A prototype device of microliter volume voltammetric pH sensor based on carbazole–quinone redox-probe tethered MWCNT modified three-in-one screen-printed electrode

Abstract

As an alternate for the conventional glass-based pH sensor which is associated with problems like fragile nature, alkaline error, and potential drift, the development of a new redox-sensitive pH probe-modified electrode that could show potential, current-drift and surface-fouling free voltammetric pH sensing is a demanding research interest, recently. Herein, we report a substituted carbazole-quinone (Car-HQ) based new redox-active pH-sensitive probe that contains benzyl and bromo-substituents, immobilized multiwalled carbon nanotube modified glassy carbon (GCE/MWCNT@Car-HQ) and screen-printed three-in-one (SPE/MWCNT@Car-HQ) electrodes for selective, surface-fouling free pH sensor application. This new system showed a well-defined surface-confined redox peak at an apparent standard electrode potential, Eo′ = − 0.160 V versus Ag/AgCl with surface-excess value, Γ = 47 n mol cm−2 in pH 7 phosphate buffer solution. When tested with various electroactive chemicals and biochemicals such as cysteine, hydrazine, NADH, uric acid, and ascorbic acid, MWCNT@Car-HQ showed an unaltered redox-peak potential and current values without mediated oxidation/reduction behavior unlike the conventional hydroquinone, anthraquinone and other redox mediators based voltammetry sensors with serious electrocatalytic effects and in turn potential and current drifts. A strong π–π interaction, nitrogen-atom assisted surface orientation and C–C bond formation on the graphitic structure of MWCNT are the plausible reasons for stable and selective voltammetric pH sensing application of MWCNT@Car-HQ system. Using a programed/in-built three-in-one screen printed compatible potentiostat system, voltammetric pH sensing of 3 μL sample of urine, saliva, and orange juice samples with pH values comparable to that of milliliter volume-based pH-glass electrode measurements has been demonstrated.

A Conductive Microcavity Created by Assembly of Carbon Nanotube Buckypapers for Developing Electrochemically Wired Enzyme Cascades

“…The resulting bioelectrodes exhibited the conventional electrochemical behavior expected for the entrapped redox mediators with electrochemically quasi-reversible systems at E 1/2 = 474 mV, E 1/2 = 57 mV, and E 1/2 = 65 mV vs. Ag/AgCl for ABTS, hydroquinone, and hexacyanoferrate (III), respectively. Such mid-potential values of the redox couple peaks observed on the buckypaper sandwich electrodes align with those reported in the literature (ABTS [26], hydroquinone [27][28][29], and hexacyanoferrate (III) [30]). This confirms the penetration of water into the microcavity and the solubilization of redox compounds.…”

Sensors for in situ monitoring of oral and dental health parameters in saliva

“…Even though the sensor monitored salivary pH continuously, there were several limitations. Glass electrodes have the disadvantage of being fragile and suffering from potential drifts [ 113 ]. In addition, replacing some molars was necessary, possible leakage of the internal solution could occur, and the need for a time-consuming calibration step contributed to the disadvantages of the sensor [ 22 ].…”

Perspective—Thick Film Technology

“…TFT introduces a new platform in the electrochemistry. It is not only the cheap production of electrodes but their miniaturization, their connection with microfluidics, [1][2][3] capillary electrophoresis [4][5][6][7] and HPLC [8][9][10] for example.…”