Controllable colours and shapes of silver nanostructures based on pH: application to surface-enhanced Raman scattering

This paper reports for the first time that the shape of silver nanostructures on quartz slides, from a nanoprism to a nanodisc, can be easily realized within a few minutes simply by adjusting the pH value of the immersion solution. Different colours of the quartz slide covered with Ag nanostructures appeared, from deep blue to yellow, corresponding to the shapes of Ag nanostructures changing from nanoprisms to nanodiscs. Surface-enhanced Raman scattering (SERS) activities of the silver nanoprisms and nanodiscs (obtained through adjusting the pH values) were checked using p-aminothiophenol (p-ATP) as a probe molecule at both near-infrared (1064 nm) and visible light (514.5 nm) excitation. The results obtained further confirmed the enhancement mechanism of SERS based on the coupling between the surface plasmon resonance (SPR) of the substrates and the laser excitation wavelength. This work will be of great significance in understanding the SERS enhancement mechanism and in the fabrication of nanoparticle films for biosensing.