Digital Assays

Biosensors and Biointerfaces Group - Research Projects

Surface Plasmon-based Digital Assays - Sensitive Biosensors for the Digital Age


The detection of disease biomarkers (such as proteins, DNA fragments and RNAs) in biological fluid (like blood) is essential for the early detection of diseases. One of the primary challenges is the low concentration (typically in the femtomolar range) of the biomarkers. We are looking into new approaches to construct digital biosensors based on plasmonic nanoparticles. The optical properties of the plasmonic nanoparticles are dependent on the size, shape and the refractive index surrounding the nanoparticle.

With the help of a dark-field optical microscope, we can look at the scattering arising from individual nanoparticles. The wide field nature of this measurement allows for the simultaneous characterization of thousand nanoparticles. With the help of computer algorithms, we track the colour of each nanoparticle and their optical signatures are represented in a digital array format. When a biochemical sensing reaction is performed, the optical signature of the nanoparticle is altered thereby leading to change in the colour of the nanoparticle. By setting a threshold, we digitalize the data to 0 (unreacted) and 1 (reacted) nanoparticles. Our aim is to push this approach for the detection of individual biomarkers on individual nanoparticles.