Edwin K. L. Yeow

Near‐Infrared Light‐Mediated Photoactivation of a Platinum Antitumor Prodrug and Simultaneous Cellular Apoptosis Imaging by Upconversion‐Luminescent Nanoparticles

Platinum-based drugs are among the most active antitumor reagents in clinical practice; their application is limited by side effects and drug resistance. A novel and personalized near-infrared (NIR) light-activated nanoplatform is obtained by combining a photoactivatable platinum(IV) prodrug and a caspase imaging peptide conjugated with silica-coated upconversion-luminescent nanoparticles (UCNPs) for the remote control of antitumor platinum prodrug activation, and simultaneously for real-time imaging of apoptosis induced by activated cytotoxicity. Upon NIR light illumination, the Pt(IV) prodrug complex is activated at the surface of the nanoparticle and active components are selectively released which display cytotoxicity against human ovarian carcinoma A2780 cells and its cisplatin-resistant variant A2780cis cells. More importantly, the caspases enzymes triggered by cytotoxicity would effectively cleave the probe peptide, thereby allowing the direct imaging of apoptosis in living cells.

Nonblinking, Intense Two-Dimensional Light Emitter: Monolayer WS2 Triangles

Monolayer WS2 (1L-WS2), with a direct band gap, provides an ideal platform to investigate unique properties of two-dimensional semiconductors. In this work, light emission of a 1L-WS2 triangle has been studied by using steady-state, time-resolved, and temperature-dependent photoluminescence (PL) spectroscopy. Two groups of 1L-WS2 triangles have been grown by chemical vapor deposition, which exhibit nonuniform and uniform PL, respectively. Observed nonuniform PL features, i.e., quenching and blue-shift in certain areas, are caused by structural imperfection and n-doping induced by charged defects. Uniform PL is found to be intrinsic, intense, and nonblinking, which are attributed to high crystalline quality. The binding energy of the A-exciton is extracted experimentally, which gives direct evidence for the large excitonic effect in 1L-WS2. These superior photon emission features make 1L-WS2 an appealing material for optoelectronic applications such as novel light-emitting and biosensing devices.

In vivo covalent cross-linking of photon-converted rare-earth nanostructures for tumour localization and theranostics

The development of precision nanomedicines to direct nanostructure-based reagents into tumour-targeted areas remains a critical challenge in clinics. Chemical reaction-mediated localization in response to tumour environmental perturbations offers promising opportunities for rational design of effective nano-theranostics. Here, we present a unique microenvironment-sensitive strategy for localization of peptide-premodified upconversion nanocrystals (UCNs) within tumour areas. Upon tumour-specific cathepsin protease reactions, the cleavage of peptides induces covalent cross-linking between the exposed cysteine and 2-cyanobenzothiazole on neighbouring particles, thus triggering the accumulation of UCNs into tumour site. Such enzyme-triggered cross-linking of UCNs leads to enhanced upconversion emission upon 808 nm laser irradiation, and in turn amplifies the singlet oxygen generation from the photosensitizers attached on UCNs. Importantly, this design enables remarkable tumour inhibition through either intratumoral UCNs injection or intravenous injection of nanoparticles modified with the targeting ligand. Our strategy may provide a multimodality solution for effective molecular sensing and site-specific tumour treatment.

Ultralow-threshold two-photon pumped amplified spontaneous emission and lasing from seeded CdSe/CdS nanorod heterostructures

Ultralow-threshold two-photon pumped amplified spontaneous emission (2ASE) and lasing in seeded CdSe/CdS nanodot/nanorod heterostructures is demonstrated for the first time. Such heterostructures allow the independent tunability of the two-photon absorption (2PA) cross-section (σ(2)) through varying the CdS rod size, and that of the emission wavelength through varying the CdSe dot size. With an enhanced σ(2), 2ASE in these heterostructures is achieved with an ultralow threshold fluence of ~1.5 mJ/cm(2), which is as much as one order less than that required for spherical semiconductor NCs. Importantly, by exploiting this unique property of the seeded nanorods exhibiting strong quantum confinement even at relatively large rod sizes, a near reciprocal relation between the 2ASE threshold and the 2PA action cross-section (σ(2)η) (where η is the quantum yield) was found and validated over a wide volume range for II-VI semiconductor nanostructures. Ultrafast optical spectroscopy verified that while the Auger processes in these heterostructures are indeed suppressed, ASE in these samples could also be strongly affected by a fast hole-trapping process to the NR surface states. Lastly, to exemplify the potential of these seeded CdSe/CdS nanodot/nanorod heterostructures as a viable gain media for achieving two-photon lasing, a highly photostable microsphere laser with an ultralow pump threshold is showcased.

Uncovering loss mechanisms in silver nanoparticle-blended plasmonic organic solar cells

There has been much controversy over the incorporation of organic-ligand-encapsulated plasmonic nanoparticles in the active layer of bulk heterojunction organic solar cells, where both enhancement and detraction in performance have been reported. Here through comprehensive transient optical spectroscopy and electrical characterization, we demonstrate evidence of traps responsible for performance degradation in plasmonic organic solar cells fabricated with oleylamine-capped silver nanoparticles blended in the poly (3-hexylthiophene):[6,6]-phenyl-C 61-butyric acid methyl ester active layer. Despite an initial increase in exciton generation promoted by the presence of silver nanoparticles, transient absorption spectroscopy reveals no increase in the later free polaron population-attributed to fast trapping of polarons by nearby nanoparticles. The increased trap-assisted recombination is also reconfirmed by light intensity-dependent electrical measurements. These new insights into the photophysics and charge dynamics of plasmonic organic solar cells would resolve the existing controversy and provide clear guidelines for device design and fabrication.

A Green Approach to the Synthesis of High-Quality Graphene Oxide Flakes via Electrochemical Exfoliation of Pencil Core

A simple, green and cost-effective approach has been reported to synthesize high-quality graphene oxide (GO) flakes via electrochemical exfoliation of pencil cores in aqueous electrolytes. The exfoliated GO flakes exhibit excellent electrocatalytic activity and toxicity tolerance for oxygen reduction reactions in alkaline solution. Our present results are promising for scaled-up preparation and further commercialization of graphene oxide in a low-cost and environmentally friendly way.

Recent advance of biological molecular imaging based on lanthanide-doped upconversion-luminescent nanomaterials

Lanthanide-doped upconversion-luminescent nanoparticles (UCNPs), which can be excited by near-infrared (NIR) laser irradiation to emit multiplex light, have been proven to be very useful for in vitro and in vivo molecular imaging studies. In comparison with the conventionally used down-conversion fluorescence imaging strategies, the NIR light excited luminescence of UCNPs displays high photostability, low cytotoxicity, little background auto-fluorescence, which allows for deep tissue penetration, making them attractive as contrast agents for biomedical imaging applications. In this review, we will mainly focus on the latest development of a new type of lanthanide-doped UCNP material and its main applications for in vitro and in vivo molecular imaging and we will also discuss the challenges and future perspectives.

Enzyme-Responsive Cell-Penetrating Peptide Conjugated Mesoporous Silica Quantum Dot Nanocarriers for Controlled Release of Nucleus-Targeted Drug Molecules and Real-Time Intracellular Fluorescence Imaging of Tumor Cells

Here, a set of novel and personalized nanocarriers are presented for controlled nucleus-targeted antitumor drug delivery and real-time imaging of intracellular drug molecule trafficking by integrating an enzyme activatable cell penetrating peptide (CPP) with mesoporous silica coated quantum dots nanoparticles. Upon loading of antitumor drug, doxorubicin (DOX) and further exposure to proteases in tumor cell environment, the enzymatic cleavage of peptide sequence activates oligocationic TAT residues on the QDs@mSiO2 surface and direct the DOX delivery into cellular nucleus. The systematic cell imaging and cytotoxicity studies confirm that the enzyme responsive DOX-loaded CPP-QDs@mSiO2 nanoparticles can selectively release DOX in the tumor cells with high cathepsin B enzyme expression and greatly facilitate DOX accumulation in targeted nucleus, thus exhibiting enhanced antitumor activity in these cells. As contrast, there is limited nuclear-targeted drug accumulation and lower tumor cytotoxicity observed in the cells without enzyme expression. More importantly, significant antitumor DOX accumulation and higher tumor inactivation is also found in the drug resistant tumor cells with targeted enzyme expression. Such simple and specific enzyme responsive mesoporous silica-QDs nanoconjugates provide great promise for rational design of targeted drug delivery into biological system, and may thus greatly facilitate the medical theranostics in the near future.

Plasma Modified MoS2 Nanoflakes for Surface Enhanced Raman Scattering

Though the SERS effect based on pristine MoS2 is hardly observed, however, the plasma treated MoS2 nanoflakes can be used as an ideal substrate for surface enhanced Raman scattering. It is proved that the structural disorder induced generation of local dipoles and adsorption of oxygen on the plasma treated MoS2 nanosheets are the two basic and important driven forces for the enhancement of Raman signals of surface adsorbed R6G molecules.

Photoinduced energy and electron transfer in bis-porphyrins with quinoxaline Tröger's base and biquinoxalinyl spacers

The photophysical characterisation of bis-porphyrins consisting of two porphyrins bridged by either a quinoxaline Trogers base (1 and 2) or a biquinoxalinyl (3) spacer are reported. Efficient intramolecular electronic energy transfer (EET) between the rigidly linked free-base porphyrins in 1 and from the zinc(II) porphyrin to the free-base porphyrin in 2 has been investigated by steady-state absorption and emission spectroscopy, time-resolved fluorescence spectroscopy and semi-empirical calculations. A resonance dipole–dipole mechanism alone cannot account for the rate of EET in both 1 and 2. It is demonstrated that a superexchange mechanism ia the quinoxaline Trogers base linker is responsible for the enhanced energy transfer rates in these systems. Strong quenching of the fluorescence intensity observed in 3 is interpreted as arising from long-range (>18 A) through-biquinoxalinyl bridge mediated photoinduced electron transfer from the free-base porphyrin to the gold(III) porphyrin. These systems provide useful models for the arrangements of the primary donor–acceptor pair in photosynthetic reaction centres, and for elucidating the role of the connecting bridge in electron and energy transfer processes.