Toward an Aptasensor for Monitoring of Tacrolimus

Developing a simple and accurate method for monitoring the levels of circulating tacrolimus (TAC) can inform dosing schedule and reduce the risk of rejection in solid organ transplantation. Thus, an aptasensor was designed, fabricated, and characterized for electrochemical quantification of TAC concentration. The TAC-aptasensor comprised a gold electrode functionalized with a thiolated TAC-binding aptamer (APT122) derivatized with methylene blue. Surface plasmon resonance (SPR) was used to characterize the binding strength and specificity of the TAC:APT122 complex. Square wave voltammetry (SWV) was used to quantify the aptasensor response to varying concentrations of TAC. A dose-response curve was observed at concentrations of TAC < 7 µM, when operated at 50 and 80 Hz. Typical sensitivity of 0.07 µA· µM-1 was observed at 50 Hz. Limited specificity for the TAC aptasensors was observed with SWV against cyclosporine, amoxicillin, and tetracycline. Future efforts will explore a multi-aptamer system to extend the dynamic range and improve surface functionality to limit non-specific binding.