This work investigates the surface plasmon resonance (SPR) of monodisperse gold nanorods (AuNR) aqueous solutions (1011NP/cm3) under high-pressure conditions. We show that the longitudinal SPR of AuNR (aspect ratio: 3.4) redshifts with pressure as a consequence of two competing effects: a blueshift induced by the increase of electron density due to AuNR compression, and a large redshift due to increase of the solvent refractive index [1]. Here we show that the LSPR pressure redshift can be explained within the Mie-Gans model [2] by changes of the refractive index n of the surrounding medium. These measurements unveil the suitability of AuNRs for refractive index sensing and detection of structural changes (water→Ice VI→Ice VII) as it is shown in the figure. The so-obtained n(P) data are compared with those measured by standard interferometric and spectroscopic techniques at high pressure [3]. We will show similar results using AuNR dispersed in methanol-ethanol mixtures, which enable us to widen the hydrostatic pressure range of the transmitting medium up to 11 GPa [1]. Interestingly, high-pressure induced solvent solifification yields notablt changes in the AuNR plasmonics. We acknowledge finantial support from MINECO (MAT2015-69508-P, MAT2017-86659-R, MAT2015-71070-REDC; PGC2018-101464-B-I00).
Figure: Pressure dependence of the LSPR band of AuNRs in aqueous solutions. The plots include experimental (filled circles) and calculated (solid lines) values of λLSPR(P) using the Mie-Gans model.
[1] C. Martín-Sánchez, J. A. Barreda-Argüeso, S. Seibt, P. Mulvaney, F. Rodríguez, ACS Nano 13, 498 (2019)
[2] R. Gans, Ann. Phys. 342, 881 (1912)
[3] C. Martín-Sánchez, G. González-Rubio, P. Mulvaney, A. Guerrero-Martínez, L. M. Liz-Marzán, F.Rodríguez, J. Phys. Chem. Lett. 10, 1587 (2019)