The field of the invention relates generally to the detection of antigens, including, but not limited to, quantum dots (Qdots) and metal oxide nanoparticles. More specifically, the invention relates to the detection of antigens on a surface or in a source, which antigens include bacteria, viruses, and small proteins. In some embodiments, the invention can be used to detect biological warfare agents, such as anthrax and ricin. In some embodiments, the invention can be used for early detection of diseases in human and animals. The invention may utilize a swab-test and may further utilize a filtration process, such as with a syringe-disc.