Preparation of a Molecularly Imprinted Film on Quartz Crystal Microbalance Chip for Determination of Furanic Compounds

The structural preferences of furanic compounds were studied using a combination of a molecularly imprinted film (MIF) on a piezoelectric-quartz chip. The furanic compounds and their derivatives were used as the templates. Owing to their similar heterocyclic structures, it is difficult to verify the structural differences between the templates. Therefore, a new cross-linker (Methacr-l-Cys-NHBn)2, was employed to generate a platform on a quartz crystal microbalance (QCM) chip. The cross-linker self-assembled to link the surface of the chip to copolymerize with other functional monomers. A layered film with chiral hydrophobicity and rigidity was thus fabricated. Subsequently, Acr-l-Ser-NHBn was utilized as a chiral monomer to construct MIF on a QCM chip. Forcomparison, we synthesized a more hydrophobic monomer, Methacr-l-Ser-NHBn, to enhance the binding ability of the MIF. The QCM flow injection system was handled in an organic solvent system. The proportion of the monomers was adjusted to optimize the recognition ability of these films. As the binding ability of the MIF toward model templates and structurally-related furanic compounds was improved, a MIF derived from 2-furaldehyde (FUL) achieved a lower detection limit (10 ng/mL). The binding properties of MIFs prepared against furanic compounds exhibited strong similarities to the binding properties of other compounds with heterocyclic ring structures. For example, 2-furaldehyde is very similar to 2-formylthiazole, 2-acetylfuran is similar to 2-acetylthiazole, and 2-furfuryl alcohol is similar to imidazole-2-methanol. Such recognition ability can help distinguish between the structural counterparts of other small heterocyclic compounds.

Selective and Sensitive Determination of Folic Acid Based on Molecularly Imprinted Poly (o-aminophenol) and Reduced Graphene Oxide Decorated with Au Nanoparticles

Background: Folic acid (pteroylglutamic acid, FA), known as a water soluble vitamin of B complex family, plays an important role in the human body. However, excess intake of FA would mask the vitamin B12 deficiency symptoms which may lead to other health risks. Therefore, it is very important to develop a method for the sensitive and selective determination of FA in natural sources, fortified foods and multivitamin preparations. Methods: An electrochemical sensor was fabricated for the analysis of FA, which was based on electropolymerized molecularly imprinted poly (o-aminophenol) film and reduced graphene oxide decorated with Au nanoparticles composites (rGO-AuNPs). Transmission electron microscope, cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry were utilized for the characterization of the imprinted polymer film. Results: Under the optimized experimental conditions, the proposed sensor exhibited two distinct linear responses ranging from 0.02 to 0.8 μmol L-1 and 0.8 to 10 μmol L-1 towards the concentrations of FA, and the detection limit was found to be 2.8 nmol L-1 (S/N=3). The molecularly imprinted film proposed was also found to exhibit comparatively high selectivity toward folic acid against structurally similar analogues, and the preparation of the sensor was simple and reproducible. Conclusions: In this work, a molecularly imprinted film fabricated on a rGO-AuNPs modified electrode was developed for the sensitive and selective determination of FA. Furthermore, the method was applied to the detection of FA in infant formula milk, multivitamin tablets and blood serum sample with satisfactory results.

Study of horseradish peroxidase and hydrogen peroxide bi-analyte sensor with boronate affinity-based molecularly imprinted film

A novel electrochemical horseradish peroxidase (HRP) sensor was developed based on boronate affinity-based electropolymerized polythionine (PTh) molecularly imprinted polymer (MIP) as specific recognition element for HRP on gold nanoparticles (AuNPs) modified glassy carbon electrode, in which PTh acted as the electrochemical probe for the sensor. The sensor was characterized by scanning electron microscopy and electron dispersive spectroscopy. Electrochemical impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry were exploited for the study of the properties of the MIP sensor. The MIP sensor exhibited excellent linear response over the range of 2.0 × 10−10 mg/mL ∼ 1.0 × 10−7 mg/mL for HRP. In addition, with MIP film as HRP immobilized matrices, the sensor for the detection of H2O2 was developed with the MIP sensor based on the reduction of H2O2 catalyzed by HRP in the presence of electron mediator PTh. The sensor showed linear relationships between the current response and H2O2 concentration from 6.0 × 10−7 to 2.0 × 10−5 mol/L. HRP and H2O2 bi-analyte sensor based on MIP film was successfully developed in this work. The developed method can also be applicable for enzyme and its enzymatic substrate bi-analyte sensor.

Electrochemical determination of thrombin with molecularly imprinted polymers and multiwalled carbon nanotubes

The preparation and application of reagentless electrochemical thrombin molecularly imprinted sensors were studied using multiwalled carbon nanotubes as sensitivity-enhanced materials. The molecularly imprinted polymer film was prepared by the electropolymerization of o-phenylenediamine with thrombin as the template molecule onto the surface of multiwalled carbon nanotubes modified glassy carbon electrode. After removing thrombin, the poly-o-phenylenediamine molecularly imprinted film was obtained with specific recognition for thrombin. Using the poly-o-phenylenediamine molecularly imprinted polymers as the electron probe, the electrochemical molecularly imprinted sensor was fabricated for the detection of the protein thrombin. Under optimized experimental conditions, the sensor exhibited a good linear response from 10.0 fg/mL to 1.0 μg/mL for thrombin, with correlation coefficient 0.999 and a low detection limit of 1.7 fg/mL. The fabricated molecularly imprinted sensor can be applied to the detection of thrombin in actual sample bovine serum with satisfactory results.