ABSTRACT: Nanostructure field-effect transistor (FET) biosensors
have shown great promise for ultra sensitive biomolecular detection.
Top-down assembly of these sensors increases scalability and device
uniformity but faces fabrication challenges in achieving the small
dimensions needed for sensitivity. We report top-down fabricated
indium oxide (In2O3) nanoribbon FET biosensors using highly
scalable radio frequency (RF) sputtering to create uniform channel
thicknesses ranging from 50 to 10 nm. We combine this scalable
sensing platform with amplification from electronic enzyme-linked
immunosorbent assay (ELISA) to achieve high sensitivity to target
analytes such as streptavidin and human immunodeficiency virus type
1 (HIV-1) p24 proteins. Our approach circumvents Debye screening
in ionic solutions and detects p24 protein at 20 fg/mL (about 250 viruses/mL or about 3 orders of magnitude lower than
commercial ELISA) with a 35% conduction change in human serum. The In2O3 nanoribbon biosensors have 100% device yield
and use a simple 2 mask photolithography process. The electrical properties of 50 In2O3 nanoribbon FETs showed good
uniformity in on-state current, on/off current ratio, mobility, and threshold voltage. In addition, the sensors show excellent pH
sensitivity over a broad range (pH 4 to 9) as well as over the physiological-related pH range (pH 6.8 to 8.2). With the
demonstrated sensitivity, scalability, and uniformity, the In2O3 nanoribbon sensor platform makes great progress toward clinical
testing, such as for early diagnosis of acquired immunodeficiency syndrome (AIDS).
KEYWORDS: nanoribbon, indium oxide, biosensor, electronic ELISA, top-down fabrication