A near-infrared neutral pH fluorescent probe for monitoring minor pH changes: imaging in living HepG2 and HL-7702 cells

A New Phenothiazine-Based Fluorescent Probe for Rapid and Specific Detection of Fluoride

Fluorescent probes with specific and rapid response to fluoride ions are important mediators for detecting fluoride ions in biological systems. In this study, a phenothiazine-based fluorescent probe, PTC, was designed and synthesized, which undergoes cleavage activation and cyclization induced by fluoride ions targeting Si-O bonds. The probe exhibits strong anti-interference properties and reaches peak fluorescence within 5 min, allowing for quantitative detection of fluoride ions content in the concentration range of 0 to 12.5μM, suitable for live cell fluorescence imaging. The research findings suggest its potential application value in biological systems.

Rational design of pH-responsive near-infrared spirocyclic cyanines: the effects of substituents and the external environment

pH-responsive spirocyclic cyanine dyes were designed and synthesized. The equilibrium constant for cyclization (pKcycl) could be rationally controlled by changing the nucleophilic moiety and the side chains. Encapsulation in polymeric micelles inhibited the H-aggregation of the dye, and the pKcycl could be shifted according to the amphiphilic polymer employed.

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.

Design and Application of Fluorescent Probes to Detect Cellular Physical Microenvironments

The microenvironment is indispensable for functionality of various biomacromolecules, subcellular compartments, living cells, and organisms. In particular, physical properties within the biological microenvironment could exert profound effects on both the cellular physiology and pathology, with parameters including the polarity, viscosity, pH, and other relevant factors. There is a significant demand to directly visualize and quantitatively measure the fluctuation in the cellular microenvironment with spatiotemporal resolution. To satisfy this need, analytical methods based on fluorescence probes offer great opportunities due to the facile, sensitive, and dynamic detection that these molecules could enable in varying biological settings from in vitro samples to live animal models. Herein, we focus on various types of small molecule fluorescent probes for the detection and measurement of physical parameters of the microenvironment, including pH, polarity, viscosity, mechanical force, temperature, and electron potential. For each parameter, we primarily describe the chemical mechanisms underlying how physical properties are correlated with changes of various fluorescent signals. This review provides both an overview and a perspective for the development of small molecule fluorescent probes to visualize the dynamic changes in the cellular environment, to expand the knowledge for biological process, and to enrich diagnostic tools for human diseases.

Near-Infrared Fluorescence Probe for Indication of the Pathological Stages of Wound Healing Process and Its Clinical Application

Chronic wound healing is one of the most complicated biological processes in human life, which is also a serious challenge for human health. During the healing process, multiple biological pathways are activated, and various kinds of reactive oxygen species participate in this process. Hydrogen peroxide (H2O2) involves in chronic wounds and its concentration is fluctuated in different pathological stages during the wound healing process. Therefore, H2O2 may be recognized as a powerful biomarker to indicate the wound healing process. However, the pathological roles of H2O2 cannot be fully understood yet. Herein, we proposed a near-infrared fluorescent probe DCM-H2O2 for highly sensitive and rapid detection of H2O2 in living cells and scald and incision wound mice models. DCM-H2O2 exhibited a low detection limit and high specificity with low cytotoxicity for H2O2, which had great potential for its application in vivo. The probe was successfully utilized to monitor the fluctuation of endogenous H2O2 in the proliferation process of human immortalized epidermal (HACAT) cells, which confirmed that H2O2 participated in the cells' proliferation activity through a growth factor signaling pathway. In the scald and incision wound mice models, H2O2 concentration fluctuations at different pathological stages during the wound healing process could be obtained by in vivo fluorescence imaging. Finally, H2O2 concentrations in different stages of human diabetic foot tissues were also confirmed by the proposed probe. We expect that H2O2 could be a sensitive biomarker to indicate the wound healing process.

Synthesis of an aggregation-induced emission (AIE) dye with pH-sensitivity based on tetraphenylethylene-pyridine for fluorescent nanoparticles and its applications in bioimaging and in vitro anti-tumor effect

In this contribution, a novel AIE monomers 2-(4-styrylphenyl)- 1,2-diphenylvinyl)styryl)pyridine (SDVPY) with smart fluorescent pH-sensitivity basing on tetraphenylethylene-pyridine were successfully synthesized for the first time, subsequently, a series of amphiphilic copolymers PEG-PY were achieved by reversible addition-fragmentation chain transfer (RAFT) polymerization of SDVPY and poly(ethylene glycol) methacrylate (PEGMA), which would self-assemble in water solution to form core-shell nanoparticles (PEG-PY FONs) with about 150 nm diameter. The PEG-PY FONs showed obvious fluorescence response to Fe3+, HCO3- and CO32- ions in aqueous solution owing to their smart pH-sensitivity and AIE characteristics, and their maximum emission wavelength could reversibly change from 525 nm to 624 nm. The as-prepared PEG-PY FONs showed also prospective application in cells imaging with the variable fluorescence for different pH cells micro-environment. When PEG-PY copolymers self-assembled with the anti-tumor drug paclitaxel (PTX), the obtained PY-PTX FONs could effectively deliver and release PTX with pH-sensitivity, and could be easily internalized by A549 cells and located at the cytoplasm with high cytotoxicity, which was further confirmed by the Calcein-AM/PI staining of dead and alive A549 cells. Moreover, the flow cytometry results indicated that the PY-PTX FONs could obviously induce the apoptosis of A549 cells, which further showed the great potential of PY-PTX FONs in the application of tumors therapy.

1,2,4-Triazines and Calcium Carbide in the Catalyst-Free Synthesis of 2,3,6-Trisubstituted Pyridines and Their D-, 13 C-, and Doubly D2 -13 C2 -Labeled Analogues

A novel synthetic approach to 2,3,6-trisubstituted pyridines, their 4,5-dideuterated derivatives, 4,5-13 C2 - and doubly-labeled D2 -13 C2 -pyridines has been developed using catalyst-free [4+2] cycloaddition of 1,2,4-triazines and in situ generated acetylene or labeled acetylene. Calcium carbide and water or deuterium oxide were used for the in situ generation of acetylene and dideuteroacetylene. Calcium carbide-13 C2 in the mixture with water or deuterium oxide was applied as 13 C2 -acetylene and D2 -13 C2 -acetylene source.

A novel fluorescent dye selectively images and kills cancer stem cells by targeting mitochondria: Evidence from a cell line‑based zebrafish xenograft model

Numerous agents such as near-infrared dyes that are characterized by specialized cancer imaging and cytotoxicity effects have key roles in cancer diagnosis and therapy via molecularly targeting special biological tissues, organelles and processes. In the present study, a novel fluorescent compound was demonstrated to inhibit cancer cell proliferation in a zebrafish model with slight in vivo toxicity. Further studies demonstrated selective staining of cancer cells and even putative cancer stem cells via accumulation of the dye in the mitochondria of cancer cells, compared with normal cells. Moreover, this compound was also used to image cancer cells in vivo using a zebrafish model. The compound displayed no apparent toxicity to the host animal. Overall, the data indicated that this compound was worthy of further evaluation due to its low toxicity and selective cancer cell imaging and killing effects. It could be a useful tool in cancer research.

A swallowable X-ray dosimeter for the real-time monitoring of radiotherapy

Monitoring X-ray radiation in the gastrointestinal tract can enhance the precision of radiotherapy in patients with gastrointestinal cancer. Here we report the design and performance, in the gastrointestinal tract of rabbits, of a swallowable X-ray dosimeter for the simultaneous real-time monitoring of absolute absorbed radiation dose and of changes in pH and temperature. The dosimeter consists of a biocompatible optoelectronic capsule containing an optical fibre, lanthanide-doped persistent nanoscintillators, a pH-sensitive polyaniline film and a miniaturized system for the wireless readout of luminescence. The persistent luminescence of the nanoscintillators after irradiation can be used to continuously monitor pH without the need for external excitation. By using a neural-network-based regression model, we estimated the radiation dose from radioluminescence and afterglow intensity and temperature, and show that the dosimeter was approximately five times more accurate than standard methods for dose determination. Swallowable dosimeters may help to improve radiotherapy and to understand how radiotherapy affects tumour pH and temperature.

Supramolecular Dimer as High-Performance pH Probe: Study on the Fluorescence Properties of Halogenated Ligands in Rigid Schiff Base Complex

The development of high-performance fluorescence probes has been an active area of research. In the present work, two new pH sensors Zn-3,5-Cl-saldmpn and Zn-3,5-Br-saldmpn based on a halogenated Schiff ligand (3,5-Cl-saldmpn = N, N'-(3,3'-dipropyhnethylamine) bis (3,5-chlorosalicylidene)) with linearity and a high signal-to-noise ratio were developed. Analyses revealed an exponential intensification in their fluorescence emission and a discernible chromatic shift upon pH increase from 5.0 to 7.0. The sensors could retain over 95% of their initial signal amplitude after 20 operational cycles, demonstrating excellent stability and reversibility. To elucidate their unique fluorescence response, a non-halogenated analog was introduced for comparison. The structural and optical characterization suggested that the introduction of halogen atoms can create additional interaction pathways between adjacent molecules and enhance the strength of the interaction, which not only improves the signal-to-noise ratio but also forms a long-range interaction process in the formation of the aggregation state, thus enhancing the response range. Meanwhile, the above proposed mechanism was also verified by theoretical calculations.

Highly pH-Responsive Sensor Based on a EuIII Metal-Organic Framework with Efficient Recognition of Arginine and Lysine in Living Cells

A lanthanide-based three-dimensional metal-organic framework with excellent water, acid/base, and solvent stability, namely {[(CH3)2NH2]0.7[Eu2(BTDBA)1.5(lac)0.7(H2O)2]·2H2O·2DMF·2CH3CN}n (JXUST-29, H4BTDBA = 4',4‴-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid), Hlac = lactic acid), has been synthesized and characterized. Since the N atoms of the thiadiazole group will not coordinate with lanthanide ions, JXUST-29 has a free basic N-site accessible to small H+ ions, which allows it to be used as a promising pH fluorescence sensor. Interestingly, the luminescence signal was significantly enhanced, with an approximately 54-fold enhancement in the emission intensity when the pH value was increased from 2 to 5, which is the typical behavior of pH probes. In addition, JXUST-29 can also be used as a luminescence sensor to detect l-arginine (Arg) and l-lysine (Lys) in an aqueous solution through fluorescence enhancement and the blue-shift effect. The detection limits were 0.023 and 0.077 μM, respectively. In addition, JXUST-29-based devices were designed and developed to facilitate detection. Importantly, JXUST-29 is also capable of detecting and sensing Arg and Lys in living cells.

Long-term spatiotemporal and highly specific imaging of the plasma membrane of diverse plant cells using a near-infrared AIE probe

Fluorescent probes are valuable tools to visualize plasma membranes intuitively and clearly and their related physiological processes in a spatiotemporal manner. However, most existing probes have only realized the specific staining of the plasma membranes of animal/human cells within a very short time period, while almost no fluorescent probes have been developed for the long-term imaging of the plasma membranes of plant cells. Herein, we designed an AIE-active probe with NIR emission to achieve four-dimensional spatiotemporal imaging of the plasma membranes of plant cells based on a collaboration approach involving multiple strategies, demonstrated long-term real-time monitoring of morphological changes of plasma membranes for the first time, and further proved its wide applicability to plant cells of different types and diverse plant species. In the design concept, three effective strategies including the similarity and intermiscibility principle, antipermeability strategy and strong electrostatic interactions were combined to allow the probe to specifically target and anchor the plasma membrane for an ultralong amount of time on the premise of guaranteeing its sufficiently high aqueous solubility. The designed APMem-1 can quickly penetrate cell walls to specifically stain the plasma membranes of all plant cells in a very short time with advanced features (ultrafast staining, wash-free, and desirable biocompatibility) and the probe shows excellent plasma membrane specificity without staining other areas of the cell in comparison to commercial FM dyes. The longest imaging time of APMem-1 can be up to 10 h with comparable performance in both imaging contrast and imaging integrity. The validation experiments on different types of plant cells and diverse plants convincingly proved the universality of APMem-1. The development of plasma membrane probes with four-dimensional spatial and ultralong-term imaging ability provides a valuable tool to monitor the dynamic processes of plasma membrane-related events in an intuitive and real-time manner.

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.

One-Pot Sequential Hydroamination Protocol for N-Heterocycle Synthesis: One Method To Access Five Different Classes of Tri-Substituted Pyridines

Tri-substituted pyridines are important scaffolds that can be found in a plethora of commercially available drugs. A one-pot general method for the selective synthesis of less explored/challenging patterns of tri-substituted pyridines is described. Hydroamination of alkynes with commercially available N-triphenylsilylamine generates N-silylenamines. These in situ generated N-silylenamines, upon reaction with α,β-unsaturated carbonyl compounds and subsequent oxidation, furnish 25 examples of selectively substituted 2,4,5-, 2,3,4-, 3,4,5-, 2,3,5-, and 2,3,6-trisubstituted pyridines in up to 78% yield. The reaction features high functional group compatibility providing an expeditious and general approach for the assembly of selectively substituted tri-substituted pyridine derivatives. The robustness and practicality of the reaction have been demonstrated in a gram-scale reaction.

Design of A3B-Porphyrin Conjugates with Terpyridine as Potential Theranostic Agents: Synthesis, Complexation with Fe(III), Gd(III), and Photodynamic Activity

This paper reports on the design and synthesis of new multifunctional porphyrin-based therapeutic agents for potential therapeutic and diagnostic applications. Zinc complexes of A3B-type meso-arylporphyrins containing OH- and COOH- groups were modified with chelating ligands based on 4'-(4-methylphenyl)-2,2':6',2″-terpyridine derivatives in high yields. Novel complexes with Gd(III), Fe(III) were obtained for these conjugates. Aggregation behaviour in solutions of different solubilisers was studied to inform the selection of the optimal solubilising platform for the porphyrins obtained; their photophysical and photochemical properties were also characterised. Micellar Pluronic F127 formulation was found to be the most effective solubiliser for stabilising the fluorescence-active monomolecular form of the photosensitisers (PS). In vitro cytotoxicity of the compounds was studied on the HEP-2 cell line with and without irradiation for 1.5 and 24 h. As a result, the IC50 of compounds 12 and 14 at an irradiation dose of 8.073 J/cm2 was shown to be 1.87 ± 0.333 and 1.4 ± 0.152 μM, respectively; without irradiation, the compound had no toxic effect within the studied concentration range (1.5 h). A test for the inhibition of metabolic cooperation or promoter activity was also performed for the abovementioned compounds, showing the efficacy and safety of the conjugates obtained. Preliminary data have indicated the high potential of the new type of PS to be promising molecular theranostic agents.

Monitoring intracellular pH using a hemicyanine-based ratiometric fluorescent probe

Monitoring intracellular pH using ratiometric fluorescent probes can provide further insights into various biological processes including many diseases. Although ratiometric fluorescent probes with dual emission can efficiently exclude interferences (probe concentration, instrumental efficiency, and environmental conditions) compared with traditional off-on fluorescent probes, development of pH-responsive fluorescent probes with dual emission remains relatively unexplored and challenging. Herein we reported a new hemicyanine-based ratiometric fluorescent probe 1 with a hydroxyl group. The probe 1 exhibits dual emission and shows a real-time and selective fluorescence response to micro-environmental pH conditions in a range of 6.0 ∼ 8.0. Further studies revealed that 1 could exclusively enter and accumulate into mitochondria and monitor the pH micro-environmental conditions through fluorescence imaging in HepG2 cells. We suggest that this probe might be used as a probe to elucidate the role of pH in many physiological processes.

Multiresponsive tetrarylethylene-based fluorescent dye with multicoloreded changes: AIEE properties, acidichromism, Al3+ recognition, and applications

A novel fluorescent sensor BTAE-PA containing two tetrarylethylene (TAE) units linked through pyrimidine-2-amine was prepared, and its optical properties were systematically studied. BTAE-PA exhibited a typical aggregation-induced emission enhancement behavior, and its fluorescent properties could be efficiently modulated by acid/base and metal ions in THF. The protonated effect could induce significant acidichromism and 'turn-on' near-infrared emission with a large Stokes shift (Δλ = 225 nm). Furthermore, BTAE-PA was highly selective toward Al³⁺ with significant absorption (yellow → orange) and fluorescence (green → red) changes. A Job's plot established the 1 : 1 stoichiometry of the complex formation between BTAE-PA and Al³⁺, and the limit of detection for Al³⁺ was determined to be 1.30 × 10^-7 mol L^-1. Finally, we also demonstrated that BTAE-PA could be made into test paper strips for 'naked-eye' detection of acid/Al³⁺, and fluorescence imaging experiments proved that BTAE-PA is capable of achieving cell imaging with good biocompatibility. Therefore, the multi-stimuli-responsive and multicoloured display performance of BTAE-PA endows the material with potential applications in security ink, acid/Al³⁺ sensing, and bio-imaging.

Hydrogen-bond activated ESIPT in naphthalimide-based fluorescent probe for sensing volatile amines

Amines levels present important indicative value in food safety and human health. Although they are involved in some normal physiological responses of the organism, their overproduction or intake may cause pathological responses. Herein, we report a recyclable visual packaging bag for volatile amines detections based on the naphthylamide derivative N-S and its positive PL characteristics. Specifically, handmade test strips based on compound N-S have been applied to fish freshness labeling, and the cyclic fumigation experiment shows its restorable PL effect and efficiency. The possible PL transfer mechanism of naphthylamide derivative N-S is uncovered by the density functional theory (DFT) calculation and titration mass spectrometer and ¹H NMR. This work expands a conjugation in a molecule by hydrogen-bond activated ESIPT (H-ESIPT) and provides a portable detection method for volatile amines detection.

Spiroindeno-pyridineindoles (SIPIs) as new visible colorimetric pH indicators

Some new, highly selective, and sensitive colorimetric pH indicators, spiro[4H-indeno-[1,2-b]pyridine-4,3'-[3H]indoles] (SIPIs) in aqueous solution were developed. SIPIs were synthesized via a one-pot four-component condensation of isatin derivatives, β-diketones 1,3-indandione, and ammonium acetate using FSi-PrNH-BuSO₃H as a nanocatalyst in EtOH. According to the experimental evaluations, it was found that SIPI derivatives are pH indicators for naked-eye detection of OH- ion with intense color changes from orange to purple in the pH range of 10.3-12.

Multifunctional nanosystems sequentially regulating intratumor Fenton chemistry by remodeling the tumor microenvironment to reinforce chemodynamic therapy

The particularity of the tumor microenvironment (TME) significantly limits the efficiency of chemodynamic therapy (CDT). Although various measures have been taken to improve the efficiency of CDT, how to organically integrate them into one nanosystem to achieve efficient synergy for CDT according to predetermined procedures is still an urgent problem to be solved. This work reported a multifunctional nanosystem, TP_I@PP_CAI, which comprised the inner triphenylphosphine modified D-α-Tocopheryl polyethylene glycol 1000 succinate (TPGS-PPh₃) micelles loading iron-oxide nanoparticles (IONs), and the outer poly (dopamine-co-protocatechuic acid) (PDA-PA, PP) coating modified with carbonic anhydrase IX inhibitor (CAI). TP_I@PP_CAI remodeled TME by sequential function adjustment to make it suitable for the efficient Fenton reactions: CAI first inhibited the overexpressed CA IX to result in intracellular acidification, which combined with near-infrared light (NIR) irradiation to accelerate the PP coating degradation, thereby promoting the exposure and disintegration of the inner micellar structure to release TPGS-PPh₃ and IONs. The TPGS-PPh₃ further elevated the intracellular ROS basal level by targeting and interfering with the mitochondrial function. Therefore, the TME was transformed into an acidic microenvironment with high ROS levels, which vigorously promoted the Fenton reaction mediated by IONs with the aid of photothermal effect induced by PP coating via NIR irradiation, ultimately earning high-efficiency CDT on xenograft MDA-MB-231 tumor-bearing mice. This study improved the efficiency of Fenton reaction in biological systems through the practical design of nanostructures and provided a novel thought for ROS-mediated therapy.

Investigation of a benzodiazaborine library to identify new pH-responsive fluorophores

The detection of pH is important owing to its significance in various processes, such as clinical and industrial processes. Numerous fluorescent pH probes have been developed using a variety of fluorophores; however, most are only suitable for application in a narrow pH range (between 5 and 8) owing to the lack of diversity of the pH-sensitive units. Furthermore, probes suitable for sensing high pHs have rarely been studied despite the importance of reliable detection of high pH in various industrial processes. In this study, we prepared a benzodiazaborine (bDAB) library consisting of 238 different bDABs through combinatorial synthesis to investigate their suitability as fluorescent pH probes. Informed by the results of a fluorescence-based, high-throughput screening of the library, we identified four bDABs that exhibit promising pH-sensitive ratiometric fluorescence responses. Their pK_as vary significantly, ranging from 7.29 to 12.44, indicating their suitability for the detection of basic pHs even in extremely basic environments (pH > 10). Furthermore, their fluorescence responses show high stability, anti-interference, and reversibility under various pH conditions.

A water-soluble 1, 8-naphthalimide-based fluorescent pH probe for distinguishing tumorous tissues and inflammation mice

A water-soluble fluorescent probe BPN, by introducing a piperazine as the pH-sensitive fluorescence signaling motif to the hydrophilic propionic acid-substituted 1, 8-naphthalimide fluorophore, is highly sensitive to pH changes within cytoplasm matrix in living cells, as well as pH-related diseases models. Owing to the protonation-induced inhibition of the photoinduced electron transfer (PET) from piperazine to naphthalimide fluorophore, BPN displayed a significant fluorescence enhancement (more than 131-fold) upon the pH decreasing from 11.0 to 3.0. The linear rang was between pH 6.4 to 8.0 with a pK_a value of 6.69 near the physiological pH, which was suitable for cytosolic pH research. Furthermore, BPN exhibited a large Stokes shift (142 nm), good water solubility, excellent photostability, high selectivity and low cytotoxicity. All these advantages were particularly beneficial for intracellular pH imaging. Using BPN, we demonstrated the real-time monitoring of cytosolic pH changes in living cells. Most importantly, BPN has not only been successfully applied for distinguishing inflammation mice, but also the surgical specimens of cancer tissue, making it of great potential application in the cancer diagnosis.

Macrophage-Mimic Hollow Mesoporous Fe-Based Nanocatalysts for Self-Amplified Chemodynamic Therapy and Metastasis Inhibition via Tumor Microenvironment Remodeling

Fe-based nanomaterials with Fenton reaction activity are promising for tumor-specific chemodynamic therapy (CDT). However, most of the nanomaterials suffer from low catalytic efficiency due to its insufficient active site exposure and the relatively high tumor intracellular pH, which greatly impede its clinical application. Herein, macrophage membrane-camouflaged carbonic anhydrase IX inhibitor (CAI)-loaded hollow mesoporous ferric oxide (HMFe) nanocatalysts are designed to remodel the tumor microenvironment with decreased intracellular pH for self-amplified CDT. The HMFe not only serves as a Fenton agent with high active-atom exposure to enhance CDT but also provides hollow cavity for CAI loading. Meanwhile, the macrophage membrane-camouflaging endows the nanocatalysts with immune evading capability and improves tumoritropic accumulation by recognizing tumor endothelium and cancer cells through α4/VCAM-1 interaction. Once internalized by tumor cells, the CAI could be specifically released, which can not only inhibit CA IX to induce intracellular H⁺ accumulation for accelerating the Fenton reaction but also could prevent tumor metastasis because of the insufficient H⁺ formation outside cells for tumor extracellular matrix degradation. In addition, the HMFe can be employed to highly efficient magnetic resonance imaging to real-time monitor the agents' bio-distribution and treatment progress. Both in vitro and in vivo results well demonstrated that the nanocatalysts could realize self-amplified CDT and breast cancer metastasis inhibition via tumor microenvironment remodeling, which also provides a promising paradigm for improving CDT and antimetastatic treatment.

A new near-infrared fluorescent probe for sensing extreme acidity and bioimaging in lysosome

Since the intracellular pH plays an important role in the physiological and pathological processes, however, the probes that can be used for monitoring pH fluctuation under extreme acidic conditions are currently rare, so it is necessary to construct fluorescent probes for sensing pH less than 4. In this work, we developed a new near-infrared (NIR) fluorescent probe Cy-SNN for sensing pH fluctuation under extremely acidic conditions. For the preparation of this probe, benzothiozolium moiety was chosen as lysosomal targeting unit and NIR fluorophore, and barbituric acid moiety was fused in the polymethine chain of probe to introduce protonation center. Surprisingly, on the basis of the balance of quaternary ammonium salts and free amines, the pKa value of Cy-SNN was calculated as low as 2.96, implying that Cy-SNN can be used in acidic conditions with pH < 4. Moreover, Cy-SNN exhibited highly selective response to H+ over diverse analytes in real-time with dependable reversibility. Importantly, Cy-SNN can be used to specifically target lysosome, providing potential tools for monitoring the function of lysosome in autophagy process.

Visible-light and near-infrared fluorescence and surface-enhanced Raman scattering point-of-care sensing and bio-imaging: a review

This review article deals with the concepts, principles and applications of visible-light and near-infrared (NIR) fluorescence and surface-enhanced Raman scattering (SERS) in in vitro point-of-care testing (POCT) and in vivo bio-imaging. It has discussed how to utilize the biological transparency windows to improve the penetration depth and signal-to-noise ratio, and how to use surface plasmon resonance (SPR) to amplify fluorescence and SERS signals. This article has highlighted some plasmonic fluorescence and SERS probes. It has also reviewed the design strategies of fluorescent and SERS sensors in the detection of metal ions, small molecules, proteins and nucleic acids. Particularly, it has provided perspectives on the integration of fluorescent and SERS sensors into microfluidic chips as lab-on-chips to realize point-of-care testing. It has also discussed the design of active microfluidic devices and non-paper- or paper-based lateral flow assays for in vitro diagnostics. In addition, this article has discussed the strategies to design in vivo NIR fluorescence and SERS bio-imaging platforms for monitoring physiological processes and disease progression in live cells and tissues. Moreover, it has highlighted the applications of POCT and bio-imaging in testing toxins, heavy metals, illicit drugs, cancers, traumatic brain injuries, and infectious diseases such as COVID-19, influenza, HIV and sepsis.

Ligand-Sensitized Near-Infrared to Visible Linear Light Upconversion in a Discrete Molecular Erbium Complex

While the low-absorption cross section of lanthanide-based upconversion systems, in which the trivalent lanthanides (Ln³⁺) are responsible for converting low- to high-energy photons, has restricted their application to intense incident light, the emergence of a cascade sensitization through an organic dye antenna capable of broadly harvesting near-infrared (NIR) light in upconversion nanoparticles opened new horizons in the field. With the aim of pushing molecular upconversion within the range of practical applications, we show herein how the incorporation of an NIR organic dye antenna into the ligand scaffold of a mononuclear erbium coordination complex boosts the upconversion brightness of the molecule to such an extent that a low-power (0.7 W·cm^-2) NIR laser excitation of [L6Er(hfa)₃]⁺ (hfa = hexafluoroacetylacetonate) at 801 nm results in a measurable visible upconverted signal in a dilute solution (5 × 10^-4 M) at room temperature. Connecting the NIR dye antenna to the Er³⁺ activator in a single discrete molecule cures the inherent low-efficient metal-based excited-state absorption mechanism with a powerful indirect sensitization via an energy transfer upconversion, which drastically improves the molecular-based upconverted Er³⁺-centered visible emission.

Stimuli-activated molecular photothermal agents for cancer therapy

Taking advantage of activatable and imaging-guided properties, stimuli-activated molecular photothermal agents (MPTAs) have drawn great attention in photothermal therapy (PTT) over the past decades. In this review, the recent progress in the study of stimuli-activated MPTAs is summarized from different stimuli, including pH, bioactive small molecules, and enzymes. The features and challenges of stimuli-activated MPTAs are also discussed. This review aims to motivate readers to design and synthesise more efficient MPTAs.

STED Imaging the Dynamics of Lysosomes by Dually Fluorogenic Si-Rhodamine

Super-resolution microscopy (SRM) imaging of the finite subcellular structures and subtle bioactivities inside organelles delivers abundant cellular information with high fidelity to unravel the intricate biological processes. An ideal fluorescent probe with precise control of fluorescence is critical in SRM technique like stimulated emission depletion (STED). Si-rhodamine was decorated with both targeting group and H⁺ -receptor, affording the dually fluorogenic Si-rhodamine in which the NIR fluorescence was efficiently controlled by the coalescent of spirolactone-zwitterion equilibrium and PeT mechanism. The dually fluorogenic characters of the probe offer a perfect mutual enhancement in sensitivity, specificity and spatial resolution. Strong fluorescence only released in the existence of targeting protein at acidic lysosomal pH, ensured precisely tracking the dynamic of lysosomal structure and pH in living cells by STED.

Supramolecular Assembly of Hybrid Pt(II) Porphyrin/Tomatine Analogues with Different Nanostructures and Cytotoxic Activities

A simple strategy for synthesizing supramolecular hybrids was developed for the preparation of bioavailable nanohybrid photosensitizers by assembling visible-light-sensitive Pt(II) meso-tetrakis(4-carboxyphenyl)porphyrinporphyrin (PtTCPP)/tomatine analogues. The hybrids were self-assembled into nanofibrous or nanosheet structures approximately 3-5 nm thick and several micrometers wide. α-Tomatine generated a unique fibrous vesicle nanostructure based on intermolecular interactions, while dehydrotomatine generated nanosheet structures. Nanoassembly of these fibrous vesicles and sheets directly affected the properties of the light-responsive photosensitizer for tumor photodynamic therapy (PDT), depending on the nanostructure of the hybrid PtTCPP/tomatine analogues. The cytotoxicity of PtTCPP to cancer cells under photoirradiation was significantly enhanced by a tomatine assembly with a fibrous vesicle nanostructure, attributable to increased incorporation of the drug into cells.

Synthesis and characterization of novel photochromic and pH-sensitive colorimetric hydrogel based on azobenzene

This article reports the synthesis of new Dye A from the reaction of 4-methyl 2-nitroaniline, NaNO2/H+, and sodium 1-naphtholate. Dye A responded with an obvious colour change visible to naked eyes to pH, ultraviolet light, and fluoride ion and was studied by UV–vis spectroscopy. Next, the reaction of Dye A with crotonic anhydride leads to the formation of MDye A. Subsequently, synthesis of a new type of photochromic and pH-sensitive colorimetric hydrogel consisting of a new azobenzene (MDye A), acrylic acid, acrylamide, N,N'-methylenebisacrylic amide as a crosslinking agent, and sodium acrylate in the presence of 2,2′-azobis(isobutyronitrile) as initiator and sorbitan monostearate (Span 60) as the dispersant or under a LED lamp (400 nm, 20 W) in the presence of CdS nanorods and β-cyclodextrin was studied. The products were characterized using 1H NMR,13C NMR, TGA, DTG, SEM, TEM, and FTIR spectroscopy. The synthesized new hydrogel showed good pH responsiveness and photoresponsiveness, which was investigated by UV–vis spectroscopy. Also, the effects of parameters such as amounts of CdS nanorods, cross-linker, and water, duration of pre-oxygenation, light intensity on the swelling of gel, and polymerization rate in the synthesis of hydrogel were investigated.

Regiocontrolled synthesis of 2,4,6-triarylpyridines from methyl ketones, electron-deficient acetylenes and ammonium acetate

A novel one-pot two-step approach for the synthesis of 2,4,6-triarylpyridines via t-BuOK/DMSO-promoted C-vinylation of a variety of methyl ketones with electron-deficient acetylenes (alkynones) followed by a cyclization of the in situ generated unsaturated 1,5-dicarbonyl species with ammonium acetate has been developed. This approach possesses competitive advantages such as high regioselectivity, available starting materials and the absence of transition-metal catalysts, oxidants and undesirable byproducts. A wide synthetic utility of the developed approach was demonstrated by the synthesis of trisubstituted, tetrasubstituted and fused pyridines.

Machine learning based approach to pH imaging and classification of single cancer cells

The ability to identify different cell populations in a noninvasive manner and without the use of fluorescence labeling remains an important goal in biomedical research. Various techniques have been developed over the last decade, which mainly rely on fluorescent probes or nanoparticles. On the other hand, their applications to single-cell studies have been limited by the lengthy preparation and labeling protocols, as well as issues relating to reproducibility and sensitivity. Furthermore, some of these techniques require the cells to be fixed. Interestingly, it has been shown that different cell types exhibit a unique intracellular environment characterized by specific acidity conditions as a consequence of their distinct functions and metabolism. Here, we leverage a recently developed pH imaging modality and machine learning-based single-cell segmentation and classification to identify different cancer cell lines based on their characteristic intracellular pH. This simple method opens up the potential to perform rapid noninvasive identification of living cancer cells for early cancer diagnosis and further downstream analyses.

Imidazolyl-benzocoumarins as ratiometric fluorescence probes for biologically extreme acidity

A rational approach to develop a fluorescent probe for sensing biologically "extreme" acidity (pH <3) is disclosed. The probe, a push-full type 3-(imidazolyl)benzocoumarin dye, has the lowest pK_a = 1.3 among ratiometric probes known so far, which is ascribed due to a unique sensing mechanism. The probe has high quantum yields, high chemical stability and good aqueous solubility. The probe was successfully applied to ratiometric fluorescence imaging of intrabacterial acidity from pH 4.0-1.0, offering a practical means for studying biological systems under the extreme pH conditions.

Reversible Chemosensor for Bioimaging and Biosensing of Zn(II) and hpH in Cells, Larval Zebrafish, and Plants with Dual-Channel Fluorescence Signals

Zinc/Zn(II) is an essential trace element for humans and acts as an important substance that maintains the normal growth, development, and metabolism of the body. Excess or deficient Zn(II) can cause abnormal metabolism in the human body, leading to a series of diseases. Moreover, biosystems have complex homeostasis systems, especially harsh pH (OH^-) environments. Thus, investigating the variation in the levels of Zn(II) and OH^- is extremely important in clinical, medical, and environmental testing. Nevertheless, the lack of practical and convenient fluorescence imaging tools limits the tracing of Zn(II) and OH^- in biosystems. In this work, a well-designed dual-channel fluorescent signal response chemosensor (DACH-fhba) was assembled for selective sensing of Zn(II) and OH^- in the biosystem using a fluorescence turn-on strategy. On encountering Zn(II), the chemosensor emitted a blue fluorescence signal (455 nm). Meanwhile, the bright green fluorescence signal (530 nm) increased with OH^- addition simultaneously. With the blue/green dual fluorescence response of DACH-fhba, the sensor exhibited high stability and reversibility. Notably, the bioimaging revealed that DACH-fhba successfully tracked Zn(II) and OH^- in live cells, larval zebrafish, and plants. Further results implied that DACH-fhba can be used to achieve visual detection of Zn(II) and OH^- in organisms. Altogether, this work is conducive to the monitoring of Zn(II) and OH^- in organisms and promotes the understanding of the function of Zn(II) and OH^- in biosystems.

A novel photochemical sensor based on quinoline-functionalized phenazine derivatives for multiple substrate detection

A novel photochemical sensor based on quinoline-functionalized phenazine derivatives for highly sensitive detection of multiple substrates (l-Arg, CO₂, and pH) was designed and synthesized.

Bis(terpyridine) Ru(iii) complex functionalized porous polycarbazole for visible-light driven chemical reactions

Bis(terpyridine)Ru(iii) complex functionalized porous polycarbazole for photocatalytic amine coupling, aerobic hydroxylation of arylboronic acids, and selective oxidation of sulfides.

Yellow emission carbon dots for highly selective and sensitive OFF-ON sensing of ferric and pyrophosphate ions in living cells

A simple "OFF-ON" fluorescent system was proposed for selective and sensitive detection of ferric ion (Fe³⁺) and pyrophosphate (PPi) in living cells. The method was constructed based on the bright yellow emission of carbon dots (y-CDs), which were prepared using o-phenylenediamine (OPD) as the precursor via a facile hydrothermal treatment. The as-obtained y-CDs, with an average size of 2.6 nm, exhibited an excitation-independent emission peak at 574 nm. The fluorescence of y-CDs can be remarkably quenched by Fe³⁺ with high selectivity and sensitivity. Interestingly, the quenched fluorescence can be recovered regularly upon addition of PPi, showing a promising detection for PPi. The linear ranges for Fe³⁺ and PPi detections were 0.05-80 and 0.5-120 μM, respectively, and the corresponding limit of detections (LODs) were 22.1 and 73.9 nM. As we proved the y-CDs have negligible cytotoxicity and excellent biocompatibility, further application to the fluorescence imaging of intracellular Fe³⁺ and PPi were conducted, suggesting the prepared y-CDs can be used to monitor Fe³⁺ and PPi variation in living cells. Overall, our developed y-CDs-based OFF-ON switch fluorescent probe has the advantages of simplicity, agility, high sensitivity and selectivity, which provides a promising platform for environmental and biology applications, and paves a new avenue for monitoring the hydrolysis process of adenosine triphosphate disodium salt (ATP) by detection of PPi in organisms.

A novel near-infrared fluorescent probe with large stokes shifts for sensing extreme acidity and its application in bioimaging

In this work, we reported a novel near-infrared (NIR) fluorescent probe RQNN with large Stokes shift (98 nm) for monitoring pH under extremely acidic conditions. For the preparation of this probe, a 1,4-diethylpiperazine moiety was introduced in rhodamine scaffold to tune the electron-donating character, and an o-phenylenediamine was introduced in spironolactone to provide larger steric hindrance. The deprotonated-protonated equilibrium between RQNN, RQNN-H⁺ and RQNN-H⁺⁺ were evaluated in different pH by absorption and emission spectra. As expected, RQNN exhibited lower pk_a values (pk_a1 = 4.83, pk_a2 = 2.99), indicating that the probe can be used in extremely acidic pH. Moreover, RQNN possessed highly selective response to H⁺ over essential metal ions and biologically related redox molecules, high photo-stability, rapid response time, and excellent reversibility. Importantly, the probe had excellent cell membrane permeability and was further applied successfully to monitor pH fluctuations in live cells.

Research progress of near-infrared fluorescence probes based on indole heptamethine cyanine dyes in vivo and in vitro

Near-infrared (NIR) fluorescence imaging is a noninvasive technique that provides numerous advantages for the real-time in vivo monitoring of biological information in living subjects without the use of ionizing radiation. Near-infrared fluorescent (NIRF) dyes are widely used as fluorescent imaging probes. These fluorescent dyes remarkably decrease the interference caused by the self-absorption of substances and autofluorescence, increase detection selectivity and sensitivity, and reduce damage to the human body. Thus, they are beneficial for bioassays. Indole heptamethine cyanine dyes are widely investigated in the field of near-infrared fluorescence imaging. They are mainly composed of indole heterocyclics, heptamethine chains, and N-substituent side chains. With indole heptamethine cyanine dyes as the parent, introducing reactive groups to the parent compounds or changing their structures can make fluorescent probes have different functions like labeling protein and tumor, detecting intracellular metal cations, which has become the hotspot in the field of fluorescence imaging of biological research. Therefore, this study reviewed the applications of indole heptamethine cyanine fluorescent probes to metal cation detection, pH, molecules, tumor imaging, and protein in vivo. The distribution, imaging results, and metabolism of the probes in vivo and in vitro were described. The biological application trends and existing problems of fluorescent probes were discussed.

BF2-Oxasmaragdyrin Nanoparticles: A Non-toxic, Photostable, Enhanced Non-radiative Decay-Assisted Efficient Photothermal Cancer Theragnostic Agent

Photothermal therapy (PTT), a simple and minimally invasive procedure, is an attractive option for cancer therapy. To date, inorganic agents have been widely employed as photothermal agents; however, organic molecules may provide a solution to rapid metabolic/in vivo clearance. Herein, we prepared lipid (S 75)-stabilized meso-tritolyl-BF₂-oxasmaragdyrin nanoparticles (TBSNPs) using thin-film hydration and homogenization. Assessment of the physicochemical properties of the TBSNPs reveals the formation of particles of size <12 nm stabilized within the lipid matrix. The TBSNPs exhibit near infrared fluorescence (NIRF) being accompanied by an increase in non-radiative decay, leading to excellent photothermal properties. In vitro studies demonstrate excellent biocompatibility, hemocompatibility, cellular internalization, and photothermal efficacy (p = 0.0004). Extensive in vivo assessment of TBSNPs also highlights the non-toxic nature of the material and passive tumor homing. The strong NIRF exhibited by the material is exploited for whole-body imaging in the rodent model. The novel material also shows excellent photothermal efficacy (p = 0.0002) in a 4T1 xenograft mice model. The organic nature of the material coupled with its small size and strong NIRF provides an advantage for bio-elimination and potential clinical image-guided therapy over the inorganic counterparts.

A pH-Sensing Fluorescent Metal-Organic Framework: pH-Triggered Fluorescence Transition and Detection of Mycotoxin

Due to its great relevance to environmental, biological, and chemical processes, the precise detection of pH or acidic/basic species is an ongoing and imperative need. In this context, pH-sensitive luminescent systems are highly desired. We reported a three-dimensional Zn(II) MOF synthesized from a bipyridyl-tetracarboxylic ligand and composed of 4-fold interpenetrated diamond frameworks. Because the steric hindrance in the ligand prevents metal coordination with the pyridyl group, the MOF features free basic N sites accessible to the small H⁺ ions, which renders pH responsivity. The aqueous dispersion exhibits an abrupt, high-contrast, and reversible on-off fluorescence transition in the narrow pH range of 5.4-6.2. The sensitive bistable system can be used for the precise monitoring of pH within the range and for use as a pH-triggered optical switch. The responsive mechanism through pyridyl protonation is collaboratively supported by data fitting, absorption spectra, and molecular orbital calculations. In particular, spectral and theoretical analyses reveal the destruction of n → π* transitions and the appearance of intramolecular charge-transfer transitions upon pyridyl protonation. Moreover, by virtue of the pH-responsive fluorescence, the MOF shows appealing sensing performance for the detection of 3-nitropropionic acid, a major mycotoxin in moldy sugar cane.