Sofia Teixeira

Label-free human chorionic gonadotropin detection at picogram levels using oriented antibodies bound to graphene screen-printed electrodes

Human chorionic gonadotropin (hCG) is a key diagnostic marker of pregnancy and an important biomarker for cancers in the prostate, ovaries and bladder and therefore of great importance in diagnosis. For this purpose, a new immunosensor of screen-printed electrodes (SPEs) is presented here. The device was fabricated by introducing a polyaniline (PANI) conductive layer, via in situ electropolymerization of aniline, onto a screen-printed graphene support. The PANI-coated graphene acts as the working electrode of a three terminal electrochemical sensor. The working electrode is functionalised with anti-hCG, by means of a simple process that enabled oriented antibody binding to the PANI layer. The antibody was attached to PANI following activation of the -COOH group at the Fc terminal. Functionalisation of the electrode was analysed and optimized using Electrochemical Impedance Spectroscopy (EIS). Chemical modification of the surface was characterised using Fourier transform infrared, and Raman spectroscopy with confocal microscopy. The graphene-SPE-PANI devices displayed linear responses to hCG in EIS assays from 0.001 to 50 ng mL-1 in real urine, with a detection limit of 0.286 pg mL-1. High selectivity was observed with respect to the presence of the constituent components of urine (urea, creatinine, magnesium chloride, calcium chloride, sodium dihydrogen phosphate, ammonium chloride, potassium sulphate and sodium chloride) at their normal levels, with a negligible sensor response to these chemicals. Successful detection of hCG was also achieved in spiked samples of real urine from a pregnant woman. The immunosensor developed is a promising tool for point-of-care detection of hCG, due to its excellent detection capability, simplicity of fabrication, low-cost, high sensitivity and selectivity.

Polyaniline-graphene based α-amylase biosensor with a linear dynamic range in excess of 6 orders of magnitude.

α-amylase is an established marker for diagnosis of pancreatic and salivary disease, and recent research has seen a substantial expansion of its use in therapeutic and diagnostic applications for infection, cancer and wound healing. The lack of bedside monitoring devices for α-amylase detection has hitherto restricted the clinical progress of such applications. We have developed a highly sensitive α-amylase immunosensor platform, produced via in situ electropolymerization of aniline onto a screen-printed graphene support (SPE). Covalently binding an α-amylase specific antibody to a polyaniline (PANI) layer and controlling device assembly using electrochemical impedance spectroscopy (EIS), we have achieved a highly linear response against α-amylase concentration. Each stage of the assembly was characterized using a suite of high-resolution topographical, chemical and mechanical techniques. Quantitative, highly sensitive detection was demonstrated using an artificially spiked human blood plasma samples. The device has a remarkably wide limit of quantification (0.025-1000IU/L) compared to α-amylase assays in current clinical use. With potential for simple scale up to volume manufacturing though standard semiconductor production techniques and subsequently clinical application, this biosensor will enable clinical benefit through early disease detection, and better informed administration of correct therapeutic dose of drugs used to treat α-amylase related diseases.

Food safety management system implementation and certification: survey results

The worldwide implementation and certification of food safety management systems (FSMS) have increased significantly during the last few years, thus reflecting the importance of assuming these standards in some activity sectors. Based on the literature review carried out, there are a large number of research projects that have been conducted in this area. However, as far as Portugal is concerned, the nationwide research projects related to ISO 22000 are scarce. Therefore, this paper reflects what we believe to be a pioneering contribution in order to study FSMS adoption by Portuguese companies. In more detail, our aim is to provide fact-based insights, among others, into the following issues: (1) What are the motivations and benefits of ISO 22000 certification? (2) What are the main obstacles, difficulties and drawbacks of ISO 22000? (3) What are the benefits and costs directly related to the food management system implementation, certification and maintenance? (4) What are the market evolution perspectives of the food management system? In order to answer these questions, we used a research methodology that was based on a survey that was e-mailed to the ISO 22000-certified Portuguese companies.

Electrochemical impedence spectroscopy enabled CA125 detection; toward early ovarian cancer diagnosis using graphene biosensors: EIS Enable Early CA125 Detection Using Sensors

With current diagnostic methods detection of stage 1 or 2 ovarian cancer using CA125 is possible in only 75% of cases. The ability to detect CA125 at lower concentrations could significantly improve such early stage diagnosis. Here, the use of screen‐printed graphene biosensors as a label‐free detection platform for CA125 was evaluated. The sensor was fabricated through deposition of a polyaniline layer via electropolymerisation on to a graphene screen‐printed electrode. The sensor surface was functionalised with anti‐CA125 antibody via covalent cross linking to polyaniline. The fabrication process was characterised through cyclic voltammetry and electrochemical impedance spectroscopy. The limit of detection achieved was 0.923 ng/μL across a dynamic range of 0.92 pg/μL–15.20 ng/μL and represents the most sensitive CA125 detection reported to date. With sensitivity limits at this level, it will now be possible to conduct clinical trials using serum samples collected from early stage ovarian cancer patients and at risk individuals.

Ultrasensitive environmental assessment of xeno-estrogens in water samples using label-free graphene immunosensors

There is a growing interest in the possible environmental health impact posed by endocrine-disrupting chemicals (EDCs). A challenge to the field of endocrine disruption is that these substances are diverse and may not appear to share any structural similarity other than usually being low molecular mass (<1000 Da) compounds. Here we demonstrate the effectiveness of sensor device for the detection of low molecular weight, poorly water soluble, estrogenic compounds E1, E2 and EE2, fabricated by electropolymerization over graphene screen printed electrode (SPE). The PANI/Gr-SPE-devices displayed linear responses to estrogenic substances, in EIS assays, from 0.0975 ng/L to 200 ng/L in water samples, with a detection limit of 0.043 pg/L for E1, 0.19 ng/L for E2 and 0.070 pg/L for EE2 which is lower than other current biosensing techniques. This portable, disposable immunosensor offers a solution for immediate measurement at sample collection sites, due to its excellent sensitivity and selectivity when testing water samples obtained directly from rivers and waste water treatment facilities. The simple screen printing production method will enable the low cost, high volume production required for this type of environmental analysis.

Synthesis and Characterization of (3-Aminopropyl)Triethoxysilane-Modified Epitaxial Graphene

Electrochemical immunosensor devices comprise of an antibody immobilised onto a semiconducting or conducting substrate. The use of epitaxial graphene in immunosensors allows for the detection of an antigen specifically bound to the immobilised antibody by monitoring the current modulation of lithographically fabricated graphene channel devices. Multilayer epitaxial graphene (MEG) was produced on semi-insulating 4H-SiC(0001) substrates by annealing at 1700°C at 1x 10-5 mbar using a graphite cap. Thickness and morphology of the graphene was studied using Raman spectroscopy, XPS, AFM, and SEM. Selective areas of graphene were targeted for modification by adding a protective window of PMMA. In order to immobilise the antibody to the graphene substrate, an amine-terminated surface is required. (3-aminopropyl) triethoxysilane (APTES), is used to achieve amine termination, which is itself bound to a hydroxyliated graphene surface. Hydroxylation was achieved using Fenton chemistry and changes in surface hydrophobicity are confirmed using contact angle measurements. Attachment of APTES to the hydroxyl terminated graphene channel was confirmed using cyclic voltammetry (CV), XPS, and Raman spectroscopy. This functionalization method can be used to attach any antibody to the graphene substrate that can bind to an amine group. This platform is therefore easily adaptable for the fabrication of a range of immunosensor devices for the detection of different biomarkers.