An electrochemical sensor for detection of trace-level endocrine disruptor bisphenol A using Mo2Ti2AlC3 MAX phase/MWCNT composite modified electrode

β-cyclodextrin/spiropyran-functionalized optical-driven hydrogel film for bisphenol A detection in food packaging

Bisphenol A (BPA), an endocrine disruptor, is widely used in food packaging materials, including drink containers. Sensitive detection of BPA is crucial to food safety. Herein, we have developed a novel optical-driven hydrogel film sensor for sensitive BPA detection based on the displacement of spiropyran (SP) from β-cyclodextrin (β-CD) cavity by BPA followed by the photochromism of the released SP. The released SP converts to the ring-opened merocyanine form which shows an enhanced red fluorescence in the dark. The sensor demonstrates a linear detection range from 0.1 to 20 μg mL-1 with a limit of detection at 0.027 μg mL-1 and a limit of quantification at 0.089 μg mL-1. Notably, the proposed β-CD/SP hydrogel can be reused due to the reversible isomerization of SP and the reversible host-guest interaction. This sensor also shows good performance for BPA determination in real samples, indicating its great potential for food safety monitoring.

Green sonochemical synthesis of ZnCo2O4 decorated with carbon nanofibers for enhanced electrochemical detection of bisphenol A in food products

The facile sonochemical synthesis is reported of zinc cobalt oxide (ZnCo2O4) composited with carbon nanofiber (CNF). Structural, chemical, and morphological were characterized by X-ray diffraction (XRD), X-ray photoluminescent spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and transmittance electron microscopy (TEM), respectively. ZnCo2O4/CNF-modified GCE was applied to the detection of bisphenol A (BPA). The modified GCE shows enhanced sensing performance towards BPA, which includes a linear range (0.2 to 120 μM L-1) alongside a low limit of detection (38.2 nM L-1), low interference, and good stability. Detection of lower concentrations of BPA enables real sample analysis in the food industries (milk, orange juice, yogurt, tap water, and baby feeding bottles). Surprisingly, the BPA was detected in milk 510 nM L-1, orange juice 340 nM L-1, yogurt 1050 nM L-1, and tap water 140 nM L-1. Moreover, an interaction mechanism between the BPA analyte and ZnCo2O4 was discussed.

Platforms of graphene/MXene heterostructure for electrochemical monitoring of rutin in drug and Tartary buckwheat tea

The use of two-dimensional heterostructure composite as electrode modification material has become a new strategy to improve the electrocatalytic activity and electroactive sites of electrochemical sensor. Herein, a soluble heterostructure, namely rGO-PSS@MXene, was designed and synthesized by integrating poly (sodium p-styrenesulfonate)-functionalized reduced graphene oxide into MXene nanosheets via ultrasonic method. The interactive heterostructure can effectively alleviate the self-stacking of MXene and rGO, endowing them with superior electron transfer capacity and large specific surface area, thereby producing prominent synergistic electrocatalytic effect towards rutin. In addition, the excellent enrichment effect of rGO-PSS@MXene for rutin also plays an important role through the electrostatic and π-π stacking interactions. The electrochemical characteristics of rutin on the sensor were examined in detail and a sensitive sensing method was proposed. Under optimized conditions, the method showed satisfactory linear relationship for rutin in the concentration range of 0.005-10.0 μM, with limit of detection of 1.8 nM (S/N = 3). The quantitative validation results in herbal medicine and commercial Tartary buckwheat tea were highly consistent with the labeled quantity and the results of HPLC determination, respectively, suggesting the sensor possessed excellent selectivity and accuracy. This proposed strategy for rutin determination is expected to expand the application of MXene heterostructure in electrochemical sensors, and is envisioned as a promising candidate for quality monitoring of drugs and foods.

Molybdenum disulfide nanosheet induced reactive oxygen species for high-efficiency luminol chemiluminescence

BACKGROUND

Luminol chemiluminescence (CL) sensing system remains an excellent candidate for application in bioanalysis due to its good water solubility. However, traditional luminol CL system usually requires the addition of oxidizing agents and sensitizers to obtain high efficiency for the improvement of detection sensitivity. Although numerous studies on the nanomaterial-enhanced luminol CL systems have been carried out, there is still great potential to develop inexpensive, readily available and easily handled catalysts to construct simple and effective CL platform for biomolecular sensing.

RESULTS

Few-layered MoS2 nanosheets (NS) prepared by sonication-assisted exfoliation of commercially available bulk MoS2 were found to significantly enhance the CL of luminol‒dissolved oxygen in the absence of additional oxidants. The mechanism study demonstrated that exfoliated MoS2 NS could catalyze the decomposition of dissolved oxygen by virtue of its exposed active sites on the surface, generating increased reactive oxygen intermediates, which then oxidize luminol and produce intense CL emission. The proposed high-efficiency luminol CL system was then employed for the extremely sensitive identification of dopamine based on the quenching of CL by dopamine. The limit of detection (LOD) for dopamine can be as low as 2.07 nM. Besides, it also works well in the actual urine sample with good recoveries (99.6-100.6 %), confirming the practicability of the method.

SIGNIFICANCE

As a new type of CL catalyst, MoS2 NS developed in this work are easy to obtain, simple to prepare and can be produced in large quantities, which lays a foundation for extending applicability of MoS2 NS in the CL field, and provides a new idea for developing simple and highly sensitive CL sensing system.

A novel differential ratiometric molecularly imprinted electrochemical sensor for determination of sulfadiazine in food samples

Herein, we report a novel differential ratiometric molecularly imprinted polymer (MIP) electrochemical sensor for sulfadiazine (SDZ). An MIP membrane with double templates, SDZ and propyl gallate (PG), was fabricated on glassy carbon electrode (GCE) modified by CuInS2/ZnS nanocomposites. After adding PG in the samples as the reference, the current differences between MIP@CuInS2/ZnS/GCE and non-imprinted polymer@CuInS2/ZnS/GCE at the potentials of 0.18 V (ΔIPG) and 0.92 V (ΔISDZ) were measured. The ratio of ΔISDZ/ΔIPG was used for SDZ determination in the differential and ratiometric dual-mode. The influence of the variations in electrode modification and sample enrichment conditions on the determination of SDZ can be suppressed by 2.8 ∼ 13.2-fold, enhancing the reproducibility and stability of the MIP sensor. The interference level was reduced by one order of magnitude compared with the normal MIP mode. The proposed sensors were used to determine SDZ in food samples, with the detection limit of 2.1 nM.

Recent Advances on Electrochemical Sensors for Detection of Contaminants of Emerging Concern (CECs)

Contaminants of Emerging Concern (CECs), a new category of contaminants currently in the limelight, are a major issue of global concern. The pervasive nature of CECs and their harmful effects, such as cancer, reproductive disorders, neurotoxicity, etc., make the situation alarming. The perilous nature of CECs lies in the fact that even very small concentrations of CECs can cause great impacts on living beings. They also have a nature of bioaccumulation. Thus, there is a great need to have efficient sensors for the detection of CECs to ensure a safe living environment. Electrochemical sensors are an efficient platform for CEC detection as they are highly selective, sensitive, stable, reproducible, and prompt, and can detect very low concentrations of the analyte. Major classes of CECs are pharmaceuticals, illicit drugs, personal care products, endocrine disruptors, newly registered pesticides, and disinfection by-products. This review focusses on CECs, including their sources and pathways, health effects caused by them, and electrochemical sensors as reported in the literature under each category for the detection of major CECs.

A flexible electrochemical sensor for bisphenol A detection based on photoinitiated molecular imprinting on CdS functionalized carbon felt

Long-term and excessive exposure to bisphenol A (BPA) has an extremely detrimental effect on human health and ecological system. Hence, there is an urgent need to develop a sensitive and selective sensor for precisely monitoring BPA levels. In this work, a flexible and tailor-made electrochemical sensor for BPA has been fabricated based on in situ photopolymerization of molecular imprinting on cadmium sulfide (CdS) modified carbon felt (MIP@CdS-CF). It is worth nothing that CdS acts as a photocatalyst to enhance the capacity of photopolymerization, accordingly upgrading imprinting efficiency. Meanwhile, carbon felt (CF) exhibits attractive merits in term of superior electrical conductivity, enlarged electrochemical active areas and unique flexibility. Consequently, the novel MIP@CdS-CF electrochemical sensor shows superior sensitivity, high selectivity, extraordinary reproducibility and stability to detect BPA. The detection limit is 1.5 nM, which is lower than those of previously reported electrochemical sensors for the detection of BPA. More importantly, this newly developed electrochemical sensor can be utilized for detecting BPA in plastic bottles with satisfactory results.

Palladium-Copper Bimetallic Aerogel as New Modifier for Highly Sensitive Determination of Bisphenol A in Real Samples

In this study, a bimetallic palladium-copper aerogel was synthesized and used for modification of a graphite paste electrode (Pd-Cu/GPE), allowing the sensitive determination of bisphenol A (BPA). Different techniques, such as SEM, TEM, XPS, and AFM, were used for characterization of the Pd-Cu aerogel. To elucidate the properties of the Pd-Cu/GPE, the electrochemistry methods such as differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy were used. DPV measurements were conducted in phosphate electrolyte and buffer solution (0.2 M PBS, pH 5) at a potential range from 0.4 to 0.9 V vs. Ag/AgCl. The DPVs peaks currents increased linearly with BPA concentrations in the 0.04-85 and 85-305 µM ranges, with a limit of detection of 20 nM. The modified electrode was successfully used in real samples to determine BPA, and the results were compared to the standard HPLC method. The results showed that the Pd-Cu/GPE had good selectivity, stability, and sensitivity for BPA determination.

Bisphenol A Imprinted Electrochemical Sensor Based on Graphene Quantum Dots with Boron Functionalized g-C3N4 in Food Samples

A molecular imprinted electrochemical sensor based on boron-functionalized graphitic carbon nitride (B-g-C₃N₄) and graphene quantum dots (GQDs) was presented for selective determination of bisphenol A (BPA). In particular, by combining the selectivity and high stability properties, which are the most important advantages of molecular imprinted polymers, and the highly sensitive properties of GQDs/B-g-C₃N₄ nanocomposite, a highly selective and sensitive analytical method was developed for BPA analysis. Firstly, GQDs/B-g-C₃N₄ nanocomposite was characterized by using microscopic, spectroscopic, and electrochemical techniques. This novel molecular imprinted electrochemical sensor for BPA detection demonstrated a linearity of 1.0 × 10^-11-1.0 × 10^-9 M and a low detection limit (LOD, 3.0 × 10^-12 M). BPA-imprinted polymer on GQDs/B-g-C₃N₄ nanocomposite also showed good stability, repeatability and selectivity in food samples.

A highly selective and sensitive europium-organic framework sensor for the fluorescence detection of fipronil in tea

A europium-based metal organic framework (Eu-TFPA-MOF) was used for the fluorescence detection of fipronil in green tea and oolong tea for the first time. The red fluorescence of Eu-TFPA-MOF could be quenched significantly by low concentration (0.24 mM) of fipronil, and the "turn off" process exhibited quick response time (2 min), high sensitivity and selectivity, low detection limits (4.4 nM) and wide linear range (0-0.15 mM). The mechanism of fluorescence quenching was mainly attributed to static quenching process and the competitive absorption of excitation energy. Besides, the spiked and recovery test indicated that Eu-TFPA-MOF could be used in the fluorescence detection of fipronil in real green tea and oolong tea sample and the process had the advantages of simple pretreatment and satisfactory recoveries (98.33-106.17 %). More importantly, a simple, portable and low-cost smartphone-assisted test strip were designed for the visual detection of fipronil in real tea samples. The detection platform will be beneficial for tea quality safety and human heath, and is expected to be applied in other agricultural product safety field.

Facile synthesis of Ag@Fe3O4/ZnO nanomaterial for label-free electrochemical detection of methemoglobin in anemic patients

Methemoglobinemia (MetHb, Fe³⁺) is a chronic disease arising from the unequal distribution of oxyhemoglobin (HbFe²⁺, OHb) in the blood circulatory system. The oxidation of standard oxyhemoglobin forms methemoglobin, causing cyanosis (skin bluish staining). Methemoglobin cannot bind the pulmonary gaseous ligands such as oxygen (O₂) and carbon monoxide (CO). As an oxidizing agent, the biochemical approach (MetHb, Fe³⁺) is modified in vitro by sodium nitrite (NaNO₂). The silver-doped iron zinc oxide (Ag@Fe₃O₄/ZnO) is hydrothermally synthesized and characterized by analytical and spectroscopic techniques for the electrochemical sensing of methemoglobin via cyclic voltammetry (CV). Detection parameters such as concentration, pH, scan rate, electrochemical active surface area (ECSA), and electrochemical impedance spectroscopy (EIS) are optimized. The linear limit of detection for Ag@Fe₃O₄/ZnO is 0.17 µM. The stability is determined by 100 cycles of CV and chronoamperometry for 40 h. The serum samples of anemia patients with different hemoglobin levels (Hb) are analyzed using Ag@Fe₃O₄/ZnO modified biosensor. The sensor's stability, selectivity, and response suggest its use in methemoglobinemia monitoring.

Graphene and gold nanoparticle-based bionanocomposite for the voltammetric determination of bisphenol A in (micro)plastics

The monitoring of endocrine disruptors in the environment is one of the main strategies in the investigation of potential risks associated with exposure to these chemicals. Bisphenol A is one of the most prevalent endocrine-disrupting compounds and is prone to leaching out from polycarbonate plastic in both freshwater and marine environments. Additionally, microplastics also can leach out bisphenol A during their fragmentation in the water environment. In the quest for a highly sensitive sensor to determine bisphenol A in different matrices, an innovative bionanocomposite material has been achieved. This material is composed of gold nanoparticles and graphene, and was synthesized using a green approach that utilized guava (Psidium guajava) extract for reduction, stabilization, and dispersion purposes. Transmission electron microscopy images revealed well-spread gold nanoparticles with an average diameter of 31 nm on laminated graphene sheets in the composite material. An electrochemical sensor was developed by depositing the bionanocomposite onto a glassy carbon surface, which displayed remarkable responsiveness towards bisphenol A. Experimental conditions such as the amount of graphene, extract: water ratio of bionanocomposite and pH of the supporting electrolyte were optimized to improve the electrochemical performance. The modified electrode displayed a marked improvement in current responses for the oxidation of bisphenol A as compared to the uncovered glassy carbon electrode. A calibration plot was established for bisphenol A in 0.1 mol L^-1 Britton-Robinson buffer (pH 4.0), and the detection limit was determined to equal to 15.0 nmol L^-1. Recovery data from 92 to 109% were obtained in (micro)plastics samples using the electrochemical sensor and were compared with UV-vis spectrometry, demonstrating its successful application with accurate responses.

Recent Advances in Sources, Migration, Public Health, and Surveillance of Bisphenol A and Its Structural Analogs in Canned Foods

The occurrence of bisphenol A (BPA) and its structural analogs, known as endocrine disruptors is widely reported. Consumers could be exposed to these chemicals through canned foods, leading to health risks. Considerable advances have occurred in the pathogenic mechanism, migration law, and analytical methodologies for these compounds in canned foods. However, the confusion and controversies on sources, migration, and health impacts have plagued researchers. This review aimed to provide insights and perspectives on sources, migration, effects on human health, and surveillance of these chemicals in canned food products. Current trends in the determination of BPA and its structural analogs have focused on mass spectroscopy and electrochemical sensor techniques. Several factors, including pH, time, temperature, and volume of the headspace in canned foods, could affect the migration of the chemicals. Moreover, it is necessary to quantify the proportion of them originating from the can material used in canned product manufacturing. In addition, adverse reaction research about exposure to low doses and combined exposure with other food contaminants will be required. We strongly believe that the information presented in this paper will assist in highlighting the research needs on these chemicals in canned foods for future risk evaluations.

A sensing platform for on-site detection of glutathione S-transferase using oxidized Pi@Ce-doped Zr-based metal-organic frameworks(MOFs)

The development of point-of-care testing (POCT) for glutathione S-transferase (GST) is an effective way to establish the mechanism of targeted monitoring of cancer chemotherapy drug metabolism. Assays for GST with high sensitivity as well as on-site screening have been urgently required to monitor this process. Herein, we synthesized oxidized Pi@Ce-doped Zr-based metal-organic frameworks (MOFs) by electrostatic self-assembly between phosphate and oxidized Ce-doped Zr-based MOFs. It was found that the oxidase-like activity of oxidized Pi@Ce-doped Zr-based MOFs was substantially increased after phosphate ion (Pi) assembly. And a stimulus-responsive hydrogel-based kit was constructed by embedding oxidized Pi@Ce-doped Zr-based MOFs into a PVA (polyvinyl alcohol) hydrogel system, we integrated a portable hydrogel kit with a smartphone for real-time monitoring of GST for quantitative and accurate analysis. The color reaction was triggered based on oxidized Pi@Ce-doped Zr-based MOFs with 3,3',5,5'-tetramethylbenzidine (TMB). However, in the presence of glutathione (GSH), the above color reaction was hindered due to the reducibility of GSH. Catalyzed by GST, GSH can react with 1-chloro-2,4-dinitrobenzo (CDNB) to form an adduct, which caused the color reaction to occur again, resulting in the color response of the kit. In combination with ImageJ software, the kit image information acquired by smartphone could be converted into hue intensity, providing a direct quantitative tool for the detection of GST with a detection limit of 0.19mU·L^-1. Based on the advantages of simple operation and cost-effectiveness, the introduction of the POCT miniaturized biosensor platform will meet the requirements of on-site quantitative analysis of GST.

A portable paper-based aptasensor for simultaneous visual detection of two mycotoxins in corn flour using dual-color upconversion nanoparticles and Cu-TCPP nanosheets

A portable paper-based microfluidic aptasensor is established to simultaneously and visually detect zearalenone (ZEN) and ochratoxin A (OTA). The targets at the sample zone can migrate to two detection zones through dual-channels and result in green and blue fluorescence recovery. This is due to the specific recognition by a respective aptamer that destroys fluorescence resonance energy transfer (FRET) from dual-color upconversion nanoparticles (UCNPs) to Cu-TCPP nanosheets. By capturing fluorescent images and analyzing the corresponding RGB value via a smartphone, ZEN and OTA can be analyzed with limits of detection down to 0.44 ng/mL and 0.098 ng/mL in the linear ranges of 0.5-100 ng/mL and 0.1-50 ng/mL, respectively. Satisfactory recoveries are also obtained for ZEN (94.5-103.7 %) and OTA (92.2-106.8 %) in corn flour. With the advantages of simple operation, low sample consumption, and broad adaptability, this promising platform allows for the on-site detection of multiple hazards in food.

Label-Free Electrochemical Biosensor Platforms for Cancer Diagnosis: Recent Achievements and Challenges

With its fatal effects, cancer is still one of the most important diseases of today's world. The underlying fact behind this scenario is most probably due to its late diagnosis. That is why the necessity for the detection of different cancer types is obvious. Cancer studies including cancer diagnosis and therapy have been one of the most laborious tasks. Since its early detection significantly affects the following therapy steps, cancer diagnosis is very important. Despite researchers' best efforts, the accurate and rapid diagnosis of cancer is still challenging and difficult to investigate. It is known that electrochemical techniques have been successfully adapted into the cancer diagnosis field. Electrochemical sensor platforms that are brought together with the excellent selectivity of biosensing elements, such as nucleic acids, aptamers or antibodies, have put forth very successful outputs. One of the remarkable achievements of these biomolecule-attached sensors is their lack of need for additional labeling steps, which bring extra burdens such as interference effects or demanding modification protocols. In this review, we aim to outline label-free cancer diagnosis platforms that use electrochemical methods to acquire signals. The classification of the sensing platforms is generally presented according to their recognition element, and the most recent achievements by using these attractive sensing substrates are described in detail. In addition, the current challenges are discussed.

An electrochemical sensing platform based on carbon black and chitosan-stabilized platinum nanoparticles

The versatility of chitosan (Ch) biopolymer as a metallic nanoparticle stabilizing agent and excellent former of thin films on glassy carbon was explored in this work for the sustainable manufacture of novel electrochemical sensors based on carbon black (CB) and chitosan-stabilized platinum nanoparticles (Ch-PtNPs). Platinum nanoparticles highly stabilized by chitosan were easily synthesized at room temperature and characterized by HR-TEM, UV-vis, and voltammetry. Ch-PtNPs presented an average diameter of 2.7 nm, and typical voltammetric peaks of Pt in sulfuric acid medium were detected for films containing Ch-PtNPs. As a proof of concept, the CB-Ch-PtNP electrode was applied in the determination of hydrogen peroxide (H₂O₂) and the endocrine disruptor bisphenol A (BPA). Pronounced electrocatalytic activity towards H₂O₂ reduction was observed in the presence of Ch-PtNPs in the films, guaranteeing the non-enzymatic determination of H₂O₂ by chronoamperometry, with a limit of detection of 10 μmol L^-1. In the determination of BPA by differential pulse adsorptive anodic stripping voltammetry (DPAdASV), under optimal experimental conditions, a wide linear response range and a limit of detection at the nanomolar level (7.9 nmol L^-1) were achieved. In addition, excellent repeatabilities of sensor response and sensor fabrication, and accuracy in the analysis of natural water samples were obtained.

Enhancement of electrode properties using carbon dots functionalized magnetite nanoparticles for azo dye decolorization in microbial fuel cell

Technology integration of nanomaterials with microbial fuel cell (MFC) have led to simultaneous degradation of recalcitrant dyes and energy extraction from textile wastewater. Limited electron transfer capacity and hydrophobicity of electrode are the bottlenecks for enhancing the performance of MFC. Nanomaterials can provide surface functionalities for electron transfers and serve as catalyst for pollutant degradation. In this paper, magnetite nanoparticles functionalized with carbon dots (Fe₃O₄@CDs) were used to enhance the electron transfer capacity of the electrodes due to numerous surface-active functional groups of CDs and the reversible redox reaction of Fe²⁺/Fe³⁺. Polydopamine (PDA) was used as binder to coat Fe₃O₄@CDs onto the surface of carbon felt (CF) electrodes in a sono-chemical reaction, favoring to form biocompatible electrodes. Charge transfer resistance of Fe₃O₄@CDs@PDA-CF was 5.02Ω as compared to 293.34Ω of unmodified CF. Fe₃O₄@CDs@PDA-CF installed MFC could achieve almost 98% dye degradation efficiency within 48 h and 18.30 mW m^-2 power output as compared to 77% dye degradation and 0.34 mW m^-2 power output by unmodified CF electrode MFC. Moreover, metagenomic analysis of microbial consortia developed in Fe₃O₄@CDs@PDA-CF MFC showed enrichment of electrogenic and dye degrading microbial communities of Achromobacter. Delftia, Geobacter and Pseudomonas.

Electrochemical (bio)sensors based on carbon quantum dots, ionic liquid and gold nanoparticles for bisphenol A

Electrochemical (bio)sensors were developed for bisphenol A (BPA) determination. Screen printed carbon electrode (SPCE) was modified with ionic liquid 1- butyl-3-methylimidazolium tetrafluoroborate (IL), carbon quantum dots (CQD) and gold nanoparticles (AuNP) for the fabrication of the BPA sensor. Electrode surface composition was optimized for the deposition time of AuNP, amount of CQD and percentage of IL using the central composite design (CCD) method. The results of the CCD study indicated that maximum amperometric response was recorded when 9.8 μg CQD, 3% IL and 284 s AuNP deposition time were used in modification. Tyrosinase (Ty) was further modified on the AuNP/CQD-IL/SPCE to fabricate the biosensor. Analytical performance characteristics of the BPA sensor were investigated by differential pulse anodic adsorptive stripping voltammetry and the AuNP/CQD-IL/SPCE sensor exhibited a linear response to BPA in the range of 2.0 × 10^-8 - 3.6 × 10^-6 M with a detection limit of 1.1 × 10^-8 M. Amperometric measurements showed that the linear dynamic range and detection limit of the Ty/AuNP/CQD-IL/SPCE were 2.0 × 10^-8 - 4.0 × 10^-6 M and 6.2 × 10^-9 M, respectively. Analytical performance characteristics such as sensitivity, reproducibility and selectivity were investigated for the presented (bio)sensors. The analytical applicability of the (bio)sensors to the analysis of BPA in mineral water samples was also tested.

An ultrasensitive electrochemical biosensor for bisphenol A based on aptamer-modified MrGO@AuNPs and ssDNA-functionalized AuNP@MBs synergistic amplification

Bisphenol A (BPA) is a harmful endocrine disruptor, sensitive and rapid quantification of BPA is highly desirable. In this work, a novel synergistic signal-amplifying electrochemical biosensor was developed for BPA detection by using a recognition probe (RP) constructed by BPA aptamer modified gold nanoparticles-loaded magnetic reduced graphene oxide (Aptamer-MrGO@AuNPs), and a signal probe (SP) constructed by BPA aptamer-complementary single-stranded DNA (ssDNA) functionalized methylene blue (MB)-loaded gold nanoparticle (ssDNA-AuNP@MBs). The RP and SP can self-assemble to form a stable RP-SP complex through complementary base pairing. The current intensity of the biosensor correlates with the number of RP-SP complexes. In the presence of BPA, the BPA aptamer can capture BPA with high selectivity and affinity, form an RP-BPA complex and dissociate the RP-SP complex to release SP, resulting in a decrease in the current signal intensity of the biosensor. A single AuNP could be loaded with multiple BPA aptamers and MBs, which improves the recognition efficiency and enhances the signal intensity. Due to the magnetic properties of MrGO@AuNPs, the magnetic separation and adsorption of RP or RP-SP complex is very convenient, enabling all reaction processes to be carried out in solution, which not only improves the mass transfer efficiency, but also simplifies the operation. Under optimal conditions, the developed biosensor had a detection limit as low as 0.141 pg/mL and had been successfully applied to the detection of real environmental water samples. Therefore, the synergistic signal amplification strategy of RP and SP has potential value in the detection of trace pollutants in the water environment.

Flexible Electrochemical Platform Coupled with In Situ Prepared Synthetic Receptors for Sensitive Detection of Bisphenol A

A flexible electrochemical sensor based on the carbon felt (CF) functionalized with Bisphenol A (BPA) synthetic receptors was developed. The artificial Bisphenol A receptors were grafted on the CF by a simple thermal polymerization molecular imprinting process. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and electrochemical characterizations were used to analyze the receptors. Characterization results demonstrated that the Bisphenol A synthetic receptors successfully formed on the CFs surface. Because the synthetic receptor and the porous CFs were successfully combined, the sensor displayed a better current response once Bisphenol A was identified. The sensor's linear range was determined to be from 0.5 to 8.0 nM and 10.0 to 300.0 nM, with a detection limit of 0.36 nM. Even after being bent and stretched repeatedly, the electrode's performance was unaffected, demonstrating the robustness, adaptability and viability of installing the sensor on flat or curved surfaces for on-site detection. The designed electrochemical sensor has been used successfully to identify Bisphenol A in milk samples with satisfactory results. This work provided a promising platform for the design of implantable, portable and miniaturized sensors.

Facile synthesis of Cu NPs@Fe3O4-lignosulfonate: Study of catalytic and antibacterial/antioxidant activities

Environmental pollution is one of the important concerns for human health. There are different types of pollutants and techniques to eliminate them from the environment. We hereby report an efficient method for the remediation of environmental contaminants through the catalytic reduction of the selected pollutants. A green method has been developed for the immobilization of copper nanoparticles on magnetic lignosulfonate (Cu NPs@Fe₃O₄-LS) using the aqueous extract of Filago arvensis L. as a non-toxic reducing and stabilizing agent. The characterization of the prepared Cu NPs@Fe₃O₄-LS was achieved by vibrating sample magnetometer (VSM), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), high resolution TEM (HRTEM), X-ray diffraction (XRD), scanning TEM (STEM), thermogravimetry-differential thermal analysis (TG/DTA), fast Fourier transform (FFT), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron (XPS) analyses. The synthesized Cu NPs@Fe₃O₄-LS was applied as a magnetic and green catalyst in the reduction of Congo Red (CR), 4-nitrophenol (4-NP), and methylene blue (MB). The progress of the reduction reactions was monitored by UV-Vis spectroscopy. Finally, the biological properties of the Cu NPs@Fe₃O₄-LS were investigated. The prepared catalyst demonstrated excellent catalytic efficiency in the reduction of CR, 4-NP, and MB in the presence of sodium borohydride (NaBH₄) as the reducing agent. The appropriate magnetism of Cu NPs@Fe₃O₄-LS made its recovery very simple. The advantages of this process include a simple reaction set-up, high and catalytic antibacterial/antioxidant activities, short reaction time, environmentally friendliness, high stability, and easy separation of the catalyst. In addition, the prepared Cu NPs@Fe₃O₄-LS could be reused for four cycles with no significant decline in performance.

Synthesis, Toxicity Assessment, Environmental and Biomedical Applications of MXenes: A Review

MXenes are a family of two-dimensional (2D) composite materials based on transition metal carbides, nitrides and carbonitrides that have been attracting attention since 2011. Combination of electrical and mechanical properties with hydrophilicity makes them promising materials for biomedical applications. This review briefly discusses methods for the synthesis of MXenes, their potential applications in medicine, ranging from sensors and antibacterial agents to targeted drug delivery, cancer photo/chemotherapy, tissue engineering, bioimaging, and environmental applications such as sensors and adsorbents. We focus on in vitro and in vivo toxicity and possible mechanisms. We discuss the toxicity analogies of MXenes and other 2D materials such as graphene, mentioning the greater biocompatibility of MXenes. We identify existing barriers that hinder the formation of objective knowledge about the toxicity of MXenes. The most important of these barriers are the differences in the methods of synthesis of MXenes, their composition and structure, including the level of oxidation, the number of layers and flake size; functionalization, test concentrations, duration of exposure, and individual characteristics of biological test objects Finally, we discuss key areas for further research that need to involve new methods of nanotoxicology, including predictive computational methods. Such studies will bring closer the prospect of widespread industrial production and safe use of MXene-based products.

Chitosan/Gold Nanoparticles Nanocomposite Film for Bisphenol A Electrochemical Sensing

Bisphenol A (BPA) is considered an endocrine-disrupting compound and can cause toxicological effects, even at low doses. The development of sensitive and reliable sensors that would allow the detection of such contaminant is highly pursued. Herein, we report an electrochemical sensing strategy based on a simple and low-cost nanocomposite film sensor platform for BPA detection. The platform was developed by modifying a fluorine-doped tin oxide (FTO) electrode with layer-by-layer (LbL) films of chitosan (Chi) and gold nanoparticles functionalized with a polythiophene derivative (AuNPs:PTS). The growth of the Chi/AuNPs:PTS LbL films was monitored by UV–Vis spectroscopy. Electrochemical characterization revealed that the three-bilayer film exhibited the highest electrocatalytic performance and differential-pulse voltammetry (DPV) measurements demonstrated that the modified electrode was suitable for BPA detection through a quasi-reversible and adsorption-controlled electrochemical oxidation and reduction process. The developed sensor exhibited a linear response range from 0.4 to 20 μmol L−1, with a detection limit of 0.32 μmol L−1. The sensor showed good reproducibility with relative standard deviations of 2.12% and 3.73% to intra- and inter-electrode, respectively. Furthermore, the platform demonstrated to be suitable to detect BPA in real water samples, as well as selective for BPA detection in solutions with 100-fold excess of common interfering compounds.

Ultrasensitive electrochemical sensor for detection of rutin antioxidant by layered Ti3Al0.5Cu0.5C2 MAX phase

MAX phases have attracted great attention due to unique features such as thermal and electrical conductivity, easy fabrication, heat resistant, and lightweight. In this study, an easy and green method was employed to successfully develop a Ti₃Al_0.5Cu_0.5C₂ MAX phase structure, and a Ti₃Al_0.5Cu_0.5C₂ based glassy carbon electrode (GCE) was applied for the electrochemical determination of rutin antioxidants in mandarin and kiwi samples. The developed Ti₃Al_0.5Cu_0.5C₂ MAX phase was characterized by different techniques such as X-ray photoelectron spectroscopy (XPS), thermogravimetry and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) to obtain information on the structural and morphological properties. Electrochemical methods such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed for the determination of rutin using Ti₃Al_0.5Cu_0.5C₂/GCE. The GCE modified with Ti₃Al_0.5Cu_0.5C₂ demonstrated amplified electrochemical response (ca. 4.25 times) in comparison to the bare GCE towards rutin, and exhibited ultra-sensitivity and selectivity in the presence of other interfering antioxidants. Under the optimum conditions, good linearity in the range of 0.02-50.00 μmol L^-1 was obtained for rutin analysis by the Ti₃Al_0.5Cu_0.5C₂-based sensor with a limit of detection (LOD, 3σ/K) as low as 0.015 μmol L^-1. The fabricated Ti₃Al_0.5Cu_0.5C₂ MAX phase was applied to determine trace levels of rutin in mandarin and kiwi samples with validation by high-performance liquid chromatography (HPLC), thus highlighting its potential for the electrochemical determination of small molecules in the agricultural field.