An array-based CMOS biochip for electrical detection of DNA with multilayer self-assembly gold nanoparticles

This paper presents an array-based CMOS biochip for DNA detection using self-assembly multilayer gold nanoparticles (AuNPs). The biochip is fabricated by a TSMC 0.35 mu m standard CMOS process and post-CMOS micromachining processes. Before taking DNA detection measurements, self-assembly monolayer of AuNPs is established on SiO2 surface between two microelectrodes. The gap distance between the two microelectrodes in this study is less than 800 nm. First, capture oligonucleotide strands are immobilized on the top surface of self-assembly monolayer of AuNPs. On each measuring spot, selective binding occurs among thiol-modified probe oligonucleotide strands, capture oligonucleotide strands, and target oligonucleotide strands if the target oligonucleotide strands are complementary with the probe and capture oligonucleotide strands in the sample solution. Finally, through a self-assembly process between suspended gold nanoparticles and the thiol-modified end of probe oligonucleotide strand, a multilayer of AuNPs on the nanogap surface can be established. The DNA hybridization can be determined by a sharp decrease in impedance over the nanogap between the two microelectrodes, which results from an increase in the number of AuNPs layers. Measured results show that the electric current of multilayer AuNPs is about 1000 times greater than that of monolayer AuNPs. The effect of nanogap distance is also investigated. It is shown that the electrical conductivity decreases with the increase of gap distance. (C) 2005 Elsevier B.V. All rights reserved.