Developing new approaches to monitor critical analytes in complex biological environments is key to the development of new diagnostic tools for application in a range of fields including the biomedical, environmental and food sciences. Of the 80,000 Victorians presenting to hospital each year with acute chest pain, only 15% require treatment, and the decision to treat is based on blood tests showing elevated levels of troponinI.1 Lab-based automated immunoassays are the gold-standard diagnostic platform, requiring symptomatic patients to present to hospitals for testing. Hand-held devices for use outside of hospitals (POC or “point-of-care” devices) are not yet sensitive enough to make reliable clinical decisions, however they could lead to cTnI detection in the ambulance, the local clinic or in the home. Development of simpler biosensor chemistries with equivalent sensitivity could hasten the development of POC and associated devices.
One approach to simplify immunoassay chemistry is to reduce the number of assay steps required, which could lead to simpler manual assays, less reliance on laboratory infrastructure, or simpler POC designs. We have developed a biosensor approach based on direct detection of antigen-antibody binding in a single step.2 Using a site-specific approach to incorporate fluorescent dyes into anti-cTnI antibody fragments, we screened a range of positional mutants and identified several that showed antigen-dependent spectral changes. These changes were observed to be dose-dependent in both buffer and diluted plasma samples. Herein we will present our latest results on developing this concept into an assay platform for applications in cardiology and beyond.