Interplay between surface chemistry and optical behavior of semiconductor-biomolecule functionalized sensing systems: an
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1133-AA07-13
Interplay between surface chemistry and optical behavior of semiconductor-biomolecule functionalized sensing systems: an optical investigation by spectroscopic ellipsometry Maria Losurdo,1 Scott D. Wolter,2 Maria M. Giangregorio,1 Fabiana Lisco,1 Michael Angelo,2 William V. Lampert,3 Giovanni Bruno,1and April Brown2 1
Institute of Inorganic Methodologies and of Plasma, IMIP-CNR, and INSTM, via Orabona, 470126 Bari, Italy 2 Electrical and Computer Engineering, Duke University, Durham, NC 27709, USA 3 U.S. Army Research Office, Research Triangle Park, NC 27709, USA
ABSTRACT Chemical functionalization of bio-molecules, including hemin (an iron porphyrin) and bovine albumin onto Si (100) and GaAs (100) surfaces is reported. Spectroscopic ellipsometry analysis on the optical response of functionalized surfaces provides information on molecular coverage and effective thickness as well as the kinetics of surface attachment. Topographic features of the chemically functionalized surfaces are investigated by atomic force microscopy.
INTRODUCTION Self-assembled monolayers of bio-molecules on solid surfaces have become indispensable systems for modeling and controlling biologically relevant surfaces. Solid surfaces functionalized by bio-recognition molecules have applications ranging from medical diagnostics and analytical chemistry to micro and nano-electromechanical systems. Metalloporphyrins, for instance, are being investigated as optical biosensors for protein characterization [1] and sensors for NO and NO2 [2]. A method of selective detection of NO [3] uses a GaAs based sensor, where the semiconductor surface is chemically functionalized with hemin porphyrin. We extended this pioneering work to InAs and InP semiconductors for target recognition of NO and other small metabolites [4,5]. For semiconductor-biomolecule based sensors, the degree of coverage, aggregation, substrate binding affinity and chemistry, and the orientation of is the surface groups are important for ultimate sensor character. In this frame, this contribution presents a comparative analysis of the chemistry and kinetics of chemical functionalization with hemin and bovine serum albumin (BSA) of Si(100) and GaAs(100). In this study, spectroscopy ellipsometry is used as a non-invasive technique, to analyze the surface of the functionalized semiconductors, to obtain information on the surface coverage by the bio-molecule and on parameters affecting the kinetics of formation of monolayer coverage of hemin and albumin on the semiconductor surfaces. EXPERIMENTAL Biomolecular layers were formed on n-type (100)-oriented Si and GaAs wafers. The ellipsometric measurements showed that both surfaces had a layer of native oxide of 2.5 nm. Sample surfaces were degreased in solutions of trichloroethylene, acetone, methanol, and de-
ionized water in an ultrasonic bath and then dried with high purity N2 gas. Some of the wafers were also etched to remove the native oxide, the Si was etched by the diluted HF(1%), while the GaAs was etched by HCl:HF=10:1 s
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