Fluorescence imaging beyond the ballistic regime by ultrasound-pulse-guided digital phase conjugation

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Fluorescence imaging has revolutionized biomedical research over the past three decades. Its high molecular specificity and unrivalled single-molecule-level sensitivity have enabled breakthroughs in a number of research fields. For in vivo applications its major limitation is its superficial imaging depth, a result of random scattering in biological tissues causing exponential attenuation of the ballistic component of a light wave. Here, we present fluorescence imaging beyond the ballistic regime by combining single-cycle pulsed ultrasound modulation and digital optical phase conjugation. We demonstrate a near-isotropic three-dimensional localized sound–light interaction zone. With the exceptionally high optical gain provided by the digital optical phase conjugation system, we can deliver sufficient optical power to a focus inside highly scattering media for not only fluorescence imaging but also a variety of linear and nonlinear spectroscopy measurements. This technology paves the way for many important applications in both fundamental biology research and clinical studies.

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Figure 1: Experimental scheme and set-up.
Figure 2: PSF measurement.
Figure 3: Fluorescence imaging.


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The authors thank C. Shank, Y.M. Wang and C. Yang for helpful discussions, T.-W. Chen for instructions on the micropipette puller and A. Hu for preparing the fixed rat brain slices. The research was supported by the Howard Hughes Medical Institute.

Author information

The experiment was designed and implemented by M.C. The fluorescence pattern was created by K.S. The scattering coefficient and the speckle correlation were measured by R.F. All authors contribute to the data analysis and preparation of the manuscript.

Correspondence to Meng Cui.

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The authors declare no competing financial interests.

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