Towards wireless highly sensitive capacitive strain sensors based on gold colloidal nanoparticles.

We designed, produced and characterized new capacitive strain sensors based on colloidal gold nanoparticles. The active area of these sensors, made up of a 1 mm2 close-packed assembly of gold nanoparticles between interdigitated electrodes, was designed to achieve measurable capacitance (>∼1 pF) and overcome parasitic capacitances. Electro-mechanical experiments revealed that the sensitivity of such capacitive sensors increases in relation to the size of the nanoparticles. In the case of 14 nm gold NPs, such sensors present a relative capacitance variation of -5.2% for a strain of 1.5%, which is more than 5 times higher than that observed for conventional capacitive strain gauges. The existence of two domains (pure capacitive domain and mixed capacitive-resistance domain) as a function of the frequency measurement allows for the adaptation of sensitivity of these capacitive sensors. A simple low-cost circuit based on a microcontroller board was finally developed to detect the capacitance variations of such NP based strain sensors. This low-cost equipment paves the way for the development of an entirely wireless application set-up.