Controllable Photoreduction of Graphene Oxide/Gold Composite Using a Shaped Femtosecond Laser for Multifunctional Sensors.

The mixture of graphene oxide and noble metal nanoparticles has been widely used in flexible multifunctional sensors. Femtosecond lasers are regarded as useful tools for sensor fabrication through direct inscribing. Normally, the laser power is adjusted to optimize the sensing performances. However, the process between the laser and the sample can be effectively altered by the temporal distribution of the pulse and the laser wavelength. This paper proposes a controllable photoreduction of graphene oxide/gold composite method using a shaped femtosecond laser and promotes its application on multifunctional sensors. Different from the strong reliance of the photoreduction process on laser fluence, femtosecond laser shaping expands the controllability range of the photoreduction degree. By combining the parameters of fluence, temporal distribution, laser wavelength, humidity, and strain multifunctional sensors can be both optimized by controlling the laser reduction. The strain sensor exhibits good linearity with a gauge factor of 67.2 in a strain range of 28.2%; the sensitivity of the humidity sensor is improved by 68.4%. The humidity sensor maintains its performance after 28 days, and the strain sensor maintains its stability after 5000 cycles of stretching. The multifunctional sensor can be applied to detect human breath and human pulse and holds value for human health monitoring.