Provided herein are surface enhanced Raman scattering (SERS)-active reagents and methods for detecting one or more analyte in a sample. Said SERS-active reagents are adaptable, sensitive, and easy-to-use in the diagnosis of infectious diseases in a patient, or the detection of toxins, bacteria, viruses, pathogens, hormones, cytokines, antigens, antibodies or illicit drugs in a biological sample. Such methods may be handled by police, soldiers, or health care workers in the field, and do not require specialized training.