Four-Component Domino Synthesis of Pyrazolo[3,4-h]quinoline-3-carbonitriles: “Turn-Off” Fluorescent Chemosensor for Fe3+ Ions

Luminous Insights: Exploring Organic Fluorescent "Turn-On" Chemosensors for Metal-Ion (Cu+2, Al+3, Zn+2, Fe+3) Detection

There are several metal ions that are vital for the growth of the environmental field as well as for the biological field but only up to the maximum limit. If they are present in excess, it could be hazardous for the human health. With the growing technology, a series of various detection techniques are employed in order to recognize those metal ions, some of them include voltammetry, electrochemical methods, inductively couples, etc. However, these techniques are expensive, time consuming, requires large storage, advanced instrumentation, and a skilled person to operate. So, here comes the need of a sensor and it is defined as a miniature device which detects the substance of interest by giving response in the form of energy change. So, from past few decades, many sensors have been formulated for detecting metal ions with some basic characteristics like selectivity, specificity, sensitivity, high accuracy, lower detection limit, and response time. Detecting various metal ions by employing chemosensors involves different techniques such as fluorescence, phosphorescence, chemiluminescence, electrochemical, and colorimetry. The fluorescence technique has certain advantages over the other techniques. This review mainly focuses on the chemosensors that show a signal in the form of fluorescence to detect Al+3, Zn+2, Cu+2, and Fe+3 ions.

Highly Sensitive and Selective Detection of Melatonin in Biofluids by Antipyrine Based Fluorophore

A simple fluorescent based organic fluorophore was synthesized and it shows significant fluorescent intensity with melatonin (MLN). Hence, it was applicable to the detection of MLN by colorimetric and fluorimetric techniques at neutral pH. Under optimized experimental condition, the synthesized organic fluorophore detects MLN selectively in the presence of other interfering biomolecules through ICT mechanism. The melatonin sensing mechanism is supported by DFT and ¹H-NMR titration. Based on the findings, this method can be applied to design a simple clinical diagnostic tool for MLN.

A novel fluorescent probe with a pyrazolo[4,3-c]quinoline core selectively recognizes c-MYC promoter G-quadruplexes

An aptamer combined with a c-MYC-selective fluorophore could work as the fluorescent core of nucleic acid mimics of fluorescent proteins to locate and image functional biomolecules in cells.

Synthesis of indenophenanthridine via a [4+2] annulation strategy: a “turn-off’’ Fe3+ ion sensor, practical application in live cell imaging and reversible acidochromism studies

An efficient protocol has been developed for the synthesis of a novel fluorescent probe, 1,2-disubstituted-indeno[1,2,3-gh]phenanthridine, derived from a series of α-oxo-ketene dithioacetals (OKDTAs) and indenoquinoline under essential conditions via a [4+2] annulation in excellent yield.

A bi-modal, cellulose-based sensor for fluorometric detection of Fe(III) and antimicrobial studies of its silver-loaded form

The study reports designing of a new, low-cost and environmentally friendly colorimetric and fluorometric sensor by using cellulose-based materials for detection and determination of Fe(III). To make powder cellulose (Cel) and filter paper (PCel) fluorescent, they were modified with hexamethylene diisocyanate (HMDI) and 4-sulfo-1,8-naphthalimide (Nap). Fluorescent Cel-Nap and PCel-Nap materials were used for spectroscopic detection of Fe(III). The working range of the designed sensor was determined as 1.0 × 10^-5-4.5 × 10^-5 M with a low limit of detection (LOD) (7.51 μM). Antimicrobial properties of cel-based compounds and Ag(I)-containing compounds were tested against five bacteria; Bacillus cereus, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and two fungi; Candida albicans and Candida tropicalis. The materials exhibited antimicrobial effects and their antifungal properties were more effective than their antibacterial properties.

Chromene–triazole-pyrimidine based chemosensor therapeutics for the in vivo and in vitro detection of Fe3+ ions

MCR and click synthesis of selective and sensitive Fe³⁺ sensors that can interact with CDK2 proteins and cytotoxicity against the human cervical cancer cell line HeLa is developed.

Improving Ion Selectivity of 1,4,7-Triazacyclononane-Based Receptor by Zinc Coordination: "Turn-On" Chemosensor for Br- and Fe3+ Ions

Ion-responsive probes have gathered significant attention because of health and environmental factors, but there are few reports on the "turn-on" mechanism of Fe³⁺ and sensitive detection of Br^- by fluorescence measurement. Herein, a green luminescence material, N-5-acetyl-2-hydroxy-benzamide-1,4,7-triazacyclononane (btacn), was successfully synthesized for the first time and comprehensively characterized. As expected, btacn exhibits high sensitive, but nonspecific, extensive interaction with Cu²⁺, Co²⁺, Zn²⁺, Mn²⁺, and Fe³⁺ ions. Therefore, to improve the specificity of the probe, we tried to synthesize transition metal complexes of btacn, but all failed except Zn(btacn)Cl₂. In addition, the preformed complex, Zn(btacn)Cl₂, was used as a special "turn-on" chemosensor for detecting trace amounts of Br^- and Fe³⁺. The electrostatic interaction with Fe³⁺ and the hydrogen bond of PhO-H···Br^- leads to obvious changes in the electronic cloud of Zn(btacn)Cl₂, which are reflected in different spectral responses.

A rhodamine based biocompatible chemosensor for Al3+, Cr3+ and Fe3+ ions: extraordinary fluorescence enhancement and a precursor for future chemosensors

A rhodamine based chemosensor, 3-(((2-(3',6'-bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindoline-1,9'-xanthen]-2-yl)ethyl)imino)methyl)-2-hydroxy-5-methylbenzaldehyde (HL-CHO), has been developed for the detection of Al3+, Cr3+ and Fe3+ ions. The absorbance of HL-CHO at 528 nm increases significantly in HEPES buffer in methanol : water (9 : 1, v/v) (pH 7.4) in the presence of Al3+, Cr3+ and Fe3+ ions with the alteration of solution color from colorless to pink. The fluorescence intensity of the probe at 550 nm enhances by 1465, 588 and 800 fold in the presence of Al3+, Cr3+ and Fe3+ ions, respectively. To the best of our knowledge, this huge increase in fluorescence intensity with Al3+ and Cr3+ has not been observed for other rhodamine based chemosensing systems. The weak fluorescence and no coloration of the probe are due to the existence of a spirolactam ring. The trivalent cations induce the opening of the spirolactam ring and consequently change the color and the fluorescence intensity followed by the 1 : 1 complex formation with HL-CHO which are evident from Job's analysis, ESI mass spectral analysis and elemental analysis. The quantum yield and lifetime of HL-CHO have increased considerably in the presence of the trivalent cations. The high sensitivity of the probe towards all the cations is evident from the nM order of LOD values. This has been used in living cell imaging studies with the human neuroblastoma SH-SY5Y cell line. Having appended -CHO groups for Schiff-base condensation with other amines, HL-CHO could be a potential precursor for future chemosensors.

Two-dimensional Cd(ii) coordination polymer encapsulated by Tb3+ as a reversible luminescent probe for Fe3

A two-dimensional luminescent cadmium(ii) coordination polymer, [Cd(modbc)2] n (Cd-P); modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4'-bipyridine-5-carbonitrile, was successfully synthesized by a solvothermal reaction and fully characterized. Cd-P exhibited excellent luminescence emission, and detected Cu2+, Co2+, Fe2+, Hg2+, Ni2+ and Fe3+ ions with high sensitivity and showed good anti-interference performance. After encapsulation of Tb3+ ions in Cd-P, the as-obtained fluorescent functionalized Tb3+@Cd-P maintained distinct chemical stabilities in different pHs and metal salt solutions. Subsequently, we explored the potential application of Tb3+@Cd-P as a probe for Fe3+ ions. A new and convenient method for individual identification of Fe3+ ions by the combination of Cd-P and Tb3+@Cd-P was successfully established. A possible sensing mechanism is discussed in detail.