(789f) A Rapid Diagnostic Assay for Protein Biomarkers Using Whole Cell Biosensors

Synthetic biology is an emerging discipline which seeks to develop new biological systems with user-defined properties by adopting an engineering approach based largely on standardization, characterization, and modularity. Biosensors are one area where synthetic biology has been successfully applied with examples ranging from small molecule metabolites through to toxins and environmental contaminants.

Whole cell biosensors offer a convenient platform for detection as they are self-renewing and easy to transport. However, when trying to sense proteins, designers of whole cell biosensors are faced with an issue of how to transmit information across the cell membrane. To address this challenge, we have developed a class of whole cell biosensors based on the bacterial surface display of an antibody fragments that bind different epitopes of a protein biomarker. The presence of the biomarker induces cell aggregation, which can be transmitted as a downstream signal through optical assays or more sophisticated genetic circuitry, such as activation of bacterial quorum sensing.

Using a dimeric GFP as a model protein biomarker, we developed a semi-quantitative assay procedure that leads to a visual output in as little as 15 minutes. We then showed that the assay can be easily developed for a new biomarker by exchanging the nanobody on the cell surface for one that binds to fibrinogen. Further, we have developed a predictive mathematical model based on the aggregation of colloidal particles to help optimise the procedure for detection within a specific range by modulating nanobody expression level and the number of cells used in the assay. In summary, our 'whole cell ELISA' procedure combines the advantages of traditional antibody detection with the cost effectiveness of whole cell biosensors.