DNA/ligand/ion-based ensemble for fluorescence turn on detection of cysteine and histidine with tunable dynamic range.

A new type of rapid, highly sensitive, and selective fluorescence turn-on assay for detection of cysteine and histidine using a DNA/ligand/ion ensemble is developed. This assay is based on the highly specific interaction between the amino acids and the metal ions and the strong fluorescence thiazole orange (TO)/DNA probe in a competition assay format. The resulting high sensitivity and selectivity for cysteine and histidine was achieved by changing the metal ions. The system is simple in design and fast in operation and is more convenient and promising than other methods. The novel strategy eliminated the need of organic cosolvents, enzymatic reactions, separation processes, chemical modifications, and sophisticated instrumentations. The detection and discrimination process can be seen with the naked eye under a hand-held UV lamp and can be easily adapted to automated high-throughput screening. The detection limit of this method is lower than or at least comparable to previous fluorescence-based methods. The dynamic range of the sensor can be tuned simply by adjusting the concentration of metal ions. Importantly, the protocol offers high selectivity for the determination of cysteine among amino acids found in proteins and in serum samples. The assay shows great potential for practical application as a disease-associated biomarker and will be needed to satisfy the great demand of amino acid determination in fields such as food processing, biochemistry, pharmaceuticals, and clinical analysis.