Microfluidics integrated with inkjet-printed SERS substrate for in-operando reaction kinetic monitoring

The study of kinetics and reaction mechanisms is fundamental in the chemical sciences, and various optical, magnetic, and electrochemical techniques are used today. Microfluidics offer the unique opportunity of achieving accurate control over the reagent mixture, but appropriate strategies must be incorporated to track the reactive environment. It is herein presented the implementation of the kinetic monitoring of a biomimetic reaction of high interest within a microfluidic device by means of the product's SERS signals. The chip involves an aluminum foil inkjet-printed with a gold nanoparticle (AuNP) ink, resulting in a rough film of 200 nm in thickness. The same is patterned according to microfluidic side walls obtained from a 500 mu m brass foil, closed at the top with a glass coverslip. The result is a microfluidic device in which the entire length of the channel serves as an efficient SERS substrate, which is used to monitor laminar flows and species diffusion, as well as the second-order reaction kinetic constant between the cofactor pyridoxal 5'-phosphate (PLP) and a modified aniline. The success of the presented approach constitutes a first prototype of a continuous SERS monitoring of reactive components within microfluidic chips, paving the way for a variety of other conditions and configurations.