Fig. 1. (a) A schematic of the experimental setup used to detect the photoacoustic signals generated from AuNRs with latitudinal widths of 10, 25, 40 and 50 nm along with the (b) normalised measured absorbance spectra displaying SPR peaks at 811 ± 2 nm, 803 ± 2 nm, 790 ± 2 nm, and 841 ± 2 nm, respectively. The SPR of the Au50s showed a 50 nm shift compared with that of the Au40s, which can be ascribed to a combined effect of the AuNR width and aspect ratio on the SPR position of AuNRs.