Browsing by Author "Carneiro, Mariana C.C.G."
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- Homemade 3-carbon electrode system for electrochemical sensing: Application to microRNA detectionPublication . Carneiro, Mariana C.C.G.; Moreira, Felismina T.C.; Dutra, Rosa A.F.; Fernandes, Rúben; Sales, M. Goreti F.The homemade production of carbon screen-printed electrodes (C-SPEs) with a three‑carbon electrode system is reported, along with its application in electrochemical sensing. It is highlighted herein as main novelty that a simple carbon ink may be employed in the preparation of the 3-electrode system, including the pseudo-reference electrode, thereby avoiding the addition of silver or other suitable metal and simplify the construction of such devices, reducing costs and time. Screen-printed technology was employed to produce the 3-electrodes and the corresponding electrical paths. This was achieved by the manual application of a commercial carbon ink into a polyvinyl chloride (PVC) substrate allowing the production of > 20 SPEs. The optimization of the SPE assembly was made by univariate mode, until the best electrical features of the electrode-solution interface were achieved. Several electrochemical techniques were used for this purpose, namely cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). Raman Spectroscopy and Thermogravimetric Analysis (TGA) were also used for materials and electrode surface characterization. The usefulness of such devices was tested by modifying the working electrode with a sensing layer for microRNA-107, a potential biomarker in Alzheimer's Disease (AD). For this purpose, the surface was functionalized with carboxylic groups, activated by carbodiimide reaction and bound to a suitable oligonucleotide probe containing the complementary sequence. Finally, the microRNA-107 sequence hybridized with its probe, proving the efficiency of the C-SPEs in electrochemical sensing. Overall, this study brings into light the possibility of preparing simple homemade electrodes with a 3‑carbon electrode system that stands out by the low cost, disposability and versatility of the presented platform, holding a great potential for application in point-of-care devices using electrochemical sensing.
- Nanocellulose- based biosensor for colorimetric detection of glucosePublication . Neubauerova, Katrin; Carneiro, Mariana C.C.G.; Rodrigues, Lígia R.; Moreira, Felismina; Sales, Maria Goreti FerreiraThis work reports for the first time a colorimetric based biosensor using nanocellulose (NC) based supports drop-deposited onto a cellulose paper substrate for glucose detection in point-of-care. For this purpose, microcrystalline cellulose (MCC) samples were oxidized with 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO), sodium hypochlorite, and potassium bromide, to produce carboxylated NC. For the characterization, we used several methods: TEM, FTIR and conductometric titration. In all samples, the primary alcohol groups were selectively oxidized into carboxyl groups, provided the sodium hypochlorite is added dropwise and the reaction is performed at constant pH 10. Carboxyl- NC was further casted on a cellulose substrate and used as support for glucose oxidase (GOx), horseradish peroxidase (HRP) and 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) reactions, aiming to yield a coloured detection system for glucose. The sensing system was generated by integrating GOx on the carboxyl- NC /cellulose substrate. Upon reaction with glucose, the enzyme produced hydrogen peroxide, which was converted into a blue-coloured product by reaction with HRP and the chromogenic reagent ABTS. The test-strip was calibrated by incubating it in different concentrations of glucose. The colours obtained were further analysed by a suitable image analysis software. Linear response for glucose ranged from 1.5 to 13.0 mM. Overall, this new test-strip used renewable material for glucose determination, which is an advantage when compared to other systems that require more complex technological approaches. Moreover, it was found that carboxyl- NC improved the colour homogeneity of the test-strip and the intrinsic linear response of concentration range.
- Paper-based ELISA for fast CA 15–3 detection in point-of-carePublication . Carneiro, Mariana C.C.G.; Rodrigues, R. V.; Moreira, Felismina; Sales, Maria Goreti FerreiraThe paper-based Enzyme-Linked Immunosorbent Assay (P-ELISA) is a promising tool for diagnostic applications because the paper matrix is characterised by low cost, short analysis time, portability, and a high surface-to-volume ratio that allows the use of a small sample and reagent volume of a few microliters. In addition, colorimetric assays are suitable for low-resource areas due to their simplicity and naked-eye detectability. Although several works have been reported using paper-based colorimetric sensors for cancer biomarkers, P-ELISA for cancer antigen 15–3 (CA 15–3) has never been reported. Thus, this work reports the development of a rapid, simple and relatively inexpensive paper-based colorimetric assay for the detection of CA 15–3 as cancer biomarker. The assay was developed on a filter paper that was previously washed and chemically oxidized with periodate to generate aldehyde functional groups on the cellulose surface. After covalent binding of the first antibody, detection was performed by a colorimetric reaction based on the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by a peroxidase enzyme in the presence of H2O2. The colorimetric measurement was based on digital image acquisition analysed using ImageJ software. The linear range of the assay in buffer ranged 2 to 1100 U/mL. The performance of the assay was also successfully tested in human serum from Cormay®, offering a linear range from 2 to 200 U/mL. Thus, this P-ELISA sensor is suitable for the analysis of serum samples, since the physiological value in cancer patients is 30 U/mL. We believe that this proof-of-concept has the potential to be extended to be applied to other protein biomarkers and to be a suitable tool for cancer screening in developing countries.