An optical analysis apparatus, including: a sample delivery system from which a liquid sample may be delivered in operation; a flow cell defining a channel through which, in operation, the delivered liquid sample may flow at a controllable rate, the channel including an optical analysis region; an illumination source focused on a portion of the optical analysis region that, in operation, illuminates a single particle at a time in a stream of the sample wider than the single particle; a detector that, in operation, detects light resulting from the illumination of the sample and outputting a signal representative of the detected light; and an analysis system receiving the representative signal.