3D printable self-propelling sensors for the assessment of water quality via surface tension

Hypothesis: Water contamination is a serious global challenge and an on-site and out-of-lab method of assessment of contamination level is highly needed. In this study, we report the potential of using printable and biodegradable propelling sensors as indicators of water contamination in sewage wastewater. Experiments: We used reactive 3D inkjet printing technology to fabricate self-propelling sensors which can quickly indicate the lowering of surface tension value caused by sewage contamination, and other surface tension lowering pollutants. The Z-shaped sensors were fabricated, with the dimensions of 2.0 ​mm at the longest side and 0.1 ​mm in thickness, from regenerated silk fibroin which is an environmentally friendly and biodegradable material. Inkjet printing has the advantage of high resolution and precise deposition of materials allowing the fabrication of small millimetre-sized sensors doped with a surface tension modifying polymer which acts as the ‘fuel’ to drive the sensors on the water surface via surface tension gradient. Findings: Our results showed that the sensor's propulsion velocity decay rate is an excellent metric to indicate the presence and approximate level of sewage contamination.