Recent advances on the methods developed for the identification and detection of emerging contaminant microplastics: a review

The widespread use of plastics, popular for their versatility and cost-efficiency in mass production, has led to their essential role in modern society. Their remarkable attributes, such as flexibility, mechanical strength, lightweight, and affordability, have further strengthened their importance. However, the emergence of microplastics (MPs), minute plastic particles, has raised environmental concerns. Over the last decade, numerous studies have uncovered MPs of varying sizes in diverse environments. They primarily originate from textile fibres and cosmetic products, with large plastic items undergoing degradation and contributing as secondary sources. The bioaccumulation of MPs, with potential ingestion by humans through the food chain, underscores their significance as environmental contaminants. Therefore, continuous monitoring of environmental and food samples is imperative. A range of spectroscopic techniques, including vibrational spectroscopy, Raman spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, hyperspectral imaging, and nuclear magnetic resonance (NMR) spectroscopy, facilitates the detection of MPs. This review offers a comprehensive overview of the analytical methods employed for sample collection, characterization, and analysis of MPs. It also emphasizes the crucial criteria for selecting practical and standardized techniques for the detection of MPs. Despite advancements, challenges persist in this field, and this review suggests potential strategies to address these limitations. The development of effective protocols for the accurate identification and quantification of MPs in real-world samples is of paramount importance. This review further highlights the accumulation of microplastics in various edible species, such as crabs, pelagic fish, finfish, shellfish, American oysters, and mussels, shedding light on the extreme implications of MPs on our food chain

Graphene nanoribbons/manganese oxide nanocomposite modified electrode for detection of antimicrobial drug nitrofurantoin

The design and development of a new kind of cost-effective electrode material with excellent selectivity and stability are still a great challenge in the field of electrochemical sensors. Recently, researchers have paid more attention to the electrochemical reduction of nitro compounds due to their hazardous nature. Nitro compounds play a vital role in various industrial applications. However, the direct discharge of nitro compounds to the environment as industrial wastewater is harmful. In this study, a nanocomposite made of 1D graphene nanoribbons decorated with manganese dioxide (GNR-MnO2) was prepared to fabricate an electrochemical transducer for the determination of nitrofurantoin (NFT) in biofluids. First, 1D GNR was prepared by unzipping of multiwalled carbon nanotubes. Second, the GNR was decorated with MnO2 by the hydrothermal reduction method. As-prepared GNR-MnO2 nanocomposite was comprehensively characterized by field emission scanning electron microscopy with EDX, XRD, UV–visible, electrochemical impedance spectroscopy, and cyclic voltammetry. Moreover, GNR-MnO2-coated glassy carbon electrode (GCE) exhibited good electrocatalytic activity toward NFT. The electroreduction of NFT was found at −0.40 V which was 50 mV lower than bare GCE. GNR-MnO2 nanocomposite modified GCE showed a well-defined linear reduction peak current for NFT from 10 nM to 1,000 µM. The selectivity of the sensor was also analyzed in the presence of other nitro compounds which confirmed that NFT can be selectively detected at −0.4 V. The GNR-MnO2 modified electrode was also able to separate reduction peaks of other nitro compounds. In addition, the detection of NFT was carried out in human urine samples with a good recovery of 99.60%–98.60%

EDITORIAL (Hot topic : new developments on nanomaterials for electrochemical applications)

Nanomaterials and their composites (various forms) (both inorganic and organic) are still evolving and encouraging scientist community to explore their various possibilities and applications in developing Science and technology. In this era, we are experiencing and realizing a vital role of Nanotechnology as we are seeing in smart phones, millimeter sized storage devices, micro devices, digital voice/telecommunications etc. All these developments are possible because of small matters so called “Nanoparticles”. In the same way, electrochemistry is undertaking a big role in all areas of science and engineering. For ex; Electroanalytical methods have potential advantages in (bio) chemical sensing and biomedical science. Cyclic voltammetry is a classical tool to investigate and derive the reaction mechanisms of electroactive inorganic and organic materials. This special issue of article will address the recent developments of nanomaterials and their applications in the electrochemical solid-state science. In the first article, Prof. Subramaniam et al. reported about graphene and its charge storage performance. His group found that graphene enhanced charge storage performance in the Electrochemical Double Layer Capacitors (EDLC). Secondly, Karthick et al. developed a reliable method for the green synthesis of gold nanoparticles (Au- NPs) using a medicinally valued Adhatoda vasica Nees. It is a rapid and eco-friendly method which may help researchers to synthesize Au-NPs covered with bioactive compounds and is expected to have potential applications in biomedical science. Thirdly, Felix et al. have successfully synthesized IrO2 and demonstrated it as an effective anodic electrocatalyst for the oxygen evolution reaction (OER) in solid polymer electrolyte. In the fourth article, Arockiasamy et al. deposited titanium nitride (TiN)/nickel (Ni) composite by plasma assisted metal-organic chemical vapor deposition (PAMOCVD) using organo-metallic and metal-organic complexes. They proposed that Ni/TiN composite is useful to create super hard coatings. Lastly, Sundramoorthy et al. have proposed a conducting redox-polymer coated sensor for the detection of reduced form of nicotinamide adenine dinucleotide in physiological condition with lower detection limit. This new electrode system may be useful for real-sample analysis. We kindly appreciate all of the contributors for their timely support and co-operation. We hope our articles will be useful for academic and industrial researchers

In vitro and in vivo characterization of mineralized hydroxyapatite/polycaprolactone-graphene oxide based bioactive multifunctional coating on Ti alloy for bone implant applications

Hydroxyapatite (HAP) is a form of naturally occurring calcium apatite present in bone and tooth enamel. It is an important biomaterial with diverse biomedical applications such as a surface coating for metallic orthopedic implants. Synthesized pristine HAP has poor mechanical properties, inferior wear resistance and has limits for directly used in bone tissue engineering applications. To address these limitations, we synthesized a suitable orthopedic implant hybrid material (M-HAP/PCL/GO) by using positively charged calcium ions of mineralized HAP (M-HAP) combined with Polycaprolactone-negatively charged graphene oxide (PCL-GO). The successfully synthesized M-HAP/PCL/GO composite was comprehensively characterized by Fourier-transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The micro-hardness technique was used to determine the mechanical strength of M-HAP (315 ± 4 Hv), M-HAP/GO (370 ± 3 Hv) and M-HAP/PCL/GO (455 ± 5 Hv). M-HAP/PCL/GO was also tested for its anti-bactericidal impact against Staphylococcus aureus and Escherichia coli. MG63 osteoblast cells cultured on the M-HAP/PCL/GO composite (10 mg/mL) coated sample, displayed outstanding viability after 3 and 5 days of incubation at pH 7.4, which indicated that the composite is suitable material for bone implants and induces the cell proliferation. It was also tested in vivo in Wistar rats and was observably beneficial bone formation within 28 days post-implant operation. These tests proved that the M-HAP/PCL/GO composite can be considered as a prospective candidate for future bone implant applications. Keywords: Polycaprolactone, Graphene oxide, Hydroxyapatite, Bone implants, Antibacterial activity, MG63 osteoblasts cells, Surface coatin

Electroanalysis of nickel ions released in artificial saliva from three orthodontic arch wires: Stainless Steel (SS), NiTi, and CuNiTi

Background: Nickel titanium wires are superior for first alignment because they have exceptional shape memory and super-elasticity. Increased concerns have been raised about the high rate of nickel (Ni) allergy and the growing usage of dental biomaterials that contain Ni. Aim: The aim of the study was to analyze and evaluate the rate of nickel release from different types of orthodontic arch wires. Materials and methods: A set of arch wires of nickel titanium (NiTi), SS and Cu-NiTi were immersed in artificial saliva for three days and analyzed after three days. The amount of Ni ions released from the sample were evaluated using electrochemical techniques such as Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and polarization (Tafel) plot. Results: The EIS and Tafel graph confirmed the s-NiTi, s-CuNiTi showed an excellent corrosion resistance than the s-SS. From all the above measurements, we can conclude that the saliva can affect the corrosion resistance property of the SS, NiTi, CuNiTi day by day. Conclusion: From this study it was concluded that the saliva can affect the corrosion resistance property of the SS, NiTi, CuNiTi day by day, and there was nickel ion release but at a very negligible rate

Disposable redox polymer coated screen-printed carbon electrode for NADH sensing

Electrochemical behavior of electro-generated poly-pyronin B (PyB) film was reported at a screen-printed carbon electrode (SPCE). The poly(PyB) modified SPCE showed excellent redox activity in neutral and alkaline media. Surface topography of poly(PyB) film modified electrode was analyzed by using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Poly(PyB) film coated electrode was characterized by electrochemical impedance spectroscopy (EIS), UV–visible absorption spectroscopy (UV–vis) and cyclic voltammetry (CV). The poly(PyB) modified electrode showed electrocatalytic response to the reduced form of nicotinamide adenine dinucleotide (NADH) in physiological condition, and was used for the detection of NADH with high selectivity. The anodic peak current was linearly related to concentrations of NADH over the range from 1x10-5 M to 5.2x10-4 M, and the detection limit was 5x10-7 M (S/N = 3)

Electrochemical detection of uric acid on exfoliated nanosheets of graphitic-like carbon nitride (g-C3N4) based sensor

A highly sensitive, selective and stable electrochemical sensor for detection of uric acid (UA) in aqueous solution has been successfully developed by deposition of exfoliated graphitic-like carbon nitride (g-C3N4) nanosheets on glassy carbon electrode (GCE). The synthesized g-C3N4 was confirmed by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) and Raman spectroscopies. Field-emission scanning electron microscopy (FE-SEM) and High-resolution transmission electron microscopy (HR-TEM) were used to investigate the crystalline structure of g-C3N4. The elemental composition was characterized by energy-dispersive X-ray spectroscopy (EDXS). Compared to bare GCE, exfoliated g-C3N4 nanosheets (NS) modified GCE exhibited higher catalytic current for UA electro-oxidation at reduced over potential in 0.1 M phosphate buffered saline solution (PBS), which is essential to discriminate interfering analytes. g-C3N4 NS modified GCE showed a linear relationship between the electrochemical signal and the UA concentration from 100 to 1000 μM with fast response by differential pulse voltammetry (DPV). The common interferent molecules such as dopamine, ascorbic acid, folic acid, paracetamol, lactic acid, oxalic acid, cysteine, and ciprofloxacin were tested in 0.1 M PBS for the g-C3N4 NS modified GCE. It was found that these molecules did not affect the oxidation current of UA when they co-existed in the same buffer solution. Moreover, the modified sensor probe was tested for UA in urine samples with satisfactory recovery values. The proposed sensor offers high accuracy, sensitivity, simple fabrication and low cost. We suggest that g-C3N4 NS based sensor can be useful for UA analysis in medical, environmental, food and industrial applications.Published versio

Highly Selective Mercury Detection at Partially Oxidized Graphene/Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Nanocomposite Film Modified Electrode

Partially oxidized graphene flakes (po-Gr) were obtained from graphite electrode by an electrochemical exfoliation method. As-produced po-Gr flakes were dispersed in water with the assistance of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS). The po-Gr flakes and the po-Gr/PEDOT:PSS nanocomposite (po-Gr/PEDOT:PSS) were characterized by Raman spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), UV-Vis spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, we demonstrated the potential use of po-Gr/PEDOT:PSS electrode in electrochemical detection of mercury ions (Hg2+) in water samples. The presence of po-Gr sheets in PEDOT:PSS film greatly enhanced the electrochemical response for Hg2+. Cyclic voltammetry measurements showed a well-defined Hg2+ redox peaks with a cathodic peak at 0.23 V, and an anodic peak at 0.42 V. Using differential pulse stripping voltammetry, detection of Hg2+ was achieved in the range of 0.2 to 14 µM (R2 = 0.991), with a limit of detection (LOD) of 0.19 µM for Hg2+. The electrode performed satisfactorily for sensitive and selective detection of Hg2+ in real samples, and the po-Gr/PEDOT:PSS film remains stable on the electrode surface for repeated use. Therefore, our method is potentially suitable for routine Hg2+ sensing in environmental water samples

Upcycling of surgical facemasks into carbon based thin film electrode for supercapacitor technology

Abstract Polypropylene (PP), a commonly used plastic, is used for making the outer layers of a surgical face mask. In 2020, around 3 billion surgical face masks were disposed into the environment, causing a huge threat to wildlife, aquatic life, and ecosystems. In this work, we have reported the sulfonation technique for stabilizing the surgical face masks and their conversion into carbon nanoparticles for application as a supercapacitor electrode. The electrode is fabricated by preparing a slurry paste of carbon nanoparticles and pasting it on a conductive wearable fabric. To investigate the performance of the carbon thin film electrode, electrochemical techniques are employed. The Cyclic Voltammetry (CV) analysis performed at different scan rates in a 6 molar KOH electrolyte reveals that the carbon thin film acts as a positive electrode. At 4 A g−1, the electrode shows a specific capacitance of 366.22 F g−1 and 100% retention of specific capacitance for 8000 cycles. A two-electrode asymmetric device is fabricated using carbon thin film as the positive electrode, NiO thin film as the negative electrode, and a KOH separator between two electrodes. The device shows a specific capacitance of 113.73 F g−1 at 1.3 A g−1 and glows a red LED for 6 min. This work is a step towards upcycling the waste produced from surgical face masks used during the COVID-19 pandemic and its application for energy storage

Biocompatible MXene (Ti3C2Tx) Immobilized with Flavin Adenine Dinucleotide as an Electrochemical Transducer for Hydrogen Peroxide Detection in Ovarian Cancer Cell Lines

Flavin adenine dinucleotide (FAD) is a coenzyme and acts as a redox cofactor in metabolic process. Owing to such problems as poor electron transfer properties, unfavorable adsorption, and lack of stability on rigid electrodes, the bio-electrochemical applications of FAD have been limited. Herein, a novel fabrication method was developed for the immobilization process using 2D MXene (Ti3C2Tx), which enhanced the redox property of FAD and improved the electro-catalytic reduction of hydrogen peroxide (H2O2) in neutral medium. The FAD-immobilized Ti3C2Tx electrode (FAD/Ti3C2Tx) was studied by UV-Visible and Raman spectroscopies, which confirmed the successful adsorption of FAD on the Ti3C2Tx surface. The surface morphology and the elemental composition of Ti3C2Tx were investigated by high resolution transmission electron microscopy and the energy dispersive X-ray analysis. The redox property of the FAD/Ti3C2Tx modified glassy carbon electrode (FAD/Ti3C2Tx/GCE) was highly dependent on pH and exhibited a stable redox peak at −0.455 V in neutral medium. Higher amounts of FAD molecules were loaded onto the 2D MXene (Ti3C2Tx)-modified electrode, which was two times higher than the values in the reported work, and the surface coverage (ᴦFAD) was 0.8 × 10−10 mol/cm2. The FAD/Ti3C2Tx modified sensor showed the electrocatalytic reduction of H2O2 at −0.47 V, which was 130 mV lower than the bare electrode. The FAD/Ti3C2Tx/GCE sensor showed a linear detection of H2O2 from 5 nM to 2 µM. The optimization of FAD deposition, amount of Ti3C2Tx loading, effect of pH and the interference study with common biochemicals such as glucose, lactose, dopamine (DA), potassium chloride (KCl), ascorbic acid (AA), amino acids, uric acid (UA), oxalic acid (OA), sodium chloride (NaCl) and acetaminophen (PA) have been carried out. The FAD/Ti3C2Tx/GCE showed high selectivity and reproducibility. Finally, the FAD/Ti3C2Tx modified electrode was successfully applied to detect H2O2 in ovarian cancer cell lines