DNA-copper hybrid nanoflowers as efficient laccase mimics for colorimetric detection of phenolic compounds in paper microfluidic devices.

Laccases are important multicopper oxidases that are involved in many biotechnological processes; however, they suffer from poor stability as well as high cost for production/purification. Herein, we found that DNA-copper hybrid nanoflowers, prepared via simple self-assembly of DNA and copper ions, exhibit an intrinsic laccase-mimicking activity, which is significantly higher than that of control materials formed in the absence of DNA. Upon testing all four nucleobases, we found that hybrid nanoflowers composed of guanine-rich ssDNA and copper phosphate (GNFs) showed the highest catalytic activity, presumably due to the affirmative coordination between guanine and copper ions. At the same mass concentration, GNFs had similar Km but 3.5-fold higher Vmax compared with those of free laccase, and furthermore, they exhibited significantly-enhanced stability in ranges of pH, temperature, ionic strength, and incubation period of time. Based on these advantageous features, GNFs were applied to paper microfluidic devices for colorimetric detection of diverse phenolic compounds such as dopamine, catechol, and hydroquinone. In the presence of phenolic compounds, GNFs catalyzed their oxidation to react with 4-aminoantipyrine for producing a colored adduct, which was conveniently quantified from an image acquired using a conventional smartphone with ImageJ software. Besides, GNFs successfully catalyzed the decolorization of neutral red dye much faster than free laccase. This work will facilitate the development of nanoflower-type nanozymes for a wide range of applications in biosensors and bioremediation.