Reverse current pulse method to restore uniform concentration profiles in ion-selective membranes. 1. Galvanostatic pulse methods with decreased cycle time

Chronopotentiometric sensors for antimicrobial peptide-based biosensing of Staphylococcus aureus

Charged antimicrobial peptides can be used for direct potentiometric biosensing, but have never been explored. We report here a galvanostatically-controlled potentiometric sensor for antimicrobial peptide-based biosensing. Solid-state pulsed galvanostatic sensors that showed excellent stability under continuous galvanostatic polarization were prepared by utilizing reduced graphene oxide/poly (3,4-ethylenedioxythiophene): poly (4-styrenesulfonate) (rGO/PEDOT: PSS) as a solid contact. More importantly, the chronopotentiometric sensor can be made sensitive to antimicrobial peptides with intrinsic charge on demand via a current pulse. In this study, a positively charged antimicrobial peptide that can bind to Staphylococcus aureus with high affinity and good selectivity was designed as a model. Two arginine residues with positive charges were linked to the C-terminal of the peptide sequence to increase its potentiometric responses on the electrode. The bacteria binding-induced charge or charge density change of the antimicrobial peptide enables the direct chronopotentiometric detection of the target. Under the optimized conditions, the concentration of Staphylococcus aureus can be determined in the linear range 10-1.0 × 105 CFU mL-1 with a detection limit of 10 CFU mL-1. It is anticipated that such a chronopotentiometric sensing platform is readily adaptable to detect other bacteria by choosing the peptides.

Ion transfer through solvent polymeric membranes driven by an exponential current flux

General analytical equations which govern ion transfer through liquid membranes with one and two polarized interfaces driven by an exponential current flux are derived. Expressions for the transient and stationary E-t, dt/dE-E and dI/dE-E curves are obtained, and the evolution from transient to steady behaviour has been analyzed in depth. We have also shown mathematically that the voltammetric and stationary chronopotentiometric I(N)-E curves are identical (with E being the applied potential for voltammetric techniques and the measured potential for chronopotentiometric techniques), and hence, their derivatives provide identical information.

Interpretation of chronopotentiometric transients of ion-selective membranes with two transition times

Passing currents through ion-selective membranes has contributed to the development of a variety of novel methods. In this work, chronopotentiometric (CP) transients with two transition times (breakpoints) are presented for the first time, with the theoretical interpretation of such voltage transients. The validity of our theory has been confirmed in experiments utilizing ETH 5294 chromoionophore-based pH sensitive membranes with and without lipophilic background electrolyte and ETH 5234 ionophore-based calcium selective membranes in which the ionophore forms 3:1 complexes with Ca(2+) ions. The conditions under which two breakpoints can be identified in the chronopotentiometric voltage transients are discussed.Spectroelectrochemical microscopy (SpECM) is used to show that the two breakpoints in the CP curves emerge approximately when the free ionophore and ion-ionophore complex concentrations approach zero at the opposite membrane-solution interfaces. The two breakpoint times can be utilized to follow simultaneously the concentration changes of the free ionophore, the ion-ionophore complex, and the mobile anionic sites in cation-selective membranes. In membranes with known composition, the time instances where breakpoints occur can be used to estimate the free ionophore and the ion-ionophore complex diffusion coefficients.