Optofluidic platforms have manifold potential applications as lab-on-chip or organ-on-chip systems for cell, bio- or environmental-analytics as well as pharmaceutical research and diagnostics. An optofluidic platform was developed and applied for label-free infrared (IR) microscopic bio-sensing, which can be extended for combinatorial IR and Raman spectroscopic applications. The platform combines metallic island enhancement substrates with microfluidic chips of selectable material. It is constructed for measurements in a reflection geometry which leaves a high degree of freedom in the used microfluidic structures. By the involvement of substrates with a gradient in the effective thickness of the island film the enhancement conditions can be optimized up to a signal enhancement factors on the order of 10 to 100 resulting in a detection limit of about 0.03 nmol/cm<sup>2</sup> and sub-monolayer sensitivity for microfluidic sensing. This enables one to in situ monitor the growth of a self assembling monolayer (SAM) with temporal resolution in the minute scale. An exemplaric study of the formation of a monolayer of the tripeptide glutathione (GSH) in aqueous environment is discussed. Furthermore it is shown that chemical modifications in the ultrathin molecular layer can be monitored in dependence of environmental pH and that the binding of the model compound Streptavidin can be monitored and evaluated. Methodical future work is directed towards the integration of other spectroscopic techniques and involvement of laser-based infrared spectroscopy, enabling for even faster analytics on the sub-s range with further increased spectral resolution.

Infrared microfluidic biosensing of submonolayers

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.