The authors describe an electrochemical method for aptamer-based determination of insulin at femtomolar concentrations. The
surface of a screen printed electrode was modified with ordered mesoporous carbon that was chemically modified with 1,3,6,8-
pyrenetetrasulfonate (TPS). The amino-terminated aptamer was then covalently linked to TPS via reactive sulfonyl chloride
groups. Subsequently, the redox probe Methylene Blue (MB) was interacted into the aptamer. The MB-modified binds to insulin
and this results in the release of MB and a decreased signal as obtained by differential pulse voltammetry, best at a working
voltage of −0.3 V (versus silver pseudo-reference electrode). Insulin can be quantified by this method in the 1.0 fM to 10.0 pM
concentration range, with a 0.18 f. limit of detection (at 3σ/slope). The assay was applied to the determination of insulin in spiked
human serum samples. The method is highly sensitive, selective, stable, and has a wide analytical range.

• An electrochemical aptamer-based assay for femtomolar determination of insulin using a screen printed electrode modified with mesoporous carbon and 1,3,6,8-pyrenetetrasulfonate