IR microfluidics for in situ sensing of molecular interfaces

Recent developments in infrared (IR) microfluidics for sensitive monitoring of molecular adsorption at solid–liquid interfaces are briefly reviewed. A microfluidic platform is presented that uses a metallic island film for surface enhanced IR absorption (SEIRA) coupled to IR spectroscopies for bio-sensing and vibrational investigations of molecular monolayers and their adsorption kinetics. Exemplarily, IR spectral monitoring of the monolayer formation of 4-mercaptobenzonitrile (4-MBN) in liquid environment is discussed as a Langmuir isotherm. Adsorption isotherms of specific molecular vibrations are analyzed from the time-dependent evolution of band amplitudes and peak areas during adsorption. Given the detection limit of 0.03 nmol/cm2 , the isotherms of 4-MBN, gluthathione (GSH) monolayer formation, and the sensing of 4-nitrobenzylmercaptan (4-NBM) by the MP/graphene surface are compared. Potential applications are bio- and bio-medical sensing as well as the study of processes, e. g., enzymatic reactions, chemical or catalytic reactions, receptor–ligand interactions, and structural changes of molecules due to environmental stimuli.