Immobilization of horseradish peroxidase on amino-functionalized carbon dots for the sensitive detection of hydrogen peroxide

The authors describe the preparation of amino-functionalized carbon dots (NH₂-CDs) via a one-step hydrothermal process using silver nitrate and chitosan as the precursors. The NH₂-CDs have a fairly consistent size distribution with an average size of 2.8 ± 0.5 nm. This is attributed to the introduction of Ag(I) both as a catalyst and a precipitant. The NH₂-CDs are highly crystalline. Their surface carries amino groups and carboxy groups which is confirmed by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Horseradish peroxidase (HRP) was immobilized in the NH₂-CDs and then placed on a glassy carbon electrode (GCE). Spectroscopic and electrochemical analyses evidenced the stability and good bioactivity of the immobilized HRP. This reveals that NH₂-CD is a desirable matrix for enzyme immobilization. The modified GCE exhibits enhanced electro-catalytic activity towards hydrogen peroxide (H₂O₂) reduction as compared to that of plain CDs. The effects of pH value and loading on the performances of the modified GCEs were studied. Under optimized conditions, the biosensor has a linear response in the 5 to 590 nM H₂O₂ concentration range, with a 1.8 nM defection limit (at an S/N ratio of 3). The sensor is stable, reproducible and selective. Finally, the sensor was applied to determine H₂O₂ in real samples, and satisfactory recoveries were achieved. Graphical abstract Amino-functionalized carbon dots (NH₂-CDs) can provide more active sites and a friendly microenvironment for horseradish peroxidase (HRP) immobilization. Thus, a novel sensitive H₂O₂ biosensor has been developed.