Label-Free, Quantitative Imaging of MoS₂ -Nanosheets in Live Cells with Simultaneous Stimulated Raman Scattering and...

Probing nanoparticle-cell interactions in vivo plays a key role in the research and development of nanomedicine and nano-biophotonics. However, simultaneously imaging nanoparticles and intracellular biomolecules in a label-free manner has been a challenge, especially for the majority of nanoparticles that do not emit one- or two-photon excited fluorescence. In this work, a strong optical transient absorption (TA) signal is observed for synthesized MoS₂ nanosheets that could be used for sensitive and quantitative imaging of their intracellular distributions. Furthermore, a dual-modal microscopy technique is developed to simultaneously image MoS₂ with TA microscopy and cellular lipids/proteins with stimulated Raman scattering (SRS) microscopy. This technique is based on precise pulse engineering and dual-phase lock-in detection. Its capability to quantify the uptake dynamics of MoS₂ into live HeLa cells is demonstrated and the colocalization of MoS₂ nanosheets with intracellular lipid rich organelles is observed. Different sized MoS₂ nanosheets are found to have distinct uptake dynamics as well as transient photocarrier dynamics. These results indicate that dual-modal SRS/TA microscopy may provide a general solution for investigating a large variety of nanomaterials that absorb light but do not fluoresce.