A Portable Setup for Molecular Detection by Transmission LSPR
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A Portable Setup for Molecular Detection by Transmission LSPR Giulia Cappi1, Enrico Accastelli1, Fabio M. Spiga1, Vera Cantale2, Maria A. Rampi2, Luca Benini3, Carlotta Guiducci1. 1 Laboratory of Life Sciences Electronics, Swiss Federal Institute of Technology (EPFL), 1015 Lausanne, Switzerland. 2 Dipartimento di Chimica, Università di Ferrara, via Borsari 46, 44121 Ferrara, Italy. 3 Dipartimento di Elettronica, Informatica e Sistemistica, Università di Bologna, Viale Risorgimento 2, 40136 Bologna, Italy. Contact author’s e-mail: [email protected] ABSTRACT In the framework of bioanalytics and multiple array detection, we developed a fully portable and low-cost detection system based on Localized Surface Plasmon Resonance (LSPR) in a transmission configuration (T-LSPR). The transmission approach is suitable to be scaled to small dimension systems and to enable high-density array measurements on the same platform. Our setup is made out of off-the-shelf components and consists of a set of discrete light sources and a couple of light-detectors which enable a differential measurement setup. An algorithm fits the measured data and extracts the information of the plasmon peak position in the spectrum. The performance of our T-LSPR measurement system has been characterized on a set of Fluorinated Tin Oxide-coated glass slides covered with gold Nanoislands (NIs). The samples have been modified with a single-stranded DNA layer and a real-time DNA hybridization experiment has been performed. Here we demonstrate that the proposed T-LSPR device, based on the characterization of the plasmon peak with a differential approach, is able to monitor realtime DNA hybridization on surface, and to precisely measure the position of the peak with a standard deviation in wavelength of 0.2 nm. Keywords: sensor, biological, optical. INTRODUCTION Parallel detection of multiple analytes by means of high-throughput self-contained automated analytical systems is at the basis of future diagnostics. T-LSPR [1-4] is a very sensitive label-free technique suitable for arrays implementation [5]. It is based on the excitation of the interface between a dielectric and a non connected pattern of metal, on which a localized surface plasmon wave arises. Surface plasmons are very sensitive to changes occurring in the immediate surroundings of the metal nanoparticles, including molecular binding events on the sensor surface. The presence of biomolecules on surface alters the local refractive index causing a shift of the plasmon towards higher wavelengths [6, 7]. Quantitative characterization of the molecular layer on the surface can be obtained from the location of the peak position in the spectrum. The peak wavelength of the plasmon depends on the metal, on the geometry and on the properties of the surrounding dielectric [8]. The sensitivity of a sensor is proportional to the sharpness of its plasmon, which can be narrowed by enhancing the regularity of the nanostructures and of the patterns [9]. In T-LSPR, the plasmon phenomenon can be observed as
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