Anthraquinone Based Sensors for the Selective Detection of Cyanide Ion with Turn on Fluorescence with Logic Gate & Real Sample Applications.

In recent years, there is an increasing interest in finding better and more efficient ways to detect CN- ions. Most of the anthraquinone-based probes show less fluorescence This paper presents the design and synthesis of a new anthraquinone based imine probe with good colorimetric sensing property and fluorescent turn on behavior toward CN- ion. Herein, we report a receptor with both colorimetric and fluorescent enhancement of cyanide ion in DMSO medium is synthesized. The synthesized receptor shows an immediate color change from orange to pink when cyanide is added; and it can be readily observed visually due to the presence of diverse p-conjugated systems in the receptor. These studies were confirmed by UV-Visible, PL studies, DFT, HRMS and 1H NMR titration. Moreover, this receptor shows 1:1 stoichiometry and micromolar detection limit. Further the receptor was applied to a real sample in finger millet (Eleusine Coracana) to detect the presence of cyanide ion. Moreover, the receptor is applicable toward INHIBITION, IMPLICATION logic gates with two input systems.

3,3',5,5'-tetramethylbenzidine as multi-colorimetric indicator of chlorine in water in line with health guideline values.

Sanitizing solutions against bacterial and viral pathogens are of utmost importance in general and, in particular, in these times of pandemic due to Sars-Cov2. They frequently consist of chlorine-based solutions, or in the direct input of a certain amount of chlorine in water supply systems and swimming pools. Colorimetry is one of the techniques used to measure the crucial persistence of chlorine in water, including household chlorine test kits commonly based on colorimetric indicators. Here, we show a simple and cheap colorimetric method based on 3,3',5,5'-tetramethylbenzidine (TMB), commonly used as chromogenic reagent for enzyme-linked immunosorbent assays. TMB is converted by chlorine to a colored molecule through a pH-dependent multi-step oxidation process where the chromaticity of TMB is directly proportional to chlorine content. This molecule offers several advantages over other commonly used reagents in terms of safety, sensitivity, and, peculiarly, hue modulation, giving rise to the detection of chlorine in water with a multi-color change of the indicator solution (transparent/blue/green/yellow). Moreover, through the appropriate setting of reaction conditions, such coloration is finely tunable to cover the range of chlorine concentration recommended by international health agencies for treatment of drinking water and swimming pools and to test homemade solutions prepared by dilution of household bleach during health emergency events such as during the current pandemic. Graphical abstract.

Naked Eye Chemosensing of Anions by Schiff Bases.

Spectacular color change during a chemical reaction is always fascinating. A variety of chemosensors including Schiff bases have been reported for selective as well as sensitive recognition of ions. This review explains the use of Schiff bases as color changing agents in the detection of anions. This magic of colors is attributed to change in the electronic structure of the system during reaction. Schiff base chemosensors are easy to synthesize, inexpensive and can be used for visual sensing of different ions. Development of Schiff base chemosensors is commonly based on the interactions between polar groups of Schiff bases and ionic species and the process of charge transfer, electron transfer and hydrogen bonding between Schiff bases and ionic species cause the color of the resultant to be changed. Therefore, designing of simple Schiff base chemosensors which are capable of selective sensing of different anions has attracted considerable interest. In particular, naked eye sensing through color change is important and useful since it allows sensing of ions through color changes without using any instrumental technique.HighlightsNaked eye sensors are of much interest these days due to their visual detection properties rather employing complex instrumentation.Optical sensors are sensitive, selective, cost effective and robust.The magic of color change is fascinating factor in detection by these sensors.The color change may be attributed by interaction between anion and Schiff base by different mechanism i.e. electron transfer, charge transfer, hydrogen bonding, ICT etc.LOD data is an evidence of their great efficiency.

Sulfonamides as Optical Chemosensors.

Sulfonamides are auspicious chemosensors which are capable to bind with ionic species through various ways like complexation, charge transfer, proton transfer etc. and produce a detection signal in the form of an optical change either in visible or UV-light and for electronic as well as fluorimetric spectra. Sulfonamides have gained much attention of analytical chemists these days as these are inexpensive, robust, green in nature and some what sensitive and selective to many anionic and cationic species. Due to their promising versatility in sensing properties, these are under great consideration in forensic, environmental, analytical and biochemistry laboratories. This review narrates how sulfonamides are being used to optically sense ionic species.

HIGHLIGHTSOptical sensors are of great importance these days because of their optical detection properties rather using Hi-tech techniques.Optical sensors are economical, robust, selective, sensitive and green in nature.The color change, shifts in electronic spectra or alterations in fluorescence pattern may be attributed by interaction between species to be sensed and Sulfonamides by different mechanism i.e. electron transfer, fluorescence energy transfer, charge transfer, hydrogen bonding, etc.LOD data is a proof of their prodigious efficiency of Sulfonamides as optical sensors.

Anion binding studies with anthraimidazoledione-based positional isomers: A comprehensive analysis of different strategies for improved selectivity.

In the present work, we have reported the design of three different positional isomers of anthraimidazoledione-based charge transfer probes and their anion-binding properties under various conditions. In the acetonitrile medium, the meta isomer showed ratiometric optical response towards basic anions, such as F-, CN-, AcO- and H2PO4-. Based on the differences in the hydrogen bonding ability of these anions, we observed distinguishable output signal, particularly in fluorescence. Though meta and para isomers showed effective interaction with anions, the response was relatively weak for the ortho isomer. We suspected that the presence intramolecular hydrogen bond between pyridine nitrogen and imidazole -NH group might be responsible for such poor performance. Further, we have employed two different strategies to improve the selectivity towards anions. In the first case, selective recognition of anions was achieved using suitable metal ions (Cu2+, Zn2+, Ca2+, and Al3+) as masking agents. On the contrary, we have varied the water content (0, 10, 30 and 50% v/v) in the acetonitrile-water mixture in the second case. The anions with relatively large hydration enthalpy showed no detectable interaction with probe in presence of water. Finally, we used the present system to detect cyanide ion in various natural water samples (tap, pond, and seawater). Also, low-cost reusable paper strips were developed as an alternative method for rapid, on-location detection of CN- ions.

Coordination-driven reversible supramolecular assembly formation at biological pH: Trace-level detection of Hg2+ and I- ions in real life samples.

Pyridine coupled bisbenzimidazole probe has been developed for colorimetric sensing of heavy metal pollutants in the aqueous medium. Mechanistic investigation indicates that Hg2+ ions (detection limit: 7.5 ppb) bind to the pyridyl nitrogen ends and form linear supramolecular assembly. Red-shifted absorption and fluorescence maxima upon addition of Hg2+ ions were observed, presumably caused by charge transfer interaction and coordination-driven planarization of the biphenyl backbone. Additionally, the in-situ formed mercury complex was utilized for selective recognition of iodide ion (detection limit: 20.2 ppb). Considering its high sensitivity, the present system was utilized in analysing Hg2+ in natural water and in presence of albumin protein. The high recovery values ranging from 95 to 98% with substantially low relative standard deviation (<4%) confirm the suitability of the present method in estimating trace-level of Hg2+ even in real-life samples. Imaging of intracellular Hg2+ ion was also achieved in cervical cancer cells. Low-cost paper strips are designed for rapid, on-site detection of Hg2+ without engaging any sophisticated analytical tools or trained personnel.

Naked-eye sensing and target-guiding treatment of bacterial infection using pH-tunable multicolor luminescent lanthanide-based hydrogel.

In this work, a pH-tunable multicolor luminescent lanthanide-based hydrogel (CS/DEX/CP) was prepared based on lanthanide coordination polymer (CP), dextran aldehyde (DEX) and chitosan (CS). The CP was obtained by the self-assembly of guanosine acid (GMP), ciprofloxacin (CIP), Eu3+, and Tb3+. As-prepared CS/DEX/CP hydrogel could emit blue, green, and red luminescence of CIP, Tb3+, and Eu3+, respectively. It was also found that the luminescence of CS/DEX/CP hydrogel exhibited visual color change in the pH range of 5.5 to 8. Such pH-sensitive hydrogel was multicolor-responsive to protons produced by bacterial growth, therefore, it could provide early warning of bacterial infection by naked-eye. In addition, the increased acidity resulted in not only the degradation of acid-labile Schiff base linkages between DEX and CS, but also the fracture of coordination between CIP and lanthanide ions. As a result, the released CIP and CS showed significantly antibacterial activity against both S. aureus and E. coli.

Efficient and very selective dual mode chemosensor for Cd(II) ions in live cells.

A sensitive dual mode chemosensor NS-1 comprising Nitrobenzoxadiazole and salicylhydrazide conjugate has been synthesized via single step reaction. The probe NS-1 is characterized by analytical techniques such as multi nuclear NMR techniques and Mass spectrometry. The probe is showing a strong change in color from yellow to red on treatment of Cd(II) ions, interestingly its shows bright "Switch-ON" fluorescence state upon binding of Cd2+ ions in buffer solution whereas other cations did not showed any color change as well as fluorescent change. Interestingly the probe NS-1 did not results in the any color and fluorescence change with the adding together of Zn(II) ions, hence the probe is able to differentiate between Cd(II) ions from Zn(II). Further the color change and turn-on fluorescence can be rationalized by the interruption of internal charge transfer upon binding of Cd(II) ions with NS-1. The Internal charge transfer disturbance led to fluorescence change of the receptor NS-1 upon addition of Cd2+ has been further supported by TD-DFT calculations. The limit of detection was found to be 6.31 nano molar. The association constant was found to be 7.97*104 M-1 using Benesi-Hildebrand plot method. MTT assay suggesting that the probe NS-1 is least toxic to cells and it will be widely applicable to image Cd(II) ions in living cells via fluorescence imaging.

Multi-Responsive Lanthanide-Based Hydrogel with Encryption, Naked Eye Sensing, Shape Memory, Self-Healing, and Antibacterial Activity.

In this work, we reported a multi-responsive luminescent hydrogel with properties of encryption, naked eye sensing of glucose, shape memory, self-healing, and antibacterial activity. The hydrogel (GA/CCS/DNSA/Eu3+) was obtained by mixing phenylboronic acid-modified gelatin (GA-DBA), catechol-modified carboxymethyl chitosan (CCS-PCA), 3,5-dinitrosalicylic acid (DNSA), and Eu3+ ions through a facile heating-cooling process. The resultant hydrogel exhibits reversible luminescence and color and phase changes in response to temperature, acid/base, salt, and redox stimuli. Based on the multiple responsiveness, information encryption and decryption, naked eye sensing of glucose, remarkable shape memory, and enhanced mechanical properties of the as-prepared hydrogel were realized. In addition, the self-healing capacity was also achieved due to the dynamic bonds in GA/CCS/DNSA/Eu3+ hydrogels. Specifically, the GA/CCS/DNSA/Eu3+ hydrogels possess antibacterial activity owing to the bacteriostasis of the CCS-PCA and DNSA/Eu3+ complex. Thus, GA/CCS/DNSA/Eu3+ hydrogels have potential applications in the fields of anticounterfeiting, wearable devices, biomedicine, sensing, etc.

Harnessing a pyrimidine based molecular switch to construct reversible test strips for F-/AcO- with respect to Al3+: A colorimetric approach.

We report novel compound 4-nitro-2-((pyrimidin-2-ylamino) methyl) phenol (1) synthesized by the condensation of 5-nitro salicylaldehyde with 2-amino pyridine. Compound 1 serves as a dual signalling chromogenic receptor for F-/AcO- and Al3+ ions. The chromogenic response of 1 towards the aforementioned analytes is reversible with respect to either Al3+/X (=F/AcO)- or X(F/AcO)-/Al3+. The limit of detection of 1 for F- and AcO- are 1.0025×10-7M and 0.79×10-7M, respectively. The optical switching has been rationalized on the basis of UV-Vis titrations and 1H NMR titrations respectively. The optical switching has been successfully use by constructing reversible paper strips for detecting Al3+ as well as F-/AcO-.