Thin film preparation of polyphenol oxidase enzyme (PPO) and investigation of its organic vapor interaction mechanism

Abstract

This study investigated spin coated thin films of polyphenol oxidase enzyme (PPO) as vapor sensor to detect chloroform, acetone, ethyl acetate, isopropyl alcohol and toluene. Thin film of enzyme was produced onto a bio-composite (gelatine chitosan) first layer via 5000 rpm spin speed. UV-visible spectroscopy and Quartz Crystal Microbalance (QCM) measurements were carried out to analyze the reproducibility of PPO spun film. It was found that the PPO enzyme can be transferred onto a solid substrate as a solid state thin film form. 
The sensor films of PPO enzyme were exposed to various VOCs (chloroform, acetone, ethyl acetate, isopropyl alcohol and toluene) with different fixed concentrations. The sensing responses of PPO thin films versus five vapors were investigated using QCM as the time dependence frequency recording method. The PPO sensor films exhibited high sensitivity and fast responses against all VOCs. But the response rate and magnitude were changed depending on the chemical structure and the molecular size of the analyte vapor. Recorded frequency changes as monitored by QCM technique have been integrated with the Fick’s second law of diffusion to determine the diffusion coefficients of analyte vapors. 
The results showed that the interaction characteristics between PPO and the analytes can be considered in terms of two main processes which are surface interaction and diffusion. And it was concluded that the formation of these two processes during the interaction depend on the molecular size and functional group of the analytes. These results showed that enzymes can be integrated into vapor sensor system as active layer and are promising for further sensor studies.