Highly loaded COOH functionalized silica particles

• Highly loaded silica particles bearing carboxylic acid groups have been prepared.
• The overall strategy was to make the particles using different kinds of protected acids and to deprotect them after particle fabrication.
• The loading of the acid groups on the various particles has been determined and their ability to immobilize a biomolecule has been demonstrated.

Highly functionalized monodisperse silica particles are attractive as unique additives and fillers and as carriers for biomolecule immobilization. Uniform micron and nanometer scale silica particles are well known and coating methods have been developed for their surface modification. However, such coatings provide only limited loading capacity. Hybrid silica particles whose physical and chemical properties are controlled by a very high loading of non-hydrolyzable pendant group have been developed based on different functionalized silanes. The more polar and/or reactive the pendant functionality, the more difficult it is to achieve uniform, stable, particle formation. Nevertheless, making hybrid particles with masked carboxylic acids is a worthwhile goal since they should enable the production of highly acid-functionalized particles.Various kinds of protected carboxylic acids have been considered and their respective advantages and disadvantages have been established. These included esters and thioesters wherein deprotection is by hydrolysis, and terminal olefins wherein the acid group is created by ozonolysis.Systems were identified wherein particle synthesis and subsequent installation of carboxylic acids could be achieved in high yield and with excellent control over particle size and uniformity. The loading of acid groups in these particles has been established and the ability to use these acid groups for anchoring active biomolecules has been demonstrated.

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