Characterization of anhydrous silanization and antibody

IEEE/EMBS International Summer School on Medical Devices and Biosensors (ISSS-MD)

Characterization of Anhydrous Silanization and Antibody Immobilization on Silicon dioxide Surface Manoj Joshil, M.Goyal', R.Pinto2, S. Mukherjil*

'School of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, India. 2 Department of Electrical Engineering, Indian Institute of Technology Bombay, Mumbai, India. Abstract- Formation of uniform and cluster free silane monolayer is one of the fundamental prerequisite for affinity cantflever based biosensors. We report anhydrous silanization protocol for uniform silane monolayer on silicon dioxide (SiO2) surface using [3-(2-aminoethyl) aminopropyll-trimethoxysiane (APTES) and characterized by AFM, spectroscopic ellipsometry and FTIR. Silanization coverage is controled by availability of surface water. The roughness of the resulting silanized surface following our protocol is in the range of SiO2 surface roughness. Silanized SiO2surface is used to immobilize human immunoglobulin (HlgG) on it. FITC tagged goat antihuman IgG is allowed to react with HIgG. The immobilized surface is further characterized using Fluorescent spectroscopy and Fluorescent Microscope. Characterization results obtained from anhydrous silanization protocol are compared with the

The thicker silane layer on the sensor surface alters the mechanical properties of the biosensor. It also induces stresses on the sensor surface which may leads to difficulties s n the s ensor suracewicayi edo difficulTi anticipate these problems silane monolayer with controlled thickness on biosensor is essential. In the conventional protocol of aqueous phase silanization, the aminosilanes undergo hydrolysis and polymerization in the bulk phase before depositing and forming bonds with the silicon dioxide surface [1]. However, this results in the formation of polysilane networks prior to deposition. Thus polymerization of multifunctional silane molecules is observed both parallel and perpendicular to the te solfces leadtoforatoofiane me cule surface. This leads to formation of silane molecule clusters conventional aqueous silanization protocol. and non-uniform silane layer thickness on sensor surface. In anhydrous silanization, trace water molecules on the Keywords - affinity cantilever, silanization, APTES, FITC support surface are utilized to hydrolyze the silane molecules to form siloxane bonds. The degree of I. INTRODUCTION silanization depends on the concentration of water Chemical modification of SiO2 surface by molecules present on the surface when the aminosilane is organofunctional silane is a well-known technique for applied. Reduced silane coverage can be obtained by heating biosensor applications. Most of the approaches however the surface at high temperature (to remove adsorbed water produce non-uniform silane thickness and clustering of molecules) prior to application of the aminosilane [2]. The main goal of this paper is to demonstrate the silane molecules on the sensor surface which reduce the sensitivity of affinity cantilever. The sensitivity of the qualitative improvement of silanized surface in anhydrous affinity cantilever biosensor depends on maximum silanization, which is a prerequisite for improving the deflection of cantilever due to surface force generated by sensitivity of affinity based cantilever biosensors. The immobilized antibody on its surface as shown in Fig.l. surface morphology of the silanized surface is studied with Maximally reproducible surface force can be achieved only AFM and thickness measurement using spectroscopic if antibodies immobilized on cantilever are in uniform single ellipsometer. The orientation of silane molecule is layer. investigated using FTIR. It is shown that anhydrous Cantilever Antiboies Surface Force silanization technique produce dense and uniform antibody Xs