Friday July 8, 2005
11:30 AM - 12:30 PM
ENG Z-50 Auditorium

Office Hours:
Friday July 8, 2005
3:30 PM - 4 PM
ENG B-29

"Membrane imaging with second-harmonic generation microscopy"
Prof. Jerome Mertz
Boston University

Nonlinear optics has played a significant role in the development of new biological imaging techniques. The most well-known example of nonlinear microscopy is based on the generation of two-photon excited fluorescence (TPEF). Recently, another type of contrast mechanism based on second harmonic generation (SHG) has gained renewed interest SHG requires a non-centrosymmetric source. In biological tissue, this source may be endogenous, such as fibrilous collagen, tubulin, actin, etc.. Alternatively, the sample can be labeled with exogenous markers designed to distribute themselves non-centrosymmetrically and produce SHG. A labeling technique with amphiphilic hyperpolarizable chromophores has been especially successful for cell membrane imaging. Because it is coherent, SHG reveals information that is inaccessible to fluorescence. Applications include the possibility of monitoring trans-membrane voltages. Because of its implications in biology, this possibility has been the subject of concerted investigation. SHG voltage sensitivity has been demonstrated and characterized in model membranes. More recently, several groups are reporting SHG voltage sensitivity in living cells with high spatial and temporal resolution. Other applications include monitoring the local flip-flop dynamics of chromophores in membranes. Recently, we used SHG microscopy to demonstrate that flip-flop rates can be increased several orders of magnitude by a mechanism of two-photon-induced photo-isomerization.