Stacked Gold Nanodisks for Bimodal Photoacoustic and Optical

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Stacked Gold Nanodisks for Bimodal Photoacoustic and Optical Coherence Imaging Jung-Sub Wi, Jisoo Park, Heesung Kang, Donggeun Jung, Sang-Won Lee, and Tae Geol Lee ACS Nano, Just Accepted Manuscript • Publication Date (Web): 22 May 2017 Downloaded from http://pubs.acs.org on May 27, 2017

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Stacked Gold Nanodisks for Bimodal Photoacoustic and Optical Coherence Imaging Jung-Sub Wi,1,+,* Jisoo Park,1,2,+ Heesung Kang,1,+ Donggeun Jung,2 Sang-Won Lee,1 and Tae Geol Lee1,* 1

Center for Nano-Bio Measurement, Korea Research Institute of Standards and Science, Daejeon

305-340, Rep. of Korea 2

Department of Physics, Sungkyunkwan University, Suwon 440-746, Rep. of Korea

*E-mail: [email protected], [email protected]

(ABSTRACT) Herein, we report on biological imaging nanoprobes: physically-synthesized gold nanodisks that have inherent optical advantages—a wide range of resonant wavelengths, tunable ratio of light absorption-to-scattering, and responsiveness to random incident light—due to their two-dimensional circular nanostructure. Based on our proposed physical synthesis where gold is vacuum-deposited onto a pre-patterned polymer template and released from the substrate in the form of a nanodisk, monodisperse two-dimensional gold nanodisks were prepared with independent control of their diameter and thickness. The optical benefits of the Au nanodisk were successfully demonstrated by the measurement of light absorbance of the nanodisks and the application of stacked nanodisks, where a smaller sized Au nanodisk was laid atop a larger

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nanodisk, as bimodal contrast agents for photoacoustic microscopy and optical coherence tomography.

KEYWORDS. Gold nanoparticle, Plasmonic, Photoacoustic, OCT, Contrast agent

Light absorption and scattering are greatly enhanced by the light-induced collective oscillation of free electrons in a nanostructured noble metal, namely a localized surface plasmon.1-8 This enhanced light-matter interaction allows plasmonic nanoparticles to be promising contrast agents for laser-based biological imaging such as photoacoustic tomography,9-16 optical coherence tomography,17-21 and surface enhanced Raman scattering-based imaging.22-25 Accordingly, much effort has been made to synthesize plasmonic nanoparticles that have well-controlled geometries, as these geometries strongly correlate to the plasmonic nanoparticles’ light-absorbing and lightscattering properties, as well as the resonant wavelengths. In this report, we propose that twodimensional (2D) Au nanodisks and their stacked form resembling that of a fried egg sunny side up, as advanced nanoprobes for laser-based imaging because their 2D forms are intrinsically conducive to a wide range of resonant wavelengths, tunable ratio of light absorption-toscattering, and responsiveness to random incident light. Here, we have judged the use of “2D” to most expeditiously convey the meaning of flatness and to differentiate these nanodisks from other, more obvious one dimensional (1D) or three dimensional (3D) forms.

To fabricate the nanodisks, a top-down physical synthesis—in which Au is vacuum-deposited onto a nanoimprinted polymer template and released from the substrate in the form of a 2D


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nanodisk—was used to avoid the kinetic or thermodynamic considerations necessary in typical colloidal syntheses of nanoparticles. Although 2D plate-like anisotropic shapes are preferred in a colloidal synthesis when the growth rate of a specific crystal plane is much slower than of others, Au nanospheres whose isotropic shape is thermodynamically preferred are usually synthesized together as byproducts.26-28 In addition, 2D nanoplates obtained from colloidal synthesis (typically trianglular nanoplates) have sharp corners and straight edges that require additional effort to smooth out in order to form circular nanodisks.29,30 Compared to chemical synthesis, 2D circular patterns are more easily formed using a lithographical method because a Gaussian beam of electrons or photons is more conducive to the circular shape. Lithographically-defined 2D nanodisks, however, are usually substrate-bound and utilized for studies on their plasmonic sensing properties.2,3,7,31,32 In this work, substrate-released monodisperse 2D Au nanodisks were synthesized by our proposed physical synthesis. The diameters and thicknesses of the Au nanodisks were independently controlled, which allowed the resonant frequency tuning of the nanodisk as well as its light absorption and scattering properties. In short, we show that by stacking two different-sized Au nanodisks it is possible to synthesize bimodal contrast agents that can interact with incident light at two different resonant wavelengths by two different interacting modes: light absorption for photoacoustic imaging and light scattering for optical coherence imaging.

RESULTS AND DISCUSSION As illustrated in Figure 1, the Au nanodisks were prepared using physical synthesis. The method includes steps for nanoimprint lithography (NIL); O2 plasma etching of the residual imprinting


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resist (polymethyl methacrylate, PMMA); wet chemical development of an undercutting layer (polymethylglutarimide, PMGI); vacuum-deposition of Au; Au lift-off; and final release of the nanodisks by dissolution of the sacrificial under-layer (benzocyclobutene, BCB). The released Au nanodisks were then re-dispersed in deionized water after centrifugation. The physical synthesis of artificially designed nanoparticles based on NIL and vacuum deposition has been highlighted in previous reports.33,34 In this work, by utilizing an array of truncated Si nanocones as the NIL mold and by applying an oblique-angle deposition of Au, differently sized twodimensional Au nanodisks and their stacked forms were synthesized and used as contrast agents in laser-based biological imaging.

In this process, the array of truncated Si nanocones shown in Figure S1 was used as the NIL mold and served to enable the synthesis of differently sized Au nanodisks. Since the sloped sidewall of the Si nanocone is transferred to the PMMA layer during the NIL step, the diameter of the cavity at the bottom of the PMMA and the diameters of the Au nanodisks could be increased from 65 nm to 166 nm by increasing the O2 plasma etching time from 4 s to 20 s (Supporting information, Figure S1). Independent control of the lateral and vertical dimensions of the Au nanodisk, then, is possible by varying the etching time of the PMMA and the deposition time of the Au, respectively. The SEM images shown in Figure 2(a-d), observed after drying the aliquots of each nanodisk solution on the Si substrate, clearly demonstrate the role of the Si nanocone as a universal NIL mold that can offer various-sized nanodisks. The average diameters of the Au nanodisks and their deviations were evaluated according to the protocols proposed by NIST for measuring nanoparticle size using SEM35 and showed that the physically synthesized nanodisks had a narrow size distribution of approximately 3 nm (Supporting


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Information, Figure S2). The zeta potential of the Au nanodisks in deionized water was evaluated to be −23.4 ± 9.3 mV, which was suitable for dispersing the nanodisks in for several days and re-dispersing by gentle shaking due to the electrostatic repulsion between the nanodisks. As well as the water-dispersibility, the bare surface of the proposed Au nanodisk without toxic surfactant molecules serves its biocompatibility. As demonstrated in our previous study,36 the physicallysynthesized Au nanodisks show no noticeable influence to the cell viability (up to 104 nanodisks per cell) and also to the apoptotic activity (under 1 µL administration of 10-pM-concentation nanodisks in 6-week-old mice).

As illustrated in Figure 1 and shown in Figure 2(e,f), by tilting the deposition angle and rotating the sample during deposition, it was possible to synthesize a stacked Au nanodisk (SAN) composed of two differently sized nanodisks. Compared to the outer region of the disk where the Au flux is deposited at a specific angle of the sample rotation, the central region of the disk is exposed to the incident Au flux during the entire deposition time. This led to a natural formation of the central protrusion (i.e. upper disk) in the SAN, whose lateral size could be controlled by the incline angle of the Au flux. The three inset images in Figure 2(f) show that the sizes of the protrusions decreased as the deposition angle increased. In fact, at an extreme tilting angle of the Au flux, the central protrusion disappeared, and the Au films that were deposited at the bottom and sidewall surfaces of the polymer pores could be shaped into Au nanodishes.37,38 In the current study, the lateral size of the protrusion was defined as almost half of the overall lateral dimension of the SAN to ensure two different light-interacting windows as discussed below.


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Figure 2(e,f) shows the SEM images of the SAN with an 80 nm sized upper disk and 180 nm sized lower disk. The overall height of the SAN was approximately 60 nm.

To assess the optical characteristics of the physically synthesized stacked Au nanodisks, the extinction spectra of the aqueous solutions of the nanodisks were examined. Figure 3(a) shows that the resonant wavelengths of the 20 nm thick Au nanodisks increased from 670 nm to 830 nm when their diameters were increased from 81 nm to 166 nm. This spectral shift in plasmon resonance was attributed to the increased oscillation length of the surface plasmon as the geometrical size of the nanodisk increased, which aligns with our calculated results (Supporting Information, Figure S3). Further, by changing the thickness of the nanodisk it is also possible to shift its resonant frequency while maintaining the lateral size of the nanodisk. Figure 3(a,b) show that 81-nm-sized Au nanodisks with different thicknesses ranging from 10 nm to 30 nm can be excited in a broad spectral window, meaning that the two dimensions of the Au disk—diameter and thickness—can be tuned independently to synthesize near infrared (NIR)-active contrast agents.

As tabulated in Figure 3(b), another distinct benefit of using 2D Au nanodisks as contrast agents for light-based imaging is their large molar extinction coefficients. The experimentally averaged molar extinction coefficients of the 2D nanodisks in Figure 3(b), ranging from 1010 to 1011 M1

cm-1, clearly demonstrate their superior response to light, compared to 1D nanorods or their

derivatives such as nanorices and nanostars, whose extinction coefficients have been reported to be about 109 M-1cm-1.12 This is due to the responsiveness of 2D nanodisks to the random


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direction and polarization of incident light. To maximize the extinction cross-section of a nanorod, the light should be irradiated in a direction perpendicular to the long axis of the nanorod while the polarization direction is parallel to it; without these conditions, the nanorods are not sufficiently activated (Supporting Information, Figure S4). For the 2D nanodisk, however, maximum extinction is assured with random polarization angles if the incident direction of the light is perpendicular to the lateral plane of the nanodisk. Additionally, the incident light from a random direction can maximize the extinction probability if the light polarization is parallel to the lateral plane of the nanodisk (Supporting Information, Figure S4).

The two optical benefits of the 2D nanodisks, namely, the wide range of resonant wavelengths and superior light responsiveness, are both embodied in our proposed nanodisk stack, i.e. SAN. The extinction spectrum in Figure 3(c) measured from the SAN aqueous solution can be fitted by the envelope curve of two Gaussian peaks (dotted lines in Figure 3(c)), meaning that the two different-sized disks inside the SAN interact with the light of two different wavelengths, as expected. The calculated local electric field contours in Figure 3(d) also show the two different interacting modes of SAN and that these two modes are not as sensitive to the direction of incident light as are 2D nanodisks. The locally amplified electric fields around the edges of the upper and lower disks visually demonstrate that two different geometrical lengths of SAN successfully function to host localized surface plasmon polaritons of two different oscillation lengths. It is notable that the relative ratio of absorption and scattering of the total extinction is sensitive to the lateral dimension of the nanodisk. Measurements taken of the substrate-bound nanodisks by Langhammer et al.32 and our calculations on the substrate-released nanodisks by the FDTD simulation in this report (Figure S3) both show that Au nanodisks with relatively


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small diameters—generally below 100 nm diameter for a 10-30-nm thick nanodisk—are effective for light-absorption while nanodisks with diameters larger than 100 nm are effective for light-scattering. Therefore, the upper (i.e. smaller) and lower (i.e. larger) disks that make up the SAN allow interaction with incident light by two different modes of light-absorption and scattering at the two different resonant wavelengths of 630 nm and 850 nm.

To utilize the two different light interaction modes of SANs, the SANs were applied as bimodal contrast agents for photoacoustic microscopy (PAM) and optical coherent tomography (OCT). The highly effective light absorption and scattering by the SANs fulfilled the principles of signal acquisition in PAM and OCT, respectively. Therefore, the SANs that were visible in both PAM and OCT functioned to enhance the image contrast in both PAM and OCT, as well as to correlate the two different types of biological information obtained from PAM (by which vascular structures are imaged due to the strong light absorption by hemoglobin) and OCT (by which tissue morphologies are obtained due to their intrinsic scattering differences). As illustrated in Figure 4(a), if a PAM-sensitive blood substitute flowed through one of the three tubes imbedded in a phantom tissue, it would be difficult to pinpoint the tube that contained the blood substitute, even with contrast agents for PAM or OCT flowing together in another tube. However, by utilizing bimodal contrast agents for PAM and OCT, we were able to correlate the two images obtained from PAM and OCT and to identify the blood-phantom-containing tube in the OCT image. Figure 4(b) shows a cross-sectional OCT image and a plane-view PAM image of the agarose tissue phantom in which four silicone tubes were embedded. The four tubes contained aqueous solutions of a black-colored ink (blood phantom), gold nanorods (GNRs) (PAM contrast agents), SANs (bimodal contrast agents), and gold nanospheres (GNSs) (OCT contrast agents).


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The concentrations of the three nanoparticles were all 140 ppm (GNRs: 2.4 × 1011 mL-1, SANs: 7 × 109 mL-1, GNSs: 1.7 × 109 mL-1). The GNRs and the GNSs were resonant with the excitation lights for PAM (wavelength = 650 nm) and OCT (wavelength = 850 nm), respectively. As demonstrated in Figure 4(b), only the SANs were visible in both PAM and OCT, which made it possible to identify the ink-containing tube in the OCT image. More quantitative comparision of the average PAM and OCT intensities from the three nanoparticles are described in Supporting Information (Figure S5). Briefly, the average PAM intensity of a single SAN is two orders of magnitude larger than that of a GNR. The average OCT intensity of a single SAN is approximately four times smaller than that of a GNS, but the the average OCT intensities normalized by the Au mass are similar in SAN and GNS. Moreover, the photostability of the SANs is better than the GNR under the PAM imaging conditions used (Supporting information, Figure S6), and it would be another advantage of the SANs.

Finally, the SANs were applied to in vivo imaging of a chick embryo. The images to the left in Figure 5(a) show the cross-sectional and 3D-recontructed views of the OCT images of the chick embryo after partial removal of the eggshell. Because the scattering difference originated from structural differences makes the OCT signal, the inner and outer shell membranes in the chick embryo as well as the wall of the blood vessels underneath the inner membrane were clearly observed in the OCT images. These two membranes separate the outermost air cell, the thin intermediate albumin layer, and the thick inner albumin layer. Into the intermediate albumin layer was injected 1 µL of aqueous SANs solution (concentration = 7 × 109 mL-1) using a syringe. As shown in the images on the right in Figure 5(a) and Supporting Movie 1, the injected SANs diffused well between the two membranes and produced a bright OCT signal. The SAN-


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injected chick embryo was also imaged using PAM to demonstrate the potential of SANs as bimodal contrast agents for both PAM and OCT. The incident light of the wavelengths 650 nm and 532 nm was irradiated to observe the PA signals from the SANs and blood flow, respectively. Under the 650-nm laser irradiation, absorption coefficient of oxygenated whole blood is known to about 1 cm-1,39 which is approximately 1011 orders of magnitude smaller than that of the SANs. This is why the PA signal of such a low dosage (12 pM, 1 µL) of SANs overwhelms the PA signal of blood in the left image of Figure 5(b). This image of nanoparticle distribution could be overlapped with the PAM image of the vascular network obtained under the 532-nm laser irradiation as shown in the right image in Figure 5(b). Because the PA signals originate from wavelength-specific light absorption and its consequent conversion to ultrasound waves, the PAM images in Figure 5(b) show only the signals from light absorbers―the SANs and hemoglobins―without background signals from the surrounding environment. Therefore, as discussed previously, the contrast enhancing effect of the SANs in PAM and OCT is useful in isolating the location of the nanoparticle by PAM and correlating the nanoparticle distribution with their surrounding tissue structures by OCT. In our current study, the bare SANs move freely and become distributed randomly during imaging, which makes it challenging to correlate the information from PAM and OCT. However target-specific distribution of the SANs, which can be made possible by introducing target-specific ligands on the nanoparticle surface or by simply using the enhanced permeability and retention effects of the nanoparticle, is expected to become routine.

CONCLUSION


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In summary, we physically synthesized 2D Au nanodisks that have the intrinsic optical advantages of a wide range of resonant wavelengths, tunable ratio of light absorption-toscattering, and responsiveness to random incident light. Based on our nanofabrication process with a controlled plasma etching time and vacuum deposition angle, we were able to synthesize variously sized 2D Au nanodisks with a narrow size distribution and SANs of a two-tiered form. The measured absorbance of the SANs and the calculated electromagnetic fields near the SANs clearly demonstrate that they combine the optical functionalities of the two nanodisks, as well as their external geometries. The combined optical properties of the SANs were successfully utilized to improve the image contrast for PAM and OCT. In light of these results, it is clear that the Au nanodisks and their stacked form can be applied as highly sensitive contrast agents for laser-based biological imaging. We expect that nanodisks containing magnetic elements or disease-targeting ligands, which are incorporated by successive vacuum-deposition or by goldthiol chemistry, would also be useful as multifunctional in vitro or in vivo imaging agents.


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METHODS Synthesis of gold nanodisks. To fabricate the lithographically patterned polymer template, a 1.3 µm thick benzocyclobutene (Cyclotene3022-35, Dow Chemical) layer was spin-coated on a Si substrate and baked at 230 °C for 5 min. Next, a 90 nm thick polymethylglutarimide (PMGISF3, MicroChem) layer was spin-coated on a Si substrate and baked at 200 °C for 5 min. Then, a 100 nm thick nanoimprint resist (PMMA, Microresist technology) was spin-coated on PMGI and baked at 100 °C for 2 min. After preparing the tri-layered polymer stack, the wafers were subjected to thermal nanoimprinting at 200 °C under a pressure of 30 bar for 3 min using a commercial nanoimprint tool (ANT-4H, Exatech). After nanoimprinting, the PMMA was etched using O2 plasma, and the PMGI layer was dissolved by a commercial wet chemical developer (AZ 300 MIF, AZ electronic materials) for 3 s to form an undercut profile. Then, a Au thin film was deposited by thermal evaporation. After the Au deposition, the PMMA and PMGI layers were removed with acetone and AZ 300 MIF, respectively, and the synthesized Au nanodisks were released from the sample surface by dissolving BCB with a commercial solution (Primary Stripper A, Dow Chemical). The Au nanodisks were then collected by centrifugation. After solvent exchange, the nanodisks were finally suspended in water.

Optical Coherence Tomography Imaging. A superluminescent diode (SLD) with a center wavelength of 849 nm (BLM2-D-840-B-I-10, Superlum, Ireland) and a −3 dB bandwidth of 100 nm was used as the broadband light source in the OCT system. The emitted light from the SLD was coupled to a 2 × 2 optical fiber coupler and split into reference and sample arms in a 50:50 ratio. In the sample arm, the collimated light was incident to the sample via a 2D galvanometer scanner and an objective lens. The light reflected from the reference and sample arms was


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recombined and directed to a linear-wavenumber spectrometer. The interference signals generated by the path length differences between the reference and sample arms were detected by the spectrometer at the 125 kHz A-line rate. For 3D volume data, 800 cross-sectional images with 800 A-lines/image were acquired. 3D image was reconstructed by commercial software (Amira 6, FEI, USA).

Photoacoustic Microscopy Imaging A tunable wavelength nanosecond pulsed laser (NT242, EKSPLA, Lithuania) with a pulse width of 5 ns and repetition rate of 1 kHz was used to excite the nanoparticles. The collimated laser beam was focused through an objective lens and scanned across the sample using a 2D galvanometer scanner. For reflection mode PA signal detection, a customized module was used to confocally align the illuminated laser beam and generate an ultrasound.40 An unfocused ultrasonic transducer (V326-SU, Olympus-NDT, Japan) with a center frequency of 5 MHz and a -6 dB bandwidth of 76.2% was used to collect the PA signals. During chick embryo imaging, the light fluences were 552 and 780 nJ at 532 and 650 nm, respectively. The collected signals were amplified and converted using a high-speed digitizer to obtain cross-sectional PA images (x-z plane), finally expressed as a maximum amplitude projection (MAP) image. The MAP image projected the maximum signal of each A-line onto the corresponding 2D plane (x-y plane). The GNRs and GNSs for PAM and OCT imaging were purchased from Nanopartz (product name: AC12-25-650) and BBI Solutions (product name: EM.GC200), respectively.


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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], [email protected] Author Contributions J.-S.W. and T.G.L. developed the idea and designed the experiments; J.-S.W. and J.P. fabricated the samples; H.K. carried out the optical measurements; S.-W.L and D.J. contributed the data interpretation; J.-S.W. and T.G.L. prepared the manuscript and all authors contributed to its revision. +These authors contributed equally.

ACKNOWLEDGMENT This study was supported by Development of Platform Technology for Innovative Medical Measurements funded by Korea research Institute of Standards and Science (KRISS-2017GP2017-0020), the Pioneer Research Center Program (NRF-2012-0009541), the Global Frontier Project (H-GUARD_2013M3A6B2078962), and the Bio & Medical Technology Development Program (2015M3A9D7029894) of the National Research Foundation (NRF) funded by the Ministry of Science, ICT & Future Planning.

ASSOCIATED CONTENT Supporting Information. Additional data of FDTD calculations, SEM images, and OCT movies. This material is available free of charge via the Internet at http:\\pubs.acs.org.


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REFERENCES 1. Hutter, E.; Fendler, J. H. Exploitation of Localized Surface Plasmon Resonance. Adv. Mater. 2004, 16, 1685–1706. 2. Willets, K. A.; Van Duyne, R. P. Localized Surface Plasmon Resonance Spectroscopy and Sensing. Ann. Rev. Phys. Chem. 2007, 58, 267–297. 3. Anker, J. N.; Hall, W. P.; Lyandres, O.; Shah, N. C.; Zhao, J.; Van Duyne, R. P. Biosensing with Plasmonic Nanosensors. Nat. Mater. 2008, 7, 442–453. 4. Lal, S.; Grady, N. K.; Kundu, J.; Levin, C. S.; Lassiter, J. B.; Halas, N. J. Tailoring Plasmonic Substrates for Surface Enhanced Spectroscopies. Chem. Soc. Rev. 2008, 37, 898–911. 5. Schuller, J. A.; Barnard, E. S.; Cai, W.; Jun, Y. C.; White, J. S.; Brongersma, M. L. Plasmonics for Extreme Light Concentration and Manipulation. Nat. Mater. 2010, 9, 193–204. 6. Tadaaki, N.; Gui, H.; ChungVu, H.; Jung-Sub, W.; Annemarie, P.; Daniel, W.; Frank, N.; Vyacheslav, M. S.; Dominik, E.; Osamu, S.; Masud, R. Plasmons in Nanoscale and Atomic-Scale Systems. Sci. Tech. Adv. Mater. 2010, 11, 054506. 7. Mayer, K. M.; Hafner, J. H. Localized Surface Plasmon Resonance Sensors. Chem. Rev. 2011, 111, 3828–3857. 8. Tokel, O.; Inci, F.; Demirci, U. Advances in Plasmonic Technologies for Point of Care Applications. Chem. Rev. 2014, 114, 5728–5752. 9. Wang, L. V. Multiscale Photoacoustic Microscopy and Computed Tomography. Nat. Photonics 2009, 3, 503–509. 10. Kim, C.; Favazza, C.; Wang, L. V. In Vivo Photoacoustic Tomography of Chemicals: HighResolution Functional and Molecular Optical Imaging at New Depths. Chem. Rev. 2010, 110, 2756–2782. 11. Wang, L. V.; Hu, S. Photoacoustic Tomography: In Vivo Imaging from Organelles to Organs. Science 2012, 335, 1458–1462. 12. Weber, J.; Beard, P. C.; Bohndiek, S. E. Contrast Agents for Molecular Photoacoustic Imaging. Nat. Methods 2016, 13, 639–650. 13. Lemaster, J. E.; Jokerst, J. V. What Is New in Nanoparticle-Based Photoacoustic Imaging? Wiley Interdiscip. Rev.: Nanomed. Nanobiotechnol. 2017, 9, e1404. 14. Jokerst, J. V.; Cole, A. J.; Van de Sompel, D.; Gambhir, S. S. Gold Nanorods for Ovarian Cancer Detection with Photoacoustic Imaging and Resection Guidance via Raman Imaging in Living Mice. ACS Nano 2012, 6, 10366–10377. 15. Pu, K.; Shuhendler, A. J.; Jokerst, J. V.; Mei, J.; Gambhir, S. S.; Bao, Z.; Rao, J. Semiconducting Polymer Nanoparticles as Photoacoustic Molecular Imaging Probes in Living Mice. Nat. Nanotechnol. 2014, 9, 233–239. 16. Miao, Q.; Pu, K. Emerging Designs of Activatable Photoacoustic Probes for Molecular Imaging. Bioconjugate Chem. 2016, 27, 2808–2823. 17. Cang, H.; Sun, T.; Li, Z.-Y.; Chen, J.; Wiley, B. J.; Xia, Y.; Li, X. Gold Nanocages as Contrast Agents for Spectroscopic Optical Coherence Tomography. Opt. Lett. 2005, 30, 3048–3050. 18. Chen, J.; Wiley, B.; Li, Z. Y.; Campbell, D.; Saeki, F.; Cang, H.; Au, L.; Lee, J.; Li, X.; Xia, Y. Gold Nanocages: Engineering Their Structure for Biomedical Applications. Adv. Mater. 2005, 17, 2255– 2261. 19. Adler, D. C.; Huang, S.-W.; Huber, R.; Fujimoto, J. G. Photothermal Detection of Gold Nanoparticles Using Phase-Sensitive Optical Coherence Tomography. Opt. Express 2008, 16, 4376–4393.


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20. Skala, M. C.; Crow, M. J.; Wax, A.; Izatt, J. A. Photothermal Optical Coherence Tomography of Epidermal Growth Factor Receptor in Live Cells Using Immunotargeted Gold Nanospheres. Nano Lett. 2008, 8, 3461–3467. 21. Liba, O.; SoRelle, E. D.; Sen, D.; de la Zerda, A. Contrast-Enhanced Optical Coherence Tomography with Picomolar Sensitivity for Functional In Vivo Imaging. Sci. Rep. 2016, 6, 23337. 22. Qian, X.; Peng, X.-H.; Ansari, D. O.; Yin-Goen, Q.; Chen, G. Z.; Shin, D. M.; Yang, L.; Young, A. N.; Wang, M. D.; Nie, S. In Vivo Tumor Targeting and Spectroscopic Detection with Surface-Enhanced Raman Nanoparticle Tags. Nat. Biotechnol. 2008, 26, 83–90. 23. von Maltzahn, G.; Centrone, A.; Park, J.-H.; Ramanathan, R.; Sailor, M. J.; Hatton, T. A.; Bhatia, S. N. SERS-Coded Gold Nanorods as a Multifunctional Platform for Densely Multiplexed Near-Infrared Imaging and Photothermal Heating. Adv. Mater. 2009, 21, 3175–3180. 24. Zavaleta, C. L.; Garai, E.; Liu, J. T. C.; Sensarn, S.; Mandella, M. J.; Van de Sompel, D.; Friedland, S.; Van Dam, J.; Contag, C. H.; Gambhir, S. S. A Raman-Based Endoscopic Strategy for Multiplexed Molecular Imaging. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, E2288–E2297. 25. Garai, E.; Sensarn, S.; Zavaleta, C. L.; Loewke, N. O.; Rogalla, S.; Mandella, M. J.; Felt, S. A.; Friedland, S.; Liu, J. T. C.; Gambhir, S. S.; Contag, C. H. A Real-Time Clinical Endoscopic System for Intraluminal, Multiplexed Imaging of Surface-Enhanced Raman Scattering Nanoparticles. PLOS ONE 2015, 10, e0123185. 26. Shankar, S. S.; Rai, A.; Ankamwar, B.; Singh, A.; Ahmad, A.; Sastry, M. Biological Synthesis of Triangular Gold Nanoprisms. Nat. Mater. 2004, 3, 482–488. 27. Millstone, J. E.; Park, S.; Shuford, K. L.; Qin, L.; Schatz, G. C.; Mirkin, C. A. Observation of a Quadrupole Plasmon Mode for a Colloidal Solution of Gold Nanoprisms. J. Am. Chem. Soc. 2005, 127, 5312–5313. 28. Jones, M. R.; Mirkin, C. A. Bypassing the Limitations of Classical Chemical Purification with DNA-Programmable Nanoparticle Recrystallization. Angew. Chem. Int. Ed. 2013, 52, 2886–2891. 29. O’Brien, M. N.; Jones, M. R.; Kohlstedt, K. L.; Schatz, G. C.; Mirkin, C. A. Uniform Circular Disks With Synthetically Tailorable Diameters: Two-Dimensional Nanoparticles for Plasmonics. Nano Lett. 2015, 15, 1012–1017. 30. Qin, F.; Zhao, T.; Jiang, R.; Jiang, N.; Ruan, Q.; Wang, J.; Sun, L.-D.; Yan, C.-H.; Lin, H.-Q. Thickness Control Produces Gold Nanoplates with Their Plasmon in the Visible and Near-Infrared Regions. Adv. Opt. Mater. 2016, 4, 76–85. 31. Wi, J.-S.; Tominaka, S.; Uosaki, K.; Nagao, T. Porous Gold Nanodisks with Multiple Internal Hot Spots. Phys. Chem. Chem. Phys. 2012, 14, 9131–9136. 32. Langhammer, C.; Kasemo, B.; Zorić, I. Absorption and Scattering of Light by Pt, Pd, Ag, and Au Nanodisks: Absolute Cross Sections and Branching Ratios. J. Chem. Phys. 2007, 126, 194702. 33. Wi, J.-S.; Barnard, E. S.; Wilson, R. J.; Zhang, M.; Tang, M.; Brongersma, M. L.; Wang, S. X. Sombrero-Shaped Plasmonic Nanoparticles with Molecular-Level Sensitivity and Multifunctionality. ACS Nano 2011, 5, 6449–6457. 34. Park, J.; Kang, H.; Kim, Y. H.; Lee, S.-W.; Lee, T. G.; Wi, J.-S. Physically-Synthesized Gold Nanoparticles Containing Multiple Nanopores for Enhanced Photothermal Conversion and Photoacoustic Imaging. Nanoscale 2016, 8, 15514–15520. 35. Vladar, A. E.; Ming, B. Measuring the Size of Colloidal Gold Nano-particles Using HighResolution Scanning Electron Microscopy; NIST-NCL Joint Assay Protocol, PCC-15, version 1.1; National Institute of Standards and Technology−Nanotechnology Characterization Laboratory: Gaithersburg, MD and Frederick, MD, 2011; 1−20.


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36. Song, H. B.; Wi, J.-S.; Jo, D. H.; Kim, J. H.; Lee, S.-W.; Lee, T. G.; Kim, J. H. Intraocular Application of Gold Nanodisks Optically Tuned for Optical Coherence Tomography: Inhibitory Effect on Retinal Neovascularization without Unbearable Toxicity. Nanomedicine: NBM 2017, in press, http://dx.doi.org/10.1016/j.nano.2017.03.016. 37. Wi, J.-S.; Tominaka, S.; Nagao, T. Arrays of Nanoscale Gold Dishes Containing Engineered Substructures. Adv. Opt. Mater. 2013, 1, 814–818. 38. Wi, J.-S.; Son, J. G.; Han, S. W.; Lee, T. G. Nanoparticles inside Nanodishes for Plasmon Excitations. Appl. Phys. Lett. 2015, 107, 203102. 39. Jacques, S. L. Optical Properties of Biological Tissues: a Review. Phys. Med. Biol. 2013, 58, R37-R61. 40. Rao, B.; Li, L.; Maslov, K.; Wang, L. Hybrid-Scanning Optical-Resolution Photoacoustic Microscopy for In Vivo Vasculature Imaging. Opt. Lett. 2010, 35, 1521–1523.


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Figure 1. Schematic illustration of the overall process adopted in this study: nanoimprint lithography using a truncated Si nanocone array; O2 plasma etching for a controlled time to adjust the diameter of the PMMA opening; wet chemical dissolution of PMGI; vacuum deposition of Au with a surface-normal- or oblique-angle. After Au lift-off, the Au nanodisks were released from the BCB surface, and collected by centrifugation. PMMA, PMGI, and BCB are polymethylmethacrylate, polymethylglutarimide, and bisbenzocyclobutene, respectively.


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Figure 2. Physically synthesized Au nanodisks. SEM images of (a-d) Au nanodisks and (e-f) fried-egg-shaped Au nanodisks. Diameters of the 20 nm thick Au nanodisks in (a-d) are 81, 105, 130, and 166 nm, respectively. The Au nanodisks in (a-e) were observed after drying the aliquots of each nanodisk solution on the Si substrate, and the cross-sectional image in (f) was observed before the nanodisk release step. The inset images in (f) show the Au nanodisks from three different deposition angles of Au. The scale bars are all 500 nm.


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Figure 3. Optical characteristics of physically synthesized Au nanodisks and the SANs. a) Measured extinction curves of the aqueous solutions of the Au nanodisks. The diameters and thicknesses of the Au nanodisks are (black) 81 nm and 30 nm, (gray) 81 nm and 20 nm, (red) 105 nm and 20 nm, and (purple) 166 nm and 20 nm, respectively. (b) Measurements for the resonant wavelengths and molar extinction coefficients for the Au nanodisks synthesized in this study. (c) Measurements for the extinction curves of the aqueous solutions of the SANs. (d) Squared amplitude of the local electric field of the SAN. The wavelength of the incident light was (upper) 630 nm and (lower) 850 nm. Light directions (black arrows), polarization angles (blue arrows), and positions of electric field monitors (dish-dot lines) are noted in the levitating figures. The scale bars are all 100 nm.


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Figure 4. Phantom study of the SANs for OCT and PAM. (a) Schematic illustration of a crosssectional OCT image and plane-view PAM image of the tissue phantom where three silicone tubes are embedded. Two of the tubes are filled with (left) blood phantom and OCT contrast agent, and (right) blood phantom and OCT-PAM bimodal contrast agents, respectively. (b) Cross-sectional OCT image and plane-view PAM image of the tissue phantom where four silicone tubes are embedded. Black-colored ink, gold nanorods (GNRs), SANs, and gold nanospheres (GNSs) are contained in the tubes (from left to right: ink, GNRs, SANs, and GNSs). The scale bars are all 1 mm.


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Figure 5. In vivo application of the SANs for bimodal imaging of OCT and PAM. (a) Crosssectional and projective-view of OCT images of a 5-day old developed chick embryo (left) before and (right) after injection of SANs. The a.c., o.m., i.m. and b.v. represent the air cell, outer membrane, inner membrane, and blood vessels, respectively. (b) Plane-view PAM images of (left) the injected SANs only and (right) the injected-SANs overlapped with blood flows. The SANs and vasculature images were observed by light of wavelengths 650 nm and 532 nm, respectively. The colors in the right image are for clear visualization (red: blood flows, green: SANs). The hole indicated by the circular dashed line in the left image shows the entry point for the needle when injecting the SANs. The scale bars are all 500 µm. The color bars for OCT and PAM are logarithmic and linear scale, respectively. The intensity registered in the OCT image (Iimage) and the raw OCT signal (Iraw) have the following relation: Iimage = 20 log Iraw.


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Stacked Gold Nanodisks for Bimodal Photoacoustic and Optical

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