Microfabricated interdigitated Au electrode for voltammetric determination of lead and cadmium in Chinese mitten crab (Eriocheir sinensis)

Recent development of eco-friendly nanocomposite carbon paste electrode for voltammetric determination of Cd(II) in real samples

Using eco-friendly, cheap, and available adsorbents is promising for the determination of metal ions. So, this study focuses on the modification of graphite reinforcement carbon paste electrode (GRCPE) with mango seed kernel (MSK) for voltammetric determination of Cd(II). Moreover, to increase the surface area of this adsorbent, it was prepared in nanosized that formed nanoparticles of mango seed kernel (MSK-NPs). The developed nanocomposite electrode of carbon paste electrode modified with nanoparticles of mango seed kernel (MSK-NPs@GRCPE) was characterized using Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM). The effect of pH, buffer solution, and supporting electrolyte as experimental conditions were optimized through differential pulse adsorptive anodic stripping voltammetric method (DPA_dASV). Britton-Robinson buffer pH = 3.9 at E_acc = - 1400 mV, t_acc = 30 s, pulse width = 10 ms and sampling time = 8 ms were the optimum conditions for determination of Cd(II). The LOD and LOQ of MSK-NPs@GRCPE were calculated at 5.44 × 10^-9 and 1.65 × 10^-8 M, respectively. Compared with bare graphite reinforcement carbon paste electrode (BGRCPE), the nanocomposite MSK-NPs@GRCPE has a lower detection limit, indicating that the presence of MSK-NPs could greatly improve the response to Cd(II). The practical applicability of the electrode was verified by the determination of Cd(II) in chocolate and white rice samples. The results show high selectivity and sensitivity for Cd(II) in real samples.

Electrochemical sensor based on Bi/Bi2O3 doped porous carbon composite derived from Bi-MOFs for Pb2+ sensitive detection

It is of great significance to develop electrochemical sensors based on novel functional nanomaterials for heavy metal ions detection. In this work, a novel Bi/Bi₂O₃ co-doped porous carbon composite (Bi/Bi₂O₃@C) was prepared by simple carbonization of bismuth-based metal-organic frameworks (Bi-MOFs). The micromorphology, internal structure, crystal and elemental composition, specific surface area and porous structure of the composite were characterized by SEM, TEM, XRD, XPS, and BET. Further, a sensitive electrochemical sensor for Pb²⁺ detection was constructed by modifying Bi/Bi₂O₃@C on the surface of the glassy carbon electrode (GCE) based on the square wave anodic stripping voltammetric (SWASV). The different factors affecting the analytical performance were optimized systematically, such as material modification concentration, deposition time, deposition potential, and pH value. Under optimized conditions, the proposed sensor exhibited a wide linear range from 37.5 nM to 2.0 μM with a low detection limit of 6.3 nM. Meanwhile, the proposed sensor showed good stability, acceptable reproducibility, and satisfactory selectivity. The reliability of the as-proposed sensor was confirmed by the ICP-MS method for Pb²⁺ detection in different samples.

Electric Field-Induced Specific Preconcentration to Enhance DNA-Based Electrochemical Sensing of Hg2+ via the Synergy of Enrichment and Self-Cleaning

Efficient preconcentration is critical for sensitive and selective electrochemical detection of metal ions, but rapid specific enrichment with depressed absorption of interfering ions at the electrode is challenging. Here, we proposed an electric field-induced specific preconcentration to boost the analytical performance of DNA-based electrochemical sensors for Hg²⁺ detection. As for such preconcentration, a positive external electric field was first used to enrich Hg²⁺ at an electrode assembled with T-rich DNA, thus boosting T-Hg²⁺-T recognitions. The following applied inverse electric field strips the nonspecifically absorbed Hg²⁺ and other interfering ions, thus depressing matrix interferences via self-cleaning. Based on this principle, we designed a portable device to realize programmable control of electric fields; a T-Hg²⁺-T recognition-based electrochemical sensor was thus fabricated as a model platform to assess the feasibility of electric field-induced preconcentration. The experimental results revealed that such a strategy decreased the time of T-Hg²⁺-T-based recognition from 60 to 20 min and led to detection with better reproducibility by depressing the influence of free Hg²⁺ as well as interfering ions. This strategy offered Hg²⁺ detection limits of 0.01 pM─three-fold better than that without preconcentration─within 22 min. The proposed preconcentration strategy offers a new way to enhance the analytical performance of sensing at the solid-liquid interface.

Sensing Material-Dependent Interference of Multiple Heavy Metal Ions: Experimental and Simulated Thermodynamics Study on Cu(II), Cd(II), and As(III) Electroanalysis

Interference among multiple heavy metal ions (HMIs) is a significant problem that must be solved in electroanalysis, which extremely restricts the practical popularization of electrochemical sensors. However, due to the limited exploration of the intrinsic mechanism, it is still difficult to confirm the influencing factors. In this work, a series of experimental and theoretical electroanalysis models have been established to investigate the electroanalysis results of Cu(II), Cd(II), As(III), and their mixtures, which were based on the simple structure and stable coordination of nickel single-atom catalysts. X-ray absorption spectroscopy and density functional theory calculations were used to reveal the underlying detection mechanism of the 50-fold boosting effect of Cu(II) on As(III) while Cd(II) inhibits As(III). Combining the application of the thermodynamic model and Fourier transform infrared reflection, the specific interaction of the nanomaterials and HMIs on the interface is considered to be the fundamental source of the interference. This work opens up a new way of thinking about utilizing the unique modes of interplay between nanomaterials and HMIs to achieve anti-interference intelligent electrodes in stripping analysis.

A novel miniaturized electroanalytical device integrated with gas extraction for the voltammetric determination of sulfite in beverages

Voltammetry and amperometry are inexpensive and high-performance analytical techniques. However, their lack of selectivity limits their use in complex matrices such as biological, environmental, and food samples. Therefore, voltammetric and amperometric analyses of these samples usually require time-consuming and laborious sample pretreatments. In this study, we present a simple and cost-effective approach to fabricate a miniaturized electrochemical cell that can be easily coupled to a head space-like gas extraction procedure in such a way the sample pretreatment and voltammetric detection are performed in a single step. As a proof of concept, we have used the proposed system to quantify sulfite in beverage samples after its conversion to SO_2(g). Despite the simplicity and low cost of the proposed system, it provided good analytical performance and a limit of detection of 4.0 μmol L^-1 was achieved after only 10 min of extraction. The proposed system is quite versatile since it can be applied to quantify any volatile electroactive species. Also, the proposed system provides a unique way to assess real-time extraction curves, which are essential to study and optimize new gas extraction procedures. Therefore, the approach described in this study could contribute to both applied and fundamental Analytical Chemistry.

Electrochemical detection of heavy metal ions in water

Heavy metal ions are one of the main sources of water pollution. Most heavy metal ions are carcinogens that pose a threat to both ecological balance and human health. With the increasing demand for heavy metal detection, electrochemical detection is favorable due to its high sensitivity and efficiency. Here, after discussing the pollution sources and toxicities of Hg(ii), Cd(ii), As(iii), Pb(ii), UO₂(ii), Tl(i), Cr(vi), Ag(i), and Cu(ii), we review a variety of recent electrochemical methods for detecting heavy metal ions. Compared with traditional methods, electrochemical methods are portable, fast, and cost-effective, and they can be adapted to various on-site inspection sites. Our review shows that the electrochemical detection of heavy metal ions is a very promising strategy that has attracted widespread attention and can be applied in agriculture, life science, clinical diagnosis, and analysis.

Quantitative benefit and risk assessment of cadmium and nutrient levels in Chinese mitten crab (Eriocheir sinensis)

The use of Chinese mitten crabs for human consumption is controversial due to their uptake of heavy metals, such as cadmium (Cd). We developed a formula for quantification of benefit and risk assessment (hazard quotient) for the intake of a product containing essential polyunsaturated fatty acids versus heavy metals. A total of 70 samples (2100 individuals) of crabs were collected from 6 representative basins in Jiangsu province to determine Cd levels. Cd levels ranged from 0.028 to 5.015 mg kg^-1, and the levels among the basin regions were similar (p > 0.05). To determine the nutritional differences between crabs fed with iced trash fish and formulated feed, we conducted a comparative aquaculture experiment. We simulated the cultivation conditions of crabs in China and found that the nutritional content in the trash fish group (28.724 ± 2.301 mg kg^-1) was significantly higher than in the formulated food group (19.278 ± 3.556 mg kg^-1; p < 0.05). The differences in the hazard quotient of benefit and risk balance between these two diets were not significant (p > 0.05). The average hazard quotient of iced trash fish feed culture was 0.023 ± 0.019, compared with the formulated feed culture (0.034 ± 0.028). Formulated feed and iced trash fish produce similar results as culture food for the Chinese mitten crab. In terms of cadmium exposure risk, the appropriate daily consumption of crabs is less than eight. These data can help justify culture using formulated food and the sustainable development of the Chinese mitten crab industry.

Synthesis of imprinted chitosan/AuNPs/graphene-coated MWCNTs/Nafion film for detection of lead ions

An ultrasensitive electrochemical platform based on ion-imprinted nanocomposites for monitoring Pb²⁺ was proposed for environmental protection and food safety applications.

Geospatial visualisation of food contaminant distributions: Polychlorinated naphthalenes (PCNs), potentially toxic elements (PTEs) and aflatoxins

Large volume of multidimensional data can be summarised, both in terms of tabulated statistics, and as graphic geospatial visualisations. The latter approach allows rapid interpretation and communication of complex information to stake-holders such as regulators, risk assessors and policy makers. In the main study on polychlorinated naphthalene (PCN), individual samples representing different edible fish species were analysed from around the UK. PCNs were observed in all samples with nearly all of the twelve measured congeners being detected. Summed congener concentrations ranged from 0.7 ng/kg ww (turbot) to 265 ng/kg ww (sprats). The highest contamination levels were recorded for sprats and mackerel with mean summed concentrations of 67 ng/kg ww and 68 ng/kg ww respectively. Two ancillary studies, on potentially toxic elements (PTEs) in crabs from China and aflatoxin in children's blood from Tanzania, demonstrate the wide applicability of this approach. The PTE contents in crab showed strong dependence on the tested tissues and elements, and crabs from Tai and Yangcheng Lakes showed obviously higher PTE levels than the other lakes. Geospatial distribution of the aflatoxin biomarker AF-alb in children's serum from 3 locations showed how individual anthropometric or socio-economic data reveals the relationship between family size, socio-economic score and magnitude of serum aflatoxin levels. In addition to facilitating the flow of interpreted data to stakeholders, these techniques can direct the formulation of risk mitigation activities and help with the identification of data gaps. When combined with hierarchical cluster analyses, correlations within the data can also be predicted.

A High Sensitivity IDC-Electronic Tongue Using Dielectric/Sensing Membranes with Solvatochromic Dyes

In this paper, an electronic tongue/taste sensor array containing different interdigitated capacitor (IDC) sensing elements to detect different types of tastes, such as sweetness (glucose), saltiness (NaCl), sourness (HCl), bitterness (quinine-HCl), and umami (monosodium glutamate) is proposed. We present for the first time an IDC electronic tongue using sensing membranes containing solvatochromic dyes. The proposed highly sensitive (30.64 mV/decade sensitivity) IDC electronic tongue has fast response and recovery times of about 6 s and 5 s, respectively, with extremely stable responses, and is capable of linear sensing performance (R² ≈ 0.985 correlation coefficient) over the wide dynamic range of 1 µM to 1 M. The designed IDC electronic tongue offers excellent reproducibility, with a relative standard deviation (RSD) of about 0.029. The proposed device was found to have better sensing performance than potentiometric-, cascoded compatible lateral bipolar transistor (C-CLBT)-, Electronic Tongue (SA402)-, and fiber-optic-based taste sensing systems in what concerns dynamic range width, response time, sensitivity, and linearity. Finally, we applied principal component analysis (PCA) to distinguish between various kinds of taste in mixed taste compounds.

Microwave-assisted synthesis of BSA-stabilised gold nanoclusters for the sensitive and selective detection of lead(ii) and melamine in aqueous solution

MW-assisted synthesis of fluorescent BSA-AuNCs for the turn-off sensing of Pb(ii) and turn-on sensing of melamine.