Electrochemical Characterisation of thiols and di-sulphide Modified Gold Nanoparticles in a Physiological Medium

Many different biosensors are currently used in medicinal applications to help detect pathogens and toxins.1 Current techniques, such as PCR (polymerase chain reaction) and immunological based detection lack in versatility, are expensive and complicated to use.2–4 Due to these limitations, there is an increasing need for rapid, real-time, selective and low cost techniques. 5 Advancements in nanotechnology and the use of surface modified gold nanoparticles could potentially overcome these present-day limitations, leading to new areas of detection using nano-biosensors. 1 In addition, the use of electrochemical biosensors have successfully been used in the detection of bacteria and pathogens without many of the limitations listed above. Electrochemical biosensors are based on the idea that electrochemical species, such as electrons, are consumed or generated and produce an electrochemical signal; which can be measured by an electrochemical detector.6 Here, gold nanoparticles were synthesized by the colloidal seed mediated method. The characterisation of gold nanoparticles were performed by UV-Vis, TEM, SEM and XRD. The electrochemical cleansing of the gold nanoparticles was also characterised by using Pb underpotential deposition. In order to make a platform to detect toxins, modification was required to the gold nanoparticles in order to start designing the building blocks of the electrochemical biosensor. The stability of the functionalised gold nanoparticles by molecules 1,4-dithiothreitol, thioctic acid and 3-mercaptopropionic acid were monitored by cyclic voltammetry, whilst in a neutral medium. From the three different molecules, experiments demonstrate that the disulphides are more stable at negative potentials in comparison to the thiol, as a result of having two coordinating sulphur atoms in their structure. The most stable thiol or disulphide is most desirable as the fundamental part of the sensor is the sulphur containing molecule. From all three molecules, thioctic acid desorption from the electrode surface occurred at the lowest potentials, therefore the most stable and most suitable out of three molecules if used for sensing