A ratiometric and colorimetric fluorescent probe for the detection of mercury ion based on rhodamine and quinoline–benzothiazole conjugated dyad

Development of a novel sensory material for rapid detection of mercury ions in various water sources: Solution and solid-state analysis

A xanthene propane nitrile-based sensor material was successfully prepared, and an attempt towards the preparation of polymer bead form was made for the sensitive or selective detection of mercury ions (Hg2+) in water. The sensor material in solution as well as in polymeric form showed amazing selectivity over other added metal ions with a naked eye color change, UV visible spectral and fluorescence spectral change, and a rapid and excellent color change from colorless to purple. The 1H NMR study exposed the probable binding site of the probe with the added mercury ion. In this study, the imine nitrogen and the C = O interact with the mercury ion, resulting in the ring opening of lactam with a vivid color change. The EDTA test was done to verify the reversible behavior of the probe and confirmed its reversibility by UV-visible and fluorescence spectral studies. The polymer bead made using this probe can be used as a tool for monitoring mercury ions in real time in different sources of water samples. The sensor molecule itself senses the mercury ion in its solid state by simple grinding and changes its color from pale yellow to deep purple. The sensor color change response is very rapid towards mercury detection, which is confirmed by the prepared test strip.

In situ microwave-assisted preparation of NS-codoped carbon dots stabilized silver nanoparticles as an off-on fluorescent probe for trace Hg2+ detection

An off-on fluorescent probe (NS-CDs-AgNPs) was synthesized based on a one-pot microwave process by utilizing N, S co-doping carbon dots (NS-CDs) and silver nitrate as precursors. The significant peak of NS-CDs-AgNPs at 393 nm in ultraviolet spectrum indicated silver nanoparticle (AgNPs) were successfully synthesized. A faint blue fluorescence emission (442 nm) was displayed when excited NS-CDs-AgNPs at 371 nm. A remarkable fluorescence recovery was observed upon adding of trance Hg2+, whereas the other heavy metal ions did not elicit this response. The reason for this phenomenon was revealed in this work that a spontaneous redox reaction occurred between NS-CDs-AgNPs and Hg2+, which leaded to the formation of NS-CDs-Agn-2NPsHg complexes. On the basis of this mechanism, a new off-on fluorescent analytical method was constructed for Hg2+ detection with linear range of 10-400 nM (R2 = 0.9941), and the detection limit (LOD) of 5.16 nM. Additionally, satisfactory recovery (90.28%-106.13%) and the relative standard deviation (RSD) (RSD＜5.21%) were obtained in water sample detection. More importantly, the NS-CDs-AgNPs exhibited lower cytotoxicity and better biocompatibility, indicating a huge potential in cell imaging and clinical medicine.

Bio-mimetic selectivity in Hg2+ sensing developed via electro-copolymerized PEDOT and benzothiazole-Au nanoparticles composite

To eliminate the potential health risks of mercury, development of stable and selective mercury sensor with high sensitivity is the need of the hour. To address this, a novel PEDOT-AA-BTZ-Au-based Hg2+ selective, hybrid electrochemical sensor has been designed by following a simple protocol for electrode fabrication. The electrode was designed by carefully optimizing the onset oxidation potential of supramolecule 2-(anthracen-9-yl)benzo[d]thiazole (AA-BTZ) and conducting polymer poly-(3,4-ethylenedioxythiophene) (PEDOT), using copolymerization approach followed by dropcasting of gold nanoparticles (AuNPs). The designed electrode offered synergistic effects thus augmenting the electrical conductivity and adsorption capacity as depicted by its porous surface morphology. The highly sensitive analytical signal was generated by sulphur pockets present in AA-BTZ and PEDOT conducting framework. This is further complemented by the selectivity offered by the soft interactions between AuNPs and Hg2+ resulting in a low detection limit of 0.60 nM. The prepared system was further utilized for sensing Hg2+ ion in real systems including lake water and cosmetic samples. Low interference from other ions and better reproducibility further established the suitability of the designed transducer system for future on-site sensing.

A simple quinoline-thiophene Schiff base turn-off chemosensor for Hg2+ detection: spectroscopy, sensing properties and applications

A new Schiff base probe (QT) consisting of 8-aminoquinoline (Q) and thiophene-2-carboxaldehyde (T) moieties has been synthesized. QT undergoes chelation-enhanced fluorescence quenching when exposed to Hg²⁺ due to coordination by the sulfur and nitrogen atoms of QT thus forming a facile "turn-off" sensor. The formation of the chelation complex was confirmed by UV-visible absorption and emission spectral measurements, ¹H NMR titration and density functional theory calculations. These studies revealed that the probe exhibits high selectivity and sensitivity towards Hg²⁺ in the presence of other common metal ions. A low detection limit of 23.4 nM was determined and a Job plot confirmed a 2:1 stoichiometry between QT and Hg²⁺. The potential utility of QT as a sensor for Hg²⁺ ions in human HeLa cells was determined by confocal fluorescence microscopy, and its suitability for use in the field with environmental samples was tested with Whatman filter paper strips.

A quinoline-based fluorescent chemosensor for palladium ion (Pd2+)-selective detection in aqueous solution

Quinoline-based fluorescent chemosensors have been extensively developed for various metal cations, but it was still rare for Pd²⁺-selective detection. In this work, a novel quinoline-benzimidazole conjugate containing one carboxylic acid group (QBM) was designed, and the QBM displayed highly selective fluorescence quenching response towards Pd²⁺ over other metal cations in aqueous solution. The fluorescence titration revealed a good linear relationship between the fluorescence intensity and the Pd²⁺ concentration in the range of 0.5-10 μmol L^-1, with the detection limit of 0.26 μmol L^-1 (S/N = 3). Fluorescence detection of Pd²⁺ in practical water sample was also successfully achieved.

Mercury Toxicity and Detection Using Chromo-Fluorogenic Chemosensors

Mercury (Hg), this non-essential heavy metal released from both industrial and natural sources entered into living bodies, and cause grievous detrimental effects to the human health and ecosystem. The monitoring of Hg2+ excessive accumulation can be beneficial to fight against the risk associated with mercury toxicity to living systems. Therefore, there is an emergent need of novel and facile analytical approaches for the monitoring of mercury levels in various environmental, industrial, and biological samples. The chromo-fluorogenic chemosensors possess the attractive analytical parameters of low-cost, enhanced detection ability with high sensitivity, simplicity, rapid on-site monitoring ability, etc. This review was narrated to summarize the mercuric ion selective chromo-fluorogenic chemosensors reported in the year 2020. The design of sensors, mechanisms, fluorophores used, analytical performance, etc. are summarized and discussed.