Ratiometric Fluorescent pH Research Articles

Ratiometric Fluorescent pH Sensing with Carbon Dots: Fluorescence Mapping across pH Levels for Potential Underwater Applications.

Ocean acidification has become a major climate change concern requiring continuous observation. Additionally, in the industry, pH surveillance is of great importance. Consequently, there is a pressing demand to develop robust and inexpensive pH sensors. Ratiometric fluorescence pH sensing stands out as a promising concept. The application of carbon dots in fluorescent sensing presents a compelling avenue for the advancement of pH-sensing solutions. This potential is underpinned by the affordability of carbon dots, their straightforward manufacturing process, low toxicity, and minimal susceptibility to photobleaching. Thus, investigating novel carbon dots is essential to identify optimal pH-sensitive candidates. In this study, five carbon dots were synthesized through a simple solvothermal treatment, and their fluorescence was examined as a function of pH within the range of 5-9, across an excitation range of 200-550 nm and an emission range of 250-750 nm. The resulting optical features showed that all five carbon dots exhibited pH sensitivity in both the UV and visible regions. One type of carbon dot, synthesized from m-phenylenediamine, displayed ratiometric properties at four excitation wavelengths, with the best results observed when excited in the visible spectrum at 475 nm. Indeed, these carbon dots exhibited good linearity over pH values of 6-9 in aqueous Carmody buffer solution by calculating the ratio of the green emission band at 525 nm to the orange one at 630 nm (I525nm/I630nm), demonstrating highly suitable properties for ratiometric sensing.

Mechanism study of Dual-Emission ratiometric fluorescent pH-Sensitive carbon quantum dots and its application on mornitoring enzymatic catalysis

Carbon dots (CQD) have received significant attention as a novel ratiometric fluorescent pH nanoprobe, owing to their favorable optical properties and excellent biocompatibility. Despite their appealing features, the precise mechanism behind the pH-sensitive photoluminescence of CQDs remains to be fully understood. This study endeavors to unravel the mechanism underlying the pH-responsive ratiometric fluorescence in dual-emission CQDs, synthesized through a one-step hydrothermal method using o-phenylenediamine and oxalic acid as precursors. The resultant CQDs exhibit inherent dual-emission at wavelengths of 383 nm and 566 nm, with the ratiometric fluorescence response tailored by the ratio of precursors, providing a robust tool for pH sensing across a range of 2 to 6. Detailed characterizations, including chemical, morphological, and optical analyses, alongside theoretical insights from time-dependent density functional theory (TD-DFT), elucidate the mechanism underlying the pH-dependent luminescence, attributed to the electron cloud transmission between amide and adjacent carboxyl groups on the CQD surface. The superior performance of these CQDs in real-time pH monitoring is demonstrated through their application in glucose oxidase-catalyzed reactions, showcasing their potential as efficient, reliable nanoprobes for biomedical research and diagnostic applications.

Boron Complexes with Propiolamidinato Ligands: Synthesis, Structure, and Photophysical Properties.

Two series of boron derivatives with propiolamidinato ligands, [BPh2{C(C≡CAr)(NR)2}] (Ar = Ph, p-MeOPh, p-FPh, p-Me2NPh, or phen; R = iPr or p-tolyl), were synthesized and structurally characterized. The corresponding propiolamidine (or propargylamidine) proligands have been obtained through sustainable methods. One is the catalytic hydroalkynylation of diisopropylcarbodiimide with different terminal alkynes, using simple ZnEt2 as a precatalyst. Alternatively, to obtain propiolamidines with aromatic groups on the nitrogen atoms, the formation of lithiated derivatives of terminal alkynes by reaction with n-BuLi in air and at room temperature, and subsequent addition to the di-p-tolylcarbodiimide, under the same conditions and using 2-MeTHF as a sustainable solvent, has been used for the first time. After reaction with BPh3, the corresponding boron amidinates were obtained, which are emissive in the solution state. The influence of the different substituents introduced into the ligands on the photophysical properties of the boron compounds has been studied. One of the obtained compounds can be used as a ratiometric fluorescent pH sensor in the acidic range.

Ratiometric fiber optic fluorescent pH sensor for hydroxide diffusion measurements in concrete

This article delineates the development of an advanced ratiometric pH optode designed for protracted monitoring of pH dynamics in cementitious materials—a crucial aspect of structural management. The optode features a dual-layer Hydromed™ D4 polymer pellet incorporating a pH-sensitive Naphth-AlkyneOMe fluorescent probe (pKa ≈ 12) and CdSe quantum dots as an internal reference. The polymer matrix, optimized with diamond powder and carbon black, enhances the signal while minimizing light artifacts. Demonstrating a robust response to pH fluctuations, the optode, utilizing ratiometric measurements, enables steadfast monitoring for up to 75 days.The experimental setup includes a Delrin® sample compartment housing a glass slide with the optode connected to an optical fiber via an SMA connector. HydroMed™ D4 films, forming the pH-sensitive layer, are deposited on the glass slide and secured. The optode configuration is fine-tuned to optimize signal intensity by reducing its length. For optode-detector coupling, a 1000 µm core diameter optical fiber links the optode, and a 405 nm LED illuminates the sensing film. The emission signal is collected through the optical fiber, and signals are processed using computer-controlled lock-in amplifiers.In the investigation of hydroxide ion diffusion through a concrete sample, the optode's efficacy was validated, aligning with pH electrode measurements. Addressing long-term stability, a degradation model uncovered leisurely kinetics with commendable stability. Slow degradation kinetics, with a reaction rate coefficient of 1.6 × 10⁻⁷ s⁻¹ and a half-life of 1180 h, exceeded expectations.This pH optode, showcasing an accurate and resilient response to pH variations within the 10 to 12.5 range, stands as a promising tool for monitoring pH dynamics in low-pH cementitious materials. The incorporation of a degradation model underscores fidelity over prolonged durations and offers a blueprint for enduring surveillance of concrete structures.

Albumin Hydrogel-Coated Mesoporous Silica Nanoparticle as a Carrier of Cationic Porphyrin and Ratiometric Fluorescence pH Sensor.

Here, we report that a mesoporous silica nanoparticle (MSN) coated with a fluoresceine-labeled bovine serum albumin (F-BSA) hydrogel layer works as a temperature-responsive nanocarrier for tetrakis-N-methylpyridyl porphyrin (TMPyP) and as a fluorescence ratiometric pH probe. F-BSA hydrogel-coated MSN containing TMPyP (F-BSA/MSN/TMPyP) was synthesized by thermal gelation of denatured F-BSA on the external surface of MSN. The F-BSA hydrogel layer was composed of an inner hard corona layer and an outer soft layer and was stable under physiological conditions. F-BSA/MSN/TMPyP exhibited temperature-dependent exponential release of TMPyP. In this release profile, the MSN was found to be a suitable host for stable encapsulation of tetracationic TMPyP by electrostatic interactions, and the F-BSA hydrogel layer mediated the diffusion of TMPyP from the MSN pore interior into the solution phase. Increasing temperature promoted partitioning of TMPyP from the pore interior to the F-BSA hydrogel layer, from where it was spontaneously released into the bulk solution phase by cation exchange. F-BSA/MSN/TMPyP also gave a linear ratiometric fluorescence response (1.3 per pH unit) in the pH range from 6.1 to 8.9.

Preparation of near-infrared photoacoustic imaging and photothermal treatment agent for cancer using a modifiable acid-triggered molecular platform.

Ratiometric near-infrared fluorescent pH probes with various pKa values were innovatively designed and synthesized based on cyanine with a diamine moiety. The photochemical properties of these probes were thoroughly evaluated. Among the series, IR-PHA exhibited an optimal pKa value of approximately 6.40, closely matching the pH of cancerous tissues. This feature is particularly valuable for real-time pH monitoring in both living cells and living mice. Moreover, when administered intravenously to tumor-bearing mice, IR-PHA demonstrated rapid and significant enhancement of near-infrared fluorescence and photoacoustic signals within the tumor region. This outcome underscores the probe's exceptional capability for dual-modal cancer imaging utilizing near-infrared fluorescence (NIRF) and photoacoustic (PA) modalities. Concurrently, the application of a continuous-wave near-infrared laser efficiently ablated cancer cells in vivo, attributed to the photothermal effect induced by IR-PHA. The results strongly indicate that IR-PHA is well-suited for NIRF/PA dual-modality imaging and photothermal therapy of tumors. This makes it a promising candidate for theranostic applications involving small molecules.

Preparation of a Novel Ratiometric Fluorescent Capillary-based pH Sensor

Preparation of a Novel Ratiometric Fluorescent Capillary-based pH Sensor

Carbon dots-based fluorescent films to act as a potential antioxidant agent and pH ratiometric sensor for skin applications

The wound healing process is accompanied by changes in pH values. Monitoring this physicochemical parameter can indicate the effectiveness of the applied treatment and act as early identification of wound infection. This study focuses on the development of a fluorescent film-based polyvinyl alcohol (PVA) and carbon dots (CDs) derived from lemon bagasse (CD-L) and ortho-phenylenediamine (CD-oPD) named to act as antioxidants and potential ratiometric fluorescent pH sensors, in wound applications. The I460/I550 intensity ratio, as a function of pH value for the dual-system CDs prepared from the mixture of CD-L and CD-oPD, named CD-L/oPD, was investigated. The fit corresponded to a sigmoidal function in the pH range of 5–10, with a relationship having a r2 = 0.992. The variation in the values of the I460/I550 ratio allows for the visualization of the color change from yellowish-green to green with increasing pH. Through a simulated ex vivo pig skin model, it was possible to note that the films prepared from mixed of the CD-L and CD-oPD carbon dots incorporated in a matrix PVA named CD-L/oPD-F was more efficient at visually discriminating color in relation to changes in pH than the films prepared from both individual CD-L (CD-L-F) and CD-oPD (CD-oPD-F) carbon dots. CD-L and CD-oPD demonstrated antioxidant capacity against reactive oxygen species (ROS). The IC50 values for CD-L and CD-oPD were 56.7 and 39.5 μg mL−1 in the DPPH● inhibition assay, and 25.1 and 63.4 μg mL−1 in the HOCl scavenging one, respectively. MTT viability assays using human non-tumoral skin fibroblast (HFF-1) cell showed a cell survival rate of over 80% for both CDs up to a concentration of 1,000 μg mL−1. Finally, the developed films can act in a bifunctional way, by monitoring healing through pH changes and by acting as an antioxidant agent in the treatment of wounds.

A Ratiometric Fluorescent Probe for pH Measurement over a Wide Range Composed of Three Types of Fluorophores Assembled on a DNA Scaffold

The desirable properties of the sophisticated fluorescent pH probe are ratiometric detection properties and a wide detection range. In this study, three types of fluorophores with different fluorescence properties were assembled on a DNA origami nanostructure. DNA nanostructure has the advantage of being a scaffold that can assemble different types of fluorophores with control over their number and position. The defined number of three different fluorophores, i.e., pH-sensitive fluorescein (CF) and Oregon Green (OG), and pH-insensitive tetramethylrhodamine (CR), assembled on the DNA scaffold provided a ratiometric fluorescent pH probe with a wide pH detection range that could cover the variation of intracellular pH.

Photoluminescent gold nanoclusters as two-photon excited ratiometric pH sensor and photoactivated peroxidase.

Atwo-photon excited ratiometric fluorescent pH sensor is reportedby combining L-cysteine-protected AuNCs (Cys@AuNCs) with fluorescein isothiocyanate (FITC). Cys@AuNCs were synthesized through a one-step self-reduction route and showed pH-responsive photoluminescence at 650 nm. Benefiting from the opposite pH response of Cys@AuNCs and FITC, the fluorescence ratio (F515 nm/F650 nm) of FITC&Cys@AuNCs provided a large dynamic range of 200-fold for pH measurement in the response interval of pH 5.0-8.0. Based on the excellent two-photon absorption coefficient of Cys@AuNCs, the sensor was expected to achieve sensitive quantitation of pH in living cells under two-photon excitation. In addition, colorimetric biosensing based on enzyme-like metal nanoclusters has attracted wide attention due to their low-cost, simplicity, and practicality. It is crucial to develop high catalytic activity nanozyme from the viewpoint of practical application. The synthesized Cys@AuNCs exhibited excellent photoactivated peroxidase-like activity with high substrate affinity and catalytic reaction rate, promising for rapid colorimetric biosensing of field analysis and the control of catalytic reactions by photostimulation.

High quantum-yield lignin fluorescence materials based on polymer confinement strategy and its application as a natural ratiometric pH sensor film

The high quantum-yield (QY) lignin fluorescence material at solid state was obtained via the polymer confinement strategy, using polyvinyl alcohol (PVA) as polymer matrix and organic solvent lignin (OL) as luminescent material. The absolute QY of lignin/PVA film could reach 13.68 % by optimizing the raw material of OL, of which was even higher than that in THF medium due to their hydrogen bond interaction for inhibiting aggregation and rigid environment for decreasing molecular rotation and vibration. In addition, under the encapsulation of PVA, the resistance of photobleaching of lignin fluorescence was also enhanced. Finally, OL was proved as a natural ratiometric fluorescence pH sensor from the electronegativity change of phenylpropane unit, and the fluorescence of lignin/PVA film showed a naked-eye recognition for spoiled pork detection. This work provided a new perspective to lignin fluorescence for really using as a feedstock for luminescent materials.

Acidic pH-Triggered Live-Cell Lysosome Specific Tracking, Ratiometric pH Sensing, and Multicolor Imaging by Visible to NIR Switchable Cy-7 Dyes.

We have demonstrated an efficient synthetic route with crystal structures for the construction of acidic pH-triggered visible-to-NIR interchangeable ratiometric fluorescent pH sensors. This bioresponsive probe exhibits pH-sensitive reversible absorption/emission features, low cytotoxicity, a huge 322 nm bathochromic spectral shift with augmented quantum yield from neutral to acidic pH, high sensitivity and selective targeting ability of live-cell lysosomes with ideal pKa , off-to-on narrow NIR absorption/fluorescence signals with high molar absorption coefficient at acidic lysosomal lumen, and in-situ live-cell pH-activated ratiometric imaging of lysosomal pH. Selective staining and ratiometric pH imaging in human carcinoma live-cell lysosomes were monitored by dual-channel confocal laser scanning microscope using a pH-activatable organic fluorescent dye comprising a morpholine moiety for lysosome targeting and an acidic pH openable oxazolidine ring. Moreover, real-time tracking of lysosomes, 3D, and multicolor live-cell imaging have been achieved using the synthesized pH-activatable probe.

Highly Photostable and pH−Sensitive Nanosensors

Determination of pH values has a vital influence in many chemical and biological processes. To accurately determine pH values, we fabricated a highly photostable ratiometric fluorescent pH−sensitive nanosensor by staining the core of mesoporous silica nanoparticle with a rhodol dye and chemically labelling its outer shell with a rhodamine derivative dye. The two dyes possess opposite pH−responding directions, which increases the band of the signal change. There is a nine−fold change in fluorescence intensity ratios when the solution pH changes from 3.0 and 9.0. Meanwhile, the nanosensors displayed yellowish emission in low pH value, orange emission in mid pH value, and reddish emission in high pH value, which can be readily inspected by bare eyes. Last but not least, excellent photostability and reversibility features make the nanosensors useful for the continuous measuring of pH with high accuracy.

Micellar Ratiometric Fluorescent Blood pH Probe Based on Triplet-Sensitized Upconversion and Energy-Transfer Behaviors.

The measurement of pH is greatly significant in monitoring physiological and biochemical states. In this work, a novel micellar ratiometric fluorescent probe featuring sophisticated energy-transfer (ET) behaviors with p-nitrophenol (PNP) as the energy acceptor and a triplet-triplet annihilation upconversion (TTA-UC) system as the energy donor was designed. The pH-induced molecular configuration of PNP determined the process for the transfer of energy from TTA-UC to PNP. The introduction of the TTA-UC system enabled probe excitation under a long wavelength and afforded a ratiometric signal for pH detection with excellent reliability over diverse interfering factors. This TTA-UC/ET pH probe demonstrated a high sensitivity to hydronium below nanomolar concentrations and an excellent anti-interference ability in serum samples, which provided a novel significant strategy for rapid and accurate detection of blood pH in vitro.

An AIE-Active probe for detection and bioimaging of pH values based on lactone hydrolysis reaction.

Cellular pH homeostasis is essential for many physiological and pathological processes. pH monitoring is helpful for the diagnosis, treatment and prevention of disorders and diseases. Herein, we developed a ratiometric fluorescent pH probe (TCC) based on a coumarin derivative containing a highly active lactone ring. TCC exhibited a typical AIE effect and emitted blue fluorescence under weak acidic condition. When under weak basic condition, the active lactone moiety underwent a hydrolysis reaction to afford a water-soluble product, which gave red-shifted emission. The emission color change from blue through cyan and then to yellow within pH 6.5-9.0 which is approximate to the biological pH range. And the fluorescence color change along with pH value is reversible. Furthermore, TCC was successfully utilized in the detection of the intracellular pH change of live HeLa cells, which indicated that TCC had practical potential in biomedical research.

Fluorescein isothiocyanate-doped conjugated polymer nanoparticles for two-photon ratiometric fluorescent imaging of intracellular pH fluctuations

Herein, we report a two-photon ratiometric fluorescent pH nanosensor based on conjugated polymer poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) nanoparticles loaded with pH-sensitive fluorescein isothiocyanate (FITC) for intracellular pH monitoring. The obtained nanosensor (FITC-PFO NPs) possesses high sensitivity, excellent stability, good reversibility, favorable two-photon excitability and low cytotoxicity. The ratiometric fluorescence of FITC and PFO (F517/F417) in FITC-PFO NPs solution shows an efficient pH-sensitive response over the pH range from 3 to 10 (pKa = 6.43) under two-photon excitation. Additionally, the FITC-PFO NPs is successfully applied for ratiometric imaging of intracellular pH and its fluctuation in both one-photon and two-photon excitation modes. Overall, the two-photon pH nanosensor based on FITC-PFO NPs exhibits great potential in crucial physiological and biological processes related to intracellular pH fluctuations.

An FRET-ICT-based ratiometric fluorescent and colorimetric probe for pH monitoring in lysosomes and water

A novel FRET-ICT-based ratiometric fluorescent and colorimetric pH probe (BDMNP) was developed. BDMNP exhibited 96% energy transfer efficiency and good linear response in the pH ranges of 5.4–6.8 (pKa = 6.10) with high selectivity and sensitivity. BDMNP has been successfully applied to monitor lysosomal pH changes in living cells. Meanwhile, BDMNP can also be used to detect the subtle pH changes of a variety of environmental water samples.

Developed a ratiometric fluorescence pH nanosensor based on label-free carbon dots for intracellular lysosome imaging and water pH monitoring with a smartphone

It is necessary to measure lysosomal pH in living cells in order to maintain the normal performance of cell functions. Herein, a novel ratiometric fluorescence nanosensor based on carbon dots for lysosomal pH sensing was successfully developed via one-pot solvothermal means. The CDs have two pH-dependent emission wavelengths locating at 415 and 555 nm with distinct fluorescence color change switching between blue and yellow from pH 3.0 to 8.0. Due to its plentiful amino groups on the surface, the probe is lysosome-targeted. It is demonstrated that intensity ratios (F555/F415) against pH = 3.0–8.0 are fitted with the Boltzmann equation with a pKa of 5.47 matched well with lysosomal pH. Because of the merits of great pH sensitivity, selectivity, biocompatibility and photostability, the probe was successfully applied for lysosomal pH detection during cells imaging. Besides, CDs were further used for acidic and neutral water pH sensing by a smartphone in a fast and expedient way.

New properties of carbon nanomaterials through zinc doping and application as a ratiometric fluorescence pH sensor

Fluorescence intensity of carbon nanomaterials (CNMs) synthesized with ethanolamine hardly changed with pH value. Doping Zinc into CNMs improved optical properties of CNMs. On the one hand, the fluorescence quantum yield of CNMs increased, on the other hand, the fluorescence intensity of Zn-doped CNMs decreased with pH value. Coupling Zn-doped CNMs with ZnCdS quantum dots (QDs) as a dual emission system, the blue fluorescence intensity of CNMs (I450) decreased while the orange fluorescence intensity of QDs (I580) enhanced with pH value increasing. The ratio (I450/I580) varied linearly with pH value in the range of 1–9 and correlation coefficient (R2) was 0.991. Furthermore, using the system as a ratiometric fluorescence pH sensor to determine ascorbic acid, a good linear relationship (R2 = 0.998) was found when the concentration of ascorbic acid ranged from 0–1600 μM and limit of detection (LOD) was as low as 0.082 μM.

Evaluating visually a new apoptosis-induced reagent by a ratiometric two-photon fluorescent pH probe

The level of apoptosis is directly related to the occurrence of cancer and other diseases. Real-time continuous monitoring of apoptotic process of living cells has great potential for early diagnosis of related diseases, as well as evaluation of therapeutic effect and screening of apoptotic drugs. This work proposed a ratiometric two-photon fluorescent probe Lyso-PCE equipped with a dual-function pyridine, as a pH-sensitive and specific lysosome-targeted group. A clear linearity relationship between two-channel fluorescence intensity ratios of Lyso-PCE and pH values was established in both solutions and living cells. Thanks to its ability of quantitative detection of pH, probe Lyso-PCE can detect the dynamic pH changes of lysosomes treated by chloroquine, and also can be used to in situ monitor dexamethasone-induced apoptosis. More importantly, reagent potassium bisperoxo (1,10-phenanthroline) oxovanadate (bpV(phen)) was evaluated and testified as a new apoptotic drug by Lyso-PCE, and the real-time visualization of bpV(phen)-induced apoptosis was realized under two-photon excitation. Our results provide a new and promising strategy for evaluating and screening apoptosis-related drugs.