Germán A. Messina

Recent Applications of Carbon-Based Nanomaterials in Analytical Chemistry: Critical Review

The objective of this review is to provide a broad overview of the advantages and limitations of carbon-based nanomaterials with respect to analytical chemistry. Aiming to illustrate the impact of nanomaterials on the development of novel analytical applications, developments reported in the 2005-2010 period have been included and divided into sample preparation, separation, and detection. Within each section, fullerenes, carbon nanotubes, graphene, and composite materials will be addressed specifically. Although only briefly discussed, included is a section highlighting nanomaterials with interesting catalytic properties that can be used in the design of future devices for analytical chemistry.

Determination of melatonin in wine and plant extracts by capillary electrochromatography with immobilized carboxylic multi-walled carbon nanotubes as stationary phase

The finding of melatonin, the often called “hormone of darkness” in plants opens an interesting perspective associated to the plethora of health benefits related to the moderate consumption of red wine. In this study, the implementation of a new method for the determination of melatonin in complex food matrices by CEC with immobilized carboxylic multi‐walled carbon nanotubes as stationary phase is demonstrated. The results indicated high electrochromatographic resolution, good capillary efficiencies and improved sensitivity respect to those obtained with conventional capillaries. In addition, it was demonstrated highly reproducible results between runs, days and columns. The LOD for melatonin was 0.01u2009ng/mL. The method was successfully applied to the determination of melatonin in red and white wine, grape skin and plant extracts of Salvia officinalis L.

Microfluidic immunosensor design for the quantification of interleukin-6 in human serum samples.

Interleukin-6 (IL-6), an inflammatory cytokine, is one of the most important mediators of fever, the acute phase response, and inflammatory conditions. Described here is an integrated microfluidic immunosensor capable of detecting the concentration of IL-6 in human serum samples by use of an electrochemical method in a microfluidic biochip format. The detection of IL-6 was carried out using a sandwich immunoassay method based on the use of anti-IL-6 monoclonal antibodies, immobilized on a 3-aminopropyl-modified controlled-pore glass (APCPG) packet in a central channel (CC) of the microfluidic system. The IL-6 in the serum sample is allowed to react immunologically with the immobilized anti-IL-6 and biotin-labeled second antibodies specific to IL-6. After washing, the streptavidin-alkaline phosphatase conjugate is added. p-Aminophenyl phosphate is converted to p-aminophenol by alkaline phosphatase, and the electroactive product is quantified on a gold electrode at 0.10 V. For electrochemical detection and enzyme immunoassay, the LOD was 0.41 and 1.56 pg mL(-1), respectively. Reproducibility assays employed repetitive standards of IL-6, and the intra- and inter-assay coefficients of variation were below 6.5%. Compared with the traditional IL-6 sensing method, the integrated microfluidic immunosensor required smaller amounts of sample to perform faster detection.

Microfluidic immunosensor with gold nanoparticle platform for the determination of immunoglobulin G anti-Echinococcus granulosus antibodies

This article describes a microfluidic immunosensor, developed for the detection of IgG antibodies specific to Echinococcus granulosus in human serum samples, which represents an alternative tool that can be used for the immunodiagnosis of hydatidosis in an automated way. Our device consists of a Plexiglas system with a central channel and a gold electrode. For immobilization of the E. granulosus antigen, a gold electrode was modified with the incorporation of gold nanoparticles. Immobilized antigen was allowed to react with IgG-anti-E. granulosus antibodies in samples, and these were quantified by horseradish peroxidase (HRP) enzyme-labeled secondary antibodies specific to human IgG using catechol (Q) as enzymatic mediator. HRP in the presence of hydrogen peroxide (H(2)O(2)) catalyzes the oxidation of Q to o-benzoquinone (P). The electrochemical reduction back to Q was detected on the gold electrode (AuE) at -0.15 V. The current obtained was proportional to the activity of the enzyme and to the concentration of antibodies of interest. The detection limit for electrochemical detection was 0.091 ng ml(-1), and the within- and between-assay coefficients of variation were below 6.7%. The proposed system presents many benefits, the more relevant are: reduced complexity and costs that are considered as the most wanted features for the clinical-immunodiagnostic field.

Continuous-flow/stopped-flow system for determination of ascorbic acid using an enzymatic rotating bioreactor

The high sensitivity that can be attained using an enzymatic system and mediated by hydroquinone, has been verified by on-line interfacing of a rotating bioreactor and continuous flow/stopped-flow/continuous-flow processing. Horseradish peroxidase, HRP, [EC 1.11.1.7], immobilized on a rotating disk, in presence of hydrogen peroxide catalyses the oxidation of hydroquinone to p-benzoquinone, whose electrochemical reduction back to hydroquinone is detected on glassy carbon electrode (GCE) surface at -0.15V. Thus, when l-ascorbic acid is added to the solution, this acid is reduced chemically (p-benzoquinone to hydroquinone) and acts as mediator of HRP, decreasing the peak current obtained proportionally to the increase of its concentration. The recovery of l-ascorbic acid from four samples ranged from 99.09 to 101.10%. This method could be used to determine l-ascorbic acid concentration in the range 12nM-3.5muM (r = 0.998). The determination of l-ascorbic acid was possible with a limit of detection of 6nM in the processing of as many as 25 samplesh(-1). The method was successfully applied for the analysis of l-ascorbic acid in pharmaceutical formulations.

Microfluidic Immunosensor with Micromagnetic Beads Coupled to Carbon-Based Screen-Printed Electrodes (SPCEs) for Determination of Botrytis cinerea in Tissue of Fruits

A wide range of plant species, including economically important crops such as vegetables, ornamentals, bulbs, and fundamentally fruits, can be affected by gray mold caused by the fungal pathogen Botrytis cinerea . This paper describes the development of a microfluidic immunosensor with micromagnetic beads (MMBs) coupled to carbon-based screen-printed electrodes (SPCEs) for the rapid and sensitive quantification of B. cinerea in apple (Red Delicious), table grape (pink Moscatel), and pear (Williams) tissues. The detection of B. cinerea was carried out using a competitive immunoassay method based on the use of purified B. cinerea antigens immobilized on 3-aminopropyl-modified MMBs. The total assay time was 40 min, and the calculated detection limit was 0.008 μg mL(-1). Moreover, the intra- and interassay coefficients of variation were below 7%. The developed method allowed detects B. cinerea even in asymptomatic fruits and promises to be particularly useful for application in the agricultural industry.

A combination of single-drop microextraction and open tubular capillary electrochromatography with carbon nanotubes as stationary phase for the determination of low concentration of illicit drugs in horse urine

In this study we developed an interesting alternative to HPLC-mass spectrometry for the quantification of seven important drugs of abuse in racehorses. The procedure proposed in this work is a combination of single-drop microextraction (SDME) and an open tubular capillary electrochromatography (OT-CEC) using multi-wall carbon nanotubes (MWCTs) immobilized into a fused-silica capillary as a stationary phase. The SDME showed to be a powerful tool for extraction/preconcentration of the seven drugs analyzed in the study, showing an enrichment factor between 38- and 102-fold depending on the drug. We have investigated the electrophoretic features of MWCTs immobilized fused-silica capillary by covalent modification of the inner surface of the capillary. The results show a good run-to-run, day-to-day and capillary-to-capillary reproducibility of the method. Compared with the capillary zone electrophoresis (CZE), the coating of the capillary allowed the separation of the analytes with high resolution, with less band-broadening and without distortion of the baseline. The interactions between the analytes and the MWCTs resulted in an increased migration time and probably this was the reason of the front tailing effect. The results showed a good capillary efficiencies and an improved of the electrophoretic separation.

Online immunoaffinity assay-CE using magnetic nanobeads for the determination of anti-Helicobacter pylori IgG in human serum.

About two‐thirds of the worlds population is infected with Helicobacter pylori (H. pylori). This Gram‐negative bacterium is the most important etiological agent of chronic active type B gastritis and peptic ulcer diseases. Conventional methods such as gastric biopsy, ELISA and culture, require a long time for the determination of H. pylori infections. Moreover, the antibodies in human serum sample are capable to react immunologically with the purified H. pylori antigens immobilized on different kinds of support like magnetic nanobeads. In this study, we have developed an online immunoaffinity assay‐CE to determine the concentration of anti‐H. pylori IgG using magnetic nanobeads as a support of the immunological affinity ligands and an LIF as a detector. The separation was performed in 0.1u2009M glycine–HCl, pH 2, as the background electrolyte. The linear calibration curve to predict the concentration of H. pylori‐specific immunoglobulin G antibodies in serum was produced within the range of 0.12–100u2009U/mL. The linear regression equation was i=492.86+96.03×Canti‐H. pylori, with the linear regression coefficient r2=0.999. The LOD calculated by fluorescence detection procedure was of 0.06u2009U/mL. The whole assay was done in no more than 35u2009min and it was entirely automatized. The development of immunoaffinity assay‐CE in this study demonstrates that there is a large possibility to introduce nanotechnology in several fields with significant advantages over the classic methodologies. Our proposition comprises the diagnosis and screening field.

Environmental monitoring of phenolic pollutants in water by cloud point extraction prior to micellar electrokinetic chromatography.

AbstractMany aromatic compounds can be found in the environment as a result of anthropogenic activities and some of them are highly toxic. The need to determine low concentrations of pollutants requires analytical methods with high sensitivity, selectivity, and resolution for application to soil, sediment, water, and other environmental samples. Complex sample preparation involving analyte isolation and enrichment is generally necessary before the final analysis. The present paper outlines a novel, simple, low-cost, and environmentally friendly method for the simultaneous determination of p-nitrophenol (PNP), p-aminophenol (PAP), and hydroquinone (HQ) by micellar electrokinetic capillary chromatography after preconcentration by cloud point extraction. Enrichment factors of 180 to 200 were achieved. The limits of detection of the analytes for the preconcentration of 50-ml sample volume were 0.10xa0μg L−1 for PNP, 0.20xa0μg L−1 for PAP, and 0.16xa0μg L−1 for HQ. The optimized procedure was applied to the determination of phenolic pollutants in natural waters from San Luis, Argentina.n FigureSchematic representation of the cloud point extraction process.

Electrochemical immunosensing using a nanostructured functional platform for determination of α-zearalanol

AbstractWe describe an electrochemical immunosensor for the determination of the growth promoter α-zearalanol in bovine serum. The sensing scheme is based on a nanocomposite consisting of gold nanoparticles electrodeposited on multi-walled carbon nanotubes that were modified with poly (vinylpyridine) through in-situ polymerization. The electrodeposition of the gold nanoparticles enlarges the surface available for immobilization of antibodies against α-zearalanol. The nanocomposite film was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and cyclic voltammetry. The calibration plot has a linear response in the concentrations range from 0.05 to 50xa0ngxa0mL−1, and the detection limit is 16xa0pgxa0mL−1. The time required for analysis is 12xa0min only which compares quite favorably with the time (90xa0min) required by the conventional ELISA. The method exhibits good selectivity, stability and reproducibility for detecting α-zearalanol in the livestock production.n Graphical AbstractSchematic representation of the immunocapture procedure and subsequent determination of α-zearalanol.