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Developing fluoran dyes for fluorescent material is significant but challenging because they are notorious for terrible luminescent efficiency. In this manuscript, two fluoran dyes (F3 and F4) were synthesized by the introduction of thiazole and indazole into the fluoran skeleton, which showed colored and fluorescent spirolactone opening form in a wide pH range (F3 : 1–10, F4 : 1–13). In addition, the absorption and emission spectra of methyl esterification products F3Me and F4Me showed large Stokes shifts (over 75 nm) in water and achieved an improved fluorescence quantum yield of 30.1% in CHCl 3. Based on the dye F4Me, a new fluorescent probe F4HP was developed, which showed high selectivity and high sensitivity (LOD of 2.0 nM) to copper ions in H 2 O/CH 3 CN (v/v, 3/2) system. Moreover, the sensing experiment was allowed in the pH range of 4.0–7.5. Furthermore, the F4HP exhibits suitable cell cytotoxicity and can be applied for imaging intracellular copper ions by confocal fluorescence imaging technology. Thiazole and indazole functionalized fluoran dyes were prepared with improved fluorescence and application in the construction of a novel copper-selective and sensitive fluorescent probe. [Display omitted] • Two modified fluoran dyes were prepared with stable fluorescence in water. • F4Me achieved a fluorescence quantum yield of 30.1% in CHCl 3. • A novel probe F4HP for Cu2+ was prepared with high selectivity and sensitivity. • F4HP could be employed as a tool for imaging intracellular Cu2+. [ABSTRACT FROM AUTHOR]

A new biscarbazole-fused xanthene hybrid dye MeBCX has been prepared by CH3SO3H-promoted condensation of 4-hydroxycarbazole and o-phthalic anhydride, followed by esterification with methanol, which exhibits good cell membrane permeability. Taking advantage of the spiro-controlled xanthene platform of the dye, a Cu2+-selective fluorescence "off-on" probe BCX-Cu has been successfully prepared with excellent performances in selectivity and sensitivity, and the detection limit is calculated to be 88.7 nM. The sensing mechanism is confirmed to involve a specific cascade reactions of Cu2+-induced spirolactam ring-opening and hydrolysis. In addition, living L929 cell imaging demonstrates the probe has living cell membrane permeability and shows great potential for tracing intracellular Cu2+ through fluorescence imaging technology. [ABSTRACT FROM AUTHOR]

Fluoran dyes, a large family of colourants, have been widely used as thermosensitive dyes in print industry by taking advantage of the thermo-controlled interconversions between the colorless spirolactone and the colored zwitterion forms. But few attentions have been paid to their fluorescence properties. In this paper, the fluorescence regulation of 4-aminobenzofluoran dye 1 by introducing of electron-deficient acetyl group to tune the energy level of the highest occupied molecular orbital (HOMO) of the amino group has been carried out. Based on this strategy, the N -acetylated product BF derived from its precursor 1 shows stable UV–Vis and fluorescence spectra in water from pH 1.0 to 12.0 due to the blocking of the photoinduced electron transfer (PET) process from the amino group to the excited state of fluoran chromophore. Moreover, BF is cell permeable and can be used as signal reporter for the design of fluorescence probes by taking advantage of the fluorescence controlled mechanism of the ring opening and closing chemical processes of the spirolactone platform. By using BF as precursor, a highly sensitive and selective fluorescent probe BF-Cu for Cu 2+ was synthesized by introducing a Cu 2+ -responsive water soluble 2-hydroxylethyl hydrazine functional group. We expect that the fluorescence recovery of fluoran dyes via the regulation of the HOMO energy level of the amino group enable an additional synthetic effort on the development of fluorescence fluoran dyes and expansion of their applications. [ABSTRACT FROM AUTHOR]

A novel fluoran-based fluorescent probe 2 has been designed and synthesized by using a strategy of blocking the intramolecular photoinduced electron transfer (PET) process. The probe keeps a ring-closed spirolactone structure in aqueous buffer solution. However, the oxidation of the probe by ClO − perturbs a new equilibrium of the structural interconversion between the nonfluorescent spirolactone and the fluorescent ring-opened zwitterion, which generates a highly selective fluorescent probe for ClO − . Meanwhile, the probe is cell membrane permeable and can be utilized as fluorescent probe for imaging ClO − in living cells. [ABSTRACT FROM AUTHOR]

A novel pyridyl functionalized rhodamine dye with large Stokes shift and stable fluorescence in water was facilely prepared and utilized for a Hg2+-selective probe. [Display omitted] • A Rhodamine derivative PR has been prepared with Stokes shift of 81 nm. • Probe PRHg is synthesized, presenting high selectivity and sensitivity (LOD: 8.5 nM) to Hg2+. • PRHg exhibits great potential for tracing Hg2+ in living cells. Rhodamines gain sustained attention owing to their great potential for probe design applications. Herein, the facile preparation of a new pyridyl functionalized rhodamine dye PR is reported, which has stable fluorescence signal in water with maximum emission peak at 594 nm and Stokes shift of 81 nm. Based on dye PR , a new fluorescent probe PRHg has been developed by modifying the spirolactone of PR with hydrazine hydrate so as to produce spirolactam recognizing group for sensing of Hg2+. PRHg exhibits high selectivity and sensitivity towards Hg2+ in water/ethanol (v/v = 4/1, pH = 7.0) by a specific Hg2+-binding promoted spirolactam ring opening and hydrolyzing process. And, the detection limit for Hg2+ is evaluated to be 8.5 nM. Besides, the probe can respond to Hg2+ within 40 min and over a wide pH range from 4.0 to 10.0. Moreover, PRHg (40 µM) performs low cytotoxicity to HeLa cells (over 91.0 % cell survival rate), which allows the probe to be employed for tracing intracellular Hg2+ by fluorescence imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel quinoline-rhodamine hybrid probe P7RHg has been facilely prepared. • P7RHg can be used for raitiomet-ricly sensing of Hg2+ in water with well separated emission peaks. • P7RHg exhibits selectivity to Hg2+ with nearly 90-fold fluorescent ratio enhancement. • P7RHg shows promising potential in tracing intracellular Hg2+. To develop efficient tools for monitoring toxicant Hg2+ in aqueous solution attracts great attention because the abnormal distribution of Hg2+ in environment poses great threat to human health. We here report the preparation of a novel quinoline-rhodamine hybrid fluorescent probe P7RHg for ratiometricly sensing of Hg2+ in water, with a spirolactam-thiosemicarbazide reaction group. Upon treatment by Hg2+, the ratio of fluorescence intensity (F 600 /F 460) exhibits nearly 90-fold enhancement, presenting two well-resolved emission peaks (140 nm). Meanwhile, the specific Hg2+-induced desulfurization provides probe P7RHg an excellent selectivity to Hg2+, with a detection limit of 8.6 nM. Moreover, the low cytotoxicity allows P7RHg to be employed for tracing Hg2+ in living cells by confocal fluorescence imaging. [ABSTRACT FROM AUTHOR]

A new N-heterocyclic fluoran based dye BiF is facilely prepared in high yield by reaction of 5-methoxybenzimidazole and 2-(4-diethylamino-2-hydroxy)benzoylbenzoic acid in concentrated H 2 SO 4 , which keeps stable optical signals in water at pH values ranging from 4 to 10 and exhibits good living cell membrane permeability. By modification of the spirolactone in molecule BiF , a fluorescent probe BiF–Cu with specific and sensitive response to Cu2+ has been further developed, which contains a six-membered spirolic hydroxyethylhydrazide moiety that can be selectively triggered by Cu2+ among various metal ions through a specific cascade reaction of Cu2+-promoted spirolactam ring-opening and hydrolysis. A limit of detection for Cu2+ is calculated as 7.12 × 10−8 mol/L. In addition, the utilization of BiF–Cu for bioimaging Cu2+ in L929 cells demonstrates its living cell membrane permeability and makes it promising candidate for monitoring Cu2+ by cell imaging technology. A new N-heterocyclic fluoran BiF has been efficiently prepared by hybridizing benzimidazole and fluoran moieties. Based on this dye, fluorescent probe BiF–Cu with unique six-membered spirocyclic hydrazide has been developed for selective and sensitive detection of Cu2+ and cell imaging. Image 1 • A new N -heterocyclic fluoran dye was prepared with stable optical signal over a wide pH range. • A fluorescent probe containing a novel six-membered spirocyclic hydrazide trigger has been developed. • The probe was empolyed for highly selective and sensitive detection of Cu2+ with a detection limit of 71.2 nM. • The probe can be utilized in tracing Cu2+ in living cell. [ABSTRACT FROM AUTHOR]

Based on a fluoran skeleton, we herein reported a new fluorescent probe FLACu for Cu2+ by facile modification of the spirolactone of dye 1 with phenylhydrazine. Taking advantage of the spirolactam moiety, FLACu only delivers a specific "off-on" fluorescence signal output towards Cu2+ when treated with various metal ions, which has been well elucidated as the result of spirolactam ring opening and hydrolysis processes induced by copper ion. Meanwhile, the limit of detection (LOD) for FLACu has been estimated to be 35.4 nM and a pH range of 5.0–9.0 is evaluated to be suitable for Cu2+ detection. Significantly, FLACu shows low cell cytotoxicity and can be further ultilzied in the detection of exogenous Cu2+ in the living Hela cells. [ABSTRACT FROM AUTHOR]

A novel indazole fused rhodamine fluorescent dye with large Stokes shift and stable fluorescence in water for constructing an Hg2+-selective probe and cell imaging applications. [Display omitted] • A indazole fused rhodamine dye InRh has been prepared with stable fluroescence in water. • Probe InRhH can respond to Hg2+ with high selectivity and sensitivity by fluorescence and absorption spectra. • Probe InRhH shows promising application in tracing Hg2+ in living cells. Developing selective and sensitive probes for mercury ion (Hg2+) is of great significance because Hg2+ exhibits high toxicity and poses a potential threat to public health and the environment. Herein, a newly designed indazole fused rhodamine dye InRh has been prepared, which shows stable fluorescent signals in water at a wide pH range of 1.0–10.0. Based on the dye InRh, a novel fluorescent probe InRhH for Hg2+ is further developed by modifying the spirolactone ring of InRh to form a closed spirolactam ring. The probe shows selective fluorescence "off–on" signal changes to Hg2+ with a visible color change and response time of 40 min in H 2 O/CH 3 CN (pH = 6.0, v/v = 4/1), and the detection limit for Hg2+ is measured to be 0.33 nM. The recognition mechanism for Hg2+ can be ascribed to the binding interactions between Hg2+ and probe in a 2: 1 coordination mode, which promotes the occurrence of spirolactam ring opening and further hydrolysis. In addition, the InRhH can be applied for test strip experiments and tracing 10−6 M level Hg2+ with visible color change. Furthermore, the suitable cytotoxicity allows the probe to apply for sensing Hg2+ in living HeLa cells by fluorescence imaging. [ABSTRACT FROM AUTHOR]

• A novel quinoline-fluoran hybrid fluorescent dye QF has been easily prepared. • A copper ion-selective fluorescent probe QFH has been developed based on QF. • QFH shows good performance in tracing intracellular copper ions by fluorescence imaging. Developing fluoran dyes as fluorescent probes is interesting because it is of great significance to extend their applications from the printing industry to other fields such as fluorescence analysis and medicine. We here present a new quinoline-fluoran hybrid dye QF , which delivers fluorescent signals in water (pH: 4.0 - 9.0) with the maximum absorption and emission centered at 514 nm and 597 nm, respectively. In addition, a large Stokes shift (83 nm) can be observed when compared to that of rhodamine B. QF is further employed for the preparation of a new fluorescent probe QFH , which exhibits high selectivity towards copper ions with the limit of detection down to 1.54 nM via a Cu2+-triggered spirolactam ring opening and hydrolysis process. Significantly, QFH can be applied for the detection of copper ions at physiological pH conditions (pH: 6.0 - 9.0) and shows low cell cytotoxicity, which allows it to be a candidate for tracing Cu2+ by cell imaging. A novel quinoline-fluoran hybrid fluorescent probe for copper ion-selective detection and application in cell imaging. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of mercury ion selective fluorescent probe is significant because it is one of toxic heavy metals and poses great risks and hazards to human health. Herein, we develop a mercury ion-selective fluorescent probe, namely IB, based on imidazole decorated benzothiadiazole that obtained by a facile palladium catalytic C-N coupling reaction. IB exhibits high selectivity and sensitivity towards mercury ion in water with nearly 32-fold fluorescent enhancement. The detection limit is calculated to be 0.93 nmol/L. In addition, the sensing of mercury ion can be conducted in a wide pH scope ranging from 4.0 to 10.0. Subsequently, the mercury ion elicits fluorescence of IB solution can be quenched by the addition of cyanide anions, showing "off-on-off" fluorescence transformation with at least 5 cycles, demonstrating the reversible sensing ability of IB. Furthermore, an INHIBIT logical detector has been developed using mercury ion and cyanide anions as inputs and fluorescence of IB as output. Significantly, IB can be utilized for mercury ion detection in real water sample. [ABSTRACT FROM AUTHOR]

• Two thiazole-fused fluoran-based fluorescent probes for copper ions have been prepared. • The two probes show high selectivity and sensitivity for copper ions. • MTFH achieves red emission (632 nm) towards copper ions due to the methyl functionalization. • The two probes can be utilized for tracing intracellular copper ions. In this work, two thiazole-fused fluoran-based fluorescent probes 8′-(diethylamino)-2-((2-hydroxyethyl) amino)spiro[isoindoline-1,11′-xantheno[2, 1- d ]thiazol]-3-one (TFH) and (8′-(diethylamino)-2-((2-hydroxyethyl)amino)-3′-methyl-3-oxospiro[isoindoline-1,11′-xantheno[2,1- d ]thiazol]-3′-ium).BF 4 (MTFH) have been prepared for copper ions. It should be noted that MTFH achieves red emission (632 nm) compared with TFH in the presence of copper ion, which mainly can be attributed to the methylation of molecule MTFH that induced more stronger ICT effect. The two probes show selective fluorescence off-on signal changes towards copper ions with detection limits of 8.8 and 60.8 nM. Copper ion detection can be conducted in a wide pH range including the physiological pH environment. Both TFH and MTFH exhibit suitable cytotoxicity and have been used for copper ion tracing in living cells. However, no other significant improvements of MTFH in sensing performance can be observed when compared with TFH. Two thiazole-fused fluoran-based fluorescent probes have been prepared for selectively and sensitively sensing copper ions, in particular, the methyl functionalization probe achieves red emission mainly due to a stronger ICT effect. [Display omitted] [ABSTRACT FROM AUTHOR]

A terpyridyl-rhodamine based probe has been designed and prepared for the sensitive and discriminative detection of Hg2+ and Cu2+ in water by dual/single emission change and applications in constructing a combinatorial logic gate and cell imaging. [Display omitted] • A new terpyridyl-rhodamine hybrid dye TR and sensor TRH have been facilely prepared. • TRH can discriminatively sense Hg2+ and Cu2+ in water with high sensitivity. • TRH can be employed for the construction of a combinatorial logic gate. • TRH can be applied for the discriminative sensing of Hg2+ and Cu2+ in living cells. Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F 595 /F 485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells. [ABSTRACT FROM AUTHOR]

Mango peel was chosen as the carbon source to generate carbon dots (CDs), for its green and potential satisfactory photoluminescent nature in addition to the waste recycling usage of mango peel. An eco-friendly approach which combined pyrolyzation with oxygenolysis was adopted to produce CDs from mango peel without any other treatment. The prepared CDs were 2–6 nm nanoparticles with a high fluorescence quantum yield of 8.5 ± 0.2%. Additionally, the CDs exhibited excellent fluorescent stability towards salt and ultraviolet irradiation, and reversible fluorescence between acid and base conditions. Owing to their low toxicity, good biocompatibility and multicolor fluorescence, CDs were successfully applied to cellular labeling on A549 cells in three colors (blue, green and red). Additionally, the fluorescence of CDs could be significantly quenched by Fe2+. Thus the CDs were applied as the fluorescent probe for detection of Fe2+ in ferrous succinate tablets with the linearity range of 4 μM–16 μM and the detection limit of 1.2 μM. The CDs from the mango peel were promising for multiple applications. [ABSTRACT FROM AUTHOR]

Natural source is an effective carbon precursor to produce carbon dots (CDs) with prominent physicochemical and photoluminescent properties. To enrich the CDs’ type and widen their applications, more natural sources are desired. Herein, Hongcaitai ( Brassica compestris L. var. purpurea Bailey), one of the popular and cheap vegetables in Hubei province of China, was attempted as the carbon precursor for synthesis of CDs by hydrothermal method. The obtained CDs were divided into two parts based on different solubilities in ethanol, CDs-A (ethanol soluble) and CDs-B (ethanol insoluble). Both CDs possessed multi functionalities; however, CDs-B contained sulfur element while CDs-A did not. Fluorescence quenching occured for both CDs in the presence of ClO − and Hg 2+ . However, CDs-A were more sensitive towards ClO − , while CDs-B were more sensitive towards Hg 2+ . Thus, CDs-A were successful to determine ClO − in tap water with limit of detection at 0.015 μM. CDs-B were successful to determine Hg 2+ in river water with limit of detection at 0.06 μM. The results demonstrate that the sub-classfication of CDs by the subtle different properties, e.g. ethanol solubility, is necessary for better application performance of CDs. In addition, thanks to their low toxicity, both CDs were suitable for cellular labelling on HepG2 cells. [ABSTRACT FROM AUTHOR]

Biological thiols, such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) are important for maintaining the cellular redox equilibrium and play critical roles in physiological and pathological processes. It is necessary to detect Cys, Hcy and GSH for obtaining important physiological and pathological information, which would promote the development of the medical profession. In this paper, we have successfully developed a new fluorescent probe OH1-NBD for Hcy detection. Based on the nucleophilic aromatic substitution (S N Ar) and rearrangement cascade reaction and the distance-dependent PET process, OH1-NBD shows to be a selective turn-on fluorescent probe for Hcy with a fast (a few minutes) and sensitive (16 nM) response. It can function as a fluorescence probe for imaging of Hcy in the living cell. At the same time, it can also be used for living cells as a potential probe for biothiol-relevant oxidant-governed redox status assay. We expect that the probe will provide a valuable approach to gain a better understanding of the roles of biothiols especially Hcy. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel sensor array was constructed based on two oxidants doped carbon dots. • The array discriminated and quantified amyloidogenic proteins with high accuracy. • The array could monitor the fibrillation process of amyloidogenic proteins. • The array could discriminate cancer patients and healthy people based on serum. • It provided a discriminative and adaptive tool for biomedical research and disease diagnosis. Disease-related proteins are biomarkers for disease diagnosis and treatment, e.g. amyloidogenic proteins are highly related to neurodegenerative diseases. Detection and monitoring of disease-related proteins is significant for the biomedical research and early disease diagnosis. Thus, the rapid, sensitive and low-cost approach is highly desired. For this purpose, herein, a novel dual-element sensor array was constructed based on two carbon nanodots (CDs). The CDs were prepared using citric acid and Congo red as carbon source by deliberately doping with two different oxidants, i.e. ammonium persulfate and hydrogen peroxide. The fluorescence of CDs could be efficiently and selectively quenched by proteins to different degrees, in which electrostatic and hydrophobic interactions might co-contribute to the sensing process. In the differentiability test, the established sensor array could accurately discriminate four amyloidogenic proteins and two serum proteins with a classification accuracy of 100%. The applicability could be extended to proteins quantification and mixture proteins discrimination. Typically, fibrillation stages of amyloidogenic protein (α-synuclein as example) in artificial cerebrospinal fluid were differentiated by the array, which was meaningful to illustrate the process of neurodegenerative diseases. Moreover, the sensor array successfully distinguished cancer patients (liver and breast cancers) and healthy people based on μL-level of serum sample, demonstrating its potential for fast screen of cancer at large scale. The constructed sensor array based on the oxidants doped CDs was promising for disease-related proteins discrimination, quantification and progressive fibrillation monitoring, and afforded a powerful discriminative and adaptive tool for biomedical research and disease diagnosis. [ABSTRACT FROM AUTHOR]

A fluoran-phenothiazine hybrid fluorescent probe for selective sensing of Fe3+ and ClO− has been rationally designed and prepared with application in fluorescence imaging. [Display omitted] • A fluoran-phenothiazine hybrid fluorescent probe FP has been designed and prepared. • FP shows high selectivity and sensitivity towards Fe3+ and ClO− by dual emission. • The low cytotoxicity allows FP to trace intracellular Fe3+ by cell imaging. Bifunctional fluorescent probes with dual-emission response attract extensive attention. A novel fluorescent probe FP , a hybrid of fluoran and phenothiazine, has been designed and synthesized for selective sensing of Fe3+ and ClO− with dual-emission changes, which involes mechanisms of Fe3+-promoted spirolactone ring opening and ClO−-induced oxidation of phenothiazine moiety, respectively. In addition, the detection limits for Fe3+ and ClO− were estimated to be 49.1 and 35.9 nM, respectively. Significantly, FP can be employed as an tracer for the detection of Fe3+ ions within living HeLa cells by fluorescence imaging. [ABSTRACT FROM AUTHOR]

A new fluorescent probe Lyso-Fl has been facilely prepared by an esterification reaction of spironolactone fluoran dye Rdi with ethanol, which shows viscosity-selective response by fluorescence. The new probe delivers obvious fluorescence signal enhancement when environmental viscosity changes from 1.01 cP (water) to 1256 cP (98% glycerol). And, both the emission intensity (575 nm) and fluorescence lifetime of Lyso-Fl exhibit individually good linear relationships with the solution viscosity. Besides, Lyso-Fl gives a selective response to viscosity among various biological species and exhibits pH-independent (1–10) fluorescent signals towards viscosity. More importantly, Lyso-Fl shows low cytotoxicity and can be utilized for monitoring of dexamethasone-stimulated viscosity enhancement by cell imaging with excellent lysosome-targeted performance, promoting it a promising fluorescent probe for lysosomal viscosity detection. A fluoran-based fluorescent probe Lyso-Fl for viscosity has been conveniently prepared with excellent performance in monitoring of lysosomal viscosity changes via fluorescence imaging. Unlabelled Image • A fluoran-based fluorescent probe Lyso-Fl has been facilely prepared. • Lyso-Fl delivers obvious fluorescence enhancement with viscosity increase. • Lyso-Fl shows low cytotoxicity. • Lyso-Fl can be utilized for monitoring of viscosity enhancement by cell imaging with excellent lysosome-targeted performance. [ABSTRACT FROM AUTHOR]