Ultrasensitive detection of proteins and antibodies by absorption-based laser wave-mixing detection using a chromophore label

Nonlinear laser wave mixing is presented as an ultrasensitive absorption-based method for the detection of proteins and antibodies using a nonfluorescing chromophore label, Coomassie Brilliant Blue (CBB). The complexes are flowed through a 150-μm (i.d.) capillary cell and detected using a low-power He–Ne laser. The wave-mixing signal is detected after 10 min of room temperature incubation for the antibody complex and after 18 min for the protein complex. All solutions are prepared in an aqueous buffer without the addition of organic modifiers. Concentration detection limits of 3.4 × 10–19 and 6.4 × 10–14 M (signal-to-noise ratio [S/N] = 2) are determined for bovine serum albumin (BSA) and human papillomavirus (HPV) antibody, respectively. Based on the small laser probe volume used (i.e., overlap volume of the two input beams), mass detection limits of 1.7 × 10–22 and 2.6 × 10–17 mol are determined for BSA and HPV antibody, respectively.