Synthesis of a novel electrode material containing phytic acid-polyaniline nanofibers for simultaneous determination of cadmium and lead ions

Electrospun nanofiber-based sensors for the detection of chemical and biological contaminants/hazards in the food industries

Food contamination reveals a major health risk globally and presents a significant challenge for the food industry. It can stem from biological contaminants like pathogens, parasites, and viruses, or chemical contaminants such as heavy metals, pesticides, drugs, and hormones. There is also the possibility of naturally occurring hazardous chemicals. Consequently, the development of sensing platforms has become crucial to accurately and rapidly identify contaminants and hazards in food products. Electrospun nanofibers (NFs) offer a promising solution due to their unique three-dimensional architecture, large specific surface area, and ease of preparation. Moreover, NFs exhibit excellent biocompatibility, degradability, and adaptability, making monitoring more convenient and environmentally friendly. These characteristics also significantly reduce the detection process of contaminants. NF-based sensors have the ability to detect a wide range of biological, chemicals, and physical hazards. Recent research on NFs-based sensors for the detection of various food contaminants/hazards, such as pathogens, pesticide/drugs residues, toxins, allergens, and heavy metals, is presented in this review.

Utilization of nitrogen, sulfur co-doped porous carbon micron spheres as bifunctional electrocatalysts for electrochemical detection of cadmium, lead and mercury ions and oxygen evolution reaction

The development of high-performance bifunctional electrocatalysts for oxygen evolution reaction and heavy metal ion (HMI) detection is significant and challenging. Here, a novel nitrogen, sulfur co-doped porous carbon sphere bifunctional catalyst was designed and fabricated by hydrothermal followed by carbonization using starch as carbon source and thiourea as nitrogen, sulfur source for HMI detection and oxygen evolution reactions. Under the synergistic effect of pore structure, active sites and nitrogen, sulfur functional groups, C-S_0.75-HT-C₈₀₀ demonstrated excellent HMI detection performance and oxygen evolution reaction activity. Under optimized conditions, the detection limits (LODs) of C-S_0.75-HT-C₈₀₀ sensor were 3.90, 3.86 and 4.91 nM for Cd²⁺, Pb²⁺ and Hg²⁺ when detected individually; and the sensitivities were 13.12, 19.50 and 21.19 μA/μM. The sensor also obtained high recoveries of Cd²⁺, Hg²⁺ and Pb²⁺ in river water samples. During the oxygen evolution reaction, a Tafel slope of 70.1 mV/dec and a low overpotential of 277 mV were obtained for C-S_0.75-HT-C₈₀₀ electrocatalyst with a current density of 10 mA/cm² in basic electrolyte. This research offers a neoteric and simple strategy in the design as well as fabrication of bifunctional carbon-based electrocatalysts.

A Review on Electrospinning as Versatile Supports for Diverse Nanofibers and Their Applications in Environmental Sensing

Rapid industrialization is accompanied by the deterioration of the natural environment. The deepening crisis associated with the ecological environment has garnered widespread attention toward strengthening environmental monitoring and protection. Environmental sensors are one of the key technologies for environmental monitoring, ultimately enabling environmental protection. In recent decades, micro/nanomaterials have been widely studied and applied in environmental sensing owing to their unique dimensional properties. Electrospinning has been developed and adopted as a facile, quick, and effective technology to produce continuous micro- and nanofiber materials. The technology has advanced rapidly and become one of the hotspots in the field of nanomaterials research. Environmental sensors made from electrospun nanofibers possess many advantages, such as having a porous structure and high specific surface area, which effectively improve their performance in environmental sensing. Furthermore, by introducing functional nanomaterials (carbon nanotubes, metal oxides, conjugated polymers, etc.) into electrospun fibers, synergistic effects between different materials can be utilized to improve the catalytic activity and sensitivity of the sensors. In this review, we aimed to outline the progress of research over the past decade on electrospinning nanofibers with different morphologies and functional characteristics in environmental sensors.

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.

Phytic acid functionalized ZIF-67 decorated graphene nanosheets with remarkably boosted electrochemical sensing performance

Recently, metal-organic frameworks (MOFs) display great application potential in the field of electrochemical catalysis and sensing due to its extraordinary properties. Herein, Co-based MOFs (ZIF-67) decorated graphene nanosheets (GS) heterogeneous hybrids (ZIF-67@GS) with sandwich-like morphology is first prepared by a facile in situ synthesis method. The electrochemical activity of ZIF-67 polyhedrons is effectively enhanced for the introduction of the high conductivity of graphene nanosheets. Subsequently, phytic acid functionalized ZIF-67 with unique core-shell structure decorated GS (PA-ZIF-67@GS) is prepared through the chemical etching effect of phytic acid. Surprisingly, the exposure level of metal active sites, electrochemical active surface area, electron transfer kinetic of the chemically etched ZIF-67@GS are further significantly boosted. Benefiting from the greatly modified interface property, the as-obtained PA-ZIF-67@GS hybrids exhibit excellent electrocatalytic activity toward the oxidation of glucose, and an ultrasensitive nonenzymatic electrochemical sensing platform is then developed. It is believed that this work may provide effective guidance for optimizing the electrochemical catalytic and sensing performance of other series of MOFs.

Electrochemical determination of lead(II) and copper(II) by using phytic acid and polypyrrole functionalized metal-organic frameworks

A glassy carbon electrode (GCE) was modified with a composite prepared from phytic acid, polypyrrole and a ZIF type metal-organic framework (PA/PPy)/ZIF-8@ZIF-67). The nanocomposite was prepared by in-situ chemical polymerization in the presence of ferric chloride and subsequently functionalized with PA to form PA/PPy/ZIF-8@ZIF-67. The materials were characterized by XRD, FT-IR, BET, XPS, SEM and TEM. The modified GCE was applied to individual and simultaneous detection of Pb(II) and Cu(II), with peak voltages of -0.6 and - 0.1 V, respectively (vs. SCE). The amount of PPy, the ZIF-8@ZIF-67 concentration, polymerization potential, polymerization time and pH value were optimized. Under optimized conditions, the calibration plots have two linear ranges. These are from 0.02 to 200 μM and from 200 to 600 μM for Pb(II), and from 0.2 to 200 μM and 200 to 600 μM for Cu(II). The detection limits are 2.9 nM and 14.8 nM, respectively. Simultaneous detection of Pb(II) and Cu(II) is also demonstrated. The good performance of the electrode is attributed to the large surface area of ZIF-8@ZIF-67, the good electrical conductivity of PPy, and the metal complexation power of PA. The modified GCE was successfully applied to the determination of Pb(II) and Cu(II) in real samples and gave satisfactory recoveries. Graphical abstractSchematic presentation of the construction process of PA/PPy/ZIF-8@ZIF-67/GCE sensor, and the mechanism of Pb(II) and Cu(II) at the prepared sensor.

A highly sensitive electrochemical sensor for Cd(II) based on protic salt derived nitrogen and sulfur co-doped porous carbon

Lately, an "all-in-one" strategy via direct pyrolysis of protic salt has attracted great attention in the preparation of hetero-doped porous carbons due to its distinctive simplicity. However, protic salt derived carbons usually process large grain sizes thus hamper their applications. Herein, a protic salt derived N, S co-doped porous carbon (N, S-PC) with improved porosity was synthesized by nanocasting and carbonization of protic salt. In the nanocasting silica sphere was used as auxiliary template and an easily obtained protic salt ([pPDA][nHSO₄]) was served as C, N and S sources. The obtained N, S-PC contains rich N, S contents and hierarchical textural porosity, thus favors the electrochemical detection of toxic cadmium ions. The N, S-PC based sensor shows excellent sensitivity and selectivity for Cd(II) versus other metals, with a low detection limit of 0.1 μg L^-1 (S/N = 3) over a wide concentration range of 4-80 μg L^-1. Applications of the N, S-PC based sensor for Cd(II) assay in tap water samples achieved results with good recoveries, indicating that the N, S-PC based electrode is promising in real sample analysis.

A Facile Electrochemical Sensor Based on PyTS⁻CNTs for Simultaneous Determination of Cadmium and Lead Ions

A simple and easy method was implemented for the contemporary detection of cadmium (Cd²⁺) and lead (Pb²⁺) ions using 1,3,6,8-pyrenetetrasulfonic acid sodium salt-functionalized carbon nanotubes nanocomposites (PyTS⁻CNTs). The morphology and composition of the obtained PyTS⁻CNTs were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The experimental results confirmed that the fabricated PyTS⁻CNTs exhibited good selectivity and sensitivity for metal ion-sensing owing to the insertion of sulfonic acid groups. For Cd²⁺ and Pb²⁺, some of the electrochemical sensing parameters were evaluated by varying data such as the PyTS⁻CNT quantity loaded on the pyrolytic graphite electrode (PGE), pH of the acetate buffer, deposition time, and deposition potential. These parameters were optimized with differential pulse anodic sweeping voltammetry (DPASV). Under the optimal condition, the stripping peak current of the PyTS⁻CNTs/Nafion/PGE varies linearly with the heavy metal ion concentration, ranging from 1.0 μg L^-1 to 90 μg L^-1 for Cd²⁺ and from 1.0 μg L^-1 to 110 μg L^-1 for Pb²⁺. The limits of detection were estimated to be approximately 0.8 μg L^-1 for Cd²⁺ and 0.02 μg L^-1 for Pb²⁺. The proposed PyTS⁻CNTs/Nafion/PGE can be used as a rapid, simple, and controllable electrochemical sensor for the determination of toxic Cd²⁺ and Pb²⁺.