Flower-like ZIF-8 enhance the peroxidase-like activity of nanoenzymes at neutral pH for detection of heparin and protamine

The peroxide-like catalytic activity of gold nanoclusters (Au-NCs) is very low under physiological conditions (pH 7.4), which greatly limits its biological detection applications. A new nanoenzyme platform was constructed by self-assembly of Au-NCs and ZIF-8/CQDs. It was found that heparin can significantly promote the peroxidase-like activity of Au-NCs on the nanoenzyme platform at pH 7.4. In the presence of H2O2, the catalytic activity of Au-NCs on the nanoenzyme platform for TMB increased nearly 50 times. Based on this phenomenon, a colorimetric method was developed to determine heparin in the range of 0.0185-9.25 U/mL, with a detection limit of 0.0027 U/mL. When protamine is introduced, heparin and protamine take the lead in specific binding due to antagonism, which makes heparin unable to adsorb on the surface of ZIF-8/CQDS, thus inhibiting the enhancement of the catalytic activity of Au-NCs. Based on this phenomenon, a colorimetric method was developed to determine protamine in the range of 0.01-0.5 μg/mL, with a detection limit of 0.003 μg/mL. Therefore, this method provides a new idea for the visual detection of heparin and protamine under physiological conditions.