  Fluidic iontronics offer a unique capability for emulating the chemical
processes found in neurons. We extract multiple distinct chemically regulated
synaptic features from a single conical microfluidic channel carrying
functionalized surface groups, using finite-element calculations of continuum
transport equations. Such channels have long been employed for fluidic sensing
and are therefore experimentally well established. By modeling a Langmuir-type
surface reaction on the channel wall we couple fast voltage-induced volumetric
salt accumulation with a long-term channel surface charge modulation by means
of fast charging and slow discharging. These nonlinear charging dynamics are
understood through an analytic approximation rooted in first-principles. We
show how short-and long-term potentiation and depression, frequency-dependent
plasticity, and chemical-electrical signal coincidence detection (acting like a
chemical-electrical AND logic gate), akin to the NMDA mechanism for Hebbian
learning in biological synapses, can all be emulated with a single channel.
