Tunable and highly accessible plasmonic gap nanostructures on flexible film as a high-performance surface-enhanced Raman scattering sensor

Tunable plasmonic gap nanostructures on flexible substrates have been considered as an evolutionary development in diverse fields. The size-controllable nano-gaps can process optical signals on the deep nanoscale to provide optimal and strong signal generation in a spatially controlled manner and flexible devices can realize rapid analysis, easy operation and cost-effectiveness. In addition, the creation of a number of exposed and vacant nano-gaps on flexible materials is essential for target molecules to diffuse into the nano-gaps. However, it remains challenging to synthesize a structure that satisfies these requirements. Herein, we present size-controllable, unoccupied, and exteriorly exposed nano-gaps on a flexible plasmonic sensor; control of the signal amplification ability is realized by changing the nano-gap distance. We prepared a graphene modified polyimide film and silver dendrites structures were electro-deposited. Then, secondary protruding gold nano-islands were deposited on silver dendrites via galvanic replacement. Controlling the morphology of gold nano-islands with different sizes and densities yielded different nano-gap lengths of 3–30 nm between the gold nano-islands in a controlled manner. It was achieved by manipulating the amount of injected gold precursor, reaction time, and solvent volume. Therefore, it was possible to control the degree of Raman signal enhancement with respect to the diminished nano-gap length. Benefiting from direct contact with the target area and the free diffusion of surrounding molecules to the void nano-gaps, this flexible plasmonic sensor was successfully used as a potent surface-enhanced Raman scattering sensor for monitoring the trace-amounts of a drug molecule on an arbitrary curved surface.