Valve-controlled needle-type "mix and detect" integrated distance-based sensor with visual color zoning for point-of-care testing of tacrolimus.

The concentration of tacrolimus (TAC) must be controlled within a certain range for homebound patients on long-term TAC after organ transplantation to avoid acute rejection risk. Routine clinical TAC detections suffer from expensive instruments and the lag time between sampling and results, making it difficult to apply in resource-limited environment. Rapid and user-friendly point-of-care testing biosensors significantly benefit homebound transplantation patients by avoiding the need for frequent medical visits and reducing meaningless healthcare expenditures. In this study, a simple and portable visual valve-controlled needle-type "mix and detect" integrated distance-based biosensor was carefully designed for homebound patients. Pt/MnO₂ NRs nanocomposite with enhanced catalytic activity and stability was used as the signal probe to realize highly sensitive detection. The lateral flow immunoassay-based detection process can be completed within 13 min. The dynamic detection range of TAC was 0.10-1000 ng mL^-1 with a detection limit of 0.03 ng mL^-1, which covered the whole therapeutic drug concentration range. The recoveries of spiked samples in pre-diluted milk, urine, saliva, and plasma ranged from 88.26 % to 116.72 %, confirming the reliability and applicability of this biosensor in real samples. There was no significant difference between the results of the developed method and the clinical reference method, indicating its reliability for further potential application. Concentration-dependent visual color zones facilitated homebound transplantation patients on long-term TAC to make reasonable medical choices. It showed unparalleled remarkable performance in real-time detection, offering a new reference method for future medical field diagnosis when the large, multicenter cohort studies were conducted.