Improvement in the Reproducibility of a Paper-based Analytical Device (PAD) Using Stable Covalent Binding between Proteins and Cellulose Paper.

Paper-based analytical devices (PADs) have been widely used in many fields because they are affordable and portable. For reproducible quantitative analysis, it is crucial to strongly immobilize proteins on PADs. Conventional techniques for immobilizing proteins on PADs are based on physical adsorption, but proteins can be easily removed by weak physical forces. Therefore, it is difficult to ensure the reproducibility of the analytical results of PADs using physical adsorption. To overcome this limitation, in this study, we showed a method of covalent binding of proteins to cellulose paper. This method consists of three steps, which include periodate oxidation of paper, the formation of a Schiff base, and reductive amination. We identified aldehyde and imine groups formed on paper using FT-IR analysis. This covalent bonding approach enhanced the binding force and binding capacity of proteins. We confirmed the activity of an immobilized antibody through a sandwich immunoassay. We expect that this immobilization method will contribute to the commercialization of PADs with high reproducibility and sensitivity.

Synthesis of silica nanoparticles using biomimetic mineralization with polyallylamine hydrochloride.

To synthesize silica particles under mild conditions, we proposed a biomimetic synthesis method. The synthesis process was carried out based on a biphasic sol-gel synthesis method using TEOS (tetraethyl orthosilicate) as a silica source and PAH (polyallylamine) as a substitute for proteins of marine microorganisms for biosilicification. The function and activity of the PAH, used as a replacement for bioactive substances, were confirmed through comparisons between control experiments and designed experiments. The PAH exhibited the ability accelerate condensation with hydrolyzed TEOS in aqueous solutions. The PAH also exhibited high condensation activity in acidic and neutral conditions to produce silica particles. Moreover, PAH also created the nuclei of the silica particles, and the number of nuclei could be controlled by the concentration of PAH. In addition to exhibiting these unique capabilities, PAH did not generate any complexes or composites with the silica species. Depending on the synthesis conditions, the synthesized silica particles exhibited various shapes, such as sponge-like, self-assembled, irregular spherical and completely spherical shapes. The sizes of the primary particles were diverse, with a range from 10nm to 50nm. In particular, by adjusting the PAH concentration, it was possible to obtain nearly perfect spherical-shaped silica nanoparticles with uniform sizes, which has rarely been reported. Above all, using this paper, we can get closer to understanding the principles of silica formation using PAH as a replacement for the bioactive proteins of microorganisms.