Silica nanoparticles coencapsulating gadolinium oxide and horseradish peroxidase for imaging and therapeutic applications

Abstract

Mesoporous silica nanoparticles coencapsulating gadolinium oxide and horseradish peroxidase (HRP) have been synthesized in the aqueous core of sodium bis-(2-ethylhexyl) sulfosuccinate (AOT)–hexane–water reverse micelle. The average diameter of these silica particles is around 25 nm and the particles are spherical and highly monodispersed as depicted using transmission electron microscopy. The entrapment efficiency of HRP was found to be as high as 95%. Practically, the entrapped enzyme shows zero leachability up to 90 days. The enzyme entrapped in these silica nanoparticles follows Michaelis–Menten kinetics. Peroxidase entrapped in silica nanoparticles shows higher stability towards temperature and pH change as compared to free enzymes. The gadolinium oxide-doped silica nanoparticles are paramagnetic as observed from the nuclear magnetic resonance line-broadening effect on the proton spectrum of the surrounding water molecule. The entrapped enzyme, HRP, has been used to convert a benign prodrug, indole-3-acetic acid (IAA), to a toxic oxidized product and its toxic effect has been tested on cancerous cell lines through thiazolyl blue tetrazolium blue (MTT) assay. In vitro studies on different cancerous cell lines show that the enzyme has been entrapped and retains its activity inside the silica nanoparticles. IAA alone has no cytotoxic effect and it becomes active only after oxidative decarboxylation by HRP.

Keywords:

• indole-3-acetic acid
• HRP
• free radical
• cytotoxicity
• MRI

Acknowledgments

NG and RKS are grateful for financial assistance from the University Grants Commission, Government of India, and the University of Delhi. NG is grateful for the award of a Senior Research Fellowship by the Council of Scientific and Industrial Research (CSIR, Delhi). AS is grateful for a DU-DST Purse grant from the University of Delhi and DST. The authors are grateful for the valuable comments and fruitful discussion with Prof Amarnath Maitra and Dr Indrajit Roy, Department of Chemistry, University of Delhi.

Disclosure

The authors report no conflicts of interest in this work.