Maria Conceição Freitas

Iron oxide/gold core/shell nanomagnetic probes and CdS biolabels for amplified electrochemical immunosensing of Salmonella typhimurium.

There is an imminent need for rapid methods to detect and determine pathogenic bacteria in food products as alternatives to the laborious and time-consuming culture procedures. In this work, an electrochemical immunoassay using iron/gold core/shell nanoparticles (Fe@Au) conjugated with anti-Salmonella antibodies was developed. The chemical synthesis and functionalization of magnetic and gold-coated magnetic nanoparticles is reported. Fe@Au nanoparticles were functionalized with different self-assembled monolayers and characterized using ultraviolet-visible spectrometry, transmission electron microscopy, and voltammetric techniques. The determination of Salmonella typhimurium, on screen-printed carbon electrodes, was performed by square-wave anodic stripping voltammetry through the use of CdS nanocrystals. The calibration curve was established between 1×10(1) and 1×10(6) cells/mL and the limit of detection was 13 cells/mL. The developed method showed that it is possible to determine the bacteria in milk at low concentrations and is suitable for the rapid (less than 1h) and sensitive detection of S. typhimurium in real samples. Therefore, the developed methodology could contribute to the improvement of the quality control of food samples.

3D-nanostructured Au electrodes for the event-specific detection of MON810 transgenic maize

In the present work, the development of a genosensor for the event-specific detection of MON810 transgenic maize is proposed. Taking advantage of nanostructuration, a cost-effective three dimensional electrode was fabricated and a ternary monolayer containing a dithiol, a monothiol and the thiolated capture probe was optimized to minimize the unspecific signals. A sandwich format assay was selected as a way of precluding inefficient hybridization associated with stable secondary target structures. A comparison between the analytical performance of the Au nanostructured electrodes and commercially available screen-printed electrodes highlighted the superior performance of the nanostructured ones. Finally, the genosensor was effectively applied to detect the transgenic sequence in real samples, showing its potential for future quantitative analysis.

Magnetic dispersive micro solid-phase extraction and gas chromatography determination of organophosphorus pesticides in strawberries

Magnetic nanoparticles (MNPs) with different sizes and characteristics were synthesized to be used as a QuEChERS sorbents for the determination of seven organophosphorus pesticides (OPPs) in strawberries by gas chromatography analysis with flame photometric and mass spectrometry detection. To achieve the optimum conditions of modified QuEChERS procedure several parameters affecting the cleanup efficiency including the amount of the sorbents and cleanup time were investigated. The results were compared with classical QuEChERS methodologies and the modified QuEChERS procedure using MNPs showed the better performance. Under the optimum conditions of the new methodology, three spiking levels (25, 50 and 100u202fμg kg-1) were evaluated in a strawberry sample. The results showed that the average recovery was 93% and the relative standard deviation was less than 12%. The enrichment factor ranged from 111 to 145%. The good linearity with coefficients of determination of 0.9904-0.9991 was obtained over the range of 25-250u202fμgu202fkg-1 for 7 OPPs. It was determined that the MNPs have an excellent function as sorbent when purified even using less amount of sorbents and the magnetic properties allowed non-use of the centrifugation in cleanup step. The new methodology was applied in strawberry samples from conventional and organic farming. The new sorbents were successfully applied for extraction and determination of OPPs in strawberries.

Graphene as a Material for Bioelectrochemistry

Graphene is constituted by an individual layer sheet of carbon atoms organized in a 2D structure. Since its discovery, it has been attracting huge interest in the bioelectrochemistry area due to its remarkable physicochemical properties, namely high surface area, electrical conductivity, mechanical strength, and thermal stability coupled with high thermal conductivity. Several routes are available for successful graphene synthesis, being the most relevant mechanical exfoliation of graphite, chemical vapor deposition, electric arc discharge, and chemical or thermal reduction of graphene oxide, while comprehensive characterization is mainly performed by microscopy (scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force (AFM) microscopy) and spectroscopy techniques (FTIR-Raman). Due to graphenes exceptional properties coupled with its biocompatibility, it has been widely used in (bio)sensors development as well as in biofuel cells. Graphene-sheets functionalization and combination of graphene with nanoparticles (noble metal nanoparticles, iron oxide, etc.) into nanocomposites are being intensively explored due to the improved performance that can be achieved. Graphene and graphene-nanocomposites can be used as substrates for biorecognition elements immobilization, as carriers, and/or as electrocatalysts, and allow effective electrical wiring of the redox centers of relevant metalloproteins supporting studies of redox protein kinetics and thermodynamics. Graphene characteristics predict more promising applications in the bioelectrochemical field in the near future.