Hollow mesoporous silica nanoparticles for intracellular delivery of fluorescent dye

For many years, silica has been employed as a versatile and relatively benign material in material sciences and engineering due to the variety of available chemical and physical modifications that it offers as well as the biocompatibility feature that it display. It is thus not surprising that silica nanoparticles have recently emerged as an attractive and widely used chemical/drug delivery vehicle for basic research and clinical trials. In fact, amongst these carriers made of silica, hollow spherical silica nanoparticles with mesoporous walls stands out as a class of nanomaterials with many distinctive advantages, such as having a non-toxic nature, good surface permeability, large specific surface area, tunable pore structures, excellent physicochemical stability and chemically modifiable surfaces, all of which allow them to be potential hosts for various chemical agents/therapeutic drugs. These hollow mesoporous silica nanoparticles (HMSNs) are especially useful when used to host therapeutic compounds such as enzymes that are easily degraded in the hostile biological environment when delivered per se without encapsulation. Besides encapsulation, these therapeutic agents can also be covalently attached, or adsorbed onto such silica nanocarriers that has been pre-surface modified. Indeed, these approaches can easily overcome drug solubility and stability issues, besides having control over the rate in which the drugs are released. Thus, wide attention has been placed on the recent application of HMSNs in the field of biomedicine, including its use as novel materials in catalysis, separation, cell-labeling and capsule agent for drug delivery [1,2].To date, a number of approaches have been employed to fabricate oxide and sulfide hollow spheres [3,4]. Deposition of silica layer on latex or colloid templates and subsequent removal of the hard templates by calcination or corrosion has been known to be the conventional approach for preparation of HMSNs [5-7]. Sol-gel/emul