Linear sweep anodic stripping voltammetry of heavy metals from nitrogen doped tetrahedral amorphous carbon thin films

L-Tryptophan-based pyrene conjugate for intracellular zinc-guided excimer emission and controlled nano-assembly

This article describes intracellular zinc-induced excimer emission and tuning of self-assembly from L-tryptophan-pyrene conjugate (1). The zinc-guided excimer formation is due to the interaction of the pyrene moiety in an excited state. AFM studies show the structural modification in the supramolecular nano-assembly of 1 from dome-shaped to porous surface after complexation with zinc ions. Further, the interaction of 1 with Zn(II) ion is also studied using DFT, Job's plot, NMR titration and HRMS. The results of Zn(II) ion determination in natural water samples and RAW 264.7 cells demonstrate the practical utility of 1.

Synthesis of carbazole-based dendritic conjugated polymer: a dual channel optical probe for the detection of I- and Hg2

A new type of carbazole-based blue-emitting dendritic conjugated polymer, poly[(9,9-dioctyl)-2,7-fluorene-co-4,4’,4”-triphenylamine-co-9-(4-(9H-carbazol-9-yl)butyl)-3,6-carbazole](P), was successfully synthesized by Suzuki coupling reaction. Chemical structures of monomers and polymer were verified by FI-IR and ¹HNMR characterizations. We found that polymer showed a special selectivity and high sensitivity for I⁻. With the addition of I⁻, the fluorescent polymer solution was obviously quenched. The polymer showed a special detection effect on I⁻. However, the fluorescent polymer was obviously restored when Hg²⁺ was added to the P/I⁻ system due to the large complexation between I⁻ and Hg²⁺. The anti-interference experiments of probe P/I⁻ showed that other background cations have a slight influence on detecting Hg²⁺, and the calculated detection limit of Hg²⁺ reached 9.7 × 10⁻⁸ M, which could be a potential application for a two-channel cyclic detection of I⁻ and Hg²⁺. Additionally, it was found that the theoretical values were in agreement with the experimental data.

An Efficient Inclusion Complex Based Fluorescent Sensor for Mercury (II) and its Application in Live-Cell Imaging

The formation of an inclusion complex between hydroxypropyl-β-cyclodextrin (H-CD) and 4-acetylphenyl-4-(((6-chlorobenzo[d]thiazol-2-yl)-imino)-methyl)-benzoate (L) was investigated by FT-IR, ¹H-NMR, X-ray diffraction (XRD), FT-Raman, scanning electron microscope (SEM) techniques in the solid-state, absorption and emission spectroscopy in the liquid state and the virtual state as molecular docking technique. The binding properties of the inclusion complex (H-CD: L) with cations in deionized water was observed via absorbance and photoluminescence (PL) emission spectroscopy. The fluorescence probe (H-CD: L) inclusion complex (IC) was examined for several heavy metal cations, and identified that the PL emission wavelength of the complex displayed a continuous rise in the fluorescence intensity for Hg²⁺. A linearity range of 1 × 10^-8 - 11 × 10^-8 M and limit of detection value of 2.71 × 10^-10 M was found to be achieved for the detection of Hg²⁺. This outcome proves that the inclusion complex H-CD: L would be a promising material for the development a solid-state fluorescence probe for detecting Hg²⁺. It also shows application in real sample analysis and cell imaging.

Suppression of Surface Oxygen on Nanocarbon Film Electrodes for Maintaining Electrode Activity

We investigated sputtered nanocarbon films with respect to the effect of suppressing surface oxygen on their electrochemical properties. The nanocarbon film consisted of nanocrystallites with mixed sp² and sp³ bonds formed by unbalanced magnetron sputtering. Ultraviolet/ozone (UV/O₃) irradiation and electrochemical pretreatment (ECP) were conducted to change the surface oxygen concentration of nanocarbon film. X-ray photoelectron spectroscopy (XPS) measurements revealed that nanocarbon films with different amounts of surface oxygen could be prepared. In addition, we observed no significant increase of the surface roughness (R_a) at the angstrom level after treatments, owing to a stable structure containing 40% of sp³ bonds. The electrode characteristics, including the potential window and electrochemical properties for some redox species, such as Ru(NH₃)₆^3+/2+, were investigated. Some electrochemical measurements of zinc ions (Zn²⁺) and hydrogen peroxide (H₂O₂) showed that the electrochemical reaction was improved by suppressing the surface oxygen. These results clearly indicated that the low surface oxygen concentration plays an important role in these electrochemical reactions.

Electrospun Nanofibers and Electrochemical Techniques for the Detection of Heavy Metal Ions

Contamination by heavy metals is currently one of the most environmental concerns especially due to the toxicity, pervasiveness, and persistence of these substances. As they are not biodegradable, heavy metals are harmful not only for water, air, and soil but also for human health, even in very low traces. There is therefore a pressing need to develop an efficient, economic, and rapid analysis method to be applied in a wide range of conditions and able to detect very low contaminants concentrations. Currently, the most novel solution in this field is represented by the combination of electrospun nanofibers and highly sensitive electrochemical techniques. It has been proved that nanofibers, due to their outstanding properties, perfectly fit as sensing material when trace concentrations of heavy metals were investigated by anodic stripping voltammetry, envisaged as the most sensitive electrochemical technique for this kind of measurements. This work aims to provide an overview of the latest trends in the detection of contaminants by the simultaneous use of electrospun fibers and anodic stripping voltammetry. Indeed, a clear and comprehensive vision of the current status of this research may drive future improvements and new challenges.

Bovine Serum Albumin Enhances Silver Nanoparticle Dissolution Kinetics in a Size- and Concentration-Dependent Manner

The dissolution of silver nanoparticles (AgNPs) to release Ag(I)(aq) is an important mechanism in potentiating AgNP cytotoxicity and imparting their antibacterial properties. However, AgNPs can undergo other simultaneous biophysicochemical transformations, such as protein adsorption, which can mediate AgNP dissolution behaviors. We report the comprehensive analysis of AgNP dissolution and protein adsorption behaviors with monolayer surface coverage of AgNPs by bovine serum albumin (BSA). AgNP dissolution rate constants, k_dissolution, were quantified over several particle sizes (10, 20, and 40 nm) and BSA concentrations (0-2 nM) using linear sweep stripping voltammetry. Across all particle sizes, the dissolution rate constant increased with increasing BSA concentrations. However, protein-enhanced dissolution behaviors were most pronounced for 10 nm AgNPs, which exhibited 3.6-fold and 7.7-fold relative enhancement when compared to 20 and 40 nm AgNPs, respectively. Changes to AgNP surface properties upon interaction with BSA were monitored using dynamic light scattering and zeta potential measurements, while BSA-AgNP complex formation was evaluated using UV-vis spectroscopy and circular dichroism spectroscopy. A subtle increase in the BSA-AgNP association constant was observed with an increase in the AgNP size. Together, these results suggest that the AgNP size dependence of BSA-enhanced dissolution of AgNPs is possibly mediated through both displacement of Ag(I)(aq)-loaded BSA by excess protein in the bulk solution and minimized accessibility of the AgNP surface because of BSA adsorption.

Determination of Heavy Metals in Herbal Food Supplements using Bismuth/Multi-walled Carbon Nanotubes/Nafion modified Graphite Electrodes sourced from Waste Batteries

An electrochemical sensor based on graphite electrode extracted from waste zinc-carbon battery is developed. The graphite electrode was modified with bismuth nanoparticles (BiNP), multi-walled carbon nanotubes (MWCNT) and Nafion via the drop coating method. The bare and modified graphite electrodes were used as the working electrode in anodic stripping voltammetry for the determination of trace amounts of cadmium (Cd²⁺) and lead (Pb²⁺). The modified electrode exhibited excellent electroanalytical performance for heavy metal detection in comparison with the bare graphite electrode. The linear concentration range from 5 parts per billion (ppb) to 1000 ppb (R² = 0.996), as well as detection limits of 1.06 ppb for Cd²⁺ and 0.72 ppb for Pb²⁺ were obtained at optimized experimental conditions and parameters. The sensor was successfully utilized for the quantification of Cd²⁺ and Pb²⁺ in herbal food supplement samples with good agreement to the results obtained by atomic absorption spectroscopy. Thus, the BiNP/MWCNT/Nafion modified graphite electrode is a cost-effective and environment-friendly sensor for monitoring heavy metal contamination.

A novel coumarin-based fluorescence chemosensor for Al3+ and its application in cell imaging

As an efficient turn-on fluorescent chemosensor for Al³⁺, a new coumarin derivative (CND) has been designed and synthesized by the condensation of 8-formyl-7-hydroxycoumarin with niacin hydrazide. The spectroscopic studies revealed that the sensor CND exhibited a remarkable fluorescence enhancement towards Al³⁺ with high selectivity and sensitivity in EtOH-HEPES (95:5, v/v, pH = 7.40), which was attributed to the photoinduced electron transfer (PET) and CN isomerization mechanism. Fluorescence titration calculations data showed that the detection limit and the association constants of CND for Al³⁺ were found to be 2.51 × 10^-7 M and 9.64 × 10⁴ M^-1, respectively. The results of experiments, including Job's plot, ¹H NMR titration and ESI-MS, revealed that the stoichiometric binding between CND and Al³⁺ was 1:1. The investigations of the pH dependency of CND for Al³⁺ detection, and the cell imaging suggested the sensor CND could be promisingly applied for the recognition of Al³⁺ in biological cells.

Raspberry-Like Bismuth Oxychloride on Mesoporous Siliceous Support for Sensitive Electrochemical Stripping Analysis of Cadmium

BiOCl-SiO₂ KIT-6 composite materials with raspberry-like structures are facilely prepared under hydrothermal conditions. The mesoporous siliceous support of SiO₂ KIT-6-incorporated BiOCl with enlarged yet refined surface morphology characterized by physiochemical methods exhibits an improved electrochemical performance. A sensitive electrochemical detection method of cadmium concentration using square wave anodic stripping voltammetry was developed based on BiOCl-SiO₂ KIT-6 composite-modified glassy carbon electrodes, which displayed wide linear ranges of 0.5 to 10 μg/L and 10 to 300 μg/L and a detection limit of 65 ng/L. The sensitive, versatile and eco-friendly sensor was successfully applied for the determination of cadmium-spiked human blood samples.

Recent development of carbon electrode materials and their bioanalytical and environmental applications

New synthetic approaches, materials, properties, electroanalytical applications and perspectives of carbon materials are presented.

Modified electrodes used for electrochemical detection of metal ions in environmental analysis

Heavy metal pollution is one of the most serious environmental problems, and regulations are becoming stricter. Many efforts have been made to develop sensors for monitoring heavy metals in the environment. This review aims at presenting the different label-free strategies used to develop electrochemical sensors for the detection of heavy metals such as lead, cadmium, mercury, arsenic etc. The first part of this review will be dedicated to stripping voltammetry techniques, on unmodified electrodes (mercury, bismuth or noble metals in the bulk form), or electrodes modified at their surface by nanoparticles, nanostructures (CNT, graphene) or other innovative materials such as boron-doped diamond. The second part will be dedicated to chemically modified electrodes especially those with conducting polymers. The last part of this review will focus on bio-modified electrodes. Special attention will be paid to strategies using biomolecules (DNA, peptide or proteins), enzymes or whole cells.

Recent trends in monitoring of European water framework directive priority substances using micro-sensors: a 2007-2009 review

This review discusses from a critical perspective the development of new sensors for the measurement of priority pollutants targeted in the E.U. Water Framework Directive. Significant advances are reported in the paper and their advantages and limitations are also discussed. Future perspectives in this area are also pointed out in the conclusions. This review covers publications appeared since December 2006 (the publication date of the Swift report). Among priority substances, sensors for monitoring the four WFD metals represent 81% of published papers. None of analyzed publications present a micro-sensor totally validated in laboratory, ready for tests under real conditions in the field. The researches are mainly focused on the sensing part of the micro-sensors. Nevertheless, the main factor limiting micro-sensor applications in the environment is the ruggedness of the receptor towards environmental conditions. This point constitutes the first technological obstacle to be overcome for any long-term field tests.