Characterizing cellular morphology by photoacoustic spectrum analysis with an ultra-broadband optical ultrasonic detector.

Photoacoustic spectrum analysis (PASA) has been demonstrated as a new method for quantitative tissue imaging and characterization. The ability of PASA in evaluating micro-size tissue features was limited by the bandwidth of detectors for photoacoustic (PA) signal acquisition. We improve upon such a limit, and report on developments of PASA facilitated by an optical ultrasonic detector based on micro-ring resonator. The detector's broad and flat frequency response significantly improves the performance of PASA and extents its characterization capability from the tissue level to cellular level. The performance of the system in characterizing cellular level (a few microns) stochastic objects was first shown via a study on size-controlled optically absorbing phantoms. As a further demonstration of PASA's potential clinical application, it was employed to characterize the morphological changes of red blood cells (RBCs) from a biconcave shape to a spherical shape as a result of aging. This work demonstrates that PASA equipped with the micro-ring ultrasonic detectors is an effective technique in characterizing cellular-level micro-features of biological samples.