POM@PMO plastic electrode for phosphate electrochemical detection: a further improvement of the detection limit.

The development of a highly sensitive electrochemical sensor (E-sensor) is described based on stand-alone plastic electrodes (PE) for phosphate detection, being an essential nutrient in the marine environment. The detection mechanism is based on the chemical affinity between polyoxomolybdate anions (POM) and orthophosphate to form an electroactive phosphomolybdate complex. The custom-made E-sensor was formulated with an organic octamolybdate derivative (TBA4Mo8O26) incorporated with periodic mesoporous organosilica (PMO) to obtain a significant improvement in the analytical performances of phosphate determination. This POM@PMO combination was found to be advantageous in the determination of low concentrations of phosphate in standard solutions ranging from 1 to 500 nM, using square wave voltammetry as the detection technique. This sensitivity enhancement can be attributed to the effect of hydrophobic PMO in loading more POM moieties, owing to its highly porous structure and charged shell. Consequently, the POM@PMO-PE sensor achieved a competitive sensitivity of 4.43 ± 0.14 µA.nM-1.cm-2 and a limit of detection of 0.16 nM with good selectivity against silicates. Finally, seawater and treated wastewater samples have been tested to validate the sensor response in comparison to the official method of phosphate determination.

Advances in Colorimetric Strategies for Mycotoxins Detection: Toward Rapid Industrial Monitoring.

Mycotoxins contamination is a global public health concern. Therefore, highly sensitive and selective techniques are needed for their on-site monitoring. Several approaches are conceivable for mycotoxins analysis, among which colorimetric methods are the most attractive for commercialization purposes thanks to their visual read-out, easy operation, cost-effectiveness, and rapid response. This review covers the latest achievements in the last five years for the development of colorimetric methods specific to mycotoxins analysis, with a particular emphasis on their potential for large-scale applications in food industries. Gathering all types of (bio)receptors, main colorimetric methods are critically discussed, including enzyme-linked assays, lateral flow-assays, microfluidic devices, and homogenous in-solution strategies. This special focus on colorimetry as a versatile transduction method for mycotoxins analysis is comprehensively reviewed for the first time.

Investigation of a Truncated Aptamer for Ofloxacin Detection Using a Rapid FRET-Based Apta-Assay.

In this work, we describe the use of a new truncated aptamer for the determination of ofloxacin (OFL), being a principal quinolone commonly used in both human and animal healthcare. Since the affinity of a 72-mer ssDNA sequence has been previously described without further investigations, this paper demonstrates the first computational prediction of the binding motif between this aptamer and OFL through in silico molecular docking studies. Besides, we suggest the application of the characterized recognition mechanism in a simple FRET (Förster Resonance Energy Transfer) pattern for the rapid aptasensing of the quinolone of interest. Accordingly, our approach harnesses the fluorescence quenching of the fluorescein-tagged aptamer (FAM-APT) induced by its partial hybridization to a tetramethyl rhodamine-labelled complementary ssDNA (TAMRA-cDNA). In such a structure, dye labels brought into close proximity act as a FRET pair. Upon ofloxacin addition, an affinity competition occurs to form a more stable FAM-APT/OFL complex, thus unquenching the FAM-APT signal. Interestingly, the recovered fluorescence intensity was found to correlate well with the antibiotic's concentrations in the range of 0.2-200 µM in HEPES buffer, with a linear response that ranged between 0.2 and 20 µM. The rapid apta-assay achieved limits of detection and quantification of 0.12 and 0.40 µM, respectively. The truncated aptamer has also shown an improved specificity toward OFL than other quinolones, compared to the original full-length aptamer described in previous works. Finally, the practical application of the developed apta-assay was successfully confirmed to detect OFL quinolone in spiked milk samples, with satisfactory recoveries ranging between 97.4% and 111.4%.

Development of an Impedimetric Aptasensor for Label Free Detection of Patulin in Apple Juice.

In the present work, an aptasensing platform was developed for the detection of a carcinogenic mycotoxin termed patulin (PAT) using a label-free approach. The detection was mainly based on a specific interaction of an aptamer immobilized on carbon-based electrode. A long linear spacer of carboxy-amine polyethylene glycol chain (PEG) was chemically grafted on screen-printed carbon electrodes (SPCEs) via diazonium salt in the aptasensor design. The NH2-modified aptamer was then attached covalently to carboxylic acid groups of previously immobilized bifunctional PEG to build a diblock macromolecule. The immobilized diblocked molecules resulted in the formation of long tunnels on a carbon interface, while the aptamer was assumed as the gate of these tunnels. Upon target analyte binding, the gates were assumed to be closed due to conformational changes in the structure of the aptamer, increasing the resistance to the charge transfer. This increase in resistance was measured by electrochemical impedance spectroscopy, the main analytical technique for the quantitative detection of PAT. Encouragingly, a good linear range between 1 and 25 ng was obtained. The limit of detection and limit of quantification was 2.8 ng L-1 and 4.0 ng L-1, respectively. Selectivity of the aptasensor was confirmed with mycotoxins commonly occurring in food. The developed apta-assay was also applied to a real sample, i.e., fresh apple juice spiked with PAT, and toxin recovery up to 99% was observed. The results obtained validated the suitability and selectivity of the developed apta-assay for the identification and quantification of PAT in real food samples.

Design of a redox-active surface for ultrasensitive redox capacitive aptasensing of aflatoxin M1 in milk.

Herein, we report the design of a novel label-free aptasensor based on ferrocene and silicon nanoparticles (SiNPs) for ultrasensitive detection of aflatoxin M1 (AFM1) in milk. Given that silicon nanomaterials stand out by their high capacitive power, we used them to develop a novel capacitive transduction system based on electrochemical capacitance spectroscopy (ECS). This strategy relies on the changes of the redox capacitance signal owed to the surface-tethered ferrocene film, by performing electrochemical impedance spectroscopy (EIS) measurements without using an external redox probe. The redox capacitance variation was found to correlate well with the increasing concentrations of AFM1 in the linear range from 10 to 500 fmol⋅L-1 with a sensitivity of 0.46 µF*fM-1*cm - 2. Furthermore, the aptasensor allowed to reach very low limits of detection and quantification equal to 4.53 fM and 14.95 fM, respectively. The platform revealed a high selectivity toward the target analyte, and it was applied to quantify very low concentrations of AFM1 in commercial pasteurized milk. Finally, the results of real sample analysis were successfully gauged against those obtained using commercially available enzyme-linked immunoassay (ELISA) kits.