Highly selective in situ metal ion determination by hybrid electrochemical “adsorption–desorption” and colorimetric methods

Conductive electrospun composite fibers based on solid-state polymerized Poly(3,4-ethylenedioxythiophene) for simultaneous electrochemical detection of metal ions

Conductive composite fibers containing poly (3,4-ethylenedioxythiophene) (PEDOT) and silver nanoparticles (AgNPs) were fabricated by emulsion electrospinning of 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) in toluene together with aqueous solution of poly (vinyl alcohol) (PVA) and silver nanoparticles (AgNPs) in the presence of sodium dodecylsulfate followed by heat treatment at 70 °C to convert DBEDOT to conductive PEDOT via solid state polymerization (SSP). The composite fibers were characterized by scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and thermogravimetric analysis. The PEDOT/PVA/AgNPs composite fibers deposited on a screen-printed carbon electrode (SPCE) surface exhibited good electrochemical response and was applied for simultaneous detection of heavy metal ions in a mixture, namely Zn(II), Cd(II), and Pb(II) via square wave anodic stripping voltammetry (SWASV). With added Bi⁺³ into the detection system, the bismuth film formed on the electrode allows effective alloy formation with the deposited heavy metals obtained upon reduction of the heavy metal ions, the detection of heavy metal ions after stripping was successfully accomplished with a linear range of 10-80 ppb and limits of detections (LOD) of 6, 3 and 8 ppb for Zn(II), Cd(II), and Pb(II), respectively.

Method for analysis of environmental lead contamination in soils

A method for lead (Pb) detection in soil is presented. Pb is a dangerous environmental pollutant that is present in soils, posing a health risk to millions of people worldwide, and regular monitoring of Pb contamination in soils is essential to public health. Many sensitive methods for detection of heavy metals in solid matrices exist, but they cannot be performed on-site because they are costly (>$30 per sample), require trained personnel, and many classical sample preparation methods are not safe to bring into the field. We describe an alternative process, combining a safer sample preparation method with electrochemical analysis. The process requires minimal training, making it an attractive overall method for regular environmental screening of Pb in soils. Extract obtained from the soil is pH adjusted and analyzed using a stencil-printed carbon electrode and square wave anodic stripping voltammetry. In this work, a study of 15 neighborhood soils examining the concentration of Pb present post-extraction was performed to demonstrate the method. The limit of detection for the electrochemical analysis was calculated to be 16 ppb-well below the United States Environmental Protection Agency's action limit for Pb in soils (400 mg kg^-1 or 4000 ppb)-and third party inductively coupled plasma-optical emission spectroscopy analysis validated the results obtained in this study to within ±17% on average.

Novel electro self-assembled DNA nanospheres as a drug delivery system for atenolol

We describe new method for preparing DNA nanospheres for a self-assembled atenolol@DNA (core/shell) drug delivery system. In this paper, we propose the electrochemical transformation of an alkaline polyelectrolyte solution of DNA into DNA nanospheres. We successfully electrosynthesized DNA nanospheres that were stable for at least 2 months at 4 °C. UV-visible spectra of the prepared nanospheres revealed a peak ranging from 372 to 392 nm depending on the DNA concentration and from 361 to 398.3 nm depending on the electrospherization time. This result, confirmed with size distribution curves worked out from transmission electron microscopy (TEM) images, showed that increasing electrospherization time (6, 12 and 24 h) induces an increase in the average size of DNA nanospheres (48, 65.5 and 117 nm, respectively). In addition, the average size of DNA nanospheres becomes larger (37.8, 48 and 76.5 nm) with increasing DNA concentration (0.05, 0.1 and 0.2 wt%, respectively). Also, the affinity of DNA chains for the surrounding solvent molecules changed from favorable to bad with concomitant extreme reduction in the zeta potential from -31 mV to -17 mV. Principally, the attractive and hydrophobic interactions tend to compact the DNA chain into a globule, as confirmed by Fourier transform infrared spectroscopy (FTIR) and TEM. To advance possible applications, we successfully electro self-assembled an atenolol@DNA drug delivery system. Our findings showed that electrospherization as a cost-benefit technique could be effectively employed for sustained drug release. This delivery system achieved a high entrapment efficiency of 68.03 ± 2.7% and a moderate drug-loading efficiency of 3.73%. The FTIR spectra verified the absence of any chemical interaction between the drug and the DNA during the electrospherization process. X-ray diffraction analysis indicated noteworthy lessening in atenolol crystallinity. The present findings could aid the effectiveness of electrospherized DNA for use in various other pharmaceutical and biomedical applications.

Hierarchical Porous Carbon Electrodes with Sponge-Like Edge Structures for the Sensitive Electrochemical Detection of Heavy Metals

This article presents the development of a highly sensitive electrochemical heavy metal sensor based on hierarchical porous carbon electrodes with sponge-like edge structures. Micrometer-scale hierarchical nanoporous carbon electrodes were fabricated at a wafer-scale using cost-effective batch microfabrication technologies, including the carbon microelectromechanical systems technology and oxygen plasma etching. The sponge-like hierarchical porous structure and sub-micrometer edges of the nanoporous carbon electrodes facilitate fast electron transfer rate and large active sites, leading to the efficient formation of dense heavy metal alloy particles of small sizes during the preconcentration step. This enhanced the peak current response during the square wave anodic stripping voltammetry, enabling the detection of Cd(II) and Pb(II) at concentrations as low as 0.41 and 0.7 μg L⁻¹, respectively, with high sensitivity per unit sensing area (Cd: 109.45 nA μg⁻¹ L mm⁻², Pb: 100.37 nA μg⁻¹ L mm⁻²).

A dual-responsive biosensor for blood lead detection

Simple and accurate detection of trace heavy metals in blood is very important. A novel dual-responsive electrochemical/fluorescent biosensor based on magnetic hyperbranched polyamide with heparin modification (MHPAM-H) for blood lead detection has been successfully developed. Upon conjugated with blood lead ions, dual-biosensor could not only display electrochemical signal but also fluorescence signal owing to the enriched amino groups, cavity structure, and good fluorescence properties of HPAM. Blood biocompatibility, construction of the dual-responsive biosensor, electrochemical/fluorescent detection of lead ions in water phase and blood condition, selectivity and stability of the dual-responsive biosensor were investigated in detail. The proposed dual-responsive biosensor displays good linear relationship (1.5 pM- 4.8 × 10³ pM for electrochemical detection and 0.5 pM-4.8 × 10³ pM for fluorescent detection) with low detection limit (4.4 pM for electrochemical detection and 1.0 pM for fluorescent detection) for blood lead, providing potential application for blood lead detection in the future.

A multi-functional minimally-disruptive portable electrochemical system based on yeast/Co3O4/Au/SPEs for blood lead (II) measurement

A minimally-disruptive portable electrochemical system is constructed by combining a hand-held syringe as reservoir with disposable screen-printed electrodes (SPEs) modified with a simple and efficient yeast/Co₃O₄/Au material for lead determination by a square-wave voltammetry (SWV) method. Not only can it preserve the operation and advantages of the conventional electrochemical procedure, but it also integrates sampling, filtering and analysis to make the determination of lead convenient and effective at higher and lower concentration levels. This is the first report of a microbial biosensor based on active yeast crosslinked to Co₃O₄/Au particles using glutaraldehyde as the crosslinking agent. The determination process is simplified by introducing a fiber filter and takes only 150 s with the developed system, which illustrates its simplicity, speed and detection accuracy. Also, the design shows a wide log-linear dynamic range (LDR) from 10^-8 to 10^-14 g·L^-1, with a limit of detection (LOD) of 3.45 × 10^-15 g·L^-1 (S/N = 3). Additionally, the proposed system was used to determine lead in blood samples, which demonstrated the potential of this biosensor for use in practical applications. Furthermore, this study provides a basis for the development of microscale blood devices for lead measurement.

Non-innocent PNN ligand is important for CO oxidation by N2O catalyzed by a (PNN)Ru-H pincer complex: insights from DFT calculations

Milstein et al. developed an efficient and mild method for CO oxidation by N₂O to give CO₂ and N₂ catalyzed by a (PNN)Ru-H pincer complex. To gain mechanistic information on this catalytic transformation, the reaction mechanism has been studied using density functional theory (DFT) calculations. It was found that the catalytic cycle for CO oxidation by N₂O proceeds in three stages: N₂O activation to form a (PNN)Ru-OH intermediate, CO insertion into the Ru-OH bond to form a (PNN)Ru-COOH intermediate and CO₂ release from (PNN)Ru-COOH. In the CO₂ release stage, CO₂ is not released via a β-H elimination mechanism as proposed in experiments, instead it is released via a deprotonation mechanism. The calculations demonstrated that the Ru-H bond of the catalyst plays an important role in facilitating the activation of N₂O, which is the rate-determining step for the whole catalytic cycle, and the non-innocent PNN ligand is very important for CO oxidation by N₂O. Our theoretical results are consistent with the experimental observations and could help design highly efficient catalysts for N₂O activation.

The screening of metal ion inhibitors for glucose oxidase based on the peroxidase-like activity of nano-Fe3O4

In this study, a colorimetric method is proposed based on the peroxidase-like activity of Fe₃O₄magnetic nanoparticles for screening metal ion inhibitors for glucose oxidase activity.

Recent Advances in the Fabrication and Application of Screen-Printed Electrochemical (Bio)Sensors Based on Carbon Materials for Biomedical, Agri-Food and Environmental Analyses

This review describes recent advances in the fabrication of electrochemical (bio)sensors based on screen-printing technology involving carbon materials and their application in biomedical, agri-food and environmental analyses. It will focus on the various strategies employed in the fabrication of screen-printed (bio)sensors, together with their performance characteristics; the application of these devices for the measurement of selected naturally occurring biomolecules, environmental pollutants and toxins will be discussed.

Sensitive electrochemical sensor using a graphene-polyaniline nanocomposite for simultaneous detection of Zn(II), Cd(II), and Pb(II)

This work describes the development of an electrochemical sensor for simultaneous detection of Zn(II), Cd(II), and Pb(II) using a graphene-polyaniline (G/PANI) nanocomposite electrode prepared by reverse-phase polymerization in the presence of polyvinylpyrrolidone (PVP). Two substrate materials (plastic film and filter paper) and two nanocomposite deposition methods (drop-casting and electrospraying) were investigated. Square-wave anodic stripping voltammetry currents were higher for plastic vs. paper substrates. Performance of the G/PANI nanocomposites was characterized by scanning electron microscopy (SEM) and cyclic voltammetry. The G/PANI-modified electrode exhibited high electrochemical conductivity, producing a three-fold increase in anodic peak current (vs. the unmodified electrode). The G/PANI-modified electrode also showed evidence of increased surface area under SEM. Square-wave anodic stripping voltammetry was used to measure Zn(II), Cd(II), and Pb(II) in the presence of Bi(III). A linear working range of 1-300 μg L(-1) was established between anodic current and metal ion concentration with detection limits (S/N=3) of 1.0 μg L(-1) for Zn(II), and 0.1 μg L(-1) for both Cd(II) and Pb(II). The G/PANI-modified electrode allowed selective determination of the target metals in the presence of common metal interferences including Mn(II), Cu(II), Fe(III), Fe(II), Co(III), and Ni(II). Repeat assays on the same device demonstrated good reproducibility (%RSD<11) over 10 serial runs. Finally, this system was utilized for determining Zn(II), Cd(II), and Pb(II) in human serum using the standard addition method.

Ion-selective gold-thiol film on integrated screen-printed electrodes for analysis of Cu(II) ions

A novel type of ion-selective electrode (ISE) was manufactured for detecting trace amounts of Cu(II) ions. The basic substrates of ISE were fabricated using screen-printing technology, which could produce disposable electrodes on a large-scale with good repeatability. Moreover, the printed integrated three-electrode system of ISE could be directly used to read out the open-circuit potentials by a handheld device through a USB port. The ion-selective film was composed of gold nanorods (GNRs) and 6-(bis(pyridin-2-ylmethyl)amino)hexane-1-thiol (compound ), which were layer-by-layer modified on the electrode through an easily controlled self-assembly method. Compound contained the 2,2'-dipyridylamine (dpa) group that could coordinate with Cu(II) ions to form a 2 : 1 complex, therefore the screen-printed ISEs exhibited Nernstian potentiometric responses to Cu(II) ions with a detection limit of 6.3 × 10(-7) mol L(-1) over the range of 1.0 × 10(-6) to 1.0 × 10(-2) mol L(-1). The easily prepared screen-printed ion-selective electrode reported here was appropriate for in field analysis and pollutant detection in remote environments.

Fabrication of gold nanoparticles by laser ablation in liquid and their application for simultaneous electrochemical detection of Cd2+, Pb2+, Cu2+, Hg2+

In this paper, we demonstrated the fabrication of high active and high sensitive Au nanoparticles by laser ablation in liquid (LAL) method, and their application in electrochemical detection of heavy metal ions. First, LAL method are used to fabricate Au nanoparticles in water in a clean way. Second, the Au nanoparticles were assembled onto the surface of the glassy carbon (GC) electrode by an electrophoretic deposition method to form an AuNPs/GC electrode for electrochemical characterization and detection. Through differential pulse anodic stripping voltammetry method, it shows that the AuNPs/GC electrode could be used for the simultaneous and selective electrochemical detection of Cd(2+), Pb(2+), Cu(2+), and Hg(2+). By studying the influence of test conditions to optimize the electrochemical detection, we can detect Cd(2+), Pb(2+), Cu(2+), and Hg(2+) simultaneously with a low concentration of 3 × 10(-7) M in the experiments.