Browsing by Author "Abdelmohsen, Benoudjit"

Poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is widely used in the fabrication of capacitors, solar cells, transistors, and especially biosensors. Stability and adhesion of a PEDOT:PSS transducer in liquid media are major problems in the fabrication of robust sensors owing to the easy disintegration of PEDOT:PSS from electrode surfaces. In this study, the effect of using electropolymerization deposition (EPD) and drop-casting (DC) on the stability and adhesion of the PEDOT:PSS transducer were studied. Furthermore, the effect of PEDOT:PSS ratio on the stability of the transducer in liquid media was investigated and a glucose biosensor was synthesized and characterized based on an electropolymerized PEDOT:PSS transducer. The galvanostatic mode was employed using a potentiostat/galvanostat at 100 µA and 400 mV for electropolymerization deposition of EDOT and PSS to PEDOT:PSS on electrode surfaces. A PEDOT:PSS transducer deposited on a flat platinum electrode (FPtE) and soaked in phosphate-buffered saline (PBS) solution for more than 15 days showed long-term stability, retaining almost 99% of its original activity. For further confirmation of the robustness of a PEDOT:PSS transducer synthesized by EPD, a commercially available aqueous dispersion of PEDOT:PSS was deposited by DC on FPtE as transducer for comparison purposes. The stability and adhesion of PEDOT:PSS deposited via EPD and DC were tested in dynamic liquid media. A PEDOT:PSS transducer fabricated using EPD maintained almost 99.9% of its original activity after a water-flow test; in contrast, the one fabricated using DC lost 95% of its original activity. Field emission scanning electron microscope (FESEM) results revealed that the structure of the PEDOT:PSS transducer fabricated using EPD remains intact on electrode surfaces after a water-flow test. Moreover, with EPD, the PEDOT:PSS ratio did not have any effect on the stability of a PEDOT:PSS transducer. Finally, a glucose biosensor with a PEDOT:PSS transducer was successfully fabricated, and the sensitivity and efficiency were 285.2 nA/mM and 17.68 µA/mM cm2, respectively. The results suggest that using EPD to synthesize a PEDOT:PSS transducer could enhance the robustness of the transducer in liquid media, thereby providing a future platform for electrochemical biosensors with high sensitivity and stability, especially for dynamic liquid media use.

An all-solid-state ion-selective electrode (AS- NH4+ISE) for ammonium-ion-sensing based on stable conductive polymer (CPs) as a solid contact transducer and ionophore-free ion-selective membrane for mobile sensor application was fabricated. Poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) electropolymerized onto screen-printed carbon electrodes (SPCEs), and screen-printed platinum electrodes (SPPEs) as solid contact transducer was characterized for its morphology and electrochemical performance and was studied for stability – the ability of the sensing solid contact transducer to adhere to the working electrode surface and maintain electrochemical cycle stability. The stability of the solid contact transducer was studied in static measurements condition – a condition where the electrodes are submerged in aqueous solution and not moving, and there is no water flow on the electrode surface when the measurements are taken, and dynamic measurements condition – a condition where an aqueous solution flows across the electrode surface and the sensor is not moving when measurements are taken. Cyclic voltammetry (CV) showed that the electron transfer ability of SPCEs and SPPEs was significantly improved when electropolymerized PEDOT:PSS was used as the transducer. Moreover, the CVs' redox peak current showed that both electrodes could maintain the electrode’s mechanical and electrochemical functional integrity for over 30 days. The results suggest that the electropolymerized PEDOT:PSS had good adhesion to SPCEs and SPPEs working electrode surfaces. There was no significant change in the cycle stability curve in PBS, pH 7.1, after 3000 cycles conducted over 12 hours, compared to the initial cycle. Furthermore, no significant change in the cycle stability curve was observed after 30 days of undergoing CV cycles in PBS, pH 7.1, compared to the first day for both electrodes. The results suggest that electrode stability of PEDOT:PSS/SPCEs and PEDOT:PSS/SPPEs was maintained after repetitive CV cycles in aqueous media. After characterisation of solid contact transducer, the PEDOT:PSS/SPCEs were integrated into a sensing cell to investigate the electrochemical behaviour of electropolymerized PEDOT:PSS in dynamic measurement conditions. The results showed that the PEDOT:PSS/SPCEs maintained their peak potential (Ep) and peak current (Ip) after they were exposed to different flow rates of 10, 20, 30 and 40 ml/min. Furthermore, the effect of the flow rates on the Ep and Ip was investigated. The results showed that flow rates range between 0 to 40 ml/min did not affect the Ep and Ip value of the PEDOT:PSS/SPCEs. Finally, o-phenylenediamine (o-PD) as an ammonium ion-selective membrane (ISM) was electropolymerized to poly(o-phenylenediamine) and deposited simultaneously on top of the PEDOT:PSS/SPCEs solid contact transducer to fabricate AS-NH4+ISEs. The ISM's electropolymerization deposition was obtained by cyclic voltammetry (CV) with potential from 0.0 V to 0.8 V and a scan rate of 50 mV/s. The fabricated AS-NH4+ISEs can detect ammonium ions (NH4+) as low as 5.7×10-5 M with a slope of 58.49 mV/decade (R2 > 0.99) and a linear detection range from 10-3 M to 1 M. These results provide an initial insight into the applicability of the stable PEDOT:PSS/SPCE solid contact transducers for the development of AS-NH4+ISEs with high potential for scaling-up purposes and the ability for miniaturization and integration into a mobile sensor platform.