Fig. 3

Composition of the photoacoustic signal for uncoated gold sphere. a No fluid shell. b\(15\) nm fluid shell. c 45 nm fluid shell. d\(60\) nm fluid shell. e \(90\) nm fluid shell. f \(180\) nm fluid shell. The core radius is \(a=30\) and it is placed in water with \({G}_{12}=200\,{\mathrm{{{MW}}}}\,{\mathrm{{{m}}}}^{-2}\,{\mathrm{{{K}}}}^{-1}\), computed at \({r}_{{\mathrm{{d}}}}=10a=300\) nm, with the differentiating feature in each panel being the thickness of the surrounding fluid region (“fluid shell”); revealing a signal generating volume (“fluid shell”) with a thickness >\(2a=60\) nm