Chitin, a tough semitransparent substance that forms part of the protective outer casing cuticle of some insects and other arthropods, and the cell walls of some fungi, is quite abundant in nature. This material is a renewable resource having potential for many applications in bioengineering. For example, chitin can easily be processed into a number of derivatives, such as chitosan, which have shown promising applicability in a number of broad range areas including food science, medicine, agriculture and the biomedical field. Awkwardly, solubilizing chitin and recrystallizing it has for a while been the stumbling block inhibiting it full exploitation. Fortunately, a new analytical technique: surface plasmon resonance, has been observed to offer possible solution to this drawback. This technique has already been successfully employed to evaluate a chitin-coated surface in the past using ionic liquids as solvent. Unfortunately, no simple protocol for the preparation of thin chitin layers using dimethylacetamide (DMA) and lithium chloride (LiCl) as solvent on surface plasmon resonance gold sensors has been established yet.
To this note, a team of Finish researchers: Marco Casteleijn, Dominique Richardson, Petteri Parkkila, Arto Urtti, Tapani Viitala from the Drug Research Program, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki in collaboration with Niko Granqvist at BioNavis Ltd. (a company specialized in Multi-Parametric Surface Plasmon Resonance) proposed a study whose main objective was to demonstrate that the precipitation of chitin, derived from shrimp shell, using the common DMA/LiCl solvation method onto a gold surface for subsequent surface plasmon resonance analysis posed a challenge due to the surface properties of gold, but could be protected by an additional coating of polystyrene prior to chitin coating. Moreover, they purposed to comparatively assess the usefulness of a chitin surface preparation, either on gold or on polystyrene. Their work is currently published in the research journal, Colloids and Surfaces A.
The research method employed here commenced with the application of the most basic technique of dissolving chitin closely followed by a simple-spin coating procedure. Next, multi-parametric surface plasmon resonance, modeling of the optical properties of the chitin layers, scanning electron microscopy, and contact angle goniometry were then used to confirm: the thickness of the layers in air and buffer, the refractive indices of the chitin layers in air and buffer, the hydrophobicity, the binding properties of the chitin binding domain of chitinase A1 derived from Bacillus circulans, and the split-intein capture process.
The authors observed that the binding of the chitin binding domain differed between chitin on the gold versus chitin on polystyrene in terms of binding strength and binding specificity. The researchers attributed this to be as a result of a less homogenous structured chitin-surface on gold in comparison to chitin on polystyrene, despite a similar thickness of both chitin layers in air and after running buffer over the surfaces. Additionally, the researchers noted that the use of polystyrene on the gold sensor protected the gold layer from the solvent well enough for a homogeneous chitin layer to form during the spin-coating process.
Marco Casteleijn and colleagues study highlighted the differences between two different sensor chips and their implication for the study of chitin binding proteins and chitin binding domain as an immobilizing agent for the study of split-inteins. Altogether, the results presented in their work are expected to be stepping stones that will enable studies of chitin layer properties and interactions with biomolecules without the use of labels in real-time with high sensitivity.
Marco G. Casteleijn, Dominique Richardson, Petteri Parkkila, Niko Granqvist, Arto Urtti, Tapani Viitala. Spin coated chitin films for biosensors and its analysis are dependent on chitin-surface interactions. Colloids and Surfaces A, volume 539 (2018) page 261–272.Go To Colloids and Surfaces A