Colorimetric Detection Of Hg2 Research Articles

Colorimetric detection of Hg2+ based on the enhanced oxidase-mimic activity of CuO/Au@Cu3(BTC)2 triggered by Hg2.

It is imperative to develop a rapid detection method for Hg2+ due to its harm to human health and the ecological environment. In this research, CuO/Au@Cu3(BTC)2 was synthesized through reducing HAuCl4 by CuxO@Cu3(BTC)2, which was obtained by reducing Cu3(BTC)2 with hydrazine hydrate. The oxidase-mimic activity of CuO/Au@Cu3(BTC)2 can be enhanced by Hg2+ through forming a Au-Hg alloy. Therefore, a colorimetric method was designed for Hg2+ detection with a linear relationship in the 0.05-25 μM range and a limit of detection of 9.7 nM. This strategy exhibited a strong selectivity to Hg2+ and was applied in a real water sample with reliable recoveries. This work provides a possibility for the rapid detection of Hg2+.

A colorimetric detection of Hg2+ based on gold nanoparticles synthesized oxidized N-methylpyrrolidone as a reducing agent

In this study, a gold nanoparticles colorimetric probe (AuNPs) with direct response to mercury ions (Hg2+) were developed using treated N-methylpyrrolidone (NMP) and chloroauric acid (HAuCl4) as precursors. NMP showed good reducibility after high temperature hydrolysis and could be used as reducing and stabilizing agent to synthesize AuNPs. The prepared AuNPs have obvious characteristic absorption peaks and appear wine-red. At the same time, it was found that the presence of Hg2+ can cause the aggregation of AuNPs, increased the absorbance at 700 nm, and changed the color of the solution into blue-gray. This method is capable of sensitive and specific determination of Hg2+ ranging from 1 to 30 μM, with the limit of detection (LOD) at 0.3 μM. The method showed good specificity for the determination of Hg2+ and has the potential to be applied to Hg2+ detection in sewage samples in the environment.

Effective degradation of azo dyes and colorimetric detection of Hg2+ by biogenic silver nanoparticles of Pichia manshurica

A novel biogenic silver nanoparticle production has been done using a yeast Pichia manshurica, strain CD1 cell resuspension exudates. The characterization of AgNPs by DLS, Zeta Potential, FTIR, XRD, SEM, and TEM was done to obtain spherical particle morphology with 22 nM diameter. Biocatalysis of CD1-NPs was done to obtain the catalytic degradation of azo dyes, Congo red, and Malachite green. Degradation occurred within 30 min for Congo red and 40 min for Malachite green with degradation efficiency of 98.86 % and 97.54 % respectively. High reusability (approximately 94 %) was observed of CD1-NPs up to 5 recycles. CD1-NPs were further tested for selectivity and sensitivity towards Hg2+ by colorimetric detection with a limit of 21.04 nM in the linear range of 10–80 nM. The nanosensor has been tested for Hg2+ ions in mercury-treated tap water samples. The efficiency of the biocatalysts was accessed for practical applicability.

Colorimetric and Photocurrent-Polarity-Switching Photoelectrochemical Dual-Mode Sensing Platform for Highly Selective Detection of Mercury Ions Based on the Split G-Quadruplex-Hemin Complex.

Mercury ion (Hg2+) is one of the most harmful heavy metal ions with the greatest impact on public health. Herein, based on the excellent catalytic activity toward 3,3',5,5'-tetramethylbenzidine (TMB) and the strong photocurrent-polarity-switching ability to SnS2 photoanode of the split G-quadruplex-hemin complex, the magnetic NiCo2O4@SiO2-NH2 sphere-assisted colorimetric and photoelectrochemical (PEC) dual-mode sensing platform was developed for the Hg2+ assay. First, the amino-labelled single-stranded DNA1 (S1) was immobilized on NiCo2O4@SiO2-NH2 and then partly hybridized with another single-stranded DNA2 (S2). When Hg2+ was present, the thymine-Hg2+-thymine base pairs between S1 and S2 were formed, causing the formation of the split G-quadruplex in the presence of K+. After addition of hemin, the split G-quadruplex-hemin complex was obtained and effectually catalyzed the H2O2-mediated oxidation of TMB. Thus, the color and absorbance intensity of the TMB solution were changed, resulting in the visual and colorimetric detection of Hg2+. The linear response range is 10 pM to 10 nM, and the detection limit is 3.8 pM. Meanwhile, the above G-quadruplex-hemin complex effectively switched the photocurrent polarity of SnS2-modified indium tin oxide electrode, leading to the sensitive and selective PEC assay of Hg2+ with a linear response range of 5 pM to 500 nM and a detection limit of 2.3 pM. Moreover, the developed dual-mode sensing platform provided mutual authentication of detection results in different modes, effectively improving the assay accuracy and confidence, and may have a good potential application in highly sensitive, selective, and accurate determination of Hg2+ in environmental fields.

Development of heterocyclic 2,7-diamino-3-phenylazo-6-phenylpyrazolo[1,5-a]pyrimidine as antimicrobial agent and selective probe for UV–visible and colorimetric detection of Hg2+ ions

Mercury is considered as a highly toxic metal ion due to its lethal effects on humans and the ecological system. The increasing level of antimicrobial resistance are threatening to the ecosystem, public health and economy. The development of new environmentally safe organic molecules can be a potential cure for both of the above-mentioned problems. Herein, we have synthesized 2,7-diamino-3-phenylazo-6-phenylpyrazolo[1,5-a]pyrimidine (PPD) as a new hetero-cyclic ligand, act as a selective Hg2+ ion chemosensor. The developed sensing probe PPD exhibited limit of detection (LOD) 1.31 × 10−6 M, and limit of quantitation (LOQ) 4.39 × 10−6 M in the linear range2.7–45.65 × 10−6 M with good association affinity of 1.668x 104 M−1for Hg2+ ions. Interestingly, the synthesized heterocyclic motif (PPD) provided a significant colorimetric change from colorless to yellow upon binding with Hg2+ ions. Moreover, the developed probe exhibited tremendous antimicrobial activity against seven bacterial strains and one fungal strain. Cytotoxic studies on normal cell lines were also carried out for this compound which proved that compound is non-toxic (91–100 % cell survival) and can be applied to living system for mercury poisoning detection.

New NIR spectroscopic probe with a large Stokes shift for Hg2+ and Ag+ detection and living cells imaging

A new near-infrared (NIR) probe based on a coumarinyl ligand (CL) was designed and synthesized. The probe CL can be used for simultaneous fluorescent turn-on and colorimetric detection of Hg2+ and Ag+ in ethanol/water medium. Colorless solution of probe CL changed to light yellow or dark yellow after addition of Hg2+ or Ag+ ions. Meanwhile the maximum absorption band shifted from 379 nm to 404 nm and the intensity increased enormously (for Hg2+) or moderately (for Ag+). Probe CL displayed an extraordinarily large Stokes shift of 316 nm and addition of Hg2+ or Ag+ to probe CL induced enhancement in the intensity of fluorescence emission at 695 nm by 15 or 8 fold. The detection limit of CL for Hg2+ and Ag+ ions is 0.83 and 8.8 μM, respectively. The applicable pH for sensing Hg2+ by probe CL is in a broad range of 2–12. Application of probe CL for in vitro U87MG cell imaging to detect Hg2+ ions was confirmed.

Colorimetric detection of Hg2+ ion using fluorescein/thiourea sensor as a receptor in aqueous medium

A simple and selective colorimetric method was used for detection of mercury ions (Hg2+) in the aqueous medium and environmental water sample. Fluorescein-thiourea (FLTU) conjugate complex as receptor was prepared by 1:1 M ratio of 10 µmol L−1 fluorescein dye and thiourea in phosphate buffer solution at pH 7.00. The IR spectra of FLTU receptor have illustrated the formation of H-bond between thiourea and fluorescein dye. The receptor fluorescein-thiourea (FLTU) was used as a chemo-sensor highly selectively to detect the Hg2+ ion by changing the receptor color from a yellow color to red through the quenching of fluorescence intensity of the receptor. The lower detection limit (LOD) and quantitation limit (LOQ) of Hg2+ ions with the receptor FLTU are 0.24 and 0.73 nmol L–1 (correlation coefficient R2 = 0.985) as determined through the absorption spectroscopic method, respectively. The mercury ions are promising and could be achieved via the formation of the complex in a 1:1 stoichiometric ratio of receptor to Hg2+ ions.

A Novel Diarylethene-rhodamine Unit Based Chemosensor for Fluorimetric and Colorimetric Detection of Hg2.

A novel fluorimetric and colorimetric chemosensor (1O) was synthesized with diarylethene-rhodamine unit and characterized by ESI-MS, 1H NMR, and 13C NMR. The chemosensor can selectively recognize extremely low concentrations of Hg2+ over a variety of metal ions with remarkable colorimetric and fluorescent responses. The colorimetric and fluorescent changes were ascribed the reaction between 1O and Hg2+ destructed the rhodamine hydrazide into open-ring form which was provedby mass spectrometry and nuclear magnetic titration analyses. The detection limits of the UV absorption and fluorescence methods for Hg2+ were found to be 0.708μM and 24.6nM, respectively. Moreover, the chemosensor exhibited excellent photochromism and outstanding fatigue resistance property under alternating UV and visible light irradiation. The application potential of the chemosensor was demonstrated with the qualitative detection of Hg2+ in real water samples.

Indigoidine biosynthesis triggered by the heavy metal-responsive transcription regulator: a visual whole-cell biosensor.

During the last few decades, whole-cell biosensors have attracted increasing attention for their enormous potential in monitoring bioavailable heavy metal contaminations in the ecosystem. Visual and measurable output signals by employing natural pigments have been demonstrated to offer another potential choice to indicate the existence of bioavailable heavy metals in recent years. The biosynthesis of the blue pigment indigoidine has been achieved in E. coli following heterologous expression of both BpsA (a single-module non-ribosomal peptide synthetase) and PcpS (a PPTase to activate apo-BpsA). Moreover, we demonstrated herein the development of the indigoidine-based whole-cell biosensors to detect bioavailable Hg(II) and Pb(II) in water samples by employing metal-responsive transcriptional regulator MerR and PbrR as the sensory elements, and the indigoidine biosynthesis gene cluster as a reporter element. The resulting indigoidine-based biosensors presented a good selectivity and high sensitivity to target metal ions. High concentration of target metal exposure could be clearly recognized by the naked eye due to the color change by the secretion of indigoidine, and quantified by measuring the absorbance of the culture supernatants at 600 nm. Dose-response relationships existed between the exposure concentrations of target heavy metals and the production of indigoidine. Although fairly good linear relationships were obtained in a relatively limited concentration range of the concentrations of heavy metal ions, these findings suggest that genetically controlled indigoidine biosynthesis triggered by the MerR family transcriptional regulator can enable a sensitive, visual, and qualitative whole-cell biosensor for bioindicating the presence of bioaccessible heavy metal in environmental water samples. KEY POINTS: • Biosynthesis pathway of indigoidine reconstructed in a high copy number plasmid in E. coli. • Visual and colorimetric detection of Hg(II) and Pb(II) by manipulation of indigoidine biosynthesis through MerR family metalloregulator. •Enhanced detection sensitivity toward Hg(II) and Pb(II) achieved using novel pigment-based whole-cell biosensors.

Colorimetric detection of Hg(II) by γ-aminobutyric acid-silver nanoparticles in water and the assessment of antibacterial activities

In this work, we report the synthesis of silver nanoparticles (AgNPs) via a wet-chemical reduction procedure using citrate (Cit) and γ-aminobutyric acid (GABA) as stabilizers. The formation of GABA-Cit@AgNPs was confirmed by UV–vis spectroscopy with a surface plasmon resonance band at 393 nm clearly confirming the formation of silver nanoparticles. AgNPs were characterized using UV–vis spectroscopy, attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), dynamic light scattering (DLS), and zeta potential. The as-prepared AgNPs can be used for the detection of hazardous mercury ions (Hg2+) in water by colorimetric method with a limit of detection (LOD) and limit of quantitation (LOQ) of 2.37 μM and 3.99 μM, respectively. The linear working range for Hg2+ detection is 5–35 μM and the sensor probe was applied to investigate Hg2+ in real drinking water samples with satisfied results. Rapid response to Hg2+ is also observed when the nanoparticles are composited within hydrogels. Moreover, GABA-Cit@AgNPs shows antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The fast and sensitive response of the proposed Hg2+ sensor, together with its antibacterial activities, makes GABA-Cit@AgNPs potentially applicable for the development of cheap, portable, colorimetric sensors in fieldwork.

Colorimetric detection of Hg2+ and CH3Hg+ by a novel spirooxazine derivative as a highly sensitive and selective probe

6'-(indolin-1-yl)-1-(4-methoxybenzyl)-3,3-dimethylspiro[indoline-2,3′-naphtho[2,1-b][1,4]oxazine] (SPO), a novel colorimetric probe in a spirooxazine class, was successfully synthesized. Its molecular structure was confirmed by the single crystal and spectroscopic analyses. Upon UV activation, SPO in a 1,4-dioxane solution possessed superior selectivity and sensitivity for colorimetric detection of CH3Hg+ over other cations, including Hg2+. The results from the absorption study showed that the mixtures of SPO and Hg2+ or CH3Hg+ exhibited a new absorption band at 590 nm. This indicates the structural isomerization of SPO into an open-form merocyanine which acts as a ligand to form an SPO-Hg2+ or SPO-CH3Hg+ complex. The stoichiometric ratio of SPO to each mercuric cation in the complexes was determined using Job's method and the results suggested that the complexes were formed at a 1:1 mol ratio. The detection limit of Hg2+ and CH3Hg+ in 1,4-dioxane was investigated and the results showed the values at nM level (152 nM for Hg2+ and 150 nM for CH3Hg+). Moreover, the test strips coated with SPO were also demonstrated to provide a practically highly sensitive detection of CH3Hg+ in mixed 1,4-dioxane:water solutions.

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].

Aggregation-free optical and colorimetric detection of Hg(II) with M13 bacteriophage-templated Au nanowires

An optical and colorimetric biosensor comprising gold nanowires (Au NWs) templated with genetically engineered M13 bacteriophages expressing a specific Au binding peptides tyrosine–glutamic acid–glutamic acid–glutamic acid (Y3E) is fabricated by silver nitrate and surfactant-mediated biomineralization process. The diameter of the Y3E–Au NWs is around 10 nm and an oriented growth mechanism is identified for the continuous growth of the NWs by interconnecting M13 bacteriophages. The flexible Au NWs have formed an enriched Hg(II) binding sites on its surface and the surface-coated silver nanophase functions as a receptor for more efficient Hg(II) binding. Amalgamation-based colorimetric and optical Hg(II) biosensing of Au NWs are scrutinized in the presence of wild-type M13 bacteriophage-templated Au NWs and spherical Au nanoparticles. It is demonstrated that in comparison with the spherical Au nanoparticles, Y3E–Au NWs exhibits an aggregation-free optical and colorimetric sensor for Hg(II). Mechanistic investigation for the aggregation-free sensor and the Au–Hg amalgam crystals are carried out using TEM, STEM-EDX and XPS analyses.

Colorimetric detection of Hg(ii) based on the gold amalgam-triggered reductase mimetic activity in aqueous solution by employing AuNP@MOF nanoparticles.

Although the potential of gold amalgam as a nanoenzyme has been demonstrated, its practical utility has been limited by its low catalytic activity caused by the aggregation of Au nanoparticles (Au NPs). Thus, there is a need to further engineer Au NPs to prevent aggregation and then to achieve higher enzyme activities for the detection of Hg2+ ions. Metal organic frameworks (MOFs), as one kind of promising material, have attracted particular attention due to their unique characteristics of uniform cavities and very high porosity. Herein, a hybrid material of Au nanoparticles and a MOF (AuNP@MOF), constructed by immobilization of Au NPs uniformly on the cavity surface of an iron-5,10,15,20-tetrakis (4-carboxyl)-21H,23H-porphyrin-based MOF (Fe-TCPP-MOF), has been successfully synthesized. Based on Hg2+ ion triggered Au catalysis of methylene blue (MB) reduction, a colorimetric method for highly sensitive and selective detection of Hg2+ ions has been established. The Hg2+ ions were first bound to the Au NP surface to form gold amalgam, and then the catalytic activity of Au NPs was initiated. This detection method showed the advantages of a fast response time, and high sensitivity and selectivity. The response time and the limit of detection were as low as 2 s and 103 pM, respectively, benefiting from the uniform cavities and the large specific surface area of Fe-TCPP-MOF, which ensure: (1) uniform dispersion of the Au NPs on the surface of the cavity; and (2) a higher chance of interaction of mercury and MB owing to the gathering effect of Fe-TCPP-MOF.

Ultrasensitive colorimetric detection of Hg2+ in urine based on single hairpin DNA-based self-propelled dual-cycle targets recycling amplification strategy

ABSTRACT This work reported a label-free single hairpin DNA-based self-propelled dual-cycle targets recycling strategy for ultra sensitive detection of Hg2+ based on T-Hg2+-T structure, exonuclease Ш (Exo Ш)-assisted self-propelled dual-cycle targets recycling and haemin/G-quadruplex (DNAzyme) signal amplification. The hairpin DNA probe with G-quadruplex fragment and continuously repeated sequences was specially designed for this strategy. Hg2+ could assist the combination between Hg2+ binding probe and free 3ʹ-terminus of hairpin DNA probe by T-Hg2+-T coordination to form the blunt 3ʹterminus that triggered Exo III-assisted digestion, and set free Hg2+, Hg2+ binding probe, and free G-quadruplex fragment. The released Hg2+ and Hg2+ binding probe is recycled through cycle 1. The released free G-quadruplex fragments are recycled through cycle 2. Single hairpin DNA-propelled dual-cycle targets recycling triggered by ultra-trace Hg2+ produce massive G-quadruplex fragments that bind haemin to yield G-quadruplex−haemin DNAzymes, which can efficiently catalyse ABTS-H2O2 system and convert ABTS2- to the coloured products. This ultra-sensitive colorimetric assay successfully achieved Hg2+ analysis in urine as low as 0.07 pmol/L with a linear calibration range from 0.1 pmol/L to 50 pmol/L (R2 = 0.992), and was amenable to quantification of Hg2+ in complex biological matrixes. This proposed single hairpin DNA-propelled signal amplification strategy displayed excellent sensitivity, remarkable specificity, high capacity of resisting disturbance, simplicity, low-cost, and was successfully applied for colorimetric detection of Hg2+ in urine samples with good recovery and accuracy.

Colorimetric Detection of Hg(II) Ion Using Silver Nanoparticles Capped with 3-Hydroxybenzoic Acid

In this paper, we report for the first time thesimple method for detection of Hg(II) ion in anaqueousmedium using silver nanoparticles capped with 3-hydroxybenzoic acid. Silver nanoparticles capped with 3-hydroxybenzoic acid were preparedby reduction of the silver ion with 3-hydroxybenzoic acid and without surface functionalization. The formation of silver nanoparticles was characterized by a UV-Visible spectrophotometer. The yellowcolloid of prepared silver nanoparticles capped with 3-hydroxybenzoic acid showed a surface plasmon resonance peak at 420 nm. The ability of silver nanoparticles capped with 3-hydroxybenzoic acid in detection was tested by doing a reaction with several metal ions individually(Na(I), K(I), Cu(II), Zn(II), Ca(II), Mg(II), Hg(II), Mn(II), Ni(II), Pb(II), and Co(II)). It was foundthat silver nanoparticles capped with 3-hydroxybenzoic acid highly selective toHg(II) and then the prepared silver nanoparticles were developedfor detection of Hg(II) ion. Addition of 1 mL Hg(II) ion into 4mL the as-preparedsilver nanoparticles reducedthe peak of surface plasmon resonance spectra, andthe reduction of peak intensity was proportional to the concentration of Hg(II) ion. A goodlinear relationship (R2= 0.998) between absorbance at 420 nm and concentrationof Hg(II) over the range 1.0x10-3to 5.5x10-3M was obtained. Silver nanoparticles capped with 3-hydroxybenzoic acid were highly sensitive to Hg (II) ion with the detection limit down to 4.7x10-5M. Application the method to the real water sample showed the excellentresult with recovery ranged from 98 to 101%. The proposed method was found to be useful forthe colorimetric detection of Hg(II) ion in an aqueousmedium.

Colorimetric determination of Hg(II) sensor based on magnetic nanocomposite (Fe3O4@ZIF-67) acting as peroxidase mimics

An extremely sensitive colorimetric sensor has been developed for selective determination of Hg2+ in aqueous solution based on magnetic nanocomposite (Fe3O4@ZIF-67), which results in an effective intrinsic peroxidase mimicking activities and makes the composites oxidize the 3, 3′, 5, 5′- tetramethyl benzidine (TMB) in the presence of hydrogen peroxide (H2O2) to produce a blue coloured solution. Significantly, the oxidation of TMB was retarded or prevented in the presence of antiradical biomolecules Glutathione (GSH) because of its strong cation restoration property. When Hg2+ is added, the strong affinity of mercury ions with thiol groups of GSH provokes the oxidation of the substrates, which helps the solution turn into blue colour. The absorbance intensity was proportional to the concentration of Hg2+ in the wide range of 0–30 nM and detection limit was successfully as low as 0.36 nM. The resultant nanocomposite based peroxidase mimicking activity applied as a versatile platform in the colorimetric detection of Hg2+ was established the other co-existing metal ions in aqueous solutions. Finally the sensor was applied to detect Hg2+ in real water sample with satisfactory recovery results. Interestingly, the proposed colorimetric sensing platform held great potential in the application of mercury contamination in industrial sewage.

Colorimetric detection of Hg2+ using a mixture of an anionic azo dye and a cationic polyelectrolyte in aqueous solution

AbstractWe investigated a colorimetric chemosensor for Hg2+ based on a mixture of xylidyl blue I as an anionic organic dye and poly(diallyldimethylammonium chloride) as a cationic polyelectrolyte in an aqueous solution at pH 7.5. The addition of Hg2+ to the mixture induced a bathochromic shift in the absorption spectra with a distinct color change from red to green which was readily identifiable by the naked eye, whereas the other metal ions gave rise to insignificant color changes. By contrast, upon adding Hg2+ to xylidyl blue I alone, the solution underwent no significant change in color. Moreover, a stoichiometric ratio for the complex between xylidyl blue I and Hg2+ in the presence of poly(diallyldimethylammonium chloride) was determined to be 1:1 by the absorption titration curve and Job's plot. Thus, the mixture can be used as a selective naked‐eye colorimetric chemosensor for Hg2+ over other common metal ions. This study raises the possibility that the combination of an organic dye and an oppositely charged polyelectrolyte is a potential candidate for the easy construction of a new chemosensor system. © 2018 Society of Chemical Industry

Colorimetric detection of Hg(II) by measurement the color alterations from the "before" and "after" RGB images of etched triangular silver nanoplates.

It is shown that triangular silver nanoplates (TAgNPs) are viable colorimetric probes for the fast, sensitive and selective detection of Hg(II). Detection is accomplished by reducing Hg(II) ions to elemental Hg so that an Ag/Hg amalgam is formed on the surface of the TAgNPs. This leads to the inhibition of the etching TAgNPs by chloride ions. Correspondingly, a distinct color transition can be observed that goes from yellow to brown, purple, and blue. The color alterations extracted from the red, green, and blue part of digital (RGB) images can be applied to the determination of Hg(II). The relationship between the Euclidean distances (EDs), i.e. the square roots of the sums of the squares of the ΔRGB values, vary in the 5nM to 100nM Hg(II) concentration range, and the limit of detection is as low as 0.35nM. The color changes also allow for a visual estimation of the concentrations of Hg(II). The method is simple in that it only requires a digital camera for data acquisition and a Photoshop software for extracting RGB variations and data processing. Graphical abstract Hg2+ detection was achieved by anti-etching of TAgNPs caused by the formation of silver amalgam, along with vivid multicolor variations from yellow to brown, purple, and eventually to be blue.

Dispersion-aggregation-dispersion colorimetric detection for mercury ions based on an assembly of gold nanoparticles and carbon nanodots.

Mercury is a common heavy metal element in natural systems and is highly toxic to the human body. Herein, a novel colorimetric detection of Hg2+ ions is proposed based on the aggregation of gold nanoparticles (AuNPs) induced by carbon quantum dots (CDs) with the assistance of glutathione (GSH). In this sensing system, the AuNP/CDs composite forms through Au-N bonds. Simultaneously, the color of the solution turns from wine red to blue. The well-dispersed AuNPs can be restored after the addition of GSH, because GSH competes with CDs to bind onto the surface of AuNPs and protect AuNPs from aggregation. In the presence of Hg2+ ions, GSH can chelate with Hg2+ to form a complex, which subsequently enables CDs to facilitate the aggregation of the AuNPs again. Therefore, according to the red-to-blue color change, a colorimetric sensor is established for the sensitive and selective detection of Hg2+ with a detection limit of 7.5 nM. Moreover, this sensor is successfully used to detect Hg2+ spiked in environmental water. This very simple and cost-effective strategy will promote the development of a colorimetric sensor for the determination of other metal ions in biological and environmental fields.