Determination of cystatin C using paper-based analytical devices for early detection of renal failure

Renal failure is often detected when it has reached the last stage. The amount of cystatin C in blood serum can be used as a biomarker for early identification of renal function failure. This work reported a fast and environmentally friendly microfluidic paper-based analytical device (μPAD) to determine the amount of cystatin C in the artificial blood serum samples. Functionalized gold nanoparticles (AuNPs) were prepared by capping the surface of AuNPs with papain to form AuNPs-papain. The aggregate of functionalized AuNPs-papain and Cu2+ ion could be formed due to coordination interaction between Cu2+ ion and papain attached to AuNPs. In the presence of cystatin C, the amount of aggregate decreased because the functionalized AuNPs-papain would bind easily with cystatin C as the substrate of papain. The intensity of aggregate on μPAD was scanned using a paper scanner. The difference intensity of aggregate in the presence of cystatin C was proportional to the concentration of cystatin C in the artificial blood serum sample. The linearity range obtained by this work was 0.5-10.0 mg/L with regression of y=0.3302x+3.488 and linearity of r2=0.998. The limit of detection (LOD) and limit of quantitation (LOQ) were 0.511 (3xSD/slope) and 2.044 mg/L (12xSD/slope), respectively. The linearity range and the LOD were wide enough to detect cystatin C in normal people or people with renal diseases.