摘要
Nitrogen-incorporated ovoid-shaped nanodiamond (NOND) film exhibits excellent electrochemical sensing properties owing to its unique characteristics. In this study, to improve the sensitivity of NOND-based biosensors for dopamine (DA) detection, a detailed investigation concerning the growth mechanism of NOND films was conducted, it is found that the NOND films did not directly grow on a Si substrate during the growth process but preferentially originated from the formation of a thin Si3N4 interlayer attributed to the reactions of Si substrate and nitrogen atoms in the plasma in the very early stage of deposition. Subsequently, the diffusion of nitrogen from the inner Si3N4 to the Si3N4/plasma interface produces more active sites for the adsorption of the ionized carbon atoms. As the process proceeded further, the growth of ovoid-shaped diamonds accompanies the decrease of the Si3N4 interlayer thickness owing to the diffusion of nitrogen from Si3N4. Significant Si3N4 peaks are observed from both the Raman and X-ray diffraction analyses when the sample was subjected to NOND deposition for less than 20 min. These peaks then completely disappeared after deposition for 60 min, demonstrating the proposed mechanism. Furthermore, it is also observed that the deposition of the Si3N4 interlayer increased the hydrophilicity of the substrate, which is ascribed to the lower surface free energy of the NOND. To enhance the sensitivity of the NOND, the synthesis of NOND with patterned arrays (P-NOND) is proposed. The high specific surface area of the highly hydrophilic P-NOND obviously enhances the sensitivity of the P-NOND-based electrodes. Application of the P-NOND electrode for DA detection is successfully demonstrated in the mixed DA electrolyte, showing a better performance than that of the pristine NOND. This work reveals that the P-NOND electrode possesses superior sensitivity and selectivity, which is very favorable for DA sensing.