Mimicking peroxidase-like activity of nitrogen-doped carbon dots coupled with laminated three-dimension microfluidic paper-based analytical device for determination of total cholesterol in whole blood

This thesis presents a simple hydrothermal synthesis of nitrogen-doped carbon dots (N-CDs), a fabrication of microfluidic paper-based analytical device (μPAD), and their application for colorimetric determination of total cholesterol (TC) in human blood. The N-CDs were characterized by various techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) and the optical and electronic properties of computational models by using time-dependent density functional theory (TD-DFT). The characterization results confirmed the successful doping of nitrogen onto the carbon dot surface. The N-CDs exhibited high affinity with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)-
diammonium salt (ABTS) with the Michaelis–Menten constant (KM) of 0.018 mM in a test for their peroxidase-like activity. In particularly, since hydrogen peroxide (H2O2) is the oxidative product of cholesterol in the presence of cholesterol oxidase, a sensitive and selective method of cholesterol detection was developed. Overall, the obtained results from TD-DFT confirm the strong adsorption of H2O2 on the graphitic N positions
of the N-CDs. The laminated 3D-μPAD featuring a 6-mm circular detection zone was fabricated using a simple wax screen printing technique. Classification of TC according to the clinically relevant criteria (Healthy 96-201 mg dL-1 (2.5 - 5.2 mM), Borderline 201-274 mg dL-1 (5.2 - 7.5 mM) and High risk >274 mg dL-1 (>7.5 mM)) could be determined by the naked eye within 10 minutes by simple comparison using color chart. Overall, the proposed colorimetric device serves as a low-cost, rapid, simple, sensitive, and selective alternative for TC detection in whole blood samples that is friendly to unskilled end users.