Our body has a rich microbiota – an ecological community of commensal, symbiotic and pathogenic microorganisms. They include bacteria, archaea, protists, fungi and viruses. The symbiotic peaceful coexistence of these microbiota keeps us hail and healthy. These microorganisms are much smaller than human cells. However, they vary in their size and shape: long, disc, round, cylindrical etc. They are very small ranging from few microns to tens of nanometers in length.  Despite so tiny, they define our health condition. They are present in our bodily fluids, like urine and saliva. If we can monitor our body fluids for these microorganisms we could potentially diagnose various diseases. The question we ask is, can we rapidly measure mass of each of these microorganism in our body fluids for fast diagnosis. The challenge is, how to measure mass of such tiny microorganisms inside liquid. To overcome this challenge, we developed a tiny picolitre (10^-12 L) volume microfluidic channel device.  By continuously monitoring the resonance frequency of this vibrating microfluidic channel we measure the mass of single bacterium. The resonance frequency shifts as soon as the bacterium enters the vibrating channel. By making very small microfluidic channels, we are able to measure mass of these tiny microorganisms. The channels are about 200 microns long, 10 microns wide, 1 micron high and a wall thickness of 1 micron. Our devices have a mass resolution of 30 attograms (10^-18 g), equal to about 4 orders smaller than the mass of an E-coli bacterium. Basically, we use microfluidic tools to do physical characterisation (e.g. mass) of micro and nanoscale objects suspended in liquid.