An aggregation-induced emission-based fluorescence turn-on probe for Hg2+ and its application to detect Hg2+ in food samples

A Dual Functional Fluorescent Probe Based on Phenothiazine for Detecting Hg2+ and ClO- and its Applications

For the efficient detection of Hg2+ and ClO-, a double-analyte-responsive fluorescent probe PTB was successfully synthesized by combining N-butyl-3-formyl phenothiazine with hydrazine benzothiazole, and designing a specific reaction site for recognizing two analytes (Hg2+ and ClO-) in a compound. It was shown that probe PTB successfully formed a stable complex with Hg2+ in the coordination ratio of 2:1 by using the strong sulfur affinity of Hg2+, which resulted in a remarkable "turn-off" effect, with a quenching efficiency of 92.5% and four reversible cycles of Hg2+ fluorescence detection. For the fluorescence detection of Hg2+, the response time is fast (≤ 2 min) and the detection limit is low (7.8 nM), showing extremely high sensitivity, and the performance is obviously better than that of the reported fluorescent probes for detecting Hg2+. In particular, probe PTB has low toxicity and good biocompatibility, and has been successfully used for imaging of Hg2+ in living cells. Moreover, probe PTB uses thioether bond and carbon-nitrogen double bond as reaction sites to detect ClO-, which has large Stokes Shift (149 nm), good selectivity, high quenching efficiency (96.5%) and fast time response (about 10 s), and successfully detects ClO- in actual water samples.

Recent advances in colorimetric and photoluminescent fibrillar devices, photonic crystals and carbon dot-based sensors for mercury (II) ion detection

The escalating environmental contamination with mercury has become a pressing issue, significantly impacting human beings and nature. For instance, small-scale gold mining has led to severe contamination in the Brazilian Yanomami village, highlighting the urgent need for action. The development of fibrillar-based sensors for mercury (II) ions represents an important issue to be considered in the point-of-care and simple detection of contaminants in water. Herein, this review discussed different colorimetric/photoluminescent-based prototypes for Hg2+ ions sensors and corresponding strategies to improve selectivity and sensitivity associated with the regeneration and reuse of the devices. Given these aspects, the electrospinning technique is promising for developing advanced mercury (II) ion sensors.

Accurate and rapid mercury susceptibility detection in aquatic samples using fluorescent probe integrated rhodamine with pyridyl isothiocyanate

Mercury, one of the various harmful metals, is particularly significant in affecting aquatic organisms, currently gaining more attentions and sparking discussions. In response to the limitations of traditional detections, fluorescent probes have emerged as a promising solution with some advantages, such as weaker background interference, shorter processing time, higher accuracy. Thus, a novel fluorescent probe, FS-Hg-1, has been developed for assessing mercury ion (Hg2+) concentrations in aquatic products. This probe displays specific recognition of mercury ions in fluorescence spectra. Notably, FS-Hg-1 exhibits a distinct color change to pink when combined with Hg2+ (with a 948-fold increase in absorption at 568 nm) and a substantial fluorescence change towards Hg2+ (361-fold increase, excitation at 562 nm, emission at 594 nm) in N, N-dimethylformamide. The probe boasts a detection limit of 0.14 μM and rapid reaction with Hg2+ within 10 s, showing an excellent linear correlation with [Hg2+] in the range of 0 to 10 μM. Through thorough analysis using FS-Hg-1, the results align with those from the standard method (P > 0.05), with spiked recovery rates ranging from 108.4% to 113.2%. With its precise recognition, low detection limit, and remarkable sensitivity, this fluorescent assay proves effective in mercury concentration determination in aquatic samples without interference. The potential of FS-Hg-1 is promising for speedy detection of residual Hg2+ and holds significance in ensuring food safety.

Real-time optical detection of mercury contamination in drinking water using an amphiphilic recognition probe at liquid crystal/aqueous interfaces

Mercury contamination is a global environmental issue due to its toxicity and persistence in ecosystems. It poses a particular risk in aquatic systems, where it bioaccumulates and biomagnifies, leading to serious health impacts on humans. Therefore, effective detection technologies for mercuric ions in natural water resources are highly desirable. However, most existing detection methods are time-consuming, require complicated sample pre-treatment, and rely on expensive equipment, which hinders their widespread use in real-time detection. Here, we present a convenient, rapid, portable, user-friendly, and cost-effective sensing system for detecting Hg2+ ion contamination in water. This system utilizes a highly selective, amphiphilic, and structurally simple molecular probe, N-dodecylamine-di-thiocarbamate (DDC). DDC molecules align at the interface between the liquid crystal (LC) and water, inducing a homeotropic LC orientation. In water samples contaminated with Hg2+, a bright optical texture is observed, indicating the alignment of the 5CB LC in a planar manner at the LC/aqueous boundary. The minimum detectable concentration (LOD) for Hg2+ ions is 5.0 μM in distilled water, with a broad detection range from 5.0 μM to 2 mM. The sensor selectively detects Hg2+ ions over other common interfering metal ions, including Pb2+, Co2+, Ni2+, Cu2+, Cd2+, Zn2+, Cr2+, Mg2+, Na+, K+, and Ca2+. Boolean logic gates, bar graphs, and truth tables are employed to explain the selectivity of this liquid crystal-based sensor. This work demonstrates the significant potential of the sensor for monitoring mercuric ions in natural water resources, offering a promising strategy for controlling mercury pollution.

A novel dual-detection electrochemiluminescence sensor for the selective detection of Hg2⁺ and Zn2⁺: Signal suppression and activation mechanisms

In this study, we developed a novel covalent organic framework (COF) material, termed RuCOFs, specifically designed and synthesized for electrochemiluminescence (ECL) sensor applications. RuCOFs are based on the classic ECL emitter Ru(dcbpy)32+, ingeniously integrating 4,4',4''-(1,3,5-triazine-2,4,6-triyl) triphenylamine (TAPT) with [2,2'-bipyridine]-5,5'-diamine (BPYDA), forming a structure with a high specific surface area. This configuration not only significantly enhances the stability of the ECL signal but also provides ideal N,N'-bipyridine chelating sites for efficient metal ion recognition. Utilizing Ru(dcbpy)32+-functionalized COF (RuCOFs), a novel dual-function ECL sensor was developed, achieving high sensitivity and selectivity in detecting mercury (Hg2⁺) and zinc (Zn2⁺) ions. Experimental results indicate that Hg2⁺ significantly quenches the ECL signal, while Zn2⁺ markedly enhances it, with detection limits of 4.71 nM for Hg2⁺ and 6.57 nM for Zn2⁺ across a wide linear response range from 1 μM to 1 nM. This research not only demonstrates the significant advantages of COF-based ECL sensing platforms in tracking environmental metal ions but also opens new possibilities for environmental monitoring.

A dual-response fluorescence sensor for SO2 derivatives and polarity and its application in real water and food samples

As an important gaseous pollutant, SO2 derivatives generally exist and significantly threaten the environment and organism health. Meanwhile, polarity is a disease-related indicator in the organism's microenvironment, where an unregulated variation may disturb the physiological metabolisms. Hence, a superior FRET-based fluorescent sensor (TLA) is presented to track polarity and sulfur dioxide derivatives by dual emission channel, i.e. an elevated red emission at 633 nm with decreasing polarity as well as a reduced red emission at 633 nm and improved blue emission at 449 nm with increasing concentration of SO2 derivatives. The probe TLA could sensitively detect SO2 derivatives with ultra-large Stokes shift (273 nm), excellent stability, high selectivity, and low detection limit. Importantly, TLA can accurately detect sulfur dioxide derivatives in real food as well as water samples. Besides, TLA was also fabricated as testing strips and applied to detect SO2 derivatives in the solution.

Thiourea Functionalised Receptor for Selective Detection of Mercury Ions and its Application in Serum Sample

A thiourea functionalised fluorescent probe 1-phenyl-3-(pyridin-4-yl)thiourea was synthesized and utilised as a fluorescent turn-on chemosensor for the selective recognition of Hg2+ ion over competitive metal ions including Na+, Mn2+, Li+, Cr2+, Ni2+, Ca2+, Cd2+, Mg2+, K+, Co2+, Cu2+, Zn2+, Al3+ and Fe2+ ions based on the inter-molecular charge transfer (ICT). Intriguingly, the receptor demonstrated unique sensing capabilities for Hg2+ in DMSO: H2O (10:90, v/v). The addition of Hg2+ ions to the sensor resulted in a blue shift in the absorption intensity and also enhancement in fluorescence intensity at 435 nm. Fluorescence emission intensity increased linearly with Hg2+ concentration ranging from 0 to 80 µL. The detection limit and binding constant were determined as 0.134 × 10-6 M and 1.733 × 107 M-1, respectively. The sensing behavior of Hg2+ was further examined using DLS, SEM and FTIR. The probe could detect Hg2+ ions across a wide pH range. Furthermore, the receptor L demonstrated good sensing performance for Hg2+ in bovine serum albumin and actual water samples.

Recent Advances in the Application of Bionanosensors for the Analysis of Heavy Metals in Aquatic Environments

Heavy-metal ions (HMIs) as a pollutant, if not properly processed, used, and disposed of, will not only have an influence on the ecological environment but also pose significant health hazards to humans, making them a primary factor that endangers human health and harms the environment. Heavy metals come from a variety of sources, the most common of which are agriculture, industry, and sewerage. As a result, there is an urgent demand for portable, low-cost, and effective analytical tools. Bionanosensors have been rapidly developed in recent years due to their advantages of speed, mobility, and high sensitivity. To accomplish effective HMI pollution control, it is important not only to precisely pinpoint the source and content of pollution but also to perform real-time and speedy in situ detection of its composition. This study summarizes heavy-metal-ion (HMI) sensing research advances over the last five years (2019-2023), describing and analyzing major examples of electrochemical and optical bionanosensors for Hg2+, Cu2+, Pb2+, Cd2+, Cr6+, and Zn2+.

Lysosome-targeted dual-emissive carbon dots for ratiometric optical dual-readout and smartphone-assisted visual determination of Hg2+ and SO32

Smartphone-assisted visual assay not only expands quantitative analysis but also enhance real-time on-site sensing capabilities. Herein, lysosome-targeted dual-emissive carbon dots (L-CDs) can not only recognize Hg2+ and SO32- by ratiometric fluorescence and ratiometric absorption, but also visually quantify Hg2+ and SO32- by smartphone-assisted method. With monitoring of intrinsic ratiometric fluorescent variation (I580/I468), L-CDs are developed as an effective sensing platform for ratiometric fluorescent successive identification of Hg2+ and SO32- accompanying with continuous fluorescence variation of blue, purplish pink, pink, and light yellow. With detecting of inherent ratiometric absorption change (A538/A206), L-CDs are also constructed as an efficacious sensing terrace for ratiometric absorption consecutive discrimination of Hg2+ and SO32-. More crucially, integrating continuous fluorescence color change and color recognizer APP in the smartphone, visual quantification of Hg2+ and SO32- can be accomplished on the basis of the ratio of red value and blue value (R/B) with linear ranges of 0-130 and 0-850 µM, respectively, as well as LOD of 8.4 and 12.9 nM, respectively. More interestingly, confocal fluorescent imaging of HeLa cells further verifies that L-CDs can be regarded as favorable biosensors for on-site, real-time differentiation of Hg2+ and SO32- in vitro and in vivo with ratiometric manners.

An efficient chitosan-naphthalimide fluorescent probe for simultaneous detection and adsorption of Hg2+ and its application in seafood, water and soil environments

As a virulent heavy metal ion, Hg2+ will lead to a serious threat to ecosystem and human health. In this work, we reported a chitosan-naphthalimide fluorescent probe CS-NA-ITC for specific recognition and efficient adsorption of Hg2+. CS-NA-ITC showed no fluorescence in solution state, while the fluorescence intensity increased obviously at the presence of Hg2+, accompanied by the fluorescence color becomes from colorless to bright yellow. It displayed favorable properties like low detection limit (73 nM), extensive pH detection range (5-10) and excellent anti-interference ability. The binding pattern of CS-NA-ITC to Hg2+ was verified by Job's plot, XPS analysis and FT-IR test. In addition, CS-NA-ITC was utilized to recognition of Hg2+ in actual water and soil samples and seafood products. Furthermore, the CS-NA-ITC hydrogel could be employed as an efficient Hg2+ adsorbent with good reusability, which adsorption ability was enhanced compared to chitosan hydrogel.

Recent Progress on Fluorescent Probes in Heavy Metal Determinations for Food Safety: A Review

One of the main challenges faced in food safety is the accumulation of toxic heavy metals from environmental sources, which can sequentially endanger human health when they are consumed. It is invaluable to establish a practical assay for the determination of heavy metals for food safety. Among the current detection methods, technology based on fluorescent probes, with the advantages of sensitivity, convenience, accuracy, cost, and reliability, has recently shown pluralistic applications in the food industry, which is significant to ensure food safety. Hence, this review systematically presents the recent progress on novel fluorescent probes in determining heavy metals for food safety over the past five years, according to fluorophores and newly emerging sensing cores, which could contribute to broadening the prospects of fluorescent materials and establishing more practical assays for heavy metal determinations.

An “AIE + ESIPT” mechanism-based benzothiazole-derived fluorescent probe for the detection of Hg2+ and its applications

A simple “AIE + ESIPT” mechanism-based fluorescent probe for Hg2+ detection has been developed. The probe is applicable to detect Hg2+ in living cells, natural water, and seafood samples.

An activatable near-infrared hemicyanine-based probe for selective detection and imaging of Hg2+ in living cells and animals

A near-infrared hemicyanine-based probe (CyP) was designed for selective detection and imaging of Hg2+ in living cells and animals.

Colorimetric detection of Hg2+ with an azulene-containing chemodosimeter via dithioacetal hydrolysis

Azulene is a bicyclic aromatic chromophore that absorbs in the visible region. Its absorption maximum undergoes a hypsochromic shift if a conjugated electron-withdrawing group is introduced at the C1 position. This fact can be exploited in the design of a colorimetric chemodosimeter that functions by the transformation of a dithioacetal to the corresponding aldehyde upon exposure to Hg2+ ions. This chemodosimeter exhibits good chemoselectivity over other metal cations, and responds with an unambiguous colour change clearly visible to the naked eye. Its synthesis is concise and its ease of use makes it appropriate in resource-constrained environments, for example in determing mercury content of drinking water sources in the developing world.

AIEgens: An emerging fluorescent sensing tool to aid food safety and quality control

As a global public health problem, food safety has attracted increasing concern. To minimize the risk exposure of food to harmful ingredients, food quality and safety inspection that covers the whole process of "from farm to fork" is much desired. Fluorescent sensing is a promising and powerful screening tool for sensing hazardous substances in food and thus plays a crucial role in promoting food safety assurance. However, traditional fluorphores generally suffer the problem of aggregation-caused quenching (ACQ) effect, which limit their application in food quality and safety inspection. In this regard, luminogens with aggregation-induced emission property (AIEgens) showed large potential in food analysis since AIEgens effectively surmount the ACQ effect with much better detection sensitivity, accuracy, and robustness. In this contribution, we review the latest developments of food safety monitoring by AIEgens, which will focus on the molecular design of AIEgens and their sensing principles. Several examples of AIE-based sensing applications for screening food contaminations are highlighted, and future perspectives and challenges in this emerging field are tentatively elaborated. We hope this review can motivate new research ideas and interest to aid food safety and quality control, and facilitate more collaborative endeavors to advance the state-of-the-art sensing developments and reduce actual translational gap between laboratory research and industrial production.

Sequential colorimetric sensing of cupric and mercuric ions by regulating the etching process of triangular gold nanoplates

A triangular gold nanoplate (AuNPL)-based colorimetric assay is presented for ultrasensitive determination of cupric ions (Cu²⁺⁾ and mercuric ions (Hg²⁺) in sequence. AuNPLs were found to be etched efficiently when producing triiodide ions (I₃^-) by a redox reaction between Cu²⁺ and iodide ions (I^-), leading to a change of the shape of AuNPLs from triangular to sphere along with a color change from blue to pink. In the presence of Hg²⁺ the etching of AuNPLs was suppressed due to the consumption of I^- by the formation of HgI₂. With an increase of the concentration of the Hg²⁺ a transformation from sphere to triangular in the shape of AuNPLs occurred with a color change from pink to blue. The evolution of AuNPLs from etching to anti-etching state by sequential addition of Cu²⁺ and Hg²⁺ was accompanied with color variations and band shifts of localized surface plasmon resonance (LSPR), allowing for visual and spectroscopic determination of Cu²⁺ and Hg²⁺ successively within 15 min. In the range 0.01-1.5 μM for Cu²⁺ and 0.02-3.0 μM for Hg²⁺, the linear relationship between the band shift values and the target ions concentration was found good (R² > 0.996). The limit of detections (3S/k) was 19 nM for Cu²⁺ and 9 nM for Hg²⁺, respectively. The lowest visual estimation concentration was 80 nM for both Cu²⁺ and Hg²⁺ through the distinguishable color changes. This system exhibited desirable selectivity for Cu²⁺ and Hg²⁺ over other common ions tested. The method has been successfully applied to sequential determination of Cu²⁺ and Hg²⁺ in real water and food samples. Graphical abstract Scheme 1 Schematic illustration for sequential detection of Cu²⁺ and Hg²⁺ based on etching of AuNPLs.

Interfacial Synthesis of a Monolayered Fluorescent Two-Dimensional Polymer through Dynamic Imine Chemistry

A fluorescent monolayered two-dimensional polymer (2DP) containing both tetraphenylethylene (TPE) and imine linkages is synthesized at air-water interface using the Langmuir-Blodgett method. We designed TPE-based monomers with long distances between the TPE and the imine linkages to avoid the charge transfer and therefore keep the fluorescence. A monolayered 2DP provided with more than 104 μm2 in domain size and around 0.8 nm thickness was obtained through a successive Schiff base reaction at air-water interface. The nanostructures and fluorescent property of 2DP films were characterized by optical microscopy, SEM, TEM, AFM and fluorescence spectrum. Most importantly, the tip-enhanced Raman spectroscopy (TERS) was utilized here to confirm the success of the polycondensation of monolayered 2DP.