A fractionated photoacoustic flow cytometry (PAFC) system and methods for the in vivo detection of target objects in biofluidic systems (e.g., blood, lymph, urine, or cerebrospinal fluid) of a living organism is described. The fractionated system includes a fractionated laser system, a fractionated optical system, a fractionated acoustic system, and combinations thereof. The fractionated laser system includes at least one laser or laser array for pulsing a target object within the circulatory vessel with fractionated focused laser beams. The fractionated optical system separates one or several laser beams into multiple beams in a spatial configuration on the skin above the circulatory vessel of the living organism. The fractionated acoustic system includes multiple focused ultrasound transducers for receiving photoacoustic signals emitted by the target object in response to the fractionated laser beams. The target objects have intrinsic photoacoustic contrast or may be labeled with photoswitchable or spaser-based probes. Fractioned beams may be used also for diagnostics with other spectroscopic methods (e.g., fluorescence, Raman or scattering) and energy sources both coherent and conventional such as lamp and LED in the broad spectral range from 10 Å to 1 cm (e.g., X-ray, UV, visible, NIR or microwaves) in continuous wave and pulse modes.
