A method of detecting melamine which includes providing a quantity of SERS-active particles and mixing the SERS-active particles with a solution containing melamine. The method further includes detecting a surface enhanced Raman spectrum of the melamine. The foregoing method may optionally include aggregating the SERS-active particles. Aggregation may occur before or after the SERS-active particles are mixed with a solution containing melamine. The method of detecting melamine may optionally include concentration of the SERS-active particles. The method may further include mixing a chaotropic agent having a higher affinity for a selected binding site than melamine into the solution containing melamine. The method may further include mixing a quantity of a SERS-active standard having a known SERS spectrum with the solution containing melamine and SERS-active particles. Assay apparatus and systems are also disclosed.