Miniaturization of bioassays for analytical toxicology

Abstract

Miniaturized clinical and environmental analyzers could have enormous impact on our ability to make reliable field measurements. The goal of the work described in this dissertation is to explore some miniaturized methods for application in toxicological analysis. The first application introduces a flow injection solid phase extraction technique for immunoassay. Advantages of this method are robustness and simplicity among others that are described. In order to make truly portable hand-held devices, however, it was clear that it was necessary to explore other avenues. Therefore, the remainder of the dissertation focuses on the development of lab-on-a-chip devices that are gaining interest and momentum at a tremendous rate. While the impact of miniaturization of chemical analysis is potentially far-reaching, several poorly understood physical and chemical measurement issues may impede the widespread application of these devices. Some of the major obstacles to commercialization of reliable "lab-on-a-chip" devices include: (1) a lack of fundamental understanding of the surface processes that affect sample recovery; (2) the absence of reliable methods for harnessing flow in microchannels, and (3) the scarcity of generally applicable chemistries that allow for sensitive chemical measurement. Since the lab-on-a-chip technology is still in its infancy, commercial devices are not available; therefore, fabrication methods were developed in-house. Two imprinting methods are reported for producing devices in plastic materials. These techniques allow for the fabrication of reproducible microchannels with diameters as small as 15 microns. The majority of this work explores the application of plastic imprinted microchannel devices for biochemical analyses using electrokinetic separation. Homogeneous immunoassays were performed for both large (IgG), and small analytes (morphine) in these devices. Due to limitations in sensitivity with homogeneous immunoassays, liposomes were employed for signal amplification in heterogeneous affinity-based assays in plastic devices. Much of this research focuses on the issues that limit the ability to make reproducible biochemical measurements in plastic microfluid channels. Flow control, sample injection methods, analyte adsorption, sample recovery, signal amplification and device stability were all studied to improve the reliability of analytical data obtained in field analytical devices for applications in toxicology.