A novel electrochemical sensor based on Au@PANI composites film modified glassy carbon electrode binding molecular imprinting technique for the determination of melamine

Label-Free detection of Poly-Cystic Ovarian Syndrome using a highly conductive 2-D rGO/MoS2/PANI nanocomposite based immunosensor

Polycystic ovarian syndrome (PCOS) is an endocrinal disorder characterized by multiple tiny cysts, amenorrhea, dysmenorrhea, hirsutism, and infertility. The current diagnostic tools comprise of expensive, time-consuming ultrasonography to serological test, which have low patient compliance. To address these limitations, we have developed a highly sensitive, cost effective and ultrafast immunosensor for the diagnosis of PCOS. Herein, we have fabricated a 2-D electro conductive composites of reduced Graphene oxide (rGO), Molybdenum disulfide (MoS2), and Polyaniline (PANI) as electrode material. Furthermore, for detecting an early and non-cyclic biomarker of PCOS, i.e. anti-Mullerian hormone (AMH). We utilize the specific antigen-antibody mechanism, in which monoclonal Anti-AMH antibodies were covalently immobilized using EDC-NHS chemistry on electrode. The developed biosensor was physicochemical and electrochemically characterized to demonstrate its efficiency. Further we have investigated the biosensor's performance with Cyclic Voltammetry, Differential Pulse Voltammetry, and Electrochemical Impedance Spectroscopy. We have validated that under the optimized condition the immunosensor exhibits higher sensitivity with a LOD of ∼ 2.0 ng/mL with a linear range up to 100 ng/mL. Furthermore, this immunosensor works efficiently with a lower sample volume (>5 μL), which provides a sensitive, reproducible, low-cost, rapid analysis to detect AMH level in PCOS diagnosis.

Au/PANI@PtCu-based electrochemical immunosensor for ultrasensitive determination of pro-gastrin-releasing peptide

An ultrasensitive sandwich-type electrochemical immunosensor for pro-gastrin-releasing peptide (ProGRP) detection was constructed based on PtCu nanodendrites functionalized Au/polyaniline nanospheres (Au/PANI@PtCu). The prepared Au/PANI@PtCu nanocomposites not only possessed excellent electro-catalytic activity of H2O2 reduction due to the synergistic effect between the Au/PANI and PtCu NDs but also provided large specific surface area for detection of antibodies (Ab2) immobilization. In addition, Au nanoparticles encapsulated multi-wall carbon nanotubes (AuNPs@MWCNTs) were also applied to modify the glassy carbon electrode interface for loading numerous capture antibodies (Ab1). In the presence of target ProGRP, a sandwich-type electrochemical immunosensor showed a strong current response from the electro-catalysis of Au/PANI@PtCu toward H2O2 reduction. Benefiting from the exceptional electro-catalytic performance of Au/PANI@PtCu and the high conductivity of AuNPs@MWCNTs, the sandwich-type immunoassay exhibited remarkable sensitivity in detection. The linear range extended from 100 fg/mL to 10 ng/mL, while achieving an impressively low limit of detection of 77.62 fg/mL.

Advances in the Use of Conducting Polymers for Healthcare Monitoring

Conducting polymers (CPs) are an innovative class of materials recognized for their high flexibility and biocompatibility, making them an ideal choice for health monitoring applications that require flexibility. They are active in their design. Advances in fabrication technology allow the incorporation of CPs at various levels, by combining diverse CPs monomers with metal particles, 2D materials, carbon nanomaterials, and copolymers through the process of polymerization and mixing. This method produces materials with unique physicochemical properties and is highly customizable. In particular, the development of CPs with expanded surface area and high conductivity has significantly improved the performance of the sensors, providing high sensitivity and flexibility and expanding the range of available options. However, due to the morphological diversity of new materials and thus the variety of characteristics that can be synthesized by combining CPs and other types of functionalities, choosing the right combination for a sensor application is difficult but becomes important. This review focuses on classifying the role of CP and highlights recent advances in sensor design, especially in the field of healthcare monitoring. It also synthesizes the sensing mechanisms and evaluates the performance of CPs on electrochemical surfaces and in the sensor design. Furthermore, the applications that can be revolutionized by CPs will be discussed in detail.

Nootkatone Mitigated Melamine-Evoked Hepatotoxicity by Featuring Oxidative Stress and Inflammation Interconnected Mechanisms: In Vivo and In Silico Approaches

Melamine (ML) is a common environmental contaminant, commonly used in food fraud, representing a serious health hazard and jeopardizing human and animal health. Recently, nootkatone (NK), a naturally occurring sesquiterpenoid, has garnered considerable attention due to its potential therapeutic advantages. We investigated the potential mechanisms underlying the protective effects of NK against ML-induced liver injury in rats. Five groups were utilized: control, ML, NK10, ML-NK5, and ML-NK10. ML induced substantial hepatotoxicity, including considerable alterations in biochemical parameters and histology. The oxidative distress triggered by ML increased the generation of malondialdehyde (MDA) and nitric oxide (NO) and decreased levels of reduced glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD) activities. In addition, decreased expression of nuclear factor-erythroid 2-related factor 2 (Nrf2) and increased nuclear factor kappa beta (NF-κB) expression levels were observed in hepatocytes, which indicated the occurrence of inflammatory changes following ML exposure. These alterations were alleviated by NK supplementation in a dose-dependent manner. The data revealed that the favorable effects of NK were attributed, at least in part, to its antioxidant and anti-inflammatory properties. Moreover, our results were supported by molecular docking studies that revealed a good fit and interactions between NK and antioxidant enzymes. Thus, the current study demonstrated that NK is a potential new food additive for the prevention or treatment of ML-induced toxicity.

Electrochemical immunosensor AuNPs/NG-PANI/ITO-PET for the determination of BDNF in depressed mice serum

A novel electrochemical immunosensor was developed for highly sensitive detection of brain-derived neurotrophic factor (BDNF), a well-known depression marker. The immunosensor was fabricated by modifying indium tin oxide-coated polyethylene terephthalate (ITO-PET) with N-doped graphene-polyaniline (NG-PANI) and gold nanoparticles (AuNPs) to enhance the conductivity and protein loading capacity. Subsequently, BDNF was immobilized onto the electrode surface via gold-sulfur bonds, followed by the attachment of biotinylated antibody (Biotin-Ab) and horseradish peroxidase-avidin (HRP-Avidin) to create the final immunosensor (HRP-Avidin-Biotin-Ab-BDNF-AuNPs/NG-PANI/ITO-PET). The proposed immunosensor exhibited a linear range of determination (0.781-400 pg/mL) with a low limit of detection (LOD) of 0.261 pg/mL (S/N = 3) and excellent reproducibility (RSD = 1.4%) and stability (92.7%, RSD = 3.1%). Additionally, the immunosensor demonstrated good anti-interference performance and good recovery (98.1-107%). To evaluate the practical utility of the immunosensor, BDNF levels were quantified in the serum of mice with depression induced by chronic unpredictable mild stress (CUMS). The results indicated that the serum BDNF levels were significantly decreased in the depression model group compared with the control group, highlighting the potential of this immunosensor for clinical detection of BDNF in depression diagnosis and treatment.

Detection of nitrification inhibitor dicyandiamide: A direct electrochemical approach

A single run approach for rapid detection of nitrification inhibitor, dicyandiamide (DCD) using electrogenerated chlorine assisted polymerization through azo bond, under acidic conditions and at a preanodized screen printed carbon electrode (SPCE*) is presented. The role of chloride containing support electrolyte in acidic medium along with oxygen functionalities/edge sites are found to be crucial for the successful oxidative polymerization and subsequent adsorption of oxidized products on the electrode surface. The SEM, cyclic voltammetry and X-ray photoelectron spectroscopy studies were used to characterize the polymer film formation. The system exhibited a linear range between 20 and 170 μM with a detection limit of 3 μM (S/N = 3). The method was successfully tested for the detection of DCD in dairy and water samples. Simultaneous detection of DCD in the presence of melamine has also been demonstrated.

Molecularly imprinted polypyrrole based electrochemical sensor for selective determination of ethanethiol

This work describes a molecularly imprinted (MIP) sensor, based on the electropolymerization of pyrrole on a glassy carbon electrode (GCE), for the determination of ethanethiol. Ethanethiol was used as a template molecule for the formation of cavities in the imprinted polymer. The effect of molar ratios template molecules/functional monomers and time needed to remove the template were optimized. The developed MIP/GCE sensor presented a linear range from 6.1 to 32.4 mg L^-1 with capability detection and reproducibility values of 7.2 mg L^-1 and 10.4%, respectively. The sensitivity of the developed sensor was enhanced by the incorporation of gold nanoparticles (AuNPs). The AuNPs/MIP/GCE showed a capability of detection and reproducibility values of 0.4 mg L^-1 and 4.1%, respectively (calibration range from 0.3 to 3.1 mg L^-1). The sensor was successfully applied to the determination of ethanethiol in spiked wine samples with recoveries ranging from 99% to 107%.

Valorization of Agricultural Waste as a Chemiresistor H2S-Gas Sensor: A Composite of Biodegradable-Electroactive Polyurethane-Urea and Activated-Carbon Composite Derived from Coconut-Shell Waste

In this study, a high-performance H2S sensor that operates at RT was successfully fabricated using biodegradable electroactive polymer-polyurethane-urea (PUU) and PUU-activated-carbon (AC) composites as sensitive material. The PUU was synthesized through the copolymerization of biodegradable polycaprolactone diol and an electroactive amine-capped aniline trimer. AC, with a large surface area of 1620 m2/g and a pore diameter of 2 nm, was derived from coconut-shell waste. The composites, labeled PUU-AC1 and PUU-AC3, were prepared using a physical mixing method. The H2S-gas-sensing performance of PUU-AC0, PUU-AC1, and PUU-AC3 was evaluated. It was found that the PUU sensor demonstrated good H2S-sensing performance, with a sensitivity of 0.1269 ppm-1 H2S. The H2S-gas-sensing results indicated that the PUU-AC composites showed a higher response, compared with PUU-AC0. The enhanced H2S-response of the PUU-AC composites was speculated to be due to the high surface-area and abounding reaction-sites, which accelerated gas diffusion and adsorption and electron transfer. When detecting trace levels of H2S gas at 20 ppm, the sensitivity of the sensors based on PUU-AC1 and PUU-AC3 increased significantly. An observed 1.66 and 2.42 times' enhancement, respectively, in the sensors' sensitivity was evident, compared with PUU-AC0 alone. Moreover, the as-prepared sensors exhibited significantly high selectivity toward H2S, with minimal to almost negligible responses toward other gases, such as SO2, NO2, NH3, CO, and CO2.

Construction of a Molecularly Imprinted Sensor Modified with Tea Branch Biochar and Its Rapid Detection of Norfloxacin Residues in Animal-Derived Foods

Norfloxacin (NOR) is a common antibiotic used in humans and animals, and its high levels can cause intolerance or poisoning. Therefore, NOR levels in animal-derived foods must be monitored due to potential side effects and illegal use phenomena. This research centered on the development of an environmentally friendly electrochemical sensor for NOR detection. Potassium carbonate activated tea branch biochar (K-TBC) as an efficient use of waste was coated on the surface of glassy carbon electrode (GCE), and a molecular-imprinted polymer (MIP) layer was subsequently electropolymerized onto the modified electrode. NOR was used as template molecule and o-phenylenediamine (o-PD) and o-aminophenol (o-AP) were used as bifunctional monomers. The electrochemical sensor was built and its electrochemical behavior on NOR was investigated. The sensor demonstrated an excellent linear current response to NOR concentrations in the ranges of 0.1-0.5 nM and 0.5-100 nM under ideal experimental circumstances, with a detection limit of 0.028 nM (S/N = 3). With recoveries ranging from 85.90% to 101.71%, the designed sensor was effectively used to detect NOR in actual samples of milk, honey, and pork. Besides, the fabricated sensor had low price, short detection time, good selectivity and stability, which can provide a theoretical and practical basis for the actual monitoring of NOR residues.

Application of Molecularly Imprinted Electrochemical Biomimetic Sensors for Detecting Small Molecule Food Contaminants

Environmental chemical contaminants in food seriously impact human health and food safety. Successful detection methods can effectively monitor the potential risk of emerging chemical contaminants. Among them, molecularly imprinted polymers (MIPs) based on electrochemical biomimetic sensors overcome many drawbacks of conventional detection methods and offer opportunities to detect contaminants with simple equipment in an efficient, sensitive, and low-cost manner. We searched eligible papers through the Web of Science (2000-2022) and PubMed databases. Then, we introduced the sensing mechanism of MIPs, outlined the sample preparation methods, and summarized the MIP characterization and performance. The classification of electrochemistry, as well as its advantages and disadvantages, are also discussed. Furthermore, the representative application of MIP-based electrochemical biomimetic sensors for detecting small molecular chemical contaminants, such as antibiotics, pesticides, toxins, food additives, illegal additions, organic pollutants, and heavy metal ions in food, is demonstrated. Finally, the conclusions and future perspectives are summarized and discussed.

Development of a New Electrochemical Sensor Based on Molecularly Imprinted Biopolymer for Determination of 4,4'-Methylene Diphenyl Diamine

A new molecularly imprinted electrochemical sensor was proposed to determine 4,4'-methylene diphenyl diamine (MDA) using molecularly imprinted polymer-multiwalled carbon nanotubes modified glassy carbon electrode (MIP/MWCNTs/GCE). GCE was coated by MWCNTs (MWCNTs/GCE) because of their antifouling qualities and in order to improve the sensor sensitivity. To make the whole sensor, a polymeric film made up of chitosan nanoparticles was electrodeposited by the cyclic voltammetry method on the surface of MWCNTs/GCE in the presence of MDA as a template. Different parameters such as scan cycles, elution time, incubation time, molar ratio of template molecules to functional monomers, and pH were optimized to increase the performance of the MIP sensor. With a detection limit of 15 nM, a linear response to MDA was seen in the concentration range of 0.5-100 µM. The imprinting factor (IF) of the proposed sensor was also calculated at around 3.66, demonstrating the extremely high recognition performance of a MIP/MWCNT-modified electrode. Moreover, the sensor exhibited good reproducibility and selectivity. Finally, the proposed sensor was efficiently used to determine MDA in real samples with satisfactory recoveries ranging from 94.10% to 106.76%.

Review of Electrochemical Biosensors for Food Safety Detection

Food safety issues are directly related to people's quality of life, so there is a need to develop efficient and reliable food contaminants' detection devices to ensure the safety and quality of food. Electrochemical biosensors have the significant advantages of miniaturization, low cost, high sensitivity, high selectivity, rapid detection, and low detection limits using small amounts of samples, which are expected to enable on-site analysis of food products. In this paper, the latest electrochemical biosensors for the detection of biological contaminants, chemical contaminants, and genetically modified crops are reviewed based on the analytes of interest, electrode materials and modification methods, electrochemical methods, and detection limits. This review shows that electrochemical biosensors are poised to provide miniaturized, specific, selective, fast detection, and high-sensitivity sensor platforms for food safety.

Development of an ultrasensitive molecularly imprinted poly-(ortho-phenylenediamine) based sensor for the determination of melamine adulteration in milk and infant formula

A sensitive molecularly imprinted poly-(ortho-phenylenediamine) electrochemical sensor was fabricated for selective melamine detection in milk and infant formula. The pencil graphite electrode (PGE) was modified by deposition of Au nanoparticles and reduced graphene oxide (RGO) on its surface. The fabrication of the electrode in various stages was monitored using cyclic voltammetry. The immobilized RGO, MIP, and gold nanoparticles on the PGE surface were morphologically characterized by field-emission scanning electron microscopy (FESEM). Under the optimized conditions, the linear range and the limit of detection (LOD) were 10-17-10-8 M and 2.64 × 10-16 M (S/N = 3), respectively. The prepared sensor exhibited a good reproducibility and repeatability response. The recovery range of melamine-spiked milk and infant formula was 92.7%-103.9% and 93.5%-105.8%, respectively. The sensor could apply successfully for melamine determination in milk and infant formula samples.

One step construction of an electrochemical sensor for melamine detection in milk towards an integrated portable system

Excessive intake of melamine (MEL) can be harmful to human health, and it is important to establish a rapid and accurate MEL detection method. As the electrochemical activity of MEL is very low, ferrocenylglutathione (Fc-ECG) was used as an electron transfer mediator to assist with the detection of MEL using screen-printed carbon electrode (SPCE). This modified electrode (MEL/Fc-ECG/SPCE) was prepared by stepwise drop-casting and was fully characterized. Results showed that MEL significantly enhanced signal of Fc-ECG/SPCE sensor due to the three p-π conjugated double bonds that facilitated electron transfer. Under optimal conditions, the sensor exhibits two linearities in the range of 0.20-2.00 μM and 8.00-800 μM, with a sensitivity of 15.03 μA·μM^-1·cm^-2. The selectivity, stability, and reproducibility were investigated and successfully used to detect MEL in raw milk and confirms safety verification of foods. Moreover, a portable testing platform was designed for MEL detection based on a CH32 chip.

Nano-Scaled Materials and Polymer Integration in Biosensing Tools

The evolution of biosensors and diagnostic devices has been thriving in its ability to provide reliable tools with simplified operation steps. These evolutions have paved the way for further advances in sensing materials, strategies, and device structures. Polymeric composite materials can be formed into nanostructures and networks of different types, including hydrogels, vesicles, dendrimers, molecularly imprinted polymers (MIP), etc. Due to their biocompatibility, flexibility, and low prices, they are promising tools for future lab-on-chip devices as both manufacturing materials and immobilization surfaces. Polymers can also allow the construction of scaffold materials and 3D structures that further elevate the sensing capabilities of traditional 2D biosensors. This review discusses the latest developments in nano-scaled materials and synthesis techniques for polymer structures and their integration into sensing applications by highlighting their various structural advantages in producing highly sensitive tools that rival bench-top instruments. The developments in material design open a new door for decentralized medicine and public protection that allows effective onsite and point-of-care diagnostics.

Polyaniline-Pectin nanoparticles immobilized paper based colorimetric sensor for detection of Escherichia coli in milk and milk products

In the food quality and safety arena, there is a need to develop novel and sustainable methodologies that can help in the prevention of foodborne diseases. Herein, we report the development of a rapid conducting polymer strip-based sensor using Polyaniline-pectin (PANI-PEC) for the detection of Escherichia coli in milk and milk products. Polyaniline-pectin nanoparticles stabilized with biopolymer pectin were synthesized and its characterization studies such as FTIR, UV-Vis spectroscopy, electrical conductivity and particle size analysis were done. The assay parameters were optimized for the selective detection of E. coli in milk and milk products. The concentration of PANI-PEC solution immobilized/strip was optimized to be 3 mg/mL as it exhibited good sensitivity and colour intensity. Based on acid production and selectivity for E.coli, concentrations of media components like lactose, tryptophan, yeast extract, chondroitin sulphate, sodium lauryl sulphate, potassium chloride, tergitol-7, gentamycin sulphate and ampicillin trihydrate were optimized as 0.9, 0.1, 0.45, 0.015, 0.1, 2, 0.0125, 0.00016 and 0.015 respectively and sample volume was optimized to 500 μL. The developed PANI-PEC colorimetric strip-based sensor detects 0.52 ± 0.17 log CFU/mL E. coli within 10: 21 h (h). Further shelf-life study revealed that the developed PANI-PEC colorimetric sensor strips are stable at room temperature up to six months exhibiting the same sensitivity. The results obtained here indicate that this novel and simple paper based colorimetric sensor holds potential for application in food industries as a reliable and rapid method for detection of E. coli in milk and milk products at various stages of production and processing.

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Rapid conducting polymer strip-based sensor has been developed for the detection of E. coli in milk and milk products.

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PANI-PEC colorimetric strip-based sensor detects 0.52 ± 0.17 log CFU/mL E. coli within 10: 21 h (h).

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PANI-PEC colorimetric sensor strips are stable at room temperature up to six months exhibiting the same sensitivity.

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PANI-PEC colorimetric strip-based sensor assay is a sensitive, cost effective and simple to use method.

An Electrochemical Immunosensor Based on SPA and rGO-PEI-Ag-Nf for the Detection of Arsanilic Acid

A sensitive electrochemical immunosensor was prepared for rapid detection of ASA based on arsanilic acid (ASA) monoclonal antibody with high affinity. In the preparation of nanomaterials, polyethyleneimine (PEI) improved the stability of the solution and acted as a reducing agent to generate reduced graphene oxide (rGO) with relatively strong conductivity, thereby promoting the transfer of electrons. The dual conductivity of rGO and silver nanoparticles (AgNPs) improved the sensitivity of the sensor. The synthesis of nanomaterials were confirmed by UV-Vis spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy. In the optimal experiment conditions, the sensor could achieve the detection range of 0.50–500 ng mL⁻¹ and the limit of detection (LOD) of 0.38 ng mL⁻¹ (S/N = 3). Moreover, the sensor exhibited excellent specificity and acceptable stability, suggesting that the proposed sensor possessed a good potential in ASA detection. Thus, the as-prepared biosensor may be a potential way for detecting other antibiotics in meat and animal-derived foods.

Molecularly Imprinted Polymers (MIPs) in Sensors for Environmental and Biomedical Applications: A Review

Molecular imprinted polymers are custom made materials with specific recognition sites for a target molecule. Their specificity and the variety of materials and physical shapes in which they can be fabricated make them ideal components for sensing platforms. Despite their excellent properties, MIP-based sensors have rarely left the academic laboratory environment. This work presents a comprehensive review of recent reports in the environmental and biomedical fields, with a focus on electrochemical and optical signaling mechanisms. The discussion aims to identify knowledge gaps that hinder the translation of MIP-based technology from research laboratories to commercialization.

Sensor Based on a Poly[2-(Dimethylamino)ethyl Methacrylate-Co-Styrene], Gold Nanoparticles, and Methylene Blue-Modified Glassy Carbon Electrode for Melamine Detection

Melamine has been used as a non-protein nitrogenous additive in food products to artificially increase the apparent “false” protein content. Melamine is known as a dangerous and poisonous substance for human health and it causes diverse diseases. An electrochemical sensor for melamine detection has been developed by modification of a glassy carbon electrode using copolymer poly[DMAEMA-co-styrene], gold nanoparticles, and methylene blue. The characterization of the modified electrode was conducted using several analysis techniques including cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The electrochemical detection of melamine was performed by impedance spectroscopy. Obtained results revealed that the developed sensor has a large detection range from 5.0 × 10⁻¹³ to 3.8 × 10⁻⁸ M with a low detection limit of 1.8 × 10⁻¹² M (at S/N = 3). Various interfering species such as phenol, hydroquinone, and bisphenol A have been used and their behavior on modified electrode has been studied.

Electrochemical Biosensor with Enhanced Antifouling Capability for COVID-19 Nucleic Acid Detection in Complex Biological Media

Biofouling caused by the accumulation of biomolecules on sensing surfaces is one of the major problems and challenges to realize the practical application of electrochemical biosensors, and an effective way to counter this problem is the construction of antifouling biosensors. Herein, an antifouling electrochemical biosensor was constructed based on electropolymerized polyaniline (PANI) nanowires and newly designed peptides for the detection of the COVID-19 N-gene. The inverted Y-shaped peptides were designed with excellent antifouling properties and two anchoring branches, and their antifouling performances against proteins and complex biological media were investigated using different approaches. Based on the biotin-streptavidin affinity system, biotin-labeled probes specific to the N-gene (nucleocapsid phosphoprotein) of COVID-19 were immobilized onto the peptide-coated PANI nanowires, forming a highly sensitive and antifouling electrochemical sensing interface for the detection of COVID-19 nucleic acid. The antifouling genosensor demonstrated a wide linear range (10-14 to 10-9 M) and an exceptional low detection limit (3.5 fM). The remarkable performance of the genosensor derives from the high peak current of PANI, which is chosen as the sensing signal, and the extraordinary antifouling properties of designed peptides, which guarantee accurate detection in complex systems. These crucial features represent essential elements for future rapid and decentralized clinical testing.

Imprinted Polymers as Synthetic Receptors in Sensors for Food Safety

Foodborne illnesses represent high costs worldwide in terms of medical care and productivity. To ensure safety along the food chain, technologies that help to monitor and improve food preservation have emerged in a multidisciplinary context. These technologies focus on the detection and/or removal of either biological (e.g., bacteria, virus, etc.) or chemical (e.g., drugs and pesticides) safety hazards. Imprinted polymers are synthetic receptors able of recognizing both chemical and biological contaminants. While numerous reviews have focused on the use of these robust materials in extraction and separation applications, little bibliography summarizes the research that has been performed on their coupling to sensing platforms for food safety. The aim of this work is therefore to fill this gap and highlight the multidisciplinary aspects involved in the application of imprinting technology in the whole value chain ranging from IP preparation to integrated sensor systems for the specific recognition and quantification of chemical and microbiological contaminants in food samples.

Recent developments in voltammetric and amperometric sensors for cysteine detection

This review article aims to provide an overview of the recent advances in the voltammetric and amperometric sensing of cysteine (Cys). The introduction summarizes the important role of Cys as an essential amino acid, techniques for its sensing, and the utilization of electrochemical methods and chemically modified electrodes for its determination. The main section covers voltammetric and amperometric sensing of Cys based on glassy carbon electrodes, screen printed electrodes, and carbon paste electrodes, modified with various electrocatalytic materials. The conclusion section discusses the current challenges of Cys determination and the future perspectives.

A novel electrochemical paper sensor for low-cost detection of 5-methyltetrahydrofolate in egg yolk

An electrochemical deposition method was used to fabricate a gold nanoflower (AuNF) and carbon nanoparticle (CNP) modified carbon paper (CP) sensor (AuNFs-CNPs/CP) for the low-cost detection of 5-methyltetrahydrofolate (5-mTHF) in egg yolk. AuNF morphology and structures were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), revealing nanoflower sizes in the 50 to 200 nm range. AuNFs formed on the sensor were in the Au⁰. We evaluated 5-mTHF assay performance using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The AuNFs-CNPs/CP sensor detected 5-mTHF concentrations in the ranges from 1 to 5 mg L^-1 and 1-20 μg L^-1, with an excellent limit of detection of 1 μg L^-1 and good selectivity toward 5-mTHF, when compared to other potentially interfering molecules in samples. The AuNFs-CNPs/CP sensor was also used to detect 5-mTHF in folate-rich, and was found to be twice than that of ordinary egg yolk.

Pillar[6]arene-modified gold nanoparticles grafted on cellulose nanocrystals for the electrochemical detection of bisphenol A

The as-prepared CNCs@CP6-AuNP nanohybrid and its application in sensing BPA.

Directly assembled electrochemical sensor by combining self-supported CoN nanoarray platform grown on carbon cloth with molecularly imprinted polymers for the detection of Tylosin

Molecularly imprinted polymers (MIPs) based on electrochemical sensors (MIP-EC sensors) have obtained ideal achievements in recent years. However, some challenges are still need to be addressed, such as adjustable preparation, unstable sensing interface and great signal-to-noise ratio. Here, based on the ingenious combination of the MIP and the self-supported CoN nanowire arrays grown on carbon cloth (CoN NWs/CC), a robust MIP-EC sensor was developed, in which the MIP film was uniformly coated on the CoN NWs/CC via a bulk polymerization crosslinking process. Especially, CoN NWs/CC were prepared via in-situ transformation of their oxide precursors and then directly as a candidate of EC electrode. Under the optimal conditions, the MIP-EC sensor can detect Tylosin (TS) in the concentration range from 8.6 × 10^-11 to 6.7 × 10^-5 mol L^-1, and the low detection limit (LOD) is 5.5 × 10^-12 mol L^-1 (S/N = 3). Furthermore, the MIP-EC sensor showed high selectivity, reproducibility and stability. The practicability of the MIP-EC sensor was tested in the actual samples of surface water and soil with the comparison of the traditional ELISA method. The developed MIP-EC sensor with simple and fabrication process can provide a versatile and reliable method, which has great potential application value for the detection of small hazardous molecules.

A novel SWCNT-amplified "signal-on" electrochemical aptasensor for the determination of trace level of bisphenol A in human serum and lake water

A novel "signal-on" electrochemical aptasensor was developed for ultrasensitive and specific detection of BPA, using single-walled carbon nanotubes (SWCNT) as the electro-catalytic probe for further signal amplification. The multi-walled carbon nanotubes (MWCNT), amino-functionalized magnetite, and gold nanoparticles (NH₂-Fe₃O₄/Au NPs) were applied first to modify the glassy carbon electrode (GCE) surface and to form a nanomaterial film with satisfactory conductive properties, stability, and biocompatibility. The BPA aptamer was then loaded onto the sensing platform by hybridization with complementary DNA (CDNA). In the presence of BPA it combines with the aptamer and the BPA-aptamer conjugate was released from the electrode;subsequently the added SWCNT and CDNA assembled quickly. Thus, the dual-amplification of the "signal-on" electrochemical aptasensor takes effect. The [Fe (CN)₆]^3-/4- redox probe signal (∆I) detected by DPV (differential pulse voltammetry) is proportional to the negative logarithm of BPA concentration between 10^-19 M and 10^-14 M. The detection limit is 0.08 aM. Importantly, the proposed biosensor represents a successful application for determination of BPA in human serum and lake water. Schematic representation of SWCNT-amplified "signal-on" electrochemical aptasensor for the detection of trace level of bisphenol A in human serum and lake water.

A Portable Visual Sensor by Molecularly Imprinted Hydrogels for HRP Recognition

Background:

Molecular imprinting is a technology used to produce artificial receptors that simulate the molecular recognition in the nature and prepare the polymer network structure in the presence of template molecule. Molecularly imprinted visual sensor combines the advantages of specific recognition via molecular imprinting and fast response speed via visualization. The aims of this paper are to prepare a portable visual sensor for Horseradish Peroxidase (HRP) recognition based on molecularly imprinted hydrogel.

Methods:

At first, HRP-imprinted polyacrylamide hydrogels with 1 mm thickness were obtained by one-step synthesis via radical induced in-situ polymerization of acrylamide using acrylamide (AAm) as the functional monomer, N,N'-Methylenebisacrylamide (MBA) as the crosslink agent and HRP as the template molecule.

Results:

Compared with nonimprinted hydrogels, the HRP-imprinted hydrogel sensor showed significant color changes in response to the target HRP. This visual sensor was constructed based on 3, 3', 5, 5'- tetramethyl benzidine (TMB) - H2O2 color reaction system by HRP catalyzing to produce color change through digital photography and image analysis (RGB system). The HRP-imprinted hydrogel showed good response in the range of 0.001-0.5 mg/mL and had a significant specific recognition compared to other proteins via selective test.

Conclusion:

The proposed portable visual sensor could be used for qualitative and semi-quantitative analysis of HRP with high selectivity and reasonable regeneration. The sensor has the advantages of simple operation, low cost, no special equipment, and can be applied to serum sample with less sample consumption and no need of sample preparation. It has wide application prospects in microfluidic devices, biomimetic sensors, flexible biosensor and membrane separation technology.

Sensitive electrochemical detection of aflatoxin B1 using DNA tetrahedron-nanostructure as substrate of antibody ordered assembly and template of aniline polymerization

A novel strategy for AFB1 detection in grains was proposed based on DNA tetrahedron-structured probe (DTP) and horseradish peroxidase (HRP) triggered polyaniline (PANI) deposition. Briefly, the DNA tetrahedron nanostructures were assembled on the gold electrode, with carboxylic group designed on top vertex of them. The carboxylic group was conjugated with the AFB1 monoclonal antibody (mAb) to form DTP. The test sample and a known fixed concentration of HRP-labeled AFB1 were mixed and they compete for binding to DTP. The HRP assembled on the gold electrode catalyzed the polymerization of aniline on DTP. AFB1 in grains could be determined by using PANI as electrochemical signal molecules. Interestingly, DNA tetrahedron-structure, which has mechanical rigidity and structural stability, can improve antigen-antibody specific recognition and binding efficiency through the use of mAb ordered assembly. Meanwhile, nucleic acid backbone with a large amount of negative charge is good template for aniline polymerization under mild conditions.

Perovskite nanocrystals fluorescence nanosensor for ultrasensitive detection of trace melamine in dairy products by the manipulation of inner filter effect of gold nanoparticles

Barium sulfate-coated CsPbBr₃ perovskite nanocrystals (CsPbBr₃ NCs@BaSO₄) was successfully synthesized that exhibited stable and intense fluorescence property in aqueous buffer. With the CsPbBr₃ NCs@BaSO₄ as signal readout, an ultrasensitive fluorescence nanosensor was developed for turn-on determination of melamine by the manipulation of inner filter effect of citrate-protected gold nanoparticles (AuNPs). The fluorescence of the CsPbBr₃ NCs@BaSO₄ was remarkably quenched by the AuNPs due to inner filter effect. This inner filter effect could be weakened by the addition of melamine as a result of melamine-triggering aggregation of the AuNPs and subsequently led to a recovery in the fluorescence of the CsPbBr₃ NCs@BaSO₄. The recovery ratio was proportional to the concentration of melamine in the range of 5.0-500.0 nmol/L. The limit of detection was 0.42 nmol/L and the relative standard deviation was 4.0% for the repetitive determination of 500.0 nmol/L melamine solution (n = 11). The nanosensor was successfully applied to analysis of melamine in dairy product samples.

Electrochemical Detection of Melamine by Using Reduced Graphene Oxide-Copper Nanoflowers Modified Glassy Carbon Electrode

In this work, a robust and reliable electrochemical sensor was developed for sensitive detection of non-electroactive melamine (MEL) using a modified glassy carbon electrode with ascorbic acid (AA) as the active recognition element. To increase the current signal of AA, the working electrode was successively modified with l-arginine (l-Arg) and reduced graphene oxide-copper nanoflower composite. The voltammetry measurements denoted that the hydrogen bonding was formed between AA and MEL. Using the optimum conditions, the proposed enhanced sensor can detect MEL concentrations ranging from 10 × 10^-9 to 9.0 × 10^-8 M with a detection limit of 5.0 × 10^-9 M that is proportional to the decrease of AA in the anodic peak current. Finally, the proposed sensor was successfully applied for the determination of MEL in commercial infant milk samples and good recovery values were obtained.