Small-molecule based fluorescent probes are increasingly important for the detection and imaging of biological signaling molecules due to their simplicity, high selectivity and sensitivity, whilst being non-invasive, and suitable for real-time analysis of living systems. With this perspective we highlight sensing mechanisms including Forster resonance energy transfer (FRET), intramolecular charge transfer (ICT), photoinduced electron transfer (PeT), excited state intramolecular proton transfer (ESIPT), aggregation induced emission (AIE) and multiple modality fluorescence approaches including dual/triple sensing mechanisms (DSM or TSM). Throughout the perspective we highlight the remaining challenges and suggest potential directions for development towards improved small-molecule fluorescent probes suitable for biosensing.

/pdf/fluorescent-small-organic-probes-for-biosensing-ffejne1wl9.pdf

Fluorescent small organic probes for biosensing

Abnormal microenvironments (viscosity, polarity, pH, etc.) have been verified to be closely associated with numerous pathophysiological processes such as inflammation, neurodegenerative diseases, and cancer. As a result, deep insights into these pathophysiological microenvironments are particularly beneficial for clinical diagnosis and treatment. However, the monitoring of pathophysiological microenvironments is unattainable by the traditional clinical diagnostic techniques such as magnetic resonance imaging, computed tomography, and positron emission tomography. Recently, fluorescence imaging has shown tremendous advantages and potential in the tracing of pathophysiological microenvironment variations. In this context, a general discussion is provided on the state-of-the-art progress of fluorescent probes for visualizing pathophysiological microenvironments (viscosity, pH, and polarity), since 2016, as well as the future perspectives in this challenging field.

Fluorescence imaging of pathophysiological microenvironments

Fluorescent probes for biothiols have aroused increasing interest owing to their potential to enable better understanding of the diverse physiological and pathological processes related to the biothiol species. BODIPY fluorophores exhibit excellent optical properties, which can be readily tailored by introducing diverse functional units at various positions of the BODIPY core. In the present review, the development of fluorescent probes based on BODIPYs for the detection of biothiols are systematically summarized, with emphasis on the preferable detection of individual biothiols, as well as simultaneous discrimination among cysteine (Cys), homocysteine (Hcy), reduced glutathione (GSH). In addition, organelle-targeting probes for biothiols are also highlighted. The general design principles, various recognition mechanisms, and biological applications are elaboratively discussed, which could provide a useful reference to researchers worldwide interested in this area.

BODIPY-Based Fluorescent Probes for Biothiols

Recent progress in fluorescent probes for detection of carbonyl species: Formaldehyde, carbon monoxide and phosgene

The discovery of a near-infrared (NIR, 650-900 nm) fluorescent chromophore hemicyanine dye with high structural tailorability is of great significance in the field of detection, bioimaging, and medical therapeutic applications. It exhibits many outstanding advantages including absorption and emission in the NIR region, tunable spectral properties, high photostability as well as a large Stokes shift. These properties are superior to those of conventional fluorogens, such as coumarin, fluorescein, naphthalimides, rhodamine, and cyanine. Researchers have made remarkable progress in developing activity-based multifunctional fluorescent probes based on hemicyanine skeletons for monitoring vital biomolecules in living systems through the output of fluorescence/photoacoustic signals, and integration of diagnosis and treatment of diseases using chemotherapy or photothermal/photodynamic therapy or combination therapy. These achievements prompted researchers to develop more smart fluorescent probes using a hemicyanine fluorogen as a template. In this review, we begin by describing the brief history of the discovery of hemicyanine dyes, synthetic approaches, and design strategies for activity-based functional fluorescent probes. Then, many selected hemicyanine-based probes that can detect ions, small biomolecules, overexpressed enzymes and diagnostic reagents for diseases are systematically highlighted. Finally, potential drawbacks and the outlook for future investigation and clinical medicine transformation of hemicyanine-based activatable functional probes are also discussed.

Activity-based NIR fluorescent probes based on the versatile hemicyanine scaffold: design strategy, biomedical applications, and outlook.

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.

Functional Synthetic Probes for Selective Targeting and Multi-analyte Detection and Imaging

We report the first diselenide-based probe for the selective detection of thioredoxin reductase (TrxR), an enzyme commonly overexpressed in melanomas. The probe design involves conjugation of a seminaphthorhodafluor dye with a diselenide moiety. TrxR reduces the diselenide bond, triggering a fluorescence turn-on response of the probe. Kinetic studies reveal favorable binding of the probe with TrxR with a Michaelis-Menten constant (Km ) of 15.89 μm. Computational docking simulations predict a greater binding affinity to the TrxR active site in comparison to its disulfide analogue. In vitro imaging studies further confirmed the diselenide probe exhibited improved signaling of TrxR activity compared to the disulfide analogue.

A Diselenide Turn‐On Fluorescent Probe for the Detection of Thioredoxin Reductase

Correction for ‘Functional synthetic probes for selective targeting and multi-analyte detection and imaging’ by Yongkang Yue et al., Chem. Soc. Rev., 2019, DOI: 10.1039/c8cs01006d.

/pdf/correction-functional-synthetic-probes-for-selective-281xfmrn7o.pdf

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

The thioredoxin system is vital in maintaining the cellular redox state and is implicated in various cancers and other diseases. It comprises of thioredoxin reductase, thioredoxin and NADPH. Various methods have been developed for the detection and quantification of the thioredoxin reductase enzyme. Most of these methods suffer the shortfall of poor specificity, hence there is need to develop more robust and specific techniques. Recently, there has been an increased interest in fluorescent probes that can target thioredoxin reductase. This review highlights the progress in the synthesis and application of the different fluorescent probes that have been employed for this purpose.

/pdf/fluorogenic-probes-for-thioredoxin-reductase-activity-1ltdf1eeqi.pdf

Fluorogenic probes for thioredoxin reductase activity

Seminaphthofluorophore-selenium probes are disclosed. The probes include a seminaphthofluorophore scaffold substituted with at least one diselenide moiety having a formula –Y-C(Q)O-(CH2)m-Se-Se-(CH2)n-ORf, where Rf is hydrogen or C1-C3 alkyl, Q is O or S, Y is O or N(Rg) where Rg is H or alkyl, and m and n independently are integers. The probes may be used to detect presence of a thioredoxin reductase.

Tendai Mafireyi

Papers

Functional Synthetic Probes for Selective Targeting and Multi-analyte Detection and Imaging

A Diselenide Turn‐On Fluorescent Probe for the Detection of Thioredoxin Reductase

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

Fluorogenic probes for thioredoxin reductase activity

Seminaphthofluorophore-selenium probes for thioredoxin reductase