Detection Of pH Changes Research Articles

Polyadenosine-based fluorescent probe for reversible pH sensing based on protonated adenine-adenine base pairs: Applications to sensing of enzyme-substrate system and enzymatic logic gates

Numerous DNA-based sensors have been developed for colorimetric, fluorescent, and electrochemical detection of pH changes in an aqueous solution. However, few studies have explored the use of polyadenosine-based sensors for probing pH changes based on protonated adenine–adenine (AH+–H+A) base pairs. This study presents a fast, simple, sensitive assay for fluorescent detection of a small pH variation in an enzymatic reaction based on controlling the conformation of the polyadenosine-based probe. The DNA-based pH probe consists of a 20-mer adenosine base (A20), a Cy3 fluorophore at the 5′-end, and a BHQ2 quencher at the 3′-end. At a low DNA concentration, lowering pH activates the Cy3-A20-BHQ2 probe to fold back on itself through the formation of AH+–H+A base pairs. A short intramolecular double-stranded region is then formed in a single-stranded A20 probe. As a result, Cy3 is located close to BHQ2, leading to fluorescence quenching of Cy3 by fluorescence resonance energy transfer. The Cy3-A20-BHQ2 probe was well-suited to reversibly probe a 0.2-pH unit change in the pH range of 3.4–6. Additionally, the pH-induced conformation change of A20 allowed the Cy3-A20-BHQ2 probe to detect a slight pH fluctuation in the enzymatic reaction and construct NAND and NOR logic gates using two enzymes as inputs.

A two-photon fluorescent probe records the intracellular pH through ‘OR’ logic operation via internal calibration

Mapping the intracellular location and concentration of hydronium ions (H3O+) and their dynamics could be a useful diagnostic tool in modern clinical science. Current needs motivated us to develop a molecular pH probe 1, operating as a logic gate, and its analogue 2. The pyridyl moiety in 1 played a significant role in proton capture and release, in acidic to alkaline pH environments. In contrast, 2 failed to show a similar spectroscopic behavior. 1 shows emission maximum at 450 nm that is independent on the pH, with excitation at 353 nm or 410 nm in acid and alkaline pH, respectively. 1 was employed to provide input-dependent (excitation wavelength) fluorescence images in a cellular milieu to detect pH changes in cellular organelles such as lysosomes and mitochondria. Furthermore, 1 provided information on the variation of the pH in the presence of cellular ROS. 1 was also found to enable the real-time monitoring of cell acidification due to nutrient starvation, which is closely associated with mitochondrial malfunction, fusion and mitophagy processes. We envision that in due course 1 can open up new research avenues in the diagnostic sector for validating the pH in the cellular milieu.

Ratiometric Near-Infrared Fluorescent Probes Based On Through-Bond Energy Transfer and π-Conjugation Modulation between Tetraphenylethene and Hemicyanine Moieties for Sensitive Detection of pH Changes in Live Cells.

In this paper, we present three ratiometric near-infrared fluorescent probes (A-C) for accurate, ratiometric detection of intracellular pH changes in live cells. Probe A consists of a tetraphenylethene (TPE) donor and near-infrared hemicyanine acceptor in a through-bond energy transfer (TBET) strategy, while probes B and C are composed of TPE and hemicyanine moieties through single and double sp2 carbon-carbon bond connections in a π-conjugation modulation strategy. The specific targeting of the probes to lysosomes in live cells was achieved by introducing morpholine residues to the hemicyanine moieties to form closed spirolactam ring structures. Probe A shows aggregation-induced emission (AIE) property at neutral or basic pH, while probes B and C lack AIE properties. At basic or neutral pH, the probes only show fluorescence of TPE moieties with closed spirolactam forms of hemicyanine moieties, and effectively avoid blind fluorescence imaging spots, an issue which typical intensity-based pH fluorescent probes encounter. Three probes show ratiometric fluorescence responses to pH changes from 7.0 to 3.0 with TPE fluorescence decreases and hemicyanine fluorescence increases, because acidic pH makes the spirolactam rings open to enhance π-conjugation of hemicyanine moieties. However, probe A shows much more sensitive ratiometric fluorescence responses to pH changes from 7.0 to 3.0 with remarkable ratio increase of TPE fluorescence to hemicyanine fluorescence up to 238-fold than probes B and C because of its high efficiency of energy transfer from TPE donor to the hemicyanine acceptor in the TBET strategy. The probe offers dual Stokes shifts with a large pseudo-Stokes shift of 361 nm and well-defined dual emissions, and allows for colocalization of the imaging readouts of visible and near-infrared fluorescence channels to achieve more precisely double-checked ratiometric fluorescence imaging. These platforms could be employed to develop a variety of novel ratiometric fluorescent probes for accurate detection of different analytes in applications of chemical and biological sensing, imaging, and diagnostics by introducing appropriate sensing ligands to hemicyanine moieties to form on-off spirolactam switches.

50O - A first-in-human first-in-class (FIC) trial of the monocarboxylate transporter 1 (MCT1) inhibitor AZD3965 in patients with advanced solid tumours

2516Background: A key metabolic alteration in tumour cells is an increased dependency on the glycolysis, resulting in the production of lactate, which is transported out of cells by MCTs. Inhibition of MCT-1 leads to a profound inhibition of cancer cell growth in preclinical models. AZD3965 is a FIC inhibitor of MCT-1, and we report results from the phase I study of this agent. Methods: Patients with advanced solid tumours were treated with oral (po) AZD3965 at total daily doses of 5-30mg given once (od) and twice daily (bd). Exclusion criteria included a history of retinal or cardiac disease due to preclinical toxicology findings in the eye and heart (which express MCT-1). The primary objectives were to determine the safety, dose limiting toxicities (DLT) and maximum tolerated dose (MTD) of AZD3965. Intensive pharmacokinetic (PK) profiling was performed with subsequent modelling for receptor occupancy. Pharmacodynamic profiling included imaging to detect pH changes and tumour glucose uptake; plasma/urine...

Fluorescent probes based on π-conjugation modulation between hemicyanine and coumarin moieties for ratiometric detection of pH changes in live cells with visible and near-infrared channels

We report two ratiometric fluorescent probes based on π-conjugation modulation between coumarin and hemicyanine moieties for sensitive ratiometric detection of pH alterations in live cells by monitoring visible and near-infrared fluorescence changes. In a π-conjugation modulation strategy, a coumarin dye was conjugated to a near-infrared hemicyanine dye via a vinyl connection while lysosome-targeting morpholine ligand and o-phenylenediamine residue were introduced to the hemicyanine moieties to form closed spirolactam ring structures in probes A and B, respectively. The probes show only visible fluorescence of the coumarin moiety under physiological and basic conditions because the hemicyanine moieties retain their closed spirolactam ring structures. However, decrease of pH to acidic condition causes spirolactam ring opening, and significantly enhances π-conjugation within the probes, thus generating new near-infrared fluorescence peaks of the hemicyanine at 755 nm and 740 nm for probes A and B, respectively. Moreover, the probes display ratiometric fluorescence response to pH with decreases of the coumarin fluorescence and increases of the hemicyanine fluorescence when pH changes from 7.4 to 2.5. The probes are fully capable of imaging pH changes in live cells with good ratiometric responses in visible and near-infrared channels, and effectively avoid fluorescence blind spots under neutral and basic pH conditions – an issue that typical intensity-based pH fluorescent probes run into. The probe design platform reported herein can be easily applied to prepare a variety of ratiometric fluorescent probes for detection of biological thiols, metal ions, reactive oxygen and nitrogen species by introducing appropriate functional groups to hemicyanine moiety.

Spin-lock imaging of early tissue pH changes in ischemic rat brain.

We have previously reported that the dispersion of spin-lattice relaxation rates in the rotating frame (R1ρ ) of tissue water protons at high field can be dominated by chemical exchange contributions. Ischemia in brain causes changes in tissue pH, which in turn may affect proton exchange rates. Amide proton transfer (APT, a form of chemical exchange saturation transfer) has been shown to be sensitive to chemical exchange rates and able to detect pH changes non-invasively following ischemic stroke. However, the specificity of APT to pH changes is decreased because of the influence of several other factors that affect magnetization transfer. R1ρ is less influenced by such confounding factors and thus may be more specific for detecting variations in pH. Here, we applied a spin-locking sequence to detect ischemic stroke in animal models. Although R1ρ images acquired with a single spin-locking amplitude (ω1 ) have previously been used to assess stroke, here we use ΔR1ρ , which is the difference in R1ρ values acquired with two different locking fields to emphasize selectively the contribution of chemical exchange effects. Numerical simulations with different exchange rates and measurements of tissue homogenates with different pH were performed to evaluate the specificity of ΔR1ρ to detect tissue acidosis. Spin-lock and APT data were acquired on five rat brains after ischemic strokes induced via middle cerebral artery occlusions. Correlations between these data were analyzed at different time points after the onset of stroke. The results show that ΔR1ρ (but not R1ρ acquired with a single ω1 ) was significantly correlated with APT metrics consistent with ΔR1ρ varying with pH.

A cyanine-based fluorescent cassette with aggregation-induced emission for sensitive detection of pH changes in live cells.

An aggregation-induced emission (AIE) cyanine-based fluorescent cassette with a large pseudo-Stokes shift was designed and prepared to sensitively image pH changes in live cells via through-bond energy transfer (TBET) from a tetraphenylethene (TPE) donor to a cyanine acceptor.

Surface enhanced Raman spectroscopy measurement of surface pH at the electrode during Ni electrodeposition reaction

In this work, we developed a precise approach to analyze local proton concentration at the solid/liquid interface of electrodes, i.e. “surface pH”, during electrochemical reactions. For this, surface enhanced Raman spectroscopy (SERS) was applied to analyze pH-dependent structural changes of the –COOH group of p-mercaptobenzoic acid (p-MBA) modified onto Au nanoparticles (NPs) on the substrate close to a working electrode. Measurements using this system identified deprotonation of –COOH of p-MBA. Since preliminary experiments and density functional theory calculations suggest that the pKa of p-MBA attached to Au NPs is close to that in bulk solution, the SERS results indicate pH increase due to proton consumption by the cathodic overpotential of the working electrode. As an example, we applied this system to surface pH monitoring in electrodeposition process of Ni in an acidic bath, which indicated the validity of our method for precise detection of pH changes at electrode interfaces in situ.

Luminescent Probes for Sensitive Detection of pH Changes in Live Cells through Two Near-Infrared Luminescence Channels.

Two water-soluble near-infrared luminescent probes, which possess both conventional intense Stokes fluorescence and unique single-photon frequency upconversion luminescence (FUCL), were developed for sensitive and selective detection of pH changes in live cells. The water solubility and biocompatibility of these probes were achieved by introducing mannose residues through 2,2'-(ethylenedioxy)diethylamine tethered spacers to a near-infrared conventional fluorescence (CF) and FUCL organic fluorophore. At a pH higher than 7.4, the probes have ring-closed spirocyclic lactam structures, thus are colorless and nonfluorescent. Nevertheless, they sensitively respond to acidic pH values, with a drastic structural change to ring-opened spirocyclic lactam forms, which cause significant absorbance increases at 714 nm. Correspondingly, their near-infrared CF and FUCL intensities at 740 nm are also significantly enhanced when excited by 690 and 808 nm, respectively. The probes hold a variety of advantages such as high sensitivity, excellent reversibility and selectivity to pH over metal ions, low cellular autofluorescence background interference, good cell membrane permeability and photostability, as well as low cytotoxicity. Our results have successfully proven that these probes can visualize intracellular lysosomal pH changes in live cells by monitoring both near-infrared CF and FUCL changes.

In Vivo Indicators of Cytoplasmic, Vacuolar, and Extracellular pH Using pHluorin2 in Candida albicans.

Environmental or chemically induced stresses often trigger physiological responses that regulate intracellular pH. As such, the capacity to detect pH changes in real time and within live cells is of fundamental importance to essentially all aspects of biology. In this respect, pHluorin, a pH-sensitive variant of green fluorescent protein, has provided an invaluable tool to detect such responses. Here, we report the adaptation of pHluorin2 (PHL2), a substantially brighter variant of pHluorin, for use with the human fungal pathogen Candida albicans. As well as a cytoplasmic PHL2 indicator, we describe a version that specifically localizes within the fungal vacuole, an acidified subcellular compartment with important functions in nutrient storage and pH homeostasis. In addition, by means of a glycophosphatidylinositol-anchored PHL2-fusion protein, we generated a cell surface pH sensor. We demonstrated the utility of these tools in several applications, including accurate intracellular and extracellular pH measurements in individual cells via flow cytometry and in cell populations via a convenient plate reader-based protocol. The PHL2 tools can also be used for endpoint as well as time course experiments and to conduct chemical screens to identify drugs that alter normal pH homeostasis. These tools enable observation of the highly dynamic intracellular pH shifts that occur throughout the fungal growth cycle, as well as in response to various chemical treatments. IMPORTANCECandida albicans is an opportunistic fungal pathogen that colonizes the reproductive and gastrointestinal tracts of its human host. It can also invade the bloodstream and deeper organs of immunosuppressed individuals, and thus it encounters enormous variations in external pH in vivo. Accordingly, survival within such diverse niches necessitates robust adaptive responses to regulate intracellular pH. However, the impact of antifungal drugs upon these adaptive responses, and on intracellular pH in general, is not well characterized. Furthermore, the tools and methods currently available to directly monitor intracellular pH in C.albicans, as well as other fungal pathogens, have significant limitations. To address these issues, we developed a new and improved set of pH sensors based on the pH-responsive fluorescent protein pHluorin. This includes a cytoplasmic sensor, a probe that localizes inside the fungal vacuole (an acidified compartment that plays a central role in intracellular pH homeostasis), and a cell surface probe that can detect changes in extracellular pH. These tools can be used to monitor pH within single C.albicans cells or in cell populations in real time through convenient and high-throughput assays.

Robust and low cytotoxic betaine-based colorimetric pH sensors suitable for cancer cell discrimination

The local pH level in tumor microenvironment usually turns to an acidic range of 5.5-7.0 from the healthy level of 7.4. For this pH change, robust sensors with high sensitivity, water solubility and biocompatibility are highly desirable. Herein, novel zwitterionic betaines were designed and synthesized for the first time as sensitively colorimetric pH sensors which featured low cytotoxicity, excellent water solubility and reversibility. When the solution pH was changed from 5.0 to 7.2, new absorption bands appeared with gradually increased absorbance and were accompanied by naked-eye-visible color changes from yellow to green, indicating a new approach to detect pH changes by a simple ratiometric method. Moreover, these zwitterionic betaine sensors showed promising applications for biological and pathological samples due to their low cytotoxicity. In the pathological samples of prostate cancer cell extract solutions, they displayed sensitively colorimetric responses and strong anti-interference ability to pH changes. Therefore, it is promising for them to be as colorimetric indicators to pH changes in pathological samples for diagnostic and targeted therapeutic purposes.

A first-in-human first-in-class (FIC) trial of the monocarboxylate transporter 1 (MCT1) inhibitor AZD3965 in patients with advanced solid tumours.

2516 Background: A key metabolic alteration in tumour cells is an increased dependency on the glycolysis, resulting in the production of lactate, which is transported out of cells by MCTs. Inhibition of MCT-1 leads to a profound inhibition of cancer cell growth in preclinical models. AZD3965 is a FIC inhibitor of MCT-1, and we report results from the phase I study of this agent. Methods: Patients with advanced solid tumours were treated with oral (po) AZD3965 at total daily doses of 5-30mg given once (od) and twice daily (bd). Exclusion criteria included a history of retinal or cardiac disease due to preclinical toxicology findings in the eye and heart (which express MCT-1). The primary objectives were to determine the safety, dose limiting toxicities (DLT) and maximum tolerated dose (MTD) of AZD3965. Intensive pharmacokinetic (PK) profiling was performed with subsequent modelling for receptor occupancy. Pharmacodynamic profiling included imaging to detect pH changes and tumour glucose uptake; plasma/urine metabolomics and MCT-1 and MCT-4 tumour expression by immunohistochemistry. Results: 35 patients (20M:15F median age 65) were treated at dose levels 5, 10, 20, and 30mg od and 15 and 10mg bd. AZD3965 was generally well tolerated with nausea and fatigue (CTCAE Gr1-2) the most commonly reported side effects. A single DLT of cardiac troponin rise was observed at 20mg od. Asymptomatic, reversible retinal ERG changes were observed in all but the lowest dose levels, with DLTs observed at doses above 20mg od. PK data indicate exposures in the preclinical efficacy range. Metabolomic changes in urinary lactate and urinary ketones correlate with on-target activity. The increase in urinary ketones is likely to be attributable to the role of MCT1 in physiological ketone transport. Conclusions: The MCT1 inhibitor AZD3965 can be administered to patients at doses which engage the drug target, with a MTD of 20mg od po. DLTs seen were primarily dose dependent, asymptomatic and reversible changes in retinal function, which were an expected on-target effect. Investigation of the activity of AZD3965 is ongoing in tumours known to express MCT1. Clinical trial information: NCT01791595.

A water-soluble rhodamine B-derived fluorescent probe for pH monitoring and imaging in acidic regions

A structurally simple, water-soluble rhodamine-derivatived fluorescent probe, which is responsive to acidic pH, was conveniently synthesized via a one-step condensation reaction of rhodamine B hydrazide and 4-formybenzene–1,3-disulfonate. As a stable and highly sensitive pH sensor, the probe displays an approximately 50-fold fluorescence enhancement over the pH range of 7.16–4.89 as the structure of probe changes from spirocyclic (weak fluorescent) to ring-open (strong fluorescent) with decreasing pH. The synthesized fluorescent probe is applied to the detection of pH changes in vitro and in vivo bioimaging of immortalized gastric cancer cells, with satisfactory results.

(Invited) Potentiometric Biochemical Sensors for Diagnostic Applications

The detection of chemical and biological species is critical for applications in healthcare, environmental monitoring, food safety and drug screening. Potentiometric biochemical sensors rely on the specific adsorption of charged analytes that changes the potential of the functionalized sensor surface. The change in surface potential can be measured using a field-effect-transistor enabling low-cost fabrication, and easy integration with portable readout electronics. Over the past several decades, these sensors have been demonstrated to detect pH changes, metal ions, DNA, biomarkers, proteins, and enzymes. Although many biosensing experiments have been reported, many of the results are not well understood and several key challenges are still limiting their widespread application. The ability to stabilize and control the attachment of cells on the sensor surface is critical. Therefore, the reliability and reproducibility of self-assembled-monolayers will be presented. The experimental response from a variety of sensor surfaces (oxides or metals) and transducers (conventional silicon, nanowire, extended gate, or graphene transistors) will be presented. The results show that the choice of the active interface in contact with the electrolyte determines the sensor response and selectivity (the signal) independent of the transducer. The choice of the readout transducer mainly influences the noise limit, and, hence, the signal-to-noise ratio. Models for diffusion, attachment, and electrical response of these sensors will be described that demonstrates good agreement to experimental data. Finally, the application of these devices in the animal health sector for the diagnosis of bovine respiratory disease, which is a major cause of calf death, will also be presented.

Highly pH-responsive sensor based on amplified spontaneous emission coupled to colorimetry

We demonstrated a simple, directly-readable approach for high resolution pH sensing. The method was based on sharp changes in Amplified Spontaneous Emission (ASE) of a Stilbene 420 (ST) laser dye triggered by the pH-dependent absorption of Bromocresol Green (BG). The ASE threshold of BG:ST solution mixtures exhibited a strong dependence on BG absorption, which was drastically changed by the variations of the pH of BG solution. As a result, ASE on-off or off-on was observed with different pH levels achieved by ammonia doping. By changing the concentration of the BG solution and the BG:ST blend ratio, this approach allowed to detect pH changes with a sensitivity down to 0.05 in the 10–11 pH range.

Smart bandage with wireless connectivity for optical monitoring of pH

Wound care technologies need to adapt in order to cope with the growing socio-economic burden of chronic wounds. Non-invasive analytical systems which monitor important wound status biomarkers such as pH of wound fluid, are needed. In this work, a wireless smart bandage for optical determination of pH, as an indicator of wound status, is demonstrated and characterised. The bandage is constructed by immobilising cellulose particles, covalently modified with a pH indicator dye, within a biocompatible hydrogel. Thin layers of the pH sensitive hydrogel are cast onto a conventional dressing and interfaced to a wireless platform via a miniaturised optoelectronic probe. The smart bandage can detect pH changes in the physiologically relevant range with high accuracy and precision, and communicate this information with an external readout unit using radio-frequency identification (RFID). The new system could provide insight into temporal changes in wound status in a convenient and non-invasive manner, and prompt an appropriate response from a healthcare provider.

Ratiometric Sensing and Imaging of Intracellular pH Using Polyethylenimine-Coated Photon Upconversion Nanoprobes.

Measurement of changes of pH at various intracellular compartments has potential to solve questions concerning the processing of endocytosed material, regulation of the acidification process, and also acidification of vesicles destined for exocytosis. To monitor these events, the nanosized optical pH probes need to provide ratiometric signals in the optically transparent biological window, target to all relevant intracellular compartments, and to facilitate imaging at subcellular resolution without interference from the biological matrix. To meet these criteria we sensitize the surface conjugated pH sensitive indicator via an upconversion process utilizing an energy transfer from the nanoparticle to the indicator. Live cells were imaged with a scanning confocal microscope equipped with a low-energy 980 nm laser excitation, which facilitated high resolution and penetration depth into the specimen, and low phototoxicity needed for long-term imaging. Our upconversion nanoparticle resonance energy transfer based sensor with polyethylenimine-coating provides high colloidal stability, enhanced cellular uptake, and distribution across cellular compartments. This distribution was modulated with membrane integrity perturbing treatment that resulted into total loss of lysosomal compartments and a dramatic pH shift of endosomal compartments. These nanoprobes are well suited for detection of pH changes in in vitro models with high biological background fluorescence and in in vivo applications, e.g., for the bioimaging of small animal models.

Fluorescent Probes for Sensitive and Selective Detection of pH Changes in Live Cells in Visible and Near-infrared Channels.

We report five fluorescent probes based on coumarin-hybridized fluorescent dyes with spirolactam ring structures (A-E) to detect pH changes in live cell by monitoring visible and near-infrared fluorescence changes. Under physiological or basic conditions, the fluorescent probes A, B, C, D and E preserve their spirolactam ring-closed forms and only display fluorescent peaks in the visible region corresponding to coumarin moieties at 497, 483, 498, 497 and 482 nm, respectively. However, at acidic pH, the rings of the spirolactam forms of the fluorescent probes A, B, C, D and E open up, generating new near-infrared fluorescence peaks at 711, 696, 707, 715, and 697 nm, respectively, through significantly extended π-conjugation to coumarin moieties of the fluorophores. The fluorescent probes B and E can be applied to visualize pH changes by monitoring visible as well as near-infrared fluorescence changes. This helps avoid fluorescence imaging blind spots at neutral or basic pH, which typical pH fluorescent probes encounter. The probes exhibit high sensitivity to pH changes, excellent photostability, low auto-fluorescence background and good cell membrane permeability.

Quantitative chemical exchange saturation transfer MRI of intervertebral disc in a porcine model.

Previous studies have associated low pH in intervertebral discs (IVDs) with discogenic back pain. The purpose of this study was to determine whether quantitative CEST (qCEST) MRI can be used to detect pH changes in IVDs in vivo. The exchange rate ksw between glycosaminoglycan (GAG) protons and water protons was determined from qCEST analysis. Its dependence on pH value was investigated in GAG phantoms with varying pH and concentrations. The relationship between ksw and pH was studied further in vivo in a porcine model on a 3T MR scanner and validated using a pH meter. Sodium lactate was injected into the IVDs to induce various pH values within the discs ranging from 5 to 7. Phantom and animal results revealed that ksw measured using qCEST MRI is highly correlated with pH level. In the animal studies, the relationship can be described as ksw =9.2 × 106 × 10-pH + 196.9, R2 = 0.7883. The exchange rate between GAG and water protons determined from qCEST MRI is closely correlated with pH value. This technique has the potential to noninvasively measure pH in the IVDs of patients with discogenic pain. Magn Reson Med 76:1677-1683, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Ratiometric Fluorescent pH Probes Based on Glycopolymers.

Effectively detecting pH changes plays a critical role in exploring cellular functions and determining physiological and pathological processes. A novel ratiometric pH probe based on a glycopolymer, armored with properties of serum-stability, tumor-targeting, and pH monitoring, is designed. Random copolymers of 2-(methacrylamido) glucopyranose and fluorescein O-methacrylate are first synthesized by reversible addition fragmentation chain transfer polymerization. Acryloxyethyl thiocarbamoyl rhodamine B is then attached to the polymer chain to prepare ratiometric fluorescent pH probes via a thiol-ene reaction. The synthesized polymeric probes are characterized by NMR, gel permeation chromatography, UV-vis spectroscopy, and transmission electron microscopy, and the fluorescence responses are examined in phosphate buffer at different pHs. The cytotoxicity and confocal imaging experiments of the probes are detected using HeLa cells, demonstrating a low toxicity and superior biocompatibility for detecting pH changes in bioapplications.