Nanometer-scale particles can be separated for analysis by the impact induced by a laser shock wave, Japanese researchers report (Anal. Chem., DOI: 10.1021/ac103349z). Tetsuhiko Nagahara, Nobuyuki Ichinose, and Shinpei Nakamura of Kyoto Institute of Technology use a focused laser pulse to initiate a shock wave in a water-filled capillary. As the scheme below shows, the shock wave propagates along the length of the capillary, sweeping nanoparticles such as proteins or quantum dots along with it. By collecting fluorescence images of the capillary before and after a laser pulse, the researchers obtain a difference image that reveals how far the particles travel. The distance depends on the size and molecular weight of the particles, with larger ones traveling farther. The Kyoto team constructed a linear calibration that works for proteins up to about 300 kilodaltons. The researchers were able to separate dimers of ovalbumin and bovine serum albumin from their respective monomers. They also used shock wave chromatography to separate a mixture of two sizes of CdSe quantum dots.