A New Graphene Quantum Dot Sensor for Estimating an Antibiotic Concentration

The antibiotics have impacted the human ailments by curtailing the growth of microbes and by providing relief from microbial diseases. While there are a large number of analytical methods available for the determination of antibiotics concentration, they are time consuming and impractical for usage in the fields. This thesis is aimed at overcoming the deficiencies of those methods in developing a new sensor. It reports a study of graphene quantum dots (GQD) bound ferric ion for sensing an antibiotic, ciprofloxacin (CP). The interaction of ferric ion with CP was used as a probe for the analytical estimation of CP using differential pulse voltammetry (DPV). A solution containing ferric ion exhibits a well-defined cathodic peak at Epc=0.310 V vs saturated calomel electrode (SCE) with a peak width of 0.100V. When nanomolar to micromolar concentration of CP is present in the solution, along with ferric ion, three new peaks at EpcI=0.200V, EpcII=0.050 V and EpcIII=-0.085V are observed due to the binding of CP to ferric ion. The decrease in peak current of Epc at 0.310 V is proportional to the concentration of CP in the solution. The peak current at 0.200 V shows an increase corresponding to the CP concentration in solution. These results paved the way for examining the prospectus for developing a portable resistive sensor using interdigitated gold electrodes on alumina substrate. The principle of this sensor is based on that ferric ion bound to GQD will have a finite resistance and when it is bound to CP the resistance will increase as the charge transport faces a barrier due to bulky CP molecules. With a view to establish that ferric ion is binding to GQD, fluorescence of GQD has been recorded with ferric ion in solution. The approach adopted in developing resistive sensor is shown below. The numbers in the above picture denotes 1. Interdigitated gold electrodes 2. GQD bound interdigitated gold electrodes 3. Ferric ion bound to GQD 4. Attachment of CP to ferric ion. The sensor response is found to be dependent on the activity of the availability of ferric ion on GQD resulting in the usage of it as a disposable sensor. The interference of urea in the measurement of CP was examined for the practical usage of it in urine analysi