Winfried Denk (born November 12, 1957, in Munich) is a German physicist. He built the firsttwo-photon microscope while he was a graduate student (and briefly a postdoc) inWatt W. Webb's lab atCornell University, in 1989.
Denk was born in Munich, Germany. As a child he spent most of his playtime learning to use the tools and building materials in his father's workshop. In school it became apparent that Denk’s ‘talents were unevenly spread across subjects, math and physics being favored’.[1] Fixing and constructing electronic devices was his main hobby throughout high school.
After high school, Denk completed the mandatory 15-month stint in the German army and spent the next 3 years at theLudwig Maximilian University of Munich. In 1981 he moved to Zurich to study at theETH. During this time, he also worked in the lab of Dieter Pohl, at theIBM laboratory. There he built one of the firstsuper-resolution microscopes and developed a passion for scanning microscopy. He did his master's thesis in the lab ofKurt Wüthrich, under the direct guidance ofGerhard Wagner. But he felt that NMR spectroscopy was not for him because it did not involve enough opportunities to create new experimental gadgets.
In 1984 Denk joined the lab ofWatt W. Webb at Cornell. While Webb himself was extremely interested in methods – both fluorescence-correlation and photo bleaching-recovery spectroscopy had been invented in his lab – he gave students and postdocs a lot of freedom. Denk enjoyed his time at Cornell but was almost fired after he went to Greece for six weeks to study monk seals. Given a second chance, he started a project aimed at measuring the motion of sensory hair-bundles in the inner ear. One of the attractions of this endeavor was that it required a stay in San Francisco, in order to learn fromJim Hudspeth and his group about hair-cells in general and specifically how to prepare them for the planned measurements.
Denk returned to Cornell and invented a method sensitive enough to measure the thermal movement of hair-bundles. He went on to show that hair cells can sense their ownBrownian motion.[2]
Central to Denk's early career was his intuition that two-photon (2p) imaging might damage the sample less than one-photon confocal imaging.[3] He predicted this in spite of the fact that peak light intensity for 2p is almost one million times higher than for the confocal microscope. Equally important was his insight that infrared 2p excitation would allow scattered fluorescence to contribute to images even deep in turbid samples, improving the optical access and resolution of 2p imaging over what was possible using confocal imaging.[4]
Nowhere has this proven more valuable than when imaging neurons in living brain tissue. Two-photon microscopy remains the only technique that allows the recording of activity in living brains with high spatial resolution. 2p excitation can also be used to map cells' receptor distributions by releasing substances from their chemical "cages".[4]
Denk later demonstrated that 2p can be utilized to record activity in the visually stimulated retina.[5] He also showed that it can be combined with adaptive optics to improve resolution, and with amplified pulses to push the depth limit to 1mm in brain tissue.[6][7] Today, two-photon excitation microscopy is also used in the fields of physiology, embryology and tissue engineering, as well as in cancer research.
The sparsity of data on connectivity between neurons had been a major limitation in circuit neuroscience. Denk’s 2004 paper[8] describing automatedserial blockface microscopy rekindled the dormant science of comprehensive neural circuit mapping (connectomics), pioneered by Sydney Brenner.[9]
