Site‐Specific Surface Functionalization via Microchannel Cantilever Spotting (µCS): Comparison between Azide–Alkyne and Thiol–Alkyne Click Chemistry Reactions

Abstract

Different types of click chemistry reactions are proposed and used for the functionalization of surfaces and materials, and covalent attachment of organic molecules. In the present work, two different catalyst-free click approaches, namely azide-alkyne and thiol-alkyne click chemistry are studied and compared for the immobilization of microarrays of azide or thiol inks on functionalized glass surfaces. For this purpose, the surface of glass is first functionalized with dibenzocyclooctyne-acid (DBCO-acid), a cyclooctyne with a carboxyl group. Then, the DBCO-terminated surfaces are functionalized via microchannel cantilever spotting with different fluorescent and nonfluorescent azide and thiol inks. Although both routes work reliably for surface functionalization, the protein binding experiments reveal that using a thiol-alkyne route will obtain the highest surface density of molecular immobilization in such spotting approaches. The obtained achievements and results from this work can be used for design and manufacturing of microscale patterns suitable for biomedical and biological applications.

A Comparative Study of Thiol‐Terminated Surface Modification by Click Reactions: Thiol‐yne Coupling versus Thiol‐ene Michael Addition

“…For the biotin‐maleimide, respectively, a range from 5.1 ± 0.29 µm with 400 µg mL −1 to 6.4 ± 0.19 µm with 2000 µg mL −1 was observed. In previous work, we studied and compared two catalyst‐free immobilizing routes including SPAAC and TYC for the generation of covalently bound microarrays on alkyne functionalized glass surfaces where the protein binding experiments revealed that the reaction between thiol and cycloalkyne showed much higher efficiency than the reaction between azide and cycloalkyne . Simultaneously considering the past and present findings, it can be concluded that the surface density of molecular immobilization on the glass surface via click reaction in µCS is in order: TEMA > TYC > SPAAC.…”

“…Water contact angles on hydroxyl‐terminated and thiol‐terminated glasses over time; a) graph of contact angle over time fitted by rational functions using MATLAB software. The red and blue dashed curves are the best fit related to OH‐terminated (taken as comparison from) and SH‐terminated glass, respectively. The green horizontal dashed line denotes the contact angle of bare glass at about 46° for comparison.…”

“…Cantilever reservoirs were filled with 0.2 µl of the respective ink solution. The spotting process was implemented at an optimized relative humidity of 20%, as determined in previous study . All patterns were printed with a probe dwell time on the surface of 0.1 s.…”

“…This study first demonstrated that TYC yields higher surface coverage than TEC due to double addition of thiols to the linear alkyne . In addition to the mentioned examples, TYC has been utilized in various other functionalizations, including for microporous membranes, porous monolith surfaces, boron‐doped diamond electrodes, superparamagnetic fluorescent nanoparticles, graphene oxide, oxide‐free Si(111), poly(ethylene terephthalate) nanochannel, gold, micropatterned hydrogel, poly hydroxyethyl methacrylate hydrogel, polyurethanes, silica nanoparticle‐graphene oxide composites, degradable polylactides, and glass …”

“…To the best of our knowledge, this is the first study that unequivocally compares these two approaches. We adapt the successful methodology we have previously used for SPAAC and TYC benchmarking to judge the relative TYC and TEMA efficiency in surface coupling. For this purpose, the surface of hydroxyl‐terminated glass was initially thiolated using (3‐mercaptopropyl)trimethoxysilane (MPTMS).…”