Development of membrane-assisted microfluidic immunosensors with optical detection

Immunoassay has been developed into a mature technique that can detect and quantify biological species in "real" samples such as serum and plasma. However, enzyme-linked immuno-sorbent assay (ELISA), the most widely used immunoassay format, has to be conducted in specialized labs due to complex procedure. Consumption of a large amount of biological samples in ELISA also drives the process cost higher and generates more waste. The next generation immunoassay developed here focuses on miniaturization with microfluidic techniques. Microfluidic immunosensors consume far less sample, generate less waste, function more effectively and more importantly, if properly integrated into lab-on-a-chip devices, can be operated by people with minimal training for on-site measurement applications.;Poly(dimethylsiloxane) (PDMS) is one of the most widely used polymer materials for fabrication of microfluidic devices due to biocompatibility, favorable physical properties and ease in manufacturing procedure. However, the hydrophobicity of the PDMS surface generates high non-specific adsorption, which results in false positive response in immunoassay. Our work exploits solid supported phospholipids lipid bilayers (SLBs) as sensing interfaces in PDMS microchannels with optical detection. SLBs enable cell surface receptors to be presented in a desirable orientation for maximum affinity as well as prevent nonspecific interactions, therefore enhancing the detection sensitivity. Positively charged lipid bilayers on plasmon-oxidized PDMS are found to have enhanced stability against air damage and have been used for immunosensing of model analyte cholera toxin. A protein reinforced layer has also proved to increase bilayer air-stability and is employed for detection of Staphylococcal enterotoxin B.;When coupled with label-free detection such as surface plasmon resonance (SPR), microfluidic immunosensors can be further improved by eliminating the high cost of labeled reagents with a simplified detection scheme. SPR immunosensors have been developed for label-free screening of human immunoglobulin (IgG) in PDMS microfluidic channels. To enhance the detection sensitivity, atom transfer radical polymerization (ATRP) enhanced SPR is developed to enable femto molar detection of bacterial cholera toxin. Our method of enhanced SPR with ATRP is advantageous in many ways, opening new avenues for high sensitivity and high throughput detection of complex biological interactions.