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Ultrasensitive absorption detection of protein and DNA microarrays based on nonlinear multiphoton wave-mixing spectroscopy

Ultrasensitive optical absorption detection method based on multi-photon wave-mixing spectroscopy is inherently suitable for biochips, biosensors and microarrays. Absorption-based wave mixing offers detection sensitivity levels that are comparable or better than those of fluorescence-based methods while using micrometer-thin samples. Wave-mixing methods offer detection of biospecific interactions on antibody or oligonucleotide microarray platforms. Optical absorption measurements of protein and DNA profiles on a glass substrate can be made with excellent reproducibility. The laser probe volume, i.e., the overlap volume of two input laser beams, ranges from nanoliter to picoliter levels. Dynamic gratings created inside the absorbing sample diffract off incoming photons to create the signal beam. Unlike fluorescence methods, wave mixing generates a collimated laser-like signal beam, and hence, signal collection is efficient and convenient. Each microarray spot has a specific antibody or oligonucleotide sequence and wave mixing allows detection of corresponding target molecules with high throughput. Wave mixing also yields intra-spot spatial resolution for profiling individual array spots.