Label-free detection of human cardiac troponin I using aptamer sensor based on dipstick and tunable resistive pulse sensing (D-AptaTRPS)

An aptamer sensor using a Dipstick and Tunable Resistive Pulse Sensing (D-AptaTRPS) is proposed and demonstrated for rapid (≤10 min) and label free detection of human cardiac troponin I (cTnI), which is a myocardial infarction biomarker. The cTnI aptamers were immobilized onto the surface of a slide (used as a dipstick) to enable the immobilization of nanoparticles modified with partially complementary sequences. The presence of the target protein caused a conformational change to the aptamer, thus the release of immobilized nanoparticles into solution. The concentration of the released nanoparticles, which was counted by the TPRS, was proportional to the concentration of the target protein and optimization of the partially complementary sequence delivered a limit of detection (LOD) of 6.7 ng/mL (in a buffer solution). Quantitative detection of cTnI in serum using the proposed assay was also demonstrated and the sensitivity (LOD = 16.7 ng/mL) was physiologically relevant. The dipstick format allows rapid and affordable replicate measurements. Additionally, the proposed assay can be easily extended to multiplexed biomarker detection by involving beads of different sizes, with each bead targeting one specific protein.