Abstract: Systems and methods that allow optical detection of nanoparticles according to size and interaction with specific antibodies. Using abiological sample combined with fluorescent dyes and fluorescently labeled antibodies, implementations of the disclosed system allow for detection of >100 particles having diameters as low as 100 nm in under 10 minutes. The detection mechanisms combine confocal detection of particles in microfluidic flow devices. Concentrating the sample using hydrodynamic focusing allows detection of particles having concentrations as low as 104 particles per mL of the sample. These capabilities allow for the detection, identification, and quantitation of viruses from bodily fluids such as saliva, where biologically relevant virus concentrations of potentially infected subjects are within the range of 103-107 particles/mL.