Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

Abstract

This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and p K a values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Visual pH Sensors: From a Chemical Perspective to New Bioengineered Materials

“…Since the first pH measurement in 1909 by Sørenson, development of more selective sensors of proton H 3 O + (simply H + ) concentration in solution still fascinates chemists [ 21 ]. From the earliest pH sensors to modern pH chemosensors over a century has passed.…”

Luminescence lifetime imaging of three-dimensional biological objects

“…1; Box 1). Advances in manufacturing exogenous phosphorescent and fluorescent dyes, proteins, bioconjugates and biosensors, as well as improved characterization of endogenous fluorescence features, have allowed for the luminescence-based sensing of a plethora of physiological processes, structural components and biomarkers, ranging from protein-protein interactions to tissue oxygenation (Table 1) (Berezin and Achilefu, 2010;Blacker and Duchen, 2016;Quaranta et al, 2012;Sarder et al, 2015;Steinegger et al, 2020;Datta et al, 2020;Dmitriev, 2013, 2018b;Conway et al, 2017;Rajoria et al, 2014).…”

“…);Tian et al (2012);Steinegger et al (2020). (2) pH-sensing enhanced cyan fluorescent protein (ECFP)(O'Donnell et al, 2018; Poëa-Guyon et al, 2013).…”

Incorporating Fluorescent Nanomaterials in Organically Modified Sol-Gel Materials – Creating Single Composite Optical pH Sensors

“…[1][2] Even so, disregarding colorimetric pH indicators, commercial pH sensors are mainly potentiometric pH meters that provide a linear electromotive force (EMF) response to pH obeying the Nernst equation. [2][3][4][5][6] There are clear advantages of optical sensors, [7][8][9][10][11][12] but complications regarding calibration: optical pH sensors report optical signals fitting to a sigmoidal curve where the response range depends on the pKa of the pH-sensitive dye, [13][14] and a limited stability of the sensor material have reduced their industrial applicability. [15][16][17] We have recently reported a new sensor material for optical sensors, 18 and the first high performance pH sensor using this matrix.…”