Humanoid robots, especially those equipped with artificial intelligence algorithms, can be used not only for personal assistance and care in daily life, but also for search and rescue in dangerous tasks. The sensing system plays an indispensable role in improving the service quality and extending service life of these robots.  

Among them, the pain sensor has drawn great attention, since it can detect harmful stimulus, generate early warning signals (i.e., action potentials) and transmit them to the central nervous system, thus triggering protective reflex and minimizing potential physical injuries. 

In a study published in Nanoscale, the researchers have demonstrated a visible light-triggered artificial photonic nociceptor with a simple ITO/CeO_2-x/Pt sandwich structure, which can reproduce the pain-perceptual characteristics of the human visual system accurately. This work has applied for national invention patent (No. 202010498960.0). 

Moreover, in a study published in Advanced Science, inspired by the pain-perception system of human, they developed a multi-mode pain-perception system (MMPPS) which can provide effective protection for electronic skin (e-skin).  

By adopting the unique electrical characteristics of the liquid metal particle film when "injured" (mechanical scribing), the researchers designed a “nociceptor” that can realize "wound" perception and positioning.

Based on the central sensitization mechanism, the MMPPS can switch between different working modes and thus offer smarter protection mechanism to e-skin. Accordingly, before injury MMPPS can offer warning of excessive pressure with normal pressure threshold. After injury, extra care on the periphery of damage will be activated by decreasing the pressure threshold. Furthermore, the MMPPS will gradually recover back to normal state as damage heals. 

The proposed system can open up a new avenue for the development of intelligent sensing systems and prosthetics, and promote human-robot interaction.