  Diamagnetic levitation offers stable confinement of an object from its
environment at zero power, and thus is a promising technique for developing
next generation unclamped resonant sensors. In this work, we realize a resonant
weighing scale using a graphite plate that is diamagnetically levitating over a
checkerboard arrangement of permanent magnets. We characterize the bending
vibrations of the levitating object using laser Doppler vibrometry and use
microgram glass beads to calibrate the responsivity of the sensor's resonance
frequency to mass changes. The sensor is used for real-time measurement of the
evaporation rate of nano-litre droplets with high-accuracy. By analyzing the
resonator's frequency stability, we show that the millimeter graphite sensor
can reach mass resolutions down to 4.0ng, relevant to biological and chemical
sensing concepts.
