title: A digital microfluidic electrochemical immunoassay.
abstract: Digital microfluidics (DMF) has emerged as a popular format for implementing quantitative immunoassays for diagnostic biomarkers. All previous reports of such assays have relied on optical detection; here, we introduce the first digital microfluidic immunoassay relying on electrochemical detection. In this system, an indium tin oxide (ITO) based DMF top plate was modified to include gold sensing electrodes and silver counter/pseudoreference electrodes suitable for in-line amperometric measurements. A thyroid stimulating hormone (TSH) immunoassay procedure was developed relying on magnetic microparticles conjugated with primary antibody (Ab1). Antigen molecules are captured followed by capture of a secondary antibody (Ab2) conjugated with horseradish peroxidase enzyme (HRP). HRP catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) which can be detected amperometrically. The limit of detection of the technique (2.4 μIU mL(-1)) is compatible with clinical applications; moreover, the simplicity and the small size of the detector suggest utility in the future for portable analysis.
authors.affiliation: Department of Chemistry, University of Toronto, 80 St George St., Toronto, ON M5S 3H6, Canada. aaron.wheeler@utoronto.ca.
authors.forename: Mohtashim H
authors.initials: MH
authors.lastname: Shamsi
authors.forename: Kihwan
authors.initials: K
authors.lastname: Choi
authors.forename: Alphonsus H C
authors.initials: AH
authors.lastname: Ng
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Wheeler
mesh_terms: D000906:Antibodies / Q000276:immunology; D055664:Electrochemical Techniques / Q000295:instrumentation / Q000379:methods*; D004566:Electrodes; D005898:Glass / Q000737:chemistry; D006046:Gold / Q000737:chemistry; D006735:Horseradish Peroxidase / Q000378:metabolism; D007118:Immunoassay / Q000295:instrumentation / Q000379:methods*; D044085:Microfluidics / Q000295:instrumentation; D013972:Thyrotropin / Q000032:analysis* / Q000276:immunology; D017971:Tin Compounds / Q000737:chemistry
chemical_list: D000906:Antibodies; D017971:Tin Compounds; C109984:indium tin oxide; D006046:Gold; D013972:Thyrotropin; D006735:Horseradish Peroxidase