Self-assembled histidine acid phosphatase (HAP) nanocapsules in ionic liquid [BMIM][BF4] as functional template for hollow silica nanoparticles

Most of the self assembly studies have hitherto explored the aqueous media as fluid phase for self assembly of organic species. Ionic liquids (ILs) have recently become attractive reaction media for the 'green' synthesis of nanomaterials due to their unique physico-chemical properties such as high viscosity, high ionic conductivity, high thermal and chemical stability, and negligible volatility. No attempt has however been made to capitalize on the potential of ILs for self assembly of biomolecules, leading to biomolecular template directed synthesis of functional nanoscale materials. We report for the first time, dynamic molecular self assembly of fungal Histidine Acid Phosphatase (HAP) enzyme, in the hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), leading to formation of hollow silica nanoparticles. It is interesting to note that the same protein results in the formation of solid silica particles in the hydrophobic IL 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF6]. The HAP nanocapsules obtained via controlled self assembly in [BMIM][BF4] were utilized as functional templates for the spontaneous growth of silica hollow nanoparticles of 50-100 nm, which showed promise in enzyme encapsulation/immobilisation. Our recent efforts therefore suggest that ionic liquids (ILs) can act as designer solvent systems utilizing microbial enzymes (economical biocatalysts) for the size- and shape- controlled self assembly of nanomaterials with interesting properties. The present work can provide an exciting expansion of theoretical understanding on nano-bio interfacial molecular self assembly and will facilitate providing insights on polypeptide/protein ¿ nanomaterials hybrid composites materials with multifunctional properties.