Rapid Determination of Cr3+ and Mn2+ in Water Using Laser-Induced Breakdown Spectroscopy Combined with Filter Paper Modified with Gold Nanoclusters

Excessive emissions of heavy metals not only cause environmental pollution but also pose a direct threat to human health. Therefore, rapid and accurate detection of heavy metals in the environment is of great significance. Herein, we propose a method based on laser-induced breakdown spectroscopy (LIBS) combined with filter paper modified with bovine serum albumin-protected gold nanoclusters (LIBS-FP-AuNCs) for the rapid and sensitive detection of Cr3+ and Mn2+. The filter paper modified with AuNCs was used to selectively enrich Cr3+ and Mn2+. Combined with the multi-element detection capability of LIBS, this method achieved the simultaneous rapid detection of Cr3+ and Mn2+. Both elements showed linear ranges for concentrations of 10-1000 μg L-1, with limits of detection of 7.5 and 9.0 μg L-1 for Cr3+ and Mn2+, respectively. This method was successfully applied to the determination of Cr3+ and Mn2+ in real water samples, with satisfactory recoveries ranging from 94.6% to 105.1%. This method has potential application in the analysis of heavy metal pollution.

Green synthesis of silver nanoparticles and its environmental sensor ability to some heavy metals

This study marks a pioneering effort in utilizing Vachellia tortilis subsp. raddiana (Savi) Kyal. & Boatwr., (commonly known as acacia raddiana) leaves as both a reducing and stabilizing agent in the green "eco-friendly" synthesis of silver nanoparticles (AgNPs). The research aimed to optimize the AgNPs synthesis process by investigating the influence of pH, temperature, extract volume, and contact time on both the reaction rate and the resulting AgNPs' morphology as well as discuss the potential of AgNPs in detecting some heavy metals. Various characterization methods, such as UV-vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), Zeta sizer, EDAX, and transmitting electron microscopy (TEM), were used to thoroughly analyze the properties of the synthesized AgNPs. The XRD results verified the successful production of AgNPs with a crystallite size between 20 to 30 nm. SEM and TEM analyses revealed that the AgNPs are primarily spherical and rod-shaped, with sizes ranging from 8 to 41 nm. Significantly, the synthesis rate of AgNPs was notably higher in basic conditions (pH 10) at 70 °C. These results underscore the effectiveness of acacia raddiana as a source for sustainable AgNPs synthesis. The study also examined the AgNPs' ability to detect various heavy metal ions colorimetrically, including Hg2+, Cu2+, Pb2+, and Co2+. UV-Vis spectroscopy proved useful for this purpose. The color of AgNPs shifts from brownish-yellow to pale yellow, colorless, pale red, and reddish yellow when detecting Cu2+, Hg2+, Co2+, and Pb2+ ions, respectively. This change results in an alteration of the AgNPs' absorbance band, vanishing with Hg2+ and shifting from 423 to 352 nm, 438 nm, and 429 nm for Cu2+, Co2+, and Pb2+ ions, respectively. The AgNPs showed high sensitivity, with detection limits of 1.322 × 10-5 M, 1.37 × 10-7 M, 1.63 × 10-5 M, and 1.34 × 10-4 M for Hg2+, Cu2+, Pb2+, and Co2+, respectively. This study highlights the potential of using acacia raddiana for the eco-friendly synthesis of AgNPs and their effectiveness as environmental sensors for heavy metals, showcasing strong capabilities in colorimetric detection.

Colorimetric sensor for Cr (VI) by oxidative etching of gold nanotetrapods at room temperature

Hexavalent chromium (Cr(VI)) is highly carcinogenic and mutagenic, which is seriously harmful to human health. Hence, it is important to create a probe that can detect Cr(VI) effectively. In this work, gold nanotetrapods (Au NTPs) were applied in colorimetric detection for the first time. Based on the oxidative etching principle of Cr(VI) on Au NTPs, a sensitive and multicolor response detection method for Cr(VI) was established. The oxidative etching of Au NTPs by Cr(VI) resulted in the blue shift of plasmon resonance absorption peak of Au NTPs with the change of morphology. As the etching progress processed, Au NTPs solution exhibited obvious color changes from gray-green to blue-violet and then to pink. This multicolor response design is very convenient for naked-eye detection. The limit of detection (LOD) of Cr(VI) is 3 nM for the naked eyes and 0.5 nM for UV-vis spectrum, both of which are lower than the toxicity level of Cr(VI) (0.2 μM) set by United States Environmental Protection Agency. This sensing method exhibits good linearity between the wavelength shift and Cr(VI) concentration in the range of 0.5 nM to 8 nM. The detection results of Cr(VI) in actual environmental samples demonstrate that the Au NTPs colorimetric probe (Au-N-Probe) is expected to be applied to the detection of Cr(VI) in water environmental samples such as lake water and industrial wastewater.

Highly sensitive and selective colorimetric detection of dual metal ions (Hg2+ and Sn2+) in water: an eco-friendly approach

Application of an alliin-based precursor for the synthesis of silver nanoparticles (Ag NPs) which is an emerging, reliable and rapid sensor of heavy metal ion contaminants in water is reported here. The Ag NPs were characterized by using UV-visible spectroscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy analysis techniques. The Ag NPs simultaneously and selectively detect Hg2+ and Sn2+ ions from aqueous solution. The sensitivity and selectivity of the prepared Ag NPs towards other representative transition-metal ions, alkali metal ions and alkaline earth metal ions were also studied. For more precise evidence, a density functional theory study was carried out to understand the possible mechanism and interaction in the detection of Hg2+ and Sn2+ by Ag NPs. The limits of detection for Hg2+ and Sn2+ ions were found as 15.7 nM and 11.25 nM, respectively. This assay indicates the possible use of garlic extract-synthesized Ag NPs for sensing Hg2+ and Sn2+ in aqueous solution very significantly. So, the simple, green, eco-friendly and easy method to detect the dual metal ions may further lead to a potential sensor of heavy metal ion contaminants in water of industrial importance.

The SPE-assisted europium (III) based complex fluorometric assay for the highly selective and sensitive detection of manganese (II) in water

Detection of trace manganese (Ⅱ) ion (Mn²⁺) is crucial to water safety. Here, commercially available PS-DVB microspheres were sulfonated and then filled into the SPE column in order to separate Mn²⁺ from complex matrices. Meanwhile, europium (III) complex was prepared with a simple "one pot" method, and its fluorescence intensity was quenched gradually with the increase of Mn²⁺ concentration. Europium (III) complex combined with home-made SPE column was utilized for highly selective and sensitive measurement of Mn²⁺. The detectable concentrations of Mn²⁺ can be low as 0.2 μM, which was less than the drinking water guidelines. Consequently, this new method is promising to assess the content of Mn²⁺ rapidly and accurately in real-world water samples.

Sensitive and selective colorimetric nitrite ion assay using silver nanoparticles easily synthesized and stabilized by AHNDMS and functionalized with PABA

Nitrite ions (NO₂ ^-), as one of the important inorganic anions, exhibit considerable effects towards the environment and human health. Moreover, over intake of this anion may cause dangerous diseases. Herein, we successfully fabricated silver nanoparticles (AgNPs) using 4-amino-5-hydroxynaphthalene-2, 7-disulphonic acid monosodium salt (AHNDMS) and functionalized them with p-aminobenzoic acid (PABA), and used the functionalised AgNPs as a sensitive and selective colorimetric sensor for nitrite ions. The structure of the as-prepared pure AgNPs was experimentally characterized by different characterizations methods, namely, UV-vis, FT-IR, CV, DPVs, SEM, TEM, and XRD. Additionally, the nitrite ion sensitively and selectively changes the brownish yellow color of the dispersed AgNPs to pinkish red, indicating aggregation of AgNPs, with a detection limit of 0.016 ppm (0.348 μM) and 0.0069 ppm (0.149 μM) by the naked-eye and by UV-vis spectroscopy, respectively. The color change suggested that the aggregation of AgNPs was induced by nitrite-selective diazo-coupling. UV-vis spectra show the disappearance of the absorbance at 474 nm and appearance of a new peak at 532 nm, presumably due to the conversion of AgNPs to silver ions. Moreover, the studies of interference in the proposed sensor confirm its selectivity in the presence of anions as well as cations. Furthermore, linearity was observed between the absorption and the concentration of nitrite ions. More importantly, the proposed sensor was practicably applied for the determination of nitrite in different water samples, such as distilled water, river water, and tap water.

Ultrahigh Selective Colorimetric Quantification of Chromium(VI) Ions Based on Gold Amalgam Catalyst Oxidoreductase-like Activity in Water

Hexavalent chromium ion (Cr⁶⁺) is one of the most toxic substances for plants, for animals, and is a confirmed human respiratory carcinogen. However, so far, there are few independent and efficient colorimetric methods for detection of Cr⁶⁺. Here, we introduce a convenient, label-free, catalysis-based, and efficient strategy for quantification of Cr⁶⁺ by using a colorimetric sensing probe 3,3',5,5'-tetramethylbenzidine (TMB). In the presence of a trace amount of gold amalgam nanocomposites (Au@Hg) and Cr⁶⁺, TMB can be oxidized to oxTMB and the color changed to an intense blue that was observed by naked-eye and absorption spectroscopic method. In addition, the colorimetric method shows the high selectivity against 34 other interfering substances, and it can be performed at room temperature, in water, and requires only ∼5 min. Thus, the catalysis-based colorimetric assay for accurate and ultrahigh selective identification of Cr⁶⁺ will find widespread use in the world.

Rapid and visual readout of vitamin B1 based on the electrostatic interaction induced aggregation of gold nanoparticles

In this work, a simple and rapid colorimetric assay for the quantitative detection of vitamin B1 (VB1) has been fabricated based on citrate-stabilized gold nanoparticles (AuNPs). The UV-Vis spectra of AuNPs varied and the relative color changed from red to purple with the sequential addition of VB1. The characterization results of AuNPs with and without the addition of VB1 confirmed that the observed phenomena were attributed to the aggregation of AuNPs induced by VB1 through electrostatic interaction. The assay was rapid and sensitive to VB1 with a detection limit of 10.9 nM ranging from 30 nM to 650 nM in 15 min. Meanwhile, the developed assay displayed excellent selectivity to VB1 since AuNPs showed negligible response to common metal ions and biological molecules. Moreover, the feasibility for the quantitative detection of VB1 in tablets and human urine samples has also been demonstrated.

Schematic illustration for colorimetric detection of VB1 with AuNPs based on the electrostatic interaction.

Development of a novel tridentate ligand for colorimetric detection of Mn2+ based on AgNPs

A novel tridentate ligand nitrilotris(methylene)tris(1,2,3-triazole)triacetate (NTTTA) has been synthesized by click reaction and followed with ester hydrolysis reaction. The silver nanoparticles (AgNPs) were then modified and stabilized by this ligand, and subsequently been employed for the highly selective and sensitive colorimetric detection of Mn²⁺ in aqueous solution. The presence of Mn²⁺ can cause the aggregation of AgNPs, which leads to the color change of the dispersion from yellow to brown, as well as the decrease and red-shift of the surface plasmon resonance absorption. The detection limit of Mn²⁺ was as approximately 0.5 μM by the naked eyes. UV-vis spectroscopy analysis showed a good linear relationship between the logarithm of the ratios (A₅₅₀/A₃₉₅) and the concentration of Mn²⁺over the range of 0.05 μM-10 μM, and the LOD was calculated to be 12.6 nM (S/N = 3). The present assay showed good simplicity without the need of adjusting the pH value. The feasibility of this technique was evaluated for successful detection of Mn²⁺ in tap water and lake water samples, with good recoveries.

New portable smartphone-based PDMS microfluidic kit for the simultaneous colorimetric detection of arsenic and mercury

A smartphone-based microfluidic platform was developed for point-of-care (POC) detection using surface plasmon resonance (SPR) of gold nanoparticles (GNPs). The simultaneous colorimetric detection of trace arsenic and mercury ions (As3+ and Hg2+) was performed using a new image processing application (app). To achieve this goal, a microfluidic kit was fabricated using a polydimethylsiloxane (PDMS) substrate with the configuration of two separated sensing regions for the quantitative measurement of the color changes in GNPs to blue/gray. To fabricate the microfluidic kit, a Plexiglas mold was cut using a laser based on the model obtained from AutoCAD and Comsol outputs. The colorimetric signals originated from the formation of nanoparticle aggregates through the interaction of GNPs with dithiothreitol - 10,12-pentacosadiynoic acid (DTT-PCDA) and lysine (Lys) in the presence of As3+ and Hg2+ ions. This assembly exhibited the advantages of simplicity, low cost, and high portability along with a low volume of reagents and multiplex detection. Heavy Metals Detector (HMD), as a new app for the RGB reader, was programmed for an Android smartphone to quantify colorimetric analyses. Compared with traditional image processing, this app provided significant improvements in sensitivity, time of analysis, and simplicity because the color intensity is measured through a new normalization equation by converting RGB to an Integer system. As a simple, real-time, and portable analytical kit, the fabricated sensor could detect low concentrations of As3+ (710 to 1278 μg L-1) and Hg2+ (10.77 to 53.86 μg L-1) ions in water samples at ambient conditions.

Colorimetric assay of copper ions based on the inhibition of peroxidase-like activity of MoS2 nanosheets

The peroxidase-like catalytic activity of MoS₂ nanomaterials has been utilized for colorimetric bioassays and medical diagnostics. However, the application of peroxidase-like catalytic activity of MoS₂ nanomaterials in environmental analysis was seldom explored. Herein, copper ions were found to inhibit the peroxidase-like catalytic activity of MoS₂ nanosheets, which can catalyze the oxidation of 3, 3', 5, 5'-tetramethylbenzidine by H₂O₂ to produce a colorimetric product. Based on this finding, a simple sensitive colorimetric method for the detection of copper ions was developed. In the presence of copper ions, the absorbance and color of the solution decreased with the increasing concentration of copper ions. The color of the solution can be used to semi-quantitative on-site assay of copper ions by naked eyes. A linear relationship between the absorbance and the concentration of copper ions was observed in the range of 0.4-4.0μmolL^-1 with a detection limit of 92nmolL^-1, which was much lower than the maximum contaminant level of copper in drinking water legislated by the Environmental Protection Agency of USA and the World Health Organization. The method was applied to detect copper ions in environmental water samples with satisfactory results.

Functionalized graphene oxide quantum dot-PVA hydrogel: a colorimetric sensor for Fe²⁺, Co²⁺ and Cu²⁺ ions

Functionalized graphene oxide quantum dots (GOQDs)-poly(vinyl alcohol) (PVA) hybrid hydrogels were prepared using a simple, facile and cost-effective strategy. GOQDs bearing different surface functional groups were introduced as the cross-linking agent into the PVA matrix thereby resulting in gelation. The four different types of hybrid hydrogels were prepared using graphene oxide, reduced graphene oxide, ester functionalized graphene oxide and amine functionalized GOQDs as cross-linking agents. It was observed that the hybrid hydrogel prepared with amine functionalized GOQDs was the most stable. The potential applicability of using this solid sensing platform has been subsequently explored in an easy, simple, effective and sensitive method for optical detection of M(2+) (Fe(2+), Co(2+) and Cu(2+)) in aqueous media involving colorimetric detection. Amine functionalized GOQDs-PVA hybrid hydrogel when put into the corresponding solution of Fe(2+), Co(2+) and Cu(2+) renders brown, orange and blue coloration respectively of the solution detecting the presence of Fe(2+), Co(2+) and Cu(2+) ions in the solution. The minimum detection limit observed was 1 × 10(-7) M using UV-visible spectroscopy. Further, the applicability of the sensing material was also tested for a mixture of co-existing ions in solution to demonstrate the practical applicability of the system. Insight into the probable mechanistic pathway involved in the detection process is also being discussed.

Functionalization of silver nanoparticles with 5-sulfoanthranilic acid dithiocarbamate for selective colorimetric detection of Mn2+ and Cd2+ ions

A schematic representation of Mn²⁺ and Cd²⁺ ion-induced aggregation of SAA-DTC-Ag NPs.

Cysteine-based silver nanoparticles as dual colorimetric sensors for cations and anions

The synthesis of amide–triazole-based Ag NPs and their sensing ability towards anions and cations in aqueous solution were investigated. The importance of amide–triazole as a binding motif, in conjunction with Ag NPs, and the mode of the sensing ability of these amide–triazole Ag NPs as dual colorimetric sensors have been studied in detail.

Selective colorimetric detection of Cr(iii) and Cr(vi) using gallic acid capped gold nanoparticles

A colorimetric assay is proposed for the selective detection of Cr(iii) and Cr(vi) via the aggregation-induced color change of gallic acid capped gold nanoparticles (GA-AuNPs). The AuNPs are characterized using UV-vis spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and Fourier-transform infrared spectrometry (FT-IR). To detect Cr(iii) and Cr(vi) coexisting in a sample, citrate and thiosulfate were applied to mask Cr(vi) for the detection of Cr(iii), and ethylenediaminetetraacetic acid disodium salt (EDTA) was applied to mask Cr(iii) for the detection of Cr(vi). At optimized experimental conditions, the selectivity of these AuNPs-based detection systems is excellent for Cr(iii) and/or Cr(vi) compared with other types of metal ions. The limit of detections (LODs) of a mixture of Cr(iii) and Cr(vi), Cr(iii) and Cr(vi) by eye vision are 1.5, 1.5 and 2 μM, respectively, and those by UV-vis spectroscopy are 0.05, 0.1 and 0.1 μM, respectively. The minimum detectable concentrations for Cr(iii) or Cr(vi) are all below the guideline value set by the US Environmental Protection Agency (EPA). The applicability of the AuNPs-based colorimetric sensor is also validated by the detection of Cr(iii) and Cr(vi) in electroplating wastewater and real water samples with high recoveries.