Squaraine dyes are used to detect the presence of protein in a test sample, which is a substance that may contain protein. A squarine dye is placed in water, and in some instances joined with an aggregation agent, to create an aqueous dye solution. That dye solution is joined with a test sample. When the dye solution is joined with the test sample and the resultant test solution is excited by the application of photons, a resulting fluorescence or absence thereof reveals if protein was present in the test sample.