 Hi, I'm Arnoldo Serrano a graduate student in the guy lab in the Department of Chemistry at the University of Pennsylvania and an author of the recent reviews spectroscopic studies of protein folding linear and nonlinear methods along with Matase Weigli and Professor Guy. With this video, I hope to highlight for you some of the major points we touch on in that review and hopefully convince you of the growing importance of advanced laser spectroscopic methods for answering new questions in protein folding. The complexity and biological significance of corrective folding has stimulated decades of research into the topic from many different perspectives. While much progress has been made, two of the greatest element factors in providing more detailed information about folding are firstly, the need to trigger folding events, since the nature of this process generally requires population of thermodynamically unfavorable states and secondly, the lack of suitable windows through which folding can be viewed. For most protein studies, the kind of detail visible in the simulation you're currently watching is inaccessible experimentally and only a picture of considerably reduced resolution, both in time and in space, is achievable. For example, if the process is being probed by either infrared absorption or UV-CV, the experiment will primarily be sensitive to alpha helix formation. In the case where a fret pair is being used to probe the process, the experiment will primarily be sensitive to the relative distance of the two probe molecules from each other. While a spectroscopy that can provide atomistically detailed and high-time resolution movies of the protein folding process is if at all possible still a long way off, some of the techniques we discussed in our review provide what we believe to be huge steps in the right direction of achieving this goal. All of the methods discussed involve the application of optical spectroscopy. In particular, laser spectroscopy in the visible and infrared regions. Several of these are carried out in the following fashion, a short laser pulse ranging from femtoseconds to nanoseconds and tuned to the appropriate frequency interacts with the sample first. This can be through heating of solvent molecules or the photolytic cleavage of a chemical bond. All of these leave the sample in a high free energy state from which relaxation can be monitored by an appropriately tuned probe laser. Our group has successfully used this method to measure the folding dynamics of many different secondary structural elements and fast folding mini proteins. While these techniques have revealed a great deal about the motions involved in protein folding, new methods based on nonlinear spectroscopy and ultra-fast lasers are emerging as powerful new tools. An example of such a method is two-dimensional infrared spectroscopy or 2DIR, which we discussed briefly in our review. As depicted here, 2DIR involves the generation of three ultra-short laser pulses which are delayed relative to one another and interact with the sample in series. These three consecutive interactions induce the emission of a sample signal known as the photon echo. This signal, when combined with a fourth reference pulse and analyzed, provides information on the third-order nonlinear response of the sample, and ultimately results in the generation of a two-dimensional contour representation of the infrared transitions of the sample. As we explained in our review, these spectra provide a wealth of detail about the structure dynamics of the protein sample under study that is simply not accessible by more conventional methods and can be used in conjunction with the trigger methods discussed previously, and we believe it represents one of many large steps in the direction of generating high-resolution experimental protein movies.