Experimentally evaluating plasmonic sensing performance of silver film over nanosphere surface (AgFON)

In the present work, Silver film over nanosphere surface (AgFON) structures were fabricated on a self-assembled monolayer (SAM) of polystyrene spheres (200 nm) by a simple and cost effective drop-casting followed by thermal evaporation techniques. The thickness of Ag thin film was varied from 20 nm to 100 nm in a step of 20 nm. Field emission scanning electron microscopy (FESEM) revealed that the morphology of AgFON changes from nano island to nanoshells with increasing thickness. Reflection spectra of AgFON of thickness >60 nm exhibited a sharp minimum due to the excitation of cavity mode plasmon. Plasmonic sensing capabilities of AgFON have been investigated with respect its thickness. AgFON of 100 nm exhibited a bulk sensitivity of 632.54 nm/RIU while 80 nm showed a sensitivity of 365 nm/RIU towards a thin layer of volatile organic compounds such as ethanol, toluene and isopropyl alcohol. Biological molecules such as urea, creatinine, glucose, melamine and glutathione have been tested with the AgFON. The AgFON displays a good capability of detecting 1 mM creatinine in an aqueous solution. A successful attempt has been made to detect the creatinine of >1 mM in human urine.