Seeing Small Biological Structures with Light

We discuss two phase-sensitive optical methods, light scattering spectroscopy (LSS) and quantitative phase imaging (QPI), which can reveal structure and dynamics of living cells at the nanometer scale. The LSS technique is shown to characterize sub-micron cellular structures in pre-cancerous epithelial cells, with sensitivity down to particle diameters of 25 nm. The QPI technique measures the phase of light transmitted through or reflected from biological tissue, allowing nanometer scale sensitivity to structure and dynamics of living cells.