Article pubs.acs.org/cm
Off-Resonant Gold Superstructures as Ultrabright Minimally Invasive Surface-Enhanced Raman Scattering (SERS) Probes Limei Tian,† Sirimuvva Tadepalli,† Max Fei,† Jeremiah J. Morrissey,‡,§ Evan D. Kharasch,‡,§,∇ and Srikanth Singamaneni*,†,§ †
Department of Mechanical Engineering and Materials Science, Institute of Materials Science and Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States ‡ Department of Anesthesiology, Division of Clinical and Translational Research, Washington University in St. Louis, St. Louis, Missouri 63110, United States § Siteman Cancer Center, Washington University in St. Louis, St. Louis, Missouri 63110, United States ∇ Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, St. Louis, Missouri 63110, United States S Supporting Information *
ABSTRACT: Surface-enhanced Raman scattering (SERS) tags that serve as exogenous contrast agents for SERS-based bioimaging are comprised of size- and shape-controlled plasmonic nanostructures. For maximum SERS activity and image contrast, the localized surface plasmon resonance (LSPR) wavelength of SERS tags based on individual nanostructures must match with the excitation wavelength (typically in the near-infrared (NIR) therapeutic window, i.e., 650−900 nm). However, under the resonant excitation, these SERS tags typically exhibit very high photothermal conversion efficiency, resulting in excessive heat that can perturb or even damage the biological species being imaged. Here, we demonstrate bioenabled synthesis of a novel class of ultrabright SERS probes with built-in and accessible electromagnetic hotspots formed by densely packed satellite nanoparticles grown on a plasmonic core. Through the rational choice of the shape of the core, the LSPR wavelength of Au superstructures can be tuned to be either off- or on-resonant with the NIR excitation without sacrificing their high SERS activity. Consequently, the photothermal efficiency of these ultrabright SERS tags can be tuned to realize either contrast agents with minimal heating and perturbation or multifunctional theranostic agents that can image and photothermally kill the targeted cells.
S
specificity.9 It is known that the SERS enhancement from individual nanostructures is highly dependent on the relative positions of excitation wavelength and localized surface plasmon resonance (LSPR) wavelength of the plasmonic nanostructures employed as SERS medium. For maximum SERS enhancement, the LSPR wavelength of the nanostructures is shown to be
urface-enhanced Raman scattering (SERS), which involves the large enhancement of Raman scattering from molecules adsorbed on (or in close proximity to) nanostructured metal surfaces, is emerging as a powerful bioimaging modality for image-guided interventions in intraoperative settings.1−3 SERS offers numerous advantages such as ultrasensitivity, large multiplexing capability due to narrow line widths (∼2 nm), chemical specificity (quantized vibrational fingerprint of the Raman reporters), excellent photostability, absence of interference from water, and noninvasive near-infrared (NIR) excitation and emission, which enable deeper penetration into soft tissues.4−8 Conventional SERS probe synthesis involves the adsorption of Raman reporters on size- and shape-controlled plasmonic nanostructures, followed by coating them with glass layers (such as silica or alumina) and modification with targeting ligands such as antibodies or aptamers for biological © XXXX American Chemical Society
λLSPR ≈ λExc +
λStokes − λExc 2
Received: June 3, 2015 Revised: July 27, 2015
A
DOI: 10.1021/acs.chemmater.5b02100 Chem. Mater. XXXX, XXX, XXX−XXX
Article
Chemistry of Materials
Figure 1. Biotemplated synthesis of Au superstructures using shape-controlled Au nanostructures as cores: (A) schematic illustration depicting the synthesis of Au nanoparticles on nanosphere (AuNPS) and Au nanoparticles on nanorod (AuNPR) superstructures by modifying the Au cores with a biopolymer, poly-L-histidine (poly his), and subsequent growth of Au nanoparticles on the plasmonic core; (B) normalized extinction spectra of AuNS and AuNPS, showing the red-shift in the LSPR wavelength due to the increase in the diameter and plasmon coupling after the growth of Au nanoparticles, and corresponding representative TEM images of (C) AuNS and (D) AuNPS; (E) normalized extinction spectra of AuNR and AuNPR showing the red-shift in the transverse and longitudinal LSPR wavelengths due to the increase in the diameter and plasmon coupling after the growth of Au nanoparticles. Representative TEM images of (F) AuNR and (G) AuNPR.
where λLSPR is the LSPR wavelength of the plasmonic nanostructures, λExc is the excitation source wavelength, and λStokes is the wavelength of the Stokes-shifted Raman band.10,11 Considering the low endogenous absorption coefficient of soft tissues in the NIR window (650−900 nm), it is important to tune the excitation and emission of SERS probes to the NIR window.12−15 While most of the earlier studies employed individual spherical metal nanoparticles, they are known to be suboptimal for SERS probes, because of the relatively small electromagnetic enhancement under NIR excitation.1,2,16,17 Assemblies of plasmonic nanostructures, which host nanoscale gaps termed as electromagnetic hotspots, have been widely investigated.18−30 Some recent studies have demonstrated the use of anisotropic nanostructures such nanorods and nanostars, which offer large tunability of the LSPR wavelength with change in shape (e.g., aspect ratio, number and length of the arms), as SERS probes.31−34 In this class of nanostructures, the LSPR band of the nanostructures is tuned to obey the condition described above to maximize SERS enhancement. Such anisotropic nanostructures exhibit significantly higher (at least an order of magnitude) SERS enhancement, compared to
their spherical counterparts under NIR excitation. However, these structures exhibit very high photothermal conversion efficiency under resonance excitation, which can perturb or even damage the biological species being imaged.14,31,32 Therefore, to minimize unwanted heating in bioimaging applications, laser irradiation time is typically set to be in the range of 0.1−10 S, which either lowers the SERS signal contrast or is simply not suited for image-guided tumor resection in intraoperative settings, considering the longer time scales (1−2 h) associated with such procedures.1,2,14,35,36 While resonant nanostructures are certainly desirable for theranostic applications, having the ability to tune the photothermal effect of SERS probes while preserving their high SERS activity is critical to avoid unwanted heating during imaging. The above-mentioned issues highlight the need for a novel class of plasmonic nanostructures that exhibit strong SERS enhancement, tunable LSPR wavelength, and photothermal properties and are easy to synthesize and scale-up. Here, we demonstrate the rational design and bioenabled synthesis of a novel class of SERS probes with built-in and accessible electromagnetic hotspots formed by densely packed satellites B
DOI: 10.1021/acs.chemmater.5b02100 Chem. Mater. XXXX, XXX, XXX−XXX
Article
Chemistry of Materials
Figure 2. Shape-dependent photothermal efficiency of Au superstructures. (A) Infrared images depicting the rise in the temperature of water, AuNPS and AuNPR solutions upon irradiation with NIR laser (λex = 808 nm) at a power density of 0.3 W/cm2. (B) Plot showing the significantly higher rise in temperature of AuNPR solution (ΔT = 24 °C), compared to AuNPS solution (ΔT = 8 °C) and water (ΔT = < 1 °C) upon irradiation with NIR laser. (C) Extinction spectra of AuNPS and AuNPR solution at a Au atom concentration of ∼30 μg/mL.
confirmed using surface-enhanced Raman scattering and zetapotential measurements as shown previously.37 The strong affinity of poly his to Au0 and Au3+ ions facilitates the nucleation and growth of Au nanocrystals.38,39 To achieve Au nanoparticles on spheres (AuNPSs), we introduced chloroauric acid (HAuCl4) as a gold precursor into the AuNS structures modified with poly his (45 nm in diameter) (see Figure 1C). Subsequently, poly(vinylpyrrolidone) (PVP), as a capping agent, and ascorbic acid, as a mild reducing agent, were added into the reaction solution to induce the formation of satellite clusters (see the Methods section for details). Following the growth of Au satellites, the LSPR wavelength of AuNS exhibited a red-shift of 50.0 nm corresponding to the increase in the diameter and plasmon coupling between the core and the satellites (Figure 1B). TEM images revealed the uniform nucleation and growth of Au nanoparticles on AuNS templates (Figure 1D). Absence of the poly his coating resulted in poor control over growth of Au nanoparticles on PSS-coated AuNS, confirming the critical role of poly his in the uniform nucleation and growth of Au satellites on AuNS (see Figure S1 in the Supporting Information). The pH of the reaction solution also played a significant role in the uniform nucleation of Au satellites on the cores with optimal pH being 6.4, as demonstrated previously.37 Similar synthesis strategy has been employed for AuNR, which are particularly attractive, because of the large tunability of LSPR wavelength with aspect ratio.40−43 To realize Au nanoparticles on rods (AuNPR), AuNR structures with a diameter of ∼15 nm and a length of ∼65 nm have been employed as cores (see Figures 1F and 1G). Plasmon coupling between the core and satellite cluster and the increased diameter of AuNR resulted in a red-shift of 40.5 and 111.0 nm in the transverse and longitudinal LSPR wavelength (Figure 1E). The size and areal density of gold nanoparticles grown on the cores, which determine the optical properties of the superstructures, can be tuned over a broad range by varying the amount of Au precursor in the growth solution.
grown on a plasmonic core. Harnessing the affinity of a biopolymer, poly-L-histidine (poly his), to Au ions, we demonstrate bioenabled growth of Au satellites on shapecontrolled Au nanostructures. These Au superstructures with sub-3 nm interstices between the satellites render large electromagnetic enhancement and SERS activity. Furthermore, we show that, through a rational choice of the core shape, we can modulate the photothermal efficiency of the nanostructures to realize either imaging probes with minimal heating and perturbation of the cells being imaged or multifunctional theranostic agents that can image and photothermally kill the cells for locoregional therapy. Recently, we demonstrated the synthesis of anisotropic plasmonic superstructures by coating Au nanorod (AuNR) cores with poly his, a biopolymer that enables the uniform nucleation of Au nanoparticles (satellites) to form Au nanoparticles on rods (AuNPR).37 Relying on the strong affinity of poly his to Au0 and Au3+ ions, the novel bioenabled synthesis approach can serve as a universal method to realize size- and shape-controlled plasmonic superstructures. We show that the localized surface plasmon resonance (LSPR) wavelength of superstructures can be tuned by rationally choosing the shape of the core, resulting in different photothermal efficiencies under NIR excitation (Figure 1A). More importantly, the built-in electromagnetic hotspots of the superstructures render strong SERS signal enhancement, regardless of the resonance wavelength of the superstructures with respect to the excitation source wavelength. Realization of superstructures starts with the modification of gold nanospheres (AuNSs) and nanorods (AuNs), employed as cores, with a strong polyanion, namely, poly(styrenesulfonate) (PSS). Following the removal of excess PSS from the AuNS/ AuNR solution, poly his is adsorbed on PSS-modified AuNS/ AuNR through electrostatic interaction, which is a critical step to realize the uniform nucleation of Au nanoparticles on cores. The adsorption of PSS and poly his on the Au cores was C
DOI: 10.1021/acs.chemmater.5b02100 Chem. Mater. XXXX, XXX, XXX−XXX
Article
Chemistry of Materials It is known that the photothermal efficacy of plasmonic nanostructures is optimal under resonant excitation, i.e., excitation wavelength matching the LSPR wavelength of the nanostructures.35,44 Considering the almost two-orders-ofmagnitude lower endogenous absorption coefficient of soft tissues in the near-infrared (NIR) window (650−900 nm), compared to the visible part of electromagnetic spectrum, NIR excitation is commonly employed for optical imaging and therapeutic applications.12,35,45 By changing the shape of the core, we can tailor the LSPR wavelength of superstructures to be either off- or on-resonant with the NIR excitation (808 nm), resulting in tunable photothermal efficacy of the Au superstructures. The temperature increase in the AuNPS and AuNPR solutions at the same concentration of Au atoms upon irradiation with 808 nm laser (at a power density of 0.3 W/cm2) was monitored using an infrared (IR) camera (see Figures 2A and 2B). The temperature of the superstructure solutions exhibited significant increase within the first 90−100 S of irradiation followed by either stabilization or small increase for subsequent irradiation. At t = 300 S, AuNPR exhibited an almost 24 °C increase in temperature while AuNPS showed significantly smaller rise in temperature (∼8 °C). The significantly smaller rise in temperature of AuNPS solution can be rationalized from the vis-NIR extinction spectra of these nanostructures, which demonstrate the significantly lower absorbance of the AuNPS at 808 nm, compared to AuNPR (see Figures 2B and 2C). The low absorption coefficient of AuNPS at NIR excitation wavelength ensures minimal perturbation to the biological species during imaging process. Next, we turn our attention to the SERS performance of AuNPS under off-resonant excitation (λex = 785 nm). Electromagnetic hotspots formed by controlled aggregation or assembly of plasmonic nanostructures are known to be highly SERS-active.22,46 In fact, it has been demonstrated that the contribution of a relatively small number of electromagnetic hotspots (63 out of 106 active sites) can be quite significant (∼25%) in the overall SERS signal, which underscores the importance of electromagnetic hotspots in the design of SERS probes.47 Higher-magnification TEM images reveal sub-3 nm interstices that formed between the satellites on AuNS surface (Figure 3A). Most of these interstices are open and accessible to surrounding solvent environment, enabling facile diffusion of Raman reporter molecules into the electromagnetic hotspots. SERS spectra collected from the superstructure solutions following the adsorption of Raman reporters, p-mercaptobenzoic acid (pMBA) revealed strong SERS signals corresponding to the reporter molecules (Figure 3B). Compared to the AuNS cores, AuNPS exhibited more than 200 times higher SERS intensity. Finite-difference time-domain (FDTD) simulations confirmed the large enhancement of electromagnetic field in the interstices between the satellites (see insets in Figure 3B). The SERS intensity of pMBA adsorbed on AuNPR and AuNR of the same concentration was also measured for comparison (see Figure S3 in the Supporting Information). AuNPR showed ∼40 times higher SERS intensity, compared to that for AuNR, which is in agreement with FDTD simulations (Figure S4 in the Supporting Information). Nanostructures with such highly developed morphology and built-in electromagnetic hotpots preclude the need for controlled aggregation or assembly of plasmonic nanostructures to achieve high SERS activity. Despite the weak plasmonic extinction in the NIR region, AuNPS exhibited significantly strong SERS signals under 785 nm excitation, because of the electromagnetic hotspots formed
Figure 3. SERS activity of Au superstructures and in vitro bioimaging. (A) High-resolution TEM images showing the sub-3 nm interstices between the satellites in AuNPS, which serve as built-in electromagnetic hotspots and render large SERS activity to these superstructures. (B) Average SERS spectra obtained from AuNS and AuNPS solution following the adsorption of Raman reporters (pmercaptobenzoic acid) on the surface of the nanostructures. The SERS spectra demonstrate significantly higher SERS activity of the superstructures, compared to the cores, because of the electromagnetic hotspots associated with the superstructures. Electromagnetic field distribution around the nanostructures obtained using finite difference time domain (FDTD) simulations, shown as an inset of panel B, confirm the electromagnetic hotspots of the plasmonic superstructures. (C) Bright field and (D) dark field images of human renal adenocarcinoma cells (786-O) incubated with AuNPS. (E) SERS intensity map of 1590 cm−1 Raman band, corresponding to the aromatic ring mode of pMBA employed as a Raman reporter, showing the clear delineation of the cells spread on a silicon substrate. (F) Representative SERS spectra from each of the four cells shown in panel E, depicting the uniformity of SERS signals.
between the satellites, which is even ∼10 times stronger, compared to AuNR with the LSPR wavelength at 810 nm (Figure S3). Interestingly, the SERS enhancement factor of AuNPS under 514 nm laser excitation, which is closer to the LSPR wavelength of AuNPS (580 nm), was calculated to be at least 2 orders of magnitude lower, compared to that under 785 nm excitation (see Figure S5 in the Supporting Information). This observation is in agreement with the recent demonstration that, in a hotspot-dominated SERS system, the enhancement is not correlated with the LSPR wavelength.48 Plasmonic assemblies of different geometries and LSPR wavelengths invariably exhibited high SERS enhancement under NIR excitation source.48 The ability to efficiently decouple SERS enhancement from LSPR wavelength can be harnessed to realize ultrabright SERS probes that eliminate unwanted plasmonic heating. D
DOI: 10.1021/acs.chemmater.5b02100 Chem. Mater. XXXX, XXX, XXX−XXX
Article
Chemistry of Materials
Figure 4. Shape-dependent in vitro photothermal efficiency of Au superstructures: (A) cell viability following the NIR laser irradiation of control cells and cell incubated with AuNPS and AuNPR for different durations as quantified by MTT assay, and (B) bright field (top row), green fluorescence (middle row), and red fluorescence (bottom row) images of control cells and cells incubated with AuNPS and AuNPR. Following the irradiation with a NIR laser (λex = 808 nm), control cells and cells incubated with AuNPS exhibited green fluorescence (indicating live cells), while cells incubated with AuNPR exhibited red fluorescence (indicating dead cells).
death for different irradiation times for AuNPR compared to that of AuNPS, which is in complete agreement with the higher temperature rise of AuNPR compared to AuNPS described above (Figure 4A). Although the viability of cells incubated with AuNPS remains at 80%, even after irradiation for 6 min, the viability of cells incubated with AuNPR decreases to 10% under the same irradiation conditions. These results were further confirmed by live/dead cell assay performed after 6 min of irradiation for cells incubated with AuNPS and AuNPR. The presence of strong green fluorescence (corresponding to the live cells) and the absence of red fluorescence (corresponding to the dead cells) was noted for cells incubated with AuNPS, following the laser irradiation, whereas the inverse was noted for cells incubated with AuNPR. AuNPS exhibits weak plasmonic absorbance but strong SERS activity under NIR excitation can efficiently decouple imaging from unwanted photothermal heating. On the other hand, AuNPR, which exhibit strong SERS activity and absorbance in the NIR wavelengths, can serve as multifunctional theranostic probes to image and ablate tumor cells. In conclusion, we have demonstrated a simple and universal approach to achieve plasmonic superstructures comprised of a shape-controlled Au core and densely packed Au satellites. The biotemplated approach demonstrated here can be extended to any Au nanostructures to obtain Au superstructures with desired optical properties. As opposed to SERS probes based on individual nanostructures, in these EM hotspot-dominated superstructures, the SERS activity could be decoupled from the LSPR wavelength, making them ideal for unperturbed bioimaging. Conversely, the superstructures could be designed to serve as imaging and therapeutic agents by rational choice of the size and shape of the Au cores.
To demonstrate the imaging capability of the Au superstructures (AuNPS and AuNPR) in vitro, we have employed human renal adenocarcinoma cell line 786-O (ATTC CRL1932) as a model cell line. The serum stability of PEGylated Au superstructures was confirmed by monitoring their ultraviolet− visible light (UV-vis) extinction spectra at several time points following their dispersion in 10% fetal bovine serum (FBS) at 37 °C (see Figure S6A in the Supporting Information). The biocompatibility of the Au superstructures was confirmed by the high viability after incubating them with both human renal adenocarcinoma cells and renal primary proximal tubule epithelial cells, a model healthy kidney cell line (Figures S6B−E). AuNPS was incubated with 786-O cells seeded on poly(lysine) coated-silicon substrate for in vitro Raman imaging. Bright and dark-field optical imaging of fixed cells is employed to locate the cells for subsequent confocal Raman imaging (Figures 3C and 3D). Dark-field optical images of the cells revealed the large Rayleigh scattering from internalized and cell surface-bound AuNPS (Figure 3D). Confocal Raman images of the cells targeted with AuNPS were acquired using a 785 nm laser as the excitation source (Figure 3E). The intensity map of the 1590 cm−1 Raman band, corresponding to the aromatic ring mode of pMBA, revealed the distribution of AuNPS within the cells, enabling the clear delineation of the cells shape (Figure 3E). Representative Raman spectra collected from four different cells show small variation in the SERS intensity, possibly due to the variations in the number of internalized nanoparticles and their spatial distribution inside the cells (Figure 3D). Similarly, we have also performed Raman imaging with AuNPR, which exhibited ∼2 times higher SERS intensity, compared to AuNPS (Figures S7A−D in the Supporting Information). TEM imaging of ∼100 nm thick cell sections revealed the intact core−satellite superstructures after being internalized and encapsulated in the trafficking vesicles of 786-O cell cytosol, which is critical for the high SERS activity of these nanostructures (Figures S7E−G). These results confirm the bioimaging capability of Au superstructures (AuNPS and AuNPR), regardless of their resonance wavelength. To further investigate the photothermal effect of both superstructures in vitro, 786-O cells at 90% confluence in 24 well plates were incubated with AuNPS and AuNPR to facilitate internalization of the nanostructures. Following the removal of free Au superstructures, the cells were irradiated with 808 nm laser for different durations (0−6 min) followed by incubation in medium at 37 °C and 5% CO2 for 18 h. Cell viability quantified by MTT assay indicated significantly higher cell
■
METHODS
Synthesis of AuNPS/AuNPR. AuNPS/AuNPR were synthesized by employing AuNS/AuNR as templates. In a typical AuNPS synthesis, 100 μL of aqueous poly-L-histidine (poly his) solution (5 mg/mL) was added to 1 mL of PSS-coated AuNS (concentration adjusted to an extinction intensity of 1.0 at the LSPR wavelength per cm light path), followed by a brief vortex for 10 s and incubation for 10 min. After centrifugation at 7000 rpm for 10 min, the pellet was dispersed in nanopure water (18.2 MΩ cm). Immediately, 10 μL of aqueous HAuCl4 solution (20 mM) was added to the above solution, followed by adjusting the pH of the reaction solution to 6.4 by adding 9 μL of aqueous NaOH solution (100 mM). After 3 min, 200 μL of aqueous poly(vinylpyrrolidone) solution (PVP, 90 mM) and 20 μL of aqueous ascorbic acid solution (1 M) were added as a capping agent and reducing agent, respectively. Similarly, AuNPR were synthesized E
DOI: 10.1021/acs.chemmater.5b02100 Chem. Mater. XXXX, XXX, XXX−XXX
Chemistry of Materials
■
by adding 30 μL of HAuCl4 to AuNR solution modified with poly his (concentration adjusted to an extinction intensity of 2.0 at the longitudinal LSPR wavelength per cm light path), followed by the addition of PVP and ascorbic acid. To 1 mL of once-centrifuged AuNPS/AuNPR, 80 μL of 2 mM methoxy polyethylene glycol thiol (mPEG-SH) aqueous solution and 6 μL of 10 mM pMBA ethanol solution were added sequentially. The centrifuged PEGylated AuNPS/ AuNPR-pMBA were also dispersed in cell medium with 10% fetal bovine serum (FBS) for in vitro bioimaging and photothermal studies. In Vitro SERS Imaging of 786-O Cells. Human renal cancer cell line (786-O) and renal proximal tubule cells (RPTECs) were subcultured in RPMI-1640 medium with 10% fetal bovine serum (FBS) and antibiotics (100 μg/mL penicillin and G418 sulfate, respectively). Cells were grown in a water jacket incubator at 37 °C with 5% CO2-humidified atmosphere in 25 cm2 tissue culture flasks. Once the cells reached 90% confluence, they were washed with phosphate buffered saline (PBS) and detached with 2 mL of 0.25% trypsin-EDTA solution. Cells were dispersed in complete medium (10 mL) with 10% FBS and plated at a density of 4 × 104 cells on poly(lysine)-coated 0.5 cm × 0.5 cm silicon substrates in flat-bottom 24-well plates after centrifugation. 786-O cells plated on silicon substrates were rinsed two times with PBS and incubated with 500 μL of 45 μg/mL AuNPS/AuNPR-MBA dispersed in complete medium for 4 h at 37 °C. The cells then were fixed with 4% formalin in PBS overnight at 4 °C after rinsing with PBS three times to remove loosely bound nanoparticles. Finally, fixed cells were mapped using confocal InVia Renishaw Raman microscope by collecting a 2D array of Raman spectra with 3.0 μm spatial resolution using 785 nm laser excitations with 3 mW power using a 20× objective and an exposure time of 5 s. Raman maps were generated by plotting the intensity of 1590 cm−1 Raman band. In Vitro Photothermal Therapy. The NIR irradiation was performed using an 808 nm diode laser for various durations and at a power density of 400 mW cm−2. Following laser treatment, the cells were incubated with full medium for 18 h and then stained with fluorescent labels of ethidium homobromide-1 and calcein AM dyes to produce green and red emission from live and dead cells, respectively, which can be visualized under the fluorescence microscope. To quantify the photothermal treatment efficiency of the nanostructures, methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay was employed to probe the viability of 786-O cells incubated with 45 μg/mL of AuNPS/AuNPR-MBA before and after laser treatment, followed by 18 h of incubation with full medium. Ten microliters (10 μL) of 5 mg/mL MTT in PBS was added to each well, followed by 4 h of incubation. Then, 100 μL of dimethyl sulfoxide (DMSO) was added to each well, including controls, followed by a gentle swirl. The absorbance was measured at 570 nm using an Infinite F200 multimode reader (Tecan, Switzerland). Cell viability was normalized to that of 786-O cells cultured in the complete culture medium without the incubation with AuNPS/AuNPR-pMBA.
■
ACKNOWLEDGMENTS We would like to thank Prof. Lihong Wang from the Department Biomedical Engineering at Washington University for providing access to IR camera. The work was supported by National Science Foundation, under No. CBET-1512043. The authors thank Nano Research Facility (NRF) for providing access to electron microscopy facilities.
■
REFERENCES
(1) Kircher, M. F.; de la Zerda, A.; Jokerst, J. V.; Zavaleta, C. L.; Kempen, P. J.; Mittra, E.; Pitter, K.; Huang, R.; Campos, C.; Habte, F.; Sinclair, R.; Brennan, C. W.; Mellinghoff, I. K.; Holland, E. C.; Gambhir, S. S. A brain tumor molecular imaging strategy using a new triple-modality MRI-photoacoustic-Raman nanoparticle. Nat. Med. 2012, 18, 829−834. (2) 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. 2007, 26, 83−90. (3) 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. (4) Wang, Y.; Yan, B.; Chen, L. SERS Tags: Novel Optical Nanoprobes for Bioanalysis. Chem. Rev. 2013, 113, 1391−1428. (5) Gandra, N.; Singamaneni, S. Surface-enhanced Raman scattering for in vivo imaging: The future looks BRIGHT? Nanomedicine 2013, 8, 317−320. (6) Bohndiek, S. E.; Wagadarikar, A.; Zavaleta, C. L.; Van de Sompel, D.; Garai, E.; Jokerst, J. V.; Yazdanfar, S.; Gambhir, S. S. A small animal Raman instrument for rapid, wide-area, spectroscopic imaging. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 12408−12413. (7) Keereweer, S.; Kerrebijn, J. F.; van Driel, P. B. A. A.; Xie, B.; Kaijzel, E.; Snoeks, T. A.; Que, I.; Hutteman, M.; van der Vorst, J. R.; Mieog, J. S.; Vahrmeijer, A.; van de Velde, C. J. H.; Baatenburg de Jong, R.; Löwik, C. G. M. Optical Image-guided SurgeryWhere Do We Stand? Mol. Imaging Biol. 2011, 13, 199−207. (8) Keereweer, S.; Van Driel, P. B. A. A.; Snoeks, T. J. A.; Kerrebijn, J. D. F.; Baatenburg de Jong, R. J.; Vahrmeijer, A. L.; Sterenborg, H. J. C. M.; Löwik, C. W. G. M. Optical Image-Guided Cancer Surgery: Challenges and Limitations. Clin. Cancer Res. 2013, 19, 3745−3754. (9) Wang, Y.; Yan, B.; Chen, L. SERS Tags: Novel Optical Nanoprobes for Bioanalysis. Chem. Rev. 2013, 113, 1391−1428. (10) McFarland, A. D.; Young, M. A.; Dieringer, J. A.; Van Duyne, R. P. Wavelength-Scanned Surface-Enhanced Raman Excitation Spectroscopy. J. Phys. Chem. B 2005, 109, 11279−11285. (11) Stiles, P. L.; Dieringer, J. A.; Shah, N. C.; Van Duyne, R. P. Surface-Enhanced Raman Spectroscopy. Annu. Rev. Anal. Chem. 2008, 1, 601−626. (12) Frangioni, J. V. In vivo near-infrared fluorescence imaging. Curr. Opin. Chem. Biol. 2003, 7, 626−634. (13) Barone, P. W.; Baik, S.; Heller, D. A.; Strano, M. S. Nearinfrared optical sensors based on single-walled carbon nanotubes. Nat. Mater. 2004, 4, 86−92. (14) Wang, Y.; Black, K. C. L.; Luehmann, H.; Li, W.; Zhang, Y.; Cai, X.; Wan, D.; Liu, S.-Y.; Li, M.; Kim, P.; Li, Z.-Y.; Wang, L. V.; Liu, Y.; Xia, Y. Comparison Study of Gold Nanohexapods, Nanorods, and Nanocages for Photothermal Cancer Treatment. ACS Nano 2013, 7, 2068−2077. (15) Tian, L.; Gandra, N.; Singamaneni, S. Monitoring Controlled Release of Payload from Gold Nanocages Using Surface Enhanced Raman Scattering. ACS Nano 2013, 7, 4252−4260. (16) Gandra, N.; Singamaneni, S. Bilayered Raman-Intense Gold Nanostructures with Hidden Tags (BRIGHTs) for High-Resolution Bioimaging. Adv. Mater. 2013, 25, 1022−1027. (17) Kneipp, J.; Kneipp, H.; Wittig, B.; Kneipp, K. One- and TwoPhoton Excited Optical pH Probing for Cells Using Surface-Enhanced
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.5b02100. Detailed methods, SERS enhancement factor calculation, photothermal conversion efficiency calculation, TEM images, additional SERS spectra and finite-difference time-domain simulations, and cell viability quantified by MTT assay (PDF)
■
Article
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest. F
DOI: 10.1021/acs.chemmater.5b02100 Chem. Mater. XXXX, XXX, XXX−XXX
Article
Chemistry of Materials Raman and Hyper-Raman Nanosensors. Nano Lett. 2007, 7, 2819− 2823. (18) Li, W.; Camargo, P. H. C.; Lu, X.; Xia, Y. Dimers of Silver Nanospheres: Facile Synthesis and Their Use as Hot Spots for SurfaceEnhanced Raman Scattering. Nano Lett. 2009, 9, 485−490. (19) Gandra, N.; Abbas, A.; Tian, L.; Singamaneni, S. Plasmonic Planet−Satellite Analogues: Hierarchical Self-Assembly of Gold Nanostructures. Nano Lett. 2012, 12, 2645−2651. (20) Cong, V. T.; Ganbold, E.-O.; Saha, J. K.; Jang, J.; Min, J.; Choo, J.; Kim, S.; Song, N. W.; Son, S. J.; Lee, S. B.; Joo, S.-W. Gold Nanoparticle Silica Nanopeapods. J. Am. Chem. Soc. 2014, 136, 3833− 3841. (21) Yap, F. L.; Thoniyot, P.; Krishnan, S.; Krishnamoorthy, S. Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers. ACS Nano 2012, 6, 2056−2070. (22) Yoon, J. H.; Lim, J.; Yoon, S. Controlled Assembly and Plasmonic Properties of Asymmetric Core−Satellite Nanoassemblies. ACS Nano 2012, 6, 7199−7208. (23) Scarabelli, L.; Coronado-Puchau, M.; Giner-Casares, J. J.; Langer, J.; Liz-Marzán, L. M. Monodisperse Gold Nanotriangles: Size Control, Large-Scale Self-Assembly, and Performance in SurfaceEnhanced Raman Scattering. ACS Nano 2014, 8, 5833−5842. (24) Gandra, N.; Singamaneni, S. “Clicked” plasmonic core-satellites: Covalently assembled gold nanoparticles. Chem. Commun. 2012, 48, 11540−11542. (25) Zheng, Y.; Thai, T.; Reineck, P.; Qiu, L.; Guo, Y.; Bach, U. DNA-Directed Self-Assembly of Core-Satellite Plasmonic Nanostructures: A Highly Sensitive and Reproducible Near-IR SERS Sensor. Adv. Funct. Mater. 2013, 23, 1519−1526. (26) Guerrini, L.; Graham, D. Molecularly-mediated assemblies of plasmonic nanoparticles for Surface-Enhanced Raman Spectroscopy applications. Chem. Soc. Rev. 2012, 41, 7085−7107. (27) Lim, D.-K.; Jeon, K.-S.; Hwang, J.-H.; Kim, H.; Kwon, S.; Suh, Y. D.; Nam, J.-M. Highly uniform and reproducible surface-enhanced Raman scattering from DNA-tailorable nanoparticles with 1-nm interior gap. Nat. Nanotechnol. 2011, 6, 452−460. (28) Song, J.; Duan, B.; Wang, C.; Zhou, J.; Pu, L.; Fang, Z.; Wang, P.; Lim, T. T.; Duan, H. SERS-Encoded Nanogapped Plasmonic Nanoparticles: Growth of Metallic Nanoshell by Templating RedoxActive Polymer Brushes. J. Am. Chem. Soc. 2014, 136, 6838−6841. (29) Oh, J.-W.; Lim, D.-K.; Kim, G.-H.; Suh, Y. D.; Nam, J.-M. Thiolated DNA-Based Chemistry and Control in the Structure and Optical Properties of Plasmonic Nanoparticles with Ultrasmall Interior Nanogap. J. Am. Chem. Soc. 2014, 136, 14052−14059. (30) Jaiswal, A.; Tian, L.; Tadepalli, S.; Liu, K.-k.; Fei, M.; Farrell, M. E.; Pellegrino, P. M.; Singamaneni, S. Plasmonic Nanorattles with Intrinsic Electromagnetic Hot-Spots for Surface Enhanced Raman Scattering. Small 2014, 10, 4287−4292. (31) 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. (32) Yuan, H.; Liu, Y.; Fales, A. M.; Li, Y. L.; Liu, J.; Vo-Dinh, T. Quantitative Surface-Enhanced Resonant Raman Scattering Multiplexing of Biocompatible Gold Nanostars for In Vitro and Ex Vivo Detection. Anal. Chem. 2013, 85, 208−212. (33) Nergiz, S. Z.; Gandra, N.; Tadepalli, S.; Singamaneni, S. Multifunctional Hybrid Nanopatches of Graphene Oxide and Gold Nanostars for Ultraefficient Photothermal Cancer Therapy. ACS Appl. Mater. Interfaces 2014, 6, 16395−16402. (34) Sivapalan, S. T.; DeVetter, B. M.; Yang, T. K.; van Dijk, T.; Schulmerich, M. V.; Carney, P. S.; Bhargava, R.; Murphy, C. J. OffResonance Surface-Enhanced Raman Spectroscopy from Gold Nanorod Suspensions as a Function of Aspect Ratio: Not What We Thought. ACS Nano 2013, 7, 2099−2105. (35) Chen, H.; Shao, L.; Ming, T.; Sun, Z.; Zhao, C.; Yang, B.; Wang, J. Understanding the Photothermal Conversion Efficiency of Gold Nanocrystals. Small 2010, 6, 2272−2280.
(36) Lu, W.; Singh, A. K.; Khan, S. A.; Senapati, D.; Yu, H.; Ray, P. C. Gold Nano-Popcorn-Based Targeted Diagnosis, Nanotherapy Treatment, and In Situ Monitoring of Photothermal Therapy Response of Prostate Cancer Cells Using Surface-Enhanced Raman Spectroscopy. J. Am. Chem. Soc. 2010, 132, 18103−18114. (37) Tian, L.; Fei, M.; Tadepalli, S.; Morrissey, J. J.; Kharasch, E. D.; Singamaneni, S. Bio-Enabled Gold Superstructures with Built-In and Accessible Electromagnetic Hotspots. Adv. Healthcare Mater. 2015, 4, 1502−1509. (38) Jin, Y.; Gao, X. Plasmonic fluorescent quantum dots. Nat. Nanotechnol. 2009, 4, 571−576. (39) Djalali, R.; Chen, Y.-f.; Matsui, H. Au Nanocrystal Growth on Nanotubes Controlled by Conformations and Charges of Sequenced Peptide Templates. J. Am. Chem. Soc. 2003, 125, 5873−5879. (40) Chen, H.; Shao, L.; Li, Q.; Wang, J. Gold nanorods and their plasmonic properties. Chem. Soc. Rev. 2013, 42, 2679−2724. (41) Jana, N. R.; Gearheart, L.; Murphy, C. J. Wet chemical synthesis of high aspect ratio cylindrical gold nanorods. J. Phys. Chem. B 2001, 105, 4065−4067. (42) Nikoobakht, B.; El-Sayed, M. A. Preparation and growth mechanism of gold nanorods (NRs) using seed-mediated growth method. Chem. Mater. 2003, 15, 1957−1962. (43) Tian, L.; Chen, E.; Gandra, N.; Abbas, A.; Singamaneni, S. Gold Nanorods as Plasmonic Nanotransducers: Distance-Dependent Refractive Index Sensitivity. Langmuir 2012, 28, 17435−17442. (44) Gupta, M. K.; Meng, F.; Johnson, B. N.; Kong, Y. L.; Tian, L.; Yeh, Y.-W.; Masters, N.; Singamaneni, S.; McAlpine, M. C. 3D Printed Programmable Release Capsules. Nano Lett. 2015, DOI: 10.1021/ acs.nanolett.5b01688. (45) Pastrana, E. Near-infrared probes. Nat. Methods 2012, 10, 36− 36. (46) Xu, L.; Hao, C.; Yin, H.; Liu, L.; Ma, W.; Wang, L.; Kuang, H.; Xu, C. Plasmonic Core−Satellites Nanostructures with High Chirality and Bioproperty. J. Phys. Chem. Lett. 2013, 4, 2379−2384. (47) Fang, Y.; Seong, N.-H.; Dlott, D. D. Measurement of the distribution of site enhancements in surface-enhanced Raman scattering. Science 2008, 321, 388−392. (48) Kleinman, S. L.; Sharma, B.; Blaber, M. G.; Henry, A.-I.; Valley, N.; Freeman, R. G.; Natan, M. J.; Schatz, G. C.; Van Duyne, R. P. Structure Enhancement Factor Relationships in Single Gold Nanoantennas by Surface-Enhanced Raman Excitation Spectroscopy. J. Am. Chem. Soc. 2013, 135, 301−308.
G
DOI: 10.1021/acs.chemmater.5b02100 Chem. Mater. XXXX, XXX, XXX−XXX
