Surface properties of sensors based on aminophenol-polymerized film

Dual dye-labeled aptamers for detection of dichlorvos using ratiometric fluorescence resonance energy transfer

BACKGROUND

Dichlorvos (DDVP) is an efficient and highly toxic organophosphorus pesticide. Considering its effects on human health and ecosystems, pesticide residue and pollution monitoring is of great significance. Traditional methods like chromatography with mass spectrometry are not portable or rapid because they use large instruments and complex pre-processing methods. Compared with other optional on-site detection technologies, like enzymatic and antibody methods, aptamers are advantageous because they are stable, readily modified, and inexpensive. Therefore, screening and developing a specific adapter for DDVP detection is necessary and will be of practical value.

RESULTS

We screened, modified, and compared two dual-labeled aptamer probes (Cy3-DV55-Cy5 and Cy3-DV65-Cy5). The kinetics studied showed that 5 min was sufficient for the detection reaction. Both aptamers showed selectivity for DDVP but DV55 was superior to DV65. To research the binding stabilities and the mechanism between the aptamers and DDVP, the secondary structures, melting temperatures, fluorescence quenching types, and constants were investigated. Which showed that DV55 was specific for DDVP and showed better binding than DV65. Comparison of the UV absorption and FRET for DV55 and the truncated structures suggested that loop 3 in DV55 might play an important role in the binding of DV55 to DDVP. The Cy3-DV55-Cy5 aptamer had a linear range of 0-100 μM for DDVP detection and the limit of detection was 150 nM. Simulated pesticide residue detection experiments showed that the method was simple, fast, and had acceptable recovery (89.8%-105.2 %).

SIGNIFICANCE

Pesticide detection is important but on-site detection methods are usually not portable or rapid. We developed two dual-labeled aptamer probes that could feasibly be practically applied to rapid on-site DDVP detection of pesticide residues and pollutants. This research provides experimental and theoretical data for the development and design of similar pesticide probes.

Voltammetric Sensor Based on the Poly(p-aminobenzoic Acid) for the Simultaneous Quantification of Aromatic Aldehydes as Markers of Cognac and Brandy Quality

Cognac and brandy quality control is an actual topic in food analysis. Aromatic aldehydes, particularly syringaldehyde and vanillin, are one of the markers used for these purposes. Therefore, simple and express methods for their simultaneous determination are required. The voltammetric sensor based on the layer-by-layer combination of multi-walled carbon nanotubes (MWCNTs) and electropolymerized p-aminobenzoic acid (p-ABA) provides full resolution of the syringaldehyde and vanillin oxidation peaks. Optimized conditions of p-ABA electropolymerization (100 µM monomer in Britton-Robinson buffer pH 2.0, twenty cycles in the polarization window of -0.5 to 2.0 V with a potential scan rate of 100 mV·s^-1) were found. The poly(p-ABA)-based electrode was characterized by scanning electron microscopy (SEM), cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Electrooxidation of syringaldehyde and vanillin is an irreversible two-electron diffusion-controlled process. In the differential pulse mode, the sensor allows quantification of aromatic aldehydes in the ranges of 0.075-7.5 and 7.5-100 µM for syringaldehyde and 0.50-7.5 and 7.5-100 µM for vanillin with the detection limits of 0.018 and 0.19 µM, respectively. The sensor was applied to cognac and brandy samples and compared to chromatography.

Detection of a specific biomarker for Epstein-Barr virus using a polymer-based genosensor

This paper describes methodology for direct and indirect detections of a specific oligonucleotide for Epstein-Barr virus (EBV) using electrochemical techniques. The sequence of oligonucleotide probe (EBV1) revealed a high sequence identity (100%) with the EBV genome. For the development of the genosensor, EBV1 was grafted to the platform sensitized with poly(4-aminothiophenol). After that, the hybridization reaction was carried out with the complementary target (EBV2) on the modified electrode surface using ethidium bromide as DNA intercalator. The oxidation peak currents of ethidium bromide increased linearly with the values of the concentration of the complementary sequences in the range from 3.78 to 756 μmol·L⁻¹. In nonstringent experimental conditions, this genosensor can detect 17.32 nmol·L⁻¹ (three independent experiments) of oligonucleotide target, discriminating between complementary and non-complementary oligonucleotides, as well as differentiating one-base mismatch, as required for detection of genetic diseases caused by point mutations. The biosensor also displayed high specificity to the EBV target with elimination of interference from mix (alanine, glucose, uric acid, ascorbic acid, bovine serum albumin (BSA), glutamate and glycine) and good stability (120 days). In addition, it was possible to observe differences between hybridized and non-hybridized surfaces through atomic force microscopy.