Highly reproducible and fast detection of 6-thioguanine in human serum using a droplet-based microfluidic SERS system

6-thioguanine is an anticancer drug with narrow safe dose range and intense toxic reactions, so it is urgently necessary to evaluate its clinical usage. Reproducibility and analysis speed are important factors to take into account when analyzing drug concentration in body fluids. In this work, we fabricated a droplet-based microfluidic chip for detecting 6-thioguanine in human serum by using the surface-enhanced Raman scattering (SERS) technique. The easily-prepared Au nanoparticles were used as SERS substrates, and reagent mixing and signal acquiring happened in droplets one by one. This assay device is endowed with the superiority in improving determination repeatability with coefficient of variation of no more than 5% (n = 25) and high speed of 10 s each assay. The SERS peak at 1295 cm −1 originated from N1-C6 stretching vibration mode of purine ring was selected for quantitating 6-thioguanine. The signals indicated a satisfied linear relationship with the concentrations of 6-thioguanine in the range of 0.010 μM to 10 μM, with a detection limit of 0.032 μM. The droplet-based microfluidic SERS system was successfully applied for credible and rapid analysis of 6-thioguanine in human serum, and is pretty promising for performing the therapeutic drug monitoring.