A dual channel rhodamine appended smart probe for selective recognition of Cu2+ and Hg2+ via "turn on" optical readout

A new rhodamine-6G hydrazone RHMA has been synthesized using rhodamine-6G hydrazide and 5-Allyl-3-methoxysalicylaldehyde. RHMA has been fully characterized with different spectroscopic methods and single crystal XRD. RHMA can selectively recognize Cu²⁺ and Hg²⁺ in aqueous media amongst other common competitive metal ions. A significant change in absorbance was observed with Cu²⁺ and Hg²⁺ ions with emergence of a new peak at λ_max 524 nm and 531 nm respectively. Hg²⁺ ions lead to "turn-on" fluorescence enhancement at λ_max 555 nm. This event of absorbance and fluorescence marks the opening of spirolactum ring causing visual color change from colorless to magenta and light pink.RHMA-Cu²⁺ and RHMA- Hg²⁺complexes are found to be reversible in presence of EDTA^2-ions. RHMA has real application in form of test strip. Additionally, the probe exhibits turn-on readout-based sequential logic gate-based monitoring of Cu²⁺ and Hg²⁺ at ppm levels, which may be able to address real-world challenges through simple synthesis, quick recovery, response in water, "by-eye" detection, reversible response, great selectivity, and a variety of output for accurate investigation.

'AIE + ESIPT' Active 2-hydroxy-naphthalene Hydrazone for the Fluorescence Turn-on Sensing of Al3

The aggregation-induced emission (AIE) behaviour of an easy-to-prepare Schiff base 2-hydroxy-naphthalene hydrazone (L) was explored in mixed DMSO/HEPES medium by selecting DMSO as a good solvent, whereas HEPES buffer (H₂O, 10 mM, pH 7.4) as a poor solvent. The weakly fluorescent L in pure DMSO showed a fluorescence enhancement at 532 nm upon increasing the fraction of HEPES above 70% because of the self-aggregation of L and excited state intramolecular proton transfer (ESIPT) process. The AIE luminogen (AIEgen) L was applied for the sensing of metal ions in HEPES buffer (5% DMSO, 10 mM, pH 7.4). Among the fourteen different metal ions (Cu²⁺, Co²⁺, Ni²⁺, Mn²⁺, Mg²⁺, Fe³⁺, Fe²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Al³⁺, Cr³⁺), AIEgen L showed a selective fluorescence enhancement at 435 nm in the presence of Al³⁺ without disturbing the fluorescence intensity at 532 nm due to the chelation-enhanced fluorescence effect (CHEF). The detection limit of 20 nM was estimated by performing the fluorescence titration of AIEgen L with Al³⁺. The reversibility of the Al³⁺ selective AIEgen L was demonstrated by adding a strong chelating agent EDTA. Finally, the practical utility of AIEgen L was validated by quantifying Al³⁺ in river and tap water samples.

Selective Recognition and Reversible “Turn-Off” Fluorescence Sensing of Acetate (CH3COO−) Anion at Ppb Level Using a Simple Quinizarin Fluorescent Dye

A simple and cost-effective optical sensing system based on quinizarin fluorescent dye (QZ) for the selective and reversible sensing of CH3COO− anions is reported. The anion binding affinity of QZ towards different anions was monitored using electronic absorption and fluorescence emission titration studies in DMSO. The UV-visible absorption spectrum of QZ showed a decrease in the intensity of the characteristic absorption peaks at λ = 280, 323, and 475 nm, while a new peak appeared at λ = 586 nm after the addition of CH3COO− anions. Similarly, the initial strong emission intensity of QZ was attenuated following titration with CH3COO− anions. Notably, similar titration using other anions, such as F−, Cl−, I−, NO3−, NO2−, and H2PO4-, caused no observable changes in both absorption and emission spectra. The selective sensing of CH3COO− anions was also reflected by a sharp visual color change from bright green to faint green under room light. Further, the binding was found to be reversible, and this makes QZ a potential optical and colorimetric sensor for selective, reversible, and ppb-level detection of CH3COO− anions in a DMSO medium.

Fluorescent pattern recognition of metal ions by nanoparticles of bovine serum albumin as a chemical nose/tongue

A sensor array mimicking a chemical nose/tongue based on bovine serum albumin nanoparticles (BSANsn) has been developed for the fluorescence pattern recognition of metal ions in biofluids. Three types of BSANsn (BSANs10, BSANs20, and BSANs40) show the same excitation/emission peak at 478/526 nm. According to the differential fluorescence variation, the sensor array shows particular fluorescence response patterns depending upon metal ions. Upon principal component analysis (PCA), it was found that the sensor array can distinguish 18 metal ions clearly at a concentration of as low as 10 μM. Moreover, different concentrations of metal ions and mixed metal ions of diverse kinds or valence states can be differentiated by the sensor in biofluids. In addition, the results were well consistent with those obtained with the traditional ICP-AES method.

New thiophene hydrazide dual-functional chemosensor: Colorimetric sensor for Cu2+ & fluorescent sensor for Al3

A new thiophene hydrazide derivative TSB was synthesized and utilized as naked-eye colorimetric sensor for Cu²⁺ by the color changed from colorless to yellow as well as green fluorescent turn on sensor for Al³⁺ in DMSO/H₂O (1/1, V/V) solution. The dual-functional chemosensor TSB for Cu²⁺/Al³⁺ sensing displayed excellent properties of special selectivity, superior sensitivity, outstanding anti-interference performance, instantaneous response, wide pH working range and good reversibility. The detection limits of TSB for Cu²⁺/Al³⁺ were determined as low as 46.5 nM and 32.7 nM, respectively. The 1:1 binding mode of TSB with Cu²⁺/Al³⁺ was proved by spectrometric titrations, Job's plots, FTIR, ¹H NMR and HRMS analysis. Moreover, chemosensor TSB was successfully utilized for detection of Cu²⁺ and Al³⁺ in real environmental water and food samples with high reliability, demonstrating its practical applicability.

A Silyl Ether Based Fluorescent Probe for Rapid Monitoring of Endogenous Peroxynitrite Concentration and Imaging in Living Cells through Multicolor Emission

The peroxynitrite ion (ONOO^- ) has important roles in many biological processes. We have developed a multicolor ONOO^- -sensing probe (SiONNOH) that undergoes deprotonation and desilylation processes, which result in several changes in the emission wavelengths. In response to different concentrations of ONOO^- , the probe exhibits fluorescence changes from pink (595 nm at 2 eq. ONOO^- ) to green (540 nm at 6 eq. ONOO^- ) via orange (3 eq. ONOO^- ) and yellow (4 eq. ONOO^- ) under physiological conditions until no fluorescence signal is observed after ONOO^- is completely eliminated by lipoic acid. The probe shows the high selectivity for ONOO^- and the limit of detection is calculated to be 1.27 μM. Moreover, the probe shows the capacity to monitor the concentration ranges of ONOO^- through multicolor fluorescence in living cells, which will greatly facilitate the rapid detection of ONOO^- concentration ranges by the naked eye under a UV light without any precision instrumentation.

Dual-response detection of Ni2+ and Cu2+ ions by a pyrazolopyrimidine-based fluorescent sensor and the application of this sensor in bioimaging

Herein, a dual-response fluorescent sensor, L, based on pyrazolopyrimidine was designed and developed for the simultaneous detection of Ni²⁺ and Cu²⁺ ions in the presence of other metal ions; the structural characterization of L was carried out by FTIR spectroscopy, NMR spectroscopy, HRMS and X-ray diffraction analysis. The sensor L effectively displayed fluorescence quenching towards the Ni²⁺ and Cu²⁺ ions with high sensitivity without interference from other metal ions. The results reveal that L binds to Ni²⁺ and Cu²⁺ in a 2 : 1 pattern, which matches well with the result of the Job's plot. The association constants of L with Ni²⁺ and Cu²⁺ were 3.2 × 10⁴ M⁻¹ and 7.57 × 10⁴ M⁻¹, respectively. The detection limits (DLs) are down to 8.9 nM for Ni²⁺ and 8.7 nM for Cu²⁺. The fluorescence imaging of L in T-24 cells was investigated because of the low cytotoxicity of L, indicating that L could be used to detect Ni²⁺ and Cu²⁺ in living cells.

A pyrazolopyrimidine-based fluorescent sensor L was developed and applied for detection of Cu²⁺ and Ni²⁺ in ethanol solution by photoluminescence quenching. It shows low cytotoxicity and good imaging characteristics for Cu²⁺ and Ni²⁺ in living cells.

Rhodamine scaffolds as real time chemosensors for selective detection of bisulfite in aqueous medium

Rhodamine and its derivatives have been widely used in designing fluorescent ‘turn on’ cation sensors, while very few rhodamine based fluorescent probes have been reported to date for the detection of anions in water.

A hydrazone based probe for selective sensing of Al(iii) and Al(iii)-probe complex mediated secondary sensing of PPi: framing of molecular logic circuit and memory device and computational studies

A hydrazone-based conjugate acts as a dual channel sensor towards Al³⁺and PPi in H₂O–MeOH with excellent sensing capability in live cells.

Sensitive ratiometric detection of Al(iii) ions in a 100% aqueous buffered solution using a fluorescent probe based on a peptide receptor

The peptidyl bioprobe detected Al(iii) ions sensitively in a 100% aqueous buffered solution through ratiometric response.

'Naked-eye' detection of biologically important anions in aqueous media by colorimetric receptor and its real life applications

A colorimetric receptor R 2-[(2-Hydroxy-naphthalen-1-ylmethylene)-hydrazonomethyl]-quinolin-8-ol has been designed and synthesized with good yield and characterized by the standard spectroscopic techniques such as FT-IR, UV-Visible, ¹H NMR, ¹³C NMR and ESI-MS. The receptor R showed naked-eye detection and spectral change in the presence of F^-, AcO^- and H₂PO₄^- over other anions. Interestingly, receptor R displaying high selective recognition towards F^-, AcO^- ion with a drastic color change from pale yellow to red in dry DMSO solvent and orange in mixed solvent DMSO/H₂O (9:1, v/v). The behavior of receptor R towards F^-, AcO^- ion was investigated using UV-Vis and ¹H NMR experiment. The detailed ¹H NMR experiment result revealed that the receptor R is forming the hydrogen bonding between imine nitrogen and phenolic OH proton towards anions. The receptor R is able to detect sodium salts of flouride (NaF) and acetate (NaAcO) in aqueous medium and it exhibited dramatic color change from pale yellow to red. The receptor R demonstrated itself to be useful for real life application by detecting flouride and acetate ion in sea-water and commercially available product such as toothpaste, mouthwash and vinegar solution.

2-Hydroxy-naphthyl functionalized mesoporous silica for fluorescence sensing and removal of aluminum ions

2-Hydroxy-naphthyl functionalized mesoporous silica has been used as a turn-on fluorescent chemosensor for Al³⁺ and used to remove it with high efficiency.

Highly sensitive and selective detection of Al(III) ions in aqueous buffered solution with fluorescent peptide-based sensor

A fluorescent sensor based on a tripeptide (SerGluGlu) with a dansyl fluorophore detected selectively Al(III) among 16 metal ions in aqueous buffered solutions without any organic cosolvent. The peptide-based sensor showed a highly sensitive turn on response to aluminium ion with high binding affinity (1.84×10(4)M(-1)) in aqueous buffered solutions. The detection limit (230nM, 5.98ppb) of the peptide-based sensor was much lower than the maximum allowable level (7.41μM) of aluminium ions in drinking water demanded by EPA. The binding mode of the peptide sensor with aluminium ions was characterized using ESI mass spectrometry, NMR titration, and pH titration experiments.