Fabrication of Carboxylated
Silicon Nitride Sensor
Chips for Detection of Antigen–Antibody Reaction Using Microfluidic
Reflectometric Interference Spectroscopy
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Abstract
In this study, we report label-free detection of alpha-fetoprotein
(AFP), which has been used as a biomarker for hepatocellular carcinoma,
by a microfluidic reflectometric interference spectroscopy (RIfS)
system adopting a simple halogen light source and an inexpensive silicon-based
sensor chip. Introduction of carboxy groups on a silicon nitride sensor
chip to immobilize anti-AFP monoclonal antibody (anti-AFP) was carried
out simply by immersion in aqueous solution containing triethoxysilylpropylmaleamic
acid bearing a carboxy group and a silanol group. The RIfS system
with the anti-AFP-immobilized sensor chip was found to give a reversible
response through 100 on/off cycles using a regeneration buffer with
high reproducibility (coefficient of variation (CV) = 5.7%). The limit
of detection (LOD) of AFP was 100 ng mL<sup>–1</sup>, and the
measurement range spanned 3 orders of magnitude. Furthermore, the
sensor chip showed no cross-reactivity with human serum albumin, Immunoglobulin
G, transferrin, or fibrinogen at 100 μg mL<sup>–1</sup> without the use of blocking reagents such as bovine serum albumin.
Consequently, the proposed RIfS system is a potentially effective
tool for biomarker detection and in vitro diagnostics