Methods for amplifying the Raman signal of primary SERS nanoparticles are provided. One method generally includes binding secondary SERS particles to the primary SERS nanoparticles after binding of the primary SERS nanoparticles. In another method, secondary SERS nanoparticles are brought in close proximity to the primary SERS nanoparticles, wherein the secondary nanoparticles are free of a reporter molecule or have a reporter molecule different from that of the primary SERS nanoparticles.