Guanine-rich DNA-based peroxidase mimetics for colorimetric assays of alkaline phosphatase

DNA-based peroxidase mimetics are facilely constructed through Cu(II)-coordination with different oligonucleotides involving G20, C20, A20 and T20, respectively, with high peroxidase mimicking activity as well as high stability against proteins. Peroxidase-like activities of DNA-Cu(II) complexes are greatly associated with the sequence composition of DNA templates, which decrease in the following order: G20>C20>A20>T20. G20-Cu(II) complex ([Cu(2+)]/[base]=0.05) possesses the Km value of 0.257 mM toward 3,3',5,5'-tetramethylbenzidine and 102.3mM toward hydrogen peroxide at 25 °C. G20-Cu(II) complexes are employed to develop a colorimetric turn-on assay of alkaline phosphatase with high sensitivity and selectivity, on the basis of pyrophosphate-induced inhibition of their intrinsic peroxidase-like activities. The limit of detection is achieved as 0.84 U/L with the linear response region of 20-200 U/L. Such colorimetric assay system is probably applicable for the quantitative determination of ALP in biological fluids.