Approaches for determining the delivery success of a particle, such as a drug particle, are disclosed. A system for monitoring delivery of particles to biological tissue includes a volume, an optical component, a detector, and an analyzer. The volume comprises a space through which a particle can pass in a desired direction. The optical component is configured to provide a measurement light. The detector is positioned to detect light emanating from the particle in response to the measurement light. The detected light is modulated as the particle moves along a detection axis. The detector is configured to generate a time-varying signal in response to the detected light. The analyzer is configured to receive the time-varying signal and determine a delivery success of the particle into a biological tissue based upon characteristics of the time-varying signal.