Optical Ion Sensing Platform Based on Potential-Modulated Release of Enzyme

Abstract

We report here on an optical ion sensing platform, in which a polymeric membrane ion-selective electrode (ISE) serves as not only a potentiometric transducer for ion activities in the sample solution but also a reference electrode for the potential-modulated release of enzyme from an iron-alginate-horseradish peroxidase (HRP) thin film modified working electrode. The ISE and working electrode are physically separated by a salt bridge. The dissolution of the HRP-embedded thin film can be triggered by the reduction of Fe3+, which is modulated by the potential response of the ISE to the target ion in the sample. The released enzyme induces the oxidation of its substrate mediated by H2O2 to produce a visual color change. With this setup, an optical ion sensing platform for both cations (e.g., NH4 +) and anions (e.g., Cl–) can be obtained. The proposed platform provides a general and versatile visual-sensing strategy for ions and allows optical ion sensing in colored and turbid solutions.

Ionophore-based ion-selective electrodes: signal transduction and amplification from potentiometry

“…67 With a similar three-electrode setup, Qin and coworkers utilized the potential of ISEs to control the release of the enzyme horseradish peroxidase (HRP) from an iron-alginate gel layer. 68 As shown in Fig. 3b, the gel layer was deposited…”

“…67 With a similar three-electrode setup, Qin and coworkers utilized the potential of ISEs to control the release of the enzyme horseradish peroxidase (HRP) from an iron-alginate gel layer. 68 As shown in Fig. 3b, the gel layer was deposited on top of the working electrode and the ISE was placed in the sample solution and physically separated from the detection compartment.…”

Translating potentiometric detection into non-enzymatic amperometric measurement of H2O2

“…For example, Bakker's group reported an electrogenerated chemiluminescence (ECL) readout for the potentiometric sensors, which applied the change in the ion concentration to control both the potential response of the ISE and the ECL intensity [18,19]. Qin' s group developed an optical ion sensing platform for the ISEs, which employed the ISEs to modulate the release of enzyme and produce a visual color change [20]. Moreover, the photoelectric current is also proposed for reading out the potential response through the control of the photoactive material by using an ISE [21].…”

A label-free protamine-assisted colorimetric sensor for highly sensitive detection of S1 nuclease activity

“…10 As an alternative, we designed ion sensing platforms by converting potentiometric signals to a colorimetric readout through the potential-modulated release of enzyme, which could increase the detection sensitivity due to the enzyme amplification effect. 11 A colorimetric readout can also be obtained by the turnover of a redox indicator in a thin layer using a closed bipolar electrode. 12 Recently, Maksymiuk et al proposed an approach based on a selffeeding bipolar electrode system for reading the potential response of ISEs with fluorescence.…”

“…21 Accordingly, sufficiently large currents are expected when a small potential change occurs on the working electrode during PEC measurements. Since the ISE can be used as the reference electrode to modulate the working electrode potential, 7,8,11 in principle, a small potential variation can be converted to an obvious change in the photocurrent output. As a proof of concept experiment, a solid-contact ISE for the detection of calcium ions in seawater was prepared and used as a reference electrode for the PEC measurement system.…”