Naked-eye colorimetric and turn-on fluorescent Schiff base sensor for cyanide and aluminum (III) detection in food samples and cell imaging applications

Tailored fluorophore design: Enhancing selectivity for cyanide ion sensing in water and food samples, and innovative device development

A rigid fluorophore unit of Julolidine/coumarin fused with an indolium-conjugated system was built for the immediate and effective recognition of cyanide ions in a 90 % aq. DMSO solution. The probes are capable of displaying better sensitivity/selectivity for the cyanide ion over a wide range of other interfering ions. The probe JI showed an instant colorimetric variation, whereas the modified probe JCI showed both colorimetric and fluorimetric variation with cyanide ion. The observed detection limit values indicated excellent sensitivity of the probe to the cyanide ion. HRMS and 1H NMR studies confirmed that the mechanism of detection of CN- is via the nucleophilic attack on the electron-deficient indolium moiety of the molecule. Moreover, the probes are well proficient in selective recognition of cyanide in various real time applications (test strips, electronic sensor kit, food and water sample analysis).

A Novel Naphthylidene-diimine Chemosensor for Selective Colorimetric and Fluorometric Detection of Al3+ and CN- Ions

A naphthylidene-diimine L2 was newly designed, and its structure was identified by elemental analysis and spectroscopic methods. The effect of temperature, acid-base and light on enol-keto tautomerism in this Schiff base was evaluated by colorimetry, UV-Vis and fluorescence spectroscopy. Under irradiation 365 nm, L2 emitted yellow, orange and strong green emission in pure, basic and aqueous DMSO media (v/v, 1/1), respectively. Its ionochromic behavior against various cations (Fe3+, Al3+, Cr3+, Cu2+, Co2+, Ni2+, Zn2+, Cd2+, Pb2+, Ba2+ and Ag+) and anions (F-, Cl-, CH3COO-, SO32-, S2O32-, HSO4-, H2PO4-, NO3-, CN-, and OH-) was investigated in aqueous DMSO media (v/v, 1/1) by UV-Vis and fluorescence experiments. Dark yellow color of L2 changed to colorless for Fe3+, Cr3+ and HSO4- ions, and turned to light yellow for Al3+ and Cu2+ ions, and to orange for CN- and OH- ions. According to UV-Vis data, the chemosensor displayed selective recognition towards Fe3+, Al3+, Cu2+, HSO4-, CN- and OH- with a 1:1 stoichiometric ratio. At the excitation wavelength of 365 nm, L2 gave strong yellowish white emission (λem = 445 and 539 nm) in the presence of Al3+, and the intensity increased about 12.5 times. On the other hand, the chemosensor displayed one emission band at 452 nm and 450 nm in the presence of CN- and OH- with 1.9 fold and 2.3 fold fluorescence enhancement, respectively.

A colorimetric and turn-on fluorescent sensor for cyanide and acetate-based Schiff base compound of 2,2'-((1E,11E)-5,8-dioxa-2,11-diazadodeca-1,11-diene-1,12-diyl)bis(4-((E)-phenyldiazenyl)phenol)

A novel Schiff base-based sensor (L) has been designed, synthesized, and developed as a fluorescent and colorimetric sensor for cyanide and acetate. This L exhibited a quick response with rapid sensitivity to CN^- and AcO^- through a remarkable color change from yellow to red which was detectable by the naked eyes. It also sensed CN^- and AcO^- in a fluorescent way via an enhancement in fluorescence intensity. The interaction between L and anions (CN^- and AcO^-) was investigated by using UV-Vis studies, and ¹H NMR titration. The theoretical DFT calculations were also employed to support the results, which displayed good agreement with the experimental value acquisition. As the detection limit for cyanide and acetate were 2.1 × 10^-9 M and 1.7 × 10^-9 M; respectively, low concentrations of these anions could be detectable in the proposed L sensor. In addition, L showed significant reversibility of CN^- detection by using Cu²⁺ as a proper reagent with two different sensing methods including color change and UV-Vis. Last but not least, L could be applied to rapidly detect CN^- in a wide range of pH. As a result, the proposed sensor is promising to identify cyanide and acetate in practical applications in medical, biological, and chemical fields.

A dimedone-phenylalanine-based fluorescent sensor for the detection of iron (III), copper (II), L-cysteine, and L-tryptophan in solution and pharmaceutical samples

The development of fluorescence molecules for the fast and effective detection of L-tryptophan (L-Trp) has attracted a lot of attention because it is an important amino acid for baby growth, nitrogen equilibrium in adults, improving sleep, and mood regulation. A dimedone-phenylalanine-based chiral sensor (SDPA) was synthesized and exhibited a strong fluorescence quenching by Fe³⁺ and Cu²⁺ in a water/DMSO (3/7) solution with a detection limit of 2.29 × 10^-6 M and 6.37 × 10^-6 M, respectively. The factors affecting fluorescence sensings, such as the pH and competing cations, were studied. The sensor can be reused at least five times after being treated with EDTA. The Job plot, ESI-MS spectra, ¹H NMR spectra, absorbance, and fluorescence titration experiments were investigated to study the mechanism of SDPA-Fe³⁺ and SDPA-Cu²⁺ complexation. The SDPA-Cu²⁺ complex can detect L-tryptophan and L-cysteine at trace levels by turn-on fluorescence with a detection limit of 9.35 × 10^-6 M and 8.86 × 10^-6 M, respectively. Moreover, applying the SDPA-Cu²⁺ complex for quantitative analysis of L-tryptophan in real sleep-improving capsules resulted in good recovery. The L-tryptophan level of the Elining capsule was determined at 190.8 ± 10.5 mg/g (mg L-tryptophan/g medicine), which is close to the announced quantity of 180 mg/g. Besides, the SDPA-Cu²⁺ complex can selectively detect free L-Try molecules and L-Try residues in proteins.

A benzothiazole-based new fluorogenic chemosensor for the detection of CN− and its real-time application in environmental water samples and living cells

Since the cyanide ion is used in a wide range of industries and is harmful to both human health and the environment, a number of research efforts are dedicated to creating fluorescence sensors for the detection of cyanide (CN⁻). Herein, for the fluorescence detection of CN⁻, a new highly selective and sensitive sensor 2-(3-(benzo[d]thiazol-2-yl)-4-hydroxybenzylidene)-1H-indene-1,3(2H)-dione (BID) was created by conjugating a benzothiazole moiety with 1H-indene-1,3(2H)-dione. The donor and acceptor components of this hybrid receptor were covalently connected through a double bond. The nucleophilic addition of a cyanide anion to the BID inhibits the intramolecular charge transfer (ICT) transition, resulting in spectral and colour alterations in the receptor. When the solvent polarity was increased from n-hexane to methanol, this molecule exhibited a bathochromic shift in the emission wavelength (610 to 632 nm), suggesting the presence of a solvatochromic action. The sensor BID has shown strong specificity towards CN⁻ by interrupting its internal charge transfer (ICT), resulting in a significant change in the UV-vis spectrum and a notable blue shift in the fluorescence emission spectrum. The cyanide anion (CN⁻) is responsible for the optical alterations observed by BID, as opposed to the other anions examined. The detection limit was 5.97 nM, significantly less than the WHO's permitted amount of CN⁻ in drinking water. The experimental findings indicate that BID's fluorescence response to CN⁻ is pH insensitive throughout a wide pH range of 6.0 to 12.0. The interaction mechanism between the BID and CN⁻ ions has been studied by HRMS, ¹H-NMR titration experiments, FT-IR, and DFT, which confirmed the nucleophilic addition of CN⁻ on vinylidene and subsequent disturbance of ICT. Additionally, we demonstrated the real-time detection application of CN⁻ in environmental water samples and live-cell imaging.

Since the cyanide ion is used in a wide range of industries and is harmful to both human health and the environment, a number of research efforts are dedicated to creating fluorescence sensors for the detection of cyanide (CN⁻).