Enrique Valera

Development of a Coulombimetric immunosensor based on specific antibodies labeled with CdS nanoparticles for sulfonamide antibiotic residues analysis and its application to honey samples

A new electrochemical immunosensor has been developed to detect sulfonamide antibiotic residues in food samples. The immunosensor presented uses immunoreagents specifically developed for the broad recognition of the sulfonamide antibiotic family, a graphite composite electrode (GEC), biofunctionalized magnetic μ-particles and electrochemical nanoprobes prepared by labeling the specific antibodies with CdS nanoparticles (CdSNP). After the immunochemical reaction, the CdSNP are dissolved and the metal ions released are reduced at the electrode and read as in the form of current or charge signal, by the well-known anodic stripping technique. Due to the amplification effect on the amperometric/coulombimetric signal produced by the CdSNP, a high detectability can be reached. Thus, sulfapyridine (SPY), one of the most widely used sulfonamide congeners, can be detected in buffer with an IC50current of 0.20±0.25μgL(-1). The immunosensor has been applied to the analysis of residues of this antibiotic in honey samples. Due to the reported formation of sulfonamide-sugar conjugates in this type of matrix, honey samples are first hydrolyzed in acidic media. The use of magnetic particles minimizes the matrix effect allowing to reach a detectability (LOD, limit of detection) of 0.11μgkg(-1) (current measurements), far below the limits established in some countries for these types of residues in honey samples. Due to the use of magnetic racks, multiple samples can be run simultaneously. The whole analysis process can be performed in around 22min.

An electrochemical magneto immunosensor (EMIS) for the determination of paraquat residues in potato samples

An electrochemical magneto immunosensor for the detection of low concentrations of paraquat (PQ) in food samples has been developed and its performance evaluated in a complex sample such as potato extracts. The immunosensor presented uses immunoreagents specifically developed for the recognition of paraquat, a magnetic graphite–epoxy composite (m-GEC) electrode and biofunctionalized magnetic micro-particles (PQ1-BSAMP) that allow reduction of the potential interferences caused by the matrix components. The amperometric signal is provided by an enzymatic probe prepared by covalently linking an enzyme to the specific antibodies (Ab198-cc-HRP). The use of hydroquinone, as mediator, allows recording of the signal at a low potential, which also contributes to reducing the background noise potentially caused by the sample matrix. The immunocomplexes formed on top of the modified MP are easily captured by the m-GEC, which acts simultaneously as transducer. PQ can be detected at concentrations as low as 0.18u2009±u20090.09xa0μgxa0L−1. Combined with an efficient extraction procedure, PQ residues can be directly detected and accurately quantified in potato extracts without additional clean-up or purification steps, with a limit of detection (90xa0% of the maximum signal) of 2.18u2009±u20092.08xa0μgxa0kg−1, far below the maximum residue level (20xa0μgxa0kg−1) established by the EC. The immunosensor presented here is suitable for on-site analysis. Combined with the use of magnetic racks, multiple samples can be run simultaneously in a reasonable time.

Steady-State and Transient Conductivity of Colloidal Solutions of Gold Nanobeads

Steady-state and transient conductance measurements of gold nanobeads solutions deposited on top of interdigitated electrodes have been performed. It is shown that the application of an electric field of moderate value between electrodes during the drying process of the droplet makes the resulting steady-state conductance value to increase significantly. The dynamics of the gold nanobeads in the solution has been studied by means of transient current measurements during the drying process and the effects correlated to the changes in the morphology of the association of the gold nanobeads when they reach the substrate. It is seen that the application of the electric field foster the formation of gold beads monolayers, chains, and dendritic associations which, in combination with the humidity conditions of the sample surface, are believed to be the reasons for the conductance increase.

Chapter 2.8 Application of bioassays/biosensors for the analysis of pharmaceuticals in environmental samples

Abstract With the ever-increasing use of pharmaceuticals and the subsequent release into the environment comes the need for reliable detection methods. While the emphasis continues to be on chromatographic methods, every time, there are more and more biologically based assays being developed for the detection of pharmaceuticals in the environment. This chapter affords an overview of the currently available bioassays, biochemical assays, and biosensors focusing on the most commonly used pharmaceuticals—antibiotics, hormones, and analgesics. Bioassays rely on biological indicators, whether it be cells, tissues, or whole organisms, to evaluate an analyte according to its biological activity, whereas biochemical assays and biosensors incorporate biorecognition elements such as enzymes, proteins, or antibodies but the signal is enhanced by physical or chemical means. There has been more emphasis given on biosensors, especially immunologic sensors, for as the reader will appreciate, they show greater promise as alternatives to chromatography as they are fast, robust, specific, and quantifiable and may be performed on-site.

μ-Porous silicon (μPS) gas sensor based on interdigitated μ-electrodes (IDμE's)

A μ-porous silicon (μPS) gas sensor based on interdigitated μ-electrodes (IDμEs) has been designed and developed. μPS obtained by means of electrochemical anodization of a p-type silicon (c-Si) wafer was used as active layer. The μPS layers are supported by the bulk of the c-Si wafer. Interdigitated μ-electrodes, which work as transducers, were deposited on the μPS surface by means of gold evaporation using shadow mask technique. Different IDμEs, with different geometries and dimensions have been deposited. Additionally, different conditions of μPS formation, as i.e. electrolyte concentration, current density and anodization time, were used in order to obtain different actives layers with different absorption capabilities. Clear responses to organic vapors such us ethanol have been obtained.

High frequency response of a novel biosensor based on interdigitated μ-electrodes (IDμE's)

A novel impedimetric biosensor for detection of a wide variety of compounds has been designed and developed. The biosensor is based on a non-isolated surface and non-labelled immunoreactives. The chemical recognition layer was deposited on the surface of the interdigitated μ-electrodes (IDμEs) area (fingers and inter-digits space). Typically, the biosensors and their functionalization are characterized by chemical affinity methods, and impedance spectroscopy in frequencies ranges of 0.1 mHz to 100 kHz. This work describes the biosensor characterization to 1 MHz and the biosensor response without buffer solution to the pesticide atrazine. This work presents an alternative detection method using this biosensor, which was designed to be characterized in the range of frequencies usual in impedance spectroscopy. This detection method allows a simple measure, an easy interpretation and from the electronic point of view is very suitable.