Noninvasive, label-free, and quantitative monitoring of lipase kinetics using terahertz emission technology.

Enzymes catalyze chemical transformations of great importance in many fields, and analysis of the rate of these transformations is equally important. The latter are typically monitored using surrogate substrates that produce quantifiable optical signals, owing to limitations associated with "label-free" techniques that could be used to monitor the transformation of original substrate molecules. In this study, terahertz (THz) emission technology is used as a noninvasive and label-free technique to monitor the kinetics of lipase-induced hydrolysis of several substrate molecules (including the complex substrate whole cow's milk) and horseradish peroxidase-catalyzed oxidation of o-phenylenediamine in the presence of H2 O2 . This technique was found to be quantitative, and kinetic parameters are compared to those obtained by proton NMR spectroscopy or UV/Vis spectroscopy. This study sets the stage for investigating THz emission technology as a tool for research and development involving enzymes, and for monitoring industrial processes in the food, cosmetic, detergent, pharmaceutical, and biodiesel sectors.