Model improvement for super-Nernstian pH sensors: the effect of surface hydration

Madeira, Gustavo; Mello, Hugo José Nogueira Pedroza Dias; Faleiros, Murilo Calil; Mulato, Marcelo

doi:10.1007/s10853-020-05412-w

Cited by 21 publications

(10 citation statements)

References 31 publications

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“…The linear potential change can be explained by the modified Nernst equation, which is written aswhere E is the measured electric potential, E 0 is the electric potential at standard conditions, R is the ideal gas constant, T is the temperature, n is the number of moles of transferred electrons in the redox reaction, and F is the Faraday constant. 24 The theoretical sensitivity from equation (1) is 59.2 mV at 25°C, which is in good accordance with the value we obtained. The reason for the sensitivity slightly lower than the theoretical value from Nernst equation is probably due to the change in the surface charges of electrodes by protonation/deprotonation or specific adsorption of dissociated water ions.…”

Section: Resultssupporting

confidence: 90%

A fully textile-based skin pH sensor

Choi

Lee

Kim

et al. 2022

Journal of Industrial Textiles

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This paper presents a textile-based pH sensor with high flexibility fabricated by printing a polymer composite as a working electrode and Ag/AgCl/solid electrolyte as a reference electrode on a textile substrate. The textile working electrode is composed of polyaniline, carbon nanotubes, and agarose printed on the textile. A thermoplastic polyurethane overlayer hot-pressed on the textile substrates provides a smooth hydrophobic surface, enabling a more stable formation of the composite films with a reliable output signal. The textile reference electrode is fabricated by printing Ag/AgCl paste and solid electrolyte. The fully textile-based pH sensor, by integrating the textile working and reference electrodes, exhibits a good sensitivity of 45.9 mV/pH with high linearity. The textile pH sensor maintains excellent performance and repeatability with 93% retention even in a bent state and after 1000 bending cycles. Finally, it is demonstrated that the textile pH sensor can detect the pH change on a piece of porcine skin.

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Section: Resultssupporting

confidence: 90%

A fully textile-based skin pH sensor

Choi

Lee

Kim

et al. 2022

Journal of Industrial Textiles

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“…The PANI film transforms between the emeraldine salt and emeraldine base states in response to changes in pH [ 51–53 ] ( Figure a): a low pH shifts the equilibrium toward emeraldine salt which increases the surface potential of WE, and vice versa. Figure 5b shows a linear relationship between the OCP (WE vs RE) and pH with a super‐Nernstian sensitivity (absolute value > 59 mV dec −1 ) of −69.4 mV pH −1 consistent with observations in previous reports [ 54–56 ] (discussion in Note S3, Supporting Information). Following the same working principle, the surface potential can serve as the reverse bias (WE connected with the cathode) for wireless signal transmission (Figure 5c).…”

Section: Resultssupporting

confidence: 88%

A “Two‐Part” Resonance Circuit based Detachable Sweat Patch for Noninvasive Biochemical and Biophysical Sensing

Yan

Liu

Chen

et al. 2022

Adv Funct Materials

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Wearable electronics play important roles in noninvasive, continuous, and personalized monitoring of multiple biosignals generated by the body. To unleash their full potential for the next-generation human-centered bio-integrated electronics, wireless sensing capability is a desirable feature. However, state-of-the-art wireless sensing technologies exploit rigid and bulky electronic modules for power supply, signal generation, and data transmission. This study reports a battery-free device technology based on a "two-part" resonance circuit model with modularized, physically separated, and detachable functional units for magnetic coupling and biosensing. The resulting platform combines advantages of electronics and microfluidics with low cost, minimized form factors, and improved performance stability. Demonstration of a detachable sweat patch capable of simultaneous recording of cortisol concentration, pH value, and temperature highlights the potential of the "two-part" circuit for advanced, transformative biosensing. The resulting wireless sensors provide a new engineering solution to monitoring biosignals through intimate and seamless integration with skin surfaces.

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“…The pH in the sample was continuously monitored using a PANI-based potentiometric pH sensor with the following analytical characteristics (Figures and S4–S6): sensitivities of 67.5 ± 0.4 mV/pH and −67.9 ± 0.8 mV/pH ( n = 3) in the batch and inside the flow cell (Figure a,b), respectively, fast response time (<3 s), a wide linear range of response (from pH 2 to 10), reversibility to subsequent decreasing and increasing pH changes with the average slope and intercept of −70.7 mV/pH and 507.2 mV, respectively, with variation coefficients of less than 1 and 10% (Figure S4), and an average sensitivity of 67.5 ± 0.6 mV/pH when the pH solutions were tested in a randomized sequence (Figure S5) over four cycles. Notably, the super-Nernstian response provided by the PANI pH sensor has previously been associated with an exchange process involving more than one proton per electron transferred in the film and depending in turn on the hydration of PANI . Furthermore, the pH sensor presents a stability (drift of 2.5 mV h –1 over a period of 90 min in the beaker, Figure S6; 2.9 mV h –1 and 0.8 mV h –1 over 60 min for pH 7.2 and pH 4.0 in flow mode, respectively, Figure S7) that is considered acceptable for lab tests, where frequent recalibrations are possible, and appropriate lifetime for a testing period of 7 days (RSD of the slope and intercept lower than 1%).…”

Section: Resultsmentioning

confidence: 91%

“…Notably, the super-Nernstian response provided by the PANI pH sensor has previously been associated with an exchange process involving more than one proton per electron transferred in the film and depending in turn on the hydration of PANI. 34 Furthermore, the pH sensor presents a stability (drift of 2.5 mV h −1 over a period of 90 min in the beaker, Figure S6; 2.9 mV h −1 and 0.8 mV h −1 over 60 min for pH 7.2 and pH 4.0 in flow mode, respectively, Figure S7) that is considered acceptable for lab tests, where frequent recalibrations are possible, and appropriate lifetime for a testing period of 7 days (RSD of the slope and intercept lower than 1%). Finally, when we inspected a number of 30 calibrations provided by the PANI pH sensors used throughout this investigation and that were equally prepared, an average sensitivity of 68.5 ± 1.8 mV/pH was found, showing some slight variations between the different electrodes.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Reagentless Acid–Base Titration for Alkalinity Detection in Seawater

et al. 2021

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Herein, we report on a reagentless electroanalytical methodology for automatized acid−base titrations of water samples that are confined into very thin spatial domains. The concept is based on the recent discovery from our group (Wiorek, A. et al. Anal. Chem. 2019, 91, 14951−14959), in which polyaniline (PANI) films were found to be an excellent material to release a massive charge of protons in a short time, achieving hence the efficient (and controlled) acidification of a sample. We now demonstrate and validate the analytical usefulness of this approach with samples collected from the Baltic Sea: the titration protocol indeed acts as an alkalinity sensor via the calculation of the proton charge needed to reach pH 4.0 in the sample, as per the formal definition of the alkalinity parameter. In essence, the alkalinity sensor is based on the linear relationship found between the released charge from the PANI film and the bicarbonate concentration in the sample (i.e., the way to express alkalinity measurements). The observed alkalinity in the samples presented a good agreement with the values obtained by manual (classical) acid−base titrations (discrepancies <10%). Some crucial advantages of the new methodology are that titrations are completed in less than 1 min (end point), the PANI film can be reused at least 74 times over a 2 week period (<5% of decrease in the released charge), and the utility of the PANI film to even more decrease the final pH of the sample (pH ∼2) toward applications different from alkalinity detection. Furthermore, the acidification can be accomplished in a discrete or continuous mode depending on the application demands. The new methodology is expected to impact the future digitalization of in situ acid−base titrations to obtain high-resolution data on alkalinity in water resources.

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Model improvement for super-Nernstian pH sensors: the effect of surface hydration

Cited by 21 publications

References 31 publications

A fully textile-based skin pH sensor

A fully textile-based skin pH sensor

A “Two‐Part” Resonance Circuit based Detachable Sweat Patch for Noninvasive Biochemical and Biophysical Sensing

Reagentless Acid–Base Titration for Alkalinity Detection in Seawater

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