Development of silicon on insulator based nanogap sensor for Escherichia Coli O157:H7 detection

Abstract

Breakthrough in nanotechnology provides a great extent in biosensor development and application. Previous studies showed that nanogap sensor device provides excellent electrical behavior in sensing biomolecules samples. Nanogap sensor is a device having a pair of electrodes facing each other, which a molecule trapped in between its will be identified by observing the electrical characterization. Conventional development process requires prolonged and tedious compulsory additional method. Thus this research project focus on developing various size of uniform nanogap structure in nanometre scales which are capable of sensing Escherichia coli O157:H7 (E. coli O157:H7) at a low concentration level. The development of the device was divided into nanogap structure and gold pad structure process using electron beam lithography (EBL) method and conventional photolithography method respectively. Silicon on insulator (SOI) substrate was used to fabricate the nanogap structure and gold was used as a gold pad for a probing purpose. The developed nanogap devices was physically characterized by Field Emission Scanning Electron Microscopy and Scanning Electron Microscope. Meanwhile, the performance of the devices was tested by evaluating the capacitance and impedance reading by sweeping a frequency from 1M Hz to 0.1 Hz at room temperature with 1.0 mV input using Dielectric Analyzer. The devices were tested with de-ionized water and different pH level to optimize the sensor sensitivity that related to the nanogap size. Prior to the detection of E. coli deoxyribonucleic acid (DNA), the device was surface modified with NH2-Amine functionalized silane group using 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde for DNA to be covalently bonded with the APTES modified surface. The principle of the E. coli detection is based on charge density changes of the DNA probe immobilization and DNA target hybridization on the modified surface. The morphological testing results shows that the developed devices were observed with 40, 80 and 100 nm nanogap size. It was found that, the device with smallest gap size, 40 nm shows the highest sensitivity and stability compared to the device with bigger gap size, 80 and 100 nm. In this project 40 nm size nanogap device was successfully developed as biosensor for E. coli O157: H7 detection with capability to distinguish the impedance value between complementary, non-complementary and single mismatch DNA sequences. In addition, the device was able to detect E. coli O157: H7 DNA target at concentration limit from 10 nM to 1 pM with linear regression equation is 𝐶 (𝜇𝐹) = 3 × 10−7𝑥 + 5 × 10−9 and the correlation coefficient is 0.98.