Immobilization of urease in Langmuir-Blodgett films of di-ureasil hybrid compounds

Highlights: • Phosphotungstic acid stabilized di-ureasil hybrid monolayers to incorporate urease. • Thermodynamic parameters are determined. • Mixed monolayers present elastic behavior. • Molecular accommodation on Langmuir-Blodgett film determined by the film properties. -- Abstract: Incorporation of enzymes in matrices as nanostructured films is a strategy to achieve molecular architectures able to enhance the efficiency of sensors and optoelectronic devices. In this present work, urease was inserted in the aqueous subphase of a di-ureasil hybrid compound (DUPTS) assembled as a Langmuir monolayer. Phosphotungstic acid (PWA) was introduced in the aqueous subphase in order to stabilize DUPTS by means of electrostatic interactions. Incorporation of urease in the Langmuir film could be attested with surface pressure and surface potential-area isotherms, rheological measurements, polarization modulation infrared reflection-absorption spectroscopy, and Brewster angle microscopy. The monolayers were transferred to solid supports as Langmuir-Blodgett films and characterized with infrared and fluorescence spectroscopies, proving not only the co-transfer of urease to the solid support, but also the conservation of part of its secondary structure. The enzyme activity could be detected towards urea hydrolysis enabling the urease/PWA/DUPTS supramolecular system to be employed for sensors as well as for other optoelectronic devices.