We
observe variations in the electrical resistance across a conducting
water microdroplet when it was placed on a glass substrate before
being mechanically vibrated at natural frequency with the help of
an acoustic source. The reduction in the resistance across the droplet
was magnified owing to the formation of vortices in the matrix when
the periodic oscillation of the surface was increased. The variation
in the resistance could be tuned with the frequency of the sound source,
which was found to be maximum when a 10 μL droplet was vibrated
at ∼320 Hz. Interestingly, the variation in resistance across
the oscillating droplet could follow and distinguish the musical notes
in the octaves (“sur”) or rhythmic cycles (“taal”)
originating from musical instruments such as flute, harmonium, whistle,
and tabla. Further, when a suspension of urease-stabilized gold–cadmium–sulfide
nanocomposite was suspended inside the droplet and mixed with an analyte
containing urea solution, the change in the resistance during the
operational time period was found to monotonically vary with the concentration
of urea in the analyte. The enzymatic reaction between urea and urease
was found to follow a faster first-order chemical kinetics than the
commonly observed Michaelis–Menten pathway owing to the presence
of the moving nanocomposites and mixing vortices under the optimal
acoustic excitations. The specific lock-and-key enzymatic reaction
helped in extending these experimental results to estimate the unknown
levels of urea in human blood serum samples.