Single-Molecule Investigations of Morphology and Mass Transport Dynamics in Nanostructured Materials.

AC08CH10-Higgins

ARI

V I E W

Review in Advance first posted online on June 24, 2015. (Changes may still occur before final publication online and in print.)

N

I N A

Annual Review of Analytical Chemistry 2015.8. Downloaded from www.annualreviews.org Access provided by Yale University - Law Library on 07/04/15. For personal use only.

14:59

C E

S

R

E

21 May 2015

D V A

Single-Molecule Investigations of Morphology and Mass Transport Dynamics in Nanostructured Materials Daniel A. Higgins, Seok Chan Park, Khanh-Hoa Tran-Ba, and Takashi Ito Department of Chemistry, Kansas State University, Manhattan, Kansas 66506-0401; email: [email protected], [email protected]

Annu. Rev. Anal. Chem. 2015. 8:10.1–10.24

Keywords

The Annual Review of Analytical Chemistry is online at anchem.annualreviews.org

fluorescence correlation spectroscopy, single-molecule tracking, nanoporous materials, phase separated block copolymers, liquid crystal mesophases, mass transport mechanisms

This article’s doi: 10.1146/annurev-anchem-071114-040153 c 2015 by Annual Reviews. Copyright All rights reserved

Abstract Nanostructured materials such as mesoporous metal oxides and phaseseparated block copolymers form the basis for new monolith, membrane, and thin film technologies having applications in energy storage, chemical catalysis, and separations. Mass transport plays an integral role in governing the application-specific performance characteristics of many such materials. The majority of methods employed in their characterization provide only ensemble data, often masking the nanoscale, molecular-level details of materials morphology and mass transport. Single-molecule fluorescence methods offer direct routes to probing these characteristics on a single-molecule/singlenanostructure basis. This article provides a review of single-molecule studies focused on measurements of anisotropic diffusion, adsorption, partitioning, and confinement in nanostructured materials. Experimental methods covered include confocal and wide-field fluorescence microscopy. The results obtained promise to deepen our understanding of mass transport mechanisms in nanostructures, thus aiding in the realization of advanced materials systems.

10.1

Changes may still occur before final publication online and in print

AC08CH10-Higgins

ARI

21 May 2015

14:59

1. INTRODUCTION 1.1. Mass Transport in Nanostructured Materials MPS: mesoporous silica MCP: microporous coordination polymer BCP: block copolymer


LC: liquid crystal

The synthesis, characterization, and utilization of nanostructured materials are of contemporary interest in many science and engineering disciplines. Such materials include those comprised of chemical or physical structures (e.g., pores, domains, molecular assemblies) with characteristic dimensions in the 1–100-nm range. These structures act as pathways that may facilitate or limit the mass transport of incorporated reagents or analytes. Self-organized nanostructured materials incorporating cylindrical one-dimensional (1D) pathways attract considerable interest owing to their simplicity and ideal characteristics as model systems (1–3). Examples of relevant materials include mesoporous silica (MPS) and other mesoporous metal oxides, microporous coordination polymers (MCPs), block copolymers (BCPs), and lyotropic and thermotropic liquid crystals (LCs). Specific applications of some of these materials include their use as porous supports in chemical catalysis (4, 5), as media for solid-phase extraction and chemical separations (6, 7), and as membranes for batteries and fuel cells (8, 9). An important attribute of many nanostructured materials is their ability to selectively transport specific chemical species. Figure 1 depicts several processes that may facilitate selective transport. These are anticipated to occur both in the solvent-filled rigid nanopores of MPS and in softmatter nanostructures such as phase-separated BCPs and lyotropic LCs (10). Transport rate and selectivity are governed by the partitioning of permeants between the different phases and by mass transport within the cavities or nanoscale domains. Interfacial adsorption phenomena are also of significant importance, particularly because of the high interface-to-volume ratio of these materials. The associated material nanostructures may form impermeable or semipermeable barriers that confine molecular motions in one or more dimensions. Mass transport may also be affected by spatial permeant distributions within the nanostructures that result from solvent structuring in near-surface regions (11) and the presence of the diffuse electrical double layer (2, 3, 10). These molecular-level processes reflect steric, chemical, and electrostatic interactions between the permeants and nanostructured medium. A better understanding of the molecular mechanisms of mass transport is certain to aid in the development of new materials with properties better optimized for their intended applications.

a

b

SOLUTION

SOLID (e.g., silica) MINOR DOMAIN CAVITY

Diffusion Surface diffusion

Partitioning

MAJOR DOMAIN Diffusion

Adsorption

Cavity diffusion

Partitioning

INTERFACE

Adsorption ion

Interfacial diffus

Figure 1 Models for partitioning and mass transport (e.g., diffusion) in (a) solvent-filled 1D nanoporous media such as mesoporous silica and (b) 1D nanostructured soft matter such as phase-separated block copolymers and liquid crystals. 10.2

Higgins et al.


AC08CH10-Higgins

ARI

21 May 2015

14:59

1.2. Ensemble Methods for Characterization of Mass Transport Processes Mass transport within nanostructured materials has long been studied by ensemble methods that report on the average behavior of a large number of molecules in many different local environments. Included in this list are flux methods in which the concentration of permeants in a collection reservoir is monitored as they pass from the source reservoir through the material (2, 10). Equation 1 defines the diffusion-controlled flux, J, of permeants through a nanoporous monolith:


J = −DP

ε dC . τ dx

1.

Here, D is the diffusion coefficient of the permeant within the pores; P is its partition coefficient, defined between the external solution and the pore-filling medium; ε is the fraction of the material cross section comprising open pores, τ is the pore tortuosity; and dC/dx is the concentration gradient. This equation demonstrates that flux is related to both mass transport parameters (D and P) and the structural properties (ε and τ ) of the material. Flux measurements offer insights into the mass transport processes in Figure 1, but they do not allow for molecular motions to be explicitly visualized, nor can molecule-matrix interactions be directly detected. The dynamics of mass transport have been studied on nanosecond timescales by quasielastic neutron scattering, whereas longer (microsecond–second) motions have been probed by dielectric spectroscopy (12). Nuclear magnetic resonance (NMR) spectroscopy has been utilized to investigate both mass transport rates and anisotropies in nanostructured media (13, 14). Optical methods such as fluorescence recovery after photobleaching (FRAP) (15) have been employed for similar purposes (16) but are limited by extensive signal averaging.

FRAP: fluorescence recovery after photobleaching FCS: fluorescence correlation spectroscopy SMT: single-molecule tracking

1.3. Single-Molecule Methods for Mass Transport Studies With the advent of optical single-molecule detection methods (17–22), it became possible to observe and track the motions of individual fluorescent molecules in many transparent media. These methods are now being applied in studies of mass transport within nanostructured materials (23–26). Because single-molecule measurements avoid the signal averaging of ensemble methods, it is possible, in principle, to distinguish between the individual processes depicted in Figure 1 in one experiment, while simultaneously quantifying the characteristic temporal and distance scales over which they occur. This review covers the state of the art in single-molecule detection, tracking, and correlation spectroscopy measurements as applied to the investigation of mass transport in nanostructured materials.

2. SINGLE-MOLECULE FLUORESCENCE METHODS AND INSTRUMENTATION Detailed descriptions of contemporary single-molecule methods can be found in several recent reviews (23–34). Single molecules can now be followed with millisecond time resolution and nanometer-scale spatial precision by wide-field imaging methods (35–39). As a complementary method, confocal microscopy can be used to probe the passage of single molecules through isolated detection volumes with microsecond resolution, via the recording of single-point time transients (19, 40). Implementation of wide-field video data in single-molecule tracking (SMT) and singlepoint time transients in fluorescence correlation spectroscopy (FCS) (41, 42) allows for quantitative measurements of local concentrations, molecular diffusion coefficients, diffusion anisotropies, adsorption and reaction times, the order and orientation of nanostructures, and the confinement www.annualreviews.org • Single-Molecule Investigations


10.3

AC08CH10-Higgins

ARI

21 May 2015

14:59

Sample

a

b

Confocal microscope 100x/1.30 Oil

100x/1.49 Oil

Objective

Dichroic mirror

Laser Polarizer Filter


Wide-field microscope

Laser

Lens

Lens

Filter Polarizer

Filter

Pinhole

CCD Lens

APD

Mirror

Filter Polarizer

Beam splitter

Figure 2 Common components often found in (a) confocal microscopes and (b) wide-field microscopes. Some optics have been omitted for simplicity. Abbreviations: APD, avalanche photodiode; CCD, charge-coupled device.

of molecular motions. This section summarizes the basic principles and instrumentation employed in confocal single-point and wide-field fluorescence measurements (see Figure 2).

2.1. Confocal Single-Point Measurements

DiI: an indocarbocyanine dye often employed in single-molecule studies

10.4

A confocal fluorescence microscope (see Figure 2a) is often used to collect single-point fluorescence time transients. Laser light is usually employed to excite single-molecule fluorescence. The light is first directed through any required polarization optics and filters and is then reflected via a dichroic mirror into a high numerical aperture objective, which focuses the light into the sample. Positioning of the sample relative to the laser spot can be accomplished using either beam scanning or sample scanning methods. Fluorescence from the sample is frequently acquired in reflection, using the same objective. The collected light is passed back through the dichroic mirror and focused through an appropriately sized pinhole placed in an image plane of the microscope. Afterwards, the light is directed through any additional filters and/or polarizers and subsequently imaged onto a detector, such as a single-photon-counting avalanche photodiode. In this configuration, fluorescence time transients can be recorded from femtoliter volumes on microsecond and longer timescales. For sufficiently dilute solutions (e.g., 103 s

12

5

–10

20 nm

Mean error bar

10

y (nm)

y (nm)

15

0

50

100

Time (s)

150

200

4

5–6 nm

0 –4 –8 0

20

40

Occurrence Figure 6 Diffusion of terrylene diimide (TDI) molecules in mesoporous silica films revealing confinement of the molecules. (a) Projected x and y coordinates for a single TDI molecule diffusing in at least two distinct pores. The molecule diffuses back and forth in one pore (black squares) then switches to another pore ( green circles). (b) Trajectory of the molecule (top) and histograms of the y position for the same time intervals together with their Gaussian fits (bottom). The two maxima are separated by 5–6 nm, showing pore separation. Figure modified with permission from Reference 87. Copyright 2008 American Chemical Society.

fixed spots in the same materials. The PEO microdomain radius was estimated to be ∼11 nm, a value that compared favorably with atomic force microscopy results (14 nm) (90).

4.3. Confinement-Level Analysis from Step-Size Measurements Detailed analyses of single-molecule step-size distributions have also been used to explore molecular confinement, as in representative work by Elliott et al. (103). Diffusion in one dimension produces a distribution that is peaked at zero displacement, whereas isotropic diffusion yields a peak at nonzero step sizes. By fitting the step-size distribution to Weibull or Chi functions, the dimensionality of molecular motion was obtained (103, 104). Radius of gyration calculations were also explored as a means for quantifying the level of molecular confinement along short trajectory segments and, thus, to obtain a measure of diffusion anisotropy (103). Anisotropic diffusion can also be detected by measuring the diffusive step size as a function of step direction. Pumpa & Cichos (105) reported such measurements for PDI molecules diffusing through LCs. Diffusion anisotropies of D /D⊥ = 1.5 ± 0.2 were obtained, indicative of preferential 1D diffusion along the LC alignment direction.

4.4. Assessment of Mass Transport Anisotropy from Step Direction The direction of the individual diffusive steps taken by a single molecule provides a direct means to detect mass transport anisotropy. In early applications of this method, the angles between consecutive steps were recorded (106), and plots compiled from a large number of steps afforded the means to distinguish immobile molecules from mobile ones and isotropic (2D) diffusion from anisotropic (1D) diffusion (107). These classifications were based on the characteristic appearances of the step-angle distributions. Immobile molecules produced a U-shaped distribution owing to www.annualreviews.org • Single-Molecule Investigations


10.11

AC08CH10-Higgins

ARI

21 May 2015

14:59

a b 10

5

Occurrence

1.0 μm

c


σR

0 10

5

ΔѲ

Ѳ Ѳ

0 –90

–45

0

45

90

Step angle (°) Ѳ = 0°

σδ 0.5 μm

Figure 7 (a) Trajectories (red and blue lines) from single molecules exhibiting 1D diffusion in spin-coated CTAB-filled mesoporous silica films, along with their fits (black lines) by orthogonal regression methods. (b) Distributions of single step angles (red and blue bars) obtained from the same trajectories. (c) Parameters obtained from orthogonal regression of 1D single-molecule trajectory data (brown line). Orthogonal regression provides a measure of the trajectory angle, θ , the localization precision (standard deviation, σ δ ) (short blue bar) and the diffusion coefficient in 1D (σ R ) (long blue bar). Average trajectory alignment, θ¯ , is determined from several trajectories, allowing for the deviation of each θ from the average to be obtained. The mean deviation θ provides a measure of materials order. Figure modified with permission from Reference 25. Copyright 2013 American Chemical Society. Abbreviations: 1D, one-dimensional; CTAB, cetyltrimethylammonium bromide.

the overrepresentation of apparent backward steps. In contrast, 1D-diffusing molecules produced distributions peaked near 0o and ±180o , and 2D diffusion yielded no preference for any particular step angle. Hellriegel et al. (106) employed this type of analysis in studies of TDI diffusion in MPS. Liao et al. (88) employed similar analyses to characterize the motions of nile red in crystalline MCPs that exhibited 1D, 2D, and restricted 3D diffusion. Unfortunately, the step-angle distributions obtained provided no information on the actual alignment of the trajectories or the guiding materials nanostructures (107). When the diffusive step angles are measured relative to a fixed direction, these same data can be used both to detect 1D diffusion and to determine the average direction of the 1D motions. Tran Ba et al. (93) employed such an analysis for initial assessment of molecular motions in CTABfilled MPS films (Figure 7a,b). Unfortunately, such determinations are of limited utility because the localization precision and single-frame step size are frequently of similar magnitude, yielding relatively broad step-angle distributions.

4.5. Orthogonal Regression Analysis Quantitative assessments of mass transport dimensionality and directionality may be efficiently accessed by orthogonal regression of SMT trajectory data, as originally reported by Tran Ba et al. 10.12

Higgins et al.



AC08CH10-Higgins

ARI

21 May 2015

14:59

(93) In this method, the SMT data are fit to linear functions, providing measurements of the in-plane orientations of individual 1D (or pseudo-1D) trajectories. Values for the trajectory angle error and the position variances along and across the trajectories are also obtained. Figure 7a,c show representative trajectories and their fits, along with definitions of these parameters. The variance across a 1D trajectory includes information on the localization precision (35), whereas the variance along the trajectory is related to D. These parameters provide important routes to assessing trajectory dimensionality. In the initial report (93), a threshold for the trajectory angle error was employed to distinguish 1D trajectories from 2D diffusing and immobile molecules. The ratio of variances across and along the trajectories was also used for this purpose. In later studies, the localization precision was compared to the MSD of individual molecules to separate the populations of immobile and 2D diffusing molecules (90, 95, 102). Although orthogonal regression analysis requires the assumption of 1D motion, it allows for quantitative assessment of the error rate in assigning trajectories to different populations. Importantly, the method provides quantitative measurements of the 1D diffusion direction and can be used to determine the orientation and order of open nanostructures that support anisotropic mass transport. Orthogonal regression methods have since been applied to studies of 1D diffusion in lyotropic LCs (82), MPS monoliths (95), and phase-separated BCPs (90, 102) aligned by flow (82, 95, 102) or by directional solvent vapor penetration (90).

5. ALIGNMENT AND ORGANIZATION OF OPEN ONE-DIMENSIONAL NANOSTRUCTURES The organization of 1D nanopores or microdomains comprising nanostructured materials is also of importance in determining their mass transport characteristics. As shown in Equation 1, permeant flux is dependent on the length (dx), porosity (ε), and tortuosity (τ ) of the molecular pathways. High flux can be expected across materials incorporating densely packed, oriented, and well-ordered 1D pores/microdomains. Assessment of these attributes requires quantitative measurements of nanostructure alignment. Such measurements should reflect any correlations between the material’s mass transport characteristics and its physical morphology.

5.1. Order Parameters Order parameters are frequently used to assess materials order at the ensemble level. Equations 7 and 8 provide examples of order parameters describing materials order in 3D and 2D systems, respectively: S = 0.5(3cos2 (θ) − 1);

7.

P = 2cos2 (θ) − 1.

8. Here, θ represents the angular deviation of each nanostructure from the mean orientation θ¯ (shown in Figure 7c). The values of S and P range from one for perfectly ordered materials to zero for complete disorder. Electron microscopy has been used to assess the local orientation and order of individual 1D nanostructures (91, 92, 99), whereas X-ray scattering (99, 100) provides similar information at the ensemble level. Neither provides direct information on the ability of the nanostructures to support mass transport. Quasielastic neutron scattering (108), NMR (13), and conventional optical methods (101) provide ensemble data on the relationship between materials order and anisotropic molecular motion but little information on the alignments of individual nanostructures. www.annualreviews.org • Single-Molecule Investigations


10.13

AC08CH10-Higgins

ARI

21 May 2015

14:59

SMT methods presently provide the only means to simultaneously probe both alignment and mass transport data on the single-nanostructure level. In this case, SMT results provide maps of open nanostructure alignments and reveal their abilities to support and guide molecular motions. The measurement of trajectory orientation distributions and the calculation of S (or P ) from these results afford unique information on materials order, as directly related to their mass transport characteristics.

5.2. Trajectory Angle Distributions


Single-trajectory, single-step-angle distributions such as those shown in Figure 7b may be used to determine the (in-plane) orientation of individual nanostructures, as represented by the peak position of the distribution (93). Compiling the orientations of the individual trajectories provides a measure of local nanostructure order. However, the precision of these measurements is limited by the finite localization precision of single-molecule methods (25). Improved measurements of trajectory orientation can be obtained by orthogonal regression methods (see Section 4.5). These allow for distinction to be made between consequential steps and random noise due to the finite localization precision. Assuming that the examined trajectories are truly 1D and exhibit no curvature, orthogonal regression methods provide higher precision in trajectory orientation measurements. For example, the orientations of the trajectories in Figure 7a,b can be determined with 5–10-fold-improved precision over the single-step-angle method (25). The ability to acquire full trajectory angle distributions represents one of the main advantages of SMT methods over ensemble measurements. Figure 8 depicts representative trajectory angle histograms obtained from PDI molecules diffusing through a flow-aligned, CTAB-filled MPS monolith. Inspection of the distributions reveals that the pore alignment in one region (Figure 8a) is relatively variable around the peak, whereas the other region (Figure 8b) incorporates at least two grains with different average orientations. Although these distributions are clearly different, they both yield P = 0.59 and are thus difficult to distinguish by ensemble methods. Similar studies of spin-coated CTAB-filled MPS films have revealed the presence of wellordered grains of different average pore alignments (shown in Figure 9) (93). Figure 9c gives ¯ the order parameter P , and the average deviation of the average pore alignment direction θ,

a

b

Occurrence

30 25

= 0.59

30

= 0.59

20 20

15 10

10

5 0 –90

–45

0

Ѳ (°)

45

90

0 –90

–45

0

45

90

Ѳ (°)

Figure 8 (a,b) Trajectory angle distributions obtained by orthogonal regression of single-molecule trajectories from small regions of ﬂow-aligned, CTAB-ﬁlled mesoporous silica monoliths. The data show that similar order parameters can be obtained from distinctly different nanostructure distributions. Abbreviation: CTAB, cetyltrimethylammonium bromide. 10.14

Higgins et al.


AC08CH10-Higgins

ARI

21 May 2015

14:59

b 12

Occurrence

a

b

8 4

a

0 –90

–45

c

b c


10 μm

a

0

45

90

Ѳ (°)

c Domain

Ѳ

a b c

–64.8° –12.6° 54.8°

0.89 ± 0.05 0.89 ± 0.05 0.87 ± 0.17

13.6° 13.6° 14.8°

Figure 9 (a) Single-molecule trajectories obtained from PDI molecules diffusing through a spin-coated, CTAB-filled mesoporous silica film. (b) Histogram of trajectory angles determined by orthogonal regression methods. These data reveal the presence of three grains based on well-ordered nanopores in this region of the sample. (c) Pore orientation and order parameters for the three color-coded grains. Figure modified from Reference 93 with permission from the PCCP Owner Societies. Abbreviations: CTAB, cetyltrimethylammonium bromide; PCCP, Physical Chemistry Chemical Physics; PDI, perylene diimide.

nanopore alignment from the mean θ for each of the grains. Although mass transport was relatively facile within the individual grains, the grain boundaries serve to limit mass transport by terminating the individual nanopores (91). In subsequent investigations, this same method was applied to the analysis of 1D trajectory orientations in flow-aligned CTAB-filled MPS monoliths supported within fluidic channels (95). Mesopore alignment relative to the flow direction and pore order were explored as a function of sol aging time. The results showed that well-aligned, well-ordered (P ≥ 0.8) nanopores could be obtained over millimeter-length scales when the sols were employed prior to gelation. Misaligned, disordered (P ∼ 0.35) pores were obtained when the sols were used near or beyond the gelation time. Similar analyses have also been used to assess nanostructure organization in flow-aligned lyotropic LCs (82) and phase-separated PS-b-PEO films (102). The latter study revealed the presence of micrometer-scale grains consisting of well-ordered cylindrical PEO microdomains with orientations defined by flow-induced shear forces. The same method was also used to assess the organization of PEO microdomains induced by directional solvent vapor penetration through PS-b-PEO films (90). Individual sulforhodamine B probe molecules exhibited 1D diffusive motions aligned (P ∼ 0.9) along the vapor penetration direction over millimeter distances when 1,4dioxane vapor was employed, whereas 2D diffusion was observed for benzene or toluene vapors.

6. SINGLE-MOLECULE ORIENTATION WITHIN ONE-DIMENSIONAL NANOSTRUCTURES The confinement of molecules within 1D nanostructures may also lead to restriction of their orientational motions. Such effects play an essential role in shape-based chemical separations (3) and stereoselective catalysis (4, 5) in nanoporous materials. Thus, measurements of probe molecule orientation within 1D nanostructures are important to understanding the detailed mechanisms www.annualreviews.org • Single-Molecule Investigations


10.15

ARI

21 May 2015

14:59

of mass transport and can also be used to determine the accessible internal dimensions of the confining nanostructures (45, 109). Detection of the average orientation and relatively slow orientational motions of probe molecules can be accomplished in wide-field optical microscopes using defocused (47, 110, 111) or aberrated (48, 112) imaging methods. Direct polarization-dependent methods (113–117) are also very common and work in single-point or wide-field modes. These require insertion of appropriate polarization optics into the microscope (see Figure 2). They also require that the probe molecules absorb and emit polarized light. It is best if their absorption and emission transition dipoles are oriented parallel to each other. Families of dyes that work well in such studies are the TDIs (87) and PDIs (93). Single-point methods afford enhanced time resolution over wide-field modes and are better suited to following rapid (approximately millisecond or faster) orientational motions (114). In all cases, care must be exercised when interpreting polarization data acquired on a microscope, because the dichroic mirrors and objectives employed may alter the polarization states of both the incident and detected optical fields. Equations describing depolarization by the objective are available in the literature (113, 118).


AC08CH10-Higgins

6.1. Polarized Single-Point Measurements of Oriented Diffusion Kawai et al. (74) reported on the diffusion of oriented PDI molecules in thermotropic LCs. They employed circularly polarized excitation, while probe molecule emission was simultaneously detected in two orthogonal polarizations. Fluorescence emission was strongly polarized along the direction of LC alignment. The elongation and alignment of single conjugated polymer molecules in nematic LCs has also been investigated and analogous results obtained (76–78). While diffusion by oriented molecules is expected for certain dyes and LCs, recent reports (31, 116) suggest this may be a more general phenomenon. The development of means to control the orientations of molecules within nanostructured materials will likely lead to improved selectivity in chemical separations and enhanced reactivity in chemical catalysis.

6.2. Scanning Confocal Imaging of Oriented Diffusion Jung et al. (87, 119) described the visualization of diffusion by oriented TDI single molecules in CTAB-filled MPS films. Figure 10 depicts some of their results. Imaging experiments were initially performed under dry conditions where the molecules were largely immobile. Excitationpolarization-modulation methods were used to demonstrate that molecules found within relatively large grains were oriented along the same direction. The TDI molecules were subsequently mobilized by exposing them to chloroform vapor. In this case, the molecules diffused in one dimension. Importantly, they remained oriented in the same direction as they moved through the materials. Oriented diffusion of the molecules was attributed partly to their size (∼2.5 nm length, ∼1.1 nm diameter) relative to the silica channel dimensions (∼2–3 nm in diameter). Jung et al. (87, 119) also noted that the hydrophobic TDI molecules may be confined to hydrophobic regions of the CTAB micelles filling the silica pores.

6.3. Polarized Wide-Field Imaging for Detection of Single-Molecule Wobbling Pramanik et al. (45, 109) recently demonstrated a polarization-dependent wide-field method that allows for the assessment of probe molecule confinement in nanometer-sized cylindrical pores. This method relies on measurements of the confined orientational motions (i.e., wobbling) of single molecules as they diffuse along the pore axis. Figure 11a depicts a model for orientational 10.16

Higgins et al.


AC08CH10-Higgins

a

ARI

21 May 2015

14:59

c

Air

d 90 60 30 0 –30 –60 –90

0°

Angle (°)

0 min

500 nm

0

20

40

60

80

Time (min)

e

2 µm

f

Air SiO


+ + + + + + + + + + + + + + + + + + + + + + +2+ O O

b

Chloroform 0 min

N

N

O

O

*

++++++++++++++++++++++++

4 min

2 min

*

++++++++++++++++++++++++ O O

*

N

O N

O

O

N

O

N

+ + + +O+ + + + + + +O+ + + + + + + + + + + + +

*

Chloroform

*

SiO

2 ++++++++++++++++++++++++

O

O

N

N

O O ++++++++++++++++++++++++

*

*

++++++++++++++++++++++++ O O O O O O O O ++++++++++++++++++++++++ N

N

N

N

*

Figure 10 (a) Image showing oriented, immobile terrylene diimide (TDI) single molecules within a mesoporous silica film. The streak patterns observed for each molecule arise from modulation of the incident polarization. The yellow bars superimposed over each spot indicate the orientation of the molecule. (b) Sequence of images showing linear diffusion by oriented TDI molecules under a chloroform atmosphere. Scale bar: 2 μm. (c) Trajectory of the molecule highlighted by the white circles in panel b. (d ) Orientation time trajectory for the same molecule. (e, f ) Models for oriented immobile and mobile TDI molecules. The green shaded regions in panel f depict the solvent-filled hydrophobic core of the micelle. Figure modified with permission from Reference 87. Copyright 2008 American Chemical Society.

wobbling by PDI dyes (45, 109). Rod-shaped molecules such as the PDIs are best suited for these measurements. The probe molecules must also have lengths that are similar to the pore diameter so that polarized fluorescence is detected from confined molecules. Any orientational wobbling around their long axis leads to depolarization of the fluorescence. Taken together, the measured fluorescence polarization and average molecular orientation are then used to quantify the degree of wobbling by each molecule. The results provide an estimate of the lateral dimensions of the confining cavity. In the original reports (45, 109), PDI fluorescence was excited by circularly polarized light, while emission was recorded in two orthogonal polarizations (see Figure 11b). The single-molecule emission signals in the two detection channels, IV and IH , were used to determine the fluorescence polarization, FP (originally termed the emission dichroism) (45, 109): FP =

IV − IH . IV + IH

9.

The time-averaged molecular wobbling angle, ω, was then determined from Equation 10 (45, 109): cos(2θ) + FP(2a 2 + 1) . 10. cos2 ω = 3cos(2θ) + FP(2a 2 − 1) Here, θ is the average orientation of the molecule (taken as the trajectory orientation) in the film plane, and a2 is a constant defining the depolarization by the objective (113). The accessible radial dimension, d, of the confining cavity was then calculated from Equation 11, using the estimated molecular length, L: d = L sin ωmax .

11.

www.annualreviews.org • Single-Molecule Investigations


10.17

AC08CH10-Higgins

ARI

21 May 2015

14:59

a

c O

R N

d ωmax O

N

R

Length (nm)

–C3H6OC8H17

2.8

–C3H6OC4H9

2.5

–C3H6OCH3

2.2

–CH3

1.4

O

O

R

d 45 40

ωmax (°)


b

35 30 25 20

5 μm

1.6

2.0

2.4

2.8

Molecule length (nm)

Figure 11 (a) Model for confined orientational motions (wobbling) of dyes in CTAB-filled silica mesopores. (b) Polarization-dependent fluorescence images of single molecules exhibiting 1D diffusion. The two frames show images of the same sample region. Doubleended arrows designate the detected polarizations. (c) PDI dyes employed in studies of confined molecular wobbling and their estimated lengths. (d ) Maximum wobbling angle versus molecular length. Error bars depict the 90% confidence intervals. The black line shows a fit based on Equation 11. Figure adapted with permission from Reference 109. Copyright 2013 American Chemical Society. Abbreviations: 1D, one-dimensional; CTAB, cetyltrimethylammonium bromide; PDI, perylene diimide.

Here, ωmax is the maximum extent of wobbling, which is related to Equation 10 by Equation 12 (109): 1 1 − cos3 ωmax 12. cos2 ω = 3 1 − cos ωmax Figure 11b depicts representative polarization-dependent video data acquired in these studies. These images plot the maximum intensity observed at each pixel across 100 video frames. The 1D fluorescent streaks depict the molecular motions. Many such videos were acquired for a series of four different PDI dyes, each having a different length (see Figure 11c). Their average ωmax values are plotted as a function of molecular length in Figure 11d, along with a fit based on Equation 11. The data show that ωmax increases as the molecules become shorter, as expected, and are consistent with an average accessible cavity diameter of ∼1 nm. This value is much smaller than the physical size of the silica pores, which may be as large as ∼3.7 nm in diameter. The smaller accessible cavity diameter was attributed to partitioning of the dye into the hydrophobic region of the surfactant micelles, an effect that may be enhanced by the presence of a water-rich layer at the silica-surfactant boundary. The results of these and other studies point to how the behaviors of confined solvents and solutes differ from their bulk counterparts. The knowledge gained will allow for chemical and physical interactions occurring within tightly confined environments to be better utilized in advanced solution-phase chemical separations and catalysis. 10.18

Higgins et al.


AC08CH10-Higgins

ARI

21 May 2015

14:59


7. CONCLUSIONS AND FUTURE DIRECTIONS Monoliths, films, and membranes derived from nanostructured materials are now being designed to selectively transport specific reagents or analytes. This attribute makes them particularly useful for applications in chemical separations, catalysis, fuel cells, and batteries. To design materials best suited for their intended applications, the complex molecular-level mechanisms behind mass transport within nanostructured materials must first be fully understood. Single-molecule fluorescence methods reveal the details of mass transport within these materials at the single-nanostructure and single-molecule levels while also providing valuable information on their physical morphology. A wealth of information on probe molecule diffusion coefficients, partition coefficients, surface adsorption phenomena, and the degree of molecular confinement can be obtained by these methods. These same data provide the means to assess the ability of individual nanostructures to support mass transport, to determine the dimensionality and alignment of local nanostructures, and to quantify order in organized grains. Some of the most exciting new single-molecule methods allow for the simultaneous tracking of probe molecule translational and orientational motions. These data can be used to measure the accessible internal dimensions of individual nanostructures, which may differ from the physical size of the nanostructures owing to structuring of the internal medium, or electrostatic interactions between pore surfaces and charged probe molecules. Although significant advances are now being made with existing experimental tools, there remain a number of challenges that will drive the development of new single-molecule methods. For example, the limited brightness and photostability of many probes continues to constrain single-molecule measurements. Better probes would afford improved signal-to-noise ratios and, hence, better spatial resolution in confinement studies. The ability to record longer trajectories would allow for mapping of longer nanostructures. Luminescent polymer quantum dots (120, 121) may provide the necessary signal enhancements. Luminescent probes with a range of well-defined sizes and strongly polarized emission would also be useful for probing the accessible internal dimensions of confining nanostructures. By matching the probe size to that of the nanostructures, interesting single-file 1D diffusion observed for larger particles (122) could likely be detected at the single-molecule level. To date, mass transport studies in nanostructured materials have largely been limited to 1D systems. Continued development of methods for tracking single-molecule orientations (114–116) and positions (123–126) in 3D will expand the range of materials being investigated. Overall, single-molecule studies of mass transport in nanostructured materials are certain to continue providing fundamentally interesting and technologically useful data well into the future.

DISCLOSURE STATEMENT The authors are not aware of any affiliations, memberships, funding, or financial holdings that might be perceived as affecting the objectivity of this review.

ACKNOWLEDGMENTS This work was supported by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy (DE-FG02-12ER16095). Ruwandi Kumarasinghe is thanked for providing data for Figure 4. LITERATURE CITED 1. Deen WH. 1987. Hindered transport of large molecules in liquid-filled pores. AIChE J. 33:1409–25 2. Martin CR, Nishizawa M, Jirage K, Kang M. 2001. Investigations of the transport properties of gold nanotubule membranes. J. Phys. Chem. B 105:1925–34 www.annualreviews.org • Single-Molecule Investigations


10.19

ARI

21 May 2015

14:59

3. Baker LA, Jin P, Martin CR. 2005. Biomaterials and biotechnologies based on nanotube membranes. Crit. Rev. Solid State Mater. Sci. 30:183–205 4. Corma A. 1997. From microporous to mesoporous molecular sieve materials and their use in catalysis. Chem. Rev. 97:2373–419 5. Lee JY, Farha OK, Roberts J, Scheidt KA, Nguyen ST, Hupp JT. 2009. Metal-organic framework materials as catalysts. Chem. Soc. Rev. 38:1450–59 6. Nakanishi K, Tanaka N. 2007. Sol-gel with phase separation. Hierarchically porous materials optimized for high-performance liquid chromatography separations. Acc. Chem. Res. 40:863–73 7. Ito T. 2014. Block copolymer-derived monolithic polymer films and membranes comprising selforganized cylindrical nanopores for chemical sensing and separations. Chem. Asian J. 9:2708–18 8. Long JW, Dunn B, Rolison DR, White HS. 2004. Three-dimensional battery architectures. Chem. Rev. 104:4463–92 9. Winter M, Brodd RJ. 2004. What are batteries, fuel cells, and supercapacitors? Chem. Rev. 104:4245–69 10. Cussler EL. 2009. Diffusion: Mass Transfer in Fluid Systems. New York: Cambridge Univ. Press 11. Thompson WH. 2011. Solvation dynamics and proton transfer in nanoconfined liquids. Annu. Rev. Phys. Chem. 62:599–619 12. Takahara S, Kittaka S, Mori T, Kuroda Y, Takamuku T, Yamaguchi T. 2008. Neutron scattering and dielectric studies on dynamics of methanol and ethanol confined in MCM-41. J. Phys. Chem. C 112:14385–93 13. Cho HJ, Sigmund EE, Song Y. 2012. Magnetic resonance characterization of porous media using diffusion through internal magnetic fields. Materials 5:590–616 14. Kärger J, Valiullin R. 2013. Mass transfer in mesoporous materials: the benefit of microscopic diffusion measurement. Chem. Soc. Rev. 42:4172–97 15. Axelrod D, Koppel DE, Schlessinger J, Elson E, Webb WW. 1976. Mobility measurement by analysis of fluorescence photobleaching recovery kinetics. Biophys. J. 16:1055–69 16. Okamoto K, Shook CJ, Bivona L, Lee SB, English DS. 2004. Direct observation of wetting and diffusion in the hydrophobic interior of silica nanotubes. Nano Lett. 4:233–39 17. Moerner WE, Kador L. 1989. Optical detection and spectroscopy of single molecules in a solid. Phys. Rev. Lett. 62:2535–38 18. Orrit M, Bernard J. 1990. Single pentacene molecules detected by fluorescence excitation in a p-terphenyl crystal. Phys. Rev. Lett. 65:2716–19 19. Shera EB, Seitzinger NK, Davis LM, Keller RA, Soper SA. 1990. Detection of single fluorescent molecules. Chem. Phys. Lett. 174:553–57 20. Betzig E, Chichester RJ. 1993. Single molecules observed by near-field scanning optical microscopy. Science 262:1422–25 21. Nie S, Chiu DT, Zare RN. 1994. Probing individual molecules with confocal fluorescence microscopy. Science 266:1018–21 22. Eigen M, Rigler R. 1994. Sorting single molecules: applications to diagnostics and evolutionary biotechnology. PNAS 91:5740–47 23. Higgins DA, Collinson MM. 2005. Gaining insight into the nanoscale properties of sol-gel-derived silicate thin films by single-molecule spectroscopy. Langmuir 21:9023–31 24. Ye F, Collinson MM, Higgins DA. 2009. What can be learned from single molecule spectroscopy? Applications to sol-gel-derived silca materials. Phys. Chem. Chem. Phys. 11:66–82 25. Higgins DA, Tran-Ba K-H, Ito T. 2013. Following single molecules to a better understanding of selfassembled one-dimensional nanostructures. J. Phys. Chem. Lett. 4:3095–103 26. Lebold T, Michaelis J, Bräuchle C. 2011. The complexity of mesoporous silica nanomaterials unravelled by single molecule microscopy. Phys. Chem. Chem. Phys. 13:5017–33 27. Moerner WE, Fromm DP. 2003. Methods of single-molecule fluorescence spectroscopy and microscopy. Rev. Sci. Instrum. 74:3597–619 28. Walter NG, Huang C-Y, Manzo AJ, Sobhy MA. 2008. Do-it-yourself guide: how to use the modern single-molecule toolkit. Nat. Methods 5:475–89 29. Woll ¨ D, Braeken E, Deres A, De Schryver FC, Uji-i H, Hofkens J. 2009. Polymers and single molecule fluorescence spectroscopy, what can we learn? Chem. Soc. Rev. 38:313–28


AC08CH10-Higgins

10.20

Higgins et al.



AC08CH10-Higgins

ARI

21 May 2015

14:59

30. Kulzer F, Xia T, Orrit M. 2010. Single molecules as optical nanoprobes for soft and complex matter. Angew. Chem. Int. Ed. 49:854–66 31. Reznik C, Landes CF. 2012. Transport in supported polyelectrolyte brushes. Acc. Chem. Res. 45:1927–35 32. Kaufman LJ. 2013. Heterogeneity in single-molecule observables in the study of supercooled liquids. Annu. Rev. Phys. Chem. 64:177–200 33. Wirth MJ, Legg MA. 2007. Single-molecule probing of adsorption and diffusion on silica surfaces. Annu. Rev. Phys. Chem. 58:489–510 34. Shuang B, Chen J, Kisley L, Landes CF. 2013. Troika of single particle tracking programming: SNR enhancement, particle identification, and mapping. Phys. Chem. Chem. Phys. 16:624–34 35. Thompson RE, Larson DR, Webb WW. 2002. Precise nanometer localization analysis for individual fluorescent probes. Biophys. J. 82:2775–83 36. Schmidt T, Schuetz GJ, Baumgartner W, Gruber HJ, Schindler H. 1996. Imaging of single molecule diffusion. PNAS 93:2926–29 37. Rust MJ, Bates M, Zhuang X. 2006. Sub-diffraction-limit imaging by stochastic optical reconstruction microscopy (STORM). Nat. Methods 3:793–95 38. Betzig E, Patterson GH, Sougrat R, Lindwasser OW, Olenych S, et al. 2006. Imaging intracellular fluorescent proteins at nanometer resolution. Science 313:1642–45 39. Hess ST, Girirajan TPK, Mason MD. 2006. Ultra-high resolution imaging by fluorescence photoactivation localization microscopy. Biophys. J. 91:4258–72 40. Soper SA, Shera EB, Martin JC, Jett JH, Hahn JH, et al. 1991. Single-molecule detection of rhodamine 6G in ethanolic solutions using continuous wave laser excitation. Anal. Chem. 63:432–37 41. Elson EL, Magde D. 1974. Fluorescence correlation spectroscopy. I. Conceptual basis and theory. Biopolymers 13:1–27 42. Aragon SR, Pecora R. 1976. Fluorescence correlation spectroscopy as a probe of molecular dynamics. J. Chem. Phys. 64:1791–803 43. Ye F, Higgins DA, Collinson MM. 2007. Probing chemical interactions at the single-molecule level in mesoporous silica thin films. J. Phys. Chem. C 111:6772–80 44. Wirth MJ, Swinton DJ. 1998. Single-molecule probing of mixed-mode adsorption at a chromatographic interface. Anal. Chem. 70:5264–71 45. Pramanik R, Ito T, Higgins DA. 2013. Single molecule wobbling in cylindrical mesopores. J. Phys. Chem. C 117:3668–73 46. Giri D, Hanks CN, Collinson MM, Higgins DA. 2014. Single-molecule spectroscopic imaging studies of polarity gradients prepared by infusion-withdrawal dip-coating. J. Phys. Chem. C 118:6423–32 47. Sepiol J, Jasny J, Keller J, Wild UP. 1997. Single molecules observed by immersion mirror objective. The orientation of terrylene molecules via the direction of its transition dipole-moment. Chem. Phys. Lett. 273:444–48 48. Dickson RM, Norris DJ, Moerner WE. 1998. Simultaneous imaging of individual molecules aligned both parallel and perpendicular to the optic axis. Phys. Rev. Lett. 81:5322–25 49. Yildiz A, Selvin PR. 2005. Fluorescence imaging with one nanometer accuracy: application to molecular motors. Acc. Chem. Res. 38:574–82 50. Enderlein J, Toprak E, Selvin PR. 2006. Polarization effect on position accuracy of fluorophore localization. Opt. Express 14:8111–20 51. Robben KC, Tran-Ba K-H, Ito T, Higgins DA. 2014. Trajectory-profile-guided single molecule tracking for assessment of one-dimensional diffusion trajectories. Anal. Chem. 86:10820–27 52. Kastantin M, Walder R, Schwartz DK. 2012. Identifying mechanisms of interfacial dynamics using single-molecule tracking. Langmuir 28:12443–56 53. Peterson EM, Harris JM. 2010. Quantitative detection of single molecules in fluorescence microscopy images. Anal. Chem. 82:189–96 54. Soper SA, Legendre BL, Huang JP. 1995. Evaluation of thermodynamic and photophysical properties of tricarbocynaine near-IR dyes in organized media using single-molecule monitoring. Chem. Phys. Lett. 237:339–45 55. Cooper JT, Peterson EM, Harris JM. 2013. Fluorescence imaging of single-molecule retention trajectories in reversed-phase chromatographic particles. Anal. Chem. 85:9363–70 www.annualreviews.org • Single-Molecule Investigations


10.21

ARI

21 May 2015

14:59

56. Koynov K, Butt H-J. 2012. Fluorescence correlation spectroscopy in colloid and interface science. Curr. Opin. Colloid Interf. Sci. 17:377–87 57. Koppel DE. 1974. Statistical accuracy in fluorescence correlation spectroscopy. Phys. Rev. A 10:1938–45 58. Ye F, Collinson MM, Higgins DA. 2007. Molecular orientation and its influence on autocorrelation amplitudes in single-molecule imaging experiments. Anal. Chem. 79:6465–72 59. Sanguigno L, De Santo I, Causa F, Netti P. 2010. A closed form for fluorescence correlation spectroscopy experiments in submicrometer structures. Anal. Chem. 82:9663–70 60. Sanguigno L, De Santo I, Causa F, Netti P. 2011. Fluorescence correlation spectroscopy in semiadhesive wall proximity. Anal. Chem. 83:8101–7 61. Wirth MJ, Ludes MD, Swinton DJ. 2001. Analytic solution to the autocorrelation function for lateral diffusion and rare strong adsorption. Appl. Spectrosc. 55:663–69 62. Wirth MJ, Swinton DJ, Ludes MD. 2003. Adsorption and diffusion of single molecules at chromatographic interfaces. J. Phys. Chem. B 107:6258–68 63. Ha T, Enderle T, Chemla DS, Selvin PR, Weiss S. 1997. Quantum jumps of single molecules at room temperature. Chem. Phys. Lett. 271:1–5 64. Hohlbein J, Steinhart M, Schiene-Fischer C, Benda A, Hof M, Hubner CG. 2007. Confined diffusion ¨ in ordered nanoporous alumina membranes. Small 3:380–85 65. Zhong Z, Lowry M, Wang G, Geng L. 2005. Probing strong adsorption of solute onto C18 -silica gel by fluorescence correlation imaging and single-molecule spectroscopy under RPLC conditions. Anal. Chem. 77:2303–10 66. Cohen B, Sanchez F, Douhal A. 2010. Mapping the distribution of an individual chromophore interacting with silica-based nanomaterials. J. Am. Chem. Soc. 132:5507–14 67. Seebacher C, Hellriegel C, Deeg F-W, Bräuchle C, Altmaier S, et al. 2002. Observation of translational diffusion of single terrylenediimide molecules in a mestructured molecular sieve. J. Phys. Chem. B 106:5591–95 68. Mahurin SM, Dai S, Barnes MD. 2003. Probing the diffusion of a dilute dye solution in mesoporous glass with fluorescence correlation spectroscopy. J. Phys. Chem. B 107:13336–40 69. McCain KS, Hanley DC, Harris JM. 2003. Single-molecule fluorescence trajectories for investigating molecular transport in thin silica sol-gel films. Anal. Chem. 75:4351–59 70. Fu Y, Ye F, Sanders WG, Collinson MM, Higgins DA. 2006. Single molecule spectroscopy studies of diffusion in mesoporous silica thin films. J. Phys. Chem. B 110:9164–70 71. Ito S, Fukuya S, Kusumi T, Ishibashi Y, Miyasaka H, et al. 2009. Microscopic structure and mobility of guest molecules in mesoporous hybrid organosilica: evaluation with single-molecule tracking. J. Phys. Chem. C 113:11884–91 72. Viteri CR, Gilliland JW, Yip WT. 2003. Probing the dynamic guest-host interactions in sol-gel films using single molecule spectroscopy. J. Am. Chem. Soc. 125:1980–87 73. Zhou Y, Yip WT. 2009. Balance between coulombic interactions and physical confinement in silica hydrogel encapsulation. J. Phys. Chem. B 113:5720–27 74. Kawai T, Yoshihara S, Iwata Y, Fukaminato T, Irie M. 2004. Anisotropic translational diffusion of single fluorescent perylene molecules in a nematic liquid crystal. Chem. Phys. Chem. 5:1606–9 75. Kawai T, Kubota A, Kawamura K, Tsumatori H, Nakashima T. 2008. Single molecule fluorescence autocorrelation measurement on anisotropic molecular diffusion in nematic liquid crystal. Thin Solid Films 516:2666–69 76. Lammi RK, Fritz KP, Scholes GD, Barbara PF. 2004. Ordering of single conjugated polymers in a nematic liquid crystal host. J. Phys. Chem. B 108:4593–96 77. Link S, Hu D, Chang W-S, Scholes GD, Barbara PF. 2005. Nematic solvation of segmented polymer chains. Nano Lett. 5:1757–60 78. Chang W-S, Link S, Yethiraj A, Barbara PF. 2008. Single molecule spectroscopy of conjugated polymer chains in an electric field-aligned liquid crystal. J. Phys. Chem. B 112:448–53 79. Schulz B, Täuber D, Friedriszik F, Graaf H, Schuster J, von Borczykowski C. 2010. Optical detection of heterogeneous single molecule diffusion in thin liquid crystal films. Phys. Chem. Chem. Phys. 12:11555–64 80. Schulz B, Täuber D, Schuster J, Baumgärtel T, von Borczykowski C. 2011. Influence of mesoscopic structures on single molecule dynamics in thin smectic liquid crystal films. Soft Matter 7:7431–40


AC08CH10-Higgins

10.22

Higgins et al.



AC08CH10-Higgins

ARI

21 May 2015

14:59

81. Ghosh S, Mandal U, Adhikari A, Bhattacharyya K. 2009. Study of diffusion of organic dyes in a triblock copolymer micelle and gel by fluorescence correlation spectroscopy. Chem. Asian J. 4:948–54 82. Kirkeminde AW, Torres T, Ito T, Higgins DA. 2011. Multiple diffusion pathways in Pluronic F127 mesophases revealed by single molecule tracking and fluorescence correlation spectroscopy. J. Phys. Chem. B 115:12736–43 83. Guo L, Chowdhury P, Fang J, Gai F. 2007. Heterogeneous and anomalous diffusion inside lipid tubules. J. Phys. Chem. B 111:14244–49 84. Qian H, Sheetz MP, Elson EL. 1991. Single particle tracking. Analysis of diffusion and flow in twodimensional systems. Biophys. J. 60:910–21 85. Saxton MJ. 1997. Single-particle tracking: the distribution of diffusion coefficients. Biophys. J. 72:1744–53 86. Saxton MJ. 1993. Lateral diffusion in an archipelago. Single-particle diffusion. Biophys. J. 64:1766–80 87. Jung C, Kirstein J, Platschek B, Bein T, Budde M, et al. 2008. Diffusion of oriented single molecules with switchable mobility in networks of long unidimensional nanochannels. J. Am. Chem. Soc. 130:1638–48 88. Liao Y, Yang SK, Koh K, Matzger AJ, Biteen JS. 2012. Heterogeneous single-molecule diffusion in one, two-, and three-dimensional microporous coordination polymers: directional, trapped and immobile guests. Nano Lett. 12:3080–85 89. Yorulmaz M, Kiraz A, Demirel AL. 2009. Motion of single terrylene molecules in confined channels of poly(butadiene)-poly(ethylene oxide) diblock copolymer. J. Phys. Chem. B 113:9640–43 90. Tran-Ba K-H, Finley JJ, Higgins DA, Ito T. 2012. Single-molecule tracking studies of millimeter-scale cylindrical domain alignment in polystyrene-poly(ethylene oxide) diblock copolymer films induced by solvent vapor penetration. J. Phys. Chem. Lett. 3:1968–73 91. Zurner A, Kirstein J, Doblinger M, Bräuchle C, Bein T. 2007. Visualizing single-molecule diffusion in ¨ ¨ mesoporous materials. Nature 450:705–8 92. Kirstein J, Platschek B, Jung C, Brown R, Bein T, Bräuchle C. 2007. Exploration of nanostructured channel systems with single-molecule probes. Nat. Mater 6:303–10 93. Tran Ba KH, Everett TA, Ito T, Higgins DA. 2011. Trajectory angle determination in one dimensional single molecule tracking data by orthogonal regression analysis. Phys. Chem. Chem. Phys. 13:1827–35 94. Feil F, Cauda V, Bein T, Bräuchle C. 2012. Direct visualization of dye and oligonucleotide diffusion in silica filaments with collinear mesopores. Nano Lett. 12:1354–61 95. Park SC, Ito T, Higgins DA. 2013. Single molecule tracking studies of flow-aligned mesoporous silica monoliths: aging-time dependence of pore order. J. Phys. Chem. B 117:4222–30 96. Ma C, Yeung ES. 2010. Entrapment of individual DNA molecules and nanoparticles in porous alumina membranes. Anal. Chem. 82:654–57 97. Ma C, Yeung ES. 2010. Single molecule imaging of protein molecules in nanopores. Anal. Chem. 82:478– 82 98. Ma C, Han R, Qi S, Yeung ES. 2012. Selective transport of single protein molecules inside gold nanotubes. J. Chromatog. A 1238:11–14 99. Beck JS, Vartuli JC, Roth WJ, Leonowicz ME, Kresge CT, et al. 1992. A new family of mesoporous molecular sieves prepared with liquid crystal templates. J. Am. Chem. Soc. 114:10834–43 100. Tolbert SH, Firouzi A, Stucky GD, Chmelka BF. 1997. Magnetic field alignment of ordered silicatesurfactant composites and mesoporous silica. Science 278:264–68 101. Etchegoin P. 1999. Fluorescence photobleaching recovery spectroscopy in a dye doped nematic liquid crystal. Phys. Rev. E 59:1860–67 102. Tran-Ba K-H, Higgins DA, Ito T. 2014. Single-molecule tracking studies of flow-induced microdomain alignment in cylinder-forming polystyrene-poly(ethylene oxide) diblock copolymer films. J. Phys. Chem. B 118:11406–15 103. Elliott LCC, Barhoum M, Harris JM, Bohn PW. 2011. Trajectory analysis of single molecules exhibiting non-brownian motion. Phys. Chem. Chem. Phys. 13:4326–34 104. Ying W, Huerta G, Steinberg S, Zuniga M. 2009. Time series analysis of particle tracking data for molecular motion on the cell membrane. Bull. Math. Biol. 71:1967–2024 105. Pumpa M, Cichos F. 2012. Slow single-molecule diffusion in liquid crystals. J. Phys. Chem. B 116:14487– 93 www.annualreviews.org • Single-Molecule Investigations


10.23

ARI

21 May 2015

14:59

106. Hellriegel C, Kirstein J, Bräuchle C. 2005. Tracking of single molecules as a powerful method to characterize diffusivity of organic species in mesoporous materials. New. J. Phys. 7:1–14 107. Kirstein JU. 2007. Diffusion of single molecules in nanoporous mesostructured materials. PhD Thesis. Ludwig Maximilians Univ., Munich 108. Anovitz LM, Mamontov E, ben Ishai P, Kolesnikov AI. 2013. Anisotropic dynamics of water ultraconfined in macroscopically oriented channels of single-crystal beryl: a multifrequency analysis. Phys. Rev. E 88:052306 109. Pramanik R, Ito T, Higgins DA. 2013. Molecular length dependence of single molecule wobbling within surfactant- and solvent-filled silica mesopores. J. Phys. Chem. C 117:15438–46 110. Bohmer M, Enderlein J. 2003. Orientation imaging of single molecules by wide-field epifluorescence ¨ microscopy. J. Opt. Soc. Am. B 20:554–59 111. Jasny J, Sepiol J. 1997. Single molecules observed by immersion mirror-objective: a novel method of finding the orientation of a radiating dipole. Chem. Phys. Lett. 273:439–43 112. Bartko AP, Dickson RM. 1999. Three-dimensional orientations of polymer-bound single molecules. J. Phys. Chem. B 103:3053–56 113. Ha T, Laurence TA, Chemla DS, Weiss S. 1999. Polarization spectroscopy of single fluorescent molecules. J. Phys. Chem. B 103:6839–50 114. Fourkas JT. 2001. Rapid determination of the three-dimensional orientation of single molecules. Opt. Lett. 26:211–13 115. Rosenberg SA, Quinlan ME, Forkey JN, Goldman YE. 2005. Rotational motions of macromolecules by single-molecule fluorescence microscopy. Acc. Chem. Res. 38:583–93 116. Reznik C, Berg R, Foster E, Advincula R, Landes CF. 2011. Transient three-dimensional orientation of molecular ions in an ordered polyelectrolyte membrane. J. Phys. Chem. Lett. 2:592–98 117. Sick B, Hecht B, Novotny L. 2000. Orientational imaging of single molecules by annular illumination. Phys. Rev. Lett. 85:4482–85 118. Axelrod D. 1979. Carbocyanine dye orientation in red cell membrane studied by microscopic fluorescence polarization. Biophys. J. 26:557–73 119. Jung C, Hellriegel C, Michaelis J, Bräuchle C. 2007. Single-molecule traffic in mesoporous materials: translational, orientational, and spectral dynamics. Adv. Mater. 19:956–60 120. Pecher J, Mecking S. 2010. Nanoparticles of conjugated polymers. Chem. Rev. 110:6260–79 121. Wu C, Chiu DT. 2013. Highly fluorescent semiconducting polymer dots for biology and medicine. Angew. Chem. Int. Ed. 52:3086–109 122. Wei Q-H, Bechinger C, Leiderer P. 2000. Single-file diffusion of colloids in one-dimensional channels. Science 287:625–27 123. Pavani SRP, Thompson MA, Biteen JS, Lord SJ, Liu N, et al. 2009. Three-dimensional, single-molecule fluorescence imaging beyond the diffraction limit by using a double-helix point spread function. PNAS 106:2995–99 124. Ram S, Kim D, Ober RJ, Ward ES. 2012. 3D single molecule tracking with multifocal plane microscopy reveals rapid intercellular transferrin transport at epithelial cell barriers. Biophys. J. 103:1594–603 125. Sun W, Marchuk K, Wang G, Fang N. 2010. Autocalibrated scanning-angle prism-type total internal reflection fluorescence microscopy for nanometer-precision axial position determination. Anal. Chem. 82:2441–47 126. Katayama Y, Burkacky O, Meyer M, Bräuchle C, Gratton E, Lamb DC. 2009. Real-time nanomicroscopy via three-dimensional single-particle tracking. Chem. Phys. Chem. 10:2458–64


AC08CH10-Higgins

10.24

Higgins et al.


Cytoskeletal Network Morphology Regulates Intracellular Transport Dynamics.

Nanostructured Materials for a Sustainable Future.

Nanostructured Electrode Materials for Electrochemical Capacitor Applications.

Hierarchically nanostructured materials for sustainable environmental applications.

Investigation of the kinetic and mass transport limitations in thermoelectrochemical cells with different electrode materials.

High-strength and high-ductility nanostructured and amorphous metallic materials.

Nanostructured carbon materials decorated with organophosphorus moieties: synthesis and application.

Transport phenomena in nanoporous materials.

Nanostructured Materials for Li-Ion Batteries and Beyond.

[Pharmacochemical investigations on raw materials genus passiflora. 3. Phytochemical investigations on raw materials of passiflora edulis forma flavicarpa (author's transl)].

Irradiation Induced Microstructure Evolution in Nanostructured Materials: A Review.

Self-assembly of nanostructured materials through irreversible covalent bond formation.

Controlling the enzymatic digestion of lipids using hybrid nanostructured materials.

Nanostructured carbon materials based electrothermal air pump actuators.

2D Hybrid Nanostructured Dirac Materials for Broadband Transparent Electrodes.

Nanostructured Mo-based electrode materials for electrochemical energy storage.

Ionic self-assembly for functional hierarchical nanostructured materials.

Nanostructured materials from hydroxyethyl cellulose for skin tissue engineering.

Hydrogen transport in non-ideal crystalline materials.

Biocompatibility assessment of haemodialysis membrane materials by proteomic investigations.

Nanostructured silicon membranes for control of molecular transport.

Morphology control in biphasic hybrid systems of semiconducting materials.

Mass spectrometry imaging of fingerprint sweat on nanostructured silicon.

Dynamics of fast axonal transport.