Detection Techniques for Lead Ions in Water: A Review

Novel gold nanoparticles-Schiff base electrochemical sensor for the determination of lead (II) ions in biological samples

In this investigation, a novel tetradentate Schiff base ligand, (ligand L) was synthesized using a simple chemical route assisted by triethylenetetramine with 4-dimethylaminocinnamaldehyde in ethanol. The chemical structure of the as-synthesized ligand was characterized using nuclear magnetic resonance (NMR) and UV-visible spectroscopy. This ligand was then employed to modify the working electrode of screen-printed carbon electrode (SPCE) for developing a modified L/SPCE sensor finalized to detection of lead ions (Pb2+). The electrochemical characteristics of the sensor were assessed by Square Wave Anodic Stripping Voltammetry technique (SWASV). To further enhance the sensitivity, gold nanoparticles (AuNps) were deposited on the surface of the working electrode for obtaining an AuNps-L/SPCE sensor. This device shows a linear response to Pb2+ until to 0.6 µM, a sensitivity of 897 µA µM-1 cm-2 and a limit of detection (LOD) of 0.38 μM. This successful strategy offers promising avenues for lead ion detection also in urine.

Explicit fluorescence sensing method for sensitive detection of Pb2+ ions based on DNA aptamer folding as a molecular probe

Heavy metals can potentially create environmental and atmospheric pollution, significantly threatening human health. Lead is categorized as a hazardous heavy metal that can adversely affect the environment and human well-being. We present a novel method for detecting lead (Pb2+) ions utilizing crystal violet and thrombin binding aptamer (TBA), employing absorbance, fluorescence, and fluorescence anisotropy experiments. An increase in the absorbance peak of TBA at 300 nm and a significant decrease in the fluorescence intensity of the TBA-crystal violet complex with the addition of Pb2+ ions was observed. Fluorescence anisotropy experiments of the TBA-crystal violet complex in the presence of Pb2+ ions exhibited a decrease in the anisotropy values from 0.46 to 0.34. In the presence of Pb2+ ions, TBA exhibited a positive peak at 312 nm and a negative peak at 265 nm in the CD spectrum, indicating the formation of a G-quadruplex structure. While, in the presence of other metal ions, TBA adopted a random coil structure. A combination of absorption titration and kinetic measurements was employed to understand the role of Pb2+ ions in mediating the folding of G-quadruplex structures. A stopped-flow analysis revealed that the rate of G-quadruplex folding with Pb2+ ions was approximately 28 times faster than that of K+ ions. This method presents a rapid, accurate, and targeted approach for Pb2+ ions detection, with potential applications in environmental sample analysis. It can detect Pb2+ ions at concentrations as low as 1.18 nM (0.32 ppb), significantly lower than the WHO's drinking water limit of 72 nM.

Recent Developments in Enzyme-Free PANI-Based Electrochemical Nanosensors for Pollutant Detection in Aqueous Environments

Wastewater management has a direct impact on the supply of drinking water. New cutting-edge technologies are crucial to the ever-growing demand for tailored solutions for pollutant removal, but these pollutants first need to be detected. Traditional techniques are costly and are no longer competitive in the wastewater cleaning market. One sustainable and economically viable alternative is the fabrication of integrated nanosensors composed of conducting polymers. These include polyaniline doped with various types of nanomaterials such as nanocarbons (carbon nanotubes and graphene), metal oxide nanoparticles/nanostructures, and quantum dots. The synergistic properties of these components can endow sensing materials with enhanced surface reactivity, greater electrocatalytic activity, as well as tunable redox activity and electrical conductivity. This review covers key recent advances in the field of non-enzyme electrochemical conductive polymer nanosensors for pollutant detection in aqueous environments or simulated polluted samples. It provides an introduction to these sensors, their preparation, applications, the environmental and economic hurdles impeding the large-scale development of PANI-based nanomaterials in sensing applications, and future directions for research and real-world applications.

Fluorescent biosensor for lead ion detection based on GR-5 DNAzyme and self-hybridization chain reaction

BACKGROUND

Lead ion (Pb2+) is a typical heavy metal pollutant, and the water and food contaminated by lead may pose a potential threat to the environment and human health. In the natural environment, it can accumulate in soil and water, affecting the entire food chain. For human health, even if the Pb2+ content is very low, it can cause a series of adverse health effects. In order to effectively address the issue of lead pollution, it is particularly important to develop highly sensitive and selective Pb2+ detection technology.

RESULTS

In this study, we designed a single-hairpin based self-hybridization chain reaction (SHCR) system for Pb2+ detection based on GR-5 DNAzyme. Compared with the traditional hybridization chain reaction (HCR) which requires two hairpins, this strategy only needs one hairpin probe, this design not only reduces the experimental cost, but also simplifies the sequence design and experimental operation. Once Pb2+ was added in the system, GR-5 DNAzyme can be actived and then a trigger DNA was released to trigger the SHCR reaction, thereby a signal-amplified fluorescent biosensor for Pb2+ detection was developed, which exhibited a good linear range from 100 to 500 nM with a low detection limit of 24.8 nM, and has been successfully applied to the determination of Pb2+ in environmental water and Chinese Baijiu.

SIGNIFICANCE

This simple, sensitive, and selective Pb2+ detection system demonstrates significant potential for a wide range of practical applications in both environment and food monitoring. In addition to its specific application for Pb2+ detection, by introducing different DNAzymes, this SHCR system can be applied for the detection of other heavy metal ions.

Heterocyclic Coumarin Hybrids as Chemo Sensors of Neurotoxic Lead Ions in Safe Harmless Solvents and Ambient Temperature

Lead is a highly toxic poison for the human body. Lead poisoning is a fatal condition severely affecting the mental and physical development of children younger than 4-5 years. Among various chemo sensors, heterocyclic derivatives are widely used to chelate toxic metal ions, leading to changes in their optical, absorbance, and spectroscopic properties. In this study, coumarin heterocyclic hybrids C1-C6 were synthesized by reacting different classes of amine, pyrrole, and thiadiazoles with bromo acetyl coumarin at room temperature. The C1-C6 probes are studied for their metal binding ability in aqueous acetonitrile for Cu2+, Ni2+, Mn2+, Pb2+, and Zn2+ ions. All six probes showed significant binding with Pb2+ ions with good selectivity by UV-visible, NMR, and HPLC studies. The high binding constants and efficiency of probes between 0.00003-0.00006 range further point to their likely use in human biomatrix' s for Pb2+ detection.

A turn-on fluorescent aptasensor for Pb2+ detection based on rhodamine B dye leakage from the internal cavity of hollow gold nanoparticles

In this project, a sensitive fluorescent aptasensor was fabricated to detect lead ions (Pb2+) by applying hollow gold nanoparticles (HGNPs) as a nano-carrier and rhodamine B (RDB) fluorescent dye as the signal agent. In the aptasensor that was created, the specific attachment of the aptamers to Pb2+ ions led to the release of aptamer from the chitosan (CTS) coated-HGNPs loaded with RDB, causing an increase in fluorescence intensity due to the leakage of RDB. The method demonstrated specific detection of the target analyte, achieving a detection limit (LOD) of 1 ppb and a broad linear dynamic range spanning from 2 to 1000 ppb. The aptasensor was able to accurately measure the concentration of Pb2+ in human serum, low-fat milk, and mineral water samples. The suggested biosensor, which offers the benefits of simplicity, user-friendliness, affordability, and high sensitivity, is well-suited for use with complex samples such as environmental and clinical samples.

A disposable fiber-optic plasmonic sensor for chemical sensing

The integration of fiber optics and plasmonic sensors is promising to improve the practical usability over conventional bulky sensors and systems. To achieve high sensitivity, it typically requires fabrication of well-defined plasmonic nanostructures on optical fibers, which greatly increases the cost and complexity of the sensors. Here, we present a fiber-optic sensor system by using chemical absorption of gold nanoparticles and a replaceable configuration. By functioning gold nanoparticles with aptamers or antibodies, we demonstrate the applications in chemical sensing using two different modes. Measuring shift in resonance wavelength enables the Pb2+ detection with a high linearity and a limit of detection of 0.097 nM, and measuring absorption peak amplitude enables the detection of E. coli in urinary tract infection with a dynamic range between 103 to 108 CFU/mL. The high sensitivity, simple fabrication and disposability of this sensing approach could pave the way for point-of-care testing with fiber-optic plasmonic sensors.

Dielectric-metal hybrid structured LSPR sensor based on graphene oxide amplification for lead ion detection

The detection of lead ions (Pb2+) is crucial due to its harmful effects on health and the environment. In this article, what we believe to be a novel dielectric-metal hybrid structure localized surface plasmon resonance (LSPR) sensor for ultra-trace detection of Pb2+ is proposed, featuring a zinc sulfide layer, silver nanodisks (Ag-disks), and graphene oxide (GO) covering the Ag-disks. The sensor works by detecting the variation of gold nanoparticles (AuNPs) on its surface when Pb2+ cleaves a substrate strand linked to a DNAzyme, causing the AuNPs modified on the substrate strand to disperse. The LSPR sensor boasts superior performance with a bulk refractive index sensitivity of 714.34 nm/RIU. It also exhibits a log-linear response to Pb2+ concentrations ranging from 10 pM to 100 nM, with a sensitivity of 3.93 nm/log(µM) and a detection limit of 10 pM. This represents a 1.25-fold increase in sensitivity and an order of magnitude lower detection limit compared to the GO-uncoated sensor. The improved performance is due to the abundant reactive groups and expansive surface area of graphene oxide, which facilitate the absorption of biochemical molecules. In addition, the sensor has good specificity and stability, holding significant potential for a variety of practical applications, and paving the way for LSPR sensors in detecting trace heavy metal ions.

Interpret the potential role of zinc against oxidative stress in inflammation with a practical fluorescent assay

Zinc plays a critical role in inflammation and apoptosis, potentially offering new insights into health and disease beyond its established involvement in various biological processes. A fluorescent probe, SPI, has been designed and synthesized for the real-time detection of dynamic changes of zinc ions (Zn2+) in the potential resistance to oxidative stress, showing fluorescence enhancement at approximately 639 nm with a limit of detection of around 65 pM, which allowed it to identify even low concentrations of Zn2+ with intrinsic excellent biocompatibility. By establishing a cellular inflammation and apoptosis model using HT-DNA, hydrogen peroxide (H2O2), and dexamethasone (DXMS), the study effectively simulates conditions that can alter Zn2+ dynamics. Monitoring the fluorescence changes of SPI in response to these conditions allows researchers to observe how Zn2+ levels fluctuate in real-time, providing a clearer picture of its role in maintaining intracellular redox homeostasis. The findings indicate that SPI can be instrumental in elucidating the detailed molecular mechanisms through which Zn2+ influences immune responses and associates with cellular stress pathways. Overall, the development of SPI not only replenishes a potential assay into the toolbox to study Zn2+ in living cells but also opens new avenues for the further investigations into the therapeutic potential of modulating zinc levels in various pathological conditions.

Heterogenization of Ionic Liquid on Multiwalled Carbon Nanotubes for Lead(II) Ion Detection

The presence of lead(II) ion poses a significant threat to water systems due to their toxicity and potential health hazards. The detection of Pb2+ ions in contaminated water is very crucial. The ionic liquid functionalized multiwalled carbon nanotubes (IL@MWCNT) nanocomposite was fabricated using ionic liquid (IL) 1-methyl-3-(4-sulfobutyl)-imidazolium chloride and multiwalled carbon nanotubes (MWCNTs) for detection of lead(II) ions. It is a novel method to heterogenize the layer of IL on the surface of MWCNTs. The XPS and FTIR analyses confirm that the ionic liquid is not decomposed during annealing process. Moreover, the XRD analysis shows the presence of MWCNTs and carbon quantum dots (CQDs). The HRTEM results exhibit the aggregation of MWCNTs with IL, and formation of small distorted round shaped flakes of CQDs. Further, the successful heterogenization of IL on the surface of MWCNTs is also confirmed by TGA-DSC analysis. The quenching phenomenon of nanocomposite was observed by UV-Visible spectroscopy. The nanocomposite exhibits high performance for the selective detection of lead(II) ions in comparison to other metal ions. The presence of lead(II) ions eventually reduced the intensity of absorption. A limit of detection (LOD) of 9.16 nM was attained for Pb2+ ions in a concentration range of 0-20 nM.

Engineering a PbrR-Based Biosensor for Cell-Free Detection of Lead at the Legal Limit

Industrialization and failing infrastructure have led to a growing number of irreversible health conditions resulting from chronic lead exposure. While state-of-the-art analytical chemistry methods provide accurate and sensitive detection of lead, they are too slow, expensive, and centralized to be accessible to many. Cell-free biosensors based on allosteric transcription factors (aTFs) can address the need for accessible, on-demand lead detection at the point of use. However, known aTFs, such as PbrR, are unable to detect lead at concentrations regulated by the Environmental Protection Agency (24-72 nM). Here, we develop a rapid cell-free platform for engineering aTF biosensors with improved sensitivity, selectivity, and dynamic range characteristics. We apply this platform to engineer PbrR mutants for a shift in limit of detection from 10 μM to 50 nM lead and demonstrate use of PbrR as a cell-free biosensor. We envision that our workflow could be applied to engineer any aTF.

Photoelectrochemical analysis of Pb2+ based on Au@PTCA Schottky junction with Pb2+-G quadruplex structure

Herein, a novel photoelectrochemical (PEC) aptasensor using gold nanoparticles@3,4,9,10-perylene tetracarboxylic (Au@PTCA) Schottky junction as the effective optoelectronic material and lead ion (Pb2+)-G quadruplex structure as the efficient quencher was constructed for the detection of Pb2+ with high sensitivity and excellent selectivity. Au@PTCA Schottky junction, which was proposed by the in situ reduction of Au NPs on the PTCA surface, exhibited a strong unidirectional conductivity, which could generate a significantly enhanced PEC signal compared with the pure PTCA. The Pb2+-G quadruplex structure with a large spatial hindrance effect was formed when the target Pb2+ was present owing to the occurrence of the specific recognition between Pb2+ and its aptamer S1. The formation of a Pb2+-G quadruplex structure effectively quenched the initial signal generated by the Au@PTCA Schottky junction, which was derived from restricted electron transport and light transmission. The obtained prominently decreased PEC signal could achieve the quantitative detection of Pb2+ from 0.5 pM to 500 nM, with a low detection limit of 0.17 pM. The preparation time of this PEC aptasensor was 13 h, and the time for PEC measurement depended on the illumination time, which switched off-on-off for 10 s-20 s-10 s. The study proposed here with high sensitivity and excellent selectivity for Pb2+ analysis offered a novel and reliable tool for environmental monitoring related to heavy metal ions.

Determination of the Localized Surface Plasmon Resonance Alteration of AgNPs via Multiwavelength Evanescent Scattering Microscopy for Pb(II) Detection

We developed multiwavelength evanescent scattering microscopy (MWESM), which can acquire plasmonic nanoparticle images at the particle level using the evanescent field as the incident source and distinguish different LSPR (localized surface plasmon resonance) spectral peaks among four wavelengths. Our microscope could be easily and simply built by modifying a commercial total internal reflection fluorescence microscope (TIRFM) with the substitution of a beamsplitter and the addition of a semicircular stop. The ultrathin depth of illumination and rejection of the reflected incident source together contribute to the high sensitivity and contrast of single nanoparticle imaging. We first validated the capability of our imaging system in distinguishing plasmonic nanoparticles bearing different LSPR spectral peaks, and the results were consistent with the scattering spectra results of hyperspectral imaging. Moreover, we demonstrated high imaging quality from the aspects of the signal/noise ratio and point spread function of the single-particle images. Meaningfully, the system can be utilized in rapidly determining the concentration of toxic lead ions in environmental and biological samples with good linearity and sensitivity, based on single-particle evanescent scattering imaging through the detection of the alteration of the LSPR of silver nanoparticles. This system holds the potential to advance the field of nanoparticle imaging and foster the application of nanomaterials as sensors.

Development of electrochemical sensors for quick detection of environmental (soil and water) NPK ions

All over the world, technology is becoming more and more prevalent in agriculture. Different types of instruments are already being used in this sector. For the time being, every farmer is trying to produce more crops on a piece of land. Eventually, soil loses its nutrients; however, to grow more crops, farmers use more fertilizers without knowing the proper conditions of the soil in real time. To overcome this issue, many scientists have recently focused on developing electrochemical sensors to detect macronutrients, i.e., nitrogen (N), phosphorus (P), and potassium (K), in soil or water rapidly. In this review, we focus mainly on the recent developments in electrochemical sensors used for the detection of nutrients (NPK) in different types of samples. As it is outlined, the use of smart and portable electrochemical sensors can be helpful for the reduction of excess fertilizer and can play a vital role in maintaining suitable conditions in soils and water. We are optimistic that this review can guide researchers in the development of a portable and suitable NPK detection system for soil nutrients.

Facile colorimetric sensor using oxidase-like activity of octahedral Ag2O particles for highly selective detection of Pb(II) in water

Pb(II) is a prevalent heavy metal ion classified as a 2B carcinogen. Excessive intake of Pb(II) in the human body can damage the central nervous system, kidneys, liver, and immune system, leading to permanent brain damage, anemia, and cancer. Colorimetry can be applied to rapidly determine Pb(II) residues, but there are still many challenges in the accuracy and sensitivity of detection. Based on the inhibitory impact of Pb(II) on the oxidase-like activity of octahedral silver oxide (Ag2O), a colorimetric sensor with smartphone-assisted analysis for the Pb(II) detection was first developed. Herein, it has been found that Pb(II) can adsorb onto the surface of octahedral Ag2O, hindering the production of O2- in the reaction system. This ultimately results in the suppression of oxidase-like activity, leading to a lighter purple appearance of the colorimetric reaction solution. The sensor exhibits a high degree of sensitivity and a limit of detection (LOD) for Pb(II) was calculated as 2.2 μg L-1. Hence, the developed colorimetric sensor with high sensitivity, excellent specificity, and high tolerance to sodium ions is hopeful to have practical applications in Pb(II) detection in environmental water samples. Moreover, the sensor will provide a novel strategy for heavy metal ion detection and other substances.

Microwave synthesis of chitosan-based carbon dots for Al3+ detection and biological application

Yellow fluorescent carbon dots (Y-CDs) were prepared via microwave method using chitosan and o-phenylenediamine as the main raw materials. The obtained Y-CDs possesses good water solubility, excellent biocompatibility and luminous stability. During the microwave pyrolysis carbonization process, the surface of Y-CDs was modified with the functional groups such as amino and carboxyl, which can bind to Al3+ by forming complexes, further improving the selectivity and sensitivity of the Al3+ detection. And the fluorescence of Y-CDs was quenched by Al3+ by static quenching process. More importantly, Y-CDs as fluorescent sensor was further applied for the determination of Al3+ in the real water samples with high reliability and accuracy. In addition, Y-CDs present potential application in biological imaging. The cultivated zebrafish embryos with Y-CDs displayed clearly in vivo uptake and metabolic fluorescence images, further confirming its low toxicity and excellent biocompatibility.

Screen-Printed Carbon Electrode Modified with Carbon Nanotubes and Copper Film as a Simple Tool for Determination of Trace Concentrations of Lead Ions

A copper film-modified, carboxyl-functionalized, and multi-walled carbon nanotube (MWCNT-COOH)-modified screen-printed carbon electrode (CuF/MWCNTs/SPCE) was used for lead determination using anodic stripping voltammetry. The main parameters were investigated and optimized during the development of the research procedure. The most optimal electrolyte concentrations were determined to be 0.4 M HCl and 6.3 × 10-5 M Cu(II). The optimal parameters for voltammetric stripping measurements are as follows: an accumulation potential of -0.7 V; an accumulation time of 120 s; and a pulse amplitude and pulse time of 120 mV and 2 ms, respectively. The effect of surface active substances and humic substances as potential interferents present in aqueous environmental samples was investigated. The validation of the procedure was carried out using certified reference materials, like waste water SPS-WW1 and environmental matrix TM-25.5. In addition, the developed procedure was applied to investigate lead recovery from natural environmental water, such as rivers and lakes.

Micro/nanorobots for remediation of water resources and aquatic life

Nowadays, global water scarcity is becoming a pressing issue, and the discharge of various pollutants leads to the biological pollution of water bodies, which further leads to the poisoning of living organisms. Consequently, traditional water treatment methods are proving inadequate in addressing the growing demands of various industries. As an effective and eco-friendly water treatment method, micro/nanorobots is making significant advancements. Based on researches conducted between 2019 and 2023 in the field of water pollution using micro/nanorobots, this paper comprehensively reviews the development of micro/nanorobots in water pollution control from multiple perspectives, including propulsion methods, decontamination mechanisms, experimental techniques, and water monitoring. Furthermore, this paper highlights current challenges and provides insights into the future development of the industry, providing guidance on biological water pollution control.

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.