Elaboration of multilayered thin films based on cellulose nanocrystals and cationic xylans: application to xylanase activity detection

Multilayered thin films have been prepared by means of the "spin-assisted electrostatic layer-by-layer self-assembly" method, in which cellulose nanocrystals (CN) and cationic xylans (CX) are alternatively deposited up to 10 times on a rotating silicon wafer. The film growth process was studied and the thickness increment was found to be equal to 23 nm per bilayer. This value is relatively high in comparison with that of previous studies. Atomic force microscopy revealed that the surface of the films consists of thick layers of CX, which are deposited as a compact network of aggregates on the CN layers. After a few deposition cycles, structural color appears. When the film is submitted to enzymatic hydrolysis of xylans, the thickness of the film decreases and a visible color change is induced. The sensitivity of the test was evaluated in comparison with a usual colorimetric measurement, which relies on the detection of reducing sugars set free by enzymatic hydrolysis. The assay sensitivity was found to be similar to that of the colorimetric method. The presented new method is simple, fast, and easy to use. These findings show that the method based on multilayer thin films might open new opportunities to optimize the screening assays for xylanase discovery.