'AND'-based fluorescence scaffold for the detection of ROS/RNS and a second analyte

Enzyme-responsive, multi-lock optical probes for molecular imaging and disease theranostics

Optical imaging is an indispensable tool for non-invasive visualization of biomolecules in living organisms, thereby offering a sensitive approach for disease diagnosis and image-guided disease treatment. Single-lock activatable optical probes (SOPs) that specifically switch on optical signals in the presence of biomarkers-of-interest have shown both higher detection sensitivity and imaging quality as compared to conventional "always-on" optical probes. However, such SOPs can still show "false-positive" results in disease diagnosis due to non-specific biomarker expression in healthy tissues. By contrast, multi-lock activatable optical probes (MOPs) that simultaneously detect multiple biomarkers-of-interest could improve detection specificity towards certain biomolecular events or pathological conditions. In this Review, we discuss the recent advancements of enzyme-responsive MOPs, with a focus on their biomedical applications. The higher detection specificity of MOPs could in turn enhance disease diagnosis accuracy and improve treatment efficacy in image-guided disease therapy with minimal toxicity in the surrounding healthy tissues. Finally, we discuss the current challenges and suggest future applications of MOPs.

Levonorgestrel protected Au10 cluster for hypochlorite sensing in living organisms

BACKGROUND

Highly reactive oxygen species (ROS) could lead to serious damage in living cells and are associated with many diseases like cancers. Metal cluster with strong fluorescence has great potential in biosensing and many thiolate ligands-protected clusters have been applied in ROS sensing.

RESULTS

In this work, we synthesized levonorgestrel protected Au10 cluster with specific sensing ability for highly ROS via crystal transformation from Au8 cluster, demonstrating the significance of inner core structure on detecting performance. The detection limit of Au10 cluster for ClO- could reach as low as 0.1 μM. This fluorescent probe not only achieving detection of exogenous ClO- in living cells and zebrafish, but also successful imaging of endogenous ClO- in HeLa and HepG2 cells.

SIGNIFICANCE

In comparison to previously reported cluster-based sensors for ROS, this work proposes a different reaction mechanism of metal nanoclusters for ROS detection (breakage of gold-alkynyl bond and oxidation of alkynyl group). This provides new directions for designing specific ROS probes and broadens the applications of metal clusters in disease diagnostics.

Stimuli-responsive linkers and their application in molecular imaging

Molecular imaging is a non-invasive imaging method that is widely used for visualization and detection of biological events at cellular or molecular levels. Stimuli-responsive linkers that can be selectively cleaved by specific biomarkers at desired sites to release or activate imaging agents are appealing tools to improve the specificity, sensitivity, and efficacy of molecular imaging. This review summarizes the recent advances of stimuli-responsive linkers and their application in molecular imaging, highlighting the potential of these linkers in the design of activatable molecular imaging probes. It is hoped that this review could inspire more research interests in the development of responsive linkers and associated imaging applications.

ClO- Induced Dual-Excitation Fluorescent Probes Responding to Diverse Testing Modes with Ratio Methodology

Single-excitation ratio fluorescent probes have enabled the output signal with high signal-to-noise ratio, but are still plagued with technique challenges, including signal distortion and limited application scenario. Herein, a dual-excitation near-infrared (NIR) fluorescent probe P1 of coumarin derivatives is constructed, showing high signal output ability in the visible region and high tissue penetration depth ability in the NIR region. As NIR probe P1 selectively recognizes ClO^-, the emission signal in the visible region (480 nm) of P1 is enhanced during the recognition process. Meanwhile, the NIR emission (830 nm) of the conjugated system is weakened, finally realizing that ClO^- triggered the dual-excitation (720/400 nm) ratio fluorescence signal detection and monitoring. The signal of detection in vitro has high responsiveness. Meanwhile, in the process of NIR monitoring in vivo, positive contrast imaging of fluorescence is constructed, which can accurately monitor ClO^- changes over time. The current dual-excitation fluorescence-based data calibration and/or comparison method improves the application of the traditional single-excitation ratio fluorescence strategy and provide innovative detection tools for accurate measurement of fluorescence detection, with detection/monitoring modes suitable for different physiological environments.

Development of peroxynitrite-responsive fluorescence probe for recognition of drug-induced liver injury

Peroxynitrite (ONOO^-) as an active substance, is produced during normal physiological process, which plays an important role in maintaining cell REDOX balance and cell function. Moreover, the peroxynitrite is involved in many diseases and especially can be used as a biomarker of drug-induced liver injury (DILI). Therefore, in this work, we synthesized a fluorescent probe JQ-3 for detecting ONOO^-. The results showed the probe JQ-3 possessed excellent selectivity, fast response time (10 min) and low detection limit (32 nM). The probe JQ-3 is almost unaffected by pH, showing the potential application in biological systems. Moreover, the probe JQ-3 can be successfully used for the detection of exogenous and endogenous ONOO^- in living cells and zebrafish. At the same time, the DILI was successfully recognized by visualizing ONOO^- with JQ-3 in living cells and zebrafish. Therefore, the probe JQ-3 provides a potential tool for detecting ONOO^- to understand physiological and pathology processes of disease.

An 'AND'-based ratiometric fluorescence probe for the sequential detection of biothiols and hypochlorous acid

An 'AND'-based ratiometric fluorescence probe for the sequential detection of biothiols and hypochlorous acid was developed. FRET was observed only when RSHClO reacted with biothiols before reacting with hypochlorous acid, a phenomenon that has been confirmed in aqueous solutions and cells. This feature enables the probe to mimic biological processes and is particularly suitable for imaging oxidizing and reducing substances that cannot coexist.

Boronates as hydrogen peroxide-reactive warheads in the design of detection probes, prodrugs, and nanomedicines used in tumors and other diseases

Hydrogen peroxide (H₂O₂) has always been a topic of great interests attributed to its vital role in biological process. H₂O₂ is known as a major reactive oxygen species (ROS) which is involve in numerous physiological processes such as cell proliferation, signal transduction, differentiation, and even pathogenesis. A plenty of diseases development such as chronic disease, inflammatory disease, and organ dysfunction are found to be relevant to abnormality of H₂O₂ production. Thus, imminent and feasible strategies to modulate and detect H₂O₂ level in vitro and in vivo have gained great importance. To date, the boronate-based chemical structure probes have been widely used to address the problems from the above aspects because of the rearranged chemical bonding which can detect and quantify ROS including hydrogen peroxide (H₂O₂) and peroxynitrite (ONOO^-). This present article discusses boronate-based probes based on the chemical structure difference as well as reactivities to H₂O₂ and ONOO^-. In this review, we also focus on the application of boronate-based probes in the field of cell imaging, prodrugs nanoplatform, nanomedicines, and electrochemical biosensors for disease diagnosis and treatment. In a nutshell, we outline the recent application of boronate-based probes and represent the prospective potentiality in biomedical domain in the future.

Fluorescent probes and functional materials for biomedical applications

Due to their simplicity in preparation, sensitivity and selectivity, fluorescent probes have become the analytical tool of choice in a wide range of research and industrial fields, facilitating the rapid detection of chemical substances of interest as well as the study of important physiological and pathological processes at the cellular level. In addition, many long-wavelength fluorescent probes developed have also proven applicable for in vivo biomedical applications including fluorescence-guided disease diagnosis and theranostics (e.g., fluorogenic prodrugs). Impressive progresses have been made in the development of sensing agents and materials for the detection of ions, organic small molecules, and biomacromolecules including enzymes, DNAs/RNAs, lipids, and carbohydrates that play crucial roles in biological and disease-relevant events. Here, we highlight examples of fluorescent probes and functional materials for biological applications selected from the special issues “Fluorescent Probes” and “Molecular Sensors and Logic Gates” recently published in this journal, offering insights into the future development of powerful fluorescence-based chemical tools for basic biological studies and clinical translation.

Resorufin-based fluorescent probe with elevated water solubility for visualizing fluctuant peroxynitrite in progression of inflammation

Inflammation is a significant protective response in biological systems and associated with various diseases. Peroxynitrite (ONOO^-) as a highly active oxidant participates in the inflammatory process of organisms. Thus, it is necessary to construct novel fluorescent probes for exploring inflammation-related diseases through detecting endogenous ONOO^-. Resorufin-based fluorescent probes for testing ONOO^- were rare and suffered from poor water solubility. In this work, we elaborately designed three resorufin-based incorporating isatin derivatives probes RF-ITs and successfully obtained two highly selective probes RF-IT-OC and RF-IT-EG for ONOO^-. Comparing the other two probes, RF-IT-EG containing triethylene glycol monomethyl ether on isatin moiety displayed better water solubility (3.2 mg/L), faster response rate (60 s), larger signal-to-noise ratio (103-fold) and lower detection limit (87 nM) for monitoring ONOO^-. The cells imaging results manifested that probe RF-IT-EG could be applied to trace endogenous ONOO^- with inappreciable cytotoxicity. Moreover, the RF-IT-EG was capable of tracking the fluctuation of endogenous ONOO^- in LPS-stimulated inflamed mouse leg models. This work will provide a faithful and promising probe for illustrating the roles of ONOO^- in various inflammation-related diseases.

A novel 3D Zn-coordination polymer based on a multiresponsive fluorescent sensor demonstrating outstanding sensitivities and selectivities for the efficient detection of multiple analytes

A novel and unusual 3D luminescent coordination polymer (CP) [Zn₂(3-bpah)(bpta)(H₂O)]·3H₂O (1), where 3-bpah denotes N,N'-bis(3-pyridinecarboxamide)-1,2-cyclohexane and H₄bpta denotes 2,2',4,4'-biphenyltetracarboxylic acid, was successfully synthesized via hydrothermal methods from Zn(II) ions and 3-bpah and bpta ligands. The structure of this CP was investigated via powder X-ray diffraction (PXRD) analysis along with single crystal X-ray diffraction. Notably, 1 exhibits remarkable fluorescence behavior and stability over a wide pH range and in various pure organic solvents. More importantly, 1 can become an outstanding candidate for the selective and sensitive sensing of Fe³⁺, Mg²⁺, Cr₂O₇^2-, MnO₄^-, nitrobenzene (NB) and nitromethane (NM), at an extremely low detection limit. The changes in the fluorescence intensity exhibited by these six analytes in the presence of 1 over a wide pH range indicate that this polymer can be an excellent luminescent sensor. To the best of our knowledge, 1 is a rare example of a CP-based multiresponsive fluorescent sensor for metal cations, anions, and toxic organic solvents.

Turn on chemiluminescence-based probes for monitoring tyrosinase activity in conjunction with biological thiols

We report a chemiluminescent probe (CLPT1) that permits the paired detection of tyrosinase (Tyr) and biological thiols. Tyr only leads to a poor chemiluminescence response, a finding ascribed to the formation of a stable o-benzoquinone intermediate. The addition of glutathione (GSH), or ascorbate to the o-benzoquinone intermediate results in thiol conjugation or reduction to this intermediate, respectively. This produces a strong chemiluminescence response. Thiol co-dependence was demonstrated in live cells using the cell permeable analogue, CLPT3. The present chemiluminescence-based strategy allows the concurrent detection of tyrosinase activity and biological thiols.

Dual-locked spectroscopic probes for sensing and therapy

Optical imaging probes allow us to detect and uncover the physiological and pathological functions of an analyte of interest at the molecular level in a non-invasive, longitudinal manner. By virtue of simplicity, low cost, high sensitivity, adaptation to automated analysis, capacity for spatially resolved imaging and diverse signal output modes, optical imaging probes have been widely applied in biology, physiology, pharmacology and medicine. To build a reliable and practically/clinically relevant probe, the design process often encompasses multidisciplinary themes, including chemistry, biology and medicine. Within the repertoire of probes, dual-locked systems are particularly interesting as a result of their ability to offer enhanced specificity and multiplex detection. In addition, chemiluminescence is a low-background, excitation-free optical modality and, thus, can be integrated into dual-locked systems, permitting crosstalk-free fluorescent and chemiluminescent detection of two distinct biomarkers. For many researchers, these dual-locked systems remain a 'black box'. Therefore, this Review aims to offer a 'beginner's guide' to such dual-locked systems, providing simple explanations on how they work, what they can do and where they have been applied, in order to help readers develop a deeper understanding of this rich area of research.

A resorufin-based red-emitting fluorescent probe with high selectivity for tracking endogenous peroxynitrite in living cells and inflammatory mice

Peroxynitrite (ONOO^-) plays essential roles on various physiological and pathological processes of living systems as a short-lived and highly reactive nitrogen (RNS) specie. The construction of novel long-wavelength fluorescent probes with high specificity towards ONOO^- for imaging in vivo is still demand urgently. About this work, a novel resorufin-based red-emitting fluorescent probe for tracking ONOO^- has been constructed. The probe RFP exhibited high selectivity towards ONOO^- anion over other analytes. Utilizing the probe, ONOO^- could be directly observed by the naked eye. Furthermore, RFP was successfully applied for imaging endogenous ONOO^- in RAW264.7 cells and inflammatory mice. This work offers a convenient method for monitoring the intercellur ONOO^- that be expected to be applied for explaining the bio-functional roles of ONOO^- in living system.

Resorufin-based responsive probes for fluorescence and colorimetric analysis

The fluorescence imaging technique has attracted increasing attention in the detection of various biological molecules in situ and in real-time owing to its inherent advantages including high selectivity and sensitivity, outstanding spatiotemporal resolution and fast feedback. In the past few decades, a number of fluorescent probes have been developed for bioassays and imaging by exploiting different fluorophores. Among various fluorophores, resorufin exhibits a high fluorescence quantum yield, long excitation/emission wavelength and pronounced ability in both fluorescence and colorimetric analysis. This fluorophore has been widely utilized in the design of responsive probes specific for various bioactive species. In this review, we summarize the advances in the development of resorufin-based fluorescent probes for detecting various analytes, such as cations, anions, reactive (redox-active) sulfur species, small molecules and biological macromolecules. The chemical structures of probes, response mechanisms, detection limits and practical applications are investigated, which is followed by the discussion of recent challenges and future research perspectives. This review article is expected to promote the further development of resorufin-based responsive fluorescent probes and their biological applications.

Boronate-Based Probes for Biological Oxidants: A Novel Class of Molecular Tools for Redox Biology

Boronate-based molecular probes are emerging as one of the most effective tools for detection and quantitation of peroxynitrite and hydroperoxides. This review discusses the chemical reactivity of boronate compounds in the context of their use for detection of biological oxidants, and presents examples of the practical use of those probes in selected chemical, enzymatic, and biological systems. The particular reactivity of boronates toward nucleophilic oxidants makes them a distinct class of probes for redox biology studies. We focus on the recent progress in the design and application of boronate-based probes in redox studies and perspectives for further developments.

: a synthetic platform for the development of fluorescent probes for diagnostic and theranostic applications

Reaction-based fluorescent-probes have proven successful for the visualisation of biological species in various cellular processes. Unfortunately, in order to tailor the design of a fluorescent probe to a specific application (i.e. organelle targeting, material and theranostic applications) often requires extensive synthetic efforts and the synthetic screening of a range of fluorophores to match the required synthetic needs. In this work, we have identified Pinkment-OH as a unique “plug-and-play” synthetic platform that can be used to develop a range of ONOO⁻ responsive fluorescent probes for a variety of applications. These include theranostic-based applications and potential material-based/bioconjugation applications. The as prepared probes displayed an excellent sensitivity and selectivity for ONOO⁻ over other ROS. In vitro studies using HeLa cells and RAW 264.7 macrophages demonstrated their ability to detect exogenously and endogenously produced ONOO⁻. Evaluation in an LPS-induced inflammation mouse model illustrated the ability to monitor ONOO⁻ production in acute inflammation. Lastly, theranostic-based probes enabled the simultaneous evaluation of indomethacin-based therapeutic effects combined with the visualisation of an inflammation biomarker in RAW 264.7 cells.

Pinkment, a resorufin based ONOO⁻ selective and sensitive ‘plug and play’ fluorescence-based platform for in vitro and in vivo use, enables facile functionalisation for various imaging and theranostic applications.

A fluorescent ESIPT-based benzimidazole platform for the ratiometric two-photon imaging of ONOO- in vitro and ex vivo

In this work, we have developed an ESIPT-based benzimidazole platform (MO-E1 and MO-E2) for the two-photon cell imaging of ONOO- and a potential ONOO--activated theranostic scaffold (MO-E3). Each benzimidazole platform, MO-E1-3, were shown to rapidly detect ONOO- at micromolar concentrations (LoD = 0.28 μM, 6.53 μM and 0.81 μM respectively). The potential theranostic MO-E3 was shown to release the parent fluorophore and drug indomethacin in the presence of ONOO- but unfortunately did not perform well in vitro due to low solubility. Despite this, the parent scaffold MO-E2 demonstrated its effectiveness as a two-photon imaging tool for the ratiometric detection of endogenous ONOO- in RAW264.7 macrophages and rat hippocampus tissue. These results demonstrate the utility of this ESIPT benzimidazole-based platform for theranostic development and bioimaging applications.

Protein Encapsulation: A Nanocarrier Approach to the Fluorescence Imaging of an Enzyme-Based Biomarker

Here, we report a new pentafluoropropanamido rhodamine fluorescent probe (ACS-HNE) that allows for the selective detection of neutrophil elastase (NE). ACS-HNE displayed high sensitivity, with a low limit of detection (<5.3 nM), and excellent selectivity toward elastase over other relevant biological analytes and enzymes. The comparatively poor solubility and cell permeability of neat ACS-HNE was improved by creating an ACS-HNE-albumin complex; this approach allowed for improvements in the in situ visualization of elastase activity in RAW 264.7 cells relative to ACS-HNE alone. The present study thus serves to demonstrate a simple universal strategy that may be used to overcome cell impermeability and solubility limitations, and to prepare probes suitable for the cellular imaging of enzymatic activity in vitro.

Boronate ester cross-linked PVA hydrogels for the capture and H2O2-mediated release of active fluorophores

A new set of PVA hydrogels were formed using the boronate ester fluorescent probe PF1 and the novel boronate fluorescent probe PT1 as the covalent crosslinkers. Treatment with aqueous H2O2 allowed triggered release of the fluorescent dye accompanied by complete dissolution of the hydrogel.

Sensing Peroxynitrite in Different Organelles of Murine RAW264.7 Macrophages With Coumarin-Based Fluorescent Probes

The elucidation of biological processes involving reactive oxygen species (ROS) facilitates a better understanding of the underlying progression of non-communicable diseases. Fluorescent probes are a powerful tool to study various ROS and have the potential to become essential diagnostic tools. We have developed a series of coumarin fluorescent probes for the selective and sensitive detection of peroxynitrite (ONOO-), a key ROS. Coumarin based probes exhibit good photostability, large Stokes shift and high quantum yields. The three ratiometric probes all contain a boronate ester motif for the detection of ONOO- and a distinctive organelle targeting group. The study of ONOO- generation in a particular organelle will allow more precise disease profiling. Hence, targeting groups for the mitochondria, lysosome and endoplasmic reticulum were introduced into a coumarin scaffold. The three ratiometric probes displayed sensitive and selective detection of ONOO- over other ROS species. All three coumarin probes were evaluated in murine RAW264.7 macrophages for detection of basal and stimulated ONOO- formation.

The ICT-based fluorescence and colorimetric dual sensing of endogenous hypochlorite in living cells, bacteria, and zebrafish

This work demonstrates a novel chemosensor, SPTPA, that exhibits fluorescence and colorimetric dual sensing of hypochlorite with an ICT ON strategy.

Product-boosted fluorescence signal: a new approach for designing small-molecule probes for detection of peroxynitrite

In situ self-assembled boronate ester comprising commercially available 2-formylphenylboronic acid and 2-(2′,3′-bihydroxyphenyl)benzothiazole (BHBT) is explored for the detection of ONOO⁻ with product-boosted fluorescence.

Protein encapsulation: a new approach for improving the capability of small-molecule fluorogenic probes

Herein, we report a protein-based hybridization strategy that exploits the host-guest chemistry of HSA (human serum albumin) to solubilize the otherwise cell impermeable ONOO^- fluorescent probe Pinkment-OAc. Formation of a HSA/Pinkment-OAc supramolecular hybrid was confirmed by SAXS and solution-state analyses. This HSA/Pinkment-OAc hybrid provided an enhanced fluorescence response towards ONOO^- versus Pinkment-OAc alone, as determined by in vitro experiments. The HSA/Pinkment-OAc hybrid was also evaluated in RAW 264.7 macrophages and HeLa cancer cell lines, which displayed an enhanced cell permeability enabling the detection of SIN-1 and LPS generated ONOO^- and the in vivo imaging of acute inflammation in LPS-treated mice. A remarkable 5.6 fold (RAW 264.7), 8.7-fold (HeLa) and 2.7-fold increased response was seen relative to Pinkment-OAc alone at the cellular level and in vivo, respectively. We anticipate that HSA/fluorescent probe hybrids will soon become ubiquitous and routinely applied to overcome solubility issues associated with hydrophobic fluorescent imaging agents designed to detect disease related biomarkers.

Reaction-Based Fluorescent Probes for the Detection and Imaging of Reactive Oxygen, Nitrogen, and Sulfur Species

This Account describes a range of strategies for the development of fluorescent probes for detecting reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive (redox-active) sulfur species (RSS). Many ROS/RNS have been implicated in pathological processes such as Alzheimer's disease, cancer, diabetes mellitus, cardiovascular disease, and aging, while many RSS play important roles in maintaining redox homeostasis, serving as antioxidants and acting as free radical scavengers. Fluorescence-based systems have emerged as one of the best ways to monitor the concentrations and locations of these often very short lived species. Because of the high levels of sensitivity and in particular their ability to be used for temporal and spatial sampling for in vivo imaging applications. As a direct result, there has been a huge surge in the development of fluorescent probes for sensitive and selective detection of ROS, RNS, and RSS within cellular environments. However, cellular environments are extremely complex, often with more than one species involved in a given biochemical process. As a result, there has been a rise in the development of dual-responsive fluorescent probes (AND-logic probes) that can monitor the presence of more than one species in a biological environment. Our aim with this Account is to introduce the fluorescent probes that we have developed for in vitro and in vivo measurement of ROS, RNS, and RSS. Fluorescence-based sensing mechanisms used in the construction of the probes include photoinduced electron transfer, intramolecular charge transfer, excited-state intramolecular proton transfer (ESIPT), and fluorescence resonance energy transfer. In particular, probes for hydrogen peroxide, hypochlorous acid, superoxide, peroxynitrite, glutathione, cysteine, homocysteine, and hydrogen sulfide are discussed. In addition, we describe the development of AND-logic-based systems capable of detecting two species, such as peroxynitrite and glutathione. One of the most interesting advances contained in this Account is our extension of indicator displacement assays (IDAs) to reaction-based indicator displacement assays (RIAs). In an IDA system, an indicator is allowed to bind reversibly to a receptor. Then a competitive analyte is introduced into the system, resulting in displacement of the indicator from the host, which in turn modulates the optical signal. With an RIA-based system, the indicator is cleaved from a preformed receptor-indicator complex rather than being displaced by the analyte. Nevertheless, without a doubt the most significant result contained in this Account is the use of an ESIPT-based probe for the simultaneous sensing of fibrous proteins/peptides AND environmental ROS/RNS.

Reductive stress imaging in the endoplasmic reticulum by using living cells and zebrafish

Excessive accumulation of reducing agents in the ER leads to a constitutively high UPR. And the co-function of GSH, Cys and HOCl in biological processes is not well understood. To address this, a TP probe, NPCC, was developed for monitoring reductive stress in the ER. It can also distinguish cancer cells from normal cells.

Population analysis to increase the robustness of molecular computational identification and its extension into the near-infrared for substantial numbers of small objects

The first population analysis is presented for submillimetric polymer beads which are tagged with five multi-valued logic gates, YES, 2YES + PASS 1, YES + PASS 1, YES + 2PASS 1 and PASS 1 with H+ input, 700 nm near-infrared fluorescence output and 615 nm red excitation light as the power supply. The gates carry an azaBODIPY fluorophore and an aliphatic tertiary amine as the H+ receptor where necessary. Each logic tag has essentially identical emission characteristics except for the H+-induced fluorescence enhancement factors which consistently map onto the theoretical predictions, after allowing for bead-to-bead statistical variability for the first time. These enhancement factors are signatures which identify a given bead type within a mixed population when examined with a 'wash and watch' protocol under a fluorescence microscope. This delineates the scope of molecular computational identification (MCID) for encoding objects which are too small for radiofrequency identification (RFID) tagging.

A ratiometric fluorescent probe for detecting hypochlorite in the endoplasmic reticulum

A colorimetric and fluorescent probe ER-ClO was developed to detect cellular hypochlorite with high selectivity and sensitivity.

Coumarin-based fluorescent ‘AND’ logic gate probes for the detection of homocysteine and a chosen biological analyte

With this research we set out to develop a number of coumarin-based ‘AND’ logic fluorescence probes that were capable of detecting a chosen analyte in the presence of HCys. Probe JEG-CAB was constructed by attaching the ONOO⁻ reactive unit, benzyl boronate ester, to a HCys/Cys reactive fluorescent probe, CAH. Similarly, the core unit CAH was functionalised with the nitroreductase (NTR) reactive p-nitrobenzyl unit to produce probe JEG-CAN. Both, JEG-CAB and JEG-CAN exhibited a significant fluorescence increase when exposed to either HCys and ONOO⁻ (JEG-CAB) or HCys and NTR (JEG-CAN) thus demonstrating their effectiveness to function as AND logic gates for HCys and a chosen analyte.

With this research we set out to develop of a number of coumarin-based ‘AND’ logic fluorescence probes that were capable of detecting a chosen analyte in the presence of HCys.

ESIPT-based fluorescence probe for the rapid detection of peroxynitrite 'AND' biological thiols

An ESIPT-based 'AND' logic fluorescence probe (GSH-ABAH) was developed for the simultaneous detection of ONOO- and biological thiols. GSH-ABAH was shown to have good cell permeability and with the addition of just SIN-1 (ONOO- donor) or GSH, no fluorescence response was observed in live cells. However, in the presence of both analytes GSH-ABAH could be used to image exogenous ONOO- 'AND' GSH added to RAW264.7 cells.