Andrey M. Burov | Searcharxiv

arXiv2026

Gold Bipyramids as a Promising Alternative to Gold Nanorods for Analytical and Biomedical Applications

Pentagonal gold bipyramids with dimensions of 75x25 nm and a longitudinal plasmon resonance (PR) at 753 nm are synthesized. For comparison, gold nanorods with a diameter of 20 nm, lengths ranging from 95 to 50 nm, and longitudinal PR from 945 to 644 nm were synthesized by chemical etching. The samples were characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). It is shown that the absorption spectral quality factor of the bipyramids is significantly higher than that of the nanorods. To compare the nanoparticles as platforms for surface-enhanced Raman scattering (SERS), their surface was functionalized with thiolated nitrobenzene molecules (NBT). It is demonstrated that the SERS enhancement factor for the bipyramids is approximately three times higher than that for the nanorods. The red shift of the bipyramids' PR after functionalization with NBT molecules is also about three times greater than for nanorods with the same PR. This agrees with the theoretical estimate of the bipyramids' PR shift being more sensitive to variations in the refractive index of the external medium or the dielectric shell thickness than that of gold nanospheres and nanorods. The high efficiency of the bipyramids as thermosensitizers for converting laser radiation into heat in photothermal therapy is experimentally and theoretically demonstrated. Effective photothermal killing of E. coli was shown upon irradiation with a laser at the plasmon resonance wavelength using nanobipyramids or nanorods.

physics.optics↗

arXiv2023

Surface-Enhanced Raman Scattering from Au Nanorods, Nanotriangles, and Nanostars with Tuned Plasmon Resonances

Electromagnetic theory predicts that the optimal value of the localized plasmon resonance (LPR) wavelength for the maximal SERS enhancement factor (EF) is half the sum of the laser and Raman wavelengths. For small Raman shifts, the theoretical EF scales as the fourth power of the local field. However, experimental data often disagree with these theoretical conclusions, leaving the question of choosing the optimal plasmon resonance for the maximal SERS signal unresolved. Here, we present experimental data for gold nanorods (AuNRs), gold nanotriangles (AuNTs), and gold nanostars (AuNSTs). The LPR wavelengths were tuned by chemical etching within 550-1050 nm at constant number concentrations of the particles. The particles were functionalized with Cy7.5 and NBT, and the dependence of the intensity at 940 cm-1 (Cy7.5) and 1343 cm-1 (NBT) on the LPR wavelength was examined for laser wavelengths of 633 nm and 785 nm. The electromagnetic SERS EFs were calculated by averaging the product of the local field intensities at the laser and Raman wavelengths over the particle surface and their random orientations. The calculated SERS plasmonic profiles were redshifted compared to the laser wavelength. For 785-nm excitation, the calculated EFs were five to seven times higher than those for 633-nm excitation. With AuNR@Cy7.5 and AuNT@ Cy7.5, the experimental SERS was 35-fold stronger than it was with NBT-functionalized particles, but with AuNST@Cy7.5 and AuNST@NBT, the SERS responses were similar. With all nanoparticles tested, the SERS plasmonic profiles after 785 nm excitation were slightly blue-shifted, as compared with the laser wavelength, possibly owing to the inner filter effect. After 633-nm excitation, the SERS profiles were redshifted, in agreement with EM theory. In all cases, the plasmonic EF profiles were much broadened compared to the calculated ones and did not follow the four-power law.

physics.optics↗