The Development of Electrochemical Sensors and their Application in Real Biological Environments

Screen printed sensors and applications have been developed that utilise carbon/graphite working and counter electrodes and silver reference electrodes.The first sensor produced is a pH sensor where the working electrode hasbeen functionalised by spin coating a layer of DMSO-melanin which enablesit to become sensitive to changes in pH. This pH sensor was initially tested inreference buffer solutions where the sensitivity to pH was -49.79mV/pH±8.93over a range of pH4 to pH10. Further testing showed an improved sensitivityof -63mV/pH±4.79 over a range of pH5 to pH8 which is a biologically relevantrange. The DMSO-melanin pH sensor was tested in culturing mediathat had been inoculated and live bacteria were present where it was demonstrated to maintain sensitivity to pH in the presence of bacteria suggesting that it is suitable for the use in bacterial culturing applications. It was observed that signal measured depends on the type of culturing media used sotherefore the type of culturing media must be known in advance of testingand a standard curve for each type of media being tested must be establishedbefore testing. Testing the DMSO-melanin pH sensors with blood samplesin a preclinical model revealed challenges in obtaining repeatable results inblood samples. Subsequent investigation into this indicated that substanceswithin the blood interfere with the signal that is measured by the sensor, inparticular NaCl, KCl and MgCl2. This work also produced a nonfunctionalisedcarbon/graphite screen printed electrode that was able to accuratelymeasure the concentration of Lactobacillus casei bacteria in culturing mediasolutions using square wave voltammetry. The shape of the voltammogramsmeasured was different when cultures of Escherichia coli and Saccharomycescerevisiae were tested suggesting that there might be potential useful applications involving this technique to identify characteristics of microbiota(such as domain, species, Gram type and quantity) based on the measuredvoltammograms. However further research on an expanded number of differentprokaryotic and eukaryotic microorganisms is needed to confirm whethersuch applications are possible