Underwater flexible sensors have a future for wide application,
which is promising for attaching them to underwater creatures to monitor
vital signals and biomechanical analysis of their motion and perceive
tiny environmental disturbances. However, the pressure waves induced
by biological swimming are extremely weak and susceptible to undercurrents,
making them difficult to sense. Here, we report an ultrahighly sensitive
biomimetic electronic fish skin designed by embedding an artificial
pseudocapacitive-based hair cell into a simulated canal neuromast
encapsulation structure, in which the artificial hair cell, as the
key sensitive unit, is assembled from hybrid film electrodes and polyurethane–acidic
electrolyte foam. Such a film is prepared by inter-cross-linking MXene
and holey reduced graphene oxide with the assistance of l-cysteine, effectively increasing the interfacial capacitance and
alleviating the oxidation issues of MXene. Meanwhile, the acidic foam
with high porosity shows great compressibility to adapt to a high-pressure
underwater environment. Consequently, the device exhibits ultrahighly
sensitivity (maximum sensitivity ∼173688 kPa–1) over a wide range of depths (0–100 m) and remains stable
after 10000 repeated tests. As an example case, the device is integrated
as a motion monitoring system to identify the minor disturbances triggered
by instantaneous postural changes of fish. The electronic fish skin
is expected to demonstrate enormous potentials in flow field monitoring,
ocean current detecting, and even seismic waves warning.