6 research outputs found
PEG-Phospholipids Coated Quantum Rods as Amplifiers of the Photosensitization Process by FRET
Singlet oxygen (<sup>1</sup>O<sub>2</sub>) generated upon photostimulation of photosensitizer molecules
is a highly reactive specie which is utilized in photodynamic therapy.
Recent studies have shown that semiconductor nanoparticles can be
used as donors in fluorescence resonance energy transfer (FRET) process
to excite attached photosensitizer molecules. In these studies, their
unique properties, such as low nanoscale size, long-term photostability,
wide broad absorbance band, large absorption cross section, and narrow
and tunable emission bands were used to provide advantages over the
traditional methods to produce singlet oxygen. Previous studies that
achieved this goal, however, showed some limitations, such as low
FRET efficiency, poor colloidal stability, nonspecific interactions,
and/or complex preparation procedure. In this work, we developed and
characterized a novel system of semiconductor quantum rods (QRs) and
the photosensitizer meso-tetraÂ(hydroxyphenyl) chlorin (<i>m</i>THPC), as a model system that produces singlet oxygen without these
limitations. A simple two-step preparation method is shown; Hydrophobic
CdSe/CdS QRs are solubilized in aqueous solutions by encapsulation
with lecithin and PEGylated phospholipid (PEG–PL) of two lipid
lengths: PEG<sub>350</sub> or PEG<sub>2000</sub>. Then, the hydrophobic
photosensitizer <i>m</i>THPC, was intercalated into the
new amphiphilic PEG–PL coating of the QR, providing a strong
attachment to the nanoparticle without covalent linkage. These PEGylated
QR (eQR)–<i>m</i>THPC nanocomposites show efficient
FRET processes upon light stimulation of the QR component which results
in efficient production of singlet oxygen. The results demonstrate
the potential for future use of this concept in photodynamic therapy
schemes
Delivery of Liposomal Quantum Dots <i>via</i> Monocytes for Imaging of Inflamed Tissue
Quantum
dots (QDs), semiconductor nanocrystals, are fluorescent
nanoparticles of growing interest as an imaging tool of a diseased
tissue. However, a major concern is their biocompatibility, cytotoxicity,
and fluorescence instability in biological milieu, impeding their
use in biomedical applications, in general, and for inflammation imaging,
in particular. In addition, for an efficient fluorescent signal at
the desired tissue, and avoiding systemic biodistribution and possible
toxicity, targeting is desired. We hypothesized that phagocytic cells
of the innate immunity system (mainly circulating monocytes) can be
exploited as transporters of specially designed liposomes containing
QDs to the inflamed tissue. We developed a liposomal delivery system
of QDs (LipQDs) characterized with high encapsulation yield, enhanced
optical properties including far-red emission wavelength and fluorescent
stability, high quantum yield, and protracted fluorescent decay lifetime.
Treatment with LipQDs, rather than free QDs, exhibited high accumulation
and retention following intravenous administration in carotid-injured
rats (an inflammatory model). QD–monocyte colocalization was
detected in the inflamed arterial segment only following treatment
with LipQDs. No cytotoxicity was observed following LipQD treatment
in cell cultures, and changes in liver enzymes and gross histopathological
changes were not detected in mice and rats, respectively. Our results
suggest that the LipQD formulation could be a promising strategy for
imaging inflammation
Carbon Nanotube and Semiconductor Nanorods Hybrids: Preparation, Characterization, and Evaluation of Photocurrent Generation
Carbon
nanotubes (CNTs) and semiconductor nanocrystals (SCNCs)
are known to be interesting donor–acceptor partners due to
their unique optical and electronic properties. These exciting features
have led to the development of novel composites based on these two
nanomaterials and to their characterization for use in various applications,
such as components in sensors, transistors, solar cells and biomedical
devices. Two approaches based on covalent and noncovalent methods
have been suggested for coupling the SCNCs to CNTs. Most covalent
conjugation methods used so far were found to disrupt the electronic
structure of the CNTs or interfere with charge transfer in the CNT–SCNC
interface. Moreover, it offers random and poorly organized nanoparticle
coatings. Therefore, noncovalent methods are considered to be ideal
for better electronic coupling. However, a key common drawback of
noncovalent methods is the lack of stability which hampers their applicability.
In this article, a method has been developed to couple semiconductor
seeded nanorods onto CNTs through π–π interactions.
The CNTs and pyrene conjugated SCNC hybrid materials were characterized
by both microscopic and spectroscopic techniques. Fluorescence and
photocurrent measurements suggest the proposed pi-stacking approach
results in a strong electronic coupling between the CNTs and the SCNCs
leading to better photocurrent efficiency than that of a covalent
conjugation method reported using similar SCNC material. Overall,
the CNT–SCNC films reported in the present study open the scope
for the fabrication of optoelectronic devices for various applications
Photocatalytic Reactive Oxygen Species Formation by Semiconductor–Metal Hybrid Nanoparticles. Toward Light-Induced Modulation of Biological Processes
Semiconductor–metal
hybrid nanoparticles manifest efficient light-induced spatial charge
separation at the semiconductor–metal interface, as demonstrated
by their use for hydrogen generation via water splitting. Here, we
pioneer a study of their functionality as efficient photocatalysts
for the formation of reactive oxygen species. We observed enhanced
photocatalytic activity forming hydrogen peroxide, superoxide, and
hydroxyl radicals upon light excitation, which was significantly larger
than that of the semiconductor nanocrystals, attributed to the charge
separation and the catalytic function of the metal tip. We used this
photocatalytic functionality for modulating the enzymatic activity
of horseradish peroxidase as a model system, demonstrating the potential
use of hybrid nanoparticles as active agents for controlling biological
processes through illumination. The capability to produce reactive
oxygen species by illumination on-demand enhances the available peroxidase-based
tools for research and opens the path for studying biological processes
at high spatiotemporal resolution, laying the foundation for developing
novel therapeutic approaches
Rapid Three-Dimensional Printing in Water Using Semiconductor–Metal Hybrid Nanoparticles as Photoinitiators
Additive
manufacturing processes enable fabrication of complex
and functional three-dimensional (3D) objects ranging from engine
parts to artificial organs. Photopolymerization, which is the most
versatile technology enabling such processes through 3D printing,
utilizes photoinitiators that break into radicals upon light absorption.
We report on a new family of photoinitiators for 3D printing based
on hybrid semiconductor–metal nanoparticles. Unlike conventional
photoinitiators that are consumed upon irradiation, these particles
form radicals through a photocatalytic process. Light absorption by
the semiconductor nanorod is followed by charge separation and electron
transfer to the metal tip, enabling redox reactions to form radicals
in aerobic conditions. In particular, we demonstrate their use in
3D printing in water, where they simultaneously form hydroxyl radicals
for the polymerization and consume dissolved oxygen that is a known
inhibitor. We also demonstrate their potential for two-photon polymerization
due to their giant two-photon absorption cross section
Semiconductor Nanorod–Carbon Nanotube Biomimetic Films for Wire-Free Photostimulation of Blind Retinas
We report the development of a semiconductor
nanorod-carbon nanotube
based platform for wire-free, light induced retina stimulation. A
plasma polymerized acrylic acid midlayer was used to achieve covalent
conjugation of semiconductor nanorods directly onto neuro-adhesive,
three-dimensional carbon nanotube surfaces. Photocurrent, photovoltage,
and fluorescence lifetime measurements validate efficient charge transfer
between the nanorods and the carbon nanotube films. Successful stimulation
of a light-insensitive chick retina suggests the potential use of
this novel platform in future artificial retina applications