Abstract
A method that can rapidly quantify variations in the morphology of single red blood cells (RBCs) using light and sound is presented. When irradiated with a laser pulse, an RBC absorbs the optical energy and emits an ultrasonic pressure wave called a photoacoustic wave. The power spectrum of the resulting photoacoustic wave contains distinctive features that can be used to identify the RBC size and morphology. When particles 5-10 μm in diameter (such as RBCs) are probed with high-frequency photoacoustics, unique periodically varying minima and maxima occur throughout the photoacoustic signal power spectrum at frequencies >100 MHz. The location and distance between spectral minima scale with the size and morphology of the RBC; these shifts can be used to quantify small changes in the morphology of RBCs. Morphological deviations from the normal biconcave RBC shape are commonly associated with disease or infection. Using a single wide-bandwidth transducer sensitive to frequencies between 100 and 500 MHz, we were able to differentiate healthy RBCs from irregularly shaped RBCs (such as echinocytes, spherocytes, and swollen RBCs) with high confidence using a sample size of just 21 RBCs. As each measurement takes only seconds, these methods could eventually be translated to an automated device for rapid characterization of RBC morphology and deployed in a clinical setting to help diagnose RBC pathology.