The invention is a device for testing an individual for the presence of a entity. The entity can be a pathogen, toxin or drug. The device is adapted to collect from the individual the biological sample to be tested. The test device comprises noble metal nanoparticles (i.e. gold, silver or copper) to detect the entity. Test results are read from a window in the device. The current visual limit using aggregated noble metal nanoparticles is a clump having a diameter in a range of about 50nm to about 75 nm. One or more ligands specific for the entity are attached to two or more metal nanoparticles. Each individual nanoparticle has a diameter in a range of about 15nm to about 35 nm. Ligands attached to the nanoparticles and specific for the entity can be for example antibodies, antibody fragments, oligonucleotides, and aptamers. Different ligands specific for different sites on the entity may be used in order to increase the aggregation potential of the nanoparticles in the presence of the target. The testing is conducted within the device after sample collection. The results of assay are available promptly. Conditions that can be tested include for example viral infections, bacterial infections, exposure to toxins, and drug use. Detection of Human Immunodeficiency Virus (HIV) is described by example.
