Smartphone-assisted quantitative colorimetric identification of thrombin based on peroxidase mimetic features of fibrinogen-gold nanozymes

Fibrinogen-modified gold nanoparticles (Fib-AuNPs) and 3,3′,5,5′-tetramethylbenzidine (TMB) substrate besides hydrogen peroxide (H 2 O 2 ) were applied for assessment of the biomarker thrombin. Fib-AuNPs have catalytic active sites for the oxidation of TMB besides H 2 O 2 and cause the color change of the substrate. Moreover, they can lead to the enhancement in the absorption wavelengths of 650 and 370 nm. By the addition of thrombin to Fib-AuNPs, fibrinogen turns into fibrin, and AuNPs are surrounded by fibrin. Therefore, their active catalytic sites for the oxidation of TMB besides H 2 O 2 are covered by fibrin and cannot cause color change and absorption increase as before. The relationship between the average variations of the color intensity and changes in the absorption wavelengths at 650 and 350 nm with different concentrations of bovine thrombin added to Fib-AuNPs was studied. In such manner, three sensitive colorimetric approaches have been developed for the identification of bovine thrombin with the linear range of 20–120 pM and the limit of detection (LOD) of 17.54 pM for the average color intensity (G + B), the linear range of 20–120 pM and the LOD of 13.41 pM for the absorption peak at 650 nm, and the linear range of 40–140 pM with the LOD of 18.85 pM for absorption peak at 370 nm. The practical application of this biosensing platform was indicated through the successful determination of bovine thrombin in bovine serum. The satisfactory RSD ( < 10%) and recovery values (99.11–107.61%) confirmed the feasibility of the fabricated sensor. Graphical abstract