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In Situ Observation of Surface-Enhanced Raman Scattering From Silver Nanoparticle Dimers and Trimers Fabricated Using AFM Manipulation Taisuke Fukui, Hiroyuki Naiki, and Sadahiro Masuo J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b03709 • Publication Date (Web): 21 Aug 2017 Downloaded from http://pubs.acs.org on August 26, 2017

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The Journal of Physical Chemistry

In Situ Observation of Surface-Enhanced Raman Scattering from Silver Nanoparticle Dimers and Trimers Fabricated Using AFM Manipulation Taisuke Fukui†, Hiroyuki Naiki‡, and Sadahiro Masuo‡* †

Department of Chemistry, and ‡Department of Applied Chemistry for Environment, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan.

ABSTRACT The generation of surface-enhanced Raman scattering (SERS) was directly observed in situ during the fabrication of Ag nanoparticle (AgNP) dimers and trimers using atomic force microscopy (AFM) manipulation, and the size of the SERS hot spot was estimated using the super-resolution imaging technique. SERS from 4,4’-bipyridine was observed upon the fabrication of the AgNP dimers and trimers using AFM manipulation. Then, the SERS spots were analyzed by fitting with the point spread function for super-resolution imaging. The distribution of the centroid position of the SERS spot from the AgNP dimer was 9 nm along the x-axis and 8 nm along the y-axis, which represent the size of the SERS hot spot. The same technique was applied to the AgNP trimer. The obtained results are important not only for the

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SERS technique but also for other plasmon enhancement techniques which are useful in a wide range of research areas.

INTRODUCTION Surface-enhanced Raman scattering (SERS) by metal nanostructures has great potentials for use as an analytical technique in the fields of biomedicine,1,2 molecular biology,3−5 and environmental sciences6 due to its ability to identify and confirm molecular components at the single-molecule level. Both experimental and theoretical approaches have demonstrated that SERS is strongly scattered from junctions in metal nanoparticle (MNP) aggregates.7−10 Two main mechanisms have been suggested for the generation of SERS. The first mechanism is the so-called electrical mechanism, which is caused by the strong electric field of the localized surface plasmon resonance (LSPR) on the MNP aggregates.9−12 Upon irradiating the aggregates with resonant light, a strong electric field is generated at the junction of the aggregates, which is called a hot spot. When molecules interact with the electric field at the hot spot through dipoledipole coupling, the excitation and scattering field intensities of the Raman scattering from molecules located at the junctions increase (up to 1010 times). The second mechanism is the socalled chemical mechanism, which consists of various effects, including the resonance Raman effect, the charge-transfer effect, and the adsorption effect.10,13−14 Generally, the enhancement provided by the electrical mechanism is stronger than that from the chemical mechanism (~104 times). Combining the electrical and chemical effects, SERS enhancement from the MNP aggregates increases 1014-fold compared to conventional Raman scattering. Thus, the hot spot provided by the electrical mechanism of SERS plays the most important role in enhancing the Raman scattering of molecules.


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The importance of the SERS hot spot has been clarified trough quantitative studies.7−10 Itoh et al. investigated the necessity of the hot spot for the generation of SERS by combining SERS and scanning electron microscopy (SEM) observations. They demonstrated that AgNP dimers induced SERS, whereas SERS was not observed from the molecule adsorbed on a single AgNP. Thus, the presence of an AgNP junction was required to observe SERS. In addition, they confirmed polarization-dependent SERS generation, in which SERS was generated by irradiating with incident light at a polarization angle parallel to the long axis of the dimer.7,10 This result also indicated that the generation of a hot spot was required to observe SERS. To examine the size and location of the hot spot, Willet et al. applied the super-resolution imaging technique, which has a spatial resolution of 5 nm, to AgNP dimers, trimers, and aggregates.8−9,15−18 By analyzing the point spread function (PSF) of the SERS spot, they demonstrated that the SERS spot cab be observed at the junction of the AgNP dimer and that the size of the SERS hot spot depended on the shape and size of the AgNPs; therefore, and the morphology of the aggregates could be estimated by overcoming optical diffraction limitations. In most reports, the influence of the hot spot on SERS has been investigated using selfassembled MNP aggregates, i.e., SERS was observed from self-assembled aggregates deposited on a substrate, which was prepared by facilitating aggregation in the suspension. For example, in the reports by Willet et al., the size of the SERS hot spot was estimated with the assumption that the hot spot is located at the junction.8−9,15−18 No reports have achieved the in situ observation of hot spots resulting from the fabrication of MNP aggregates to accurately estimate the size of the hot spot. It would be interesting to determine whether SERS can be generated during the in situ fabrication of simple MNP aggregates, such as dimer and trimer structures. In principle, when MNP dimers are fabricated by combining two MNPs, SERS should be observed due to the


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generation of a hot spot. Atomic force microscopy (AFM) manipulation is a useful technique to observe in situ the generation of SERS during the fabrication of MNP dimers and trimers.19−21 Previously, Tong et al. demonstrated SERS generation using AFM manipulation.19−20 SERS was generated by aligning AuNPs with organic molecules or by moving an AuNP to the vicinity of a single carbon nanotube using the manipulation technique. In this work, to confirm whether a SERS hot spot exists at a MNP junction and to estimate the size of the SERS hot spot, we observed in situ the generation of SERS from 4,4’-bipyridine from AgNP dimers and trimers prepared using AFM manipulation. 4,4’-Bipyridine was adsorbed on the AgNPs, and then single AgNPs were moved by AFM manipulation to fabricate AgNP dimer and trimer structures. SERS was observed during the fabrication of the AgNP dimers and trimers. The observed SERS spot was analyzed using the PSF and super-resolution imaging on the order of few nanometers, and the size of the hot spot was estimated. In situ observation using the AFM manipulation technique clarified the generation of the hot spot.

EXPERIMENTAL SECTION Preparation of AgNPs with 4,4’-bipyridine AgNPs (containing sodium citrate as stabilizer) and 4,4’-bipyridine were purchased from Sigma Aldrich and Wako Pure Chemical Industries, respectively. All chemicals were used as received without further purification. An aqueous solution of 4,4’-bipyridine (2 × 10-5 M) was mixed with an aqueous suspension of the AgNPs (2 × 10-5 M) in a 1:1 volume ratio. The mixture was spin-coated onto a glass coverslip. Instrument setup for SERS measurement and fabrication of AgNP dimers and trimers using AFM manipulation As the excitation light source for SERS measurement, a 532 nm continuous-wave laser (Spectra-Physics, Excelsior-532-50) was passed through a bandpass filter


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(Semlock, LL01-532-25) and subsequently introduced into an inverted microscope (Olympus, IX-71). Then, the beam was reflected using a dichroic mirror (Semrock, FF555-Di02-25×36) and focused onto the 100-µm area of the sample using an oil-immersion objective lens (Olympus, 100×, N.A:1.4). AFM manipulation of the AgNPs was realized using an AFM (JPK instruments, NanoWizard II) placed on top of the inverted microscope stage.21 In addition to the three closedloop, piezo-driven axes of the AFM, a two-axis, closed loop, piezo-driven sample stage was employed. SERS from 4,4’-bipyridine was collected using the same objective lens and passed through a notch filter (Semrock, NF01-532U-25). The SERS image was obtained using an EMCCD (Photometrics, Cascade II 512). The SERS spectra were also measured using a spectrometer (Acton Research Corporation, SpectraPro2358) with a cooled CCD camera (Princeton Instruments, PIXIS400B) by switching the optical path of the detected SERS using a mirror. The AFM manipulation of the AgNPs along with the detection of the accompanying SERS behavior of 4,4’-bipyridine was performed using the following procedure. Initially, a silicon AFM tip (Olympus, OMLC-AC160TS-R3) was coupled to the center of the focused excitation laser by adjusting the piezo of the AFM. Then, the AFM topography and SERS images of the sample were measured before AFM manipulation. Subsequently, AgNP dimers and trimers were fabricated using the AFM tip to move one AgNP to the vicinity of another by moving the sample stage. Then, the AFM topography and SERS behavior of 4,4’-bipyridine from the AgNP dimers and trimers were measured. The AFM topography measurement and manipulation of the AgNPs were performed in tapping mode and contact mode, respectively. All measurements were performed at room temperature under ambient conditions.


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RESULTS AND DISCUSSION The AgNPs exhibited a peak LSPR wavelength at 433 nm (Figure 1a). A TEM image of the AgNPs, and a histogram of the diameter of the AgNP estimated from the TEM image are shown Figure 1b and 1c, respectively. The average diameter was estimated to be 40 nm from the histogram. Figure 2 shows the AFM topography images (a and b) and cross-sections (c and d) of the AgNPs before (a and c) and after (b and d) fabricating the AgNP dimers through AFM manipulation. Before manipulation, the AgNP was far away from the other AgNP (~ 400 nm), and the heights of the two AgNPs were estimated to be 44 nm (Figures 2a and c), which was similar to the diameter estimated from the TEM image. To fabricate the AgNP dimer, the first AgNP (red circle) was pushed to the second AgNP using the AFM tip, as shown by the arrow in Figure 2a, where the two AgNPs then combined into an AgNP dimer (Figure 2b). As the width of the AgNP dimer was larger than that of the single AgNP and the height did not change (Figure 2d), the two AgNPs were aligned in the x-y plane. The SERS images before (e) and after (f) fabricating the AgNP dimer are shown in Figure 2. Before fabricating the AgNP dimer (Figure 2e), a bright spot can be observed in the upper left region (blue circle). The spot is attributed to the SERS of 4,4’-bipyridine with the aggregated AgNPs assembled during the sample preparation. The spot was used as a maker to show the appearance of a SERS spot upon fabricating the AgNP dimer. After fabricating the AgNP dimer, a new bright spot appeared in the lower right region (green circle). The appearance of the new bright spot after AFM manipulation is also shown in the movie in the Supporting Information (see Movie S1). To confirm that the new bright spot was attributed to the SERS from the 4,4’-bipyridine, the spectrum of the bright spot was recorded and is shown in Figure 2g. The observed spectrum exhibited Raman bands, which can be attributed to the vibrational modes of the 4,4’-bipyridine molecule at 1018 cm-1


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(ring breathing), at 1080 cm-1 (in-plane ring deformation, C-H bending), at 1240 cm-1 (in-plane C-H bending), at 1300 cm-1 (inter-ring stretching), and at 1612 cm-1 (ring stretching). The peak wavenumbers and shapes of the spectrum were consistent with the reported SERS spectrum of 4,4’-bipyridine.22−27 Therefore, the new bright spot was attributed to SERS from 4,4’-bipyridine. Murakoshi et al. reported the SERS spectra of 4,4’-bipyridine enhanced by Ag dimer structure which was fabricated by vacuum deposition of Ag.26,27 The wavenumbers of the vibrational modes of our SERS spectrum were completely consistent with those of the reported SERS spectra, which indicated that the 4,4’-bipyridine did not interact with sodium citrate which was containing our AgNP suspension as stabilizer. In addition, the electric field enhancement of the AgNP dimer was investigated using the numerical simulation (details in the Supporting Information). By this simulation, we confirmed that the incident laser at 532 nm can be enhanced at the junction of the AgNPs by fabricating the AgNP dimer. From these results, SERS could be observed during the fabrication of the AgNP dimer using AFM manipulation. For PSF analysis of the SERS spot, a photoluminescence (PL) spot from a single CdSe/ZnS quantum dot (QD; Invitrogen, core radius: 2.6 nm, emission peak wavelength: 605 nm) was first measured to estimate the spatial resolution of our measurement setup. A QD suspension in toluene (~10-8 M) was spin-coated on a coverslip, and the PL spot of a single QD was detected. The PL spot was fitted by the PSF in equation (1) (further details are given in the Supporting Information): ,

1 1 − − − − − + − 2 2 . 1

= exp − + .

where I (x, y) is the intensity of the detected PL or SERS for a given position (x, y) in space, I0 is the SERS or PL intensities at the center of the fit, IB.G. is the background intensity, and wx and wy


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are the width of the Gaussian along the x- and y-axis, respectively. Here, to consider the movement of the PL or SERS spot in the diagonal direction, θ is defined as the angle of trajectory between a given position and the centroid positions (x0, y0) of the spot. The centroid positions of the spots were analyzed by fitting the PL and SERS spots using the equation (1). The distribution of the centroid positions estimated from the PL spots of a single QD is shown in Figure 3a. The x- and the y-axis lengths of the distribution were estimated to be 5 and 3 nm, respectively. The slight elongation along the x-axis length was caused by lateral stage drift during the PL measurement. From these results, the spatial resolution of our measurement setup was estimated to be these values. The distribution of the centroid positions of the SERS spot from the AgNP dimer is shown in Figure 3b. The x- and y-axis lengths of the distribution were estimated to be 9 and 8 nm, respectively. Interestingly, the distribution of the centroid positions estimated from the SERS spot was larger than the spatial resolution. This result indicates the movement of the centroid positions of the SERS spot during the SERS measurement. This movement can be attributed to the thermal diffusion of 4,4’-bipyridine in the hot spot. Generally, SERS is generated at the hot spot of the MNPs through the enhancement of the excitation and scattering processes as follows10,12,28,29: (i) excitation light is absorbed by an MNP; (ii) the absorbed light energy excites a molecule through dipole-dipole coupling with the electric field of the hot spot; (iii) some of the excited energy in the molecule is converted into Raman scattering; (iv) a Raman scattering photon is scattered back from the molecule to the MNP; and (v) SERS is scattered from the MNP as plasmon-dipole radiation. Based on this process, SERS can be scattered from hot spots of MNPs. Hence, the molecule coupled with the hot spot is important to generating SERS. In our case, SERS was observed from the hot spot generated by fabricating an AgNP dimer using AFM manipulation. The time trace of the observed SERS intensity is shown


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in Figure 4. The time trace exhibited on and off states of SERS at millisecond to second time scales, i.e., the typical blinking behavior of SERS.12,28,29 The blinking was partially attributed to the thermal diffusion of molecules in-and-out of the hot spot.12,28,29 Hence, the thermal diffusion of 4,4’-bipyridine in the hot spot of the AgNP dimer induced the coupling and uncoupling of 4,4’-bipyridine with the electric field of the hot spot. In Figure 3b, the distribution of the centroid positons of the SERS spot was larger than the spatial resolution. This result indicated that 4,4’bipyridine diffused in and out of the hot spot of the AgNP dimer and scattered SERS at the several positions in the hot spot. Therefore, the distribution of the centroid positions represented the size of the hot spot of the AgNP dimer. As shown in Figure 3b, the x-axis of the distribution of the centroid positions of the SERS spot was longer than the y-axis. As seen in the AFM image in Figure 2a, the boundary of the AgNP dimer between the two AgNPs was oblique, because the two AgNPs were moved from the upper left and lower right regions. Therefore, the distribution of the centroid positions of the SERS spot was also oblique. The generation of a hot spot was directly observed, and the size of the hot spot was estimated using a combination of AFM manipulation and super-resolution imaging. Figure 5 shows the AFM topography images (a-c) and cross-sections (d-f) of the AgNPs before (a, b, d, and e) and after (c and f) fabricating the AgNP trimer via AFM manipulation. To fabricate the AgNP trimer, an AgNP with a height of 54 nm, shown in the lower right region (blue circle) of the AFM image, was pushed to an AgNP with a height of 34 nm, shown by an arrow in the upper right region in Figure 5a. Thus, an AgNP dimer (red circle) was fabricated, as shown in Figure 5b. The height of the fabricated AgNP dimer was estimated to be 80 nm, which was almost the sum of the two AgNPs (Figure 5d and e). This increase in height indicated that the AgNPs were stacked. To fabricate the AgNP trimer, another AgNP with a height of 34 nm,


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shown in the upper left region (green circle), was pushed to the AgNP dimer, shown by an arrow in Figure 5b. Finally, the AgNP trimer was fabricated, as shown in Figure 5c. The height of the fabricated AgNP trimer was estimated to be 135 nm (Figure 5f), indicating that the three AgNPs were stacked in the vertical direction of the x-y plane. The distribution of the centroid positions of the SERS spot of the AgNP trimer is shown in Figure 5g. Because the AgNP trimer is aligned in the x-y plane, the two distributions of the centroid positions of SERS spot should be fully separated, as the distribution of the centroid positons was considerably smaller than the size of an AgNP, as indicated by the result of the AgNP dimer. For the present AgNP trimer, the distribution of the centroid positions was not separated in the x-y plane, which was caused by the AgNPs being stacked in the vertical direction, as shown in the AFM image in Figure 5c. Hence, because the hot spots overlapped in the x-y projection, a single distribution of the centroid positions was observed, as shown in Figure 5g. The distribution was estimated to be 8 nm along the x-axis and 16 nm along y-axis. The distribution of the centroid positions was larger than that of AgNP dimer (Figure 3b). Interestingly, the obtained distribution of the centroid positions showed that the length of the y-axis was longer than that of the x-axis. For the AgNP dimer, the length of the x-axis was longer than that of the y-axis. Hence, the AgNP trimer would tilt in the y-axis direction. The hot spots were not fully overlapped in the x-y projection. Therefore, the distribution of the centroid positions was observed as a single spot and was larger than that of the AgNP dimer. From these results, the distribution and location of the hot spot strongly depend on the morphology of the MNP aggregates, as determined by the combination of AFM manipulation and the super-resolution imaging.

CONCLUSIONS


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The SERS spots of AgNP dimers and trimers with 4,4’-bipyridine fabricated by AFM manipulation were observed in situ, and the distributions of the centroid positions of the SERS spots were estimated by super-resolution imaging. The distribution of the centroids on the AgNP dimer was larger than the spatial resolution of our measurement set up. The distribution of the centroid positions was attributed to the thermal diffusion of 4,4’-bipyridine at the hot spot, and the thermal diffusion was confirmed through the observation of the blinking behavior of SERS. For the AgNP trimer, the distribution of the centroid positions was generated at one location and was larger than that of the AgNP dimer. The single distribution of the centroid positions resulted from the stacking of the three AgNPs in the vertical direction of the x-y plane and the overlapping of the hot spots in the x-y projection. Therefore, the size and location of a hot spot can be observed by AFM and super-resolution imaging using AFM manipulation. The direct observation of SERS obtained by the combination of AFM manipulation and super-resolution imaging provides further understanding of the generation of SERS hot spots.

SUPPORTING INFORMATION Super-resolution imaging through point spread function fitting, numerical simulation of the AgNP dimer, and the movie of the in situ observation of SERS from an AgNP dimer fabricated using AFM manipulation (AVI). This information is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].


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ACKNOWLEDGMENTS The authors thank Dr. Li Wang and Prof. Naoto Tamai (Department of Chemistry, Kwansei Gakuin University) for the numerical simulation of AgNPs. This work was partly supported by a Grant-in-Aid for Scientific Research (No. 26390023) from the Japan Society for the Promotion of Science (JSPS) and a Grant-in-Aid for Scientific Research on Innovation Areas “Photosynergetics” (No. 26107005) from MEXT, Japan. REFERENCES 1.

Lane, L. A.; Qian, X.; Nie, S. SERS Nanoparticles in Medicine: From Label-Free

Detection to Spectroscopic Tagging. Chem. Rev. 2015, 115, 10489-10529. 2.

Song, J.; Huang, P.; Duan, H.; Chen, X. Plasmonic Vesicles of Amphiphilic

Nanocrystals: Optically Active Multifunctional Platform for Cancer Diagnosis and Therapy. Acc. Chem. Res. 2015, 48, 2506-2515. 3.

Driscoll, A. J.; Harpster, M. H.; Johnson, P. A. The Development of Surface-Enhanced

Raman Scattering as a Detection Modality for Portable in Vitro Diagnostics: Progress and Challenges. Phys. Chem. Chem. Phys. 2013, 15, 20415-20433. 4.

Schlucker, S. Surface-Enhanced Raman Spectroscopy: Concepts and Chemical

Applications. Angew. Chem. Int. Ed. 2014, 53, 4756-4795. 5.

Radziuk, D.; Moehwald, H. Prospects for Plasmonic Hot Spots in Single Molecule SERS

Towards the Chemical Imaging of Live Cells. Phys. Chem. Chem. Phys. 2015, 17, 21072-21093. 6.

Halvorson, R.; Peterj, V. Surface-Enhanced Raman Spectroscopy (SERS) for

Environmental Analyses. Environ. Sci. Technol. 2010, 44, 7749-7755.


12

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


7.

Yoshida, K.; Itoh, T.; Tamaru, H.; Biju, V.; Ishikawa, M.; Ozaki, Y. Quantitative

Evaluation of Electromagnetic Enhancement in Surface-Enhanced Resonance Raman Scattering from Plasmonic Properties and Morphologies of Individual Ag Nanostructures. Phys. Rev. B 2010, 81, 115406. 8.

Weber, M. L.; Willets, K. A. Nanoscale Studies of Plasmonic Hot Spots Using Super-

Resolution Optical Imaging. MRS Bulletin 2012, 37, 745-751. 9.

Willets, K. A. Super-Resolution Imaging of SERS Hot Spots. Chem. Soc. Rev. 2014, 43,

3854-3864. 10. Yamamoto, Y. S.; Itoh, T. Why and How Do the Shapes of Surface-Enhanced Raman Scattering Spectra Change? Recent Progress from Mechanistic Studies. J. Raman Spectros. 2016, 47, 78-88. 11. Campion, A.; Kambhampati, P. Surface-Enhanced Raman Scattering. Chem. Soc. Rev. 1998, 27, 241-250. 12. Yamamoto, Y. S.; Ishikawa, M.; Ozaki, Y.; Itoh, T. Fundamental Studies on Enhancement and Blinking Mechanism of Surface-Enhanced Raman Scattering (SERS) and Basic Applications of SERS Biological Sensing. Front. Phys. 2013, 9, 31-46. 13. Jensen, L.; Aikens, C. M.; Schatz, G. C. Electronic Structure Methods for Studying Surface-Enhanced Raman Scattering. Chem. Soc. Rev. 2008, 37, 1061-1073. 14. Morton, S. M.; Silverstein, D. W.; Jensen, L. Theoretical Studies of Plasmonics Using Electronic Structure Methods. Chem. Rev. 2011, 111, 3962-3994.


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Page 14 of 22

15. Stranahan, S. M.; Willets, K. A. Super-Resolution Optical Imaging of Single-Molecule SERS Hot Spots. Nano Lett. 2010, 10, 3777-3784. 16. Stranahan, S. M.; Titus, E. J.; Willets, K. A. SERS Orientational Imaging of Silver Nanoparticle Dimers. J. Phys. Chem. Lett. 2011, 2, 2711-2715. 17. Titus, E. J.; Weber, M. L.; Stranahan, S. M.; Willets, K. A. Super-Resolution SERS Imaging Beyond the Single-Molecule Limit: An Isotope-Edited Approach. Nano Lett. 2012, 12, 5103-5110. 18. Blythe, K. L.; Titus, E. J.; Willets, K. A. Objective-Induced Point Spread Function Aberrations and Their Impact on Super-Resolution Microscopy. Anal. Chem. 2015, 87, 64196424. 19. Tong, L.; Li, Z.; Zhu, T.; Xu, H.; Liu, Z. Single Gold-Nanoparticle-Enhanced Raman Scattering of Individual Single-Walled Carbon Nanotubes Via Atomic Force Microscope Manipulation. J. Phys. Chem. C 2008, 112, 7119–7123. 20. Tong, L.; Zhu, T.; Liu, Z. Atomic Force Microscope Manipulation of Gold Nanoparticles for Controlled Raman Enhancement. Appl. Phys. Lett. 2008, 92, 023109. 21. Masuo, S.; Kanetaka, K.; Sato, R.; Teranishi, T. Direct Observation of Multiphoton Emission Enhancement from a Single Quantum Dot Using Afm Manipulation of a Cubic Gold Nanoparticle. ACS Photonics 2016, 3, 109-116. 22. Akyüz, S.; Akyüz, T.; Dames, J. E. D. A Fourier-Transform Infrared and Laser-Raman Spectroscopic Investigation of 4,4'-Bipyridyl-Transition Metal (II) Tetracyanonickelate Clathrates. J. Incl. Phenom. Mol. Recognit. Chem. 1996, 26, 111-117.


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23. Muniz-Miranda, M. Surface Enhanced Raman Scattering of 4,4'-Bipyridine Adsorbed on Smooth Copper, Silver and Aluminium Surfaces Activated by Deposited Silver Particles. J. Raman Spectros. 1996, 27, 435-437. 24. Ould-Moussa, L.; Poizat, O.; Castella`-Ventura, M.; Buntinx, G.; Kassab, E. Ab Initio Computations of the Geometrical, Electronic, and Vibrational Properties of the Ground State, the Anion Radical, and the N,N'-Dihydro Cation Radical of 4,4'-Bipyridine Compared to Transient Raman Spectra. J. Phys. Chem. 1996, 100, 2072–2082. 25. Lim, J. K.; Joo, S.-K. Excitation-Wavelength Dependent Charge Transfer Resonance of Bipyridines on Silver Nanoparticles: Surface-Enhanced Raman Scattering Study. Surf. Interface Anal. 2007, 39, 684-690. 26. Sawai, Y.; Takimoto, B.; Nabika, H.; Ajito, K.; Murakoshi, K. Observation of a Small Number of Molecules at a Metal Nanogap Arrayed on a Solid Surface Using Surface-Enhanced Raman Scattering. J. Am. Chem. Soc. 2007, 129, 1658-1662. 27. Nagasawa, F.; Takase, M.; Nabika, H.; Murakoshi, K. Polarization Characteristics of Surface-Enhanced Raman Scattering from a Small Number of Molecules at the Gap of a Metal Nano-Dimer. Chem. Commun. 2011, 47, 4514-4516. 28. Kitahama, Y.; Tanaka, Y.; Itoh, T.; Ozaki, Y. Power-Law Analysis of Surface-PlasmonEnhanced Electromagnetic Field Dependence of Blinking SERS of Thiacyanine or Thiacarbocyanine Adsorbed on Single Silver Nanoaggregates. Phys. Chem. Chem. Phys. 2011, 13, 7439-7448.


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29. Itoh, T.; Biju, V.; Ishikawa, M. Surface-Enhanced Resonance Raman Scattering and Background Light Emission Coupled with Plasmon of Single Silver Nanoaggregates. J. Chem. Phys. 2006, 134708.


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(b)

(a)

300 400 500 600 700 800 Wavelength (nm)

(c) 20

Events

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Extinction (a.u.)

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10

0 20

30

40

50

60

Diameter (nm)

Figure 1. (a) Extinction spectrum of an aqueous suspension of the AgNPs. (b) TEM image of the AgNPs. The scale bar in the image indicates 40 nm. (c) A histogram of the diameter of the AgNP.


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(b)

(c)

(d) Height (nm)

40 20 0 0.0

0.4 0.8 1.2 Distance (µm)

(e)

(g)

40 20 0 0.0


Intensity (a.u.)

(a)

Height (nm)

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1000 1200 1400 1600 1800 Raman shift (cm-1)

(f) Marker

SERS spot of AgNP dimer

Figure 2. AFM topography of the AgNPs (a, b), cross-sections of the blue dotted line in the topography images (c, d), and Raman scattering images (e, f) before (a, c, and e) and after (b, d, and f) fabricating the AgNP dimer by AFM manipulation. (g) SERS spectrum from the AgNP dimer. The scale bars in the images (a, b) indicate 300 nm.


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40

(a) Y position (nm)

40

Y position (nm)

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20 0 -20 -40 -40

-20 0 20 X position (nm)

40

(b)

20 0 -20 -40 -40

-20 0 20 X position (nm)

40

Figure 3. Distributions of the centroid positions of PL from a single QD (a) and SERS from the AgNP dimer (b) obtained by fitting each image frame using the PSF in equation (1).


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Intensity (a. u.)


0

10

20 Time (s)

30

40

Figure 4. Time trace of the SERS intensity from the AgNP dimer obtained from Movie S1.


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(c)

(b)

(a)

40 0 0.0


80 40 0 0.0 0.4 0.8 1.2 Distance (µm)

120 (f)

Height (nm)

80

120 (e)

Height (nm)

120 (d)

80 40 0 0.0 0.4 0.8 1.2 Distance (µm)

Y position (nm)

40

Height (nm)

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(g)

20 0

-20 -40 -40 -20 0 20 40 X position(nm)

Figure 5. AFM topography images of the AgNPs (a-c), and cross-sections of the blue dotted lines in the topography image (d-f) before (a, d) after fabricating the AgNP dimer (b, e) and after fabricating the AgNP trimer (c, f). (g) Distribution of the centroid positions of the SERS spot from the AgNP trimer obtained by fitting each image frame using the PSF in equation (1). The scale bars in the images (a-c) indicate 300 nm.


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TOC Graphic


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In Situ Observation of Surface-Enhanced Raman ... - ACS Publications

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