Silicon Nanowires Length and Numbers Dependence on Sensitivity of the Field-Effect Transistor Sensor for Hepatitis B Virus Surface Antigen Detection.

Chi-Chang Wu

doi:10.3390/bios12020115

Abstract

Silicon nanowire field effect transistor (NWFET) sensors have been demonstrated to have high sensitivity, are label free, and offer specific detection. This study explored the effect of nanowire dimensions on sensors’ sensitivity. We used sidewall spacer etching to fabricate polycrystalline silicon NWFET sensors. This method does not require expensive nanoscale exposure systems and reduces fabrication costs. We designed transistor sensors with nanowires of various lengths and numbers. Hepatitis B surface antigen (HBsAg) was used as the sensing target to explore the relationships of nanowire length and number with biomolecule detection. The experimental results revealed that the sensor with a 3 µm nanowire exhibited high sensitivity in detecting low concentrations of HBsAg. However, the sensor reached saturation when the biomolecule concentration exceeded 800 fg/mL. Sensors with 1.6 and 5 µm nanowires exhibited favorable linear sensing ranges at concentrations from 800 ag/mL to 800 pg/mL. The results regarding the number of nanowires revealed that the use of few nanowires in transistor sensors increases sensitivity. The results demonstrate the effects of nanowire dimensions on the silicon NWFET biosensors.

Highlights

Interdisciplinary integration is a major research direction, and the integration of the fields of electronics and biomedicine can be highly beneficial
The sensitivity of nanowire field effect transistor (NWFET) sensors can be increased by using small silicon nanowires, which increase the ratio of surface area to volume, thereby increasing sensitivity to the external environment
The present study explored the effect of nanowire design on sensitivity by designing NWFET sensors of various sizes

Summary

Introduction

Interdisciplinary integration is a major research direction, and the integration of the fields of electronics and biomedicine can be highly beneficial. Silicon nanowire field effect transistor (NWFET) sensors, unlike traditional biomedical detection methods, have high sensitivity, are label free and compact, and provide real-time sensing [2,3]. The second type is the top-down method, in which photolithography and etching equipment for semiconductor manufacturing are used to define the dimensions and shape of the materials [13] This process ensures control of the position of the nanowires, thereby facilitating mass production of nanowires of consistent quality [14,15]. Studies have proposed several methods for increasing the sensitivity of NWFET sensors. The length and number of nanowires are related to a transistor’s subthreshold swing (SS), S/V ratio, and biological binding sites Variation in these two parameters affects sensor sensitivity; the results of this study demonstrate the effects of nanowire size on sensing sensitivity. This study used polycrystalline silicon (poly-Si) NWFET sensors with nanowires of various sizes to detect HBV. The results can assist in the diagnosis and treatment of hepatitis B

Materials

Chemical Modification of the Sensor Chip Surface