Indium tin oxide with zwitterionic interfacial design for biosensing applications in complex matrices

• Main Authors: Darwish, N.T., Alias, Y., Khor, S.M.
• Format: Article
• Language: English
• Published: 2015
• Subjects: QD Chemistry
• Online Access: http://eprints.um.edu.my/15514/1/Applied_Surface_Science_325_%282015%29_91%E2%80%9399_%28post-print_version%29.pdf; http://eprints.um.edu.my/15514/; http://www.sciencedirect.com/science/article/pii/S0169433214024337 http://ac.els-cdn.com/S0169433214024337/1-s2.0-S0169433214024337-main.pdf?tid=62ab92a6-a7a2-11e5-a76c-00000aacb35d&acdnat=1450675338186fe4660922c9a6be5c0dbfbe35971a

Biosensing interfaces consisting of linker molecules (COOH or NH2) and charged, antifouling moieties ((SO3 and N+(Me)3) for biosensing applications were prepared for the first time by the in situ deposition of mixtures of aryl diazonium cations on indium tin oxide (ITO) electrodes. A linker molecule is required for the attachment of biorecognition molecules (e.g., antibodies, enzymes, DNA chains, and aptamers) close to the transducer surface. The attached molecules improve the biosensing sensitivity and also provide a short response time for analyte detection. Thus, the incorporation of a linker and antifouling molecules is an important interfacial design for both affinity and enzymatic biosensors. The reductive adsorption behavior and electrochemical measurement were studied for (1) an individual compound and (2) a mixture of antifouling zwitterionic molecules together with linker molecules combination 1: 4-sulfophenyl (SP), 4-trimethylammoniophenyl (TMAP), and 1,4-phenylenediamine (PPD); combination 2: 4-sulfophenyl (SP), 4-trimethylammoniophenyl (TMAP), and 4-aminobenzoic acid (PABA) of aryl diazonium cations grafted onto an ITO electrode. The mixture ratios of SP:TMAP:PPD and SP:TMAP:PABA that provided the greatest resistance to non-specific protein adsorptions of bovine serum albumin labeled with fluorescein isothiocyanate (BSA�FITC) and cytochrome c labeled with rhodamine B isothiocyanate (RBITC�Cyt c) were determined by confocal laser scanning microscopy (CLSM). For the surface antifouling study, we used 2-2-(2-methoxyethoxy) ethoxyacetic acid (OEG) as a standard control because of its prominent antifouling properties. Surface compositions of combinations 1 and 2 were characterized using X-ray photoelectron spectroscopy (XPS). Field-emission scanning electron microscopy (FE-SEM) was used to characterize the morphology of the grafted films to confirm the even distribution between linker and antifouling molecules grafted onto the ITO surfaces. Combination 1 (SP:TMAP:PPD) with a ratio of 0.5:1.5:0.37 exhibited the best antifouling capability with respect to resisting the nonspecific adsorption of proteins.