In-situ preparation of norepinephrine-functionalized silver nanoparticles and application for colorimetric detection of tacrolimus in plasma samples

Tacrolimus (Tac) is a well-documented immunosuppressive agent for the prevention of graft-vs-host diseases in several types of organ transplants. The narrow therapeutic window and the individual-variable pharmacokinetics of Tac demonstrate the importance of regular therapeutic drug monitoring (TDM) as an imperative concept for its oral medication regimens. A simple, one-step, selective, and sensitive colorimetric platform is fabricated for the determination of Tac by surface modification of the silver nanoparticles (AgNPs) via norepinephrine (NE) molecules. The attachment of NE and Tac induces the aggregation of the AgNPs, which is observed by color distinction (yellow to brown) and a noteworthy shifting of the absorption peak in the visible region. The fabricated nanoprobe can detect Tac concentrations in plasma samples in two linear ranges from 2 ng/mL to 70 ng/mL and 70 ng/mL to 1000 ng/mL with R2 > 0.99. The limit of detection (LOD) was calculated as low as 0.1 ng/mL. The developed method was applied for the determination of Tac in patient’s plasma samples under Tac medication therapy.