Improved activity and thermo-stability of the horse radish peroxidase with graphene quantum dots and its application in fluorometric detection of hydrogen peroxide

• We first reported horse radish peroxidase modification with graphene quantum dots.
• N,S-doped graphene quantum dots greatly improve the enzyme activity and stability.
• The enzyme performance depends on hydrophilic groups and structure of graphene quantum dots.
• The proposed method provides the advantage of sensitivity, stability and accuracy.
• The study provides a promising approach for adjusting enzyme activity and stability.

Graphene quantum dots (GQDs) have received extensive concern in many fields such as optical probe, bioimaging and biosensor. However, few reports refer on the influence of GQDs on enzyme performance. The paper reports two kinds of graphene quantum dots (termed as GO-GQDs and N,S-GQDs) that were prepared by cutting of graphene oxide and pyrolysis of citric acid and l-cysteine, and their use for the horse radish peroxidase (HRP) modification. The study reveals that GO-GQDs and N,S-GQDs exhibit an opposite effect on the HRP performance. Only HRP modified with GO-GQDs offers an enhanced activity (more than 1.9 times of pristine enzyme) and thermo-stability. This is because GO-GQDs offer a larger conjugate rigid plane and fewer hydrophilic groups compared to N,S-GQDs. The characteristics can make GO-GQDs induce a proper conformational change in the HRP for the catalytic performance, improving the enzyme activity and thermo-stability. The HRP modified with green luminescent GO-GQDs was also employed as a biocatalyst for sensing of H2O2 by a fluorometric sensor. The colorless tetramethylbenzidine (TMB) is oxidized into blue oxidized TMB in the presence of H2O2 by the assistance of HRP/GO-GQDs, leading to an obvious fluorescence quenching. The fluorescence intensity linearly decreases with the increase of H2O2 concentration in the range from 2 × 10 − 9 to 2 × 10 − 4 M with the detection limit of 6.8 × 10 − 10 M. The analytical method provides the advantage of sensitivity, stability and accuracy compared with present H2O2 sensors based on the pristine HRP. It has been successfully applied in the determination of H2O2 in real water samples. The study also opens a new avenue for modification of enzyme activity and stability that offers great promise in applications such as biological catalysis, biosensing and enzyme engineering.

We reported an improved activity and thermo-stability of horse radish peroxidase (HRP) with the graphene quantum dot prepared by cutting of graphene oxide (GO-GQDs) and its application in fluorometric detection of hydrogen peroxide. The result demonstrates that the effect of graphene quantum dot on enzyme performance seriously depends on its hydrophilic groups and sheet size. The study also provides a promising approach for adjusting enzyme performance for many potential applications in biosensing, biocatalysis and enzyme engineering fields.Figure optionsDownload as PowerPoint slide