On-Chip Detection of Chemiluminescent Biomolecules using an Integrated Thin Film Silicon Photodiode
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1004-P04-10
On-Chip Detection of Chemiluminescent Biomolecules using an Integrated Thin Film Silicon Photodiode A. T. Pereira1,2, A. Pimentel1, V. Chu1, D. M. F. Prazeres2,3, and J. P. Conde1,3 1 INESC-MN, Rua Alves Redol, 9, Lisbon, 1000-029, Portugal 2 Centro de Engenharia BiolÛgica e QuÌmica, Instituto Superior TÈcnico, Lisbon, 1049-001, Portugal 3 Dept. of Chemical and Biological Engineering, Instituto Superior TÈcnico, Av. Rovisco Pais, Lisbon, 1049-001, Portugal ABSTRACT A hydrogenated amorphous silicon photodetector on a glass substrate is used for the integrated, real-time detection of chemiluminescent reactions in solution. The light emission at 425 nm resulting from the horseradish peroxidase-catalyzed oxidation of luminol is detected by a p-i-n amorphous silicon photodiode operated at zero bias. The limit of detection of the present device is in the range of nanomole of horseradish peroxidase per liter. INTRODUCTION Current biochip data acquisition is based primarily on the use of fluorescence microscope image capture of the emission from a fluorescent marker. Although these optical systems have high sensitivity, they require the use of complex image acquisition and processing systems. Onchip electronic data acquisition could improve both the speed and the reliability of the biochip pattern analysis. Previous work has demonstrated integrated amorphous silicon photodetectors for fluorescently-tagged biomolecule detection [1]. However, these systems require an integrated filter system to cut the excitation light. The use of chemiluminescence instead of fluorescence for on-chip detection has the advantage of not requiring either this filter or the use of an external light source. This would allow a simple integrated platform for on-chip electronic data acquisition. In a chemiluminescence analysis system, an enzymatic label such as horseradish peroxidase (HRP) or alkaline phosphatase (AP) is used to tag the biomolecule. In the presence of the appropriate reactants, these enzymes can catalyze a light-emitting reaction that can be detected by a photodetector. The quantification of biological molecules such as horseradish peroxidase (HRP) using chemiluminescent reactions have been reported in the literature using several detection systems including external photomultiplier tubes as detection devices [3,4], onchip CMOS photodetector arrays [5,6] and an amorphous silicon photodiode [7]. Two different device configurations have been developed for the successful detection of HRP in solution by capturing the light emitted by a chemiluminescent reaction using an integrated thin film amorphous silicon p-i-n photodiode. Amorphous silicon photodiodes show high photosensitivity, low dark current, and can be deposited on glass, plastic and steel substrates.
EXPERIMENTAL PROCEDURES Photosensor fabrication The bottom electrode of the photodiode is a transparent conductive oxide (ITO) deposited on a glass substrate. Next, a p-i-n a-Si:H diode is deposited by plasma enhanced chemical vapor deposition (PECVD) without breakin
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