Miniaturization of Immunoassays Using Optical Detection with Integrated Amorphous Silicon Photodiodes
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1191-OO08-04
Miniaturization of Immunoassays Using Optical Detection with Integrated Amorphous Silicon Photodiodes A. T. Pereira1,2, V. Chu1, D. M. F. Prazeres2,3 and J.P. Conde1,3 1 INESC Microsistemas e Nanotecnologias and IN- Institute of Nanoscience and Nanotechnology, Rua Alves Redol 9, Lisbon, Portugal 2 Centro de Engenharia Biológica e Química, IBB – Institute of Biotechnology and Bioengineering, Instituto Superior Técnico, Av. Rovisco Pais, Lisbon, Portugal 3 Dept. of Chemical and Biological Engineering, Instituto Superior Técnico, Av. Rovisco Pais, Lisbon, Portugal ABSTRACT Immunoassays are currently the main analytical technique for quantification of a wide range of analytes of clinical, medical, biotechnological, and environmental significance with high sensitivity and specificity. Miniaturization of immunoassays is achieved using microfluidics coupled with integrated optical detection of the antibody-antigen molecular recognition reaction using thin-film amorphous silicon (a-Si:H) photodiodes. The detection system used consists of an a-Si:H photodiode aligned with a polydimethylsiloxane (PDMS) microchannel. An enzymatic reaction taking place in the microchannel yields a product which is a light-absorbent molecule and hence can be optically detected by the integrated photodiode. Specific antigen-antibody reaction was detected and distinguished from the non-specific reaction. I"TRODUCTIO" This work combines a polydimethylsiloxane (PDMS)-based microfluidic sample handling aligned with integrated optical detection based on thin-film amorphous silicon (a-Si:H) photodiodes to achieve a miniaturized immunoassay detection system. An enzymatic reaction taking place in the microchannel yields a product that can be optically detected by the integrated photodiode. Thin-film silicon photodiodes have high photosensitivity, low dark current and can be deposited at low temperatures (below 250 °C) thus allowing the use of glass and polymer substrates. Their fabrication is an established technology allowing large area fabrication, for example in digital X-ray imagers [1] and the fabrication of a large array of sensors for multiplex measurements. a-Si:H photodiodes have been used as biosensors for chemiluminescent and colorimetric measurements, including immunoassay detection, using reaction volumes in the 1050 µL range [2-4]. Currently, the method most commonly used for immunoassays is the sandwich enzymelinked immuno sorbent assay, ELISA, in which enzymes are used as detection labels and are typically carried out in polystyrene microtiter plates [5]. Immunoassays are a multistage, laborintensive, and time consuming process. Automation of microtiter plate immunoassays can be achieved by the use of complex and bulky robotic systems for fluid manipulation. Miniaturization of immunoassays in a microfluidic system has the potential to provide fast, simple, sensitive, automated, and multiplexed immunoassays, with reduced consumption of sample and reagents and the possibility of bringing the analysis to the point-of-care. Micr
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