Disclosed is a portable fluorescence correlation spectroscopy instrument that includes an excitation source, at least one of a light focusing element positioned to receive light emitted by the excitation source, a detector for detecting light, the detector positioned to receive light emitted by a sample excited by the excitation source, and a correlator coupled to the detector, the correlator for processing data received at the detector and providing data including autocorrelation data, crosscorrelation data, or a combination thereof.