DNA-Mediated Anomalous Optical Coupling of Heterogeneous

Feb 27, 2014 - Takayasu Yoshikawa , Mamoru Tamura , Shiho Tokonami , and Takuya Iida ... Shin Tanaka , Yojiro Yamamoto , Shiho Tokonami , Takuya Iida...
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DNA-Mediated Anomalous Optical Coupling of Heterogeneous Metallic Nanostructures Shiho Tokonami,*,†,# Keisuke Nishida,†,‡ Shimpei Hidaka,†,‡ Yojiro Yamamoto,§ Hidenobu Nakao,∥ and Takuya Iida*,†,# †

Nanoscience and Nanotechnology Research Center, Osaka Prefecture University, 1-2, Gakuencho, Nakaku, Sakai, Osaka 599-8570, Japan ‡ Graduate School of Engineering, Osaka Prefecture University, 1-1, Gakuencho, Nakaku, Sakai, Osaka 599-8531, Japan § GreenChem Inc., 930-1-202, Fukuda, Nakaku, Sakai, Osaka 599-8241, Japan ∥ Nano-Architecture Group, National Institute for Materials Science, 1-1, Namiki, Tsukuba, Ibaraki, 305-0044, Japan ABSTRACT: The enhanced optical response due to localized surface plasmons (LSPs) in interacting metallic nanostructures provides a promising avenue for the detecting small biological molecules, whereas an unconventional spectral modulation of LSPs would be obtained under the coupling of the different kinds of metallic nanostructures with nanoscale separations via small molecules. Here, we unexpectedly found an anomalous condition of light scattering from heterogeneous metallic nanostructures, i.e., silver-nanoparticle fixed bead (AgNP-FB) and gold nanorods (AuNRs) coupled via DNA, in which the light scattering dramatically suppressed in the broad UV region although it was enhanced in the visible region. Based on ultrafast computation under cluster approximation, this anomaly was attributed to the broadband cancellation of collective modes of interband transitions in AuNRs and LSPs in a single AgNP-FB. This mechanism has a high potential to apply for detection of DNA in zmol order even under white light source.

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INTRODUCTION Biosensors are mainly based on the electric and optical detection of biological materials such as enzymes, nucleic acids, amino acids, sugar molecules, and antibodies with the help of their chemical molecular recognition mechanisms.1−6 As such, a highly sensitive method using a simple procedure is strongly desired for detecting analytes on the order of zmol. In particular, surface plasmon resonance (SPR) in a metallic nanostructure7 is a promising mechanism for optical detection since it exhibits strong optical responses and enhances fluorescence even at room temperature. For example, fluorescence resonance energy transfer (FRET) is thought to be a highly sensitive and real-time method of measurement,8−10 in which a weak signal can be detected for a small amount of the analyte. In addition, field enhancement effects of SPR are utilized for the highly efficient generation of fluorescence, i.e., surface plasmon-field enhanced fluorescence spectroscopy (SPFS).11−13 However, fluorescent dye molecules are expensive, easily photobleached, and require experienced personnel to perform the pretreatment. Another approach without the use of dye molecules is an SPR sensor to detect the modulation of reflectance due to the change of refractive index by the adsorption of analytes on the surface of a metallic nanofilm deposited on the surface of a prism.14−17 However, many analytes are necessary to change the refractive index and to obtain the sufficient SPR coupling. © 2014 American Chemical Society

On the other hand, back to the basics, the fundamental properties of the localized surface plasmon (LSP), as a quasiparticle state of three-dimensionally confined free electrons in a metallic nanoparticle (NP), exhibit a certain type of SPR that induces strong optical field enhancement with high sensitivity to environmental changes and highly efficient light scattering and photothermal effects.18,19 Since such optical responses of metallic NPs change depending on their size, shape, and spatial configuration,20 they have many potential applications such as in broadband optical devices whose wavelengths range from near-infrared (NIR) to ultraviolet (UV). In regards to the spatial configuration dependence, a recent theoretical study demonstrated that the radiative decay rate of LSP can be greatly enhanced and leads to spectral broadening by increasing the number of metallic NPs that are densely assembled by a light-induced force due to the plasmonic superradiance.21 This property enables us to control the light scattering efficiency dynamically and such a controllable plasmonic superradiance was verified in the recent experiment of selective trapping of AgNRs.22 Furthermore, an experimental observation of the different system, which consisted of a vast Received: February 14, 2014 Revised: February 24, 2014 Published: February 27, 2014 7235

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number of metallic NPs densely fixed on a plastic bead, i.e., metallic nanoparticle-fixed bead (MNFB), also revealed that strong scattering of broadband white light could be obtained owing to multipole superradiance23 in comparison with a small number of metallic NPs. On the other hand, unconventional properties emerged if heterogeneous metallic NPs such as Au, Ag, and Cu were chemically and physically mixed, leading to the enhancement of catalytic properties24 and spectral broadening that was useful for deep tissue bioimaging.25 If the coupling between heterogeneous metallic nanostructures at a high density was examined under the coexistence of biological molecules, unconventional functions could be obtained that may be useful as optical biosensors. However, there have been no studies examining the optical response of a system consisting of densely assembled heterogeneous metallic NPs. In this study, we experimentally and theoretically clarified the anomalous optical response of LSP modulated by the strong coupling of silver-nanoparticle-fixed beads (AgNP-FB) and gold nanorods (AuNR) as heterogeneous metallic nanostructures under high density conditions mediated by biological molecules (DNA was used here). Moreover, application of this principle may enable the highly sensitive optical biosensor to detect zmol nucleic acid molecules in a simple chemical procedure.

maintained at 298 K for 10 h, followed by centrifugation for 25 min at 14 000 rpm at ∼278 K in order to remove any unreacted oligonucleotide. After removal of the supernatant, the AuNRs and AgNP-FB were washed with 10 mM phosphate buffer solution. After another centrifugation under the same conditions, the precipitate was dispersed into 10 mM phosphate buffer. Optical Measurements. Measurement of the UV−vis spectrum in the suspension of AuNRs was carried out using UV−vis spectrophotometry (UV-2400-PC, Shimadzu, Japan). Scattering spectra of a single AgNP-FB with and without AuNRs in ultrapure water were obtained with a miniature fiberoptic spectrometer (USB4000, (Grating#3) SLIT-25, Ocean Optics), which was connected to a microscope (ECLIPSE 80i, NIKON, Japan) using an optical fiber (core diameter 50 μm). All scattering spectra of AgNP-FB were normalized by the scattering spectrum of the white light from the halogen lamp at the surface of the frosted glass diffuser (2937 WSLID-PF, Iwaki, Japan). Cluster DISC Method (Theory). In this work, we used AgNP-fixed beads with several hundreds of thousands of Ag NPs as a substrate for detection of DNA. As a result, the effective theoretical method was required to treat the optical response. Therefore, we developed a new calculation method, i.e., “Cluster DISC method”, using the discrete integral method with spherical cells (DISC) under the cluster approximation based on the discrete dipole approximation.21,23,28 It is assumed that a cluster consists of several tens of NPs as a discrete cell when the cluster DISC method is used to evaluate the vast numbers of AgNPs on a bead (the model is shown in Figure 1a). In order to self-consistently determine the electric field Ei and the induced polarization Pi on the ith cluster, the Maxwell equations in discrete integral form were solved as linear simultaneous equations of Pj as follows:

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EXPERIMENTAL AND THEORETICAL PROCEDURES Preparation of AgNP-Fixed Beads (AgNP-FB) and Au Nanorods (AuNRs). AgNPs (mean diameter 5 nm, 0.073 g/L) were densely self-assembled on each plastic bead with a mean diameter of ca. 5 μm via binder molecules.26 Plastic beads (50 mg) and 21.7 μL of the binder molecules (11-amino-1undecanethiol; 0.01 M) were added to 21.7 mL of AgNP dispersed solution, and then the mixture was stirred at room temperature for 3 h. After the beads were filtered, they were washed with an ample amount of water and then dried in a vacuum. AuNRs (mean size estimated by transmission electron microscope (TEM): 30 nm × 10 nm) were prepared as follows: Initially, 50 mL of an aqueous solution of cetyltrimethylammonium bromide (CTAB) (0.2 M) was prepared. Then, a growth solution for the AuNR is prepared. Specifically, an aqueous solution of 0.01 M silver nitrate (80 μL), 0.01 M HAuCl4 (500 μL), and an aqueous solution of 0.1 M ascorbic acid (80 μL) were mixed in this order into 5 mL of the CTAB solution, and the ascorbic acid reduced an Au ion and the color of the solvent vanished. Next, a seed solution for AuNR was prepared. Specifically, for example, 0.01 M HAuCl4 solution (250 μL) and a sufficiently cooled aqueous solution of 0.01 M NaBH4 (600 μL) were mixed into the CTAB solution (5 mL). The seed solution (12 μL) was mixed with the growth solution to grow AuNRs. The temperature of the mixed solution was maintained at 303 K for 12 h with minimal agitation. After a prescribed period had elapsed, the solution was washed away to cease growing the AuNRs. Modification of the DNA Probe on AgNP-Fixed Beads (AgNP-FB) and Au Nanorods (AuNRs). Modification of the DNA oligonucleotide to AgNP-FB and AuNRs:27 3.61 μM 5′terminally thiolated oligonucleotide (probe DNA (A): 5′-SHpoly(T)12-3′) was incubated with 1000 μL of a AuNR solution at 298 K for 12 h. In addition, 3.61 μM of the 3′-terminally thiolated oligonucleotide (probe DNA (B): 3′-SH-poly(T)125′) was incubated with 1000 μL of a AgNP-FB solution at 298 K for 12 h. In respective cases, the solution was added to 10 mM phosphate buffer (pH 7.0), and the resulting mixture was

N (c)

Ei = E(inc) + i

∑ G(m)(rij)PjV (c) + SiPi (1)

j≠i

Pj = χj(cp) Ej

(2)

(c)

(T)

(cp)

(T)

where N = N /N is the number of clusters, N is the total number of NPs, N(cp) = V(c)/{(4π/3)(ap/2)3} is the number of NPs in each cluster, ap is the diameter of each NP, V(c) = (4π/3)(Dc/2)3 is the volume of each cluster, Dc is the diameter of each cluster, E(inc) is the incident electric field, G(m) i i,j is a Green’s function in a homogeneous medium, and χ(cp) is j the optical susceptibility of each NP contained in a cluster. The integral Si = ∫ V(c)dr′ G(m)(ri − r′) in eq 1 is the self-term for i = j in each cluster assuming that the spatial variation of the internal field is negligible. This treatment is valid when the Dc is much smaller than the wavelength of the incident light. A Drude-type optical susceptibility of each NP rather than the cluster was used as follows: (cp) χj(cp) (ω) = (εbg (ω) − ε(m))

−

(ℏΩ bulk )2 (ℏω)2 + iℏω(Γbulk + ΓSD)

(3)

ε(cp) bg (ω) (m)

where is the background dielectric function of bulk metal, ε is the high-frequency dielectric constant of the surrounding medium (square of refractive index), Ωbulk is the bulk plasmon resonance frequency, Γbulk is the bulk non7236

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In order to show the validity of our calculation method “cluster DISC method” for the metallic nanoparticle-fixed bead, we show several examples of the results with this method in comparison with experimentally observed spectrum of AgNPFB. If we consider a “cluster”, i.e., a spherical cell including the aggregate of NPs whose sizes are much smaller than the light wavelength, we can reduce the required number of cells in the computation (Figure 1a−d). For example, in Figure 2a, it is

Figure 1. (a) Model for the calculation under the cluster approximation. (b) Computation time as a function of the number of cells. (c) Calculated spectra of extinction, absorption, scattering of AgNP-FB without cluster approximation. (d) Calculated spectra of extinction, absorption, scattering of AgNP-FB with cluster approximation.

Figure 2. (a) Model for the calculation corresponding to an experimentally fabricated AgNP-FB in (b). (b) Scanning electron microscope (SEM) image of AgNP-FBs with core bead of 400 nm in diameter and AgNP of 2.5 nm in diameter. The number of AgNPs on the bead is about 200 000. (c) Calculated extinction spectrum with the cluster approximation. (d) Experimentally observed extinction spectrum of AgNP-FB corresponding to the SEM image in (b). These spectra in (c) and (d) were normalized with their peak values.

radiative width, ΓSD = 2vf/ap is the size-dependent nonradiative damping, and vf is the electron velocity at the Fermi level. (Note that ΓSD is a function of the diameter of each NP (ap) rather than the diameter of the cluster (Dc).) We used the following parameters for AuNRs: ℏΩbulk = 8.958 eV, Γbulk = 72.3 meV, vf = 0.922 [nm·eV], and ε(cp) bg (ω) estimated from the experimental values with interband effects that were observed in bulk Au,18,29 where each AuNR consists of 28 cubic cells (10 nm × 35 nm). Also, for AgNPs on a bead, we use the following values: ℏΩbulk = 9.088 eV, Γbulk = 21.23 meV, vf = 0.922 [nm· eV], and ε(MNP) (ω) = 5.0 neglecting the interband effects bg beyond the observed wavelength region. As the dielectric constant, ε(m) = 1.332 was used assuming that the organic polymer core bead had a refractive index near that of water. The extinction spectrum can be calculated by evaluating the Abs Scat Abs radiation force30,31 ⟨FExt total⟩ = ⟨Ftotal⟩ + ⟨Ftotal⟩, where ⟨Ftotal⟩ is Scat the absorption component and ⟨Ftotal ⟩ is the scattering component. By using these equations, the signal intensity of the extinction, the absorption, and the scattering could be evaluated, respectively.

assumed that approximately 58 NPs are included in each cell, and the total number of cells can be reduced to 3462 from 200 000 that is estimated from the experimentally fabricated AgNPFB as shown in the SEM image of Figure 2b. We have confirmed that the calculated result of extinction spectrum of AgNP-FB in Figure 2c shows good agreement with experimental result as shown in Figure 2d. Although the calculation of optical response of 200 000 NPs takes about 8 years without the cluster approximation, we can perform the almost equivalent calculation only within 1 day by using cluster DISC method (estimated from Figure 1b). This means that we can realize approximately 3000 times speed up for the evaluation of optical response from densely assembled NPs. 7237

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RESULTS AND DISCUSSION First, in Figure 3, we investigated the change in the surface conditions of a single AgNP-FB by using a scanning electron

only one of transverse surfaces contributes to the hybridization due to the geometric restriction. (The length of each AuNR is about 30 nm, and the diameter of each AgNP is about 5 nm. This means that it is rare for a AuNR to hybridize DNA at both transverse surfaces. Also, a plastic bead has a curved surface.) Next, for clarification of the spectral modulation of LSP and spatial configurations under heterogeneous coupling of AgNPFB and AuNRs in aqueous solution (extinction spectrum of AuNRs is shown in Figure 4a), we performed dark-field optical

Figure 3. (a) Schematic image of coupling of AuNR and AgNP-FB with hybridization of thiolated DNA. (b) SEM image of AgNP-FB before hybridization (left) and corresponding EDX spectrum (right). (c) SEM image of AgNP-FB after hybridization (left) and corresponding EDX spectrum (right).

Figure 4. (a) Extinction spectrum of suspension of AuNRs. Inset: transmission electronic microscope (TEM) image of AuNRs. (b) Scattering spectra of AgNP-FB before hybridization (blue line) and after hybridization (red line). The result obtained using the mismatched DNA is also shown (green line).

microscope (SEM) before and after the addition of target DNA into the mixture of AuNRs (30 nm × 10 nm) and AgNP-FB whose surfaces were modified with DNA probes (please see Experimental and Theoretical Procedures). Figure 3a schematically illustrates the mechanism by which AuNRs bind to the surface of AgNP-FB, where the probe DNA (A) 5′-SHpoly(T)12-3′ and the probe DNA (B) 3′-SH-poly(T)12-5′ were adsorbed onto the both transverse surfaces of a single AuNR and the surface of AgNP-FB, respectively. The complementary DNA (24mer 5′-poly(A)24-3′)) and mismatched DNA (24mer 5′-poly(T)24-3′) were used as the target. Before addition of DNA, AgNPs were uniformly assembled on the surface of plastic beads as shown in Figure 3b, and similar results were obtained when mismatched DNA was used. However, after addition of complementary DNA as shown in Figure 3c, many anisotropic NPs were observed on the AgNP-FB in the SEM image and a clear signal for Au appeared in the EDX measurement. These results indicate that AuNRs with probe DNA (A) were conjugated onto the AgNP-FB with probe DNA (B) due to their hybridization with complementary DNA. In these SEM images, AuNRs seem to be lying after drying, but it is expected that AuNRs would be upright condition and fluctuated in aqueous solution since probe DNA molecules at

spectroscopy to observe the light scattering from a single AgNP-FB using different kinds of target DNA (Figure 4b). Before hybridization, the main AgNP-FB peak appears around 490 nm in the scattering spectrum; there is almost no change after addition of the mismatched DNA despite a small modulation of the long wavelength region. On the other hand, we observed a clear modulation in wavelength after adding complementary DNA. Remarkably, the main AgNP-FB peak was greatly suppressed whereas another peak near the LSP resonance of the long-axis mode of AuNR (around 750 nm) was significantly enhanced. In order to understand the physical mechanism that regulated this unexpected spectral modulation, in Figure 5, we systematically investigated the light scattering from the coupled system of AuNRs and AgNP-FB based on DISC method under cluster approximation (cluster DISC method: please see the details in Experimental and Theoretical Procedures and Figure 1). We investigated the scattered light from a coupled system of AgNP-FB and AuNRs with various spatial configurations ⟨i⟩−⟨v⟩ in Figure 5a. In order to discuss the essential mechanism by which this occurs and the 7238

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that AuNRs on a AgNP-FB at the configuration ⟨iii⟩ also affected the decrease of the peak in short wavelength region. While we consider that AuNRs remained upright on the surface of AgNP-FB in ⟨i⟩ to ⟨iv⟩, lying AuNRs are assumed in ⟨v⟩ and the corresponding spectrum is plotted in Figure 5c (purple line). In this case, the enhancement of scattering appeared over the considered wavelength region, which was significantly different from the experimentally obtained spectrum. Therefore, this tendency implies that AuNRs remain upright at the surface of AgNP-FB. For the detailed analysis, in order to understand the physics, we assumed a model in which AuNRs were in the same configuration as that seen in Figure 5a by neglecting the AgNPFB (Figure 6b). ⟨A⟩ indicates the position of the interband

Figure 5. (a) Models for the calculations. (b) Calculated scattering spectra of AgNP-FB with standing AuNRs for the geometry ⟨ii⟩−⟨iv⟩, where 1 nm separation between a AgNP and a AuNR was assumed to be similar in size to the DNA. (c) Calculated scattering spectra of AgNP-FB using AuNRs for the geometry ⟨v⟩, where the results for ⟨i⟩ and ⟨iv⟩ are shown together. The blue broken lines in (b) and (c) indicate the result when AuNR was not used for the geometry ⟨i⟩.

theoretical limitation for the detection of the modulation, we assumed a model system whose size was smaller than the experimentally observed sample consisting of a coupled system of AgNP-FB and AuNRs (a similar treatment successfully explained the collective phenomena of LSP in a AuNP-fixed bead as shown in ref 23). It was confirmed that the calculated optical spectrum of AgNP-FB without AuNRs as shown in ⟨i⟩ of Figure 5a accurately reproduced the experimental results using AgNP-FB with a diameter of 400 nm (please see Figure 2c,d). In particular, as shown in the configuration of ⟨iv⟩, AuNRs are conjugated on the surface at the side of incident light source as shown in Figure 5a ⟨iv⟩. In addition, we found that the spectrum in the short wavelength region between 350 and 400 nm decreases and that a peak at longer wavelength region near the LSP resonance of AuNRs appears (Figure 5b). This tendency is similar to the experimental result in Figure 4b since the incident light was irradiated from the bottom of the glass slide during dark-field measurement. Also, in a different configuration as shown in ⟨iii⟩, the enhancement in the longer wavelength region appears and the decrease in the short wavelength region appears between 400 and 500 nm although the scattering increases over the wide wavelength region, and the decrease in the short wavelength region is quite negligible in the low density case shown in ⟨ii⟩. Therefore, we consider

Figure 6. (a) Schematic illustration of the cancellation of collective modes of interband transition and long-axis localized surface plasmon (LSP). (b) Calculated scattering spectra of only AuNRs without AgNP-FB. (c) Calculated scattering spectra of AgNP-FB with organic NPs much larger than DNA. The result without organic NPs is shown together.

absorption of AuNRs, while ⟨B⟩ is that of the short-axis mode and ⟨C⟩ is the long-axis mode. For the high density case with angles 0°−90°, the peak position of ⟨C⟩ shifts to the shorter wavelength region due to the repulsive interaction since the standing rods have components of induced polarization of LSP that are parallel to the incident light polarization. In the case of the high angle, the rate of AuNRs perpendicular to light polarization increases. Therefore, the peak of short-axis mode ⟨B⟩ increases and a peak of the long-axis mode ⟨C⟩ decreases. In addition, the interband component indicated that ⟨A⟩ gets larger by increasing the angle from 0° to 90°. The result without interaction between AuNRs is also shown, whereas the scattering in the case of densely assembled AuNRs is much 7239

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larger. Taking into account these calculated results, the decrease of scattering in the short wavelength region can be attributed to the cancelation of the collective mode of interband electrons and the collective modes of LSP in the AgNP-FB as shown in the schematic image in Figure 6a. While the experimentally observed suppression is more prominent than the calculated value, we can consider that such a difference appears to be due to the underestimation of the interband effect in the simulation using the parameters obtained from the bulk values of Johnson and Christy.18,29 The quenching of the dye molecules has been reported under certain conditions involving coupling with AuNP,32 but our findings show that a completely different mechanism may be involved. On the other hand, the enhancement of peak in long wavelength regions arises from the plasmonic superradiance from long-axis mode in AuNRs, which is similar to the high density AuNPs.21,23 Finally, we explored the possibility of application for an optical biosensor by comparing the results with and without AuNRs (Figures 5b and 6c). In Figure 6c, 3524 large organic NPs with diameters of 10 nm were assumed to be adsorbed onto the surface of the AgNP-FB as analytes, where 1.3-fold enhancement of scattering was obtained. On the other hand, in Figure 5b, similar spectral modulations arose even when 80 AuNRs were conjugated to AgNP-FB using a similar amount of DNA. The size of a single DNA is assumed to be about 1 nm, and its effective volume is less than 1/4000 of that of an organic NP as shown in Figure 6c. The number of DNA molecules attached to the edge of the AuNR was estimated to be 1−8 from the area density of 16 zmol/cm2 of an experimentally used sample. Remarkably, from these values, we could roughly evaluate the range of enhancement factors in the detection sensitivity as 2 × 104−2 × 105 by comparing the results with and without AuNRs. This result demonstrates that zmol (∼6 × 102) levels of DNA can be detected by using a scattering spectrum under a white light irradiation and provides a guiding principle that can be used for a highly sensitive biosensor.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail [email protected] (T.I.). *E-mail [email protected] (S.T.). Author Contributions #

These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank Mr. M. Tamura, Mr. K. Nakata, Prof. H. Shiigi, Prof. T. Nagaoka, and Prof. H. Ishihara for their useful advice and kind support. A major part of this work was supported by Special Coordination Funds for Promoting Science and Technology from MEXT (Improvement of Research Environment for Young Researchers (FY 20082012)), Grants-in-Aid for Exploratory Research No. 23655072 from JSPS, Grants-in-Aid for Young Researcher (A), No. 24685013, as well as a Grant-in-Aid for Scientific Research (B) No. 23310079 from JSPS.

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REFERENCES

(1) Bănică, F.-G. Chemical Sensors and Biosensors: Fundamentals and Applications; John Wiley & Sons: West Sussex, UK, 2012. (2) Chang, T.-C.; Wu, C.-C.; Wang, S.-C.; Chau, L.-K.; Hsieh, W.-H. Using A Fiber Optic Particle Plasmon Resonance Biosensor to Determine Kinetic Constants of Antigen−Antibody Binding Reaction. Anal. Chem. 2013, 85, 245−250. (3) Szunerits, S.; Boukherroub, R. Sensing Using Localised Surface Plasmon Resonance Sensors. Chem. Commun. 2012, 48, 8999−9010. (4) Soteropulos, C. E.; Zurick, K. M.; Bernards, M. T.; Hunt, H. K. Tailoring the Protein Adsorption Properties of Whispering Gallery Mode Optical Biosensors. Langmuir 2012, 28, 15743−15750. (5) Wu, C.; Khanikaev, A. B.; Adato, R.; Arju, N.; Yanik, A. A.; Altug, H.; Shvets, G. Fano-Resonant Asymmetric Metamaterials for Ultrasensitive Spectroscopy and Identification of Molecular Monolayers. Nat. Mater. 2012, 11, 69−75. (6) Cho, H.; Yeh, E.-C.; Sinha, R.; Laurence, T. A.; Bearinger, J. P.; Lee, L. P. Single-Step Nanoplasmonic VEGF165 Aptasensor for Early Cancer Diagnosis. ACS Nano 2012, 6, 7607−7614. (7) Kawata, S. Near-Field Optics and Surface Plasmon Polaritons; Springer: Berlin, 2001. (8) Wu, P.; Brand, L. Resonance Energy Transfer: Methods and Applications. Anal. Biochem. 1994, 218, 1−13. (9) Lunz, M.; Gerard, V. A.; Gun’ko, Y. K.; Lesnyak, V.; Gaponik, N.; Susha, A. S.; Rogach, A. L.; Bradley, A. L. Surface Plasmon Enhanced Energy Transfer between Donor and Acceptor CdTe Nanocrystal Quantum Dot Monolayers. Nano Lett. 2011, 11, 3341−3345. (10) Li, H.; Wang, M.; Wang, C.; Li, W.; Qiang, W.; Xu, D. Silver Nanoparticle-Enhanced Fluorescence Resonance Energy Transfer Sensor for Human Platelet-Derived Growth Factor-BB Detection. Anal. Chem. 2013, 85, 4492−4499. (11) Knoll, W. Interfaces and Thin Films as Seen by Bound Electromagnetic Waves. Annu. Rev. Phys. Chem. 1998, 49, 569. (12) Liebermann, T.; Knoll, W. Surface-Plasmon Field-Enhanced Fluorescence Spectroscopy. Colloids Surf., A 2000, 171, 115−130. (13) Tawa, K.; Umetsu, M.; Nakazawa, H.; Hattori, T.; Kumagai, I. Application of 300× Enhanced Fluorescence on a Plasmonic Chip Modified with a Bispecific Antibody to a Sensitive Immunosensor. ACS Appl. Mater. Interfaces 2013, 5, 8628−8632. (14) Kretschmann, E.; Reather, H. Radiative Decay of Nonradiative Surface Plasmon Excited by Light. Z. Naturforsch. 1968, 23A, 2135− 2136. (15) Raether, H. Surface Plasmons on Smooth and Rough Surfaces and on Gratings; Springer-Verlag: Berlin, 1988.

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CONCLUSIONS In conclusion, we have clarified the mechanism of optical response in a high-density coupled system of Ag nanoparticlefixed beads (AgNP-FB) and Au nanorods (AuNRs) via complementary DNA and have proposed a new type of optical biosensor. In the dark-field optical microscopy with white light irradiation, the light scattering was greatly enhanced in the long wavelength region near the resonance of localized surface plasmon (LSP) in AuNRs. In particular, the suppression of the main peak of LSP in AgNP-FB was unexpectedly observed in the short wavelength region. This anomalous enhancement and suppression of light scattering were attributed to the cancellation of collective modes of interband transitions and LSPs in high density heterogeneous metallic nanostructures. Furthermore, theoretical calculation revealed that a prominent spectral modulation can be observed even with only 100−1000 target DNA molecules conjugating AuNRs to AgNP-FB. This demonstrates the feasibility of highly sensitive detection of DNA on the order of zmol with a simple optical system that uses white light. The results and discussion in this contribution will pioneer a convenient and sensitive optical biosensing system based on the biomolecule-mediated self-assembly of heterogeneous metallic nanostructures. 7240

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The Journal of Physical Chemistry C

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(16) Svedendahl, M.; Chen, S.; Dmitriev, A.; Käll, M. Refractometric Sensing Using Propagating versus Localized Surface Plasmons: A Direct Comparison. Nano Lett. 2009, 9, 4428−4433. (17) Mitchell, J. Small Molecule Immunosensing Using Surface Plasmon Resonance. Sensors 2010, 10, 7323−7346. (18) Kreibig, U.; Vollmer, M. Optical Properties of Metal Clusters; Springer-Verlag: Berlin, 1995. (19) Kojima, C.; Watanabe, Y.; Hattori, H.; Iida, T. Design of Photosensitive Gold Nanoparticles for Biomedical Applications Based on Self-Consistent Optical Response Theory. J. Phys. Chem. C 2011, 115, 19091−19095. (20) Tokonami, S.; Yamamoto, Y.; Shiigi, H.; Nagaoka, T. Synthesis and Bioanalytical Applications of Specific-Shaped Metallic Nanostructures: A review. Anal. Chim. Acta 2012, 716, 76−91. (21) Iida, T. Control of Plasmonic Superradiance in Metallic Nanoparticle Assembly by Light-Induced Force and Fluctuations. J. Phys. Chem. Lett. 2012, 3, 332−336. (22) Ito, S.; Yamauchi, H.; Tamura, M.; Hidaka, S.; Hattori, H.; Hamada, T.; Nishida, K.; Tokonami, S.; Itoh, T.; Miyasaka, H.; Iida, T. Selective Optical Assembly of Highly Uniform Nanoparticles by Doughnut-Shaped Beams. Sci. Rep. 2013, 3, 3047(1−7). (23) Tokonami, S.; Hidaka, S.; Nishida, K.; Yamamoto, Y.; Nakao, H.; Iida, T. Multipole Superradiance from Densely Assembled Metallic Nanoparticles. J. Phys. Chem. C 2013, 117, 15247−15252. (24) Tokonami, S.; Morita, N.; Takasaki, K.; Toshima, N. Novel Synthesis, Structure, and Oxidation Catalysis of Ag/Au Bimetallic Nanoparticles. J. Phys. Chem. C 2010, 114, 10336−10341. (25) Liu, X.; Lee, C.; Law, W.-C.; Zhu, D.; Liu, M.; Jeon, M.; Kim, J.; Prasad, P. N.; Kim, C.; Swihart, M. T. Au−Cu2−xSe Heterodimer Nanoparticles with Broad Localized Surface Plasmon Resonance as Contrast. Nano Lett. 2013, 13, 4333−4339. (26) Yamamoto, Y.; Takeda, S.; Shiigi, H.; Nagaoka, T. An Electroless Plating Method for Conducting Microbeads Using Gold Nanoparticles. J. Electrochem. Soc. 2007, 154, D462−D466. (27) Tokonami, S.; Shiigi, H.; Nagaoka, T. Open Bridge-Structured Gold Nanoparticle Array for Label-Free DNA Detection. Anal. Chem. 2008, 80, 8071−8075. (28) Purcell, E. M.; Pennypacker, C. R. Scattering and Absorption of Light by Nonspherical Dielectric Grains. Astrophys. J. 1973, 186, 705− 714. (29) Johnson, P. B.; Christy, R. W. Optical Constants of the Noble Metals. Phys. Rev. B 1972, 6, 4370−4379. (30) Iida, T.; Ishihara, H. Theory of Resonant Radiation Force Exerted on Nanostructures by Optical Excitation of Their Quantum States: From Microscopic to Macroscopic Descriptions. Phys. Rev. B 2008, 77, 245319. (31) Bohren, G. F.; Huffman, D. R. Absorption and Scattering of Light by Small Particles; Wiley Interscience: New York, 1983. (32) Mayilo, S.; Kloster, M. A.; Wunderlich, M.; Lutich, A.; Klar, T. A.; Nichtl, A.; Kürzinger, K.; Stefani, F. D.; Feldmann, J. Long-Range Fluorescence Quenching by Gold Nanoparticles in a Sandwich Immunoassay for Cardiac Troponin T. Nano Lett. 2009, 9, 4558− 4563.

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dx.doi.org/10.1021/jp501613b | J. Phys. Chem. C 2014, 118, 7235−7241