A biophotonic array based on gold nanoparticles functionalized with antigen proteins has been used to determine the concentrations of the respective antibodies in solution. Four proteins-fibrinogen, bovine serum albumin, transferrin, and C-reactive protein-were used to construct a test array with the assay repeated a number of times. The antibody-antigen association and dissociation rate constants were determined for the antibody assays from a series of calibration experiments. The label-free determination of the unknown antibody concentrations was performed using two related kinetic analyses. From these results, the current array assay sensitivity is 250 ng ml(-1) with an accuracy of 15% using an 8-min kinetic measurement and a 16-spot averaged assay.