Characterization of a monolithic device for detection of FRET signals
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Characterization of a monolithic device for detection of FRET signals P. Louro1,2, M. Vieira1,2,3, M. A. Vieira1,2, V. Silva1,2, J. Costa1,2 1 Electronics Telecommunications and Computer Dept, ISEL, Lisbon, Portugal. 2 CTS-UNINOVA, Lisbon, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal ABSTRACT Fluorescence Resonance Energy Transfer (FRET) is a standard technique used in many medical and biological applications. It involves the detection of transient fluorescent signals coming from the different fluorescent proteins that work in the visible range of the spectrum. Common fluorescent emissions come from the cyan/yellow fluorophores that emit respectively, at 470 nm and 588 nm. In this paper we use optical filters based on multilayered a-SiC:H heterostructures to detect optical signals at these wavelengths. The advantage of this type of sensor is that it does not rely on mechanical parts; it is compact and cost effective. The transducer consists of two heterostructures based on a-SiC:H/a-Si:H optimized for the detection of the fluorescence emissions at wavelengths 470 nm (cyan) and 588 nm (yellow). Both front and back structures were designed to optimize the detection at these wavelengths. Results show that the device photocurrent signal measured under reverse bias and using appropriate steady state optical bias, allows the separate detection of the cyan and yellow fluorescence signals. INTRODUCTION There is great interest in developing semiconductor devices able of sensing the distance between two molecular species in real time for medical and biological applications. One possible approach is to take advantage of the mechanism of Fluorescence Resonance Energy Transfer (FRET), by which the fluorescence wavelength of two labeled molecules is shifted when they are within close range. This technique has grown in popularity due to the emergence of various fluorescent mutant proteins with shifted spectral properties [1, 2]. In the past, optical color sensors based on multilayered a-SiC:H heterostructures have been used as voltage controlled optical filters in the visible range [3, 4]. In this paper we extend the application of these devices to detect cyan and yellow fluorophores. The optical transducer has to accomplish the detection of the transient fluorescent signals coming from the different fluorescent proteins without losing any information about wavelength and intensity. The advantage of this type of sensor is that it does not rely on mechanical parts; it is compact and cost effective. In alternative to FRET measurements, the sensor could be also interesting to measure fluorescent signals that show peak values in the cyan and yellow regions. Changes in the peak values of fluorescence in the cyan and yellow region can be used to detect the presence of glucose. The sensor was studied also having this application in consideration. DEVICE CONFIGURATION Figure 1 shows the simplified schematic diagram of the structure of the device, that has in the front side a very thin pin photo
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