8 research outputs found
Imaging Laser-Triggered Drug Release from Gold Nanocages with Transient Absorption Lifetime Microscopy
Nanoparticles
have shown promise in loading and delivering drugs for targeted therapy.
Many progresses have been made in the design, synthesis, and modification
of nanoparticles to fulfill such goals. However, realizing targeted
intracellular delivery and controlled release of drugs remains challenging,
partly because of the lack of reliable tools to detect the drug-releasing
process. In this paper, we applied femtosecond laser pulses to trigger
the explosion of gold nanocages (AuNCs) and control the intracellular
release of loaded aluminum phthalocyanine (AlPcS) molecules for photodynamic
therapy (PDT). AuNCs were found to enhance the encapsulation efficiency
and suppress the PDT effect of AlPcS molecules until they were released.
More importantly, we discovered that the excited-state lifetimes of
the AlPcS–AuNC conjugate (∼3 ps) and free AlPcS (∼11
ps) differ significantly, which was utilized to image the released
drug molecules using transient absorption lifetime microscopy with
the same laser source. This technique extracts information similar
to fluorescence lifetime imaging microscopy but is superior in imaging
the molecules that hardly fluoresce or are prone to photobleaching. We
further combined a dual-phase lock-in detection technique to show
the potential of real-time imaging based on the change in transient
optical behaviors. Our method may provide a new tool for investigating
nanoparticle-assisted drug delivery and release
Layer-Dependent Ultrafast Carrier and Coherent Phonon Dynamics in Black Phosphorus
Black
phosphorus is a layered semiconducting material, demonstrating
strong layer-dependent optical and electronic properties. Probing
the photophysical properties on ultrafast time scales is of central
importance in understanding many-body interactions and nonequilibrium
quasiparticle dynamics. Here, we applied temporally, spectrally, and
spatially resolved pump–probe microscopy to study the transient
optical responses of mechanically exfoliated few-layer black phosphorus,
with layer numbers ranging from 2 to 9. We have observed layer-dependent
resonant transient absorption spectra with both photobleaching and
red-shifted photoinduced absorption features, which could be attributed
to band gap renormalization of higher subband transitions. Surprisingly,
coherent phonon oscillations with unprecedented intensities were observed
when the probe photons were in resonance with the optical transitions,
which correspond to the low-frequency layer-breathing mode. Our results
reveal strong Coulomb interactions and electron–phonon couplings
in photoexcited black phosphorus, providing important insights into
the ultrafast optical, nanomechanical, and optoelectronic properties
of this novel two-dimensional material
Layer-Dependent Ultrafast Carrier and Coherent Phonon Dynamics in Black Phosphorus
Black
phosphorus is a layered semiconducting material, demonstrating
strong layer-dependent optical and electronic properties. Probing
the photophysical properties on ultrafast time scales is of central
importance in understanding many-body interactions and nonequilibrium
quasiparticle dynamics. Here, we applied temporally, spectrally, and
spatially resolved pump–probe microscopy to study the transient
optical responses of mechanically exfoliated few-layer black phosphorus,
with layer numbers ranging from 2 to 9. We have observed layer-dependent
resonant transient absorption spectra with both photobleaching and
red-shifted photoinduced absorption features, which could be attributed
to band gap renormalization of higher subband transitions. Surprisingly,
coherent phonon oscillations with unprecedented intensities were observed
when the probe photons were in resonance with the optical transitions,
which correspond to the low-frequency layer-breathing mode. Our results
reveal strong Coulomb interactions and electron–phonon couplings
in photoexcited black phosphorus, providing important insights into
the ultrafast optical, nanomechanical, and optoelectronic properties
of this novel two-dimensional material
Optimizing Nonlinear Optical Visibility of Two-Dimensional Materials
Two-dimensional (2D)
materials have attracted broad research interests across various nonlinear
optical (NLO) studies, including nonlinear photoluminescence (NPL),
second harmonic generation (SHG), transient absorption (TA), and so
forth. These studies have unveiled important features and information
of 2D materials, such as in grain boundaries, defects, and crystal
orientations. However, as most research studies focused on the intrinsic
NLO processes, little attention has been paid to the substrates underneath.
Here, we discovered that the NLO signal depends significantly on the
thickness of SiO<sub>2</sub> in SiO<sub>2</sub>/Si substrates. A 40-fold
enhancement of the NPL signal of graphene was observed when the SiO<sub>2</sub> thickness was varied from 270 to 125 nm under 800 nm excitation.
We systematically studied the NPL intensity of graphene on three different
SiO<sub>2</sub> thicknesses within a pump wavelength range of 800–1100
nm. The results agreed with a numerical model based on back reflection
and interference. Furthermore, we have extended our measurements to
include TA and SHG of graphene and MoS<sub>2</sub>, confirming that
SiO<sub>2</sub> thickness has similar effects on all of the three
major types of NLO signals. Our results will serve as an important
guidance for choosing the optimum substrates to conduct NLO research
studies on 2D materials