Fig. 2. (a) Typical examples of the averaged photoacoustic signals (8 mJ cm⁻² laser fluence) generated by all four AuNR sizes at a concentration of 1 × 10¹¹ NP ml⁻¹, detected with a 1 MHz focussed transducer, compared with the baseline signal (black). (b) Relationship between incident laser fluence and calculated photoacoustic signal amplitude generated from the same four AuNRs at a concentration of 1 × 10¹¹ NP ml⁻¹. Au10s (blue), Au25s (red), Au40s (green) and Au50s (yellow). The black line represents the water baseline signal.