http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/13709 2026-05-17T16:10:23Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/13927 Challenges and trends in the development of a magnetoresistive biochip portable platform Martins V.C.; Germano J.; Cardoso F.A.; Loureiro J.; Cardoso S.; Sousa L.; Piedade M.; Fonseca L.P.; Freitas P.P. The magnetoresistive (MR) biochip concept has emerged a decade ago and since then considerable achievements were made in the field. At the moment there is a strong effort in building up a fully integrated, portable and accessible spintronic device for bioanalytical assays. Some of the major challenges and working solutions are addressed here. In a MR-biochip platform five main components can be identified as key points for its success: the MR sensing elements, the magnetic labels, the surface chemistry, the microfluidic system and the read-out electronic set-up. Linear spin valve sensors were fabricated with good sensitivity and proper field range. Magnetic particles were carefully characterized and selected seeking for the best biomolecular labels. The surface chemistry was extensively optimized in order to get it more efficient, specific and reproducible. A microfluidic structure was designed and fabricated in polydimethilsiloxane (PDMS) to work as sample transportation and simultaneously control the wash out steps. Finally, a portable and autonomous electronic microsystem provides the electronic circuitry to control, address and read-out up to 256 sensors. From the assembling of all these components emerges a versatile portable platform. The first results from the platform in a real-time detection of 20mer single stranded DNA sequences labeled with 130 nm magnetic labels are presented. © 2009 Elsevier B.V. All rights reserved. 2010-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/13926 Microfluidic "thin chips" for chemical separations Gaspar A.; Salgado M.; Stevens S.; Gomez F.A. This paper describes the design, development and application of microfluidic "thin chips"; fabricated from PDMS. Thin chips consist of multiple layers of PDMS chemically bonded onto each other. Unlike thicker PDMS chips that suffer from lack of sensitivity due to PDMS absorption in the VIS and UV range, the thinness of these chips allows for the detection of chromophoric species within the microchannel via an external fiber optics detection system. C18-modified reversed-phase silica particles are packed into the microchannel using a temporary taper created by a magnetic valve and separations using both pressure- and electrochromatographic-driven methods are detailed. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA. 2010-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/13925 Scanning electrochemical microscopy for detection of biosensor and biochip surfaces with immobilized pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase as enzyme label Zhao C.; Wittstock G. Scanning electrochemical microscopy (SECM) was applied to study quinoprotein-based biosensor or biochip. A typical quinoprotein, pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (GDH), was taken as example. Feedback mode and generation collection (GC) mode in SECM have been explored in imaging the catalytic activity of GDH on microscopic magnetic bead domains. Biotinylated GDH was immobilized by using streptavidin-coated paramagnetic microbeads, which were deposited as microspot on a hydrophobic surface. Ferrocenemethanol and ferricyanide were used as electron mediators for feedback and GC detection, respectively. Enzymatic catalysis was further studied quantitatively using the theory developed for SECM. © 2004 Elsevier B.V. All rights reserved. 2005-01-01T00:00:00Z http://tainguyenso.vnu.edu.vn/jspui/handle/123456789/13924 Effect of spin-valve sensor magnetostatic fields on nanobead detection for biochip applications Ferreira H.A.; Feliciano N.; Graham D.L.; Freitas P.P. Spin valves are being used in biochip applications via the detection of biomolecular recognition using magnetic nanoparticles as labels. The magnetic moment of the labels and the sensor response depend on the magnetic fields involved. A calculation based on an external magnetizing field, incorporating the contribution from the magnetostatic fields created by the free and pinned layers of the sensor and the field due to the sensing current, showed that these fields are important. Experimental detection signals of high particle numbers agree with the model, showing that reasonable detection signals are possible even in the absence of an external field. © 2005 American Institute of Physics. 2005-01-01T00:00:00Z