  Nonlinear optical (NLO) imaging has emerged as a promising plant cell imaging
technique due to its large optical penetration, inherent 3D spatial resolution,
and reduced photodamage, meanwhile exogenous nanoprobes are usually needed for
non-signal target cell analysis. Here, we report in-vivo, simultaneous 3D
labeling and imaging of potato cell structures using plasmonic
nanoprobe-assisted multimodal NLO microscopy. Experimental results show that
the complete cell structure could be imaged by the combination of
second-harmonic generation (SHG) and two-photon luminescence (TPL) when noble
metal silver or gold ions are added. In contrast, without noble metal ion
solution, no NLO signals from the cell wall could be acquired. The mechanism
can be attributed to noble metal nanoprobes with strong nonlinear optical
responses formed along the cell walls via a femtosecond laser scan. During the
SHG-TPL imaging process, noble metal ions that cross the cell wall could be
rapidly reduced to plasmonic nanoparticles by fs laser and selectively anchored
onto both sides of the cell wall, thereby leading to simultaneous 3D labeling
and imaging of potato cells. Compared with traditional labeling technique that
needs in-vitro nanoprobe fabrication and cell labeling, our approach allows for
one-step, in-vivo labeling of plant cells, thus providing a rapid,
cost-effective way for cellular structure construction and imaging.
