In Situ Lysosomal Cysteine-Specific Targeting and Imaging during Dexamethasone-Induced Apoptosis

Advances in small-molecule fluorescent probes for the study of apoptosis

Apoptosis, as type I cell death, is an active death process strictly controlled by multiple genes, and plays a significant role in regulating various activities. Mounting research indicates that the unique modality of cell apoptosis is directly or indirectly related to different diseases including cancer, autoimmune diseases, viral diseases, neurodegenerative diseases, etc. However, the underlying mechanisms of cell apoptosis are complicated and not fully clarified yet, possibly due to the lack of effective chemical tools for the nondestructive and real-time visualization of apoptosis in complex biological systems. In the past 15 years, various small-molecule fluorescent probes (SMFPs) for imaging apoptosis in vitro and in vivo have attracted broad interest in related disease diagnostics and therapeutics. In this review, we aim to highlight the recent developments of SMFPs based on enzyme activity, plasma membranes, reactive oxygen species, reactive sulfur species, microenvironments and others during cell apoptosis. In particular, we generalize the mechanisms commonly used to design SMFPs for studying apoptosis. In addition, we discuss the limitations of reported probes, and emphasize the potential challenges and prospects in the future. We believe that this review will provide a comprehensive summary and challenging direction for the development of SMFPs in apoptosis related fields.

Lysosomal-targeted fluorescent probe based pH regulating reactivity for tracking cysteine dynamics under oxidative stress

The ability to detect and visualize cellular events and associated biological analytes is essential for the understanding of their physiological and pathological functions. Cysteine (Cys) plays a crucial role in biological systems and lysosomal homeostasis. This puts forward higher requirements on the performance of the probe. Herein, we rationally designed a coumarin-based probe for the reversible, specific, sensitive, and rapid detection of Cys based on pH regulating reactivity. The obtained probe (ECMA) introduces a morpholine moiety to target lysosomes, and α,β-unsaturated-ketone with an electron-withdrawing CN group served as a reversible reaction site for Cys. Importantly, ECMA was successfully applied to the real-time monitoring of Cys dynamics in living cells. Furthermore, cell imaging clearly revealed that exogenous Cys could induce the up-regulation of lysosomal ROS, which provided a powerful tool for investigating the relationship between oxidative stress and lysosomal Cys.

Treatment evaluation of Rheumatoid arthritis by in situ fluorescence imaging of the Golgi cysteine

Rheumatoid arthritis (RA) is a long-term systemic inflammatory disease that causes severe joint pain. Golgi stress caused by redox imbalance significantly involves in acute and chronic inflammatory diseases, in which cysteine (Cys), as a representative reducing agent, may be an effective biomarker for RA. Hence, in order to achieve RA early detection and drugs evaluation, based on our previous work about innovative Golgi-targeting group, we established a phenylsulfonamide-modified fluorescence probe, Golgi-Cys, for the selective fluorescence imaging of Cys in Golgi apparatus in vivo. By application of Golgi-Cys, the Cys changes under Golgi stress in cells were elucidated. More importantly, we found that the probe can be effectively utilized for the RA detection and treatment evaluation in situ.

Rational design of a near-infrared dual-emission fluorescent probe for ratiometric imaging of glutathione in cells

Sensors for which the output signal is an intensity change for a single-emission peak are easily disturbed by many factors, such as the stability of the instrument, intensity of the excitation light, and biological background. However, for ratiometric fluorescence sensors, the output signal is a change in the intensity ratio of two or more emission peaks. The fluorescence intensity of these emission peaks is similarly affected by external factors; thus, these sensors have the ability to self-correct, which can greatly improve the accuracy and reliability of the detection results. To accurately image glutathione (GSH) in cells, gold nanoclusters (AuNCs) with intrinsic double emission at wavelengths of 606 nm and 794 nm were synthesized from chloroauric acid. With the emission peak at 606 nm as the recognition signal and the emission peak at 794 nm as the reference signal, a near-infrared dual-emission ratio fluorescence sensing platform was constructed to accurately detect changes in the GSH concentration in cells. In vitro and in vivo analyses showed that the ratiometric fluorescent probe specifically detects GSH and enables ultrasensitive imaging, providing a new platform for the accurate detection of active small molecules.

A simple lysosome-targeted fluorescent probe based on flavonoid for detection of cysteine in living cells

Cysteine (Cys) is one of the most important biothiols that plays a crucial role in many physiological and pathological processes, and therefore it is of great importance to detect and analyze Cys in subcellular environments, such as in lysosomes. However, only a few fluorescent probes were reported to be capable of detecting Cys in lysosomes selectively. In this wok, we designed and developed a simple, accessible flavone-based fluorescent probe LFA for detecting Cys in lysosomes. Morpholine was employed as the targeting unit for lysosome, and acrylate group was chosen as the Cys-response unit. The probe was easily prepared by a two-step procedure and displayed large Stokes shift, high sensitivity, turn-on response toward Cys over homocysteine (Hcy), glutathione (GSH), and other amino acids. With low cytotoxicity and good cell permeability, the probe could be successfully applied for fluorescence imaging of Cys in living cells. Furthermore, colocalization experiment revealed that lysosomal-targetable ability of LFA was significant. These results indicated that such simple fluorescent probe could provide a promising tool for detection of lysosomal Cys in living biological systems.

Three-Photon AIE Pt(II) Complexes as Cysteine-Targeting Theranostic Agents for Tumor Imaging and Chemotherapy

Herein, we have synthesized a series of three-photon fluorescent Pt(II) complexes targeting a tumor-associated biothiol, cysteine (Cys), which allows it to be detected without any interference from other intracellular proteins. We focused on how to significantly improve the fluorescence response of Cys via regulating the recognition units in probes. The reaction of K₂PtCl₄ with L-CH₃ or L-COOEt in DMSO solution gave Lyso-Pt-CH₃ and Lyso-Pt-COOEt, respectively, which present four-coordinated square-planar geometries in mononuclear structures. Lyso-Pt-CH₃ consists of a Cys aptamer labeled with typical aggregation-induced emission (AIE) characteristics, which shows strong three-photon absorption cross section (3PA) only in the presence of Cys. It was found that Lyso-Pt-CH₃ displayed a perfect signal-to-noise ratio for imaging lysosomes and for rapid detection of Cys. Using Lyso-Pt-CH₃, Cys-related cellular mechanisms were proposed. We confirm that cystine (Cyss) could be absorbed in cells through cystine/glutamate antiporters (system x_c^-) and is then converted to Cys under the effect of enzymes. All of these suggest that Lyso-Pt-CH₃ might be a potential candidate as a simple and straightforward biomarker of lysosome-related Cys in vitro. Lyso-Pt-CH₃ can effectively identify tumor tissues with excessive levels of Cys. Lyso-Pt-CH₃ also showed excellent antitumor activity than cisplatin. This work provides a novel strategy for the rational design of controllably activated and Cys-targeted Pt(II) anticancer prodrugs for clinical diagnosis and treatment.

Activity-Based Photosensitizers with Optimized Triplet State Characteristics Toward Cancer Cell Selective and Image Guided Photodynamic Therapy

Activity-based theranostic photosensitizers are highly attractive in photodynamic therapy as they offer enhanced therapeutic outcome on cancer cells with an imaging opportunity at the same time. However, photosensitizers (PS) cores that can be easily converted to activity-based photosensitizers (aPSs) are still quite limited in the literature. In this study, we modified the dicyanomethylene-4H-chromene (DCM) core with a heavy iodine atom to get two different PSs (DCMO-I, I-DCMO-Cl) that can be further converted to aPS after simple modifications. The effect of iodine positioning on singlet oxygen generation capacity was also evaluated through computational studies. DCMO-I showed better performance in solution experiments and further proved to be a promising phototheranostic scaffold via cell culture studies. Later, a cysteine (Cys) activatable PS based on the DCMO-I core (DCMO-I-Cys) was developed, which induced selective photocytotoxicity along with a fluorescence turn-on response in Cys rich cancer cells.

Real-time imaging of intracellular cysteine level fluctuations during Cu2+ or H2O2 induced redox imbalance using a turn-on fluorescence sensor

Redox balance is a necessary guarantee to maintain the normal physiological activities of organisms. Cysteine (Cys), a critical biological thiol, has the effect of maintaining redox balance in the body. The concentration of intracellular Cys is abnormal under redox imbalance, thereby resulting in multiple diseases. Additionally, studies have revealed that Cu²⁺ can stimulate the body to produce excess reactive oxygen species (ROS, similar to H₂O₂), and the generated ROS will consume reducing substances (such as Cys) in the body, leading to redox imbalance. Thus, finding a simple and effective method to monitor Cys under redox imbalance is pressing. Here, a turn on probe (DDNO) was proposed by connecting SBD-Cl to a red dye (HDM). The probe can specifically recognize Cys with rapid response (180 s) and low detection limit (0.61 μM) through substitution-rearrangement reaction between sulfhydryl and chlorine atom. Bioimaging experiments indicated that the probe has good biocompatibility and cell membrane permeability, which can be applied to monitor the fluctuation of Cys levels in live cells and zebrafish under the redox imbalance induced by Cu²⁺ or H₂O₂.

Endogenous cysteine fluorescence monitoring and its deployment in tumour demarcation

A cysteine-specific fluorescent probe with a wide concentration detection range was used to monitor changes in cysteine levels in HeLa cells under stress and to demarcate the boundary of a xenograft tumour.

A long-wavelength fluorescent probe with a large Stokes shift for lysosome-targeted imaging of Cys and GSH

Biothiols including cysteine (Cys) and glutathione (GSH) are biological signaling molecules responsible for cell detoxification, cell metabolism and neutralization of reactive oxygen species. Here, we synthesized a long-wavelength fluorescent probe, DCIMA, for lysosome-targeted imaging of Cys and GSH in living cells. DCIMA is consisted of a dicyanoisophorone core modified with an acrylate group for biothiol detection through the Michael addition reaction and a morpholine group as the lysosome-targeting agent. The presence of the electron-donating morpholine group also enhances the intramolecular charge transfer mechanism of the probe, thereby enabling its long-wavelength fluorescence emission (670 nm) and large Stokes shift (180 nm). In concentration range of 0-30 μM, the probe was determined to react quickly with both Cys and GSH with low detection limits (<5 min, 35.2 nM for GSH and 34.8 nM for Cys) and achieve the sensitive fluorescence imaging of the biothiols located in the lysosomes of living cells.

Molecular-Dimension-Dependent ESIPT Break for Specific Reversible Response to GSH and Its Real-Time Bioimaging

Glutathione (GSH) plays many important roles in maintaining intracellular redox homeostasis, and determining its real-time levels in the biological system is essential for the diagnosis, treatment, and pathological research of related diseases. Fluorescence imaging has been regarded as a powerful tool for tracking biomarkers in vivo, for which specificity, reversibility, and fast response are the main issues to ensure the real-time effective detection of analytes. The determination of GSH is often interfered with by other active sulfur species. However, in addition to the common features of nucleophilic addition, GSH is unique in its large molecular scale. 2-(2-Hydroxyphenyl) benzothiazole (HBT) was often formed in the ESIPT process. In this study, HBT was installed with α,β-unsaturated ketone conjugated coumarin derivates or nitrobenzene, which were used to adjust the reactivity of α,β-unsaturated ketone. Experimental and theoretical calculations found ESIPT to be favorable in HBT-COU but not HBT-COU-NEt₂ or HBT-BEN-NO₂ due to the higher electronic energies in the keto form. Thus, for HBT-COU, in the presence of GSH, the hydrogen-bonding interaction between C═N of the HBT unit and carboxyl of GSH would inhibit the process, simultaneously promoting the Michel addition reaction between α,β-unsaturated ketone and GSH. As a consequence, probe HBT-COU could exhibit a rapid reversible ratiometric response to GSH. Small structures of Hcy and Cys are passivated for such reactions. Cell imaging demonstrated the specific response of the probe to GSH, and the probe was successfully used to monitor fluctuations in GSH concentration during cells apoptosis in real-time.

Three asymmetric BODIPY derivatives as fluorescent probes for highly selective and sensitive detection of cysteine in living cells

Biothiols are widely involved in various important physiological activities and play a significant role in maintaining redox homeostasis in living organisms. Herein, we designed and synthesized three new asymmetric fluorescent probes (BDP-S-Ph, BDP-S-ENE and BDP-S-R) to discriminate Cys from Hcy/GSH. These probes reacted with Cys to form meso-amino-BODIPYs via SNAr substitution-rearrangement, thereby inducing a fluorescence turn-on effect. Moreover, they could selectively and sensitively detect Cys in solution with low detection limits (50 nM, 28 nM and 87 nM, respectively). Through comparing the response rates of the three probes to Cys, we concluded that the increase of conformational restrictions led to a decrease in probe reactivity. Besides, the sensing mechanism was demonstrated by mass spectrometry. Furthermore, cell experiments indicated that the probes were able to image exogenous and endogenous Cys through green or red channels in living cells.

Identification and elimination of cancer cells by folate-conjugated CdTe/CdS Quantum Dots Chiral Nano-Sensors

The specific identification and elimination of cancer cells has been a great challenge in the past few decades. In this study, the circular dichroism (CD) of cells was measured by a self-designed special system through the folate-conjugated chiral nano-sensor. A novel method was established to recognize cancer cells from normal cells according to the chirality of cells based on their CD signals. After a period of interaction between the nano-sensor and cells, the sharp weakening of CD signals was induced in cancer cells but normal cells remained unchanged. The biocompatibility of the nano-sensor was evaluated and the result showed that it exhibited significant cytotoxic activity against cancer cells while no obvious damage on normal cells. Notably, the research indicated that the nano-sensor may selectively cause apoptosis in cancer cells, and thus, have the potential to act as an antitumor agent.

A lysosome-targeted near-infrared fluorescent probe for imaging endogenous cysteine (Cys) in living cells

Cysteine (Cys) is one of the most important essential biothiols in lysosomes. Highly selective probes for specific detection and imaging of lysosomal Cys over other biological thiols are rare. Herein, we developed a lysosome-targeted near-infrared fluorescent probe SHCy-C based on a novel NIR-emitting thioxanthene-indolium dye. Due to the turn-on fluorescence response elicited by the intramolecular charge transfer (ICT) processes before and after the reaction with Cys, probe SHCy-C exhibits high selectivity and sensitivity (16 nM) for the detection of Cys. More importantly, probe SHCy-C is found to precisely target lysosomes and achieves the "turn-on" detection and imaging of endogenous Cys in lysosomes.

Dual modulation sites for a reversible fluorescent probe for GSH over Cys/Hcy

An abnormal concentration of glutathione (GSH) is a health-associated risk factor, and it is an important signal for diseases such as Parkinson's disease, liver injury and cancer.

The chronological evolution of small organic molecular fluorescent probes for thiols

Abnormal concentrations of biothiols such as cysteine, homocysteine and glutathione are associated with various major diseases. In biological systems, the structural similarity and functional distinction of these three small molecular thiols has not only required rigorous molecular design of the fluorescent probes used to detect each thiol specifically, but it has also inspired scientists to uncover the ambiguous biological relationships between these bio-thiols. In this minireview, we will discuss the evolution of small organic molecular fluorescent probes for the detection of thiols over the past 60 years, highlighting the potent methodologies used in the design of thiol probes and their particular applications in the semi-quantification of cellular thiols and real-time labelling. At the same time, the present challenges that limit their further application will be discussed. We hope that this minireview will promote future research to enable deeper insight into the crucial role of thiols in biological systems.

The chronological evolution of small organic molecular fluorescent probes for thiols: from separation dependency analysis to cellular specific analysis, what's next?

The Role of Amino Acids in Neurotransmission and Fluorescent Tools for Their Detection

Neurotransmission between neurons, which can occur over the span of a few milliseconds, relies on the controlled release of small molecule neurotransmitters, many of which are amino acids. Fluorescence imaging provides the necessary speed to follow these events and has emerged as a powerful technique for investigating neurotransmission. In this review, we highlight some of the roles of the 20 canonical amino acids, GABA and β-alanine in neurotransmission. We also discuss available fluorescence-based probes for amino acids that have been shown to be compatible for live cell imaging, namely those based on synthetic dyes, nanostructures (quantum dots and nanotubes), and genetically encoded components. We aim to provide tool developers with information that may guide future engineering efforts and tool users with information regarding existing indicators to facilitate studies of amino acid dynamics.

A fluorescent probe based on reversible Michael addition-elimination reaction for the cycle between cysteine and H2O2

Cysteine oxidation by H₂O₂, generating either cysteine sulfenic acid (CSOH) or disulfide (CSSC), is involved in redox homeostasis and signaling. Compared with quantification of the cysteine content, monitoring the cysteine dynamics in real-time, in particular, takes on even greater importance. However, existing fluorescent probes suffer from low specificity or irreversible recognition mechanisms. In the present work, we have successfully developed a reversible fluorescent probe for the cycle between cysteine and H₂O₂ based on the Michael addition-elimination reaction. This probe features a specific and quantitative response to cysteine. The reversible detection was realized repeatedly with the addition of cysteine and H₂O₂ in order. We also demonstrated its usage for monitoring exogenous and endogenous cysteine in living cells. Eventually, this probe was capable of imaging cysteine dynamically in real-time.

Heat Stroke in Cell Tissues Related to Sulfur Dioxide Level Is Precisely Monitored by Light-Controlled Fluorescent Probes

Heat stroke (HS) can cause serious organism damage or even death. Early understanding of the mechanism of heat cytotoxicity can prevent or treat heat stroke related diseases. In this work, probe Ly-NT-SP was synthesized, characterized, and used for sulfur dioxide (SO₂) detection in lysosomes. PBS solutions of probe Ly-NT-SP at pH 5.0 present a marked broad emission band in the green zone (535 nm). After UV irradiation, the spiropyran group in Ly-NT-SP isomerizes to the merocyanine form (Ly-NT-MR), which presented a weak red-shifted emission at 630 nm. In addition, photocontrolled isomerization of Ly-NT-SP to Ly-NT-MR generated a C═C-C═N⁺ fragment able to react, through a Michael addition, with SO₂ to yield a highly emissive adduct with a marked fluorescence in the green channel (535 nm). In vitro studies showed a remarkable selectivity of photoactivated Ly-NT-MR to SO₂ with a limit of detection as low as 4.7 μM. MTT viability assays demonstrated that the Ly-NT-SP is nontoxic to HeLa cells and can be used to detect SO₂ in lysosomes. Taking advantage of this, the sensor is successfully applied to image increasing SO₂ values in lysosomes during heat shock for the first time. Moreover, we also confirmed that the increased SO₂ can protect the small intestine against damage induced by heat shock through regulating oxidative stress in cells and mice.

Visualization of the cysteine level during Golgi stress using a novel Golgi-targeting highly specific fluorescent probe

A novel Golgi-targeting highly specific fluorescent probe was developed to visualize the level of cysteine during Golgi stress.

A new chloro-substituted dicyanoisophorone-based near-infrared fluorophore with a larger Stokes shift and its application for detecting cysteine in cells and in vivo

Many dicyanoisophorone-based fluorophores with an optical hydroxyl group have been explored to meet different imaging needs along with the rapid and wide development of molecular fluorescence bioimaging in recent years.

Fluorescent chemosensors based on conjugated polymers with N-heterocyclic moieties: two decades of progress

A brief summary of representative fluorescent chemosensors based on conjugated polymers with N-heterocyclic moieties, followed by a discussion on the limitations and challenges of current systems, as well as possible future research directions.

Mutual correlation evaluation of Cys and Hcy in serum through reaction activity regulated fluorescence quantification

We report herein a strategy involving using a single fluorescent probe with the assistance of two pH conditions to simultaneously detect cysteine and homocysteine quantitatively.

A near-infrared biothiol-specific fluorescent probe for cancer cell recognition

Cancer is a global health issue and a leading cause of death. The discrimination of cancer cells from normal cells is of significant importance for the early diagnosis of cancers. As one of the useful biomarkers for developing cancer diagnosis and chemotherapy resistance systems, biothiols not only play an essential role in physiological and pathological processes but also exhibit cytoprotective effects in the susceptibility to carcinogenesis. It would be highly desirable to explore near-infrared biothiol-specific fluorescent probes for cancer diagnosis with outstanding specificity. In this study, a novel near-infrared fluorescent probe BPO-THAZ decorated with thiazole as a recognition site was presented for sensitive and selective detection of endogenous biothiols. BPO-THAZ can be used to not only evaluate the biothiol level in living HeLa cells upon treatment with H2O2 or anti-cancer drugs but also assess endogenous biothiols in stem cells. Furthermore, BPO-THAZ was successfully utilized to discriminate cancer cells from normal cells showing great promise for cancer diagnosis.

A selective cascade reaction-based probe for colorimetric and ratiometric fluorescence detection of benzoyl peroxide in food and living cells

A novel colorimetric and ratiometric fluorescent probe (Cou-BPO) was readily prepared for specific detection of harmful benzoyl peroxide (BPO). The probe Cou-BPO reacted with BPO via a selective oxidation cleavage-induced cascade reaction of the pinacol phenylboronate group, which resulted in an observable colorimetric and ratiometric fluorescence response towards BPO with a fast response time (<15 min) and a low detection limit (56 nM). For practical application, facile, portable and sensitive test paper of Cou-BPO has been prepared for visual detection of BPO. Furthermore, we employed Cou-BPO as a probe to determine BPO in food samples and living cells.

A Highly Selective and Ultrasensitive Fluorescent Probe for Monitoring Hg2+ and Its Applications in Real Water Samples

Mercury ions as high toxic pollutants have received wide-spread attention because of their poisonousness, persistence and enrichment. To better understand the distribution of mercury species and supplement more detailed toxicological research, it is necessary to develop some methods for monitoring mercury ions with high sensitivity and selectivity. Therefore, a simple rhodol-based highly selective fluorescent probe, RH-Hg, has been developed for monitoring Hg²⁺ with thiocarbamate as the recognition receptor. The probe RH-Hg can quantificationally detect mercury ions in aqueous solution assisted by hydrogen peroxide (H₂O₂), and it can discriminate Hg²⁺ through "naked-eye" observation of the color changes from light orange to dark pink. Finally, the practical applications of the probe RH-Hg in the river water further demonstrated that it will be an effective and economical tool for monitoring the distribution of Hg²⁺ in the environment.

An ultralow concentration of two-photon fluorescent probe for rapid and selective detection of lysosomal cysteine in living cells

Herein we reported a two-photon (TP) fluorescence "turn-on" probe MNPO, exhibiting high selectivity and sensitivity towards intracellular cysteine (Cys) with excellent lysosomal localization. The probe displayed fast response towards Cys over homocysteine (Hcy), glutathione (GSH), and other various analytes under physiological conditions. Low cytotoxicity made it successful for TP imaging of Cys in HeLa cells with an ultralow probe concentration of 250 nM, and a rapid response of only 10 min. Simultaneously, colocalization experiments in lysosome demonstrated its ability for specific in situ detection of lysosomal Cys in living cells, which shed light on its potential applications in biomedical applications. Beyond that MNPO was successfully applied for TP imaging of Cys in mice organ tissues such as heart, liver, and spleen, and the penetration depth of mice heart tissue was up to 184 μm, which disclosed the predominant TP characteristic. We believe that this study will provide some useful information toward diagnosis and treatment of pathogenesis associated with Cys or lysosomes in future.

Lysosome-Targeted Single Fluorescence Probe for Two-Channel Imaging Intracellular SO₂ and Biothiols

As the members of reactive sulfur species, SO₂ and biothiols play a significant role in physiological and pathological processes and directly influence numerous diseases. Furthermore, SO₂ and biothiols can provide a reductive environment for lysosomes to carry out their optimal functionality. To this end, the development of single fluorescent probes for imaging SO₂ and biothiols from different emission channels is highly desirable for understanding their physiological nature. Here, a lysosome-targeted fluorescent probe (BPO-DNSP) with a dual reaction site for SO₂ and biothiols was presented. BPO-DNSP can sensitively and selectively respond to SO₂ in the green channel with a large Stokes shift over 105 nm, and to biothiols in the near-infrared emission channel with a large Stokes shift over 109 nm. The emission shift for the two channels was as high as 170 nm. Colocalization experiments verified that BPO-DNSP can selectively enrich lysosomes. Notably, BPO-DNSP can not only be used to image intracellular SO₂ and biothiols from two different channels, but also to monitor the conversion of biothiols to SO₂ without adding exogenous enzymes in living HeLa cells.

A selective cascade reaction-based probe for colorimetric and ratiometric fluorescence detection of benzoyl peroxide in food and living cells

A colorimetric and ratiometric fluorescent probe (Cou-BPO) was prepared for food analysis and cell imaging; it showed high selectivity, sensitivity, visible and fast response towards BPO via a selective oxidation cleavage-induced cascade reaction.

A copper-mediated on–off–on gold nanocluster for endogenous GSH sensing to drive cancer cell recognition

The AuNCs@Tf-Cu²⁺system for the sensitive and selective detection of endogenous glutathione (GSH) can illuminate tumor cells rather than normal cells, which implied its great potential application in cancer diagnosis.

A selective cascade reaction-based probe for colorimetric and ratiometric fluorescence detection of benzoyl peroxide in food and living cells

A colorimetric and ratiometric fluorescent probe (Cou-BPO) was prepared for food analysis and cell imaging; it showed high selectivity, sensitivity, visible and fast response towards BPO via a selective oxidation cleavage-induced cascade reaction.

Functional synthetic probes for selective targeting and multi-analyte detection and imaging

In contrast to the classical design of a probe with one binding site to target one specific analyte, probes with multiple interaction sites or, alternatively, with single sites promoting tandem reactions to target one or multiple analytes, have been developed. They have been used in addressing the inherent challenges of selective targeting in the presence of structurally similar compounds and in complex matrices, as well as the visualization of the in vivo interaction or crosstalk between the analytes. Examples of analytes include reactive sulfur species, reactive oxygen species, nucleotides and enzymes. This review focuses on recent innovations in probe design, detection mechanisms and the investigation of biological processes. The vision is to promote the ongoing development of fluorescent probes to enable deeper insight into the physiology of bioactive analytes.

Constructing a far-red to near-infrared fluorescent probe for highly specific detection of cysteine and its bioimaging applications in living cells and zebrafish

A novel far-red to near-infrared fluorescent probe for highly specific detection of cysteine without interference.

Recent advances of dicyano-based materials in biology and medicine

We highlight the development of dicyano-based fluorescent materials in biology and medicine.

A NIR facile, cell-compatible fluorescent sensor for glutathione based on Michael addition induced cascade spirolactam opening and its application in hepatocellular carcinoma

A NIR fluorescence probe with NIR emission wavelength at 746 nm and high quantum yield of 0.36 was designed and synthesized to selectively detect GSH over Hcy and Cys in living systems.