A system for sampling and separating submicron-sized particles to detect the presence of an agent such as viruses in an environmental sample, which includes collecting means for collecting a sample suspected of containing submicron-sized particles from the environment, size separation means receiving the submicron-sized particles from the collecting means for separating the submicron-sized particles based on size into at least one size range, and a microscale particle counter adapted for counting the size separated submicron-sized particles received from the size separation means. The particle counter includes at least one cantilever each corresponding to submicron-sized particles of a particular size range, wherein the cantilever is deflectable from a first to a second position to permit passage of the submicron-sized particle therethrough, and wherein the corresponding deflection of the cantilever generates a count signal.