A facile and general route to synthesize silica-coated SERS tags with the enhanced signal intensity

Silica-coated SERS tags have been attracting greater attention in recent years. However, the reported methods to synthesize these tags are tedious, and often subjected to the limited signal intensity. Here, we report a facile and general method to prepare the silica-coated Ag SERS tags with the enhanced signal intensity by no introducing the primers. This approach mainly depends on the colloidal stability of the Ag NPs in alcohol solution. By decreasing the concentration of salt in Ag NP solution, the citrate-stabilized Ag NPs can be well dispersed in alcohol solution. Based on this, the Ag SERS tags can be directly coated with thickness-controlled and homogeneous silica shells. This approach is highly reproducible for silica shell growth and signal intensity, not depending on the properties of Raman molecules, proved by 7 kinds of the Raman molecules. Moreover, this kind of SERS tags coated with silica hold the stronger SERS signals than the traditional method due to no interference from the priming molecules.