Rahul P. Bagwe

Bioconjugated Luminescent Nanoparticles for Biological Applications

Abstract Inorganic nanostructures that interface with biological systems have recently attracted widespread interest in biology and medicine. Nanoparticles are thought to have potential as novel luminescent probes for both diagnostic (e.g., imaging) and therapeutic (e.g., drug delivery) purposes because of their size comparable to biomolecules and their novel optical, electronic, and magnetic properties. Critical issues for successful nanoparticle delivery include the ability to target specific tissues and cell types and escape from the biological particulate filter known as reticuloendothelial system. Three distinct types of luminescent nanoparticles have been identified which show promise in bioanalysis, namely dye‐doped nanoparticles, semiconductor and metal nanoparticles. In this article we examine the recent advances in the development of dye‐doped nanoparticles, metal and semiconductor nanoparticles, bioconjugation schemes to attach these nanoparticles to biomolecules and a few biological applications.

The Effect of Interfacial Viscosity on the Kinetics of Formation of Silver Nanoparticles Using Water-in-Oil Microemulsions as Nanoreactors

Silver nanoparticles were prepared by the method of mixing of two microemulsions having similar chemical composition but different reactants in their respective aqueous core. One microemulsion contains silver nitrate in the aqueous core and other contains sodium borohydride. The silver nanoparticles formed were characterized using UV-Visible absorption spectra and TEM micrographs. Effect of chain length of solvent and addition of Arlacel-20 to the AOT/Heptane, AOT/Decane and AOT/Dodecane microemulsion on particle size and absorption spectra of silver nanoparticles was studied. TEM photographs showed agglomerated and bigger particles in case of pure AOT/dodecane whereas addition of Arlacel-20 showed dispersed and smaller particles. Reaction kinetics was observed for silver nanoparticles using UV-visible spectrophotometer. Silver nanoparticles prepared using pure AOT surfactant showed plasmon band (416 nm) immediately after preparation whereas no absorption band of silver nanoparticles was observed for mixed surfactant microemulsion of AOT and Arlacel 20 for few hours indicating the reaction kinetics is slowed down upon addition of Arlacel-20. Growth rate of silver nanoparticles was plotted by monitoring absorption coefficient ratio (e 416 /e 475 ) as a function of time. AOT/heptane system showed slower growth rate as compared to AOT/decane and AOT/dodecane and also larger particle size. Presence of Arlacel-20 significantly decreases the growth rate in all three alkanes and this observation can be explained using the concept of rigidity of surfactant film at the oil/water interface. It is proposed that higher the interfacial viscosity, slower is the coalescence rate of nanodroplets in the microemulsion system, and hence slower the growth rate of particles and smaller is the final particle size.