Fluorescent composite films of oriented cellulose nanocrystals with fluorescein

Abstract

Thin films of cellulose nanocrystals (CNCs) with fluorescein (FL) were prepared employing the zone-casting technique. Using an aqueous CNC suspension admixed with FL allowed the preparation of fluorescent CNC/FL films with varying FL content. In the zone-cast films, the CNCs were oriented perpendicularly to the zone-casting direction. The fluorescence emission intensity depended on the FL content in the films and was the strongest at the FL to CNC weight ratios of 1/125 and 1/200. Moreover, the emission intensity and polarization depended on the excitation beam polarization. The strongest emission was recorded when the polarizer and analyzer axes were parallel to the direction of CNC orientation. Moreover, the films sprayed with aqueous solutions after drying exhibited fluorescence depending on the solution pH in a wide pH range.