A Review on Pyridine Based Colorimetric and Fluorometric Chemosensor for Detection of Hg2+ ion

Pyridine, N-containing heterocyclic organic compound, displays strong coordination capabilities with various metal ions. It can be synthesized through various methods, such as Friedlander synthesis, heterocumulene synthesis, cross-coupling reactions, the Radziszewski reaction, Bonnemann cyclization, as well as cobalt-catalyzed synthesis. Experimental and spectroscopic analyses have demonstrated a strong binding affinity between pyridine and several heavy metal ions, including Pb2+, Hg2+, and Cd2+ ions. The escalating environmental pollution caused by the disposal of heavy metal ions in rivers, open air, and water reservoirs poses a significant threat to both ecosystem and human health. To address these environmental challenges, a cost-effective and easily synthesized chemosensor has been prepared for identifying toxic heavy metal ions in various samples. Pyridine's photophysical properties make it an effective sensor for detecting Hg2+ ions, displaying fluorescence quenching or enhancement in their presence. The coordination between pyridine and Hg2+ ions lead to shifts in the absorption spectra. The pyridine-based sensor has been evaluated for its sensitivity, selectivity, and detection limits under different experimental conditions. Pyridine's solubility and environmental stability make it applicable for real-time detection, making pyridine probes valuable tool for monitoring toxic Hg2+ ions in the environment. The results demonstrate that the pyridine-based chemosensor exhibits good selectivity and sensitivity for targeting Hg2+ ions, with detection limits within acceptable ranges. This review (from years 2011 to 2023) emphasizes the preparation of various substituted pyridine compounds as selective, sensitive, and specific sensors for real-time detection of Hg2+ ions.

Colorimetric Detection of Hg2+ Based on the Promotion of Oxidase-Like Catalytic Activity of Ag Nanowires

A portable Hg[Formula: see text]nanosensor was developed based on the colorimetric reaction by using the unmodified Ag nanowires (Ag NWs). Ag NWs were synthesized by a solvothermal method, with the length longer than 20[Formula: see text][Formula: see text]m and the diameter of [Formula: see text][Formula: see text]nm. The colorimetric assay can be affected by pH, temperature and the amount of Ag NWs, with the optimum parameters being 5, [Formula: see text]C and 100[Formula: see text][Formula: see text]L, respectively. The developed nanosensor presents excellent selectivity for Hg[Formula: see text]. The dynamic detection range is 25[Formula: see text]5000 ppb, and the limit of detection (LOD) for Hg[Formula: see text] is 19.9[Formula: see text]ppb. The developed Hg[Formula: see text] sensor shows great potentials in environmental monitoring and onsite analysis of Hg[Formula: see text].

Nearly Monodisperse Copper Selenide Nanoparticles for Recognition, Enrichment, and Sensing of Mercury Ions

In the current work, Cu(I)_1.28Cu(II)_0.36Se nanoparticles were synthesized via a simple procedure and were applied for the first time for recognition, adsorption, enrichment, and detection of Hg(II) ions. The experimental results show that 99.9% Hg(II) could be adsorbed by Cu(I)_1.28Cu(II)_0.36Se nanoparticles within just 30 s, and the Hg(II) concentration could be lowered down to a super-low level of 0.01 ppb. Cu(I)_1.28Cu(II)_0.36Se nanoparticles also demonstrate high selectivity to Hg(II) and Ag(I) among nine representative metal ions. The enrichment experiments show that Hg(II) of ultratrace concentration could be enriched significantly by Cu(I)_1.28Cu(II)_0.36Se nanoparticles, and thus, the detection limit of Hg(II) based on inductively coupled plasma emission spectroscopy-mass spectrometry would be pushed down by 2 orders of magnitude. These outstanding features of Cu(I)_1.28Cu(II)_0.36Se nanoparticles could be well accounted for in terms of the solubility product principle and the high affinity between selenium and mercury. Cu(I)_1.28Cu(II)_0.36Se nanoparticles were also found to have peroxidase-like activity, which could be inhibited by Hg(II) but not by Ag(I). This unique characteristic coupled with the solubility product principle successfully allows recognition and detection of Hg(II) even in the presence of Ag(I), which has a similar pK_sp to Hg(II). As a result, the qualitative and quantitative analyses of Hg(II) could be performed by the naked eye and UV-visible spectroscopy, respectively. The current results indicate that Cu(I)_1.28Cu(II)_0.36Se nanoparticles not only have great potential in various aspects of dealing with Hg(II) pollution but would also shed light on discovering new nanomaterials to address other heavy metal ions.

A review on nanostructure-based mercury (II) detection and monitoring focusing on aptamer and oligonucleotide biosensors

Heavy metal ion pollution is a severe problem in environmental protection and especially in human health due to their bioaccumulation in organisms. Mercury (II) (Hg²⁺), even at low concentrations, can lead to DNA damage and give permanent harm to the central nervous system by easily passing through biological membranes. Therefore, sensitive detection and monitoring of Hg²⁺ is of particular interest with significant specificity. In this review, aptamer-based strategies in combination with nanostructures as well as several other strategies to solve addressed problems in sensor development for Hg²⁺ are discussed in detail. In particular, the analytical performance of different aptamer and oligonucleotide-based strategies using different signal improvement approaches based on nanoparticles were compared within each strategy and in between. Although quite a number of the suggested methodologies analyzed in this review fulfills the standard requirements, further development is still needed on real sample analysis and analytical performance parameters.

Mercaptopyridine-Functionalized Gold Nanoparticles for Fiber-Optic Surface Plasmon Resonance Hg2+ Sensing

As a highly toxic heavy metal ion, divalent mercuric ion (Hg²⁺) is one of the most widely diffused and hazardous environmental pollutants. In this work, a simple, portable, and inexpensive fiber-optic sensor based on surface plasmon resonance (SPR) effect was developed for Hg²⁺ detection, which takes advantage of 4-mercaptopyridine (4-MPY)-functionalized Au nanoparticles (Au NPs/4-MPY) as a signal amplification tag. Based on the coordination between Hg²⁺ and nitrogen in the pyridine moiety, we developed the sensor by self-assembling 4-MPY on Au film surfaces to capture Hg²⁺ and then introducing Au NPs/4-MPY to generate a plasmonic coupling structure with the configuration of nanoparticle-on-mirror. The coupling between localized SPR increased changes in SPR wavelength, which allowed highly sensitive Hg²⁺ sensing in aqueous solution. The sensor exhibited superior selectivity for Hg²⁺ detection compared with other common metal ions in water. The sensor's Hg²⁺ detection limit is 8 nM under optimal conditions. Furthermore, we validated the sensor's practicality for Hg²⁺ detection in tap water samples and demonstrated its potential application for environmental water on-site monitoring.

Ultrasensitive and selective electrochemical biosensor for detection of mercury (II) ions by nicking endonuclease-assisted target recycling and hybridization chain reaction signal amplification

In this paper, a novel and signal-on electrochemical biosensor based on Hg²⁺- triggered nicking endonuclease-assisted target recycling and hybridization chain reaction (HCR) amplification tactics was developed for sensitive and selective detection of Hg²⁺. The hairpin-shaped capture probe A (PA) contained a specific sequence which was recognized by nicking endonuclease (NEase). In the presence of Hg²⁺, probe B (PB) hybridized with PA to form stand-up duplex DNA strands via the Hg²⁺ mediated thymine-Hg²⁺-thymine (T-Hg²⁺-T) structure, which automatically triggered NEase to selectively digest duplex region from the recognition sites, spontaneously dissociating PB and Hg²⁺ and leaving the remnant initiators. The released PB and Hg²⁺ could be reused to initiate the next cycle and more initiators were generated. The long nicked double helices were formed through HCR event, which was triggered by the initiators and two hairpin-shaped signal probes labeled with methylene blue, resulting in a significant signal increase. Under optimum conditions, the resultant biosensor showed the high sensitivity and selectivity for the detection of Hg²⁺ in a linear range from 10 pM to 50nM (R²=0.9990), and a detection limit as low as 1.6 pM (S/N=3). Moreover, the proposed biosensor was successfully applied in the detection of Hg²⁺ in environment water samples with satisfactory results.

One-pot preparation of graphene–Ag nano composite for selective and environmentally-friendly recognition of trace mercury(ii)

A graphene–silver nano composite was prepared by a simple one-pot redox method, using ascorbic acid as a catalytic reagent, which was applied for colorimetric Hg²⁺ detection. The proposed method is selective and sensitive with little secondary pollution.