Nanostructured metallic surfaces of Au implemented as electrochemical glucose sensors
Creators: name: Coyle, Victoria
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340301
subject: Inorganic materials (incl. nanomaterials)
classificationCode: 340604
subject: Electrochemistry
classificationCode: 340699
subject: Physical chemistry not elsewhere classified

description: Diabetes is one of the most prevalent chronic diseases growing globally with 450 million people currently being diagnosed with the disease. With this number dramatically increasing every year the need for highly sensitive and selective glucose sensors are of great importance. Along with this, the comfort of the patient when analysing their glucose concentrations has come to the forefront of research with the push towards non-invasive sensing devices becoming the major focus in this research. The aim of this research was to develop Au-based nanostructures and study their effectiveness in detecting ultra-low concentrations (&lt;100 µM) of glucose. Au has shown excellent biocompatibility as well as its ability to be moulded for shape, size and density which can be tailored specifically to get enhanced glucose electrooxidation. Following a thorough literature review, the materials that were developed and investigated were pure mono-metallic Au structures, Au Pt alloy and Au Ni particles as well as Au Co3O4 composites.<br> <br>Initially, a pure nanostructure of Au was studied in the form of Au nanospikes where the impact of HAuCl4 concentration, Pb acetate concentration (growth agent for shape), electrodeposition time and electrodeposition potential were studied. From these studies the optimal conditions to produce Au nanospikes for optimal glucose sensing were found to have a HAuCl4 concentration of 13.6 mM, a Pb acetate concentration of 1 mM, an electrodeposition time of 12 mins and an applied electrodeposition potential of +0.05 V. Analysis of this optimal pure Au sensor was performed with calculated sensitivity of 91.8 µA·mM-1·cm-2 with no interference from common physiological contaminants making this sensor sensitive and highly selective. Further study of the Au-based sensors pushed the study to use Au in conjunction with Pt in an alloyed form. Using the hydrogen bubble template technique with varying concentrations of Pt were used to form a sensor with a very large electrochemical surface area (ECSA). In this study various concentrations of Pt were added to the electrodeposition solution with 0.5 mM of Pt showing the largest overall surface area and the highest sensitivity in the presence of glucose.<br> <br>Electrochemical glucose sensing analysis was performed on the Au-Pt alloyed sensor producing a high sensitivity of 109.3 µA·mM-1·cm-2 showing the alloyed material produced a higher sensitivity than that of the monometallic Au sensor. With the addition of Pt, a higher sensitivity was obtained whist the large presence of Au allowed for the sensor to have excellent selectivity in the presence of common physiological contaminants which has previously hindered the use of Pt in glucose sensing nanostructures.<br><br>To reduce Au content yet increase sensitivity, highly active Au nanoparticles on a Ni platform were employed. It is well known that Au nanoparticles grown by galvanic replacement are highly active however a uniform formation is a major challenge due to the mechanism by which a galvanic replacement reaction occurs. From this knowledge, Ni colloidal crystals were employed to attempt to overcome this issue. Multiple concentrations of Au were used to determine the optimal concentration of Au which was found to be 0.1 mM of HAuCl4. Analysis of this formed sensor was performed and a very large sensitivity of 506 µA·mM-1·cm-2 showing a much larger enhancement of sensitivity compared to both the pure Au and Au-Pt alloyed sensors. The Ni-Au colloidal sensor showed minimal effect from common physiological contaminants due to the presence of Au in the structure. Finally, a study of the effect of an additional material was studied in the presence of the metal oxide Co3O4 due to its excellent biocompatibility and excellent sensitivity in the presence of glucose. The hydrogen bubble templated technique was used to form a pure Au lattice structure which was then coated in pure Co3O4 nanowires using the hydrothermal technique. The formed structure had a completely cohesive structure where Co3O4 moulded over the Au allowing for synchronized sensing between the Au and Co3O4 components to occur. The electrochemical sensing analysis of the Au-Co3O4 structure showed a huge sensitivity of 2014 µA·mM-1·cm-2 within the glucose concentration range between 0.02 and 1 mM. This large sensitivity in the low region of glucose concentrations showed the possibility of the sensor performing successfully within the glucose concentration range of saliva (20 ¿ 1000 µM). Further analysis of the sensor was performed in the presence of synthetic saliva showing an excellent linearity of glucose additions and minimal to no effect from common physiological contaminants found in saliva. These findings showed the feasibility of the developed electrochemical glucose sensor to be employed for non-invasive diabetes monitoring and diagnostic applications.