A Phenanthrenequinone-Based Ratiometric Fluorescent Probe for Rapid Detection of Peroxynitrite with Imaging in Osteoblast Precursor Cells.

In the current situation, peroxynitrite (ONOO-) is drawing the increasing attention of researchers for its pivotal role in diverse pathological and physiological processes on grounds of robust oxidation and nitrification. Herein, we have successfully designed and synthesized a phenanthrenequinone benzyl borate-based chemosensor for fast and selective detection of ONOO-. The probe PTDP itself had an orange fluorescence, which was changed to strong blue fluorescence upon the addition of ONOO-, indicating the ratiometric response of the probe. This is so because of the cleavage of the benzyl boronate-protecting group of PTDP upon the addition of ONOO- with simultaneous releasing of pyridinyl-based chemosensor PPI. The PTDP showed outstanding performance in the various photophysical studies such as good selectivity, excellent sensitivity with a very low detection limit of 2.74 nM, and a very fast response time (<15 s). Furthermore, for practical applicability, it was successfully applied in the ratiometric detection of ONOO- in osteoblast precursor cells.

A chemodosimetric chemosensor for the ratiometric detection of nerve agent-mimic DCP in solution and vapor phases.

Nerve agents are among the most deadly and lethal chemical warfare agents (CWAs). Rapid identification is crucial for specialized individuals to take action against dangerous drugs. This paper describes the synthesis and characterisation of a probe (MNFZ) based on the methoxy naphthalene-furoic hydrazide group. The probe rapidly (100 s) detects and quantifies the nerve-agent simulant diethyl chlorophosphate (DCP) in both solution and vapor phases. This sensor uses a new recognition center, furoic hydrazide, where the nitrogen atom of the imine group (CN) attacks the electrophilic core phosphorus atom of DCP, followed by the hydrolysis of the imine group in the acetonitrile (ACN) solution to produce the corresponding aldehyde MNPA. The development of ICT character resulted in a distinct red-shifted ratiometric fluorescence response to DCP, with a very low limit of detection (12.2 nM). The probe is an efficient chemosensor due to its high selectivity over other organophosphorus compounds as well as its chemical stability across a wide pH range. DFT calculations, 1H NMR and HRMS were performed to finalize the sensing mechanism. Lastly, the as-designed sensor was successfully used to build a highly sensitive portable kit in test strips and a cotton biopolymer for simple and safe real-time monitoring of DCP.

Small-molecule fluorogenic probes based on indole scaffold.

Indoles are the most versatile organic N-heterocyclic compounds widely present in bioactive natural products and used in different fields such as coordination chemistry, pharmacy, dyes, and medicine, as well as in the biology and polymer industries. More recently, the indole scaffold has been widely used in analytical chemistry for the design and development of small-molecule fluorescent chemosensors in the fields of molecular recognition and molecular imaging. The indole-based chemosensor derivatives contain heteroatoms like N-, O-, and S-, through which they interact with analytes (cations, anions, and neutral species), producing measurable analytical signals that can be used for the fluorimetric and colorimetric detection of different analytes in biological, agricultural and environmental samples. This review focuses on indole-based small-molecule fluorimetric and colorimetric chemosensors for detecting cations, anions, and neutral species in a comprehensive manner. Furthermore, the recognition mechanisms are discussed in detail, which could help researchers design and develop more powerful and efficient fluorescent chemosensors in the near future.

A ratiometric small-molecule fluorescent probe for the selective detection of hypochlorite by an oxidative cyclization reaction: application to commercial disinfectants and live cells.

A highly selective thiophene-thioimidazole hydrazine-based ratiometric chemodosimeter (TPBN) was designed and synthesized to detect hypochlorite (ClO-). The probe showed yellow fluorescence and exhibited ultra sensitivity towards hypochlorite (detection limit 8.74 nM) through the oxidative intramolecular cyclization process to give a blue fluorescent triazole product (TPBN-P). Additionally, the as-designed sensor displayed a fast response (80 s) to hypochlorite with excellent selectivity over other competing analytes. DFT calculations, ESI-MS, and 1H NMR titration experiments supported the detection mechanism. The probe was a valuable and practical ratiometric sensor for test strips, commercial disinfectants, and water samples. The probe was successfully used in the bio-imaging of hypochlorite in human breast cancer cells due to its noteworthy photophysical characteristics and good cell permeability.

A turn-on fluorescent probe for selective detection of H2S in environmental samples and bio-imaging in human breast cancer cells.

A triphenylamine-benzothaizole-based turn-on fluorescent probe TPB-NO2 was designed and synthesized for tracking H2S in both environmental and biological samples depending upon the sensing strategy of thiolysis of 2,4-dinitrophenyl (DNP) ether. Due to PET (photoinduced electron transfer), occurring from donor triphenylamine moiety to acceptor DNP moiety, the probe TPB-NO2 itself is very weakly fluorescent and colorless in DMSO/H2O solution (1 : 1, v/v; 10 mM HEPES buffer, pH 7.4). But the addition of H2S leads to thiolysis of 2,4-dinitrophenyl ether to block the initial PET process and hence it exhibits naked eye detectable turn-on response with bright cyan fluorescence and intense brown color. Not only that, the probe exhibits excellent selectivity over other bio-thiols like Cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), fast response time (<2 min), and high sensitivity with a detection limit of 9.81 nM. Moreover, to explore the practical applicability of our probe we employed it to monitor H2S successfully in environmental water samples, solid-state TLC strip study, Quantitative determination of H2S in eggs, and in the bioimaging of human breast cancer cells (MDA-MB 231).

Near-infrared fluorescent turn-on probe for hydrazine detection: environmental samples and live cell imaging.

An acetoxy naphthaldehyde conjugated benzophenoxazinium chloride chromophore-based-donor-π-acceptor (D-π-A) fluorescent probe BPN (benzophenoxazinium naphthoxy imine) displaying near-infrared (NIR) emission was reported for hydrazine detection. The chosen water-soluble benzophenoxazinium chloride chromophore has excellent photostability, a high molar extinction coefficient and fluorescence quantum yield (Φ = from 0.0075 to 0.6193), higher selectivity towards hydrazine and a longer fluorescence lifetime. In the presence of hydrazine, BPN exhibits near infrared fluorescence emission at 725 nm along with color change from light blue to red, as detected by the naked eye. Moreover, the BPN probe can selectively detect hydrazine (DL = 4.5 × 10-10 M) in a 90% aqueous DMSO solution without interfering with other analytes. As proof of real samples, the probe is successfully applied to sense hydrazine in thin layer chromatography (TLC) paper strips (both solution and vapor phases) and water and soil samples, suggesting its significant potential application. Also, due to its NIR emission and aqueous solubility, the BPN probe can be successfully used in live cell imaging with low cytotoxicity.

A small-molecule fluorogenic probe for the detection of hypochlorite and its application in the bio-imaging of human breast cancer cells.

A certain amount of hypochlorite can help to regulate the body's defense system while excessive hypochlorite has some complex influence on health. Herein, a thiophene-derived biocompatible turn-on fluorescent probe (TPHZ) was synthesized and characterized for the detection of hypochlorite (ClO-). The fluorescence and colorimetric sensing of the probe followed an ICT OFF strategy. The experimental results showed a remarkable turn on fluorescence enhancement from colorless to bright blue after the addition of ClO- within 130 s in a solvent system having 80% water with high selectivity and a low detection limit of 53.8 nM. The sensing mechanism was attributed to ClO- mediated electrophilic addition to the imine bond which was justified by DFT calculations, and ESI-MS and 1H-NMR titration experiments. The probe was used in an application to visualize ClO- in human breast cancer cells which can be helpful for investigating the functions of hypochlorite in living cells. Finally, by virtue of fine photophysical properties, good sensing performance, good water solubility and low limit of detection, the probe TPHZ was successfully applied to TLC test strips, and commercial bleach and water samples.

Spiropyran-Merocyanine Based Photochromic Fluorescent Probes: Design, Synthesis, and Applications.

Due to ever-increasing insights into their fundamental properties and photochromic behaviors, spiropyran derivatives are still a target of interest for researchers. The interswitching ability of this photochrome between the spiropyran (SP) and merocyanine (MC) isoforms under external stimuli (light, cations, anions, pH etc.) with different spectral properties as well as the protonation-deprotonation of its MC form allows researchers to use it suitably in sensing purposes by developing different colorimetric and fluorometric probes. Selective and sensitive recognition can be achieved by little modification of its SP moiety and functional groups. In this review, we emphasize the recent advancements (from 2019 to 2022) of spiropyran-merocyanine based fluorogenic and chromogenic probes for selective detection of various metal ions, anions, neutral analytes, and pH. We precisely explain their design strategies, sensing mechanisms, and biological and environmental applications. This review may accelerate the improvements in designing more advanced probes with innovative applications in the near future.

Switching to a 'turn-on' fluorescent probe for rapid detection of hydrazine in human breast cancer cells using a test-strip.

A fluorescent probe TPSBT was developed to monitor hydrazine detection with a "turn on" response, converting from a "non-responsive" probe by a simple structural modification. The probe shows very weak fluorescence due to the strong ICT process and upon treatment with hydrazine, green fluorescence appears due to the blocking of this ICT by the formation of a hydrazone. The probe TPSBT can detect hydrazine with a very low detection limit (1.22 × 10-7 M) and within a very short time period of 50 s. Additionally, the probe is able to give a response in live cell imaging (MDA-MB 231) and also in the solid phase.

An ICT-guided ratiometric naphthalene-benzothiazole-based probe for the detection of cyanide with real-time applications in human breast cancer cells.

A methoxynaphthalene benzothiazole conjugate (MNBTZ) armed with CC vinylic double bonds was synthesized and utilized for the selective detection of CN- ions. The probe showed yellow fluorescence due to ICT from the methoxynaphthalene moiety to benzothiazole, which instantly changed to light purple upon the nucleophilic addition of CN- to the vinylic double bond, inhibiting ICT due to the break-in conjugation. The effectiveness of the probe was proved by this brilliant ratiometric fluorescence change, which was achieved selectively as observed by experiments with competing anions. 1H NMR titrations and DFT calculations support this mechanism. A low detection limit of 2.1(±0.0022) × 10-8 M along with good fluorescence color change on solid TLC plates and human breast cancer cells makes it amenable to CN- sensing.

A dual-channel chemodosimetric sensor for discrimination between hypochlorite and nerve-agent mimic DCP: application on human breast cancer cells.

A styryl bridge containing a triphenylamine-thioimidazole hydrazine-based dual-analyte-responsive fluorescent sensor was designed and synthesized for the detection of the nerve gas simulant diethyl chlorophosphate (DCP) and hypochlorite (OCl-) for the first time. Hypochlorite induces oxidative intramolecular cyclization to give a triazole structure, which exhibited blue fluorescence with excellent selectivity and a low detection limit (8.05 × 10-7 M) in solution. Conversely, the probe forms a phosphorylated intermediate with diethyl chlorophosphate, which undergoes further hydrolyzation and presents green fluorescence in a ratiometric mode with a low detection limit (3.56 × 10-8 M). Additionally, the as-designed sensor was utilized to construct a portable kit for real-time monitoring of DCP in a discriminatory, simple and safe manner. Lastly, the probe was also productively employed for in situ imaging of OCl- and DCP in the living cell.

A benzothiazole-based dual reaction site fluorescent probe for the selective detection of hydrazine in water and live cells.

As hydrazine is an environmental pollutant and highly toxic to living organisms, selective and rapid detection is highly needed for the benefit of living organisms as well as the environment. Here, we first introduced a novel benzothiazole conjugated methyldicyanovinyl coumarin probe BTC, with dual recognition sites for hydrazine detection. The incorporation of the methyldicyanovinyl group into the benzocoumarin fluorophore increased the electrophilicity of the lactone ring of the probe BTC facilitating the nucleophilic attack of hydrazine and rapid (within 1 min, low detection limit = 1.7 nM) turn-on sky blue fluorescence with 700-fold fluorescence intensity enhancement was observed via hydrazine-induced lactone ring-opening followed by selective cleavage of the dicyanovinyl group. According to the literature, dicyanovinyl group assisted lactone ring opening has revealed the possibility of hydrazine recognition with a large Stokes shift (140 nm) and a high fluorescence quantum yield (0.67). Here, the DFT study and practical applications of the probe BTC in different water samples have been presented. The probe BTC was also successfully applied for the detection of hydrazine in the vapor phase using paper strips and in live MDA-MB 231 cells.

Triphenylamine-based small-molecule fluorescent probes.

Ammonia with the three hydrogens substituted by phenyls is known as triphenylamine (TPA), and is one of the most useful compounds because of its vast practical applications. Chemists have produced thousands of TPA derivatives to date. Because of its biocompatibility and structural features, it has been widely used in the fields of molecular recognition, molecular imaging, materials chemistry, and also in biology and medical science. Its strong electron-donating ability encourages scientists to produce different types of probes for molecular recognition. This review is based on recent developments and advances in TPA-based small molecular fluorescent probes within the time period 2010-2021. This extensive review may expedite improvements in more advanced fluorescent probes for vast and stimulating applications in the future.