Assay development for a portable fiberoptic biosensor

The fiberoptic biosensor with tapered optical probes has been developed to perform rapid and sensitive fluoroimmunoassays. A number of assays for biologic analytes were developed using a laboratory breadboard device that employed a large, 514 nm argon ion laser. These assays, with limits of detection of 5-50 ng/ml for protein antigens, showed promise for clinical use because of their demonstrated lack of matrix effects from plasma, serum, or blood. However, such a large device was impractical for on-site diagnostics, so a new, portable, multichannel biosensor was developed. To test this new biosensor, which uses 635 nm laser diodes, the assays were converted to use the cyanine dye, Cy5. The detection antibodies were labeled with Cy5 and assays performed to detect the F1 antigen of Yersinia pestis and the protective antigen of Bacillus anthracis. The limit of detection was found to improve by a factor of 10 for each assay. The portable biosensor was then evaluated in a blind test containing F1 antigen spiked into 30 of 173 serum samples. One hundred percent detection was achieved for samples with 100 ng/ml or more F1 antigen, with a specificity of 88%.