Detection of mercury(II) ions using colorimetric gold nanoparticles on paper-based analytical devices.

Nowadays, the development of a multifunction system for the simultaneous multiple signal amplification detection and fast removal of Hg2+ remains a major challenge. Herein, we for the first time used gold nanoparticles (Au NPs) and the corresponding filter membrane as chemosensors and adsorbents for dual signal amplification detection and fast removal of Hg2+. Such a system was based on the formation of gold amalgam and a gold amalgam-based reaction between rhodamine B (RhB) and NaBH4 with fluorescence and colorimetric sensing functions. When the gold amalgam catalyzes the reduction of RhB, the red color and orange fluorescence of RhB gradually changed to colorless by switching the amount of Hg2+ deposited on 13 nm Au NPs. The detection limit of the fluorescence assay and colorimetric assay is 1.16 nM and 2.54 nM for Hg2+, respectively. Interestingly, the color and fluorescence of RhB could be recovered when the above colorless reaction solution was exposed to air for about 2 hours. Taking advantage of the above optical phenomenon, a recyclable paper-based sensor has been developed by immobilizing the Au NPs and RhB dye on filter paper and has been successfully used for detection of Hg2+ in real water samples. In addition, the filter membrane immobilized Au NPs could allow fast removal of mercury ions in Yellow river water and tap water with the removal efficiency close to 99%.

In the river bank filtration systems (RBF) the extracted water quality is strongly depending on source (river or lake) water quality. It is well known that these systems can effectively remove emerging contaminants (pharmaceuticals, personal care products or pesticides) from polluted river waters. The common river water contamination is related to nitrate which is observed at high concentrations commonly. Moreover, the nitrate concentrations in the rivers are usually very changeable seasonally. The current work presents the effectiveness of the RBF system in nitrate removal from polluted source (river) water. For this purpose, the water chemistry changes during filtration between the river and productive wells were used, while for identification of denitrification processes the isotopes of d18O and d15N dissolved in nitrate were used. The RBF site located in Śrem (Wielkopolska region, Poland) was selected for the presented research. The water samples were taken from the river and six continuously pumped wells. The water sample representing ambient groundwater was analysed as well. The wells at a close distance from the river (40-50 m) and the wells located at a greater distance from the river (70 – 95 m) were chosen for investigation. The visible differentiation of nitrate concentration was observed. The highest nitrate concentrations were observed in the river and wells located at a close distance from the river (~5 mg/l) and then the nitrate concentrations decrease (to a level of <0,5 mg/l). The spatial differentiation of the isotopes of d18O and d15N dissolved in nitrate is correlated with nitrate decrease and indicates that the denitrification processes are responsible for nitrate removal. The research presented demonstrates that RBF systems are reliable methods for nitrate removal from source water. This work has received funding from the National Science Centre of Poland (grant no. 2021/41/B/ST10/00094).

Stable isotope signatures of river and lake water from Poyang Lake, China: Implications for river–lake interactions

We described a new and sensitive method for the determination of mercury ions (Hg(2+) ) on the basis of fluorescence correlation spectroscopy (FCS) and recognition of oligonucleotides. In this assay, 30-nm gold nanoparticles (GNPs) were modified with oligonucleotides containing thymine bases (T) as fluorescent probes, and the principle of this assay was based on the specific binding of Hg(2+) by two DNA thymine bases. When two GNPs labelled with different oligonucleotides were mixed with a sample containing Hg(2+), the T-Hg(2+)-T binding reaction should cause GNPs to form dimers (or oligomers), which would lead to a significant increase in the characteristic diffusion time of GNPs in the detection volume. The FCS method is a single molecule detection method and can sensitively detect the change in the characteristic diffusion time of GNPs before and after binding reactions. The quantitative analysis was performed according to the relation between the change in the characteristic diffusion time of GNPs and the concentration of Hg(2+). Under optimal conditions, the linear range of this method was from 0.3 nM to 100 nM, and the detection limit was 0.14 nM for Hg(2+). This new method was successfully applied for direct determination of Hg(2+) levels in water and cosmetics samples.

The colorimetric detection of heavy metal ions based on gold nanoparticles (GNPs) with a functionalized surface layer has received much attention due to their unique size and the dependence of their optical and electronic properties on the degree of aggregation. We developed a simple, environmentally friendly detection technique which uses GNPs functionalized with Xanthoceras sorbifolia tannin (XT) as a colorimetric probe for the selective detection of Cr3+ based on the aggregation-induced color change in the GNPs. In the synthesis of the XT-functionalized GNPs, XT simultaneously acts as a reducing and a stabilizing agent without requiring additional reagents or treatment. The XT-stabilized GNPs obtained are almost spherical, stable and water-soluble. The XT-stabilized GNPs can be used as a high-selectivity template to chelate with Cr3+; this chelation induces the aggregation of the GNPs, resulting in a color change from red to gray/purple within a few seconds. The proposed colorimetric sensor has been successfully applied to the detection of Cr3+ in tap water and river water. Compared with the current materials and methods for Cr3+ detection based on GNPs, this approach opens up a novel and environmentally friendly technique for the efficient detection of Cr3+.

A sulfydryl-based near-infrared ratiometic fluorescent probe for assessment of acute/chronic mercury exposure via associated determination of superoxide anion and mercury ion in cells and in vivo

An inverse opal hydrogel (IOH) sensor was constructed through colloidal templating photopolymerization of acrylic acid and pemaerythritol-triacrylate. Its dual responsive behaviours to pH and mercury ions (Hg2+) were demonstrated by detecting the shift of the diffraction wavelength. The diffraction wavelength of the IOH sensor was dramatically red-shifted when the pH was increased from 11 to 13, due to the swelling of the hydrogel. The shift of the diffraction wavelength can be directly observed by the naked eye through the colour change of the IOH. A fast response behaviour of the IOH sensor to pH was approximately completed within 3 s. Furthermore, carboxyl groups were used to detect Hg2+ as recognition groups. A low detection limit of 10 nM for Hg2+ was achieved in the optimized IOH sensor. The present work indicates the prospect of constructing multi-responsive IOH sensors using a single recognition group through the facile colloidal templating route.

Ultrasensitive determination of mercury ions (Ⅱ) by analysis of the degree of quantum dots aggregation

A novel fluorescent sensor with an overtone peak reference for highly sensitive detection of mercury (II) ions and hydrogen sulfide: Mechanisms and applications in environmental monitoring and bioanalysis

Dense aqueous colloidal gold nanoparticles prepared from highly concentrated precursor solution

Functional logic gates based on lead ions (Pb(2+)) and mercury ions (Hg(2+)) that induce peroxidase-like activities in gold nanoparticles (Au NPs) in the presence of platinum (Pt(4+)) and bismuth ions (Bi(3+)) are presented. The "AND" logic gate is constructed using Pt(4+)/Pb(2+) as the input and the peroxidase-like activity of the Au NPs as the output; this logic gate is denoted as "Pt(4+)/Pb(2+)(AND)-Au NPPOX". When Pt(4+) and Pb(2+) coexist, strong metallophilic interactions (between Pt and Pb atoms/ions) and aurophilic interactions (between Au and Pb/Pt atoms/ions) result in significant increases in the deposition of Pt and Pb atoms/ions onto the Au NPs, leading to enhanced peroxidase-like activity. The "INHIBIT" logic gate is fabricated by using Bi(3+) and Hg(2+) as the input and the peroxidase-like activity of the Au NPs as the output; this logic gate is denoted as "Bi(3+)/Hg(2+)(INHIBIT)-Au NPPOX". High peroxidase-like activity of Au NPs in the presence of Bi(3+) is a result of the various valence (oxidation) states of Bi(3+) and Au (Au(+)/Au(0)) atoms on the nanoparticle's surface. When Bi(3+) and Hg(2+) coexist, strong Hg-Au amalgamation results in a large decrease in the peroxidase-like activity of the Au NPs. These two probes (Pt(4+)/Pb(2+)(AND)-Au NPPOX and Bi(3+)/Hg(2+)(INHIBIT)-Au NPPOX) allow selective detection of Pb(2+) and Hg(2+) down to nanomolar quantities. The practicality of these two probes has been validated by analysis of Pb(2+) and Hg(2+) in environmental water samples (tap water, river water, and lake water). In addition, an integrated logic circuit based on the color change (formation of reddish resorufin product) and generation of O2 bubbles from these two probes has been constructed, allowing visual detection of Pb(2+) and Hg(2+) in aqueous solution.

It has been demonstrated that thymine–guanine (T–G) mismatches in duplex DNA specifically coordinate with mercury ion (Hg2+), forming T–Hg2+–G base pairs. However, the binding performance of T–G mismatches with Hg2+ and its application in biosensors have been rarely reported so far. In this study, the binding between T–G mismatches and Hg2+ was investigated and efforts were made to systematical characterize the analytical performance of T–G mismatches in the determination of Hg2+ and glutathione (GSH), where the thymine–thymine (T–T) mismatches were used as the reference. In specific, Hg2+ induced the conformational change of the fluorescently labeled DNA (FDNA) consisted of seven T–T mismatches, resulting in the dissociation of FDNA with its complementary sequence labeled with a quencher, followed by the disappearance of the fluorescence resonance energy transfer (FRET). The experimental results suggest that the T–G mismatch showed faster signaling kinetics and high sensitivity in sensing Hg2+ with a limit of detection of 4.72 nM for Hg2+. Moreover, the platform based on the T–Hg2+–G structure was successfully applied to determine glutathione with a detection limit of 18.96 nM. These findings of this study may describe the interactions between Hg2+ and nucleobases and extend the applications of Hg2+–mediated base pairs.

In this work, the development of a novel method for the detection of mercury (II) ions in wastewater using a mercury ion-imprinted polymer (IIP) combined with a quartz crystal microbalance (QCM) is described. The IIP was successfully synthesized via the polymerization of a of a novel fluorescein- and 2-aminophenol-functionalized methacrylic acid monomer, which was noted to have high binding affinity to mercury (II) ions. This polymer was subsequently coated on a QCM chip to create an IIP-QCM sensor. This sensor was established to have high selectivity and good sensitivity to mercury (II) ions, and had a limit of detection (LOD) of 14.17 ppb, a limit of quantification (LOQ) of 42.94 ppb, a signal-to-noise ratio (S/N) of 4.29, good repeatability, and a working range of 42.94 ppb to 2 ppm. The sensor was also able to analyze tap water and wastewater samples. The IIP-QCM is, therefore, promising as a highly selective, cost-effective, and rapid mercury ion sensor for applications involving the detection of mercury in wastewater.

Synthesis, characterization and application of poly(acrylamide-co-methylenbisacrylamide) nanocomposite as a colorimetric chemosensor for visual detection of trace levels of Hg and Pb ions

Reservoirs, rivers and groundwater are the top three sources of drinking water supplies in China. As microbial contamination of drinking water is still a prominent water quality problem in rural areas, understanding the microbial quality of these sources is important to the public’s health and economic prosperity of communities. In this study, three types of source water samples were collected from three cities in China. Bacterial contamination indicators testing showed that: total coliforms (TCs) and potential E. coli were not detected in groundwater, but both were detected in river and reservoir water. Total bacteria (TB) of rivers and Res-Ⅰ (sampling site Ⅰ of reservoir water) were greater than 100 CFU/ml, while less than 100 CFU/ml from Res-Ⅱ (sampling site Ⅱ of reservoir water) and groundwater. Salmonella spp. were isolated from river water and no pathogenic microorganisms were isolated from the other two types of water sources by selective culture. Microbial communities testing by 16S rRNA gene amplicon sequencing indicated that, there were 14,114 operational taxonomic unit (OTU) of microbial abundance from all 30 samples, and most OTUs were only present in river water (15.17%), reservoir water (10.46%) or groundwater (43.91%), while 1540 OTUs (10.91%) were shared by all three types of water sources. There were significant differences in the microbial communities of the three types of source water (p < 0.05). Based on the Ace, Chao, and Shannon-Weaver, and Simpson indexes, the species diversity of bacteria in groundwater was higher than in river water or reservoir water (p < 0.05), with the reservoir water having the lowest diversity of bacteria. More than seven potential pathogenic bacteria were detected in 30 water samples, for example, E. coli, Staphylococcus aureus, Clostridioides difficile and Bacteroides fragilis were present in all three types of water sources, while other pathogenic bacteria occurred only in some of the water samples. Clostridium perfringens were detected in river water and groundwater. This study adds information on the microbial communities of various drinking water sources in rural China, which is valuable to water treatment and waterborne pathogen studies. In addition, this study supports the idea that 16S rRNA gene amplicon sequencing could be used as a supplementary tool for sources water quality monitoring.