Fig. 1. (a) Schematic of fabrication procedure of Ag nanospheres arrays formed grid, (b) The photograph of patterned Ag arrays based platform under bending and its partial enlargement in the plane, 10× microscopic images of the grid patterns (c) before and (d) after chemical reduction, (e) 30× and (f) 50× microscopic images of Ag NSs grid.

Fig. 2. The atomic force microscopy (AFM) image of (a) bare PI and (b) PI adhering Ag NSs, the corresponding scanning electron microscopy (SEM) image of (c) bare PI (inset: photograph of transparent PI film), (d-f) PI adhering Ag NSs with different size in the grid (inset: the histogram of the diameter distribution).

Fig. 3. Calculated electric field distribution for the (a-c) Ag NSs with varying size (15, 25, and 40 nm) on PI substrates, corresponding covered with (d-f) 5 nm and (g-i)10 nm PEI spacer using FDTD method.

Fig. 4. (a) The measured SPR band of PI adhered with increasing Ag NSs size, along with the absorption and photoluminescence spectra of dye excited with 460 nm light. (b) Fluorescence intensities of FITC on the PI with varying size of Ag NSs substrate (red dots), and their calculated enhanced value of electric field (blue dots). (c) The energy diagrams of the dye FITC on PI-Ag platforms with PEI spacer, where S0 and S1 are the ground and excited states of FITC, while EF and Ev are the Fermi and vacuum energy levels, respectively. (d) The structure of MEF utilized to explore the effects of PEI spacer thickness. (e) The emission intensity variation of dye on PI-Ag (25 nm) platform with different PEI spacer thickness and bare PI by comparison. (f) Fluorescence enhancement factors as a function of the PEI spacer thickness on PI-Ag NSs platform with different sizes, all the excitation wavelength was 460 nm.

Fig. 5. (a) Fluorescence lifetimes of FITC on the bare PI substrate (2.59 ns), PI-Ag (25 nm) substrate with PEI spacer thickness of 5 nm (2.43 ns) and 10 nm (2.10 ns), and PI-Ag (40 nm) substrate with 10 nm PEI (1.55 ns) are compared. (b) Durability test as comparative PL intensities after mechanical bending in half of the flexible MEF platform for 1000 cycles. (c) Optical image of the PI-Ag (25 nm) platform with 10 nm PEI spacer. (d) Corresponding fluorescence map of the immobilized FITC.