Fabrication and characterization of mono-layered polystyrene beads using nanosphere lithography (NSL) for metal-enhanced fluorescence (MEF)

Fluorescence spectroscopy is a powerful and widely used technique, which finds extensive applications in biochemistry and molecular biology. In many cases, detection of fluorescence from biological samples at low concentration demands for a sensitive technique that can enhance the weak fluorescence signal. In order to realize this, metal enhanced fluorescence technique is employed where an increase in fluorescence is observed when the fluorophore is in close proximity to a metallic surface. In order to achieve this, nano-roughened silver surfaces such as fractal structures or silver colloid-coated surfaces can be employed. However, preparation of such surfaces not only involves lengthy chemical procedures but also result in poor reproducibility. To overcome these limitations, nanosphere lithography (NSL) is proposed, which is an inexpensive, simple to implement and high throughput nanofabrication technique. In this technique, polystyrene (PS) nano-beads are used to form a 2D monolayer of nanoparticle array followed by deposition of silver to form a roughened metallic surface. The surface roughness of the silver coating is determined by the close packing and arrangement of the nanobeads. In this work, substrates are fabricated using different sizes of PS beads to result in different nanometric surface roughening for silver layer and its optimization to achieve better fluorescence enhancement is carried out.