Label-free fluorescence turn on detection of tiopronin with tunable dynamic range based on the ensemble of Alizarin Red S/copper ion

In this study, a new type of rapid, label-free fluorescence turn-on assay for detection of tiopronin using Alizarin Red S (ARS)/copper ion ensemble is developed. ARS is high fluorescence in BR buffer solution. But, the fluorescence of ARS can be significantly quenched by copper ions due to ground-state complexation. However, in the presence of tiopronin, copper ions were released from the ARS and thus restored the fluorescence of ARS. The assay has several important features. First, the system is simple in design, fast in operation and is more convenient and promising than other methods. Second, the proposed assay eliminated the separation process and sophisticated instrumentations. Third, the detection process can be seen with the naked eye and can be easily adapted to automated high-throughput screening. At last, the assay has high sensitivity and selectivity for tiopronin and the detection limit is 0.8 ng/mL which is lower than or at least comparable to the previous methods. Moreover, the dynamic range of the sensor can be tuned simply by adjusting the concentration of copper ions. Importantly, the protocol offers high selectivity for the determination of tiopronin in pharmaceutical tablets, injection and biological samples with satisfactory results. Thus, the assay shows great potential applications in the fields of pharmaceuticals and clinical analysis.