Institute of Electrical and Electronics Engineers, Journal of Lightwave Technology, 16(33), p. 3385-3393, 2015
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We describe the design and fabrication of biochips based on one dimensional photonic crystals supporting Bloch surface waves for label-free optical bio-sensing. The optical properties of Bloch surface waves are studied in relation to the geometry of the photonic crystals and on the properties of the dielectric materials used for the fabrication. The planar stacks of the biochips are composed of silica, tantala and titania that were deposited using plasma ion assisted evaporation under high vacuum conditions. The biochip surfaces were functionalized by silanization and appropriate fluidic cells were designed to operate in an automated platform. An angularly resolved ellipsometric optical sensing apparatus was assembled to carry out the sensing studies. The angular operation is obtained by a focused laser beam at a fixed wavelength and detection of the angular reflectance spectrum by means of an array detector. The results of the experimental characterization of the physical properties of the fabricated biochips show that their characteristics, in terms of sensitivity and figure of merit, match those expected from the numerical simulations. Practical application of the sensor was demonstrated by detecting a specific glycoprotein, Angio-poietin 2, that is involved in angiogenesis and inflammation processes. The protocol used for the label-free detection of Angiopoietin 2 is described and the results of an exemplary assay, carried out at a relatively high concentration of 1μg/ml, are given and confirm that an efficient detection can be achieved. The limit of detection of the biochips for Angiopoietin 2, based on the protocol used, is 1.5 pg / mm2 in buffer solution. The efficiency of the label-free assay is confirmed by independent measurements carried out by means of confocal fluorescence microscopy.