pH Detection Range Research Articles

A Mitochondria-Targeted Ratiometric Biosensor for pH Monitoring and Imaging in Living Cells with Congo-Red-Functionalized Dual-Emission Semiconducting Polymer Dots.

The accurate and sensitive monitoring and imaging of mitochondrial pH in living cells play vital roles in chemical biology and biomedicine. Herein, we design a novel ratiometric fluorescent chemical probe for monitoring and imaging the pH of mitochondria in living cells based on congo-red (CR)-modified dual-emission semiconducting polymer dots (Pdots) via a competitive fluorescence resonance energy transfer (FRET) mechanism. The Pdots are synthesized by triphenylphosphonium (TPP)-modified polyoxyethylene nonylphenylether (CO-520), poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), poly(9,9-dioctylfluorene)-co-(4,7-di-2-thienyl-2,1,3-benzothiadiazole) (PF-DBT5), and poly(styrene-co-maleic anhydride) (PSMA) via a nanoprecipitation method, and the prepared Pdots are further chemically linked with pH-sensitive, nonfluorescent CR to obtain the mitochondria-targeted pH fluorescent probes. This Pdots-based probe consists of two luminescent components including PFO and PF-DBT5 as fluorescence donors, an acid-base indicator CR as an energy acceptor, and TPP as the mitochondria-targeting group. At a different pH region, the FRET efficiency between CR and PFO or CR and PF-DBT5 can be modulated. This probe exhibits good biocompatibility, a wide pH detection range from 2.57 to 8.96, good reversibility, high selectivity, and excellent photostability for pH monitoring. This probe allows for the detecting and imaging of mitochondrial pH in living cells with satisfactory results.

A generalized ratiometric chemical exchange saturation transfer (CEST) MRI approach for mapping renal pH using iopamidol.

To extend the pH detection range of iopamidol-based ratiometric chemical exchange saturation transfer (CEST) MRI at sub-high magnetic field and establish quantitative renal pH MRI. Chemical exchange saturation transfer imaging was performed on iopamidol phantoms with pH of 5.5 to 8.0 and in vivo on rat kidneys (n = 5) during iopamidol administration at a 4.7 T. Iopamidol CEST effects were described using a multipool Lorentzian model. A generalized ratiometric analysis was conducted by ratioing resolved iopamidol CEST effects at 4.3 and 5.5 ppm obtained under 1.0 and 2.0 µT, respectively. The pH detection range was established for both the standard ratiometric analysis and the proposed resolved approach. Renal pH was mapped in vivo with regional pH assessed by one-way analysis of variance. Good-fitting performance was observed in multipool Lorentzian resolving of CEST effects (R2 s > 0.99). The proposed approach extends the in vitro pH detection range to 5.5 to 7.5 at 4.7 T. In vivo renal pH was measured to be 7.0 ± 0.1, 6.8 ± 0.1, and 6.5 ± 0.2 for cortex, medulla and calyx, respectively (P < 0.05). The proposed ratiometric approach extended the iopamidol pH detection range, enabling the renal pH mapping in vivo, which is promising for pH imaging studies at sub-high or low fields with potential clinical applicability. Magn Reson Med 79:1553-1558, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Lanthanide coordination polymer probe for time-gated luminescence sensing of pH in undiluted human serum

Lanthanide coordination polymers (LCPs) have emerged as fascinating materials because of their specific structure and properties. In this work, utilizing hydrosoluble biomolecule of guanosine-5′-monophosphate (GMP) as bridging linker, lanthanide terbium ions (Tb3+) as metal nodes, and silver ions (Ag+) as sensitizers, we synthesized a pH responsive luminescent lanthanide CP probe of Tb/GMP/Ag. The probe possesses high luminescence due to the sensitization of Ag+; While in alkaline solutions, Ag+ in Tb/GMP/Ag immediately binds to OH−, forming Ag2O precipitation and resulting in a distinct fluorescence quenching of Tb/GMP/Ag. This probe displays high selectivity for OH− and a broader pH detection range of 7.5–13.0. In addition, based on the high anti-interference ability in serum, we applied Tb/GMP/Ag to measure pH in undiluted human serum samples, yielding satisfactory results.

Development of an ‘OFF-ON-OFF’ fluorescent pH sensor suitable for the study of intracellular pH

Changes of pH in living organisms are closely related to various physiological functions, so fluorescent sensors of pH would be useful as experimental tools and possibly also for medical diagnosis. We previously reported a pH sensor with ‘OFF-ON-OFF’ -type fluorescence change, which would be potentially more useful than conventional sensors with ‘OFF-ON’ type change. It can be utilized as a sensor for a specific range of pH, however, the range with strong fluorescence is relatively wide, around pH 7–10, which renders it impractical for use in biological studies. So in the present work, we adjusted the pH detection range by the introduction of chloro groups at the ortho-positions to the phenolic hydroxyl groups, whose deprotonation could control fluorescence change, and obtained a sensor specifically responsive to pH around 6. This sensor was confirmed to be suitable for fluorescence imaging of changes of intracellular pH in living cells.

A simple rhodamine hydrazide-based turn-on fluorescent probe for HOCl detection.

Hypochlorous acid (HOCl) plays a crucial role in daily life and mediates a variety of physiological processes, however, abnormal levels of HOCl have been associated with numerous human diseases. It is therefore of significant interest to establish a simple, selective, rapid and sensitive fluorogenic method for the detection of HOCl in environmental and biological samples. A hydrazide-containing fluorescent probe based on a rhodamine scaffold was facilely developed that could selectively detect HOCl over other biologically relevant reactive oxygen species, reactive nitrogen species and most common metal ions in vitro. Via an irreversible oxidation-hydrolysis mechanism, and upon HOCl-triggered opening of the intramolecular spirocyclic ring during detection, the rhodamine hydrazide-based probe exhibited large fluorescence enhancement in the emission spectra with a fast response, low detection limit and comparatively wide pH detection range in aqueous media. The probe was further successfully applied to monitoring trace HOCl in tap water and imaging both exogenous and endogenous HOCl within living cells. It is anticipated that this simple and useful probe might be an efficient tool with which to facilitate more HOCl-related chemical and biological research. Copyright © 2015 John Wiley & Sons, Ltd.

Autonomous reagent-based microfluidic pH sensor platform

A portable sensor has been developed for in situ measurements of pH within aqueous environments.The sensor design incorporates microfluidic technology, allowing for the use of low volume of samples and reagents, and an integrated low cost detection system that uses a light emitting diode as light source and a photodiode as the detector. Different combination of dyes has been studied in order to allow for a broader pH detection range, than can be obtained using a single dye. The optimum pH range for this particular dye combination was found to be between pH 4 and pH 9.The reagents developed for pH measurement were first tested using bench-top instrumentation and once optimised, the selected formulation was then implemented in the microfluidic system.The prototype system has been characterised in terms of pH response, linear range, reproducibility and stability. Results obtained using the prototype system are in good agreement with those obtained using reference instrumentation, i.e. a glass electrode/pH meter and analysis via spectrophotometer based assays.The reagent (mixture #3) is shown to be stable for over 8 months, which is important for long term deployments. A high reproducibility is reported with a global RSD of ≤1.8% across measurements of 90 samples, i.e. with respect to concentrations reported by a calibrated pH meter.A series of real water samples from multiple sources were also analysed using the portable sensor system, of which the global error found was 3.84% showing its feasibility for real-world applications.

A dual channel optical detector for trace water chemodosimetry and imaging of live cells

A novel 3-5-dichlorosalicylaldehyde Schiff base chemodosimeter (compound 1) for water is designed and synthesized, and it works based on a water-triggered reaction of a Schiff base. Addition of trace amounts of water into 1 in various organic solvents leads to a fluorescence turn-on response and a simultaneous dual-channel signal modulation (both in the fluorescence and absorption spectra). Especially, 1 is found to be an outstanding fluorescence enhancement water sensor in methanol with an extremely low detection limit of 22 ppm. Consequently this probe can be utilized to detect trace water in commercial methanol. The quantitative detection of a wide range of water content is enhanced in THF and acetonitrile (0-35% v/v for THF and 0-20% v/v for acetonitrile), where the fluorescence peak intensity is nearly proportional to the amount of water added. Moreover, 1 can be used for monitoring pH through a novel ON-OFF-ON type signal modulation both in fluorescence and absorption spectra within a wide pH detection range. Thus, the chemodosimeter can not only be utilized to monitor the intracellular pH fluctuations, but also to accomplish simultaneous in situ staining of the cytosol and acidic organelles in two different channels, respectively.