The Circularly Polarized Luminescence of Bacterial Cellulose

Author:Zou Zuo

Supervisor:xu yan


Degree Year:2019





Cellulose is the most abundant and renewable resource in nature,which being efficiently used is great to environmental and social benefits.Bacterial cellulose,a kind of cellulose biosynthesized by bacteria,has higher purity,higher crystallinity and better biocompatibility than cellulose from other sources.It caught the researchers’eyes.Bacterial cellulose has been widely used in biomedical,electrical,optical materials and other fields.At the same time,circularly polarized light can contain and transmit more abundant information than ordinary light source.It attracted much attention in many fields such as optical display devices,information encryption materials,biological coding,optical information storage and optical devices.The circular polarization properties of other forms cellulose,especially cellulose nanocrystals,have been studied,but those of bacterial cellulose have not been reported.Base on those,focus on the two aspects:“the circular polarization potential of bacterial cellulose”and“the modification of bacterial cellulose”,the following works have been done:(1)A novel circularly polarized luminescence material was fabricated by composite bacterial cellulose and luminophore.At present,the main challenges faced by circularly polarized luminescent materials are cumbersome preparation and poor performance.For the first time,utilizing the inherent chirality of bacterial cellulose,a composite film capable of producing circularly polarized luminescence was prepared by a simple method of dropping a luminescent solution onto bacterial cellulose.The asymmetry factor glum can reach 0.03.The factors affecting the glum of the composite films,such as the fluorescence intensity and the thickness of the BC film,were demonstrated.Bacterial cellulose could load multiple types of luminophore and produce circularly polarized luminescence.Moreover,the method for preparing a circularly polarized luminescence material has universality and can be used for preparation of other chiral cellulose-based circularly polarized luminescence materials.(2)The luminophore-bacterial cellulose-chiral photonic cellulose composite film was fabricated and their circularly polarized luminescence properties were studied.The luminophore-bacterial cellulose composite membrane was successfully constructed by in situ assembly.The luminophore was added to the culture medium of Acetobacter xylinum(A.xylinum),and the luminophore was assembled in the fiber network of bacterial cellulose while the bacterial cellulose was produced.The in situ assembly method was universal and could be used to assemble a variety of luminescent objects such as gold clusters and carbon quantum dots.Then the cellulose nanocrystals film(CNC)was placed on the luminophore-bacterial cellulose composite film for in situ composite.The composite film was flexible and transparent film,which retains the chiral photonic crystal structure of CNC,and can selectively reflect left-handed circularly polarized luminescence(L-CPL)and pass through right-handed circularly polarized fluorescence(R-CPL).The glum of L-CPL of the composite film could reach 0.2,and that of R-CPL could reach-0.24,and the glum of R-CPL was always slightly larger than that of L-CPL.The band gap had a great influence on its asymmetry factor.When the overlap between the band gap and the fluorescence peak was the largest,glum is the largest,and vice versa.(3)Modification of bacterial cellulose by genetic engineering techniques,and circular polarization fluorescence properties of the product,bacterial cellulose and chitin co-polymer,were studied.The metabolic pathway of A.xylinum producing bacterial cellulose was transformed by expressing the three enzymes(AGM1,UAP1,NAG5)that biosynthesize chitin with N-acetylglucosamine(N-GlcNac)as a starting substrate.The engineered A.xylinum biosynthesis the co-polymer of bacterial cellulose and chitin.To achieve that,two commercial product plasmids,pUC19 and pBBR122,were engineered to make their multiple cloning sites more suitable for cloning and expression of the target genes.A cloning plasmid and an expression plasmid containing three enzymes and a bla promoter which biosynthesize chitin with GlcNac as a starting substrate were constructed.The expression plasmid was transformed into A.xylinum,and a biosynthetic bacterial cellulose and chitin co-polymer was biosynthesized.The bacterial cellulose and chitin co-polymer,mA-GlcNac,was type I cellulose,wherein the Iαcrystal form was reduced compared with native bacterial cellulose,the fiber was relatively dispersed,and the Glu:GlcNac in mA-GlcNac was about 56:1.Bacterial cellulose and chitin co-polymer enables left-handed circularly polarized luminescence,and its asymmetric factor glum can reach 0.02.