Fig. 1: Fabrication and characterization of the thin-film sensor.

a Typical scanning transmission electron microscopy (STEM) images showing the UHCSs and the thickness of the shell. Scale bar: 250 nm. b Typical transmission electron microscopy (TEM) images showing the spine length and the tip diameter of the sphere. Scale bars: 200 and 60 nm. c Photo of the peeled-off thin film in a petri dish. Scale bar: 15 mm. d Light transmittance from 400 to 1500 nm. e Optical photography of the urchin-like hollow carbon sphere polydimethylsiloxane film (UHCS-PDMS) pressure sensor on a fingertip and three-dimensional scheme of the tiny sensor. Scale bars: 10 mm and 3 μm.