Article pubs.acs.org/Biomac
Ultrathin Chitin Films for Nanocomposites and Biosensors Joshua D. Kittle,† Chao Wang,† Chen Qian,† Yafen Zhang,† Mingqiang Zhang,† Maren Roman,‡ John R. Morris,† Robert B. Moore,† and Alan R. Esker*,† †
Department of Chemistry and ‡Department of Wood Science and Forest Products, Virginia Tech, Blacksburg, Virginia 24061, United States S Supporting Information *
ABSTRACT: Chitin is the second most abundant biopolymer and insight into its natural synthesis, enzymatic degradation, and chemical interactions with other biopolymers is important for bioengineering with this renewable resource. This work is the first report of smooth, homogeneous, ultrathin chitin films, opening the door to surface studies of binding interactions, adsorption kinetics, and enzymatic degradation. The chitin films were formed by spincoating trimethylsilyl chitin onto gold or silica substrates, followed by regeneration to a chitin film. Infrared and X-ray photoelectron spectroscopy, X-ray diffraction, ellipsometry, and atomic force microscopy were used to confirm the formation of smooth, homogeneous, and amorphous chitin thin films. Quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange experiments showed these films swelled with 49% water by mass. The utility of these chitin films as biosensors was evident from QCM-D and surface plasmon resonance studies that revealed the adsorption of a bovine serum albumin monolayer.
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INTRODUCTION The scientific community has increasingly focused on biomaterials as candidates for renewable energy and functional materials. Cellulose and chitin are two such candidates and together represent the most abundant materials in nature.1,2 These two biopolymers are chemically similar, crystalline, and both form natural hierarchal composites. However, the strength conferred by these crystalline polymers hinders their processability for use in novel materials as well as their degradation into accessible energy. Consequently, fundamental knowledge of their natural synthesis, enzymatic degradation, and chemical interactions with other polysaccharides and proteins is important for facilitating bioengineering of a renewable and readily available resource.3,4 Chitin has shown promise in several areas due to its biocompatibility, biodegradability, antimicrobial properties, and high tensile strength. As such, chitin has found applications within the biomedical, food, cosmetic, and textile industries.5 Chitin is found naturally in arthropods and is composed of β-1,4-linked N-acetylglucosamine units (Figure 1).6 As with
water-soluble chitosan, which, due to its enhanced solubility over chitin, has been more widely studied.7 However, the direct study of chitin is important in gaining insight into enzyme degradation pathways, interactions with natural composite materials (e.g., proteins and polysaccharides), and mechanisms behind biocompatibility and biofunctionality.4,8 One significant advantage of cellulose research over that of chitin is the ability to form ultrathin (95% acetylated) was converted to trimethylsilyl chitin (TMSChi).20 Bovine serum albumin (BSA, lyophilized powder) was purchased from Sigma-Aldrich and used as received. Ultrapure water (Milli-Q Gradient A-10, Milli-Q, 18.2 MΩ·cm,
