Aluminium coated polysilicon (Al-polySi) nanoresonator has been used to design a urea biosensor. The etching characteristic of Al by the ammonium hydroxide from urea hydrolysis in the presence of urease was used to estimate the urea concentration. Urease immobilized on Al coated polySi indicated smoothening of the surface with increasing urea concentration, confirming the etching of Al. The nanoresonator could estimate between 10-1000 nM concentrations of urea. The sensing was not affected in the presence of interferents such as uric acid and ascorbic acid, thus making it specific for urea. The sensor was found to be highly sensitive and specific and can have potential application in the field of medical diagnostics and environmental monitoring. © 2019 IEEE.