A system and method for the detection and quantification of biomolecules by measuring a piezoelectric signal is described. The system comprises a plurality of elongate zinc oxide nanowires mounted generally parallel to each another on a semi conductive silicon substrate. The free ends of the nanowires are provided with biomolecules that are capable of associating with complementary biomolecules within a biological or water sample. Following incubation of the system in a sample, the association of molecules of interest with the immobilised biomolecules on the system results in the displacement of the zinc oxide nanowires. The displacement of the nanowires produces a piezoelectric voltage signal that is useful in diagnosing a pathogenic infection or the contamination of a sample.