Extraction-assisted voltammetric determination of homocysteine using magnetic nanoparticles modified with molecularly imprinted polymer.

A magnetic graphite-epoxy composite (m-GEC) electrochemical sensor is presented based on magnetic imprinted polymer (mag-MIP) to determine homocysteine (Hcy). Mag-MIP was synthesized via precipitation polymerization, using functionalized magnetic nanoparticles (Fe3O4) together with the template molecule (Hcy), the functional monomer 2-hydroxyethyl methacrylate (HEMA), and the structural monomer trimethylolpropane trimethacrylate (TRIM). For mag-NIP (magnetic non-imprinted polymer), the procedure was the same in the absence of Hcy. Morphological and structural properties of the resultant mag-MIP and mag-NIP were examined using TEM, FT-IR, and Vibrating Sample Magnetometer. Under optimized conditions, the m-GEC/mag-MIP sensor showed a linear range of 0.1-2 µmol L-1, with a limit of detection (LOD) of 0.030 µmol L-1. In addition, the proposed sensor responded selectively to Hcy compared to several interferents present in biological samples. The recovery values determined by differential pulse voltammetry (DPV) were close to 100% for natural and synthetic samples, indicating good method accuracy. The developed electrochemical sensor proves to be a suitable device for determining Hcy, with advantages related to magnetic separation and electrochemical analysis.

Molecularly Imprinted Polymer-Coated CdTe Quantum Dots for Fluorometric Detection of Sulfonamide Antibiotics in Food Samples.

This work reports the development and application of a highly selective core@shell-based quantum dot-molecularly imprinted polymer (QD@MIP) sensor for the detection of sulfadiazine (SDZ)-an antibiotic which belongs to the sulfonamide family. The synthesis of the smart material or MIP (molecularly imprinted polymer) was carried out by a precipitation method directly on the quantum dot surface, which played the role of a fluorescent probe in the optical sensor. The synthesized polymer was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Fluorescence experiments were performed in order to evaluate the effects of pH, interaction time of the QD@MIP with the analyte and SDZ concentration in different matrices. Under optimized conditions, a linear concentration range of 10.0-60.0 ppm and a limit of detection of 3.33 ppm were obtained. The repeatability and reproducibility of the proposed QD@MIP were evaluated in terms of the RSD, where RSD values of less than 5% were obtained in both tests. Selectivity studies were carried out in the presence of four possible interfering substances with quenching properties, and the signals obtained for these interferents confirmed the excellent selectivity of the proposed sensor; the imprinting factor value obtained for SDZ was 1.64. Finally, the proposed sensor was applied in real animal-based food samples using a spiked concentration of SDZ, where the recovery values obtained were above 90% (experiments were performed in triplicate).

A novel peptide-based electrochemical biosensor for breast cancer characterization over a poly 3-(3-aminophenyl) propionic acid matrix.

In this work, a new electrochemical biosensor was developed using peptides selected by Phage Display as biorecognition phase to Breast Cancer (BC) characterization. Phage clones were selected against MCF-7 (ER-positive BC) proteins, in order to characterize patients with aggressive luminal BC. Biotin-C3 and biotin-H2 peptides were chemically synthesized and validated by flow cytometry, immunofluorescence assays, and ELISA assays, being more reactive to the MCF-7 lineage. Furthermore, a new matrix for the coupling of biomolecules on the surface of graphite electrodes was generated, through electrochemical modification with a new material derived from 3-(3-aminophenyl)propionic acid (3-3-APPA). Electrochemical and morphological characterizations were carried out, and the mechanism of electropolymerization of poly(3-3-APPA) was proposed, in which the carboxylate groups are kept in the structure of the formed polymer. Then, a biosensor was developed by immobilizing the biotin-C3 and biotin-H2 peptides in the SPE/poly(3-3-APPA)/avidin system for the detection of BC tumor markers in serological samples. Finally, peptides were validated using samples from patients with BC and Benign Breast Disease. Biotin-C3 peptide characterized luminal BC according to p53 status and to HER2 expression, being the biosensor a better strategy when compared to ELISA test. This new biosensor will open a new perspective for a rapid and electrochemical platform for the characterization of BC and its molecular subtypes.

Surface molecularly imprinted core-shell nanoparticles and reflectance spectroscopy for direct determination of tartrazine in soft drinks.

The present work shows the synergistic application of reflectance spectroscopy and core-shell molecularly imprinted polymer (MIP) for rapid quantification of tartrazine in soft drinks. Studies evaluated the performance of the MIPs synthesized in the presence of silica nanoparticles unfunctionalized and functionalized with [3-(methacryloyloxy)propyl]trimethoxysilane. Although the use of functionalized silica nanoparticles promoted the highest adsorption capability of tartrazine, the material was found to be less selective when it was applied in real samples. Interestingly, the most accurate results were obtained via the application of the MIP synthesized in the presence of unfunctionalized silica nanoparticles (SiO2@MIP). The optimized core-shell MIP was also characterized by Raman spectroscopy and scanning electron microscopy. The use of direct reflectance spectroscopy in the analyte detection strategy after the template extraction from the MIPs resulted in faster and more accurate results than conventional UV-Visible spectroscopy. With regard to the analysis of the soft drink samples, no significant differences were found between the results obtained from the proposed reflectance spectroscopy-based technique and those obtained from the comparative high-performance liquid chromatography technique. Under optimized conditions, this method displayed a linear range of 1.0-12.5 µmol L-1 with LOD and LOQ values of 0.303 and 1.0 µmol L-1, respectively. The selectivity factor (ß) ranged between 1.4 up to 264 showed better recognition of tartrazine in front of other dyes. Based on the results obtained, the proposed method is found to be suitable for rapid determination of tartrazine in food samples with complex matrices without the need of applying tedious sample preparation and cost-demanding instruments.

Simultaneous determination of direct yellow 50, tryptophan, carbendazim, and caffeine in environmental and biological fluid samples using graphite pencil electrode modified with palladium nanoparticles.

The present study reports the development of graphite pencil electrode modified with palladium nanoparticles (PdNPs) and its application as an electrochemical sensor for the simultaneous detection of direct yellow 50, tryptophan, carbendazim and caffeine in river water and synthetic urine samples. The combination involving the conductive surface of the graphite pencil electrode (GPE) and the enlargement of the surface area caused by the use of palladium nanoparticles (PdNPs) led to the improvement of the analytical performance of the proposed device. The surface of the GPE-PdNPs was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The charge transfer kinetics of the electrode was evaluated based on the electrochemical analysis of the potassium ferricyanide redox probe. Using square wave voltammetry (SWV), well-defined and fully resolved anodic peaks were detected for the analytes, with peak-to-peak potential separation not less than 200 mV. Under optimised conditions, the following linear range concentrations were obtained: 0.99-9.9 µmol L-1 for direct yellow 50; 1.2-12 µmol L-1 for tryptophan; 0.20-1.6 µmol L-1 for carbendazim; and 25-190 µmol L-1 for caffeine. The sensor showed good sensitivity, repeatability, and stability. The device was successfully applied for the determination of analytes in urine and river water samples, where recovery rates close to 100% were obtained. Due to its low cost and reusability by simple polishing, the sensor has strong potential to be used as an electrochemical sensor for the determination of different analytes.

Assessment of molecularly imprinted polymers (MIPs) in the preconcentration of disperse red 73 dye prior to photoelectrocatalytic treatment.

Magnetic molecularly imprinted polymers (MMIPs) have become a research hotspot due to their two important characteristics: target recognition and magnetic separation. This paper presents the preparation, characterization, and optimization of an MMIP for the preconcentration of disperse red 73 dye (DR73) and its subsequent efficient degradation by photoelectrocatalytic treatment. The MMIPs were characterized by scanning electron microscopy (SEM), which revealed homogeneous distribution of the particles. Excellent encapsulation of magnetite was confirmed by transmission electron microscopy (TEM). A study of dye binding showed that the dye was retained more selectively in the MIP, compared to the NIP. The release of DR73 from the imprinted polymers into methanol and acetic acid was analyzed by UV-Vis spectrophotometry. The extracts showed higher absorbance values for MMIP, compared to MNIP, confirming greater adsorption of dye in the MMIP material. The extracts were then subjected to photoelectrocatalytic treatment. LC-MS/MS analysis following this treatment showed that the dye was almost completely degraded. Hence, the combination of MMIP extraction and photoelectrocatalysis offers an alternative way of selectively removing an organic contaminant, prior to proceeding with its complete degradation.