A new microvolume technique for bioaffinity assays using two-photon excitation

Bioaffinity binding assays such as the immunoassay are widely used in life science research. In an immunoassay, specific antibodies are used to bind t arget molecules in the sample, and quantification of the binding reaction r eveals the amount of the target molecules. Here we present a method to meas ure bioaffinity assays using the two-photon excitation of fluorescence. In this method, microparticles are used as solid phase in binding the target m olecules. The degree of binding is then quantified from individual micropar ticles by use of two photon excitation of fluorescence. We demonstrated the effectiveness of the method using the human alpha-fetoprotein (AFP) immuno assay, which is used to detect fetal disorders. The sensitivity and dynamic range we obtained with this assay indicate that this method can provide a cost-effective and simple way to measure various biomolecules in solution f or research and clinical applications.