Nanomatertials as Low Density Lipoprotein (LDL) Sensors
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Nanomatertials as Low Density Lipoprotein (LDL) Sensors Tao Tang, Xiaolei Liu, Chao Li, Bo Lei, Daihua Zhang, Mahsa Rouhanizadeh1, Tzung Hsiai1, and Chongwu Zhou Department of Electrical Engineering – Electrophysics, University of Southern California Los Angeles, California 90089, U. S. A 1 Deptartment of Biomedical Engineering, University of Southern California, Los Angeles, California 90089, U. S. A ABSTRACT In2O3 nanowire and carbon nanotube transistors were used to study the chemical gating effects in response to LDL particles. Low density lipoprotein (LDL) cholesterol in blood constitutes a risk factor for coronary artery disease (heart attack). The interactions of LDL particles with these two different surfaces were investigated. The degree of LDL particles binding to carbon nanotubes was ten-fold higher than to In2O3 nanowires possibly owing to the hydrophobic/hydrophilic interactions. The conductance of field effect transistors (FET) based on nanowires and nanotubes showed complementary responses after exposure to LDL particles. While In2O3 nanowire transistors exhibited higher conductance accompanied by a negative shift of the threshold voltage, nanotube transistors displayed a lower conductance. This phenomenon was attributed to the complementary doping between the n-type In2O3 nanowires and p-type carbon nanotubes. INTRODUCTION One-dimensional nanostructures, such as metal oxide nanowires and carbon nanotubes, has attracted considerable attention due to their superior sensing performance, and many applications have been demonstrated in fields such as toxic gas sensing [1-5], protein sensing [6-9] and DNA sensing [10-11]. In human olfactory system, for example, the nose is capable of distinguishing about one thousand different odors by recruiting only tens of smelling sensors, followed by “pattern recognition” in the brain [12]. Analogous to this biological approach, artificial noses can be realized by assembling multi-sensor arrays that are integrated with microprocessors. In this context, selectivity is not achieved by specific functionalization of individual sensor units, rather, by the subsequent pattern recognition process. This technique has considerable potential for sensing in a complicated environment and has been widely applied in commercial multi-sensor arrays. One key criterion is to gain complementary and sometimes redundant information on the effect of multiple sensors exposed to various chemicals. Inspired by this, we have studied the chemical gating effects of low-density lipoprotein (LDL) on two nanosensing materials: In2O3 nanowires and carbon nanotubes. These two materials are complementary to each other; that is, carbon nanotube field-effect transistors (FET) show p-type semiconductor property while In2O3 nanowires display n-type behavior. In addition, carbon nanotubes are hydrophobic while In2O3 nanowires are hydrophilic. Low density lipoprotein (LDL) was chosen as the target molecule in this paper for two main reasons: (1) it is an important marker to detect individuals at ri
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