Molecularly imprinted electrochemical sensor for the highly selective and sensitive determination of melamine

Bismuth sulfide micro flowers decorated nickel foam as a promising electrochemical sensor for quantitative analysis of melamine in bottled milk samples

Here, we demonstrate hydrothermally grown bismuth sulfide (Bi2S3) micro flowers decorated nickel foam (NF) for electrochemical detection of melamine in bottled milk samples. The orthorhombic phase of hydrothermally grown Bi2S3is confirmed by the detailed characterization of x-ray diffraction and its high surface area micro flowers-like morphology is investigated via field emission scanning electron microscope. Furthermore, the surface chemical oxidation state and binding energy of Bi2S3/NF micro flowers is analyzed by x-ray photoelectron spectroscopy studies. The sensor exhibits a wide linear range of detection from 10 ng l-1to 1 mg l-1and a superior sensitivity of 3.4 mA cm-2to melamine using differential pulse voltammetry technique, with a lower limit of detection (7.1 ng l-1). The as-fabricated sensor is highly selective against interfering species of p-phenylenediamine (PPDA), cyanuric acid (CA), aniline, ascorbic acid, glucose (Glu), and calcium ion (Ca2+). Real-time analysis done in milk by the standard addition method shows an excellent recovery percentage of ̴ 98%. The sensor's electrochemical mechanism studies reveal that the high surface area bismuth sulfide micro flowers surface interacts strongly with melamine molecules through hydrogen bonding and van der Waals forces, resulting in a significant change in the sensor's electrical properties while 3D skeletal Nickel foam as a substrate provides stability, enhances its catalytic activity by providing a more number /of active sites and facilitates rapid electron transfer. The work presented here confirms Bi2S3/NF as a high-performance electrode that can be used for the detection of other biomolecules used in clinical diagnosis and biomedical research.

Preparation of surface-modified electrode of copper(ii) oxide mixed with the molecularly imprinted polymer for enhancement of melamine detection with photoelectrochemical technique

Melamine contamination in food and beverages affects short- and long-term health. In this work, enhanced sensitivity and selectivity in photoelectrochemical determination for melamine detection was achieved using copper(ii) oxide (CuO) combined with a molecularly imprinted polymer (MIP). A CuO nanomaterial was used to achieve MIP surface modification via co-precipitation synthesis. An MIP film was deposited by polymerizing the methacrylic acid monomer and a melamine template. The properties of the CuO nanomaterials, such as the surface morphology, chemical oxidation state, and crystalline structure, were characterized using field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction patterns (XRD), respectively. The diffuse reflection spectroscopy technique was applied to evaluate the optical properties of the CuO nanoparticles. The results indicated that the synthesized CuO nanomaterials had a monoclinic structure with an optical bandgap of 1.49 eV, which corresponds to absorbance in the visible light region. CPE electrodes with surface-modified CuO/MIP were measured using the photoelectrochemical techniques of cyclic voltammetry, differential pulse voltammetry (DPV), and amperometry. The modified CuO/MIP electrode for melamine detection in 7.4 pH PBS buffer solution exhibited a high sensitivity of 0.332 nA nM-1, with a linear range of 5.0-75.0 nM and a limit of detection of 2.45 nM. Moreover, real samples of various kinds of milk were applied to evaluate the sensing response of the prepared CuO/MIP electrode. The modified CuO/MIP electrodes could be reused seven times with good reproducibility and high selectivity for melamine detection.

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.

Au nanoparticles decorated ZnO/ZnFe2O4 composite SERS-active substrate for melamine detection

Surface-enhanced Raman scattering (SERS) based on plasmonic metal nanoparticles and semiconductors has been used as performance-enhancing structures for sensing trace chemicals. We have selected a case of oxide functional oxide organic nanostructure between ZnFe₂O₄ and ZnO, denoted as ZZF. By decorating such nanostructure with AuNPs, to identify R6G in varying concentrations (10^-6 M - 10^-12 M), an enhancement factor of 1.6 × 10⁸ was observed. The material was used for the identification of melamine in the concentration range of 0.39 μM-7.92 μM. This high-performance nanocomposite provides improved melamine sensitivity towards SERS and the limit of detection as low as 0.39 μM. The Au-ZZF SERS substrate can yield a SERS enhancement factor of 1.37 × 10⁷. The experimental performance demonstrates that excellent SERS enhancement is due to electrons movement within ZZF and Au nanoparticles. Owing to its easy and effective synthesis methodology, this sensitive and specific SERS substrate is a promising technique to detect trace chemicals. We further study the best energetically favorable orientation of melamine molecules over the substrate leading to the SERS activity using density functional theoretical study.

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.

Innovations in Smart Packaging Concepts for Food: An Extensive Review

Innovation in food packaging is mainly represented by the development of active and intelligent packing technologies, which offer to deliver safer and high-quality food products. Active packaging refers to the incorporation of active component into the package with the aim of maintaining or extending the product quality and shelf-life. The intelligent systems are able to monitor the condition of packaged food in order to provide information about the quality of the product during transportation and storage. These packaging technologies can also work synergistically to yield a multipurpose food packaging system. This review is a critical and up-dated analysis of the results reported in the literature about this fascinating and growing field of research. Several aspects are considered and organized going from the definitions and the regulations, to the specific functions and the technological aspects regarding the manufacturing technologies, in order to have a complete overlook on the overall topic.

Dual-Layered Nanomaterial-Based Molecular Pattering on Polymer Surface Biomimetic Impedimetric Sensing of a Bliss Molecule, Anandamide Neurotransmitter

In this endeavor, a novel electrochemical biosensor was designed using multiwall carbon nanotubes (MWCNTs)- and nickel nanoparticles (NiNPs)-embedded anandamide (AEA) imprinted polymer. The NiNPs so synthesized were mortared with MWCNTs and molecularly imprinted polymer (MIP), which enhanced sensitivity and selectivity of the developed sensor, respectively. The characterization methods of AEA-based MIP included X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) analysis, which supported the successful synthesis of the polymer. Electrochemical studies of fabricated sensor were performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy in potentiostatic mode (PEIS). In this first phase of AEA-specific sensor development, MWCNT/NiNP/MIP@SPE was found to successfully discriminate between different concentrations of AEA. The developed sensing platform demonstrated a 100 pM-1 nM linear range with a 0.01 nM detection limit (LOD), 0.0149 mA/pM sensitivity, and 50% stability within 4 months. The sensor demonstrated selectivity toward AEA: although acetylcholine (ACh) and dopamine acted as strong interfering components because of their chemical similarity, the spiked AEA samples demonstrated ∼90% recoveries. Hence, our results have passed the first step in AEA detection at home, although with a clinical setup, future advancement is still required.

Highly Selective Detection of Metronidazole by Self-Assembly via 0D/2D N-C QDs/g-C3N4 Nanocomposites Through FRET Mechanism

A 0D/2D (0-dimensional/2-dimensional) nanostructure was designed by self-assembly of N-C QDs and carboxylated g-C3N4 nanosheets and used as a fluorescence resonance energy transfer (FRET) fluorescent sensor. The N-C QDs/g-C3N4 nanosheets were synthesized via the amino group on the N-C QD surface and the -COOH of the carboxylated g-C3N4 nanosheets. The mechanism of detection of metronidazole (MNZ) by N-C QDs/g-C3N4 nanocomposites is based on FRET between negatively charged N-QDs and positively charged carboxylated g-C3N4 nanoparticles. N-C QDs/g-C3N4 nanostructures displayed good responses for the detection of MNZ at normal temperature and pressure. The decrease in the fluorescence intensity showed a good linear relationship to MNZ concentration within 0-2.6 × 10-5 mol/L, and the detection limit was 0.66 μM. The novel FRET sensor will have a great potential in clinical analysis and biological studies.

Ramamurthy P. Development of Molecularly Imprinted Conducting Polymer Composite Film-Based Electrochemical Sensor for Melamine Detection in Infant Formula

Simple, fast, and sensitive molecularly imprinted composite thin-film-based electrochemical sensor developed by using in situ co-electropolymerization of aniline and acrylic acid in the presence of melamine as a template is described here. The prepolymerization complex formation was studied by using Fourier transform infrared (FTIR) spectrophotometry, while the film formation was performed and characterized by cyclic voltammetry, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM). The optimization of important parameters and removal of melamine generated the binding sites in the polymer matrix, which can recognize melamine specifically. Electrochemical measurements were performed to achieve the linear range, the limit of quantification, and limit of detection of 0.1-180, 0.0573, and 0.0172 nM, respectively. The sensitivity of the sensor was attributed to the synergistic effects of amine from aniline and the carboxylic group from acrylic acid to form multiple noncovalent interactions with the template. Melamine-spiked infant formula and raw milk were analyzed by the developed sensor, and the recovery range of 95.87-105.63% with a relative standard deviation of 1.11-2.23% was obtained. The results showed that the developed sensor using the new composite polymer receptor is promising for the online monitoring of melamine in the food industries in the future.

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.

Visual detection of melamine by using a ratiometric fluorescent probe consisting of a red emitting CdTe core and a green emitting CdTe shell coated with a molecularly imprinted polymer

A composite ratiometric fluorescent probe is described for visual detection of melamine (MEL) in milk samples. It is based on the use of red emitting and green emitting CdTe quantum dots, and a mesoporous molecularly imprinted polymer. The red emitting QDs are embedded in the silica microsphere to serve as a core, and the green emitting QDs are coated on the surface of the silica microsphere as a shell. A molecularly imprinted polymer (MIP) with specific recognition sites for MEL was placed on the shell. If MEL is bound by the MIP, the green fluorescence is quenched due to hydrogen bond interaction. The red emission, in contrast, remains unchanged. Quenching leads to a change in the color of fluorescence from red-green to purely red. This effect allows for visual and instrumental detection of MEL. The mesoporous structure of the MIP reduces the mass transfer resistance and enhances the accessibility of sites for MEL. Response is linear in the 50-1000 ng mL^-1 MEL concentration range, and the limit of detection is 13 ng mL^-1. The fluorescent probe was successfully applied to the analysis of MEL-spiked milk samples and gave recoveries between 94.1 and 98.7%, with 3.6-5.1% relative standard deviations. Graphical abstract Schematic of the preparation and detection of the composite probe. The probe was applied for the selective recognition and visual detection of melamine (MEL).

Cd-doped Sb2O4 nanostructures modified glassy carbon electrode for efficient detection of melamine by electrochemical approach

Cadmium doped antimony oxide (Cd-doped Sb₂O₄) nanostructures (CAO-NSs) were synthesized by a facile hydrothermal method in alkaline phase at low temperature to detect the melamine from aqueous solution. The calcined CAO-NSs were characterized systematically by FE-SEM, EDS, UV/Vis., FTIR spectroscopy, powder XRD, and XPS techniques. The glassy carbon electrode (GCE) was modified with the CAO-NSs and sensing performance towards the selective melamine was explored by the electrochemical approach in phosphate buffer solution. The melamine undergoes a reduction reaction in the presence of CAO-NSs/GCE in PBS. The CAO-NSs/GCE attained the higher sensitivity (3.153μAμM^-1cm^-2) for a wide ranges of concentration (LDR: 0.05nM-0.5mM), an ultra-low limit of detection (LOD: 14.0 ± 0.05p.M.; S/N = 3), long-term stability, excellent repeatability, and reproducibility. This method might represent an efficient way of sensitive sensor development for the toxic melamine and their derivatives for the safety of biomedical and health care fields in broad scales.

Influence of hydrogen bond accepting ability of anions on the adsorption performance of ionic liquid surface molecularly imprinted polymers

To illuminate the influence mechanism of anionic structure of ionic liquids (ILs) on the adsorption performance of surface molecularly imprinted polymers (MIPs), in this work, six newly designed MIPs were prepared on the surface of amino-poly(styrene-divinylbenzene) particles by using imidazolium ILs with the same cation [C₄mim]⁺ but different anions (Cl, CH₃SO₃, PF₆, BF₄, C₄F₇O₂, C₄F₉SO₃) as template molecules, methacrylic acid as functional monomer, and ethylene dimethacrylate as cross-linker. The resulting MIP materials were characterized by IR and SEM, and the influence of hydrogen bond accepting ability of anions on the adsorption performance of the MIPs for the ILs was investigated in acetonitrile. It was found that adsorption capacity of the MIPs towards the ILs decreased in the order MIP_[C4mim][Cl] > MIP_{[C4mim][C4F7O2]} ≥ MIP_[C4mim][BF4] and MIP_{[C4mim][CH3SO3]} > MIP_{[C4mim][C4F9SO3]} > MIP_[C4mim][PF6], which is in good agreement with the ability of anions of the ILs to form hydrogen bonds. Ultraviolet, ¹H-NMR and ³⁵Cl-NMR spectroscopy was then used to study the interactions of anions of the ILs with the functional monomer. It was found that the hydrogen bond interaction between anions of the ILs and acidic proton of the functional monomer was the main driving force for the high adsorption selectivity of the imprinted polymers, and the stronger hydrogen bond interaction indicates higher binding capacity and higher selectivity of the polymers towards the ILs. It was also verified that the ILs with stronger hydrogen bond accepting ability of anions could be selectively extracted by the corresponding IL-MIPs. These results may provide new insight into the recognition mechanism of MIPs for ILs, and are also useful for the rational design of this new class of imprinting materials.