title: Fabrication of carboxylated silicon nitride sensor chips for  detection of antigen-antibody reaction using microfluidic reflectometric interference spectroscopy.
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(-1), 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(-1) 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.
authors.affiliation: Graduate School of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Kurihara
authors.forename: Masaaki
authors.initials: M
authors.lastname: Takama
authors.forename: Tadanobu
authors.initials: T
authors.lastname: Sekiya
authors.forename: Yuka
authors.initials: Y
authors.lastname: Yoshihara
authors.forename: Tooru
authors.initials: T
authors.lastname: Ooya
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Takeuchi
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D000937:Antigen-Antibody Reactions; D015374:Biosensing Techniques / Q000295:instrumentation; D002264:Carboxylic Acids / Q000737:chemistry*; D005340:Fibrinogen / Q000032:analysis; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation; D012709:Serum Albumin / Q000032:analysis; D017655:Silicon Compounds / Q000737:chemistry*; D014168:Transferrin / Q000032:analysis; D000509:alpha-Fetoproteins / Q000032:analysis* / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D002264:Carboxylic Acids; D007074:Immunoglobulin G; D012709:Serum Albumin; D017655:Silicon Compounds; D014168:Transferrin; D000509:alpha-Fetoproteins; D005340:Fibrinogen; C032734:silicon nitride