Study On The Improvement Of Analytical Performance For All-solid-state Ion-selective Electrodes

The introduction of All-solid-state ion-selective electrodes has revived thepotentiometric sensors field, which is a quite old branch of electrochemistry. Theall-solid-state structure shows enormous advantages in terms of electrode fabricationand application comparing with that of classical ion-selective electrode. However, thistype of electrodes tends to show potential instability due to the lack of effectivetransducers that ensure the interfacial ion-to-electron transfer. In this dissertation, thehistorical background of the field is briefly reviewed, and its analytical performance isalso introduced. Lastly, the following methods are also presented to improve theanalytical performance of the all-solid-state ion-selective electrodes:1) Graphene sheets are first used to fabricate a new type of solid-contaction-selective electrodes (SC-ISEs) as the intermediate layer between anionophore-doped solvent polymeric membrane and a glassy carbon electrode. Thenew transducing layer was characterized by transmission electron microscopy, cyclicvoltammetry and electrochemical impedance spectroscopy. The performance of thenew K+-selective electrodes was examined by a potentiometric water layer test,potentiometric measurements, and current reversal chronopotentiometry. Theobtained potentiometric sensors were characterized with a calibration line of slopeclose to Nernst reaction (59.2mV/decade) within the activity from10-4.5to0.1M.The high capacitance of the graphene solid contacts results in a signal that is stableover three weeks. The short response time is less than10s for activities higher than10-5M. The potential drift of the electrodes was calculated from the slope of thecurves at longer times (ΔE/Δt=1.2×10-5V/s (I=1nA) and ΔE/Δt=5.5×10-5V/s (I=5nA)). All the results indicate that graphene is a promising material for use as atransducer layer for SC-ISEs.2) A novel method was proposed for effectively improving the hydrophobicity atthe buried interface of the SC-ISEs, based on self-assembled monolayers (SAMs) ofhexanethiolate with electrodeposited gold nanoparticles. The resultinghighly-hydrophobic graphene surface originates from the tough morphology of solidcontact, exhibiting an advanced contact angle of135.4°. The resulting ISEs with extraordinary capacitance and good mechanical strength showed great analyticalperformance such as improved potential stability, reproducibility and prolongedworking life. Additional experiments on other commonly used SC materials showedsatisfied results, indicating its broad applicability.3) High stability of the signal and simplicity in fabrication of the device are thetwo important requirements in development of potentiometric sensors. A robustsingle-piece all-solid-state potassium-selective electrode (KSPE) was developed byincorporating monolayer-protected Au clusters (MPCs) as advanced ion-to-electrontransducers into a conventional ion-selective membrane (ISM). The extraordinaryproperties of MPCs such as high solubility, profound hydrophobicity and largecapacitance make them quite suitable to be used in fabrication of single-pieceelectrodes (SPEs) with advanced performance. The developed KSPEs containingsmall amount (2.0%) of MPCs in the membrane showed a significant increase in thepotential stability (12.9μV/h), lower detection limit (10-6.1M) and prolonged life time(high performance still after3weeks). The multi-valence MPCs in the membranefacilitated the ion-to-electron transduction and fast establishment of the potentialequilibrium resulting in fast response time in potential measurements. The insertedMPCs did not cause any interference either in the potential formation process or in theselectivity of the ion-selective membrane.