the acid condition (Supporting Information 9, Figure S9). Before and after the modification, photocurrents were measured in the same condition (with the same membrane and the PA is 10.3 μm2 cm−2 before modification) to see the influence of the surface charge. The photocurrent dropped down from ca. 0.23 to 0.04 nA (Figure 3d), decreased by about 83 % after modification. Ethylenediamine is a small molecule, so the influence of the modification to the PA could be neglected. After modification, as the carboxy groups on the surface were replace by the amino groups, the negative surface would turn to neutral at pH 6.5, and the negative charge density of the channel surface declined. Coupled with that, the channel
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2014, 26, 2329–2334
www.advmat.de www.MaterialsViews.com Photocurrent Measuring: The light-responsive ion transport properties of the PECS were evaluated by measuring the ionic current through the nanochannel under exposure to cyclic ‘ON–OFF’ illumination at 30 s intervals and in an ice-water bath to preserve the activity of PSII articles. All the ionic currents in this work were measured by a Keithley 6487 picoammeter (Keithley Instruments, Cleveland, OH). Measurements of the light-induced ionic current (photocurrent) were carried out in a customdesigned conductivity cell composed of two chambers, the cathode chamber filled with the 2-mercaptoethane sulfonic acid (MES) and NaOH buffer solution (pH = 6.5) and the anode chamber filled with the same solution but containing PSII particles (PSII concentration is 32 μg Chl mL−1), separated by the PET nanochannel membrane. The effective area of the membrane contacting with solutions was 0.5 cm2. The measurement electrodes were both Ag/AgCl electrodes. Unlike previous researches, no redox mediators were applied in the photoelectrical conversion system. Current–Voltage Measuring: The ionic transportation properties of the PET membrane were studied by measuring the ionic current through unmodified and modified channels. The ionic current was measured also by the Keithley 6487 picoammeter). The PET multiporous membrane was mounted between the two chambers of the conductivity cell, and both halves of the cell were filled with the buffer solution for PSII or 0.1 M KCl. The main transmembrane potential applied in this work was a scanning voltage from –2 to +2 V, and the voltage was applied by Ag/ AgCl electrodes. Each test was repeated at least four times to obtain the average current value at different voltages.
COMMUNICATION
conductance decreased after modification under the negative bias (in Figure 3f, the tip side of the channel was set to be the negative pole of the bias). The theoretical ion distribution curves calculated by the PNP model (Supporting Information 7) with different surface charge densities (here we choose 1 and 0.5 e nm−2) could explain the effect of the surface charge on the conducting states of the nanochannels. Under the negative bias, the decrease of the negative charge density on the channel surface results in the decline of the local ionic concentrations within the channel, which inhibits the ionic transport. It should be emphasized that in all experiments of the present case, no redox mediators were applied in the photoelectrical conversion system. The system with/without a classical mediator for PSII, phenyl p-benzoquinone,[28,33] was tested under illumination, and it showed no obvious difference (Supporting Information 10, Figure S10). In summary, inspired by the structure and the function of the photosynthetic membrane in green plants, we applied the PET multiporous membrane in the PECS to functionalize as the valve of the light-induced ionic current. The artificial ion channels realize the regulation of photocurrents in the device design and the magnitude of the photocurrent is dependent on the membrane permeability area, the channel direction and the channel surface charge. Due to the controllable conductance of the channels, the PET multiporous membrane shows great potential in light-responsive sensors and photovoltaic devices with PSII, photosystem I,[34] bacteriorhodopsin,[35] and other light-responsive materials.[17]
Supporting Information Supporting Information is available from the Wiley Online Library or from the author.
Acknowledgements Experimental Section Nanochannel Fabrication: The multiporous PET membrane was fabricated by the track-etching method.[5a] PET membranes (12 μm in thickness) were purchased and had been irradiated with rapid heavy ions of intensity 1 × 108 cm−2 (GSI, Darmstadt, Germany). The asymmetry chemical etching was performed to produce conical nanochannels. The PET membrane was located between the two chambers of a conductivity cell at 35 °C, one chamber was filled with etching solution (9 M NaOH), while stopping solution (1 M KCl + 1 M HCOOH) was added in the other cell to neutralize the etchant as soon as pores opened, thus slowing down the further etching process. A voltage of 1 V was applied across the membrane to monitor the etching process. Longer time for etching leads to more open channels and larger size of channels.[36] After etching, the membrane was soaked in MilliQ water (18.2 MΩ) to remove residual salts. Permeability Area Calculating: The conductance of the PET multiporous membrane mainly depends on the number of open nanopores on it after etching and the tip radius of these open pores, and the permeability area (PA) of the membrane was defined to measure them. It means the real area per square centimeter on the membrane for ions to permeate, and can be calculated by measuring the ionic current in 1 M KCl (pH = 7) under 1 V bias with Equation 3: PA =
IL 0.5Uk (c)
(3)
This formula is derived by Ohm's law and the formula of the conductivity. I is the intensity of the light-induced ionic current, L is the length of the nanochannel, 0.5 means in this device the effective area of the membrane contacting with solutions is 0.5 cm2, U is the applied bias and it is 1 V in this condition, k(c) is the conductivity of the electrolyte, and for 1 M KCl solution at 25 °C k(c) is 0.1119 Ω−1 cm−1.
Adv. Mater. 2014, 26, 2329–2334
We thank Kefeng Wang (BUAA), Jianwei Nai (BUAA), and Dafeng Wang (PKU) for beneficial discussions. This work is supported by the National Research Fund for Fundamental Key Projects (2011CB935704, 2012CB720904), National Natural Science Foundation (21271016), Program for New Century Excellent Talents in University and Ph.D. Programs Foundation of Ministry of Education of China (30400002011127001). Received: September 22, 2013 Revised: November 18, 2013 Published online: December 17, 2013
[1] a) A. de la Escosura-Muniz, A. Merkoci, ACS Nano 2012, 6, 7556; b) E. Gouaux, R. MacKinnon, Science 2005, 310, 1461. [2] a) J. Pang, J. N. Stuecker, Y. Jiang, A. J. Bhakta, E. D. Branson, P. Li, J. Cesarano, D. Sutton, P. Calvert, C. J. Brinker, Small 2008, 4, 982; b) K. Yu, B. Smarsly, C. J. Brinker, Adv. Funct. Mater. 2003, 13, 47; c) L.-J. Cheng, L. J. Guo, Nano Lett. 2007, 7, 3165. [3] a) W. Chen, Z. Q. Wu, X. H. Xia, J. J. Xu, H. Y. Chen, Angew. Chem. Int. Ed. 2010, 49, 7943; b) N. Liu, Z. Chen, D. R. Dunphy, Y. B. Jiang, R. A. Assink, C. J. Brinker, Angew. Chem. Int. Ed. 2003, 42, 1731; c) L.-J. Cheng, L. J. Guo, ACS Nano 2009, 3, 575. [4] a) Q. Zhang, Z. Liu, X. Hou, X. Fan, J. Zhai, L. Jiang, Chem. Commun. 2012, 48, 5901; b) Y. G. Guo, J. S. Hu, H. P. Liang, L. J. Wan, C. L. Bai, Adv. Funct. Mater. 2005, 15, 196. [5] a) X. Hou, H. Zhang, L. Jiang, Angew. Chem. Int. Ed. 2012, 51, 5296; b) A. Abou Chaaya, M. Le Poitevin, S. Cabello-Aguilar, S. Balme, M. Bechelany, S. Kraszewski, F. Picaud, J. Cambedouzou, E. Balanzat, J.-M. Janot, T. Thami, P. Miele, P. Dejardin, J. Phys. Chem. C 2013, 117, 15306; c) S. b. Balme, J.-M. Janot, L. Berardo,
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
wileyonlinelibrary.com
2333
www.advmat.de
COMMUNICATION
www.MaterialsViews.com
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
2334
F. o. Henn, D. Bonhenry, S. Kraszewski, F. Picaud, C. Ramseyer, Nano Lett. 2010, 11, 712; d) D. Fink, P. S. Alegaonkar, A. V. Petrov, M. Wilhelm, P. Szimkowiak, M. Behar, D. Sinha, W. R. Fahrner, K. Hoppe, L. T. Chadderton, Nucl. Instrum. Methods Phys. Res., Sect. B 2005, 236, 11. a) J. Liu, M. Kvetny, J. Feng, D. Wang, B. Wu, W. Brown, G. Wang, Langmuir 2011, 28, 1588; b) C. Wei, A. J. Bard, S. W. Feldberg, Anal. Chem. 1997, 69, 4627; c) B. Vilozny, P. Actis, R. A. Seger, Q. Vallmajo-Martin, N. Pourmand, Anal. Chem. 2011, 83, 6121; d) L.-X. Zhang, S.-L. Cai, Y.-B. Zheng, X.-H. Cao, Y.-Q. Li, Adv . Func . Mater. 2011, 21, 2103; e) N. Sa, Y. Fu, L. A. Baker, Anal . Chem . 2010, 82, 9963. a) O. Schepelina, N. Poth, I. Zharov, Adv. Funct. Mater. 2010, 20, 1962; b) R. Schmuhl, J. Sekulic, S. Roy Chowdhury, C. J. M. van Rijn, K. Keizer, A. van den Berg, J. E. ten Elshof, D. H. A. Blank, Adv. Mater. 2004, 16, 900. a) G. Pilatos, E. C. Vermisoglou, G. E. Romanos, G. N. Karanikolos, N. Boukos, V. Likodimos, N. K. Kanellopoulos, Adv. Func. Mater. 2010, 20, 2500; b) F. Fornasiero, H. G. Park, J. K. Holt, M. Stadermann, C. P. Grigoropoulos, A. Noy, O. Bakajin, Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 17250; c) J. Wu, K. Gerstandt, H. Zhang, J. Liu, B. J. Hinds, Nat. Nano. 2012, 7, 133. a) Y. H. Lanyon, G. De Marzi, Y. E. Watson, A. J. Quinn, J. P. Gleeson, G. Redmond, D. W. M. Arrigan, Anal. Chem. 2007, 79, 3048; b) U. F. Keyser, B. N. Koeleman, S. van Dorp, D. Krapf, R. M. M. Smeets, S. G. Lemay, N. H. Dekker, C. Dekker, Nat . Phys . 2006, 2, 473; c) J. Li, D. Stein, C. McMullan, D. Branton, M. J. Aziz, J. A. Golovchenko, Nature 2001, 412, 166. a) X. Hou, H. Zhang, L. Jiang, Angew. Chem. Int. Ed. 2012, 51, 5296; b) A. Kocer, L. Tauk, P. Déjardin, Biosens. Bioelectron. 2012, 38, 1; c) Z. Siwy, E. Heins, C. C. Harrell, P. Kohli, C. R. Martin, J. Am. Chem. Soc. 2004, 126, 10850. a) X. Hou, Y. Liu, H. Dong, F. Yang, L. Li, L. Jiang, Adv. Mater. 2010, 22, 2440; b) M. Ali, P. Ramirez, S. Mafé, R. Neumann, W. Ensinger, ACS Nano 2009, 3, 603. a) W. Guo, H. Xia, F. Xia, X. Hou, L. Cao, L. Wang, J. Xue, G. Zhang, Y. Song, D. Zhu, Y. Wang, L. Jiang, ChemPhysChem 2010, 11, 859; b) B. Yameen, M. Ali, R. Neumann, W. Ensinger, W. Knoll, O. Azzaroni, Small 2009, 5, 1287; c) S. Nasir, M. Ali, W. Ensinger, Nanotechnology 2012, 23, 225502. a) X. Hou, W. Guo, F. Xia, F. Q. Nie, H. Dong, Y. Tian, L. Wen, L. Wang, L. Cao, Y. Yang, J. Xue, Y. Song, Y. Wang, D. Liu, L. Jiang, J. Am. Chem. Soc. 2009, 131, 7800; b) Y. He, D. Gillespie, D. Boda, I. Vlassiouk, R. S. Eisenberg, Z. S. Siwy, J. Am. Chem. Soc. 2009, 131, 5194; c) M. Ali, S. Nasir, P. Ramirez, J. Cervera, S. Mafe, W. Ensinger, ACS Nano 2012, 6, 9247. a) N. Liu, Y. Jiang, Y. Zhou, F. Xia, W. Guo, L. Jiang, Angew. Chem. Int. Ed. 2013, 52, 2007.; b) I. Vlassiouk, T. R. Kozel, Z. S. Siwy, J. Am. Chem. Soc. 2009, 131, 8211; c) M. Ali, S. Nasir, Q. H. Nguyen, J. K. Sahoo, M. N. Tahir, W. Tremel, W. Ensinger, J. Am. Chem. Soc. 2011, 133, 17307; d) D. Fink, I. Klinkovich, O. Bukelman, R. S. Marks, A. Kiv, D. Fuks, W. R. Fahrner, L. Alfonta, Biosens. Bioelectron. 2009, 24, 2702; e) Q. H. Nguyen, M. Ali, V. Bayer, R. Neumann, W. Ensinger, Nanotechnology 2010, 21, 365701.
wileyonlinelibrary.com
[15] a) M. Zhang, X. Hou, J. Wang, Y. Tian, X. Fan, J. Zhai, L. Jiang, Adv. Mater. 2012, 24, 2424; b) L. Wen, Q. Liu, J. Ma, Y. Tian, C. Li, Z. Bo, L. Jiang, Adv. Mater. 2012, 24, 6193. [16] Y. Xie, X. Wang, J. Xue, K. Jin, L. Chen, Y. Wang, Appl. Phys. Lett. 2008, 93. [17] L. Wen, X. Hou, Y. Tian, J. Zhai, L. Jiang, Adv. Funct. Mater. 2010, 20, 2636. [18] W. Guo, L. Cao, J. Xia, F.-Q. Nie, W. Ma, J. Xue, Y. Song, D. Zhu, Y. Wang, L. Jiang, Adv. Funct. Mater. 2010, 20, 1339. [19] R. Nevo, D. Charuvi, O. Tsabari, Z. Reich, The Plant Journal 2012, 70, 157. [20] a) C. Spetea, B. Schoefs, Commun. Integr. Biol. 2010, 3, 122; b) S. Zimmermann, T. Ehrhardt, G. Plesch, B. Müller-Röber, CMLS, Cell. Mol. Life Sci. 1999, 55, 183. [21] a) M. Kato, T. Cardona, A. W. Rutherford, E. Reisner, J. Am. Chem. Soc. 2012, 134, 8332; b) F. Kopnov, I. Cohen-Ofri, D. Noy, Angew. Chem. Int. Ed. 2011, 50, 12347; c) V. Bhalla, X. Zhao, V. Zazubovich, J. Electroanal. Chem. 2011, 657, 84. [22] M. Hambourger, G. F. Moore, D. M. Kramer, D. Gust, A. L. Moore, T. A. Moore, Chem. Soc. Rev. 2009, 38, 25. [23] M. T. Giardi, E. Pace, Trends Biotechnol. 2005, 23, 257. [24] a) M. Sjödin, S. Styring, B. Åkermark, L. Sun, L. Hammarström, J. Am. Chem. Soc. 2000, 122, 3932; b) B. A. Diner, D. A. Force, D. W. Randall, R. D. Britt, Biochemistry 1998, 37, 17931. [25] O. Yehezkeli, R. Tel-Vered, J. Wasserman, A. Trifonov, D. Michaeli, R. Nechushtai, I. Willner, Nat. Commun. 2012, 3, 742. [26] M. Nagata, M. Amano, T. Joke, K. Fujii, A. Okuda, M. Kondo, S. Ishigure, T. Dewa, K. Iida, F. Secundo, Y. Amao, H. Hashimoto, M. Nango, ACS Macro Lett. 2012, 1, 296; [27] a) Z. S. Siwy, Adv. Funct. Mater. 2006, 16, 735; b) J. Cervera, B. Schiedt, R. Neumann, S. Mafe, P. Ramirez, J. Chem. Phys. 2006, 124, 104706. [28] a) H. Bao, C. Zhang, Y. Ren, J. Zhao, Biochim. Biophys. Acta, Bioenerg. 2010, 1797, 339; b) H. Bao, C. Zhang, K. Kawakami, Y. Ren, J. R. Shen, J. Zhao, Biochim. Biophys. Acta, Bioenerg. 2008, 1777, 1109. [29] J.-R. Shen, N. Kamiya, Biochemistry 2000, 39, 14739. [30] C. Costentin, M. Robert, J.-M. Savéant, J. Am. Chem. Soc. 2007, 129, 5870. [31] a) T. Shutova, H. Kenneweg, J. Buchta, J. Nikitina, V. Terentyev, S. Chernyshov, B. Andersson, S. I. Allakhverdiev, V. V. Klimov, H. Dau, W. Junge, G. Samuelsson, EMBO J 2008, 27, 782; b) H. Ishikita, A. V. Soudackov, S. Hammes-Schiffer, J. Am. Chem. Soc. 2007, 129, 11146. [32] L.-J. Cheng, L. J. Guo, Chem. Soc. Rev. 2010, 39, 923. [33] F. Müh, C. Glöckner, J. Hellmich, A. Zouni, Biochim. Biophys. Acta, Bioenerg. 2012, 1817, 44. [34] S. C. Tan, L. I. Crouch, M. R. Jones, M. Welland, Angew. Chem. Int. Ed. 2012, 51, 6667. [35] a) N. K. Allam, C.-W. Yen, R. D. Near, M. A. El-Sayed, Energy Environ. Sci. 2011, 4, 2909; b) C. W. Yen, L. K. Chu, M. A. El-Sayed, J. Am. Chem. Soc. 2010, 132, 7250. [36] O. L. Orelovich, B. A. Sartowska, A. Presz, P. Y. Apel, J. Microsc. 2010, 237, 404.
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Mater. 2014, 26, 2329–2334
