A technique can be used to detect and/or quantify allergens in foods. In some examples, the technique involves adding magnetic particles that carry antibodies and surface-enhanced Raman scattering (SERS) tags complexed with antibodies to the sample. The antibodies associated with both the magnetic particles and the SERS tags can be selected to bind to one or more antigens that correspond to allergens being investigated. After adding magnetic particles to the sample, a magnetic field can be applied to the sample to concentrate antigens in the sample, including any SERS tags bound to the antigens. The concentrated sample can be analyzed with SERS and a concentration of the mammalian allergen determined based on the SERS response.