Abstract
Potentiometric pH measurements have long been used for the bioanalysis of biofluids, tissues, and cells. A glass pH electrode and ion-sensitive field-effect transistor (ISFET) can measure the time course of pH changes in a microenvironment as a result of physiological and biological activities. However, the signal interpretation of passive pH sensing is difficult because many biological activities influence the spatiotemporal distribution of pH in the microenvironment. Moreover, time course measurement suffers from stability because of gradual drifts in signaling. To address these issues, an active method of pH sensing was developed for the analysis of the cell barrier in vitro. The microenvironmental pH is temporarily perturbed by introducing a low concentration of weak acid (NH4+) or base (CH3COO−) to cells cultured on the gate insulator of ISFET using a superfusion system. Considering the pH perturbation originates from the semi-permeability of lipid bilayer plasma membranes, induced proton dynamics are used for analyzing the biomembrane barriers against ions and hydrated species following interaction with exogenous reagents. The unique feature of the method is the sensitivity to the formation of transmembrane pores as small as a proton (H+), enabling the analysis of cell–nanomaterial interactions at the molecular level. The new modality of cell analysis using ISFET is expected to be applied to nanomedicine, drug screening, and tissue engineering.
Highlights
Proton is involved in many essential biological reactions, such as the equilibrium of carbonate ions, glycolysis, and enzymatic reactions
Various sensing techniques have been developed for biological pH measurements, including implantable sensors, positron emission tomography (PET) imaging, magnetic resonance imaging (MRI), and electron paramagnetic resonance (EPR) imaging [4,5,6,7,8]
A potentiometric ion-sensitive field-effect transistor (ISFET) array with a perfusion system was developed to measure the acidification rate of extracellular pH for determining the respiration and glycolysis of tumor cells adhered to the gate insulator [13,14,15]
Summary
Proton (hydronium ion) is involved in many essential biological reactions, such as the equilibrium of carbonate ions, glycolysis, and enzymatic reactions. Various sensing techniques have been developed for biological pH measurements, including implantable sensors, positron emission tomography (PET) imaging, magnetic resonance imaging (MRI), and electron paramagnetic resonance (EPR) imaging [4,5,6,7,8] These techniques have shown the ability to provide semi-quantitative information during in vivo studies, the accuracy has been difficult to confirm [9]. A potentiometric ion-sensitive field-effect transistor (ISFET) array with a perfusion system was developed to measure the acidification rate of extracellular pH for determining the respiration and glycolysis of tumor cells adhered to the gate insulator [13,14,15]. The review paper describes a novel potentiometric pH sensing method with the aid of external chemical stimuli and their applications regarding the label-free sensing of unique cellular processes, such as biomembrane injury and epithelial barrier breakdown
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