An enhanced fluorescent sensor system based on molecularly imprinted polymer chips with silver nanoparticles for highly-sensitive zearalenone analysis.

A novel enhanced fluorescent sensor system for zearalenone (ZON) determination in flour samples is presented. The ZON-selective molecularly imprinted polymer (MIP) films were developed with a computational modelling method and synthesised with cyclododecyl-2,4-dihydroxybenzoate as a "dummy" template and ethylene glycol methacrylate phosphate as a functional monomer acted as the selective recognition elements for ZON fluorescence detection. Spherical silver nanoparticles (AgNPs) were embedded in the MIP films' structure to enhance the sensor sensitivity. The imprinted films showed a high ZON recognition ability compared to non-imprinted films. Various factors that affected the measurement of the analysed sample were investigated and optimised. Embedding the AgNPs in the MIP films' structure led to an enhanced sensitivity (up to a 200-fold decrease of LOD) compared to unmodified MIP films. This fluorescent sensor system provided ZON analysis with high sensitivity, specificity, and a wider linear dynamic range of 5 ng mL-1 to 25 µg mL-1. An enhanced fluorescent sensor system based on MIP chips with embedded AgNPs could detect trace amounts of ZON in foods and feedstuffs with high sensitivity and selectivity.

Sensor Based on Molecularly Imprinted Polymer Membranes and Smartphone for Detection of Fusarium Contamination in Cereals.

The combination of the generic mobile technology and inherent stability, versatility and cost-effectiveness of the synthetic receptors allows producing optical sensors for potentially any analyte of interest, and, therefore, to qualify as a platform technology for a fast routine analysis of a large number of contaminated samples. To support this statement, we present here a novel miniature sensor based on a combination of molecularly imprinted polymer (MIP) membranes and a smartphone, which could be used for the point-of-care detection of an important food contaminant, oestrogen-like toxin zearalenone associated with Fusarium contamination of cereals. The detection is based on registration of natural fluorescence of zearalenone using a digital smartphone camera after it binds to the sensor recognition element. The recorded image is further processed using a mobile application. It shows here a first example of the zearalenone-specific MIP membranes synthesised in situ using "dummy template"-based approach with cyclododecyl 2, 4-dihydroxybenzoate as the template and 1-allylpiperazine as a functional monomer. The novel smartphone sensor system based on optimized MIP membranes provides zearalenone detection in cereal samples within the range of 1-10 µg mL-1 demonstrating a detection limit of 1 µg mL-1 in a direct sensing mode. In order to reach the level of sensitivity required for practical application, a competitive sensing mode is also developed. It is based on application of a highly-fluorescent structural analogue of zearalenone (2-[(pyrene-l-carbonyl) amino]ethyl 2,4-dihydroxybenzoate) which is capable to compete with the target mycotoxin for the binding to zearalenone-selective sites in the membrane's structure. The competitive mode increases 100 times the sensor's sensitivity and allows detecting zearalenone at 10 ng mL-1. The linear dynamic range in this case comprised 10-100 ng mL-1. The sensor system is tested and found effective for zearalenone detection in maize, wheat and rye flour samples both spiked and naturally contaminated. The developed MIP membrane-based smartphone sensor system is an example of a novel, inexpensive tool for food quality analysis, which is portable and can be used for the "field" measurements and easily translated into the practice.

Spectroscopic Studies on Binding of Porphyrin-Phenazine Conjugate to Four-Stranded Poly(G).

Binding of a novel cationic porphyrin-imidazophenazine conjugate, TMPyP(3+)-ImPzn, to four-stranded poly(G) was investigated in aqueous solutions of neutral pH under near physiological ionic conditions using absorption, polarized fluorescent spectroscopy and fluorescence titration techniques. In absence of the polymer the conjugate folds into stable internal heterodimer with stacking between the porphyrin and phenazine chromophores. Binding of TMPyP(3+)-ImPzn to poly(G) is realized by two competing ways. At low polymer-to-dye ratio (P/D < 6) outside electrostatic binding of the cationic porphyrin moieties of the conjugate to anionic polynucleotide backbone with their self-stacking is predominant. It is accompanied by heterodimer dissociation and distancing of phenazine moieties from the polymer. This binding mode is characterized by strong quenching of the conjugate fluorescence. Increase of P/D results in the disintegration of the porphyrin stacks and redistribution of the bound conjugate molecules along the polymer chain. At P/D > 10 another binding mode becomes dominant, embedding of TMPyP(3+)-ImPzn heterodimers into poly(G) groove as a whole is occurred.

Fluorescent studies on cooperative binding of cationic pheophorbide-a derivative to polyphosphate.

The cooperative binding of a novel water-soluble cationic derivative of pheophorbide-a (CatPheo-a) to inorganic polyphosphate (PPS) in buffered aqueous solutions was studied by means of polarized fluorescence spectroscopy in a wide range of molar phosphate-to-dye ratios (P/D). Under low P/D values, CatPheo-a forms extended stacking associates on the PPS matrix, while under high P/D the dye binds to PPS in the dimer form. The CatPheo-a self-association is accompanied by 40-fold dye fluorescence quenching and a substantial increase in the fluorescence polarization degree. The fluorescent titration data were used for determination of cooperative binding parameters by Schwarz's method.

Self-assemblies of tricationic porphyrin on inorganic polyphosphate.

Self-assemblies formed by the new synthesized tricationic porphyrin derivative (TMPyP(3+)) on the polyanionic inorganic polyphosphate (PPS) in aqueous solution were studied using different spectroscopic techniques and DFT calculation method. From the fluorescence quenching of the bound TMPyP(3+) molecules and their Raman spectra we conclude that porphyrin chromophores form the stable π-π stacking-assemblies onto PPS polyanions. The transformation of the Soret band in absorption spectra at different PPS/TMPyP(3+)concentration ratios evidences that the assemblies are mixtures of J- and H-aggregates. Molecular modeling performed shows that the flexibility of PPS strand allows a realization of spiral or "face-to-face" one-dimensional structures formed by porphyrin molecules arranged in parallel and antiparallel modes. The peculiarity of PPS structure allows a formation of two porphyrin stacks on opposite sides of polymer strands that result in the appearance of higher-order aggregates. Their size was estimated from the light scattering data. Distinctions between TMPyP(3+) and TMPyP4 aggregation on PPS template are discussed.