Establishment of a new molecular model for mercury determination verified by single crystal X-ray diffraction, spectroscopic analysis and biological potentials

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

A Reaction-Based ESIPT Fluorescent Probe for the Detection of Hg2+ with Large Stokes Shift

A novel reaction-based fluorescent probe 1 for Hg2+ was designed and synthesized. 1 was almost nonfluoresent due to inhibition of the ESIPT process between hydroxy group and imid carbonyl oxygen by diphenylphosphinothioate group. After reacting with Hg2+, the fluorescence intensity of 1 exhibited significant enhancement owing to recovery of the ESIPT process via Hg2+-promoted desulfurization-hydrolysis of the diphenylphosphinothioate moiety and cleavage of the P-O bond. 1 not only showed rapid response, high sensitivity, excellent selectivity for Hg2+ over other metal ions, but also could detect Hg2+ with large Stokes shift (165 nm), which was attributed to the ESIPT process. Moreover, the reaction mechanism was fully validated by absorption spectra, fluorescence spectra, fluorescence color as well as ESI-MS analysis. 1 is the reaction-based ESIPT fluorescent probe for the detection of Hg2+ with large Stokes shift, rapid response, high sensitivity and selectivity.

A mitochondrion-targeted fluorescent probe based on ESIPT phthalimide for the detection of Hg2+ with large Stokes shift

A novel mitochondrion-targeted Hg2+-specific fluorescent probe 1 based on ESIPT phthalimide was designed and synthesized for the first time. Owing to the blockage of the ESIPT process between the hydroxy group and the carbonyl oxygen of the imide by the diphenylphosphinothioate group, 1 was almost nonfluorescent. After reacting with Hg2+, 1 exhibited a dramatic fluorescence enhancement due to the recovery of the ESIPT process through Hg2+-induced desulfurization-hydrolysis of the diphenylphosphinothioate moiety and the cleavage of the P-O bond. 1 showed a large Stokes shift, rapid response and high sensitivity and selectivity for Hg2+ over other metal ions. Moreover, 1 was successfully employed to image Hg2+ in the mitochondria of living cells.

A dicyanoisophorone-based ICT fluorescent probe for the detection of Hg2+ in water/food sample analysis and live cell imaging

Mercury ions are notoriously difficult to biodegradable, and its abnormal bioaccumulation in the human body through the food chain can cause various diseases. Therefore, the quantitative and real-time detection of Hg²⁺ is very extremely important. Herein, we have brilliant designed and synthesized (E)-O-(4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)phenyl) O-phenyl carbonothioate (ICM-Hg) as a selective fluorescent probe for Hg²⁺ detection in real samples and intracellular staining. ICM-Hg displayed high specificity toward Hg²⁺ by activating the intramolecular charge transfer (ICT) process, resulting in distinguished color change from colorless to bright yellow along with noticeable switch on yellow fluorescence emission. The fluorescent intensity of ICM-Hg at 585 nm shows a well linear relationship in the range of Hg²⁺ concentration (0-45 μM), and the detection of limit for Hg²⁺ is calculated to be 231 nM. Promisingly, ICM-Hg can efficiently detect Hg²⁺ in real samples including tap water, tea, shrimp, and crab with quantitative recovery as well as the intracellular fluorescence imaging.

Synthesis of Visible Light Excitable Carbon Dot Phosphor-Al2 O3 Hybrids for Anti-Counterfeiting and Information Encryption

The preparation of room temperature phosphorescent carbon dots still faces great challenges, especially in the case of carbon dots endowed of visible-light excitable room temperature phosphorescence (RTP). To date, a limited number of substrates have been exploited to synthesize room temperature phosphorescent carbon dots, and most of them can emit RTP only in solid state. Here, the synthesis of a composite obtained from the calcination of green carbon dots (g-CDs) blended with aluminum hydroxide (Al(OH)₃ ) is reported. The resultant hybrid material g-CDs@Al₂ O₃ exhibits blue fluorescence and green RTP emissions in an on/off switch process at 365 nm. Notably, this composite manifests strong resistance to extreme acid and basic conditions up to 30 days of treatment. The dense structure of Al₂ O₃ formed by calcination contributes to the phosphorescent emission of g-CDs. Surprisingly, g-CDs@Al₂ O₃ can also emit yellow RTP under irradiation with white light. The multicolor emissions can be employed for anti-counterfeiting and information encryption. This work provides a straightforward approach to produce room temperature phosphorescent carbon dots for a wide range of applications.

Solvent-Type Passivation Strategy Controls Solid-State Self-Quenching-Resistant Behavior in Sulfur Dots

Treatment of sulfur dots with polyethylene glycol (PEG) has been an efficient way to achieve a high luminescence quantum yield, and such a PEG-related quantum dot (QD)-synthesis strategy has been well documented. However, the polymeric insulating capping layer acting as the "thick shell" will significantly slow down the electron-transfer efficiency and severely hamper its practical application in an optoelectric field. Especially, the employment of synthetic polymers with long alkyl chains or large molecular weights may lead to structural complexity or even unexpected changes of physical characteristics for QDs. Therefore, in sulfur dot preparation, it is a breakthrough to use short-chain molecular species to replace PEG for better control and reproducibility. In this article, a solvent-type passivation (STP) strategy has been reported, and no PEG or any other capping agent is required. The main role of the solvent, ethanol, is to directly react with NaOH, and the generated sodium ethoxide passivates the surface defects. The afforded STP-enhanced emission sulfur dots (STPEE-SDs) possess not only the self-quenching-resistant feature in the solid state but also the extension of fluorescence band toward the wavelength as long as 645 nm. The realization of sulfur dot emission in the deep-red region with a decent yield (8.7%) has never been reported. Moreover, a super large Stokes shift (300 nm, λ_ex = 345 nm, λ_em = 645 nm) and a much longer decay lifetime (109 μs) have been found, and such values can facilitate to suppress the negative influence from background signals. Density functional theory demonstrates that the surface passivation via sodium ethoxide is dynamically favorable, and the spectroscopic insights into emission behavior could be derived from the passivation effect of the sulfur vacancy as well as the charge-transfer process dominated by the highly electronegative ethoxide layer.

Lanthanide Molecular Species Generated Fe3O4@SiO2-TbDPA Nanosphere for the Efficient Determination of Nitrite

The presence of nitrite (NO₂⁻) in water and food leads to serious problems in public health and the environment. Therefore, it is important to develop a rapid and efficient method for the selective detection of NO₂⁻. In this work, the synthesis and characterization of magnetic Fe₃O₄@SiO₂-TbDPA nanoprobe have been carried out. The Fe₃O₄@SiO₂-TbDPA aqueous solution exhibits a strong green emission. Due to the addition of various concentrations of NO₂⁻ (0–100 μM), the fluorescence intensity has been suppressed. The nanoprobe Fe₃O₄@SiO₂-TbDPA exhibits excellent selectivity and sensitivity toward NO₂⁻ ions. Excellent linearity is obtained in the range of 5–80 μM with a detection limit of 1.03 μM. Furthermore, the presence of magnetic Fe₃O₄ nanoparticles in Fe₃O₄@SiO₂-TbDPA nanospheres will also facilitate the effective separation of Fe₃O₄@SiO₂-TbDPA from the aqueous solution. Our proposed strategy is expected to fabricate an organic-inorganic hybrid magnetic nanomaterial and can be used as an efficient sensor. It has been shown that this new strategy has numerous advantages, such as high stability, selectivity, and simplicity of operation. It demonstrates great potential for simple and convenient NO₂⁻ detection. It may expand to a variety of ranges in environmental monitoring and biomedical fields.

Exploration of Sulfur-Containing Nanoparticles: Synthesis, Microstructure Analysis, and Sensing Potential

In this work, three different sulfur sources such as sulfur powder, sodium sulfide, and sodium thiosulfate are selected to prepare sulfur-derived quantum dots (S-QDs), Na₂S-derived nanoparticles (NS-NPs), and Na₂S₂O₃^--derived QDs (NSO-QDs) in the presence of NaOH or assisted by hydrogen peroxide etching. The low sulfur percentage in the above three samples and the synthesis experiments in the presence of nitrogen/oxygen all support that poly(ethylene glycol) (PEG) plays an important role during the assembly process and the definition of sulfur dots is not accurate. For photophysical features, remarkable green quantum dots (S-QDs) possess an excitation-independent emission peak at 500 nm. But NS-NPs and NSO-QDs demonstrate observable shift tendency, and the evolution of emission profiles varies from 480 to 586 nm. NSO-QDs can be used as a fluorescent probe for highly selective and quantitative detection of Ni²⁺ in an aqueous solution in the presence of potential interfering ions with a low detection limit (0.18 μM) and a wide linear range (8-380 μM). Their reusability performance has also been demonstrated by employing dimethylglyoxime as the restoration reagent.

A simple strategy for the visual detection and discrimination of Hg2+ and CH3Hg+ species using fluorescent nanoaggregates

Fluorescent nanoaggregates (FNAs) based on phenanthroline-based amphiphiles show changes in solution color from colorless to yellow upon addition of both Hg²⁺ (LOD ∼4 ppb) and CH₃Hg⁺ (LOD ∼18 ppb). However, the extent of fluorescence quenching is more prominent with Hg²⁺ (∼12 fold) than with CH₃Hg⁺ (∼4 fold). Also, unlike Hg²⁺, the interaction of CH₃Hg⁺ needs more time, ∼10 min at room temperature. Experimental evidence indicates that both mercury species coordinate with the phenanthroline unit and facilitate the charge transfer interaction while destabilizing the nanoassembly. The lower charge density on CH₃Hg⁺ along with its large size compared to Hg²⁺ may be the reason for such observations. Interestingly, FNAs show a selective response towards CH₃Hg⁺ when pre-treated with EDTA. Further, analysis of heavy metal pollutants in drinking water and biological samples was performed. High recovery values ranging from 96% to 103.0% were estimated along with relatively small standard deviations (<3%). Low-cost, reusable test strips were designed for rapid, on-site detection of mercury species. Further, the in situ formed metal complexes are allowed to interact with thiol-containing amino acids. As expected, CH₃Hg⁺, being less thiophillic, endures less interaction with cysteine. Mechanistic investigations indicate that thiolated amino acids can bind with the metal ion center and form a tertiary complex (cooperative interaction).