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

• Published in: Scientific reports 2021-07, Vol.11 (1), p.13905-13905, Article 13905
• Main Authors: Srinivas, Sakthivel, Ashokkumar, Krishnan, Sriraghavan, Kamaraj, Senthil Kumar, Annamalai
• Format: Article
• Language: English
• Subjects: 639/638/161; 692/700/139; Anthraquinone; Ascorbic acid; Carbazole; Drift; Electrodes; Fouling; Fruit juices; Humanities and Social Sciences; Hydrazine; Hydroquinone; multidisciplinary; NADH; Oxidation; pH effects; pH sensors; Quinones; Saliva; Science; Science (multidisciplinary); Sensors; Silver chloride; Uric acid; Voltammetry
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-021-93368-5

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, E o ′ = − 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.