Paper-based sensing technology was combined with direct laser writing for designing and fabricating low-cost wearable multifunctional sensors.

Ultrahigh sensitive piezoresistive sensors at small deformation are highly desired in many applications. Here, we propose a hierarchical contact design concept and implement it through a direct laser writing technique for fabricating layered carbon piezoresistive sensors with ultrahigh sensitivity. Sensors with unprecedented gauge factors (∼5000-10 000) at small deformation (ε < 0.1%) were successfully fabricated and demonstrated for their use in sensing both static and high-frequency (20-30 kHz) dynamic mechanical loads. A simple basic structure unit (BSU) contact network model was developed for understanding the importance of the BSU/BSU contact strength and network fractal dimension in dictating the piezoresistive sensitivity of the layered carbon piezoresistive sensors with designed hierarchical contact structures. The hierarchical contact design concept and the contact network model proposed in our work could open a general route for developing ultrasensitive piezoresistive sensors based on granular matter and composite materials.

The carbonization process of the cheap and renewable biomass–sodium lignosulfonate (NaLS) as a green carbon sources by an in-situ environmentally friendly processing methoddirect laser writing carbonization (DLWc)was investigated. With various characterization methods the film formation conditions and laser processing parameters were investigated for their effect on physical and chemical structures, electrical, piezoresistive, and humidity response behaviors of the carbon patterns. Besides its intrinsic piezoresistivity, the resistance of the DLWc created carbon feature can also respond to moisture change. With these dual characteristics, the carbon patterns were successfully applied as piezoresistive and humidity sensors. A high gauge factor of 120 was achieved for the piezoresistive sensor made of a square-shaped carbon pattern. The work presented in this study indicates that the application of DLWc to carbonize NaLS can create green carbon patterns suitable for a variety of force and humidity related sensing applications.

The influence of temperature on the gold nanorod synthesis process and its effect on tailoring the size and aspect ratio have not been fully investigated and understood. A comprehensive study, involving SEM and TEM microscopy, Vis-NIR spectroscopy, quantitative data analysis and theoretical simulation, is performed to understand the effect of growth temperature on size, aspect ratio, and shape uniformity of gold nanorods that are synthesized by a recently developed binary-surfactant seed-mediated AuNR synthesis method. It has been demonstrated that the temperature can be used as a simple processing parameter to viably tailor the size and aspect ratio of AuNRs as well as the corresponding surface plasmon resonance behavior. The temperature coefficients for length, diameter, and aspect ratio have been, respectively, determined to be 3.5 nm/°C, 3.9 nm/°C, and -0.18/°C. With a combination of controlling temperature and formulation, the binary surfactant seed-mediated AuNR synthesis method expects to be a convenient way for producing gold nanorods with a large range of size and aspect ratio suitable for different applications.