■ New Strategy for Efficient Chemical Targeting within Cells

Many researchers are accustomed to imaging cellular components with a limited palette of fluorescent dyestypically red, green, and blue. Wei Min and colleagues have now reported the development of a refined imaging technique along with the concurrent synthesis of finely tuned dyes that brings the number of colors available for cellular imaging to an amazing 24 hues (Nature 2017, 544, 465−470). The imaging technique begins with the traditional step of labeling target cellular components with fluorescent dyes. The cell sample is then exposed to two precisely defined laser pulses designed to stimulate the spectrally sharp vibration (which only occurs over a much narrower frequency range than that of fluorescence emission) of a specific chemical bond in one of the dyes in the sample, eliminating off-target excitation and significantly reducing background fluorescence. The dyes are excited one at a time to generate a series of images that can be overlaid to view intricate interactions between various cell structures. Because the excitation technique precisely targets specific vibrational frequencies, which are inversely proportional to the square root of masses of each atom or functional group attached to the targeted bond, even dyes with identical molecular structure but containing different isotopes can produce distinct frequencies. Min and co-workers synthesized 14 xanthene analogs with various structures and isotopic patterns, but they predict that dozens more resolvable dyes could be developed. Notably, the new dyes are relatively nontoxic and photostable, allowing the research team to perform proof-of-concept labeling experiments on live cells under normal cell culture conditions as well as in conditions designed to induce cell stress to mimic disease states. The authors expect that the technique could be further improved to allow simultaneous dye stimulation and visualization and predict that due to its sensitivity, resolution, labeling versatility, and biocompatibility, their approach will become widely applied to probing complex biological systems.