Voltammetric determination of trace mercury in chloride media at glassy carbon electrodes modified with polycationic ionomers

Fluorescent N-functionalized carbon nanodots from carboxymethylcellulose for sensing of high-valence metal ions and cell imaging

N-CDs were synthesized using simple and fast one-pot hydrothermal treatment, and were successfully applied as sensors for the selective detection of environmental high-valence metal ions and cellular imaging.

Picomolar-level detection of mercury within non-biological/biological aqueous media using ultra-sensitive polyaniline-Fe3O4-silver diethyldithiocarbamate nanostructure

Mercury as the 3rd most toxic, non-biodegradable, and carcinogenic pollutant can adversely affect the ecosystem and health of living species through its bioaccumulation within the nature that can affect the top consumer in the food chain; therefore, it is vital to sense/remove Hg²⁺ within/from aqueous media using practical approaches. To address this matter, we modified the glassy carbon electrode (GCE) with ultra-sensitive, interconnected, sulfurized, and porous nanostructure consisted of polyaniline-Fe₃O₄-silver diethyldithiocarbamate (PANi-F-S) to enhance the sensitivity, selectivity, and limit of detection (LOD) of the sensor. Obtained results showed that at optimum conditions (i.e., pH value of 7, deposition potential of - 0.8 V, and accumulation time of 120 s), for Hg²⁺ concentration ranging from 0.4 to 60 nM, the modified electrode showing linear relative coefficient of 0.9983, LOD of 0.051 nM, LOQ of 0.14 nM, and sensitivity of 1618.86 μA μM^-1 cm^-2 highlights superior sensitivity of the developed platform until picomolar level. Additionally, the modified electrode showed ideal repeatability, stability, reproducibility, and selectivity (by considering Zn²⁺, Cd²⁺ Pb²⁺, Cu²⁺, Ni²⁺, and Co²⁺ as metal interferences) and recovered more than 99% of the Hg²⁺ ions within non-biological (mineral, tap, and industrial waters) and biological (blood plasma sample) fluids. Graphical abstract.

Voltammetry at Hexamethyl-P-Terphenyl Poly(Benzimidazolium) (HMT-PMBI)-Coated Glassy Carbon Electrodes: Charge Transport Properties and Detection of Uric and Ascorbic Acid

We describe the voltammetric behavior of an anion-exchange membrane, hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI). The anion-exchange properties of HMT-PMBI chemically modified electrodes were investigated using K4Fe(CN)6 and K2IrCl6 as redox probes. The permselectivity properties of HMT-PMBI chemically modified electrodes were ascertained using tris(2-2')bipyridyl-ruthenium(II) chloride Ru(bpy)32+. Cyclic voltammetry and chronoamperometry were utilized to extract parameters such as the concentration of the redox mediators inside the films and the apparent diffusion coefficients. We found the concentration of K4Fe(CN)6 and K2IrCl6 redox species within HMT-PMBI-coated films to be on the order of 0.04-0.1 mol·dm-3, and values of Dapp ca. 10-10-10-9 cm2·s-1. To evaluate the possibility of using such a polymer coating in electroanalysis, HMT-PMBI-modified electrodes were utilized for the voltammetric detection of uric acid in artificial urine, Surine® and ascorbic acid in Vitamin C samples. The results showed that HMT-PMBI-coated electrodes can detect uric acid in Surine® with a limit of detection (LoD) of 7.7 µM, sensitivity of 0.14 µA·µM-1·cm-2, and linear range between 5 μM and 200 μM, whereas for Vitamin C tablets, the LoD is 41.4 µM, the sensitivity is 0.08 µA·µM-1·cm-2, and the linear range is between 25 μM and 450 μM.

Hg2+ detection, pH sensing and cell imaging based on bright blue-fluorescent N-doped carbon dots

A multifunctional sensing platform based on bright blue-fluorescent nitrogen-doped carbon dots (N-CDs) has been ingeniously designed for the sensitive determination of Hg²⁺ and pH.

Highly Photoluminescent and Stable N-Doped Carbon Dots as Nanoprobes for Hg2+ Detection

We developed a microreactor with porous copper fibers for synthesizing nitrogen-doped carbon dots (N-CDs) with a high stability and photoluminescence (PL) quantum yield (QY). By optimizing synthesis conditions, including the reaction temperature, flow rate, ethylenediamine dosage, and porosity of copper fibers, the N-CDs with a high PL QY of 73% were achieved. The PL QY of N-CDs was two times higher with copper fibers than without. The interrelations between the copper fibers with different porosities and the N-CDs were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectroscopy (FTIR). The results demonstrate that the elemental contents and surface functional groups of N-CDs are significantly influenced by the porosity of copper fibers. The N-CDs can be used to effectively and selectively detect Hg²⁺ ions with a good linear response in the 0~50 μM Hg²⁺ ions concentration range, and the lowest limit of detection (LOD) is 2.54 nM, suggesting that the N-CDs have great potential for applications in the fields of environmental and hazard detection. Further studies reveal that the different d orbital energy levels of Hg²⁺ compared to those of other metal ions can affect the efficiency of electron transfer and thereby result in their different response in fluorescence quenching towards N-CDs.

Highly selective monitoring of metals by using ion-imprinted polymers

Ion imprinting technology is one of the most promising tools in separation and purification sciences because of its high selectivity, good stability, simplicity and low cost. It has been mainly used for selective removal, preconcentration, sensing and few miscellaneous fields. In this review article, recent methodologies in the synthesis of IIPs have been discussed. For several applications, different parameters of IIP including complexing and leaching agent, pH, relative selectivity coefficient, detection limit and adsorption capacity have been evaluated and an attempt has been made to generalize. Biomedical applications mostly include selective removal of toxic metals from human blood plasma and urine samples. Wastewater treatment involves selective removal of highly toxic metal ions like Hg(II), Pb(II), Cd(II), As(V), etc. Preconcentration covers recovery of economically important metal ions such as gold, silver, platinum and palladium. It also includes selective preconcentration of lanthanides and actinides. In sensing, various IIP-based sensors have been fabricated for detection of toxic metal ions. This review article includes almost all metal ions based on the ion-imprinted polymer. At the end, the future outlook section presents the discussion on the advancement, corresponding merits and the need of continued research in few specific areas. Graphical Abstract IIPs for the selective monitoring of metals.

Nitrogen-doped, thiol-functionalized carbon dots for ultrasensitive Hg(ii) detection

Nitrogen-doped, PEGylated carbon dots (C-dots) have been synthesized for the ultra sensitive detection of mercury ions (Hg²⁺).

Biosensors for detection of mercury in contaminated soils

Biosensors based on whole bacterial cells and on bacterial heavy metal binding protein were used to determine the mercury concentration in soil. The soil samples were collected in a vegetable garden accidentally contaminated with elemental mercury 25 years earlier. Bioavailable mercury was measured using different sensors: a protein-based biosensor, a whole bacterial cell based biosensor, and a plant sensor, i.e. morphological and biochemical responses in primary leaves and roots of bean seedlings grown in the mercury-contaminated soil. For comparison the total mercury concentration of the soil samples was determined by AAS. Whole bacterial cell and protein-based biosensors gave accurate responses proportional to the total amount of mercury in the soil samples. On the contrary, plant sensors were found to be less useful indicators of soil mercury contamination, as determined by plant biomass, mercury content of primary leaves and enzyme activities.

Determination of selenium(IV) by a photooxidized 3,3'-diaminobenzidine/perfluorinated polymer mercury film electrode

A new, and easily fabricated, chemically modified electrode for the determination of selenium(IV) was examined by cathodic square-wave stripping voltammetry. This new electrode consisted of an anion-exchange perfluorinated polymer (Tosflex) coated thin mercury film electrode containing photooxidized 3,3'-diaminobenzidine (ODAB). The coating solution of Tosflex and ODAB was spin-coated on a glassy carbon electrode followed by electroplating of a thin film of mercury. During the preconcentration, ODAB was reduced electrochemically and selenium was accumulated simultaneously onto the electrode by interacting with the reduced ODAB. After a 5-min preconcentration period, linear response was observed from 0.5 to 50 ppb selenium, and the detection limit was 0.1 ppb. The proposed method does not require a darkened room, which was required in many of the previous methods involving 3,3'-diaminobenzidine. In addition, the resistance to interference from surface-active compounds was improved by incorporating Tosflex in the film.

Preconcentration and voltammetry of mercury on a functionalized sol-gel thin film modified glassy carbon electrode

A functionalized sol-gel thin film modified glassy carbon electrode has been prepared for the determination of mercury. The tetrasulfide in the sol-gel matrix has a high affinity for mercury species. The chemically integrated functional groups in the sol-gel precursor ensure a high chemical and mechanical stability of the modified electrodes, and therefore a stable and reproducible analytical performance. By medium exchange anodic stripping voltammetry, this modified electrode allows reliable, low cost and interference-free determination of mercury.