Acute myocardial infarction (MI) remains a leading cause of morbidity and mortality worldwide. Cardiac biomarker, troponin, is the most specific and sensitive test for detection and risk stratification of myocardial damage. However, existing immunoassay techniques are too expensive and not ideal for point-of-care and resource-limited settings. The use of label-free plasmonic biosensing is an attractive alternative to the existing immunoassay techniques. Metal nanostructures conjugated with antibody can be used to capture and detect protein biomarkers owing to refractive index sensitivity of the localized surface plasmon resonance of these nanostructures. Although natural antibodies exhibit good specificity, they suffer from poor shelf life, limited pH and temperature stability and excessive cost, making them non-ideal for point-of-care diagnostics.
Here we design and demonstrate a protein aptamer-based plasmonic biosensor to quantitatively detect troponin in physiological fluids. Considering the remarkable stability (chemical, temporal and environmental) of the aptamers, plasmonic biochips based on aptamers as recognition elements enable facile handling and storage. Furthermore, the use of protein aptamers as recognition elements results in higher sensitivity compared to antibodies considering the smaller size of the aptamers and the exponential decay in refractive index sensitivity from the surface of the nanotransducers. Finally, the plasmonic biosensing is implemented on a flexible and ubiquitous paper substrate enabling the easy translation of this technology to point-of-care and resource-limited settings.