Nonlinear laser wave-mixing detection for capillary electrophoresis and multi-channel arrays for biomedical and environmental applications

• Main Author: Maxwell, Eric J
• Format: Dissertation
• Language: English
• Subjects: biogeochemistry; chemistry
• ISBN: 9781321748055; 1321748051

Degenerate Four-Wave Mixing is demonstrated as a highly sensitive nonlinear spectroscopic detection method for small molecule and protein biomedical and environmental targets. This is achieved through refractive index change within an absorbing liquid medium, which produces a laser-like signal beam. This signal has high spatial resolution, and may be collected with high efficiency against a nearly 100% dark background. A cubic dependence on laser power and a square dependence on analyte concentration allow for high signal intensity in trace analysis applications. In this work, the Degenerate Four-Wave Mixing technique is coupled with capillary electrophoresis, immunoprecipitation or color-forming reactions to provide specificity. Coupling with multi-channel capillary arrays has also been explored as a means of high-throughput sample analysis. The veterinary drugs malachite green and crystal violet are shown to be detectable at concentrations as low as 6.9 x 10-10 M (2.5 x 10-19 mol) and 8.3 x 10-11 M (3.0 x 10-20 mol) respectively (S/N = 2). Capillary electrophoresis is used in conjunction with a 2-laser Degenerate Four-Wave Mixing detector to allow simultaneous identification of both analytes. For another small molecule target, ammonium nitrate, sample preparation with diphenylamine is used to produce a colored compound capable of absorbing 635 nm light. This explosive component is of significant forensics interest due to its use in the manufacture of improvised explosive devices. The limit of detection for ammonium nitrate in 1 mm ID capillary cells is determined to be 1.5 x 10-9 M (5.2 x 10-18 mol). The detection limit in a 1.5 mm thin-film cell is found to be 3.2 x 10-7 M (2.0 x 10-15 mol) for S/N = 2. In addition to small molecule environmental targets, a detector for the cancer biomarker carcinoembryonic antigen is demonstrated with a combination of magnetic immunoprecipitation, multi-channel capillary arrays and Degenerate Four-Wave Mixing. Isolated protein samples are reacted with bicinchoninic acid (BCA) to yield a colored product, and absorbance of a 532nm laser produces a wave-mixing signal. Multiple samples may be processed rapidly though computer-controlled positioning of the multi-channel capillary array. The limit of detection for carcinoembryonic antigen is determined to be 3.3 x 10-12 M (0.59 ng/mL), with a corresponding mass detection limit of 1.2 x 10 -21 mol (0.22 fg) for S/N = 2.