Catalytically Active Protein Coatings: Toward Enzymatic Cascade Reactions at the Intercolloidal Level

In this work, we show that different enzymes, such as horseradish peroxidase (HRP), glucose oxidase, laccase, and catalase, can be directly immobilized onto plasmonic gold nanoparticles (NPs) and superparamagnetic iron oxide NPs simply via unspecific physical adsorption, yielding catalytically active and colloidally stable NP systems. The enzyme coating on the NP surface is highly robust and enzymatically active. The colloidal stability and the enzymatic performance (Vmax and Km) of the enzyme-coated NPs (Au@enzyme) are strongly dependent on the pH of the dispersion and physicochemical properties of the respective enzyme. In particular, we observe that the colloidal stability of the enzyme-coated NPs does not necessarily lie in the pH range of the optimal catalytic performance of the enzymes (Au@HRP is unstable at pH 3, but kcat is the highest, 7.4 × 103 min–1). Understanding the relationship between the colloidal stability of the different enzyme-coated NPs at different pH values and the optimal catalytic performance of enzyme-coated NPs will allow us to perform enzymatic reactions at the colloidal level, ensuring quasi-homogeneous catalysis. We also demonstrate that the immobilization of different enzymes on different NP systems allows for the design of enzymatic cascade reactions at an intercolloidal level, with selective catalyst separation.