Abstract
An integrated optical Bragg grating sensor, capable of evanescently detecting small changes in refractive index, is employed to probe the dynamic surface-localised supramolecular interaction between an azobenzene-functionalised monolayer and cyclodextrin in solution.
Highlights
The sensor surface was cleaned by an automated series of washes with water and acetone, followed by 5.0 M potassium hydroxide to restore the hydroxyl surface (80 min). 3-APTES (10% v/v in distilled ethanol, 12 h) was flowed over this freshly prepared surface to deposit a self-assembled monolayer, affording an amine-terminated surface which was subsequently reacted with a flow of 4-phenylazophenoxyacetyl chloride, (4, 50 mg in 70 mL dimethylsulfoxide in the presence of o0.1 mL triethylamine, 12 h)
It was found that the Bragg wavelength increased by 46 (Æ4) pm during the attachment of 3-APTES, with a further increase of 761 (Æ5) pm upon attachment of 4 to the surface. This corresponds to an increase in analyte refractive index (Dnanal) of 5.1 (Æ0.4) Â 10À4 and 8.4 (Æ0.1) Â 10À3 respectively, giving a cumulative refractive index shift of B8.9 Â 10À3 for the deposition of the azobenzene-terminated self-assembled monolayer (SAM)
The dynamic assembly of the photo-switchable inclusion complex between an azobenzene-functionalised surface and a-CD has been successfully tracked in real-time via direct measurement of surface-localised refractive index
Summary
Through the investigation of non-covalent intermolecular interactions between molecules, supramolecular chemistry has applied the principles of dynamic self-assembly to create complex nano-scale architectures,[1] including molecular switches[2] and machines.[3,4,5] While supramolecular chemistry has traditionally focused upon the manipulation of molecules in the solution phase, leading to a diverse library of intricate structures evolving towards numerous potential applications,[6] there is an increasing drive to link developments in the solution phase with solid-state crystal engineering[7] through surface-based supramolecular chemistry.8–10‘artificial molecular muscle’ reported by Liu et al representing a notable example capable of performing mechanical work.[12]. Surface-enhanced Raman-based techniques have shown promise in the detection of supramolecular interactions,[16] limitations in the use of structured substrates and the difficulty in resolving individual peaks within a complex host–guest system restricts their application. Thin film techniques such as ellipsometry and the quartz crystal microbalance (QCM), in addition to detecting the deposition of covalent monolayers,[17] have been applied to the detection of the layer-by-layer deposition of supramolecular polymer films[18] and 1178 | J.
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