Real-time and label-free analyte detection in a flow-through mode using immobilized fluorescent aptamer/quantum dots molecular switches.

Inspired by the goal to create a biosensor with designer specificity for real-time detection of unlabeled analytes in a flow-through mode, we designed a miniature flow cell with interchangeable quartz window carrying immobilized aptamer/quantum dot molecular switches as a part of a portable fluorescent setup. The inner surface of the 1.5mm ID, 12µl flow cell quartz window has been modified with the aptamer sensing complexes containing highly-fluorescent quantum dots. The aptamer complexes were designed as molecular switches to undergo conformational change and release fluorescent label upon interaction with the flow of the analyte, causing fluorescence decrease. The specificity of the sensor was designed to address the light chain of Botulinum Neurotoxin A and Ricin Toxin A chain, which could be specifically and repeatedly detected in the flow of 60µl/min with sensitivity comparable to other real-time detection methods. The specifics of quantum dots use as fluorescent labels for continuous monitoring under constant UV illumination were outlined. The possibility for multispecific sensing was explored by testing of bi-specific sensor. This work shows the possibility of surface-bound aptamer sensing for flow-through analyte detection and provides a useful tool to perform surface fluorescent studies in real-time. The flexibility of the described design allows for sensor specificity change through altering the specificity of the aptamer. Future work should address response quantification. The described sensing approach can be adapted to a number of environmental or clinical targets.