A camphor-based Schiff base fluorescent probe for detection of alkaline pH and its applications in living cells

Alkaline range pH sensor based on chitosan hydrogel: A novel approach to pH sensing

Monitoring of pH under extreme alkaline range is still a challenge due to the lack of accuracy and validity. This research developed a novel pH sensor (hydrogel/BTB) based on the transition of bromothymol blue from the hydrogel matrix into the pH-examining sample solution. The hydrogel/BTB sensor was synthesized through the solvent casting of chitosan, citric acid as the crosslinker, and bromothymol blue as a pH-sensitive dye. The structure of hydrogel/BTB was characterized using Fourier-transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS), Field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) analysis, and thermogravimetric analysis (TGA). The effect of various parameters on pH determination was investigated. The developed pH sensor demonstrated a linear detection range validated from pH 10 to 14 using the gravimetric method, and from pH 11 to 14 using the colorimetric method. The sensor successfully detected pH in alkaline tap water, carbonate buffer, and ethanol amine buffer. The transition of bromothymol blue is described by the Peppas-Korsmeyer kinetic model. The activation and Gibbs free energy were obtained as 357.1 J/mol and 260 J/mol, respectively. This work furnished a new mechanism for pH detection, and it has excellent potential for developing novel sensors in this field.

Synthesis, optical properties, and application of novel chalcone skeleton as pH fluorescent probe: Based AIE + ESIPT strategy

A series of "turn off" pH fluorescence probes with chalcone skeleton for basic system have been developed. The molecules emitted bright yellow fluorescence under acidic condition, resulting AIE coupled ESIPT characteristic and ICT process. What's more, the compounds exhibited excellent sensitivity and selectivity for detecting pH as a facile "On-Off" fluorescence probe, and the fluorescence of them were quenched with the ESIPT process interrupted under alkaline condition. Theoretical calculation for the related compounds also performed to verify the electron effect on photophysical properties and confirm the rational speculation on the mechanism.

A novel ratiometric fluorescent sensor from modified coumarin-grafted cellulose for precise pH detection in strongly alkaline conditions

Accurate and convenient monitoring of pH under extreme alkaline conditions is still a challenge. In this work, 4-(3-(7-hydroxy-2-oxo-2H-chromen-3-yl)-3-oxoprop-1-en-1-yl)benzamide (HCB), a coumarin derivative, was grafted onto dialdehyde cellulose (DAC) to obtain a sensor DAC-HCB, which exhibited a ratiometric fluorescent response to the pH of alkaline solutions, resulting in a significant fluorescent color change from yellow to blue (FI459 nm/FI577 nm) at pH 7.5-14. The structure of DAC-HCB was characterized through FT-IR, XRD, XPS, SEM. The pKa of sensor DAC-HCB was 13.16, and the fluorescent intensity ratio FI459 nm/FI577 nm possessed an excellent linear characteristic with pH in the scope of 9.0-13.0. Meanwhile, sensor DAC-HCB showed good selectivity, anti-interference, and fast response time to basic pH, which is an effective fluorescent sensor for examination of pH in alkali circumstance. The recognition mechanism of DAC-HCB to OH- was elucidated with HRMS and density-functional theory (DFT) computational analyses. Sensor DAC-HCB was successfully used for precise detection of environmental water samples pH. This work furnished a new protocol for test strips as a convenient and highly efficient pH detection tool for the high pH environment, and it has great potential for application in environmental monitoring.

Turn-On Fluorescent pH Probes for Monitoring Alkaline pHs Using Bis[2-(2'-hydroxyphenyl)benzazole] Derivatives

For surveilling human health, industries, and the environment, pH monitoring is important. Numerous studies on fluorescent probes have been conducted to monitor various pH ranges. However, fluorescent probes that are capable of sensing alkaline regions are rare. In this study, we propose turn-on-type fluorescent probes for detecting alkaline pHs using bis[2-(2'-hydroxyphenyl)benzazole] (bis(HBX)) derivatives. These probes have high pK_a values (from 9.7 to 10.8) and exhibit strong fluorescence intensity and color changes at alkaline pHs. Probes derived from bis(HBX) exhibit good photostability, reversibility, and anti-interference toward pH variations, which can be identified as a certain fluorescence change toward a basic pH. Therefore, compounds would be advantageous to use fluorescent probes for monitoring alkaline pH changes.

Schiff base compounds as fluorimetric pH sensor: a review

With the recent progress of biological and environmental research, detection of pH values has become one of the most indispensable requirements. To determine the pH values of a certain medium, organic Schiff base compounds and their derivatives have been observed to play pivotal roles because of their smooth synthetic roots, easily tuneable structural architecture, non-destructive signals of emission, visually differentiable colour generation and capability of real sample analysis. Therefore with the revolutionary upgradation of wavelength radiometric techniques, the construction of molecular structures which can exhibit dual emission and absorption characteristics and which can be regulated by the change in pH values, has been a stimulating challenge. Generally a pH sensor molecule has a chromophoric or fluorophoric portion. Normally heteroatoms attached to these chromophore units either get protonated or deprotonated in acidic or basic media which gives rise to changes in absorption and emission properties of the molecule.