Gold nanostars; self-assembled monolayers; near infrared; NIR-II; metal enhanced fluorescence; localized surface plasmon resonance; fluorescence lifetime.Gold nanostars (AuNS) are receiving increasing attention for their potential applications in bionanotechnology, because of their unique optical properties related to their complex branched morphology. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 confirming that AuNS substrates are promising NIR-MEF platforms for the development of ultrasensitive biosensing applications. Using fluorescence lifetime measurements to semi-quantitatively deconvolute the excitation enhancement from emission enhancement, as well as modelling to simulate the electric field enhancement, we show that a combination of enhanced excitation and an increased radiative decay rate, accompanied by an increase to the quantum yield, contribute to the observed large enhancement. AuNS with different morphological features exhibit significantly different excitation enhancement, indicating the important role of particle morphology on the magnitude of electromagnetic field enhancement, and the resulting enhancement factor. Importantly, enhancement factors of up to 50 times are also achieved in the NIR-II region, suggesting that this system holds promise for the future development of bright probes for NIR/NIR-II biosensing and bioimaging.
The authors report an ammonia‐assisted in situ cation‐exchange method for the synthesis of dodecagon N‐doped PdCoNi carbon‐based nanosheets (Pd‐e‐NiCo‐PBA‐C) and explore the catalytic performance. Pd‐e‐NiCo‐PBA‐C exerts extremely low overpotential and Tafel slope for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) both in acidic and alkaline media, only 47 mV, 55 mV dec−1 (pH = 0, HER) and 147 mV, 67 mV dec−1 (pH = 14, HER), and 309 mV, 67 mV dec−1 (pH = 14, OER), outperforming commercial IrO2‐based and Pt‐based catalysts. In addition, after 5000 cycles, the linear sweep voltammetry curve shows a negligible shift, indicating excellent stability performance. To test its overall water‐splitting performance, Pd‐e‐NiCo‐PBA‐C is applied as both cathode and anode materials. A high current density of 33 mA cm−2 at a battery voltage of 1.6 V is obtained, with the catalytic activity maintained at 97.3% after over 50 h. To get a further insight into the superior OER and HER performance, theoretical calculations are carried out, the better performance originates from the affinity difference of Pd and Ni atoms for gas atoms, and the replacement of inert atoms can decrease the binding energy and enhance the electrocatalytic activity.
Solar water splitting by semiconductor based photoanodes and photocathodes is one of the most promising strategies to convert solar energy to chemical energy to meet the high demand for energy consumption in modern society. However, the state-of-the-art efficiency is too low to fulfill the demand. To overcome this challenge and thus enable the industrial realization of a solar water splitting device, different approaches have been taken to enhance the overall device efficiency, one of which is the incorporation of plasmonic nanostructures. Photoanodes and photocathodes coupled to the optimized plasmonic nanostructures, matching the absorption wavelength of the semiconductors, can exhibit a significantly increased efficiency. So far, gold and silver have been extensively explored to plasmonically enhance water splitting efficiency, with disadvantages of high cost and low enhancement. Instead, non-noble plasmonic metals such as aluminum and copper, are earth-abundant and low cost. In this article, we review their potentials in photoelectrolysis, towards scalable applications.
Gold nanostars (AuNSs) are promising agents for the development of high-performance diagnostic devices, by enabling metal enhanced fluorescence (MEF) in the physiological near-infrared (NIR) and second near-infrared (NIR-II) windows. The local electric field near their sharp tips and between their branches can be enhanced by several orders of magnitude, holding great promise for large fluorescence enhancements from single AuNS particles, rather than relying on interparticle coupling in nanoparticle substrates. Here, guided by electric field simulations, two different types of AuNSs with controlled morphologies and plasmonic responses in the NIR and NIR-II regions are used to investigate the mechanism of MEF from colloidal AuNSs. Fluorophore conjugation to AuNSs allows significant fluorescence enhancement of up to 30 times in the NIR window, and up to 4-fold enhancement in the NIR-II region. Together with other inherent advantages of AuNSs, including their multispike morphology offering easy access to cell membranes and their large surface area providing flexible multifunctionality, AuNS are promising for the development of in vivo imaging applications. Using time-resolved fluorescence measurements to deconvolute semi-quantitatively excitation enhancement from emission enhancement, we show that a combination of enhanced excitation and an increased radiative decay rate, both contribute to the observed large enhancement. In accordance to our electric field modelling, however, excitation enhancement is the component that varies most with particle morphology. These findings provide important insights into the mechanism of MEF from AuNSs, and can be used to further guide particle design for high contrast enhancement, enabling the development of MEF biodetection technologies.
Fabrication of heterostructured materials is a strategy to boost the charge-transfer kinetics and the performance of high-rate lithium storage. Here, a facile, lowtemperature method for the synthesis of high-area TiO2 nanospheres containing both anatase and rutile phases is described. The as-prepared materials contain a high concentration of oxygen vacancies facilitating electron conduction in the anatase phase and theoretical calculations provide evidence of a low energy barrier for Li + transport in the rutile phase. The synergy between the two phases renders the shared conduction of electrons through anatase and Li + ions via rutile at high-current rates, leading to the anodes that outperform the alternate TiO2 systems when the combination of capacity at high current densities and cycle stability are considered, displaying a capacity of 95.4 mAh g-1 at 10 A g-1 and a 97.2 % retention of capacity over 500 cycles at 1 A g-1 .
Gold nanostars increase the brightness of weakly-emitting dyes in the near-infrared biological window for cellular imaging with tunable enhancement factors.
Converting solar energy to chemical energy in the form of hydrogen via water splitting is one of the promising strategies to solve the global energy crisis. Hematite, a traditional semiconducting oxide photoelectrode, can only absorb UV and visible parts of the solar spectrum, losing 40% infrared energy. In this paper, we report a novel plasmonic enhanced water splitting photoanode based on hematite-lanthanide upconversion nanocomposites to harvest lost photons below the bandgap of hematite. NaYF4:Er, Yb upconversion nanoparticles can upconvert photons from 980 nm to 510 nm–570 nm within the bandgap of hematite. More importantly, a gold nanodisk array with a plasmonic peak centered ∼1000 nm can further boost the photocurrent by 93-fold. It is demonstrated that the excitation process of lanthanide upconversion nanoparticles can be significantly enhanced by plasmonic nanostructures and can thus improve the water oxidation activity via plasmonic enhanced upconversion and hot electron injection, respectively. This new promising strategy will pave the way for plasmonic enhanced lost photon harvesting for applications in solar energy conversion.
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