Celiac disease detection using a transglutaminase electrochemical immunosensor fabricated on nanohybrid screen-printed carbon electrodes

Celiac disease is a gluten-induced autoimmune enteropathy characterized by the presence of tissue tranglutaminase (tTG) autoantibodies. A disposable electrochemical immunosensor (EI) for the detection of IgA and IgG type anti-tTG autoantibodies in real patient’s samples is presented. Screen-printed carbon electrodes (SPCE) nanostructurized with carbon nanotubes and gold nanoparticles were used as the transducer surface. This transducer exhibits the excellent characteristics of carbon–metal nanoparticle hybrid conjugation and led to the amplification of the immunological interaction. The immunosensing strategy consisted of the immobilization of tTG on the nanostructured electrode surface followed by the electrochemical detection of the autoantibodies present in the samples using an alkaline phosphatase (AP) labelled anti-human IgA or IgG antibody. The analytical signal was based on the anodic redissolution of enzymatically generated silver by cyclic voltammetry. The results obtained were corroborated with a commercial ELISA kit indicating that the electrochemical immunosensor is a trustful analytical screening tool.

Electrochemical analysis of opiates—an overview

The analysis of opiates is of vital interest in drug abuse monitoring and research. This review presents a general overview of the electrochemical methods used for detection and quantification of opiates in a variety of matrices. Emphasis has been placed on the voltammetric methods used for study and determination of morphine, codeine, and heroin. Specific issues that need to be solved and better explained as well as future trends in the use of electrochemical methods in the examination of opiates are also discussed.

Development of electrochemical methods for determination of tramadol - analytical application to pharmaceutical dosage forms

A square-wave voltammetric (SWV) method and a flow injection analysis system with amperometric detection were developed for the determination of tramadol hydrochloride. The SWV method enables the determination of tramadol over the concentration range of 15-75 µM with a detection limit of 2.2 µM. Tramadol could be determined in concentrations between 9 and 50 µM at a sampling rate of 90 h-1, with a detection limit of 1.7 µM using the flow injection system. The electrochemical methods developed were successfully applied to the determination of tramadol in pharmaceutical dosage forms, without any pre-treatment of the samples. Recovery trials were performed to assess the accuracy of the results; the values were between 97 and 102% for both methods.

Electrochemical determination of dihydrocodeine in pharmaceuticals

Two analytical methods for the quality control of dihydrocodeine in commercial pharmaceutical formulations have been developed and compared with reference methods: a square wave voltammetric (SWV) method and a flow injection analysis system with electrochemical detection (FIA-EC). The electrochemical methods proposed were successfully applied to the determination of dihydrocodeine in pharmaceutical tablets and in oral solutions. These methods do not require any pretreatment of the samples, the formulation only being dissolved in a suitable electrolyte. Validation of the methods showed it to be precise, accurate and linear over the concentration range of analysis. The automatic procedure based on a flow injection analysis manifold allows a sampling rate of 115 determinations per hour.

Detection of the peanut allergen Ara h 6 in foodstuffs using a voltammetric biosensing approach

A voltammetric biosensor for Ara h 6 (a peanut allergen) detection in food samples was developed. Gold nanoparticle-modified screen-printed carbon electrodes were used to develop a sandwich-type immunoassay using two-monoclonal antibodies. The antibody-antigen interaction was detected through the electrochemical detection of enzymatically deposited silver. The immunosensor presented a linear range between 1 and 100 ng/ml, as well as high precision (inter-day RSD ≤9.8 %) and accuracy (recoveries ≥96.7 %). The detection and quantification limits were 0.27 and 0.88 ng/ml, respectively. It was possible to detect small levels of Ara h 6 in complex food matrices.

Electroanalytical determination of codeine in pharmaceutical preparations

A square wave voltammetric (SWV) method and a flow injection analysis systemwi th electrochemical detection (FIA-EC) using a glassy carbon electrode were evaluated for the determination of codeine in pharmaceutical preparations. The interference of several compounds, such as acetaminophen,guaiacol, parabens, ephedrine, acetylsalicylic acid and caffeine, that usually appear associated with codeine pharmaceutical preparations was studied. It was verified that these electroanalytical methods could not be used with acetaminophen present in the formulations and that with guaiacol, parabens or ephedrine present the use of the FIA-EC system was impracticable. A detection limit of 5 µmol L- 1 and a linear calibration range from 40 to 140 µmol L- 1 was obtained with the SWV method. For the flow injection analysis procedure a linear calibration range was obtained from 7 to 50 µmol L- 1 with a detection limit of 3 µmol L- 1 and the FIA-EC systemallowed a sampling rate of 115 samples per hour. The results obtained by the two methods, SWV and FIA-EC, were compared with those obtained using reference methods and demonstrated good agreement, with relative deviations lower than 4%.

Electroanalytical study of fluvoxamine

Fluvoxamine (FVX) can be reduced at a mercury- drop electrode, with a maximum peak current intensity being obtained at a potential of -0.7 V vs. Ag/ AgCl, in an aqueous electrolyte solution of pH 2. The compound was determined in a pharmaceutical product and in spiked human serum by square-wave adsorptivestripping voltammetry (SWAdSV) after accumulation at the electrode surface, under batch conditions. Because the presence of dissolved oxygen did not interfere significantly with the analysis, it was also possible to determine FVX in the pharmaceutical product by use of a flow-injection analysis (FIA) system with SWAdSV detection. The methods developed were validated and successfully applied to the quantification of FVX in a pharmaceutical product. Recoveries between 76 and 89% were obtained in serum analysis. The FIA– SWAdSV method enabled analysis of up to 120 samples per hour at reduced cost, implying the possibility of competing with the chromatographic methods usually used for this analysis.

Electroanalytical determination of paroxetine in pharmaceuticals

Electroanalytical methods based on square-wave adsorptive-stripping voltammetry (SWAdSV) and flow-injection analysis with SWAdSV detection (FIA-SWAdSV) were developed for the determination of paroxetine (PRX). The methods were based on the reduction of PRX at a mercury drop electrode at −1.55V versus Ag/AgCl, in a borate buffer of pH 8.8, and the possibility of accumulating the compound at the electrode surface. Because the presence of dissolved oxygen did not interfere significantly with the analysis, it was also possible to determine PRX using FIASWAdSV. This method enables analysis of up to 120 samples per hour at reduced costs. Both methods developed were validated and successfully applied to the quantification of PRX in pharmaceutical products.

Sarcosine oxidase composite screen-printed electrode for sarcosine determination in biological samples

As the prostate cancer (PCa) progresses, sarcosine levels increase both in tumor cells and urine samples, suggesting that this metabolite measurements can help in the creation of non-invasive diagnostic methods for this disease. In this work, a biosensor device was developed for the quantification of sarcosine via electrochemical detection of H2O2 (at 0.6 V) generated from the catalyzed oxidation of sarcosine. The detection was carried out after the modification of carbon screen printed electrodes (SPEs) by immobilization of sarcosine oxidase (SOX) on the electrode surface. The strategies used herein included the activation of the carbon films by an electrochemical step and the formation of an NHS/EDAC layer to bond the enzyme to the electrode, the use of metallic or semiconductor nanoparticles layer previously or during the enzyme immobilization. In order to improve the sensor stability and selectivity a polymeric layer with extra enzyme content was further added. The proposed methodology for the detection of sarcosine allowed obtaining a limit of detection (LOD) of 16 nM, using a linear concentration range between 10 and 100 nM. The biosensor was successfully applied to the analysis of sarcosine in urine samples.

Sarcosine oxidase composite screen-printed electrode for sarcosine determination in biological samples

XIX Meeting of the Portuguese Electrochemical Society - XVI Iberic Meeting of Electrochemistry

Electrochemical immunosensor for multiplexed detection of food-borne pathogens using nanocrystal bioconjugates and MWCNT screen-printed electrode

Bacterial food poisoning is an ever-present threat that can be prevented with proper care and handling of food products. A disposable electrochemical immunosensor for the simultaneous measurements of common food pathogenic bacteria namely Escherichia coli O157:H7 (E. coli), campylobacter and salmonella were developed. The immunosensor was fabricated by immobilizing the mixture of anti-E. coli, anticampylobacter and anti-salmonella antibodies with a ratio of 1:1:1 on the surface of the multiwall carbon nanotube-polyallylamine modified screen printed electrode (MWCNT-PAH/SPE). Bacteria suspension became attached to the immobilized antibodies when the immunosensor was incubated in liquid samples. The sandwich immunoassay was performed with three antibodies conjugated with specific nanocrystal ( -E. coli-CdS, -campylobacter-PbS and -salmonella-CuS) which has releasable metal ions for electrochemical measurements. The square wave anodic stripping voltammetry (SWASV) was employed to measure released metal ions from bound antibody nanocrystal conjugates. The calibration curves for three selected bacteria were found in the range of 1 × 103 – 5 × 105 cells mL−1 with the limit of detection (LOD) 400 cells mL−1 for salmonella, 400 cells mL−1 for campylobacter and 800 cells mL−1 for E. coli. The precision and sensitivity of this method show the feasibility of multiplexed determination of bacteria in milk samples.

Chitosan/AuNPs Modified Graphene Electrochemical Sensor for Label-Free Human Chorionic Gonadotropin Detection

A new immunosensor is presented for human chorionic gonadotropin (hCG), made by electrodepositing chitosan/gold-nanoparticles over graphene screen-printed electrode (SPE). The antibody was covalently bound to CS via its Fc-terminal. The assembly was controlled by electrochemical Impedance Spectroscopy (EIS) and followed by Fourier Transformed Infrared (FTIR). The hCG-immunosensor displayed linear response against the logarithm-hCG concentration for 0.1–25 ng/mL with limit of detection of 0.016 ng/mL. High selectivity was observed in blank urine and successful detection of hCG was also achieved in spiked samples of real urine from pregnant woman. The immunosensor showed good detection capability, simplicity of fabrication, low-cost, high sensitivity and selectivity.

Electrochemical biosensor based on biomimetic material for myoglobin detection

A novel reusable molecularly imprinted polymer (MIP) assembled on a polymeric layer of carboxylated poly(vinyl chloride) (PVCsingle bondCOOH) for myoglobin (Myo) detection was developed. This polymer was casted on the gold working area of a screen printed electrode (Au-SPE), creating a novel disposable device relying on plastic antibodies. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and Fourier transform infrared spectroscopy (FTIR) studies confirmed the surface modification. The MIP/Au-SPE devices displayed a linear behaviour in EIS from 0.852 to 4.26 μg mL−1, of positive slope 6.50 ± 1.48 (kΩ mL μg−1). The limit of detection was 2.25 μg mL−1. Square wave voltammetric (SWV) assays were made in parallel and showed linear responses between 1.1 and 2.98 μg mL−1. A current decrease was observed against Myo concentration, producing average slopes of −0.28 ± 0.038 μA mL μg−1. MIP/Au-SPE also showed good results in terms of selectivity. The error% found for each interfering species were 7% for troponin T (TnT), 11% for bovine serum albumin (BSA) and 2% for creatine kinase MB (CKMB), respectively. Overall, the technical modification over the Au-SPE was found a suitable approach for screening Myo in biological fluids.

Surface Imprinting Approach on Screen Printed Electrodes Coated with Carboxylated PVC for Myoglobin detection with Electrochemical Transduction

A novel surface molecularly-imprinted (MI) material to detect myoglobin (Myo) using gold screen printed electrodes (SPE) was developed. The sensitive detection was carry out by introducing a carboxylic polyvinyl chloride (PVC-COOH) layer on gold SPE surface. Myo was attached to the surface of gold SPE/PVC-COOH and the vacant spaces around it were filled by polymerizing acrylamide and N,N-methylenebisacrylamide (cross-linker). This polymerization was initiated by ammonium persulphate. After removing the template, the obtained material was able to rebind Myo and discriminate it among other interfering species. Various characterization techniques including electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) confirmed the surface modification. This sensor seemed a promising tool for screening Myo in point-of-care.

Detection of Arah1 (a major peanut allergen) in food using an electrochemical gold nanoparticle-coated screen-printed immunosensor

A gold nanoparticle-coated screen-printed carbon electrode was used as the transducer in the development of an electrochemical immunosensor for Ara h 1 (a major peanut allergen) detection in food samples. Gold nanoparticles (average diameter=32 nm) were electrochemically generated on the surface of screen-printed carbon electrodes. Two monoclonal antibodies were used in a sandwich-type immunoassay and the antibody–antigen interaction was electrochemically detected through stripping analysis of enzymatically (using alkaline phosphatase) deposited silver. The total time of the optimized immunoassay was 3 h 50 min. The developed immunosensor allowed the quantification of Ara h 1 between 12.6 and 2000 ng/ml, with a limit of detection of 3.8 ng/ml, and provided precise (RSD <8.7%) and accurate (recovery >96.6%) results. The immunosensor was successfully applied to the analysis of complex food matrices (cookies and chocolate), being able to detect Ara h 1 in samples containing 0.1% of peanut.