Detection of heavy metal ions using laser-induced breakdown spectroscopy combined with filter paper modified with PtAg bimetallic nanoparticles

Advances in nanoparticle-enhanced paper sensor for detecting toxic metals in water

Toxic metals in water pose a serious threat to public health and the environment, especially in regions with limited access to advanced laboratory infrastructure. Traditional methods for detecting toxic metals, such as atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS), are accurate but expensive, complex, and unsuitable for on-site use. In contrast, paper-based analytical devices (PADs) offer a low-cost, and user-friendly alternative, especially in resource-limited areas. Recent advancements have significantly improved PAD performance, especially through the integration of nanoparticles and the use of enhanced colorimetric and electrochemical detection methods. These improvements have enabled faster, more sensitive detection while maintaining simplicity and field readiness. This review explores key advancements in PAD technology from 2015 to 2025 including advances in sensitivity, nanoparticle functionalization, and smartphone-based readouts. Unlike previous reviews, this study presents a comparative analysis of PAD detection mechanisms, evaluates commercialization and regulatory challenges, and explores emerging trends such as smartphone integration and microextraction techniques. By addressing these aspects, this review highlights key advancements and optimization strategies to enhance the stability, selectivity, and practical implementation of PADs for water quality monitoring.

Paper-based sap enrichment device combined with laser-induced breakdown spectroscopy for the minimally invasive detection of Cd(Ⅱ) and Pb(Ⅱ) in plants

Detecting heavy metals in plants is highly important for diagnosing plant health and understanding the stress mechanisms induced by heavy metals. However, the minimally invasive detection of heavy metals in plants remains a challenge. A novel paper-based sap enrichment device (PBSED), combined with laser-induced breakdown spectroscopy (LIBS) was proposed for the minimally invasive detection of Cd(Ⅱ) and Pb(Ⅱ) in plants. The PBSED included a stainless-steel capillary and heavy metal ion enrichment filter paper (HMIE-FP). The stainless-steel capillary was inserted into the plant stem, where plant sap was transported onto the paper substrate through capillary action. The heavy metal ions (HMIs) in the plants were enriched on the HMIE-FP, and LIBS was used to detect Cd(Ⅱ) and Pb(Ⅱ) on the HMIE-FP to determine the Cd(Ⅱ) and Pb(Ⅱ) concentration within the plant. COMSOL simulations were employed to analyse the flow dynamics of plant sap within the PBSED. To increase the heavy metal enrichment amount, the HMIE-FP was modified with AuAg bimetallic nanoparticles (AuAgBNPs). The PBSED-LIBS method was applied to detect Cd(Ⅱ) and Pb(Ⅱ) in cucumber plants, and the results were strongly correlated with the inductively coupled plasma mass spectrometry (ICP-MS) results (R² = 0.99 for Cd(Ⅱ) and 0.96 for Pb(Ⅱ)). The proposed PBSED-LIBS method demonstrated high sensitivity and minimal invasiveness; thus, it is suitable for rapid, in vivo detection of HMIs in plants. These findings provide valuable insights for the development of efficient, nondestructive tools for environmental applications.

Detection of heavy metals in soil using Au@SiO2 nanoparticles and surface microstructure combined with laser-induced breakdown spectroscopy

The detection of heavy metals in soil is of great scientific significance for food security and human health. However, traditional detection methods are complicated, time-consuming, and labor-intensive. Herein, we developed a novel method using Au@SiO2 nanoparticles (NPs) and surface microstructure combined with laser-induced breakdown spectroscopy (Au@SiO2 NPs-SMS-LIBS) for the rapid detection of lead (Pb), chromium (Cr), and copper (Cu) in soil samples. The surface microstructures and Au@SiO2 NPs were prepared to improve detection sensitivity and stability. The limits of detection (LODs) for Pb, Cr, and Cu were 0.36 mg/kg, 0.32 mg/kg, and 0.28 mg/kg, respectively, with relative standard deviations (RSDs) of 5.47-6.72 %. The mechanisms of spectral performance enhancement of LIBS detection were thoroughly investigated. Furthermore, the stacking combination model was developed to improve quantitative accuracy, with the correlation of the prediction set (Rp2) for Pb, Cr, and Cu being 0.9285, 0.8625, and 0.9160, respectively. This work offers a very promising solution to improve the sensitivity, stability, and accuracy of heavy metal detection. The developed method holds great application potential for large-scale soil assessments and real-time heavy metal pollution monitoring.

Highly sensitive detection of mercury ions in aqueous solutions by laser-induced fluorescence spectroscopy

Laser-induced fluorescence spectroscopy was used to detect mercury ions in aqueous solutions, in which CH-95 resin was used to chelate the ions to transform the liquid samples into solid ones. The experimental results showed that the fluorescence emission of the chelated solid-state samples excited by a low-power semiconductor laser at the wavelength of 447 nm was significantly enhanced due to the chelating reaction. The fluorescence intensity was proportional to the concentration of mercury ions with a linear correlation coefficient of R2  = 0.994, and the limit of detection was 0.117 ng/L, which was about 10,000 times lower than the permissible level of 1 µg/L for Hg(II) in drinking water. The method greatly improved the sensitivity for the detection of Hg in aqueous solutions.

Label-free and ultrasensitive detection of environmental lead ions based on spatially localized DNA nanomachines driven by hyperbranched hybridization chain reaction

A label-free fluorescent sensing strategy for the rapid and highly sensitive detection of Pb2+ was developed by integrating Pb2+ DNAzyme-specific cleavage activity and a tetrahedral DNA nanostructure (TDN)-enhanced hyperbranched hybridization chain reaction (hHCR). This strategy provides accelerated reaction rates because of the highly effective collision probability and enriched local concentrations from the spatial confinement of the TDN, thus showing a higher detection sensitivity and a more rapid detection process. Moreover, a hairpin probe based on a G-triplex instead of a G-quadruplex or chemical modification makes hybridization chain reaction more controlled and flexible, greatly improving signal amplification capacities and eliminating labeled DNA probes. The enhanced reaction rates and improved signal amplification efficiency endowed the biosensors with high sensitivity and a rapid response. The label-free detection of Pb2+ based on G-triplex combined with thioflavin T can be achieved with a detection limit as low as 1.8 pM in 25 min. The proposed Pb2+-sensing platform was also demonstrated to be applicable for Pb2+ detection in tap water, river water, shrimp, rice, and soil samples, thus showing great potential for food safety and environmental monitoring.

Rapid and ultra-sensitive trace metals detection of water by partial Leidenfrost superhydrophobic array surface enhanced laser-induced breakdown spectroscopy

The rapid and ultra-sensitive detection of trace elements in liquid is a primary concern for researchers. In this study, a partial Leidenfrost effect superhydrophobic (PLSHB) array surface was used for rapid in situ evaporation enrichment of sample droplets. Within 4 min, a 50 μL droplet sample was completely evaporated, resulting in all solutes in it being concentrated within a circular range measuring approximately 350 μm in diameter, without the formation of a coffee ring structure. The limits of detection for six metals (Pb, Ba, Be, Mn, Cr, Cu) in water were determined to be as follows: 0.82 μgL-1, 0.27 μgL-1, 0.033 μgL-1, 0.136 μgL-1, 0.241 μgL-1, and 0.083 μgL-1. Furthermore, laser-induced breakdown spectroscopy (LIBS) was employed to detect the enriched solutes from ten liquid samples with identical concentrations on the PLSHB array surface; these measurements exhibited a relative standard deviation (RSD) of only 3.7%. Spike experiments involving the addition of the aforementioned six metals into drinking water demonstrated recovery rates ranging from 85.7% to 117.7%. Therefore, the application potential of PLSHB array surface enhanced LIBS for rapid, stable, and ultra-sensitive detection and analysis of trace metal elements across various fields such as industry, environmental science, and biomedicine might be highly promising.

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.

Development of smartphone-controlled and machine-learning-powered integrated equipment for automated detection of bioavailable heavy metals in soils

Rapid and accurate on-site detection of crop-absorbable cadmium (Cd) and lead (Pb) in soils is important for food security and human health. The automated soil sample pretreatment method, including the ultrasonic extraction of weakly acid-soluble heavy metals, suction-filtration, and UV photolysis, was proposed to achieve the high-efficiency preparation from soil sample to extract solution. Bismuth-film-modified glass carbon electrode combined with the homemade potentiostat was fabricated to implement the square-wave anodic stripping voltammetry (SWASV) measurements of soil extracts. The peak-information-acquisition algorithm was designed to automatically obtain peak heights and widths of Zn2+, Cd2+, Pb2+, Bi3+, and Cu2+ stripping currents, and then which were used as input variables for establishing machine-learning models to enhance the detection accuracy of SWASV to Cd2+ and Pb2+ under the coexistence of multiple heavy metal ions. Eventually, the smartphone-controlled integrated-automated detection equipment was developed and successfully applied to the automatic pretreatment of soil samples and the determination of weakly acid-soluble Cd2+ and Pb2+ in real soil samples. The detection speed was 75 min/sample, and the detection results were close to the standard method (BCR-ICP-MS). This equipment can provide powerful technical support for on-site rapid and accurate determination of crop-absorbable heavy metals in soils.

Improving the Laser-Induced Breakdown Spectroscopy for Highly Efficient Trace Measurement of Hazardous Components in Waste Oils

Improper disposal of waste oils containing hazardous components damages the environment and the ecosystem, posing a significant threat to human life and health. Here, we present a method of discharge-assisted laser-induced breakdown spectroscopy combined with filter paper sampling (DA-LIBS-FPS) to detect hazardous components and trace the source of polluting elements. DA-LIBS-FPS significantly enhances spectral intensity by 1-2 orders of magnitude due to the discharge energy deposition into the laser-induced plasma and the highly efficient laser-sample interaction on the filter paper, when compared to single-pulse LIBS with silica wafer sampling (SP-LIBS-SWS). Additionally, the signal-to-noise ratio and the signal-to-background ratio are both significantly increased. Resultantly, indiscernible lines, such as CN and Cr I, are well distinguished. In contrast with DA-LIBS combined with silica wafer sampling (DA-LIBS-SWS), the spectral signal fluctuations in DA-LIBS-FPS are reduced by up to 33%, because of the homogeneous distribution of the oil layer on the filter paper in FPS. Further examination indicates that the limit of detection for Ba is reduced from a several parts per million level in SP-LIBS-SWS to a dozens of parts per billion level in DA-LIBS-FPS, i.e., nearly 2 orders of magnitude enhancement in analysis sensitivity. This improvement is attributed to the extended plasma lifespan in DA-LIBS and the increasing electron density and plasma temperature in FPS. DA-LIBS-FPS provides a low-cost, handy, rapid, and highly sensitive avenue to analyze the hazardous components in waste oils with great potential in environmental and ecological monitoring.

Recent Advances in Organic Sensors for the Detection of Ag+ Ions: A Comprehensive Review (2019-2023)

Recently, organic sensors for the detection of Ag+ and other metal ions have experienced significant advancements. This is because there is a growing demand for reliable and sensitive tools to monitor various environmental pollutants. Organic sensors have O-, S-, and N-donor atoms, which can act as a ligand and coordinate with different metal ions, hence stabilizing them in a variety of oxidation states. This interaction gives colorimetric and fluorescence changes, which are used to monitor Ag+ and other metal ions. This comprehensive review highlights the latest developments in organic sensors for the recognition of Ag+. We present an in-depth analysis of the underlying principles and mechanisms governing Ag+ ion recognition. Various organic sensing platforms, such as fluorescent and colorimetric sensors, are discussed, shedding light on their unique advantages and limitations. Special attention is given to the diverse range of organic ligands, receptors, and functional materials used to achieve high sensitivity, selectivity, and quantification accuracy. Additionally, we delve into real-world applications of organic sensors for Ag+ ion detection, examining their performance in complex matrices such as biological, environmental, industrial and agricultural matrices.

A 3D phytic acid cross-linked high-porous conductive hydrogel integrating g-C3N4 for electrochemical multiplex sensing of heavy metal ions

It is a great challenge to develop an effective super-sensitive capture method for multiplex heavy metal ions (HMIs), because HMIs is extremely toxic to public health and the environment, what's more their contamination is usually multiplex ions pollution. In this work, a 3D high-porous conductive polymer hydrogel was designed and prepared with high-stable and easy mass production, which is very favorable for the industrialization. The polymer hydrogel (g-C₃N₄-P(Ani-Py)-PAAM) was formed from the mixture of aniline pyrrole copolymer and acrylamide cross-linked with phytic acid as dopant and cross-linker and integrated with g-C₃N₄. The 3D networked high-porous hydrogel not only exhibits excellent electrical conductivity, but also provides a large surface area for increasing the number of immobilized ions. Importantly, the 3D high-porous conductive polymer hydrogel was applied successfully in electrochemical multiplex sensing of HIMs. The prepared sensor used differential pulse anodic stripping voltammetry exhibited high sensitivities, low detection limit and wide detection ranges for Cd²⁺, Pb²⁺, Hg²⁺ and Cu²⁺, respectively. Moreover, the sensor showed a high accuracy in lake water test. The preparation and application of the hydrogel in electrochemical sensor provided an availability strategy to capture and detect the various HMIs by electrochemistry in solution and has great commercial application prospect.

Flexible carbon fiber cloth supports decorated with cerium metal- organic frameworks and multi-walled carbon nanotubes for simultaneous on-site detection of Cd2+ and Pb2+ in food and water samples

The widespread heavy metal pollution endangers human health; hence, accurate on-site detection and quantification of heavy metal content in the surroundings is a vital step in reversing the harmful effect. Herein, an electrochemical sensor based on flexible cerium metal-organic framework@multi-walled carbon nanotubes/carbon cloth (CeMOF@MWCNTs/CC) was constructed for simultaneous on-site detection of Cd²⁺ and Pb²⁺ in food and water samples. The rich carboxyl groups of MWCNTs provided abundant sites for the adsorption of Cd²⁺ and Pb²⁺, and the mutual conversion of Ce³⁺ and Ce⁴⁺ in CeMOF facilitated the reduction and reoxidation of metal ions. The prepared electrode showed excellent performance in the simultaneous measurement of Cd²⁺ and Pb²⁺, with detection limits of 2.2 ppb and 0.64 ppb, respectively. More importantly, the sensing platform has been successfully used to detect simultaneously Cd²⁺ and Pb²⁺ in grain and water samples, and the detection results were consistent with the standard methods, showing great potential in environmental monitoring and food safety.