Development of biosensors and applications for the detection of Salmonella typhi and carcinoembryonic antigen

Abstract

The development of biosensors for low-cost point-of-care diagnostic test is reported in this dissertation. Three important parts including electrochemical immunoassay, low-cost material substrate, and improvement of sensitivity were developed to achieve the low-cost biosensors. In the first part, electrochemical immunoassay for the Salmonella typhi (S. typhi) determination has been developed by using a copper-enhanced gold nanoparticle label coupled with anodic stripping voltammetry. The anodic stripping peak current was linearly dependent on the S. typhi concentration over concentration range of 1.30 × 10² to 2.6 × 10³ cfu/mL in a logarithmic plot, with a detection limit as low as 98.9 cfu/mL. In the second part, paper-based substrates were used for bioassays instead of membrane due to the ultra-low cost of the paper materials. Paper-based microfluidic devices (µPADs) were investigated in this part because they combined the simplicity of paper strip tests and the complexity of the conventional microfluidics. In this part, the use of multiple indicators for a single analyte and electrochemical detection were applied for µPADs to improve quantitative analysis. The paper-based microfluidic channels were prepared by photolithography and the working electrode was built into devices using screen-printing technology. The basic electrochemical performance of the system was demonstrated using cyclic voltammetry. The utility of our devices was then demonstrated with the determination of glucose, lactate, and uric acid in serum samples using oxidase enzyme (glucose oxidase, lactate oxidase, and uricase, respectively) reactions. Moreover, wax screen-printing as a low-cost, simple, and rapid method for fabricating paper-based microfluidic devices (µPADs) is reported here. These developed biosensors show significant promise for inexpensive bioassay for limited resource environments. Lastly, a small volume magnetic microbead-based immunoassay was developed to increase the surface area for immobilization of antigen or antibody. The utility of magnetic microbead-based immunoassay was investigated by the determination of carcinobmbryonic antigen (CEA) in human serum. The limit of detection as low as 0.69 ng/mL was achieved.