ABSTRACT:The tremendous applications of boronic acids (BAs) in chemical sensing, medical chemistry, molecular assembly, and organic synthesis lead to an urgent demand for developing effective sensing methods for BAs. This paper reports a facile and sensitive potentiometric sensor scheme for heterogeneous detection of BAs based on their unexpected potential responses on quaternary ammonium salt-doped polymeric liquid membranes. 11 B NMR data reveal that a quaternary ammonium chloride can trigger the hydrolysis of an electrically neutral BA in an aprotic solvent. Using the quaternary ammonium salt as the receptor, the BA molecules can be extracted from the sample solution into the polymeric membrane phase and undergo the concomitant hydrolysis. Such salttriggered hydrolysis generates H + ions, which can be coejected into the aqueous phase with the counterions (e.g., Cl − ) owing to their high hydrophilicities. The perturbation on the ionic partition at the sample−membrane interface changes the phase boundary potential and thus enables the potentiometric sensing of BAs. In contrast to other transduction methods for BAs, for which labeled or separate reporters are exclusively required, the present heterogeneous sensing scheme allows the direct detection of BAs without using any reporter molecules. This technique shows superior detection limits for BAs (e.g., 1.0 × 10 −6 M for phenylboronic acid) as compared to previously reported methods based on colorimetry, fluorimetry, and mass spectrometry. The proposed sensing strategy has also been successfully applied to potentiometric indication of the BA reactions with hydrogen peroxide and saccharides, which allows indirect and sensitive detection of these important species.

We report here the concept of a magnetically controlled extraction of hydrophilic bioreceptors into polymeric membranes for bioassays. The potentiometric assay relies on the intrinsic charges of an antimicrobial peptide and its unique recognition abilities, which can eliminate the probe labeling and indicator addition. The target binding event could effectively prevent the extraction of the peptide into the polymeric membrane doped with an ion exchanger, thus resulting in a potential change. The potentiometric response properties of the peptide assembled on magnetic beads can be dynamically controlled and modulated by applying a magnetic field. Staphylococcus aureus, as a model of food‐borne pathogens, was measured at levels down to 10 CFU mL−1. Based on this sensing strategy, a potentiometric array was developed for the pattern recognition of bacteria. The proposed general platform can be used for potentiometric biosensing using other hydrophilic bioreceptors.

Peptide-based sandwich assays are promising tools in molecular detection, but may be restricted by the availability of "pairs" of affinity peptides. Herein, a new potentiometric sandwich assay for bacteria based on peptide pairs derived from an antimicrobial peptide (AMP) ligand is demonstrated. As a model, the original AMP with a welldefined structure for Listeria monocytogenes (LM) can be split into two fragments to serve as the peptide pairs for the sandwich assay. The recognition and binding of the short peptide pairs to the target can be verified by circular dichroism, flow cytometry, fluorometry, and optical microscopy. The potentiometric magnetic bead-based sandwich assay is designed by using horseradish peroxidase as a label. The enzyme can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine with H 2 O 2 to induce a potential change on a polymeric membrane ionselective electrode. Under optimal conditions, the concentration of LM can be determined potentiometrically in a linear range of 1.0 × 10 2 to 1.0 × 10 6 CFU mL −1 with a detection limit of 10 CFU mL −1 (3σ). The proposed sensing strategy expands the applications of peptides in the field of bioassays.