Article pubs.acs.org/Langmuir
Mild Photochemical Biofunctionalization of Glass Microchannels Rui Rijo Carvalho,†,‡ Sidharam P. Pujari,† Digvijay Gahtory,† Elwin X. Vrouwe,‡ Bauke Albada,† and Han Zuilhof*,†,§,∥ †
Laboratory of Organic Chemistry, Wageningen University and Research, Stippeneng 4, 6708 WE, Wageningen, The Netherlands Micronit Microtechnologies B.V., Colosseum 15, 7521 PV, Enschede, The Netherlands § School of Pharmaceutical Sciences and Technology, Tianjin University, 92 Weijin Road, Tianjin, P.R. China ∥ Department of Chemical and Materials Engineering, King Abdulaziz University, Jeddah, Saudi Arabia ‡
S Supporting Information *
ABSTRACT: The ability to locally modify the inside of microfluidic channels with bioactive molecules is of ever-rising relevance. In this article, we show the direct photochemical coupling of a N-hydroxysuccinimide-terminated ω-alkene onto hydrogen-terminated silicon oxide, and its subsequent functionalization with a catalytically active DNAzyme. To achieve this local attachment of a DNAzyme, we prepared hydrogen-phenyl-terminated glass (H-Φ-glass) by the reaction of glass with H-SiPhCl2. The presence of a radical-stabilizing substituent on the Si atom (i.e., phenyl) enabled the covalent modification of bare glass substrates and of the inside of glass microchannels with a functional organic monolayer that allowed direct reaction with an amine-functionalized biomolecule. In this study, we directly attached an NHS-functionalized alkene to the modified glass surface using light with a wavelength of 328 nm, as evidenced by SCA, G-ATR, XPS, SEM, AFM and fluorescence microscopy. Using these NHS-based active esters on the surface, we performed a direct localized attachment of a horseradish peroxidase (HRP)-mimicking hemin/Gquadruplex (hGQ) DNAzyme complex inside a microfluidic channel. This wall-coated hGQ DNAzyme effectively catalyzed the in-flow oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) [ABTS] in the presence of hydrogen peroxide. This proofof-concept of mild biofunctionalization will allow the facile preparation of modified microchannels for myriad biorelevant applications.
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INTRODUCTION The localized functionalization of silicon oxide and glass surfaces with organic functional molecules is crucial for a wide range of advanced applications of glass-based biohybrid materials.1−4 Most surface modifications on glass make use of silane chemistry,5−7 although other molecule-to-surface linkages8 such as phosphonic acid,9 arsonic acid,10 and catecholbased11 have also been used. While these oxygen-based anchor groups have proven their value for thermal anchoring reactions, they are incompatible with single-step photolithographic patterning. Photolithographic patterning is the preferred way of functionalizing enclosed surfaces, such as microfluidic channels.12 In previous work, we showed that precisely positioned patterns could be achieved in glass capillaries using the photochemical attachment of alkenes.13−15 However, the light-induced reaction on those surfaces required UV light with λ < 285 nm, precluding the use of standard commercial glass microchannels. To circumvent these limitations, we recently reported a method for the light-induced hydrosilylation of hydrogen-terminated glass (H-glass), which was obtained by the surface activation of glass with HSiCl3. This chemistry allowed the use of lower-energy light (λ = 302 nm) © XXXX American Chemical Society
to locally modify the inside of microfluidic channels with functional groups that facilitated further modifications;16 this was previously feasible using only hydrogen-terminated silicon substrates.17−19 Specifically, we installed nanometer-sized hydrophobic-alkyl or fluoro-alkyl patches, de facto molecular phase guides20 or “nanodikes”, at chosen positions inside a microchannel in order to regulate its flow.16 However, our previous approach proved incompatible with photosensitive Nhydroxysuccinimide (NHS) ester moieties because of the short wavelength required (302 nm) for the functionalization of the surface. This was particularly unfortunate as the direct photochemical attachment of such a moiety would be highly advantageous for a variety of microfluidics-based biological applications (e.g., in diagnostics (immobilization of antibodies) and in-flow biocatalysis). To solve this, we aimed to reduce the Si−H bond energy to such a level that light of significantly Special Issue: Surfaces and Interfaces for Molecular Monitoring Received: November 1, 2016 Revised: December 27, 2016
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DOI: 10.1021/acs.langmuir.6b03931 Langmuir XXXX, XXX, XXX−XXX
Article
Langmuir Scheme 1. Schematic of the Fabrication of Various H-Glasses and the Subsequent Photochemical Hydrosilylationa
(a) H-glass, reactive at a wavelength of 302 nm, with R being a compatible end group. (b) Φ-glass, reactive at 328 nm, with R1 being a photosensitive group such as NHS. (c) Mixed H5-Φ1-glass, with a small fraction of Ph moieties at the surface, reactive at a wavelength of 328 nm but more homogeneous than pure Φ-glass. a
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lower energy could be used. This lower-energy light would be compatible with the use of (NHS)-containing ω-alkenes, which are photoreactive with wavelengths
