Integrated Visible optical filter and photodetector for detection of FRET signals
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Integrated Visible optical filter and photodetector for detection of FRET signals P. Louro1,2, A. Charneca4 V. Silva1, M. Vieira1,2,3, A. Karmali4 1
Electronics Telecommunications and Computer Dept, ISEL, Lisbon, Portugal. CTS-UNINOVA, Lisbon, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal 4 CIEB-ISEL, R. Conselheiro Emidio Navarro, 1, Lisbon, Portugal 2
ABSTRACT In this paper we present a multilayer device based on a-Si:H/a-SiC:H that operates as photodetector and optical filter. The use of such device in protein detection applications is pertinent in Fluorescence Resonance Energy Transfer (FRET) measurements that demand the detection of visible fluorescent signals located at specific wavelengths bands. This device was designed to operate in the visible range with a selective sensitivity dependent on the applied electrical bias. Several nanosensors were tested with a commercial spectrophotometer to judge the performance of the FRET signals using glucose solutions of different concentrations. Two nanosensors (FLIPglu-90M and FLIPglu-600M) were tested with a commercial spectrofluorimeter to judge the performance of the FRET signals by using glucose solutions of different concentrations. These measurements were carried out by using these nanosensors both in the free form and immobilized form on inner epidermis of onion bulb scale. The proposed device was used to demonstrate the possibility of FRET signals detection, using visible signals of similar wavelength and intensity. The device sensitivity was tuned to enhance the wavelength band of interest using adequate electrical biasing. INTRODUCTION Protein sensing is an issue with great interest in medical and biological applications. One possible approach to protein detection takes advantage of measuring changes in fluorescence resonance energy transfer (FRET) between a fluorescent donor and an acceptor within a protein which undergoes induced changes in conformation [1, 2]. The substrate-induced FRET change between two fluorescent proteins (FP) variants (Cyano and Yellow) bound to the Escherichia coli periplasmic glucose-binding protein can be used to quantify glucose in vitro and in vivo. In this paper we analyzed the emission spectrum obtained from fluorescent labels attached to a protein which changes its conformation in the presence of glucose. Different glucose nanosensors were used to measure the output spectra with fluorescent signals located at visible bands of the spectrum. A new device is presented based on multilayered a-SiC:H heterostructures to detect identical transient visible signals [3, 4]. The transducer consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure optimized for the detection of the fluorescence resonance energy transfer between fluorophores with excitation in the violet (430 nm) and emissions in the visible range of the spectrum. The device was characterized through spectral response measurements, under reverse electrical bias using different steady state wavelength backgrounds by front an
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