CC BY
20B-I-11
Plasmonic gap-enhanced Raman tags for biomedical applications
N. Khlebtsov1
institute of Biochemistry and Physiology of Plants and Microorganisms- RAS, Lab of Nanobiotechnology, Saratov, Russian Federation
Gold and gold/silver layered nanoparticles, in which Raman molecules (RMs) are embedded in a nanometer-sized gap between metal layers (Au@RM@Au, Au@RM@Ag), have great potential in biomedical applications as highly efficient imaging SERS probes [1]. Compared to common SERS tags with outer RMs exciting by plasmonic near field, the embedded RMs of new probes are protected from environmental conditions and subjected to the strongly enhanced internal field in the gap. Another type of efficient SERS tags are the tip functionalized Au(core)@RM@Ag(shell) nanorods (TFNRs) operating in off-resonance mode [2].
In this talk, we summarize our recent efforts in synthesis [3, 4], electromagnetic simulation [5], dip-tissue imaging [2], and lateral flow immunoassay [6] applications of GERTs and tip-finctionalized hybrid Au@RM@Ag SERS tags. In the final part of talk we present a reexamination of SERS dependence of Au nanorods (AuNRs) as a function of their aspect ratio and shape morphology. We used the etching method to prepare a set of AuNR colloids of equal number concentrations by keeping the AuNR width and shape morphology while the plasmon resonance was incrementally decreased from 920 to 650 nm through the finely tuned aspect ratio. AuNRs were functionalized with 4-nitrobenzenethiol and SERS spectra of colloids were measured under 785-nm laser excitation. We demonstrate a weak correlation between the plasmonic peak position and the SERS response. This observation contradicts the well-known four-power law for electromagnetic contribution to SERS signal. By contrast to weak plasmonic dependence of the SERS signal from the aspect ratio of AuNRs, the variations in shape morphology of AuNRs lead to strong increase in SERS response. Thus, the rational design of the nanoparticle shape morphology is more important factor towards highest SERS response compared to the on-resonance plasmonic tuning. Further work is needed to explain the discrepancy between the weak dependence of SERS enhancement on the on-resonance conditions and modern theoretical predictions based on classical electromagnetic [5] or quantum-corrected [7] models.
This research was supported by the Russian Scientific Foundation (project no. 18-14-00016) and by RFBR grants nos. 17-02-00075 and 18-52-7803.
References
[1] Jin X., Khlebtsov B.N., Khanadeev V.A., Khlebtsov N.G., Ye J. Rational design of ultra-bright SERS probes with embedded reporters for bioimaging and photothermal therapy. ACSAppl. Mater. Interfaces, 2017, 9, 30387-30397.
[2] Khlebtsov B.N., Bratashov D.N., Khlebtsov N.G. Tip-functionalized Au@Ag nanorods as ultrabright SERS probes for bioimaging in off-resonance mode. J. Phys. Chem C, 2018, 122, 17983-17993.
[3] Khlebtsov B., Khanadeev V., Khlebtsov N. Surface-enhanced Raman scattering inside Au@Ag core/shell nanorods. Nano Res. 2016, 9, 2303-2318.
[4] Khlebtsov B.N., Khlebtsov N.G. Surface morphology of a gold core controls the formation of hollow or bridged nanogaps in plasmonic nanomatryoshkas and their SERS responses. J. Phys. Chem.
C, 2016, 120,15385-15394.
[5] Khlebtsov N.G., Khlebtsov B.N. Optimal design of gold nanomatryoshkas with embedded Raman reporters. J. Quant. Spectrosc. Radiat. Transfer, 2017, 190, 89-102.
[6] Khlebtsov B.N., Bratashov D.N., Byzova N.A., Dzantiev B.B., Khlebtsov N.G. SERS-based lateral flow immunoassay of troponin I using gap-enhanced Raman tags. Nano Res., 2019, 12, 413-420.
[7] Lin L., Zhang Q., Li X., Qiu M., Jiang X., Jin W., Gu H., Lei D. Y., Ye J. Electron transport across plasmonic molecular nanogaps interrogated with surface-enhanced Raman scattering, ACS Nano, 2018, 12, 6492-6503
