Surface functionalization of gallium nitride for biosensor platform development

Matthew S Makowski, Purdue University

Abstract

Rapid and accurate molecular analysis of biological samples is essential for disease diagnosis and management. The Field Effect Transistor (FET) biosensor is a promising device architecture for advancing clinical care by offering desirable characteristics such as portability, high sensitivity, brief detection time, low manufacturing cost, multiplexing, and label-free detection. The semiconductor, gallium nitride (GaN), is an ideal material for FET biosensing applications due to its biocompatibility, chemical stability, high charge carrier mobility, and the availability of Ga-polar dangling bonds for surface functionalization. As a critical processing step in FET biosensor fabrication, surface functionalization protects devices from aqueous environments and gives the sensitivity and specificity necessary for sensing applications. The work presented here investigated functionalization of GaN surfaces through covalent binding of biomolecules and physisorption of gold nanoparticles. Covalent functionalization of GaN surfaces was achieved with olefin cross-metathesis chemistry. This functionalization scheme inhibited surface oxidation and terminated GaN surfaces with chemical functional groups for further biomolecule attachment. X-ray photoelectron spectroscopy, atomic force microscopy, and water contact angle measurements were used to characterize the functionalized surfaces. Application of the surface functionalization scheme was demonstrated by covalently binding the laminin derived IKVAV peptide to GaN surfaces and culturing PC12 cells on these functionalized surfaces. The IKVAV functionalized GaN surfaces promoted cellular adhesion and neurite growth compared to silicon control surfaces. Additionally, the chemical stability of GaN was demonstrated by the negligible levels of gallium leaching from GaN when exposed to biologically relevant aqueous solutions. GaN functionalization with physisorbed gold nanoparticles (Au NPs) was demonstrated on AlGaN/GaN high electron mobility transistors (HEMTs). The sensitivity of the Au NP/HEMT system to nearby chemical species was demonstrated by electrical detection of chemical functional group differences on the adsorbed Au NPs. A second set of experiments used the Au NP/HEMT system as a biosensor by using Au NPs that were functionalized with the kinase inhibitor PP58. PP58 served as a receptor for SRC kinase which is a cell lysate cancer biomarker. The Au NP/HEMT biosensors detected SRC at a concentration of 1 pM when exposed to a buffer solution spiked with the SRC kinase. Biosensor specificity was demonstrated by low response to a neat buffer solution and a solution containing a clinically relevant albumin concentration.

Degree

Ph.D.

Advisors

Ivanisevic, Purdue University.

Subject Area

Biomedical engineering

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