Gold nanoparticle-based colorimetric assays for coagulation-related proteins and their inhibition reactions

In this paper, we describe two simple, label-free, homogenous assays using gold nanoparticles (Au NPs)—one to detect coagulation-related proteins and the other to screen inhibition reactions. The first nanosensor functions on the basis of the fact that thrombin catalyzes fibrinogen to form long-chain fibrins, which then induce aggregation of Au NPs. We applied this sensor to study the interactions of thrombin, inhibitors, cofactors, and antidotes. We further used thrombin-conjugated Au NPs (Thr–Au NPs) to analyze the levels of fibrinogen in plasma samples via fibrinogen-induced aggregation of Thr–Au NPs. The limit of detection (LOD; S/N = 3) of this sensor for fibrinogen in plasma was 10 nM. The Thr–Au NP probe provided quantitative results for fibrinogen in plasma samples that correlated (R2 = 0.97) with those obtained using a clinical von Clauss clotting rate assay. In addition, the Thr–Au NP-based sensor could be used to monitor thrombin concentrations in plasma samples under physiological conditions. Compared with conventional assays, these label-free assays offer several advantages, such as rapid and simple readout by the naked eye or by UV–vis absorption spectroscopy.