UC San Diego

Nonlinear laser wave mixing is presented as a highly sensitive absorption-based detection method for biomarkers in a capillary electrophoresis system, and on glass surfaces or microscope slides. It offers significant advantages, including outstanding sensitivity and selectivity levels, high spatial resolution, small sample volume requirement, small probe volume (nL to pL), and portable and compact designs. Different laser wave-mixing detectors can be interfaced to capillary electrophoresis systems for enhanced chemical selectivity and microscope glass slides for inexpensive and fast detection of millimeter-thin samples.Laser wave-mixing detection interfaced with capillary electrophoresis further enhances detection sensitivity by on-line sample concentration methods. Selectivity levels are improved by separating excess labels or dyes from dye-conjugated proteins. Different modes of capillary electrophoresis can be used to separate proteins and biomarkers, including capillary zone electrophoresis, micellar electrokinetic chromatography, and capillary sieving electrophoresis. Since wave mixing is an absorption-based detection method, one can use both fluorophores and chromophores to label proteins and biomarkers. For example, Chromeo P503 and Chromeo P540 are used to label pancreatic cancer biomarker CA 19-9 with the optimal molar ratio of dye to protein. The concentration and mass detection limits for CA 19-9 are determined to be 0.0090 U/mL and 6.8 x 10-10 U, respectively. Colorimetric assays (Bradford assay and BCA assay) are used to quantify CA 19-9, and the corresponding concentration and mass detection limits for CA 19-9 are determined to be 75 pM (picomolar) and 5.6 zeptomole, respectively. This study also demonstrates ultrasensitive detection of biomarkers held between microscope glass slides or air-dried on a microscope slide for convenient and fast detection of biomarkers and viruses. Preliminary concentration and mass detection limits are determined to be 160 U/mL and 680 attomole for CA 19-9; 40 ng/mL and 91 zeptomole for human epidermal growth factor receptor 2; and 125 pg/mL and 1 zeptomole for HIV-1 p24 antigen.