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• Synthesized a unique naphthalimide-rhodamine based chemosensor (NR-HG) for the selective detection of Hg2+ ion. • NR-HG shows an impressive LOD 491 nM and exhibits reversibility. • Synthesized Probe works through PET, CHEF, and FRET leading to the chelation-induced ring opening. • TD-DFT calculation supported the origin of the fluorescence emission maxima. • NR-HG is stable in biological pH and can efficiently image Hg2+ in SiHa cells under the fluorescence microscope. In this work, we are presenting the design and synthesis of an innovative fluorescent chemosensor: NR-HG, established on a naphthalimide-based rhodamine platform for Hg2+ ion sensing. The probe operates via PET, CHEF, and FRET mechanisms. The fluorescent chemosensor shows an immense selectivity and sensitivity towards Hg2+ ion via the enhancement of ring-opening rhodamine spiro-cyclic structure, with a detection limit (LOD) of 491 nM. The DFT analysis strongly validates the experimental observations. The probe senses the Hg2+ ion reversibly upon the addition of potassium iodide (KI). From the analysis of Job's plot, it can be conclusively confirmed that the NR-HG-Hg2+ complex demonstrates a 1:1 stoichiometric ratio. We also conducted an MTT assay and cell imaging experiment to assess both the compatibility of the probe with living cells and its effectiveness in real-life imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Rhodamine-Quinoline based probe has been synthesized. • It has been used to detect trace amount of Al3+, Cr3+ and HSO 4 − ions in water. • DFT & TD-DFT calculation were done to justify the experimental results. • Turn-on emission property of the probe is utilized to fabricate molecular INHIBIT logic gate. • Cytotoxicity and cell imaging on TPC-1 & HtH-7 cell lines. A designed Rhodamine-B-quinoline based Schiff base chemosensor (RhBQ) has been synthesized and characterized using various spectroscopic techniques. It shows 'turn on' fluorescence emission and also colorimetric sensitivity and selectivity towards trivalent metal ions (Al3+ and Cr3+) and anion (HSO 4 −) present in aqueous medium. Stoichiometry of both metal (Al3+ & Cr3+) - RhBQ complexes are found to be 1:1 using Job's plot. A notable enhancement in emission intensity for RhBQ-Al3+ (∼341 fold), RhBQ-Cr3+ (∼292 fold), and RhBQ-HSO 4 − (∼136 fold) complexes compare to RhBQ are observed. Sensing mechanism i.e. opening of spirolactam ring of RhBQ has been confirmed through various spectroscopic techniques such as; 1H NMR, 13C NMR, ESI-MS, TRPL, FT-IR, and DFT based computational study. The limit of detection (LOD) for Al3+, Cr3+, and HSO 4 − are found to be 2.2 × 10−8 M, 2.12 × 10−8 M and 8.63 × 10−7 M respectively. An advanced level 3 input OR–INHIBIT logic gate are constructed using chelating ligand EDTA. For onsite detection, TLC paper strip spot of the probe, RhBQ is prepared and the detection of Al3+ in few antacid drug are presented. In addition, cell-imaging analysis of Al3+, Cr3+, and HSO 4 − ions in the Human papillary thyroid carcinoma cell line (TPC-1) & Human anaplastic thyroid cancer cell lines (HtH-7) are presented and shows promising concentration and time-dependent detection results. [ABSTRACT FROM AUTHOR]

[Display omitted] • This is a rhodamine-based "off-on" fluorescent probe with a novel structure to detect tyrosinase activity. • The rhodamine fluorophore structure was improved by expanding the π-conjugation system, asymmetric synthesis, and fixing the N terminus, which greatly improved the fluorescence quantum yield of the fluorophore. • The use of 3-hydroxybenzyl oxygen as the recognition group of the probe effectively avoids the interference of reactive oxygen species in the detection of tyrosinase and improves the selectivity of the probe for tyrosinase. Tyrosinase (TYR) detection will be crucial in the prevention and early diagnosis of some illnesses, including epilepsy, albinism, and melanoma, due to the close linkage of abnormal expression of TYR with the occurrence of these diseases. Therefore, how to obtain a fluorescent probe that has a high fluorescence quantum yield and high specificity for detecting TYR activity will be of significance. In this work, we improved the rhodamine structure by expanding the π-conjugation system and using asymmetric synthesis to provide a fluorescent probe with good optical properties for the specific detection of TYR. The fluorescence quantum yield of fluorophore released from the probe by the enzymatic reaction with TYR was as high as 0.22, which was significantly greater than that of other previously reported fluorescent probes. We also chose 3-hydroxybenzyl oxygen as the recognition group, which can successfully lessen the interference from reactive oxygen species (ROS). At the same time, the probe demonstrated great sensitivity in detecting TYR activity, and the detection limit of TYR for the probe was calculated to be 0.45 U/mL. In addition, the probe has currently been successfully utilized to evaluate TYR activity in cells. Therefore, this probe is anticipated to be crucial in identifying TYR activity in challenging settings. [ABSTRACT FROM AUTHOR]

A Rhodamine B- quinoline conjugate ( RSQ ) functions as a colorimetric and fluorescence probe for selective recognition of Bi 3+ ion based on CHEF assisted FRET process. RSQ visibly changes its colour and fluorescence profile upon addition of Bi 3+ ion. The distinctive colour change allows facile discrimination of Bi 3+ over other common cations. Lowest concentration of Bi 3+ detected by RSQ is 0.05 μM. RSQ efficiently images intracellular Bi 3+ in live SiHa cells. [ABSTRACT FROM AUTHOR]

A new rhodamine based fluorescent turn on sensor L has been reported as a highly selective and sensitive chemosensor for the Cr 3+ ion in a CH 3 CN-H 2 O solution. In presence of Cr 3+ ion, the strong fluorescence enhancement is attributed due to the interaction of Cr 3+ with L, leading to opening of the spirolactam ring of rhodamine B to the amide form. The Cr 3+ sensing mechanism is also supported by the Job’s plot, ESI-MS, 1 H NMR titration experiments. Importantly, this probe shows high selectivity over other biologically relevant metal ions. Also, anions do not show any effect. In addition, the detection limit is found to be up to 7.5 nM which is acceptable within the EPA (US) limit. The probe is also able to function within a broad biological pH range of 4–8. Furthermore, the probe L shows cellular penetrability for its potential use in confocal cell imaging studies. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new sensor, RT4 detecting Cu2+ and Fe3+ simultaneously with LOD values of 0.24 µM and 0.18 µM respectively. • MS, FTIR, 1H NMR spectra and DFT studies showing the possible binding mechanism of RT4 towards Cu2+ and Fe3+. • Inexpensive filter paper system was successfully prepared with RT4 as on-site assay kit. • Long-term MTT assay conducted showed low cytotoxicity of RT4 in living cells. • Cell imaging studies showed permeability of RT4 in detecting intracellular Fe3+. A new fluorescent sensor, RT4 has been synthesized by reacting trans -4-(diethylamino)cinnamaldehyde with rhodamine B hydrazide in a one-step reaction. The characterization of RT4 was done by using FT-IR, 1H NMR, 13C NMR, and single crystal X-ray crystallography. In aqueous acetonitrile (1:1, v/v pH 7.5), RT4 exhibited a highly selective and sensitive colorimetric response upon recognition of Cu2+ and fluorometric response with Fe3+ ions. The calculated limit of detections (LOD) of RT4 with Cu2+ and Fe3+ were 0.20 and 0.18 µM at λ abs/em = 555 and 585 nm, respectively. Test strips for colorimetric detection of Cu2+ and Fe3+ as an on-site test kit were successfully prepared. Furthermore, the MTT assay indicated that RT4 possess low cytotoxicity in human colorectal carcinoma HCT 116 after 24 h. The fluorescence microscopy experiment suggested that RT4 could also serve as a biological fluorescence probe for the detection of Fe3+in HCT 116 cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thiourea based fluorescent sensor (L) was synthesized and characterized. • Sensor L showed fluorescence turn-on response towards Hg2+, Ag+ and Au3+ in DMSO-H 2 O. • Sensor L formed complex with Hg2+, Ag+ and Au3+ in 1:1 binding stoichiometry. • Sensor L was applied to detect Hg2+ in various soil samples and living Drosophila cell. • DFT investigations and HOMO-LUMO simulations further showed a 1:1 stoichiometry. A thiourea based fluorescence chemosensor (L) was synthesized and applied for the selective detection of Hg2+, Ag+ and Au3+ions in DMSO-H 2 O (10:90, v/v). The receptor L showed a weak fluorescence emission in DMSO-H 2 O due to the photo-induced electron transfer (PET) process. The fluorescence intensity of L was enhanced upon addition of Hg2+, Ag+ and Au3+ ions because of the complexation-induced inhibition of PET process. The 1:1 binding stoichiometry between L and the metal ions (Hg2+, Ag+ and Au3+) was found from the Benesi-Hildebrand plot. The density functional theory (DFT) calculations were performed to explain the binding modes. The estimated binding constants and detection limits of L are found to be 5.87 × 106 M−1 and 5.01 × 10-7 M for Hg2+, 8.78 × 106 M−1 and 2.14 × 10-8 M for Ag+, and 7.93 × 106 M−1 and 34 × 10-7 M for Au3+, respectively. The sensor L was applied to detect Hg2+, Ag+ and Au3+ ions in living Drosophila cell lines. Also, sensor L was employed to detect Hg2+ in soil samples. [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 rhodamine derivative ( R1 ) has been synthesized by an additive reaction of rhodamine 6G hydrazide with methyl 2-isothiocyanatobenzoate, which exhibits high selectivity and sensitivity as a fluorescent sensor toward Cu 2+ under physiological conditions. The detection limit of Cu 2+ ion is 47.2 nM. Moreover, R1 could sense Cu 2+ by “naked eye” with a color change from colorless to pink. This selective signaling behavior is not affected by other canions that might be present in the environmental samples. The application of the fluorescent sensor in monitoring intracellular Cu 2+ in HeLa cells was also demonstrated. [ABSTRACT FROM AUTHOR]

A new rhodamine 6G derived chemosensor L has been synthesized that selectively detects the presence of Cu 2+ ion over a host of other biologically important and environmentally relevant metal ions in aqueous alcoholic medium under physiological pH (ethanol: water, 1:1, v/v, pH 7.2). The significant enhancement of fluorescence intensity of L is caused by Cu 2+ ion induced cleavage of spirolactum bond in the rhodamine moiety. This mechanism is well supported by the crystal structure of the L-Cu 2+ complex that depicts two ligand units are bonded to two Cu 2+ ions. Color of the solution changes from light orange to dark pink upon metal binding which allows naked eye detection ion as well. Confocal microscopic experiments validate that the dye is potentially useful for the selective detection of Cu 2+ ion in living cells. Therefore the dye is an excellent fluorogenic and chromogenic chemosensor for the Cu 2+ ion in aqueous ethanolic medium and the living cell as well. [ABSTRACT FROM AUTHOR]

A new rhodamine hydrazone obtained by the condensation of rhodamine hydrazide with 5-iodo-3-methoxy salicylaldehyde (NLAC) is synthesized and characterized using spectroscopic (IR, UV–vis, 1 H, 13 CNMR, ESI-MS) and X-ray diffraction techniques. It binds selectively with Al 3+ ions and a strong fluorescence signal is displayed from [ NLAC − Al 3+ ] ensemble and has also been supported by DFT calculation. The color change of NLAC in presence of Al 3+ ions is further corroborated by UV-visible and fluorescence spectral titrations. The spectral changes are significant in the visible region of the spectrum and enable the detection of Al 3+ ions with naked eye. The 1:1 stoichiometry of NLAC:Al 3+ is supported by Job’s plot and ESI-MS data. The fluorescence signal displayed from [ NLAC − Al 3+ ] is quenched on the addition of N 3 − ions as an aqueous solution of NaN 3 salt which reverts back further on the addition of Al 3+ ions. This recognition process is also displayed in a human cervical cancer cell lines (SiHa cells) in an aqueous-acetonitrile medium. The process is repeated several times showing that the system is robust and reversible in the recognition process. A strip tests supports its feasibility for the laboratory demonstration. [ABSTRACT FROM AUTHOR]

• A colorimetric and ratiometric fluorescent probe for highly selective recognition of Hg2+ was synthesized. • The probe could detect Hg2+ in living cells. • The emission peak red shifted 109 nm upon addition of Hg2+. Although fluorescent probes had become powerful tools to detect and image mercury ion (Hg2+), most of them suffered from a single signal change. Therefore, a new ratiometric fluorescent probe 1, with a quinoline–benzothiazole group as donor and a rhodamine as acceptor, was constructed for Hg2+ detection in this paper study. Results showed that Probe 1 was highly sensitive and selective to Hg2+, with a linear range of 0–26 μM and a detection limit (LOD) of 0.2 μM. Moreover, with excess competitive metal ions in DMF–H 2 O (v/v, 7/3), probe 1 exhibited excellent colorimetric selectivity and sensitivity to Hg2+ with the significant color change from colorless to pink with a linear range 0–28 μM and a LOD of 0.37 μM, because Hg2+ promoted the rhodamine hydrazide opening. And probe 1 finally was used to detect Hg2+ in living cells. [ABSTRACT FROM AUTHOR]

• A "turn-on" fluorescent probe ol -PIP selectively responded to Hg2+ with large Stokes shift of 180 nm. • Subsequently, strong emission of ol -PIP–Hg2+ was quenched followed by S2–. • The process of the sequential sensing was realized in cells imaging. An excited state intramolecular proton transfer (ESIPT) characteristic "turn-on" fluorescence sensor for Hg2+ with large Stokes shift was fabricated and then it had ability to sequentially detect S2– by the "turn-off" fluorescent signal in aqueous media. On account of it, a simple fluorescence probe ol -PIP based on the phenanthro[9,10- d imidazole moiety bearing two phenol fragments was synthesized. Probe ol -PIP showed gradually the fluorescence enhancement with the increasing of water fraction due to the aggregation affect. Sequentially, the moderate fluorescence emission of ol -PIP in aqueous media was continuously and selectively illumined by the successive addition of Hg2+ with about 180 nm Stokes shift. Furthermore, the persistent "turn-on" fluorescence intensity could be quenched to the original state of ol -PIP in presence of S2–. This on–off sensing process was sustained for five times with the alternative addition of Hg2+ and S2–. The limits of detection for Hg2+ and S2– were 6.45 × 10–7 and 3.46 × 10–7 M, respectively. In addition, ol -PIP was successfully applied in Hg2+ detection in real water samples; simultaneously, ol -PIP with low cytotoxicity was also successfully used as a bioimaging reagent to detect Hg2+ and S2– in living cells. [ABSTRACT FROM AUTHOR]

• Novel phenothiazine-based colorimetric and ratiometric fluorescent sensor PPM for Hg2+ is synthesized. • PPM shows high selectivity and low detection limit of 12.5 nM in a wide pH range. • The response time of PPM for Hg2+ is within 1 min and suitable for ultrafast detection of Hg2+. • PPM for Hg2+ shows good applicability for paper/TLC-based "naked-eye" colorimetric assay. • PPM was used for fluorescence imaging of Hg2+ in living cells. A new phenothiazine-based sensor PPM was successfully designed and synthesized, which shows highly selective, ultrafast, naked-eye colorimetric and turn-on ratiometric fluorescence sensing of Hg2+ on the basis of the ICT from phenothiazine to aldehyde. Upon addition of Hg2+, obvious blue fluorescence at 455 nm decreased while green fluorescence at 528 nm enhanced, which exhibits ratiometric fluorescent turn-on response along with a "naked-eye" color change from pale-blue to bright-green. The PPM for highly sensing of Hg2+ with a quite low detection limit (12.5 nM) and a wide pH application range. The sensing mechanism proved to be the Hg2+-triggered thioacetal deprotection reaction was confirmed. Importantly, PPM was successfully employed for highly selective detecting and imaging of Hg2+ in living cells, as well as on paper/TLC-based "naked-eye" colorimetric assay. [ABSTRACT FROM AUTHOR]