Fig. 6

SEM images and EDX analyses of the ridges of fingermarks and the backgrounds between ridges after collected latent fingermarks were incubated with LBA-Au NPs first and then treated with Au⁺-complex solution. No signals of Au and Au NPs were detected and observed in the backgrounds between ridges of fingermarks, but Au NPs (black arrows) with different sizes appeared in the ridges of fingermarks and EDX proved their component was Au. These results indicated the visual ridges of fingermarks were certainly due to the growth of Au NPs from Au seeds. This latent fingermark was collected using professional-grade forensic tape. The used volumes of THPC-Au NPs and LBA-Au NPs were 200 µL with particle concentrations of 132 µM. The used volumes of Au⁺-complex solution were 300 µL. Scale bars in both SEM images are 100 nm