In this work, we present the combination of an acoustic trap and attenuated total reflection (ATR) Fourier-transform infrared (FTIR) spectroscopy , to monitor the activity of immobilized enzymes. By mounting an acoustofluidic cell on top of a custom-built ATR setup, we were able to trap beads labeled with the enzyme alkaline phosphatase (AP) without the need of mechanical retention elements . To showcase potential applications of the presented setup for enzyme kinetic studies, we monitored the conversion of p-nitrophenylphosphate into p-nitrophenol and phosphate ion via beads carrying the immobilized enzyme. Multiple experiments were performed by retaining the labeled beads via ultrasound (US) particle manipulation and resulted in excellent experimental reproducibility. Beads could be discarded in a straightforward manner by switching off the ultrasound. This proves the potential of the acoustic trap combined with ATR-FTIR spectroscopy for monitoring reactions catalyzed by trapped particles