Role of decoration method of gold nanoparticles on the thermal and optical properties of mesoporous silica-Rhodamine 6G hybrids

Nanotechnology offers the potential for creating new optical imaging agents with novel properties which has been used in molecular imaging and photothermal therapy. Mesoporous silica materials have attained great attention in industry due to its high thermal and chemical stability and non toxic behavior. The performance of mesoporous silica materials depends on composition, morphology and structure of made-up materials. The synthesis of mesoporous silica nanoparticles is highly sensitive because the size, morphology and pore structure changes with small change in procedure. Surface modification of mesoporous enables to incorporate metal nanoparticles in to its pores by co-condensation and post-synthesis method and hence an enhancement in optical and thermal properties of mesoporous silica nanoparticles. In the present work, we have synthesized gold nanoparticles incorporated mesoporous silica by three methods such as non functionalized, co-condensation and post-synthesis modification which is denoted as sample I, sample II and sample III. Thermal parameters such as thermal diffusivity and effusivity of the synthesized samples are measured by thermal lens and photoacoustic techniques respectively. From the values of thermal diffusivity and effusivity, thermal conductivity is estimated and a high value of thermal conductivity is obtained for sample II because of the proper encapsulation of gold nanoparticles in mesoporous silica. The influence of Rhodamine 6G concentrations on the thermal parameters of mesoporous silica is also studied which shows that thermal conductivity decreases with the addition of higher concentration of Rhodamine 6G due to the interface thermal resistance effects. In addition, we have investigated the influence of gold nanoparticle incorporated mesoporous silica on the emission properties of Rhodamine 6G and fluorescein dyes. Irrespective of dye concentration, due to plasmonic field effect and non aggregation of dye molecules, the fluorescence signal is enhanced for both dyes with the addition of gold incorporated mesoporous silica.