Tunable Nanowrinkles on Shape Memory Polymer Sheets

Abstract

Controllable biaxial and uniaxial nanowrinkles (see figure) are fabricated by a simple two‐step approach — metal deposition and subsequent heating — based on shape memory polymer (prestressed polystyrene) sheets. The wavelengths of the wrinkles can be tuned by controlling the thickness of deposited metal. The ready integration of the nanowrinkles into microchannels and their effectiveness in surface enhanced sensing is demonstrated.

Bimetallic nanopetals for thousand-fold fluorescence enhancements

“…9 These tunable wrinkles can be easily integrated into microchannels. [9][10][11][12] In applying them for fluorescence enhancement, though, the intensity of their hotspots were hampered by their smoothness and continuousness that cannot localize and concentrate electromagnetic field as well as sharp and discrete ones. 1 Here, we present sharp nanostructures, coined nanopetals, to overcome this limitation.…”

“…1 Lowering the fabrication threshold and developing microfluidic integratable metallic nanostructures would widen their applicability and accessibility for biomedical applications. 9 We recently presented a simple, ultra-rapid low-cost method to create large scale metallic nanowrinkles on polystyrene ͑PS͒ sheets. 9 These tunable wrinkles can be easily integrated into microchannels.…”

“…9 We recently presented a simple, ultra-rapid low-cost method to create large scale metallic nanowrinkles on polystyrene ͑PS͒ sheets. 9 These tunable wrinkles can be easily integrated into microchannels. [9][10][11][12] In applying them for fluorescence enhancement, though, the intensity of their hotspots were hampered by their smoothness and continuousness that cannot localize and concentrate electromagnetic field as well as sharp and discrete ones.…”

“…1͑a͒, a 80 nm thick Ag film followed by a 80 nm thick Au film is deposited on a prestressed PS sheet ͑KSF50-C; Grafix, 2 ϫ 1 cm 2 ͒ using a sputter coater ͑Po-laron coating system͒. 9 Subsequent heating at 160°C ͑above PS glass transition temperature͒ for 6 min induces retraction of the substrate and causes the nonshrinkable metallic films to wrinkle and crack. Cracking is critical to create these nanosawtooth structures on the edges of the petals, while buckling improves the formation of nanogaps.…”

“…To determine the dimension of these nanogaps, an edge detection program ͑the Canny method, MATLAB ® software͒ was applied to the SEM followed by two-dimensional fast Fourier transform ͑2D FFT͒. 9 Distribution of gap dimensions ͓Fig. 1͑d͔͒ is obtained by further transforming corresponding power spectral densities to real space.…”