Colorimetric method based on salt-induced aggregation of gold nanoparticles and aptamer does not work for detection of tacrolimus

Tacrolimus (TAC) is used in autoimmune diseases, organ transplantation, and nephrotic syndrome treatment. Therapeutic drug monitoring (TDM) of TAC is critical since it has narrow therapeutic index. Thus, the development of an easy and sensitive method is critical for detecting TAC in blood samples. In this study, we aimed to design a fast, simple,and specific colorimetric sensor based on aptamer/AuNPs to detect. Initially, the aptamer was adsorbed on the surface of the gold nanoparticles (AuNPs). Then, it was expected that when the aptamer bound to TAC, AuNPs were aggregated by salt, and the color changed from red to blue. However, in our study, color did not change, and NaCl could not aggregate the AuNPs. In this approach, the optical properties of AuNPs and high affinity of aptamer were used for the detection of TAC. However, according to our data, this colorimetric aptasensor was not appropriate for the detection of TAC.