This work reports the in vivo uptake
and translocation of PNPs
in the one-year grown terrestrial plant, Murraya exotica (M. exotica), as investigated
by two-photon excitation and time-resolved (TPE-TR) optical imaging
with a large field of view (FOV, 32 × 32 mm2) in a
noninvasive and real-time manner. The PNPs (⟨Rh⟩ = 12 ± 4.5 nm) synthesized from poly(styrene-co-maleic anhydride) (SMA) were Eu-luminescence labeled
(λL ≈ 617 nm). On exposing the roots of living M. exotica plants to the colloidal suspension
of SMA PNPs at different concentrations, the spatiotemporal evolution
of SMA PNPs along plant stems (60 mm in length) were monitored by
TPE-TR imaging, which rendered rich information on the uptake and
translocation of PNPs without any interference from the autofluorescence
of the plant tissues. The TPE-TR imaging combined with the high-resolution
anatomy revealed an intercell-wall route in the lignified epidermis
of M. exotica plants for SMA PNP uptake and translocation,
as well as the similar accumulation kinetics at different positions
along the plant stems. We modeled the accumulation kinetics with Gaussian
distribution to account for the trapping probability of a SMA PNP
by the lignified cell walls, allowing the statistical parameters,
the average trapping time (tm) and its
variance (σ), to be derived for the quantification of the PNP
accumulation in individual plants. The TPE-TR imaging and the analysis
protocols established herein will be helpful in exploring the mechanism
of plant-PNP interaction under physiological condition.