Preparation of a SERS substrate and its sample-loading method for point-of-use application

A simple approach was demonstrated to prepare a silver (Ag) nanoparticle (NP) assembly as a SERS substrate. Just by dipping a flat silicon (Si) wafer into an aqueous deposition solution of hydrogen fluoride (HF) + silver nitrate (AgNO3), a monolayer of Ag NPs was uniformly deposited onto the Si wafer surface. In order to load the to-be-detected sample onto the as-prepared SERS substrate, three methods have been individually tested, (i) by incubating the SERS substrate in the sample solution, (ii) by dropping and drying a small volume of the sample solution (1-2 microl) onto the SERS substrate surface, or (iii) by directly introducing the sample into the deposition solution. The last approach was also employed to metalize a Si nanowire (NW). Due to the NW's highly curved surface, the Ag NPs self-assembled and aggregated along the NW with a close interdistance. The aggregated Ag NPs on the NW surface can also be used as a SERS substrate. The demonstrated approach holds the promise to prepare a fresh SERS substrate at the point-of-use with the sample already loaded to promptly collect the SERS signal for the field application.