This is a copy of the slides presented at the meeting but not formally written up for the volume.

We present a novel approach which implements metallic nanoparticles for the development of a non-invasive opto-acoustic microscopy study of cells and bio-materials for the first time. The acoustic modes of metallic nanospheres dispersed inside a bio-matrix can be excited by a pump laser beam, resulting in acoustic oscillations with frequencies on the order of GHz. The acoustic oscillations can in turn be detected using transducers. We propose a new form of acoustic microscopy using such high frequency pulses in bio-materials. This is based on a recent demonstration by Ramanathan and Cahill of imaging with picosecond ultrasonic pulses generated by nanoscale metal thin films (J. Mater. Res. Rapid Comm. 21, 1204, 2006) We develop our concept with the goal of understanding the relationship between a cell’s structural and functional properties, the efficiency of drug treatments, the evolution of disease states, and detecting the existence of disease in a cell. For example, the elasticity of red blood cells infected with malaria undergoes significant change as the disease progresses (Suresh, J. Mater. Res. 21, 1871, 2006). The intimate connection between the progression of malaria in the red blood cell and the varying mechanical properties of the cell can be probed on a finer level using high resolution acoustic biomicroscopy. GHz range acoustic biomicroscopy would extend nondestructive imaging of cellular structure to the nanometer scale for the first time and open new directions for biological imaging research. The oscillations of the metallic particles can be understood within the context of Lamb’s theory of mechanical oscillations of elastic spheres. We use Lamb’s results and basic continuum mechanics to derive relationships between the laser energy deposited in the metallic particle and the amplitude of the resulting acoustic pulses. We model the pulses using Gaussian frequency spectra to understand the attenuation while propagating through a biological medium. The predictions for the pulse attenuation and amplitude are coupled to produce a preliminary theoretical understanding of the proposed opto-acoustic system. Our results show that bio-imaging using metallic nanoparticles are both feasible and promising. For distances on the scale of 10 microns, the length of a typical human red blood cell, the metallic nanoparticles can generate acoustic pulses with frequencies ranging up to 30 GHz. Such high frequency acoustic waves can in turn lead to imaging cellular phenomena at extremely high resolution. We anticipate that our approach will open innovative nanoscale techniques for non-invasive cellular research.