One-Step Photochemical Attachment of NHS-Terminated Monolayers onto Silicon Surfaces and Subsequent Functionalization

Abstract

N-Hydroxysuccinimide (NHS)-ester-terminated monolayers were covalently attached in one step onto silicon using visible light. This mild photochemical attachment, starting from omega-NHS-functionalized 1-alkenes, yields a clean and flat monolayer-modified silicon surface and allows a mild and rapid functionalization of the surface by substitution of the NHS-ester moieties with amines at room temperature. Using a combination of analytical techniques (infrared reflection absorption spectroscopy (IRRAS), extensive X-ray photoelectron spectroscopy (XPS) in combination with density functional theory calculations of the XPS chemical shifts of the carbon atoms, atomic force microscopy (AFM), and static contact angle measurements), it was shown that the NHS-ester groups were attached fully intact onto the surface. The surface reactivity of the NHS-ester moieties toward amines was qualitatively and quantitatively evaluated via the reaction with para-trifluoromethyl benzylamine and biotin hydrazide.

Copper-Free Click Biofunctionalization of Silicon Nitride Surfaces via Strain-Promoted Alkyne–Azide Cycloaddition Reactions

“…The two O 1s peaks at 532.8 eV (oxygen in carbonyl group) and 535.5 eV (oxygen in C−O−N bonds) are characteristic for ester formation. 80 The experimental ratio of these two oxygen peaks of 6:1 exceeded the theoretically expected 3:1 ratio, which suggests an incomplete formation of the active ester. In the N 1s signal, characteristic emissions of nitrogen from the NHS moiety at 402.3 eV and the typical N 1s emission of the substrate at 398.1 eV (BE) were observed.…”

“…80 The spectrum was deconvoluted in three main contributions, as reported earlier. 80 However, the comparison of simulated XPS spectra by DFT calculations with the experimental spectrum revealed a too large contribution by the C−C bonds in the alkyl chain and confirmed once again incomplete coverage. The C 1s spectrum was fitted with three peaks centered at 285.0 eV Table 1.…”

Silicon and Silicon-Related Surfaces for Biosensor Applications

“…Nevertheless, hydrogen bonding causes acid bilayer formation, which makes these monolayers hard to clean while for further functionalization an additional activation step via carboxylic anhydrides or N-hydroxysuccinimide (NHS) chemistry is still needed [Fabre & Hauquier, 2006& Strother, et al, 2000. In addition, we note that the last years some interesting ω-functionalized monolayers are prepared, which showed no signs of upside-down attachment, are easy to clean, and allow further functionalization in a single step & Ciampi, et al, 2007& Li, et al, 2010& Ng, et al, 2009& Scheres, et al, 2010& Yang, M., et al, 2008. Finally, in view of the broad range of available patterning techniques [Garcia, et al, 2006& Woodson & Liu, 2007 it is somewhat remarkable that thus far, only a limited number of patterning routes for organic monolayers on oxide-free silicon has been reported.…”

Surface Functionalization by Strain‐Promoted Alkyne–Azide Click Reactions

“…As a result, alternative approaches have been developed over the last five years, including metal-free ligation chemistry that either requires no further activation (e.g., N-hydroxysuccinimidebased amide formations) [2] or employs activated but traceless chemistry (e.g., photoinduced thiol-ene addition reactions). [3] Recently, several examples have been published that aim to combine traceless reactions with room-temperature conditions through the application of strain-promoted alkyneazide cycloadditions (SPAAC or Huisgen-Bertozzi-type cycloadditions) [4] to surfaces.…”