Low-temperature synthesis of colloidal few-layer WTe2 nanostructures for electrochemical hydrogen evolution.

High-quality transition metal tellurides, especially for WTe2, have been demonstrated to be necessarily synthesized under close environments and high temperatures, which are restricted by the low formation Gibbs free energy, thus limiting the electrochemical reaction mechanism and application studies. Here, we report a low-temperature colloidal synthesis of few-layer WTe2 nanostructures with lateral sizes around hundreds of nanometers, which could be tuned the aggregation state to obtain the nanoflowers or nanosheets by using different surfactant agents. The crystal phase and chemical composition of WTe2 nanostructures were analyzed by combining the characterization of X-ray diffraction and high-resolution transmission electron microscopy imaging and elements mapping. The as-synthesized WTe2 nanostructures and its hybrid catalysts were found to show an excellent HER performance with low overpotential and small Tafel slope. The carbon-based WTe2-GO and WTe2-CNT hybrid catalysts also have been synthesized by the similar strategy to study the electrochemical interface. The energy diagram and microreactor devices have been used to reveal the interface contribution to electrochemical performance, which shows the identical performance results with as-synthesized WTe2-carbon hybrid catalysts. These results summarize the interface design principle for semimetallic or metallic catalysts and also confirm the possible electrochemical applications of two-dimensional transition metal tellurides.

Hydrophobic surface efficiently boosting Cu2O nanowires photoelectrochemical CO2 reduction activity.

The limited mass transfer of CO2 and the competitive hydrogen evolution reaction (HER) during photoelectrochemical (PEC) CO2 reduction usually result in low CO2 reduction activity. Here, we constructed a Cu2O/Sn/PTFE photocathode with a hydrophobic surface based on Cu2O by physical vapor deposition and a dipping method. The CO faradaic efficiency (FE) increased from 34.5% (Cu2O) to 95.1% (Cu2O/Sn/PTFE) at -0.7 V vs. RHE, and the FEH2 decreased from 27.9% (Cu2O) to 3.8% (Cu2O/Sn/PTFE). The introduction of the hydrophobic layer enhances the local CO2 concentration on the electrode surface and effectively isolates H+ from the aqueous electrolyte, thereby enhancing the CO2 reduction activity.

Plasmonic Ag-decorated Cu2O nanowires for boosting photoelectrochemical CO2 reduction to multi-carbon products.

The generation of multi-carbon products on the Cu2O photocathode remains a great challenge. Herein, effective charge separation and surface catalytic reaction are achieved for photoelectrochemical CO2 reduction through plasmon metal (Ag) decoration on Cu2O nanowires. The Cu2O/Ag composite photocathode achieves a 47.7% faradaic efficiency for CH3COOH and the generation rate is 212.7 µmol cm-2 h-1 under illumination, which is about five times that in dark (44.4 µmol cm-2 h-1) at -0.7 V vs. RHE.

Stain-free LED scanning lifetime imaging system for diabetes modified tissue matrices.

In contrast to labor intensive and destructive histological techniques, intrinsic autofluorescence lifetimes of extra cellular matrix proteins can provide label-free imaging of tissue modifications in diseases, including the diabetic ulcers. However, decoupling the complex mixture of tissue fluorophores requires costly and complicated fluorescent lifetime instrumentation. Furthermore, a list of autofluorescent and fluorogenic proteins must be characterized to profile their changes during disease progression. Towards these goals, an imaging system based on frequency domain light-emitting diode (LED) modulation was designed and demonstrated, using off-the-shelf components in a low complexity design. The system was operated by coupling and imaging fluorescence intensities using a pair of objectives. The system's scanning and signal acquisition performances were optimized with respect to etendues. To study fluorescent proteins in diabetic ulcers, lifetimes from purified and pentosidine modified collagen I, collagen III, and elastin were measured. Pentosidine measurements showed a decrease in autofluorescent lifetimes while elevated collagen III in diabetic ulcers showed increased lifetimes. These lifetimes, plus future protein measurements enabled by our system, can serve as standards for developing a biophotonic model of diabetic ulcers. As a proof-of-concept, a 3 cm × 3 cm diabetic foot ulcer was imaged using the developed system. Phasor analysis was applied to aid the interpretation of lifetime images. As a result, a compact biophotonic imaging system targeting diabetic tissue was achieved, towards making the technique accessible for clinical histology.

Three-dimensional printed miniaturized spectral system for collagen fluorescence lifetime measurements.

Various types of collagens, e.g., type I and III, represent the main load-bearing components in biological tissues. Their composition changes during processes such as wound healing and fibrosis. When excited by ultraviolet light, collagens exhibit autofluorescence distinguishable by their unique fluorescent lifetimes across a range of emission wavelengths. Here, we designed a miniaturized spectral-lifetime detection system as a noninvasive probe for monitoring tissue collagen compositions. A sine-modulated LED illumination was applied to enable frequency domain fluorescence lifetime measurements under three wavelength bands, separated via a series of longpass dichroics at 387, 409, and 435 nm. We employed a lithography-based three-dimensional (3-D) printer with <50 µm resolution to create a custom designed optomechanics in a handheld form factor. We examined the characteristics of the optomechanics with finite element modeling to simulate the effect of thermal (from LED) and mechanical (from handling) strain on the optical system. The geometry was further optimized with ray tracing to form the final 3-D printed structure. Using this device, the phase shift and demodulation of collagen types were measured, where the separate spectral bands enhanced the differentiation of their lifetimes. This system represents a low cost, handheld probe for clinical tissue monitoring applications.