In situ loading of Ag nanocontacts onto silica nanospheres: a SERS platform for ultrasensitive detection

Analytical techniques based on surface-enhanced Raman scattering (SERS) suffer from a lack of reproducibility and reliability, thus hampering their practical applications. Herein, we have developed SiO2@Ag nanospheres as an effective SERS detection platform through in situ loading Ag nanocontacts onto the SiO2 nanospheres, the well-designed and uniform nanocomposites provide highly enhanced effects for the tremendous SERS signal amplification. The huge enhanced effect might originate from the hot spots generated from the nanocontacts among the silver nanoparticles loaded onto the silica nanosphere, and also possibly from the nanogaps among the neighboring silver nanoparticles between the two silica nanospheres. The SERS enhancement factor of the SiO2@Ag nanospheres substrate is as high as 1016. Moreover, the as-fabricated SERS substrate can be employed to enhance the Raman signals of some chemicals that are harmful to environment including thiram, melamine and ethyl-parathion. The detection limits with the SERS platform are several orders of magnitude lower than the maximal residue limit (MRL) in fruit prescribed by U.S. Environmental Protection Agency (EPA). Therefore the surface lifting spectroscopic technique based on the SiO2@Ag nanosphere SERS platform offers great practical potential for the on-site assessment and identification of harmful chemicals with ultralow concentrations in agricultural products and environments.