Microscale immunosensors for biological agents

Microbead immunoassay with electrochemical detection has been developed as a sensitive and selective technique for rapid and small volume analyses. In this assay, applications of paramagnetic microbeads in a microfluidic system have aided the automation of all assay steps to enable near-continuous monitoring. These mobile microbeads can be transported through microchannels, captured and held at specific points by a magnet. Hence, by performing immunoassay on microbeads, they can be dispersed throughout a small sample of water, where they provide a large surface area to sample volume ratio that enhances the capture of the target antigen by minimizing diffusional distances. They can then be collected magnetically and manipulated to accomplish all the assay steps to determine if any target was captured. In addition, the microbeads can be accommodated in small volumes, which reduces the dilution of the enzyme product in the detection step thus maximizing sensitivity. Further, electrochemical detection coupled with enzyme-labeled immunoassay has led to the development of a sensitive analytical technique. In this area, interdigitated array electrodes are particularly suited to microfluidics. Improved sensitivity is obtained by redox cycling of the species being detected. In this work, the microbead immunoassays is demonstrated for the virus MS2 bacteriophage.