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Great attention has been paid to the impact of heavy metals due to their abundance and presence in biological and environmental systems. Cr 3+ , among the heavy metals, employed for catalysts, leather tanning, glass, and paints is almost harmless. It is worth mentioning, Cr 3+ has the major role in some metabolic processes. Therefore, there is a fundamental need to introduce a novel, efficient, selective, simple, and low-cost techniques for the determination of Cr 3+ . Herein, the poly (rutin)/carbon black-chitosan nanocomposite-modified glassy carbon electrode (PRu/CB-Chi/GCE) was employed as a selective sensor for Cr 3+ electrochemical determination using differential pulse anodic stripping voltammetry (DPASV) technique. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and field emission scanning electron microscopy (FESEM) were performed to investigate the electrodes. According to optimal conditions, the linear range was achieved between 0.05 nM and 2000 nM with the detection limit (LOD) (S/N = 3) obtained 0.016 nM. The modified electrode was found to indicate the qualities of repeatability, reproducibility, selectivity, and stability ability. To demonstrate the applicability of the sensor, the modified GCE was applied to detect chromium (III) ions in tap and river water samples with good recoveries of 91.54–103.17% – revealing that the sensor has suitable practicability toward Cr 3+ . Graphical abstract

A glassy carbon electrode (GCE) modified with electrochemically reduced graphene oxide (ErGO) and gold nanorods (AuNRs) (GCE/ErGO/AuNRs) was prepared for determining As(III) in bivalve mollusks samples ( Mytilus chilensis ). The modified electrode was characterized by cyclic voltammetry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Chemical and electrochemical parameters were optimized, observing that the presence of AuNRs provides selectivity, while the incorporation of ErGO improves the sensitivity of the modified electrode for the detection of As(III). Using square wave anodic stripping voltammetry (SWASV), a linear range of 2.0–60.0 µg L −1 with a detection limit (LOD) of 0.21 µg L −1 was obtained. The validation was made using water and mussel tissue-certified reference materials (TMDA-64.2 and ERM ® -CE278k, respectively), showing good accuracy and reproducibility. The methodology allowed the determination of As(III) in real samples of marine resources, with excellent results (RSD < 2%). Graphical abstract

A novel low-cost method for simultaneous measurement of Cd2+ and Pb2+ is proposed. In this method, the surface of the glassy carbon electrode (GCE) was modified with multi-walled carbon nanotubes (MWCNTs) and poly(thionine) (PTH), afterward, Pb2+ and Cd2+ were measured simultaneously in the presence of bismuth ions in-situ, using square wave anodic stripping voltammetry (SWASV). Scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to characterize the proposed electrode. Operational parameters affecting the measurement of metal ions were investigated, such as buffer pH and electrochemical parameters. In the optimal conditions, the linear responses were acquired in the concentration range 2.0−400.0 nM for both the analytes. The limit of detection (at S/N = 3) was found to be 0.6 nM for Pb2+and 0.4 nM for Cd2+. The reproducibility, expressed as the relative standard deviation (RSD), was obtained as 4.5% for Cd2+ and 14.7% for Pb2+, (each 5 nM level; for n = 5). The fabricated sensor was employed for the simultaneous determination of the target analytes in real samples with satisfactory results.Graphical Abstract

This paper reports on a sensitive and selective method for the detection of Michigan Cancer Foundation-7 ( MCF-7) human breast cancer cells and MUC1 biomarker by using an aptamer-based sandwich assay. A biocompatible nanocomposite consisting of multiwall carbon nanotubes (MWCNT) and poly(glutamic acid) is placed on a glassy carbon electrode (GCE). The sandwich assay relies on the use of a mucin 1 (MUC1)-binding aptamer that is first immobilized on the surface of modified GCE. Another aptamer (labeled with silver nanoparticles) is applied for secondary recognition of MCF-7 cells in order to increase selectivity and produce an amplified signal. Differential pulse anodic stripping voltammetry was used to follow the electrochemical signal of the AgNPs. Under the optimal condition, the sensor responds to MCF-7 cells in the concentration range from 1.0 × 10 2 to 1.0 × 10 7 cells·mL −1 with a detection limit of 25 cells. We also demonstrate that the MUC1 tumor marker can be detected by the present biosensor. The assay is highly selective and sensitive, acceptably stable and reproducible. This warrants the applicability of the method to early diagnosis of breast cancer. Graphical abstract Schematic of the fabrication of an aptamer-based sandwich biosensor for Michigan Cancer Foundation-7 cells (MCF-7). A MWCNT-poly(glutamic acid) nanocomposite was used as a biocompatible matrix for MUC1-aptamer immobilization. Stripping voltammetry analysis of AgNPs was performed using aptamer conjugated AgNPs as signalling probe.

A versatile voltammetric procedure for quantitative determination of Pb(II) directly in environmental water samples has been proposed. Differential pulse technique in the variant of anodic stripping voltammetry was applied to study Pb(II) at a solid bismuth microelectrode (SBiµE). The proposed procedure was tested using model solutions containing 0.1 mol L−1 acetate buffer (pH = 3.4) and 5 × 10−9 mol L−1 Pb(II). Under optimized measurement conditions, i.e., activation potential and time −2.5 V and 30 s, respectively, and accumulation potential and time −1.4 V and 30 s, respectively, a linearity range of 1 × 10−10–3 × 10−8 mol L−1, a detection limit of 3.4 × 10−11 mol L−1 and a relative standard deviation of 3.1% were obtained. The applicability of the developed procedure was confirmed by direct analysis of environmental waters, such as water from the Bystrzyca River and water from the Baltic Sea.

The authors report on a disposable sensor for the differential pulse anodic stripping voltammetric (DPASV) determination of the ions Zn(II), Pb(II) and Cu(II). Simultaneous detection is accomplished by using a screen-printed carbon electrode (SPCE) co-modified with an in-situ plated bismuth (Bi)) film and gold nanoparticles (AuNPs). The synergistic effect of the Bi film, and the large surface and good electrical conductivity of the AuNPs strongly assist in the co-deposition of the three ions. Four well-defined and fully separated anodic stripping peaks, at 540 mV for Zn(II), 50 mV for Pb(II), 140 mV for Bi(III) and 295 mV for Cu(II), all vs. Ag/AgCl, can be seen. The modified SPCE was characterized by scanning electron microscopy, X-ray diffraction, cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimized conditions, the sensor has a good response to these ions. The detection limits (at an S/N ratio of 3) are 50 ng·L −1 for Zn(II), 20 ng·L −1 for Pb(II), and 30 ng·L −1 for Cu(II). The method was applied to the determination of the 3 ions in spiked lake water samples. Graphical abstract Schematic of screen-printed carbon electrode (SPCE) co-modified with a bismuth film and gold nanoparticles for electrochemical simultaneous determination of Zn(II), Pb(II) and Cu(II) by differential pulse anodic stripping voltammetric (DPASV).

Smart monitoring has been studied and developed in recent years to create faster, cheaper, and more user-friendly on-site methods. The present study describes an innovative technology for investigative monitoring of heavy metal pollution (Cu and Pb) in surface water. It is composed of an autonomous surface vehicle capable of semiautonomous driving and equipped with a microfluidic device for detection of heavy metals. Detection is based on the method of square wave anodic stripping voltammetry using carbon-based screen-printed electrodes (SPEs). The focus of this work was to validate the ability of the integrated system to perform on-site detection of heavy metal pollution plumes in river catchments. This scenario was simulated in laboratory experiments. The main performance characteristics of the system, which was evaluated based on ISO 15839 were measurement bias (Pb 75%, Cu 65%), reproducibility (in terms of relative standard deviation: Pb 11–18%, Cu 6–10%) and the limit of detection (4 µg/L for Pb and 7 µg/L for Cu). The lowest detectable change (LDC), which is an important performance characteristic for this application, was estimated to be 4–5 µg/L for Pb and 6–7 µg/L for Cu. The life span of an SPE averaged 39 measurements per day, which is considered sufficient for intended monitoring campaigns. This work demonstrated the suitability of the integrated system for on-site detection of Pb and Cu emissions from large and medium urban areas discharging into small water bodies.

The influences of electrochemical reduction degrees of reduced graphene oxide (rGO)-based electrode on its electrochemical sensing performance toward heavy metal ions (HMIs) were investigated. Initially, graphene oxide was synthesized by the modified Hummers’ method. Then, rGO films with different degrees of electrochemical reduction were prepared by using the cyclic voltammetry (CV) technique in different numbers of voltammetric cycles x (where x  = 3, 6, 9, and 12). The structural and morphological characterizations of different degrees of reduction for rGOx were carried out by using ultraviolet–visible spectroscopy, attenuated total reflection-infrared, X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The charge transfer rate of rGOx modified glassy carbon electrodes (rGOx/GCEs) was investigated by CV and electrical impedance spectroscopy measurements using a standard ferri/ferrocyanide system. These modified electrodes were further investigated to achieve the best electrochemical performance toward HMIs detection. The modified electrode with six voltammetric cycles (rGO6/GCE) exhibited considerable improvements related to the stability, sensitivity, and well-oxidation potential definition for cadmium ion (Cd 2+ ) and lead ion (Pb 2+ ). The deposition potential, pH value, and accumulation time were optimized. The simultaneous electrochemical detection of Cd 2+ and Pb 2+ was performed using differential anodic stripping voltammetry technique under optimized conditions in the presence of bismuth ion (Bi 3+ ). The Bi/rGO6/GCE was selected as the desired electrode and employed to detect the Cd 2+ and Pb 2+ at different concentrations within a linear range between 10 and 50 μgL −1 . The detection limits for Cd 2+ and Pb 2+ were 1.2 and 0.2 μgL −1 , respectively; with a signal to noise ratio (S/N = 3). Finally, the repeatability and reproducibility were investigated which exhibited excellent stability with relative standard deviations equal to 2.9 and 0.7% for Cd 2+ and Pb 2+ respectively, and similar linear range with detection limits. Graphic abstract

Lead (Pb) and cadmium (Cd) ions have serious negative impacts on human health and the ecological environment due to toxicity, persistence and nonbiodegradability. Among various trace Pb and Cd ions detection technologies, electrochemical analysis is considered as one of the most promising methods. The deposition of Bi nanoparticles on delaminated Ti3C2Tx (DL-Ti3C2Tx) develops a sensor with good conductivity and performance. Square wave anodic stripping voltammetry (SWASV) technology was applied to simultaneously deposit Bi on DL-Ti3C2Tx/GCE and achieve the rapid detection of Pb and Cd ions. The Bi nanoparticles effectively improved the sensitivity of Bi/DL-Ti3C2Tx/GCE sensors to detect Pb and Cd ions. The preparation conditions of the Bi/DL-Ti3C2Tx/GCE were optimized, including DL-Ti3C2Tx droplet amount, solution pH, Bi3+ concentration, deposition time and deposition potential, to improve the detection ability. The Bi/DL-Ti3C2Tx/GCE sensor has detection limits of 1.73 and 1.06 μg/L for Pb and Cd ions, respectively (S/N > 3). This electrochemical sensor is easy, sensitive and selective to apply in actual water samples for trace Pb and Cd ions detection.

For the first time the development of an electrochemical method for simultaneous quantification of Zn 2+ and uric acid (UA) in sweat is described using an electrochemically treated 3D-printed working electrode. Sweat analysis can provide important information about metabolites that are valuable indicators of biological processes. Improved performance of the 3D-printed electrode was achieved after electrochemical treatment of its surface in an alkaline medium. This treatment promotes the PLA removal (insulating layer) and exposes carbon black (CB) conductive sites. The pH and the square-wave anodic stripping voltammetry technique were carefully adjusted to optimize the method. The peaks for Zn 2+ and UA were well-defined at around − 1.1 V and + 0.45 V (vs. CB/PLA pseudo-reference), respectively, using the treated surface under optimized conditions. The calibration curve showed a linear range of 1 to 70 µg L −1 and 1 to 70 µmol L −1  for Zn 2+ and UA, respectively. Relative standard deviation values were estimated as 4.8% ( n  = 10, 30 µg L −1 ) and 6.1% ( n  = 10, 30 µmol L −1 ) for Zn 2+ and UA, respectively. The detection limits for Zn 2+ and UA were 0.10 µg L −1 and 0.28 µmol L −1 , respectively. Both species were determined simultaneously in real sweat samples, and the achieved recovery percentages were between 95 and 106% for Zn 2+ and 82 and 108% for UA. Graphical abstract