Development of hybrid DNA-copper phosphate nanoflowers as peroxidase enzyme mimics and for colorimetric sensing of phenol

Abstract

A facile co-precipitation method was adapted for the synthesis of DNA coated copper phosphate nanoflowers (CuPNF_ctDNA) using calf thymus DNA (ctDNA) and the copper salt in phosphate buffer saline (PBS). The flower growth was monitored using scanning electron microscopy (SEM), wherein a fully formed floral morphology was observed after 36 h. The SEM data further supported a decrease in the size of the nanoflower (NF) and an increase in the density of petals upon increasing the added ctDNA concentration. The coated nanoflowers, viz., CuPNF_ctDNAx {‘x’ is the concentration of ctDNA used for coating} were characterized using spectroscopy, microscopy and diffraction techniques. The petals of the NFs were observed in transmission electron microscopy and the inorganic copper phosphate framework was characterized by powder X-ray diffraction. The surface charge of the NFs (CuPNF_ctDNAx) were measured using zeta potential equipment at different values of ‘x’ used in the preparation. The presence of phosphorous in DNA and that in the copper phosphate were confirmed using X-ray photoelectron spectra. The peroxidase mimetic activity of CuPNF_ctDNA0.3 was measured using 3,3′,5,5′-tetramethylbenzidine (TMB) in presence of H2O2 in acetate buffer at pH 4.5. The enzyme kinetics were evaluated using the Michaelis–Menten steady state curve along with the Lineweaver – Burk plot and the derived Km values were 0.011 and 1.36 mM for TMB and H2O2 respectively. Micromolar detection of phenol in phosphate buffer saline (PBS) at pH = 7.4 was performed using 4-aminoantipyrine as substrate to a limit of detection of 5.2 μM. Thus, the hybrid material, viz., CuPNF_ctDNA0.3 exhibited peroxidase enzyme mimetic activity, besides sensing the common pollutant, phenol.