Green tea extract assisted green synthesis of reduced graphene oxide: Application for highly sensitive electrochemical detection of sunset yellow in food products

Recent advancements of smartphone-based sensing technology for diagnosis, food safety analysis, and environmental monitoring

The emergence of computationally powerful smartphones, relatively affordable high-resolution camera, drones, and robotic sensors have ushered in a new age of advanced sensible monitoring tools. The present review article investigates the burgeoning smartphone-based sensing paradigms, including surface plasmon resonance (SPR) biosensors, electrochemical biosensors, colorimetric biosensors, and other innovations for modern healthcare. Despite the significant advancements, there are still scarcity of commercially available smart biosensors and hence need to accelerate the rates of technology transfer, application, and user acceptability. The application/necessity of smartphone-based biosensors for Point of Care (POC) testing, such as prognosis, self-diagnosis, monitoring, and treatment selection, have brought remarkable innovations which eventually eliminate sample transportation, sample processing time, and result in rapid findings. Additionally, it articulates recent advances in various smartphone-based multiplexed bio sensors as affordable and portable sensing platforms for point-of-care devices, together with statistics for point-of-care health monitoring and their prospective commercial viability.

Green Synthesis of Reduced Graphene Oxide Using the Tinospora cordifolia Plant Extract: Exploring Its Potential for Methylene Blue Dye Degradation and Antibacterial Activity

Graphene has attracted significant attention recently due to its unique mechanical, electrical, thermal, and optical properties. The present study focuses on synthesizing green rGO using the Tinospora cordifolia plant extract by mixing it in a suspension of graphene oxide. The plant extract of T. cordifolia acts as a reducing agent and is cost-effective, renewable, and eco-friendly. Green-synthesized rGO (G-rGO) was characterized using FTIR, HR-SEM, EDX, and HR-XRD analyses. G-rGO consists of nanosheets with an average width of approximately 30 nm. G-rGO has a range of hydrodynamic radius (270-470) nm and an average ζ potential of -29.9 mV. Further, G-rGO was used as a nanoadsorbent for optimal exclusion of methylene blue (MB) dye using the response surface methodology (RSM). Adsorption results confirmed 94.85% MB dye removal with 58.81 mg g-1 adsorption capacity at optimum conditions. The G-rGO's antibacterial activity was also tested against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) bacteria, finding the exhibited zone of inhibition of 10, 11, and 15 mm and 10, 13, and 17 mm at 20, 40, and 80 μg mL-1 concentrations of G-rGO, respectively.

Innovative Graphene-Based Nanocomposites for Improvement of Electrochemical Sensors: Synthesis, Characterization, and Applications

Graphene, renowned for its exceptional physicochemical attributes, has emerged as a favored substrate for integrating a wide array of inorganic and organic materials in scientific endeavors and innovations. Electrochemical graphene-based nanocomposite sensors have been developed by incorporating diverse nanoparticles into graphene, effectively immobilized onto electrodes through various techniques. These graphene-based nanocomposite sensors have effectively detected and quantified various electroactive species in samples. This review delves into using graphene nanocomposites to fabricate electrochemical sensors, leveraging the exceptional electrical, mechanical, and thermal properties inherent to graphene derivatives. These nanocomposites showcase electrocatalytic activity, substantial surface area, superior electrical conductivity, adsorption capabilities, and notable porosity, which are highly advantageous for sensing applications. A myriad of characterization techniques, including Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area analysis, and X-ray diffraction (XRD), have proven effective in exploring the properties of graphene nanocomposites and validating the adjustable formation of these nanomaterials with graphene. The applicability of these sensors across various matrices, encompassing environmental, food, and biological domains, has been evaluated through electrochemical measurements, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). This review provides a comprehensive overview of synthesis methods, characterization techniques, and sensor applications pertinent to graphene-based nanocomposites. Furthermore, it deliberates on the challenges and future prospects within this burgeoning field.

Cu-Co Bimetallic Catalyst-based Electrochemical Sensing Platform for Determination of Bisoprolol in Clinical Samples

BACKGROUND

Bisoprolol (BIS) is a selective beta-blocker. It has been successfully used to treat hypertension and angina pectoris. An overdose of BIS can lead to serious complications. An overdose is a medical emergency that requires immediate medical attention to overcome the adverse effects of the overdose. Hence, sensitive, reliable, and cost-effective methods are required for the determination of BIS.

METHODS

In this work, a new electrochemical sensing platform based on a bimetallic catalyst was developed for the determination of BIS. The Cu-Co nanocatalyst was easily synthesized by galvanic displacement onto a carbon paste electrode (CPE). Then, field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and cyclic voltammetry (CV) were utilized for the characterization of the Cu-Co catalyst.

RESULTS

The galvanic displacement of Cu metal significantly affected the electro-catalytic behavior of the Cu-Co catalyst and the Cu-Co/CPE electrode displayed a very sensitive and accurate response towards BIS. Under optimized conditions, the response was linear in the 3 to 120 μM concentration range, sensitivity of 631.1 μA mM-1 and a detection limit of as low as 0.4 μM using cyclic voltammetry. The simple proposed method was also successfully employed in the analysis of BIS in biological and pharmaceutical samples. The advantages of Cu-Co/CPE are its fast and simple manufacturing and the possibility of a repeated surface regeneration of the sensing platform, as well as its application for the detection of BIS in tablets and biological samples, making Cu-Co significant promise for use in clinical diagnostics. Besides, the synthesized catalysts showed excellent reusability and stability.

CONCLUSION

The presence of Cu metal due to galvanic displacement increased the sensitivity. These findings suggest that the new nanocatalyst has potential applications in sensors and electronics.

The Green Synthesis of Reduced Graphene Oxide Using Ellagic Acid: Improving the Contrast-Enhancing Effect of Microbubbles in Ultrasound

There is an urgent need to realize precise clinical ultrasound with ultrasound contrast agents that provide high echo intensity and mechanical index tolerance. Graphene derivatives possess exceptional characteristics, exhibiting great potential in fabricating ideal ultrasound contrast agents. Herein, we reported a facile and green approach to synthesizing reduced graphene oxide with ellagic acid (rGO-EA). To investigate the application of a graphene derivative in ultrasound contrast agents, rGO-EA was dispersed in saline solution and mixed with SonoVue (SV) to fabricate SV@rGO-EA microbubbles. To determine the properties of the product, analyses were performed, including ultraviolet-visible spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), X-ray photoelectron spectrum (XPS), X-ray diffraction analysis (XRD) and zeta potential analysis. Additionally, cell viability measurements and a hemolysis assay were conducted for a biosafety evaluation. SV@rGO-EA microbubbles were scanned at various mechanical index values to obtain the B-mode and contrast-enhanced ultrasound (CEUS) mode images in vitro. SV@rGO-EA microbubbles were administered to SD rats, and their livers and kidneys were imaged in CEUS and B-mode. The absorption of rGO-EA resulted in an enhanced echo intensity and mechanical index tolerance of SV@rGO-EA, surpassing the performance of SV microbubbles both in vitro and in vivo. This work exhibited the application potential of graphene derivatives in the field of ultrasound precision medicine.

Dynamics of reduced graphene oxide: synthesis and structural models

Technological advancements are leading to an upsurge in demand for functional materials that satisfy several of humankind's needs. In addition to this, the current global drive is to develop materials with high efficacy in intended applications whilst practising green chemistry principles to ensure sustainability. Carbon-based materials, such as reduced graphene oxide (RGO), in particular, can possibly meet this criterion because they can be derived from waste biomass (a renewable material), possibly synthesised at low temperatures without the use of hazardous chemicals, and are biodegradable (owing to their organic nature), among other characteristics. Additionally, RGO as a carbon-based material is gaining momentum in several applications due to its lightweight, nontoxicity, excellent flexibility, tuneable band gap (from reduction), higher electrical conductivity (relative to graphene oxide, GO), low cost (owing to the natural abundance of carbon), and potentially facile and scalable synthesis protocols. Despite these attributes, the possible structures of RGO are still numerous with notable critical variations and the synthesis procedures have been dynamic. Herein, we summarize the highlights from the historical breakthroughs in understanding the structure of RGO (from the perspective of GO) and the recent state-of-the-art synthesis protocols, covering the period from 2020 to 2023. These are key aspects in the realisation of the full potential of RGO materials through the tailoring of physicochemical properties and reproducibility. The reviewed work highlights the merits and prospects of the physicochemical properties of RGO toward achieving sustainable, environmentally friendly, low-cost, and high-performing materials at a large scale for use in functional devices/processes to pave the way for commercialisation. This can drive the sustainability and commercial viability aspects of RGO as a material.

Analytical Applicability of Graphene-Modified Electrode in Sunset Yellow Electrochemical Assay

Due to the recent increase in average living standards, food safety has caught public attention. It is necessary to conduct a qualitative and quantitative rapid test of prohibited food additives since the inclusion of food additives or the improper usage of synthetic dyes can negatively impact on the human health. Herein, a highly sensitive method for Sunset Yellow detection based on a glassy carbon electrode modified with few-layer graphenes was proposed. The electrochemical behavior of SY at the GR-exf/GCE modified surface was investigated by Cyclic Voltammetry, Square Wave Voltammetry, Electrochemical Impedance Spectroscopy and Amperometry. The influences of pH, scan rate, and interfering species were studied. Under optimized conditions, the developed sensor shows good linearity over a broad SY concentration range, e.g., 0.028-30 µM, with a low limit of detection (LOD = 0.0085 µM) and quantification (LOQ = 0.028 µM) (data obtained by amperometric technique). Furthermore, the modified electrode shows good selectivity, precision and sensitivity and has been successfully applied for SY quantification from commercially available pharmaceutical formulation as well as from candy bars and orange juice.

Reduced graphene oxide: Biofabrication and environmental applications

Green synthesis of high-quality reduced graphene oxide (rGO) from agro-industrial waste resources remains attractive owing to its outstanding environmental benefits. The remarkable properties of rGO include excellent morphology, uniform particle size, good optical properties, high conductivity, nontoxicity, and extraordinary chemical stability. Traditional methods for the synthesis of rGO nanomaterials involve several chemical reactions including oxidation, carbonization, toxic solvent, and pyrolysis which produce harmful byproducts. Green preparation of rGO is an emerging area of research in graphene technology which is cost-effective and sustainable in the procedure. Owing to the uniform particle rGO particle size, these smart nanomaterials have wide applicability, including in metal ions and pollutant sensing and adsorption, photocatalysis, optoelectrical devices, medical diagnosis, and drug delivery. Here we review the physicochemical properties of rGO, the biowaste sources and green methods of rGO synthesis, and the diverse applications of rGO, including in water purification and the biomedical fields. With this review, covering more than 200 research articles published on rGO in the last eight years ending in 2022, we aim to provide a quick guide for researchers seeking up-to-date information on the properties, production, and applicability of rGO, with special attention to rGO applications in water purification and the biomedical fields.

Radix Pueraria Flavonoids Assisted Green Synthesis of Reduced Gold Nanoparticles: Application for Electrochemical Nonenzymatic Detection of Cholesterol in Food Samples

Using radix pueraria flavonoids (RPFs) as a reducing and stabilizing agent, we report a simple, cost-effective, and ecologically friendly green synthesis technique for gold nanoparticles (AuNPs) in the present study. Ultraviolet-visible (UV) spectroscopy, transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) investigations were used to characterize the AuNPs. The results demonstrated that the produced AuNPs were nearly spherical and that their particle sizes had a mean diameter of 4.85 ± 0.75 nm. The "Green" AuNPs, exhibiting remarkable peroxidase-like activity and Michaelis-Menten kinetics with high affinity for H₂O₂ and 3,3',5,5'-tetramethylbenzidine (TMB), were effectively applied to the fabrication of a sensitive nonenzymatic enhanced electrochemical sensor for the detection of cholesterol (Cho). Under optimum circumstances, it was possible to establish two linear ranges of 1-100 and 250-5000 μmol/L with a detection limit of 0.259 μmol/L (signal/noise ratio (S/N) = 3). The suggested sensor was utilized with satisfactory findings to determine the amount of Cho in food samples.

Green synthesis of silver nanoparticles using the extract of spent coffee used for paper-based hydrogen peroxide sensing device

Hydrogen peroxide (H₂O₂) has attracted considerable attention for use as a disinfectant ingredient for various applications over the decades. The use of H₂O₂ within the safety regulations can avoid its toxicity to human health and the environment. In this study, a paper-based sensor containing green-synthesized silver nanoparticles (P-AgNPs) was developed for use in a smartphone in the determination of the H₂O₂ concentration. In the synthesis process, an extract of spent coffee grounds was used as a bioreducing agent. The effects of reaction time and silver nitrate (AgNO₃) concentration on the green synthesis of silver nanoparticles (AgNPs) were investigated. The optimum conditions for the preparation of P-AgNPs were determined to be 100 mM AgNO₃ (P-AgNPs-100) and 15 h synthesis time. The P-AgNPs-100 sensor exhibited high sensitivity with a detection limit of 1.26 mM H₂O₂, which might be suitable for the detection of H₂O₂-based household and beverage sanitizers. The H₂O₂ detection capability of P-AgNPs-100 was comparable to that of a commercial strip sensor. Furthermore, P-AgNPs-100 had a detection efficiency of more than 95% after long-term storage for 100 days.

A Brief Review: The Use of L-Ascorbic Acid as a Green Reducing Agent of Graphene Oxide

The reduced form of graphene oxide (r-GO) represents a versatile precursor to obtain graphene derivatives. Graphene oxide (GO) consists of a layered material based on a carbon skeleton functionalized by different oxygen-containing groups, while r-GO is obtained by the almost complete removal of these oxygen-containing functional groups. The r-GO has mechanical, electrical, and optical properties quite similar to graphene, thus, it proves to be a convenient 2D material useful for many technological applications. Nowadays, the most important aspects to consider in producing r-GO are: (i) the possibility of obtaining the highest reduction grade; (ii) the possibility of improving the dispersion stability of the resulting graphene using surfactants; (iii) the use of environmentally friendly and inexpensive reducing agents. Consequently, the availability of effective soft-chemistry approaches based on a green reducing agent for converting GO to r-GO are strongly needed. Among the green reductants, the most suitable is L-ascorbic acid (L-aa). Different studies have revealed that L-aa can achieve C/O ratio and conductivity values comparable to those obtained by hydrazine, a typical reducing agent. These aspects could promote an effective application strategy, and for this reason, this review summarizes and analyzes, in some detail, the up-to date literature on the reduction of GO by L-aa. The results are organized according to the two most important approaches, which are the reduction in liquid-phase, and the reduction in gel-phase. Reaction mechanisms and different experimental parameters affecting the processes were also compared.

Recent developments on graphene and its derivatives based electrochemical sensors for determinations of food contaminants

The sensing of food contaminants is essential to prevent their adverse health effects on the consumers. Electrochemical sensors are promising in the determination of electroactive analytes including food pollutants, biomolecules etc. Graphene nanomaterials offer many benefits as electrode material in a sensing device. To further improve the analytical performance, doped graphene or derivatives of graphene such as reduced graphene oxide and their nanocomposites were explored as electrode materials. Herein, the advancements in graphene and its derivatives-based electrochemical sensors for analysis of food pollutants were summarized. Determinations of both organic (food colourants, pesticides, drugs, etc.) and inorganic pollutants (metal cations and anions) were considered. The influencing factors including nature of electrode materials and food pollutants, pH, electroactive surface area etc., on the sensing performances of modified electrodes were highlighted. The results of pollutant detection in food samples by the graphene-based electrode have also been outlined. Lastly, conclusions and current challenges in effective real sample detection were presented.

Recent advances in carbon nanomaterials-based electrochemical sensors for food azo dyes detection

Azo dyes as widely applied food colorants are popular for their stability and affordability. On the other hand, many of these dyes can have harmful impacts on living organs, which underscores the need to control the content of this group of dyes in food. Among the various analytical approaches for detecting the azo dyes, special attention has been paid to electro-analytical techniques for reasons such as admirable sensitivity, excellent selectivity, reproducibility, miniaturization, green nature, low cost, less time to prepare and detect of specimens and the ability to modify the electrode. Satisfactory results have been obtained so far for carbon-based nanomaterials in the fabrication of electrochemical sensing systems in detecting the levels of these materials in various specimens. The purpose of this review article is to investigate carbon nanomaterial-supported techniques for electrochemical sensing systems on the analysis of azo dyes in food samples in terms of carbon nanomaterials used, like carbon nanotubes (CNT) and grapheme (Gr).

Adsorption of polycyclic aromatic hydrocarbons from wastewater using graphene-based nanomaterials synthesized by conventional chemistry and green synthesis: A critical review

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants formed mainly by the incomplete combustion of organic matter, such as oil, gas and coal. The presence of PAHs can cause irreparable damage to the environment and living beings, which has generated a global concern with the short and long term risks that the emission of these pollutants can cause. Many technologies have been developed in the last decades aiming at the identification and treatment of these compounds, mainly, the PAHs from wastewater. This review features an overview of studies on the main methods of PAHs remediation from wastewater, highlighting the adsorption processes, through the application of different adsorbent nanomaterials, with a main focus on graphene-based nanomaterials, synthesized by conventional and green routes. Batch and fixed-bed adsorptive processes were evaluated, as well as, the mechanisms associated with such processes, based on kinetic, equilibrium and thermodynamic studies. Based on the studies analyzed in this review, green nanomaterials showed higher efficiency in removing PAHs than the conventional nanomaterials. As perspectives for future research, the use of green nanomaterials has shown to be sustainable and promising for PAHs remediation, so that further studies are needed to overcome the possible challenges and limitations of green synthesis methodologies.

Latest advances on the nanomaterials-based electrochemical analysis of azo toxic dyes Sunset Yellow and Tartrazine in food samples

Azo-dyes such as Allura Red, Carmoisine, Amaranth, Sunset Yellow (SY), Brilliant Blue, Tartrazine (Tz), etc., are popular as food coloring agents due to their low cost and stability. SY and Tz are the most used members of this group of dyes since they have similar colors and are usually used together in food products. Despite their advantageous industrial use, they exhibit a risk toxicity profile with adverse effects such as allergy, asthma, carcinogenicity, genotoxicity, cytotoxicity, anxiety, etc. Therefore, the United States Food and Drug Administration (FDA) and European Food Safety Authority (EFSA) regulate the permissions for using these compounds to provide safe food products for consumers and prevent adverse effects both short and long-term. Considering all of these, for the analysis of azo toxic dyes, highly sensitive, low-cost, simple, and rapid sensors are necessary. Electrochemical nanosensors, which combine the unique features of electrochemistry and nanotechnology, are devices with all these advantages and are widely used for the determination of azo dyes. SY and Tz step forth as the most used food dyes in the class of azo-toxic dyes. They are often preferred together in food products, increasing the occurrence and exposure risk. Therefore, the analysis of Sunset Yellow and Tartrazine in food products has significant importance. In this review, the latest nanomaterial-based approaches for the electrochemical sensors on the analysis of SY and Tz in food samples were evaluated in terms of used nanomaterials and applied food samples.

Colorimetric assay based on horseradish peroxidase/reduced graphene oxide hybrid for sensitive detection of hydrogen peroxide in beverages

We reported a simple and sensitive colorimetric assay for detection of hydrogen peroxide (H₂O₂) based on the oxidation of 2,2׳-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) by UV-Vis spectroscopy method. The reduced graphene oxide (rGO) was prepared using green tea extract as bio-reducing and stabilizer agent and decorated by horseradish peroxidase (HRP). The surface of Au interface was modified with HRP-rGO hybrid. The formation of HRP-rGO hybrid was confirmed by cyclic voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray Spectroscopy (EDX) and Raman spectroscopy·H₂O₂ can be catalysed by HRP-rGO hybrid and converted into water and oxygen. The ABTS substrate takes up oxygen to form a green coloured product that has absorption peaks at 421, 655 nm and 737 nm. The colour development is linearly dependent on HRP in the range of 4-50 µg/L. The color of the green product solution is stable for 20 min. The absorption intensity is strongly related to the hydrogen peroxide concentration. The absorption intensity of the formed product scaled linearly with the hydrogen peroxide concentration in the ranges of 0.3-20 µM and 20-8000 µM with a detection limit of ≈15 nM could be achieved. The biosensor with excellent limit detection and wide linear ranges was adapted to monitor H₂O₂ in different beverages.

Physical and Biodegradation Properties of Graphene Derivatives/Thermoplastic Starch Composites

Development of biodegradable materials for packaging is an issue of the utmost importance. These materials are an alternative to petroleum-based polymers, which contribute to environment pollution after disposal. In this work, graphene oxide (GO) and glucose-reduced graphene oxide (rGO-g) were incorporated to thermoplastic starch (TPS) by melt extrusion. The TPS/GO and TPS/rGO-g composites had their physical properties and biodegradability compared. X-ray diffraction (XRD) showed that the type of graphene used led to different dispersion levels of graphene sheets, and to changes in the crystalline structure of TPS. Tensile tests carried out for the compression-molded composites indicated that TPS/rGO-g composites presented better mechanical performance. The Young’s modulus (E) increased from E = (28.6 ± 2.7) MPa, for TPS, to E = (110.6 ± 9.5) MPa and to (144.2 ± 11.2) MPa for TPS with rGO-g incorporated at 1.0 and 2.0 mass% content, respectively. The acid groups from graphene derivatives promoted glycosidic bond breakage of starch molecules and improved biodegradation of the composites. GO is well-dispersed in the TPS matrix, which contributes to biodegradation. For TPS/rGO-g materials, biodegradation was influenced by rGO-g dispersion level.

Functionalized Reduced Graphene Oxide as a Versatile Tool for Cancer Therapy

Cancer is one of the deadliest diseases in human history with extremely poor prognosis. Although many traditional therapeutic modalities-such as surgery, chemotherapy, and radiation therapy-have proved to be successful in inhibiting the growth of tumor cells, their side effects may vastly limited the actual benefits and patient acceptance. In this context, a nanomedicine approach for cancer therapy using functionalized nanomaterial has been gaining ground recently. Considering the ability to carry various anticancer drugs and to act as a photothermal agent, the use of carbon-based nanomaterials for cancer therapy has advanced rapidly. Within those nanomaterials, reduced graphene oxide (rGO), a graphene family 2D carbon nanomaterial, emerged as a good candidate for cancer photothermal therapy due to its excellent photothermal conversion in the near infrared range, large specific surface area for drug loading, as well as functional groups for functionalization with molecules such as photosensitizers, siRNA, ligands, etc. By unique design, multifunctional nanosystems could be designed based on rGO, which are endowed with promising temperature/pH-dependent drug/gene delivery abilities for multimodal cancer therapy. This could be further augmented by additional advantages offered by functionalized rGO, such as high biocompatibility, targeted delivery, and enhanced photothermal effects. Herewith, we first provide an overview of the most effective reducing agents for rGO synthesis via chemical reduction. This was followed by in-depth review of application of functionalized rGO in different cancer treatment modalities such as chemotherapy, photothermal therapy and/or photodynamic therapy, gene therapy, chemotherapy/phototherapy, and photothermal/immunotherapy.