The Surface Functionalization And Applications Of Boron-doped Diamond Thin-film Electrode And Its Relative Materials

Conducting boron-doped diamond (BDD) thin films have emerged as attractive new electrode materials because, in addition to having good electrochemical properties including: wide electrochemical potential window, very low double-layer capacitance, extreme electrochemical stability and high resistance to deactivation by fouling, it is widely considered to be biocompatible. Thus, the BDD electrodes are of interest for a variety of electrically based chemical and biological sensing applications. In this paper, the major efforts in BDD electrodes used in biosensors essentially involve elaborate surface modification steps to impart chemical functional groups for covalent coupling of biomolecules. In addition, the construction of nano-structures on diamond films, the modification of cubic boron nitride (cBN) and their applications were investigated. The main conclusions are listed as follows:1. Firstly, the hydrogen-terminated BDD surface was first functionalized by photochemically linking vinyl groups of allylamine, producing covalently linked aminoalkyl-terminated surface; Sencondly, combined chemical and electrochemical modifications of the BDD film with nitrobenzenediazonium, an aminophenyl- modified surface was produced. Then amperometric biosensors based on immobilization of tyrosinase on the above two active amine-terminated BDD surfaces were developed. The resulted enzyme electrodes exhibit a good performance in terms of dynamic range of detection, sensitivity, detection limit (0.1μM) and long-term stability to the detection of phenolic compounds. By comparison, the sensitivity of the enzyme electrode prepared via diazonium method is higher than that of the electrode constructed by photochemical method, which probably because, the aryl ring is more conductive than alkyl chain.2. Compared with microcrystalline BDD, boron-doped nanocrystalline diamond (BDND) thin-film electrodes have a smoother surface while maintaining the intact diamond properties. Importantly, in addition to boron doping, the sp2-bonded carbon phase on grain boundaries of BDND films can provide charge carriers, which lead to better reversible properties for redox systems. Cytochrome c (Cyt c) was covalently immobilized on a carboxyl-terminated BDND electrode constructed by photochemical surface modification. The Cyt c on BDND electrode exhibited a direct electrochemistry with a pair of quasi-reversible, well-defined redox peaks and a high electron transfer constant of 5.2±0.6 s-1. The prepared Cyt c-modified BDND electrode showed excellent electrocatalytic performance in terms of fast response, low detection limit and high stability towards the reduction of H2O2. In a word, BDND thin-film is an ideal substrate as a third-generation biosensor support.3. High-density, uniform diamond nanocone and nanopillar arrays were fabricated by employing bias-assisted reactive ion etching in a H/Ar-plasma. Different sizes of gold nanoparticles (AuNPs) were self-assembled on the diamond nancones surface functionalized by photochemical method and AuNPs monolayer was formed. The application of the AuNPs–modified diamond nanocones film in the surface-enhanced Raman spectroscopy (SERS) was investigated and a high Raman activity was obtained. The above reslults reflect a genuine breakthrough in developing new potential applications of the diamond nanostructures films.4. cBN is of significant interest due to its unique set of properties that are comparable or even superior to diamond. Surface functionalization and modification scheme of cBN films was demonstrated. A homogeneous layer of amino groups was bonded covalently on the B and/or N atoms of cBN surface via a photochemical reaction with allylamine. Modification of amine-terminated cBN films with amine-modified DNA probes presents an example of applications as DNA biosensors. AuNPs self-assembled on the amine-terminated cBN surface initiate the silver deposition and homogenous, cross-linked silver nano-sheets were formed. The silver nanosheets-modified cBN film demonstrated a high activity and a long-term stability for SERS. Our work is an initial but important step towards the practical sensing applications of cBN-based devices in chem- and bio-sensing technology.