Label-Free Protein Detection by ZnO Nanowire Based Bio-Sensors

There is an increasing demand for portable, reliable, and cost effective bioelectronic systems for applications ranging from clinical diagnosis to homeland security. Conventional detection systems involve labeling the probe molecules, large amount of target molecules to enable detection, and elaborate signal transduction methods. Most of them also have to couple with optical detection equipments that are bulky and expensive. One dimensional (1-D) and two dimensional (2-D) structures such as nanowire, nanobelts and films are capable of detecting the molecular interactions in terms of significant change in their electrical properties leading to ultrahigh sensitivity and easy integration. In this paper, we demonstrate ZnO nanowires based bio-sesnors to detect IgG antibodies. Current-voltage (I-V) and Scanning Electron Microscopy (SEM) characterization were used to monitor the change in the conductivity as well as morphology. By comparing with the reference sample, the specific binding event between anti-IgG and IgG antibodies was detected. The data indicated a conductivity change by more than 12% after the protein hybridization. SEM images confirm the morphological change from reference samples to reacted samples. In addition, same experiment protocols are carried out for ZnO thin film devices. Similar change in I-V characteristics and morphologies are observed. Through this work, we have demonstrated to use ZnO nanowires as building blocks to fabricate bio-sensors which can potentially detect any protein. Conductimetric sensing results in a label-free detection system as it detects the protein hybridization events electrically. It is a cost effective process, which can be exploited further by expanding into arrays and integrating with microfluidics. When integrated on the SOP platform, this technology can lead to portable, reliable and cost effective biosensors with applications in many areas.