The microchannel layer used in this work were fabricated in polydimethylsiloxane (PDMS) mixed with a cross-linking agent at a ratio of 10:1 and then casting against a mould. All moulds were fabricated by photo lithography using laminate photoresist with 50 μm height (SF4000, Mungolux, Germany) adhered to glass. Channel geometries were designed by software (AutoCAD, Autodesk, USA). The surface metrology of the embedded ATR sensing layer was measured with an optical profilometer (ContourX-200, Bruker, USA). Multi-ridge ATR crystals (Basic Universal, IRUBIS GmbH, Germany) were used without further modifications.