Gold nanoparticles based Nanosensors/Nanobeacons fabricated by bottom-up method for surface enhanced raman scattering

Abstract

The coming era of a “Trillion Sensors Universe” or “Nanosensors and the Internet of Nanothings” requires countless tiny sensor devices. Since surface enhanced Raman scattering (SERS. produces strong signals efficiently in such a tiny region of noble metal nanostructures with corresponding localized plasmon resonance, a SERS active nanostructure is promising to realize nanosensor devices. As for the costless fabrication of trillion SERS active nanostructures, the bottom-up process of self-assembled gold nanoparticles (AuNP. is desirable. The self-assembling of colloidal AuNP (40 nm. was carried out under time-controlled agitation for 1 s, 5 s, 30 s and 60 s at 500 rpm. A series of absorption spectra of these AuNP dispersions showed snapshots of the proceeding aggregation. The wavelength at the absorption maximum of AuNP dispersion under continuos agitation shifted from 425 nm to 680, 750, 870 nm and almost vanished in the visible region at 60 s. Interestingly, these aggregation dispersions were quasi-stable enough to take 785 nm SERS measurements while agitation was stopped. Comparisons between absorption the spectra and the SERS intensity strongly suggested the intensity of localized plasmon resonance both at the incident laser wavelength and at the Raman wavelength correlative to SERS intensity for the certain stages of selfassembling. We believe that these results are typical demonstrations in collective systems of colloidal AuNP assembles that support the electromagnetic mechanism of SERS. Consequently, SERS active nanostructures for nanosensors and nanobeacons were sufficiently fabricated by the bottom-up process of the diffusion-limited aggregation of colloidal AuNP under a shear force of time-controlled agitation.