Tandem Detection of Sub-Nano Molar Level CN- and Hg2+ in Aqueous Medium by a Suitable Molecular Sensor: A Viable Solution for Detection of CN- and Development of the RGB-Based Sensory Device

The fabrication of a hybrid fluorescent nanosensing system and its practical applications via film kits for the selective determination of mercury ions

Heavy metal ions especially mercury exposure have severe toxic effects on living organisms and human health. Therefore, easy, accessible, and accurate determination strategies for the selective specification of mercury ions are essential for numerous disciplines. In the presented paper, new hybrid fluorescent iron oxide nanoparticles labeled with carbazole and triazole units (CT-IONP) were prepared via surface modification for the spectrofluorimetric determination of Hg2+ in environmental samples. The structure of the new sensing system is characterized via various spectroscopic, thermal, and microscopic techniques. Under optimized conditions, the hybrid system is not only used in fully water media but also highly fluorescent which led to the "turn-off" response towards Hg2+ ion in the presence of various competitive species. The presented sensing system was successfully used for the determination of Hg2+ ions in the wide linear working range (0.02-10.00 µmol.L-1) at nanomolar levels, where the limit of detection and quantification were calculated as 7.38 and 22.14 nmol.L-1. Importantly, the practical application of hybrid material was applied by CT-IONP embedded polycaprolactone (PCL) polymer film kits. The bluish color of fabricated film kits was instantly and dramatically turned colorless-dark patterns after the addition of Hg2+ ions, which resulted in convenient and rapid film test kits for selective detection.

Dual-mode SERS/colorimetric sensing of nitrite in meat products based on multifunctional au NPs@COF composite

The presence of nitrite in food products has generated significant public concern. A simple and rapid dual-mode surface-enhanced Raman spectroscopy (SERS)/colorimetric detection of nitrite is proposed based on a diazo reaction and multifunctional gold nanoparticle-doped covalent organic framework (Au@COF) composite. Under acidic conditions, the reaction between toluidine blue and nitrite yielded a colorless diazo salt, simultaneously attenuating its characteristic absorption peak and Raman signal. The multifunctional Au@COF materials enhanced the Raman signal and ensured good reproducibility. Additionally, the reaction rates improved, and the sensitivity was enhanced due to the excellent adsorption capacity of the COF. The proposed method demonstrated high sensitivity and excellent recovery rates for nitrite detection in food samples. This approach shows potential for precisely detecting nitrite content in real-world food samples by integrating the simplicity of colorimetric analysis with the enhanced sensitivity of SERS.

Spectroscopic and Theoretical Studies on the Selective Detection of Cyanide Ions by a Turn-On Fluorescent Chemo-Dosimeter and its Application in Living Cell Imaging

A new chemo-dosimeter AK4 containing quinoline fluorophore has rationally been designed, synthesised and characterized using 1H and 13C NMR and mass spectral techniques. The probe senses explicitly CN- ion through a dramatic enhancement in fluorescence over other commonly coexistent anions in H2O:DMSO (9:1 v/v) medium over a broad pH range (4-10). 1H NMR titration revealed the deprotonation followed by nucleophilic addition reaction of CN-, which was supported by 13C NMR and mass spectral examinations. The Job's continuous variation method indicated the formation of a 1:1 adduct between AK4 and CN- with a binding constant of 1.62 × 104 M-1. A limit of detection (LOD) towards CN- of 0.69 µM has been determined, which is much lower than the World Health Organization (WHO) recommended limit of CN- in drinking water (1.9 µM). The changes in the optical properties of AK4 upon reaction with CN- were delineated using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations. Moreover, fluorescence microscopic studies established that AK4 could be an effective probe for imaging intracellular CN- in HeLa cells.

Multi-Spectroscopic and TD-DFT Studies on Chromogenic and Fluorogenic Detection of Cyanide in an Aqueous Solution

Different spectroscopic techniques and Density Functional Theory (DFT)/Time-Dependent Density Functional Theory (TDDFT) calculations have been employed to investigate the dual channel CN- detection behaviour of the developed chemo-dosimeter (AK3). The CN- with AK3 reaction triggered a colour change from pale yellow to colourless and enhanced fluorescence. UV-Vis, fluorescence, 1H & 13C NMR and mass techniques coupled with theoretical calculations (Mulliken charges, dihedral angles) revealed that the CN- sensing process mechanism involves deprotonation of the N-H group followed by nucleophilic addition reaction. Detailed TD-DFT calculations showed that the relaxation of excited electrons from LUMO and to two different ground states is responsible for the weak/moderate fluorescence of AK3. Nucleophilic addition of CN- to the C-atom of the CH = CH bridge terminated the π-conjugation between donor and acceptor regions, reduced the coplanarity, decreased the ICT transition and consequently enhanced the fluorescence of the probe. The practical utility of the probe was demonstrated by detecting cyanide in food materials and determining CN- in environmental water samples.

RGB color analysis of formaldehyde in vegetables based on DNA functionalized gold nanoparticles and triplex DNA

A highly sensitive and selective RGB color analysis for the detection of formaldehyde (FA) was developed by using a DNA functionalized gold nanoparticle (AuNPs-DNA) probe. When complementary oligonucleotides (oligo 2 and oligo 3) and a silver ion (Ag⁺) were added to the AuNPs-DNA solution, triplex DNA was formed, resulting in the aggregation of AuNPs, and accompanied by a solution color change from red to purple. With the addition of formaldehyde, it reacted with Ag⁺, decreased the stability of triplex DNA between AuNPs-DNA, induced the dispersion of AuNPs, and the color of AuNPs recovered to red. Therefore, the formaldehyde concentration could be estimated with the RGB (red, green, blue) values of the AuNP solution by using a smartphone application (APP). The R value of the system was proportional to the concentration of formaldehyde within the range of 0.23-4.50 mg L^-1, with a detection limit of 0.14 mg L^-1. The method has been successfully applied to detect the residues of formaldehyde in vegetable samples and has the potential of the on-site determination of formaldehyde.

Coumarin functionalized molecular scaffolds for the effectual detection of hazardous fluoride and cyanide

Fluoride and cyanide contamination in drinking water imposes detrimental impacts on human health above their permissible limits. Hence, the quantitative detection of these colourless water-soluble toxins has attracted attention. Even though a plethora of chemosensors have been reported so far for the detection of fluoride and cyanide from various matrices, still their applicability is limited to a few examples. Nevertheless, recent advances in the syntheses of coumarin derivatives have shown significant impact on fluoride and cyanide detection. Therefore, this present review provides a brief overview of the application of coumarin-coupled molecular scaffolds towards the detection of perilous fluoride and cyanide along with their sensing mechanisms in order to develop more innovative, simple, sensitive, real-time responsive and cost-effective coumarin-based supramolecular chemosensors to promote next generation approaches towards the ultra-trace quantitative detection of these toxic anions.

A Chemodosimetric Approach for Fluorimetric Detection of Hg2+ Ions by Trinuclear Zn(II)/Cd(II) Schiff Base Complex: First Case of Intermediate Trapping in a Chemodosimetric Approach

The present work discloses the application of two fluorescent zinc and cadmium complexes (1 and 2) for sensing of Hg(II) ions through a chemodosimetric approach. The ligand under consideration in this work is a N₂O donor Schiff base ligand (E)-4-bromo-2-(((2-morpholinoethyl)imino)methyl)phenol (HL), which has been harnessed to generate complexes [Zn₃L₂(OAc)₄] (1) and [Cd₃L₂(OAc)₄] (2). X-ray single crystal diffraction studies unveil the trinuclear skeleton of complexes 1 and 2. Both complexes have been found to be highly fluorescent in nature. However, the quantum efficiency of Zn(II) complex (1) dominates over the Cd(II) analogue (2). The absorption and emission spectroscopic properties of the complexes have been investigated by density functional theory. Complexes 1 and 2 can detect Hg²⁺ ions selectively by fluorescence quenching, and it is noteworthy to mention that the mechanism of sensing is unique as well as interesting. In the presence of Hg²⁺ ions, complexes 1 and 2 are transformed to mononuclear mercuric intermediate complex (3) and finally to a trinuclear mercuric complex (4) by hydrolysis. We have successfully trapped the intermediate complex 3, and we characterized it with the aid of X-ray crystallography. Transformation of complexes 1 and 2 to intermediate complex 3 and finally to 4 has been established by UV-vis spectroscopy, fluorescence spectroscopy, ESI-MS spectroscopy, ¹H NMR spectroscopy, and X-ray crystallography. The spontaneity of the above conversion is well supported by thermodynamic aspects as reflected from density functional theoretical calculations.