A method is provided for detecting, measuring or controlling particles and/or electromagnetic radiation, comprising providing a deformable material containing a deformable aperture defining a path for particles or radiation, adjusting the deformable aperture to a prescribed geometry and/or size by deforming the deformable material to change at least one of the parameters of the path defined by the deformable aperture, and causing the particle or radiation to be detected, measured or controlled to enter the deformable aperture. The method includes the step of monitoring the geometry and/or size of the deformable aperture and controlling the adjustment of the size of the deformable aperture in response to such monitoring. The required apparatus is easily fabricated from inexpensive materials. Furthermore the deformable aperture can be tuned to the appropriate geometry post fabrication, and the ability to adjust the aperture geometry renders it capable of discriminating a plurality of differently sized particles.