A review: Red/near-infrared (NIR) fluorescent probes based on nucleophilic reactions of H2 S since 2015

Construction of a coumarin-based fluorescent probe for accurately visualizing hydrogen sulfide in live cells and zebrafish

Hydrogen sulfide (H2S), an important gas signaling molecule, is a regulator of many physiological processes, and its abnormal levels are closely related to the onset and progression of disease. It is vital to develop methods for specific tracking of H2S in clinical diagnosis and treatment. In this study, we designed an ultrasensitive and highly stable coumarin-based fluorescent probe Cou-H2S. Through the H2S-initiated tandem reaction, Cou-H2S successfully achieved highly selective and super-fast detection of H2S. Cou-H2S was successfully applied to the monitoring of endogenous and exogenous H2S at the cellular level and verified the validity of the detection of H2S in the LPS-induced zebrafish model. Therefore, Cou-H2S might provide new insights into the study of H2S-related diseases.

Development of fluorescent probes with specific recognition moiety for hydrogen polysulfide

Hydrogen polysulfide (H2Sn, n > 1) is an important component of reactive sulfur species (RSS), which is an important substance for maintaining the redox balance in cells. However, limited recognition moieties are available for hydrogen polysulfide probe design. In this study, we have constructed a small library containing several organic molecules to explore a new specific recognition moiety for H2Sn fluorescent probe design. To validate the discovery, two fluorescent probes, 7 and BCC, were further developed based on coumarin and its derivative. The probes exhibited desirable specificity for H2Sn monitoring, which can be used for detecting H2Sn in solution and cells. The new specific recognition moiety for H2Sn fluorescent probe design discovered in this work has certain guiding significance for development of H2Sn probes exploring biological roles in the future.

A dual-responsive fluorescent probe based on cyanine and naphthalimide units for detecting HClO and H2S in living cells

Hypochlorous acid (HClO) and hydrogen sulfide (H2S) play very important roles in both physiological and pathological processes, however, the methods for simultaneously detecting HClO and H2S were rarely reported. Here, a dual-responsive fluorescent probe (CyNa-N3) based on cyanine and naphthalimide dyes was synthesized and investigated. The fluorescence probe showed better sensitivity, high selectivity response to HClO and H2S by red emission and green emission bands, and the limits of detection were 0.17 µM and 0.15 µM respectively. MS (Mass Spectrum) and 1H NMR (Nuclear Magnetic Resonance) confirmed the sensing mechanism of CyNa-N3 detected HClO and H2S, the calculation of density functional theory (DFT) further explained the internal mechanism of spectral change of CyNa-N3. Moreover, CyNa-N3 was successfully applied to image HClO and H2S in living cells, which is beneficial for more efficient application in biological imaging.

Liposome Based Near-Infrared Sensors for the Selective Detection of Hydrogen Sulfide

Cyanine dye-based new amphiphilic compound NIR-Amp has been synthesised. NIR-Amp was embedded with phospholipids DOPC and DPPC to form liposomes based nanoscale chemical sensors NIR-Lip1 and NIR-Lip2. Here, two different phospholipids were used to demonstrate the influence of lipid structure, composition and fluidity on sensing of nanosensors. Both the probes show NIR absorption maximum at 790 nm and emission maximum at 815 nm. H2 S-triggered thiolation resulted a remarkable change in color from green to pale yellow. A decrease in UV-Vis absorption and emission in the NIR region was observed only with H2 S. NIR-Lip1 and NIR-Lip2 are highly selective for H2 S with a LOD of 0.57 μM and 1.24 μM, respectively. It was observed that in a solid-like gel state, NIR-Lip1 is slightly more sensitive towards H2 S than fluid-like NIR-Lip2. The H2 S sensing mechanism was confirmed by ESI-mass and infrared (IR) spectroscopic analysis. Based on the high sensitivity and selectivity, NIR-Lip1 was employed to detect H2 S in vegetable samples. Further, the probes are found to be non-toxic and established for H2 S fluorescence imaging in live cells.

A highly selective and easily acquisitive near-infrared fluorescent probe for detection and imaging of hydrogen sulfide in cells

Hydrogen sulfide (H₂S) plays a substantial role as a messenger in the physiological and pathological processes of many diseases. Recently, the fluorescence probe of H₂S based on organic dye has attracted great attention. However, the emission of many probes is in the UV-vis region (400-600 nm), so it has the disadvantages of shallow tissue penetration and more vulnerable to spontaneous fluorescence interference. Although several H₂S probes have been developed that emit more than 650 nm, there is a complex structure difficult to synthesize or unstable in storage. Aimed at simply structural and easily synthesized H₂S fluorescent probes with emission wavelength more than 650 nm, a novel near-infrared (NIR) probe (NIR-H₂S) here was rationally designed with 4-(2-carboxyphenyl)-7-(diethylamino)-2-(4-hydroxystyryl)chromenylium (NIR-OH) as a fluorescent dye and 2,4-dinitrophenyl moiety as a recognition group. Addition of H₂S, the "turn-on" NIR fluorescence response at 736 nm of NIR-H₂S was displayed, accompanied by a visual colour change from purple to green when excited at 686 nm. As an easily acquisitive H₂S probe, NIR-H₂S has been successfully applied to cell imaging for H₂S detection with the advantages such as long fluorescence emission, low toxicity, high sensitivity and strong selectivity.

Near-Infrared Probes for Biothiols (Cysteine, Homocysteine, and Glutathione): A Comprehensive Review

Biothiols (cysteine, homocysteine, and glutathione) are an important class of compounds with a free thiol group. These biothiols plays an important role in several metabolic processes in living bodies when present in optimum concentration. Researchers have developed several probes for the detection and quantification of biothiols that can absorb in UV, visible, and near-infrared (NIR) regions of the electromagnetic spectrum. Among them, NIR organic probes have attracted significant attention due to their application in in vivo and in vitro imaging. In this review, we have summarized probes for these biothiols, which could work in the NIR region, and discussed their sensing mechanism and potential applications. Along with focusing on the pros and cons of the reported probes we have classified them according to the fluorophore used and summarized their photophysical and sensing properties (emission, response time, limit of detection).

Fe-doped MOF-derived N-rich porous carbon nanoframe for H2 S cataluminescence sensing

Metal-doped porous carbon matrix composites are considered as outstanding H₂ S cataluminescence sensing materials for their good sulfur tolerance and high cataluminescence activity. In this work, Fe-doped MOF-derived N-rich porous carbon nanoframe was successfully fabricated by pyrolysis of Fe-doped ZIF-8 in an Ar atmosphere at a temperature of 900 °C, and used for H₂ S cataluminescence sensing. Along with zinc volatilization, the obtained porous carbon nanoframe not only had high specific surface area and abundant voids, but also had well dispersed Fe species doped in the skeleton. Compared with Fe₂ O₃ /ZnO composites derived from the same precursor but different pyrolysis terms, this as-prepared Fe-doped N-rich porous carbon presented three times increase of cataluminescence intensity towards H₂ S, attributing to the porous carbon skeleton which is indispensable for dispersing catalytic active sites and providing more absorptive surface and voids. Comparably, this proposed sensor demonstrated high sensitivity and good selectivity, with the detection range of 1.57-19.58 μg·mL^-1 and detection limit as 0.13 μg·mL^-1 towards H₂ S. This work may provide a new pathway for preparing catalysts for cataluminescence sensing with better metal distribution, higher specific surface area, richer pores than ever before.

A benzophenoxazine-based NIR fluorescent probe for the detection of hydrogen sulfide and imaging in living cells

Fluorescence probe NRDNP exhibits excellent sensing performance toward H2S with about 80-fold fluorescence enhancement. The excellent sensitivity and a detection limit of 19 nM make it application for fluorescence imaging of H2S in living cells.

Synthesis and preliminary exploration of a NIR fluorescent probe for the evaluation of androgen dependence of prostate cancer

PURPOSE

Castration resistance prostate cancer patients showing resistance to the androgen deprivation therapy always have low five-year survival rate and worse prognosis. A responsive NIR fluorescent probe was designed to report the androgen dependence and monitor the development of castration resistance for prostate cancer.

METHODS

Intratumoral H₂S in prostate cancer was closely related to castration resistance. A H₂S-responsive NIR probe (HM) was developed as a dependent indicator to report the androgen dependence of prostate cancer. The specificity of HM to H₂S and the influence of normal intracellular substrates to the response between H₂S and HM were determined. Cell/in vivo animal imaging were performed on PC-3 and LnCAP cell/tumor bearing mice, which presented with androgen independence and androgen dependence, respectively.

RESULTS

When HM responded to H₂S, strong fluorescence at 770 nm could be rapidly turned on in 5 min with the stokes shift as large as 200 nm. The recognition between HM and H₂S showed high specificity. Neither other common substrates showed capacity to turn on HM's fluorescence, nor their existence demonstrated competition. The fluorescence intensity was linearly dependent to the H₂S concentration and the limited of detection was 0.15 μM. When HM was applied to PC-3/LNCaP prostate cancer cell and tumor, the intracellular and intratumoral H₂S could be clearly imaged and monitored.

CONCLUSION

HM showing obvious fluorescent behaviors in androgen dependence and independence prostate tumor, which could work as an indicator to reported the androgen dependence of prostate cancer and monitor the development of castration resistance.

Deep-Red/Near-Infrared Turn-On Fluorescence Probes for Aldehyde Dehydrogenase 1A1 in Cancer Stem Cells

Accumulating evidence supports that cancer stem cells (CSCs) are responsible for cancer proliferation, metastasis, and therapy resistance; therefore, an effective strategy to identify and isolate CSCs is required urgently. Because of their low invasiveness and high signal/noise ratio, "turn-on" fluorescence probes working in the deep-red/near-infrared (DR/NIR) region are one of the most attractive yet undeveloped tools for CSC detection. Herein, we report DR/NIR turn-on fluorescence probes, CS5-A and CS7-A, targeted to aldehyde dehydrogenase 1A1 as an intracellular CSC marker. In contrast to the conventional "always-on" green-fluorescent ALDEFLUOR, we succeeded in generating high-contrast (signal/noise ratio > 8.3) and wash-free in vitro CSC imaging with the DR probe C5S-A. This probe can facilitate CSC isolation with minimal contamination by autofluorescence from other tissues through fluorescence-activated cell sorting. Furthermore, the NIR absorbance/emission and turn-on properties of C7S-A allow simple and rapid CSC detection in vivo within 15 min.

A near-infrared-emission aza-BODIPY-based fluorescent probe for fast, selective, and "turn-on" detection of HClO/ClO. Talanta 2021;233:122581. [PMID: 34215073 DOI: 10.1016/j.talanta.2021.122581]

A novel near-infrared-emitting aza-BODIPY-based fluorescent probe with two tellurium atoms at two upper benzyl rings has been prepared and explored for its fluorescent sensing properties towards hypochlorous acid/hypochorite (HClO/ClO^-), which showed high selectivity and absolutely fluorescent "turn-on" phenomenon at 738 nm. The fluorescence of this probe was sufficiently quenched due to photoindued electron transfer by two tellurium atoms. Upon exposure to HClO/ClO^-, a strong near-infrared emission at 738 nm appeared with fluorescence quantum yields changing from 0 to 0.11. This remarkable fluorescence change was ascribed to the oxidation of both electron-rich tellurium atoms. The detection limit of this probe towards HClO/ClO^- was calculated to 0.09 μM in acetonitrile aqueous solution by the linear fluorescence change at 738 nm in the HClO/ClO^--concentration range of 0-30 μM. Interestingly, this probe was found to be applicable in a broad pH range (2-10). Meanwhile, the oxidized probe could be further responsive to biothiols with substantial fluorescence disappearance. The bioimaging experiments in RAW264.7 cells showed the appearance of intracellular near-infrared fluorescence after addition of HClO/ClO^- and PMA, and the fluorescence could also be reversed to be silenced by further introduction of GSH, confirming its potential application for exogenous and endogenous detection of HClO/ClO^- in living cells.

Synthesis and characterization of novel fluoroterphenyls: self-assembly of low-molecular-weight fluorescent organogel

Nucleophilic aromatic substitution has been highly para selective on a range of functionalized pentafluorobenzenes. Here, we demonstrate the utility of nucleophilic aromatic substitution chemistry for the preparation of fluorinated fluorescent low-molecular-weight organogels. The molecular design, synthesis and photophysical performance of a new class of thermoreversible and fluorescent low-molecular-weight organogels from para-alkoxy-functionalized fluorinated terphenyls are described. Both CuI-catalyzed decarboxylative cross-coupling and nucleophilic aromatic substitution chemistry were used for the preparation of those highly fluorinated gelators in high yields and excellent purity via simple filtration, from the corresponding potassium fluorobenzoate salts and aryl iodides. Various fluorinated symmetrical and asymmetrical para terphenyls were prepared with various para terminal alkoxy tails. Those fluorinated terphenyls were characterized using X-ray crystallography, differential scanning calorimetry, Fourier-transform infrared spectroscopy, as well as ¹ H, ¹³ C, and ¹⁹ F nuclear magnetic resonance. UV-visible light absorbance and emission spectra of those new materials displayed a solvatochromic and solvatofluorochromic behaviour, respectively. Self-assembly of the produced fluorinated terphenyls occurred via cooperative π-π stacking and van der Waals interactions, which resulted in gelating various organic solvents. Scanning electron microscopy displayed the formation of fibre-like nanostructures. The cytotoxicity of some selected fluorinated symmetrical and asymmetrical para terphenyls was explored.

Rational design of near-infrared fluorophores with a phenolic D–A type structure and construction of a fluorescent probe for cysteine imaging

The structural modulation of phenolic D–A type fluorophores and a NIR fluorescent probe for cysteine imaging in vitro and in vivo.

Fluorescent AIE-Active Materials for Two-Photon Bioimaging Applications

Fluorescence imaging has been widely used as a powerful tool for in situ and real-time visualization of important analytes and biological events in live samples with remarkably high selectivity, sensitivity, and spatial resolution. Compared with one-photon fluorescence imaging, two-photon fluorescence imaging exhibits predominant advantages of minimal photodamage to samples, deep tissue penetration, and outstanding resolution. Recently, the aggregation-induced emission (AIE) materials have become a preferred choice in two-photon fluorescence biological imaging because of its unique bright fluorescence in solid and aggregate states and strong resistance to photobleaching. In this review, we will exclusively summarize the applications of AIE-active materials in two-photon fluorescence imaging with some representative examples from four aspects: fluorescence detection, in vitro cell imaging, ex vivo tissue imaging, and in vivo vascular imaging. In addition, the current challenges and future development directions of AIE-active materials for two-photon bioimaging are briefly discussed.

Sensing and Bioimaging of the Gaseous Signaling Molecule Hydrogen Sulfide by Near-Infrared Fluorescent Probes

A fluorescent probe for the monitoring of H₂S levels in living cells and organisms is highly desirable. In this regard, near-infrared (NIR) fluorescent probes have emerged as a promising tool. NIR-I and NIR-II probes have many significant advantages; for instance, NIR light penetrates deeper into tissue than light at visible wavelengths, and it causes less photodamage during biosample analysis and less autofluorescence, enabling higher signal-to-background ratios. Therefore, it is expected that fluorescent probes having emission in the NIR region are more suitable for in vivo imaging. Consequently, a considerable increase in reports of new H₂S-responsive NIR fluorescent probes appeared in the literature. This review highlights the advances made in developing new NIR fluorescent probes aimed at the sensitive and selective detection of H₂S in biological samples. Their applications in real-time monitoring of H₂S in cells and in vivo for bioimaging of living cells/animals are emphasized. The selection of suitable dyes for designing NIR fluorescent probes, along with the principles and mechanisms involved for the sensing of H₂S in the NIR region, are described. The discussions are focused on small-molecule and nanomaterials-based NIR probes.