Dual-mode smart sensing of sarcosine by integrating nanozyme-mediated electrochemical and smartphone-readable colorimetric assays.

Sarcosine (Sar) detection plays a crucial role in the diagnosis and management of prostate cancer. We developed a dual-mode biosensing platform for the highly sensitive and specific quantification of Sar by integrating electrochemical and colorimetric detection. The sensor was fabricated using a nanocomposite consisting of riboflavin (Rf) and reduced graphene oxide nanoribbons (rGONRs), which served as a support for a bimetallic TCPP(Fe)-Zn metal-organic framework (MOF). The rGONRs significantly increased the active surface area and facilitated electron transfer, thereby enhancing the peroxidase-like activity of the TCPP(Fe)-Zn MOF. This catalytic activity promoted the oxidation of o-phenylenediamine (OPD) in the presence of H2O2 generated via an Sar-specific oxidase-mimetic reaction mediated by Rf. The dual-mode design enabled Sar detection through both electrochemical signals and color changes, with the latter quantitatively analyzed via RGB measurements. Under optimized conditions, the sensor exhibited a broad linear range of 10.0-1000.0 μmol L-1 for colorimetric detection, and 0.0010.001-500.0 μmol L-1 for electrochemical detection, achieving detection limits of 2.0 μmol L-1 and 0.04 nnmol L-1, respectively. The biosensor exhibited excellent reproducibility, stability, and selectivity, and was successfully applied to the human urine detection. The recovery obtained from healthy men and prostate cancer patients were 97.1 %-110.7 % and 98.7 %-104.4 %, respectively. This work presents a reliable, non-invasive tool for prostate cancer diagnosis with significant potential for point-of-care testing (POCT).