Non-enzymatic electrochemical sensing of glucose with nano-structured and functionalised diamond electrodes

Abstract

Electrochemical sensing is a powerful tool for the rapid detection of (bio)molecules in fluids, and is frequently used in clinical analysis and diagnostics. Diamond is arguably the best electrode material for its robustness, wide potential window, very low background current, biocompatibility and self-cleaning features.
Nowadays, there is a new trend leading to electrodes getting smaller. One of the current challenges in the development of diamond micro-electrodes is to increase the sensitivity of the diamond electrode, while the electrode’s dimensions decrease.
An interesting biomolecule to detect is glucose. 2.8% of the world population suffers from diabetes, these people need to measure their blood sugar level and manage this level by dispensing insulin in their body when needed. A glucose sensor is used to determine the amount of glucose in the blood. Boron-doped diamond (BDD) is an interesting material for the non-enzymatic detection of glucose.
In this thesis project, study has been done to the nanostructuring and functionalisation effects on the performance of sensing glucose by using diamond electrodes. Measurements have been done with different types of electrodes: bare BDD, acid cleaned BDD, BDD functionalised with gold nanoparticles, BDD with a nanowire surface structure, and BDD with a nanowire surface structure and gold nanoparticles on top. It was found possible to detect glucose with three of these samples: bare BDD, BDD with gold nanoparticles, and the nanostructured BDD functionalised with the gold nanoparticles. The other two electrode types did not give any reduction/oxidation peaks, which is attributed to the oxygenated surface resulting from their fabrication processes. The three glucose-detecting electrodes showed linear behaviour in a range of 1-10 $mM$, which is in line with the detection range of glucose in human blood. The sensitivities achieved with bare BDD, BDD with gold nanoparticles, and the nanostructured BDD functionalised with the gold nanoparticles are 0.022, 0.429, and 0.136 mA/mMcm^{2}, respectively. The addition of gold particles improves the sensitivity for glucose substantially and works like an electrocatalyst. Making use of electrocatalysts is an interesting and useful functionalisation for direct non-enzymatic glucose sensing, because sensing glucose with bare BDD is a kinetically very slow process. Results of such high sensitivities for BDD with gold nanoparticles were not published in literature yet, so this is a promising achievement that asks for continuation of research in this field.