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- Development of colorimetric cellulose-based test-strip for the rapid detection of antibodies against SARS-CoV2 virusPublication . Correia, Bárbara P.; Sousa, Mariana P.; Sousa, Cristina E. A.; Mateus, Daniela; Sebastião, Ana Isabel; Cruz, Maria Teresa; Matos, Ana Miguel; Santos Pereira, Ana Cláudia; Moreira, FelisminaGiven the pandemic situation, there is an urgent need for an accurate test to monitor antibodies anti-SARS-CoV-2, providing crucial epidemiological and clinical information to monitor the evolution of coronavirus disease in 2019 (COVID-19) and to stratify the immunized and asymptomatic population. Therefore, this paper describes a new cellulosebased test strip for rapid and cost-efective quantitative detection of antibodies to SARS-CoV2 virus by colorimetric transduction. For this purpose, Whatman paper was chemically modifed with sodium metaperiodate to introduce aldehyde groups on its surface. Subsequently, the spike protein of the virus is covalently bound by forming an imine group. The chemical control of cellulose paper modifcation was evaluated by Fourier transform infrared spectroscopy, thermogravimetry and contact angle analysis. Colorimetric detection of the antibodies was performed by a conventional staining method using Ponceau S solution as the dye. Color analysis was performed after image acquisition with a smartphone using Image J software. The color intensity varied linearly with the logarithm of the anti-S concentration (from 10 ng/mL to 1 μg/mL) in 500-fold diluted serum samples when plotted against the green coordinate extracted from digital images. The test strip was selective in the presence of nucleocapsid antibodies, urea, glucose, and bovine serum albumin with less than 15% interference, and detection of antibodies in human serum was successfully performed. Overall, this is a simple and afordable design that can be readily used for mass Abstract Given the pandemic situation, there is an population screening and does not require sophisticated equipment or qualifed personnel
- Paper-based aptasensor for colorimetric detection of osteopontinPublication . Santos Pereira, Ana Cláudia; Moreira, Felismina; Rodrigues, Lígia; Ferreira Sales, Maria GoretiThis work presents a novel cellulose-based aptasensor for the colorimetric detection of a cancer biomarker, osteopontin (OPN), in point-of-care (PoC) analysis. For this purpose, the cellulose paper was chemically modified with (mercaptopropyl)methyldimetoxisilane to attach the thiolated aptamer, which acts as a biological detection layer. The surface modification was checked by Fourier transform infrared spectroscopy and thermogravimetric analysis. Colorimetric detection was performed using a conventional staining solution, Bradford reagent. The color analysis was performed by evaluating the RGB coordinates provided by the ImageJ program from the photographs taken with a smartphone. Overall, the biosensor shows good sensitivity with a wide linear range (R > 0.998) of 5–1000 ng/mL and a detection limit lower than 5 ng/mL in buffer and commercial human serum solution, after 30 min of incubation. In addition, this aptasensor shows good selectivity to some interfering species such as bovine serum albumin and recombinant OPN. Analytical data obtained from spiked serum samples confirm the accuracy of the method. Importantly, it is a broad-spectrum method that tends to meet the criteria of REASSURED (real-time connectivity, ease of sampling, affordability, specificity, ease of use, speed and robustness, device freedom, and deliverability) for global testing.