Bi-functionalized aptasensor for ultrasensitive detection of thrombin

A novel bi-functionalized aptasensor for thrombin detection was fabricated by using electrochemiluminescence (ECL) and electrochemical impedance spectroscopy (EIS) techniques. A thiol-terminated aptamer with 15 oligonucleotides was hybridized with its complementary oligonucleotides to form a double-stranded DNA (dsDNA). Then, the thiol-labeled dsDNA was assembled on a Au electrode via Au-S bond; the other distal of the dsDNA labeled with biotin was bound to QDs through a biotin-avidin conjugation. When thrombin is present in the detection solution, the aptamer can combine with thrombin, resulting in loss of CdSe QDs from the electrode surface and thereby decreasing the ECL intensity and increasing the impedance. The decreased ECL and increased EIS signals are logarithmically linear with respect to the concentration of thrombin. The linear range was 10(-10)-10(-3) μg mL(-1) (R=0.9924) for the ECL signal and 10(-10)-10(-1) μg mL(-1) (R=0.9875) for the EIS method with a common detection limit of 10(-10) μg mL(-1) (2.7 aM). In addition, the bi-functionalized aptasensor exhibited excellent selectivity, super sensitivity, a low detection limit and a wide linear range.