Ion-Selective Electrodes Using Carbon Nanotubes as Ion-to-Electron Transducers

Abstract

This study developed a new type of all-solid-state ion-selective electrode based on a transducing layer of a network of single-walled carbon nanotubes. The extraordinary capacity of carbon nanotubes to promote electron transfer between heterogeneous phases made the presence of electroactive polymers or any other ion-to-electron-transfer promoter unnecessary. The new transducer layer was characterized by environmental scanning electron microscopy and electrochemical impedance spectroscopy. The stability of the electrical potential of the new solid-contact electrode was examined by performing current-reversal chronopotentiometry, and the influence of the interfacial water film was assessed by the potentiometric water layer test. The performance of the new electrode was evaluated by determining K+ with an ion-selective membrane that contained the well-known valinomycin ion carrier. The new electrode had a Nernstian slope (58.4 mV/decade), dynamic ranges of four logarithmic units, and selectivities and limits of detection comparable to other solid-contact electrodes. The short response time (less than 10 s for activities higher than 10(-5.5) M) and the stability of the signal over several days makes these new electrodes very promising candidates for attaining true miniaturization.

A solid-contact Pb2+-selective electrode using poly(2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene) as ion-to-electron transducer

“…As a key component, the solid contact plays a critical role in the electrode characteristics, such as linear response range, selectivity and potential stability in particular [3][4][5]. Until now, many kinds of materials, including redox-active monolayers [6], carbon materials [7][8][9][10][11], and conducting polymers (CPs) [12] have been introduced between the conducting substrates and the ion-selective membranes to obtain thermodynamically defined electrochemical interfaces.…”

A simple approach for fabricating solid-contact ion-selective electrodes using nanomaterials as transducers

“…180 mV is observed for both electrodes upon replacing the CuCl 2 solution with the NaCl solution. Such EMF change reflects the change in the outer phase boundary potential as a consequence of the selectivity behavior of the Cu 2+ -selective membrane [21]. In this process, an obvious positive potential drift is observed for the CWE, while the electrode based on ETH 500/SWCNTs exhibits a stable potential response.…”

“…The conventional solid-contact electrodes using nanomaterials as transducers were fabricated according to Rius's method with some modifications [21]. Briefly, 0.5 mg of nanomaterials were dispersed in 10 mL DMF by sonication for 4 h, and then 40 mL of nanomaterials/DMF solution was drop-cast onto the polished GCE surface and dried by an infrared lamp.…”

“…Especially, the exceptional electrical properties such as the high charge transfer, the extraordinary electrical capacities and good hydrophobicity make them suitable as transducing components in potentiometric sensors [16,17]. Recently, many nanostructured carbon materials including fullerene [18], graphene [19,20], carbon nanotubes (CNTs) [21][22][23], three-dimensionally ordered macroporous (3DOM) carbon [24] and colloid-imprinted mesoporous (CIM) carbon [25] have been utilized as ion-to-electron transducers in solid-contact ISE. The electrodes based on these nanomaterials as transducers exhibit excellent response performances such as long-term potential stability, and insensitivity to O 2 .…”

“…It has been well known that the transducer layer of solid-contact ISEs based on nanomaterials is usually formed by drop casting a suspension solution of nanomaterial onto the surface of the inner electrode (e.g., glassy carbon electrode, GCE) which is followed by heating the electrode surface to evaporate the solvent with a hot air stream or an infrared lamp. In order to obtain a homogeneous coverage of nanomaterials on the surface of the electrode, these processes have to be repeated for many times [18][19][20][21][22]. It is clear that such fabrication processes are somewhat complicated and time consuming.…”