We experimentally demonstrate the optical trapping of a single bovine serum albumin (BSA) molecule that has a hydrodynamic radius of 3.4 nm, using a double-nanohole in an Au film. The strong optical ...force in the trap not only stably traps the protein molecule but also unfolds it. The unfolding of the BSA is confirmed by experiments with changing optical power and with changing solution pH. The detection of the trapping event has a signal-to-noise ratio of 33, which shows that the setup is extremely sensitive to detect the presence of a protein, even at the single molecule level.
Optical tweezers have found many applications in biology, but for reasonable intensities, conventional traps are limited to particles >100 nm in size. We use a double-nanohole in a gold film to ...experimentally trap individual nanospheres, including 20 nm polystyrene spheres and 12 nm silica spheres, at a well-defined trapping point. We present statistical studies on the trapping time, showing an exponential dependence on the optical power. Trapping experiments are repeated for different particles and several nanoholes with different gap dimensions. Unusually, smaller particles can be more easily trapped than larger ones with the double-nanohole. The 12 nm silica sphere has a size and a refractive index comparable to the smallest virus particles and has a spherical shape which is the worst case scenario for trapping.
Dietary patterns and daily life habits have been reported to be associated with cognitive function in European populations. We aimed to examine the associations of dietary patterns and daily life ...habits with cognitive function among Chinese old people.
We used 2011-2014 longitudinal data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) comprising 5716 participants with an average age of 82 years. Cognitive function was measured in 2014 based on the results of Mini-Mental Status Examination. Data on participants' dietary patterns and daily life habits were collected during baseline survey. Logistic regression models and general linear models were adopted to estimate the associations of dietary pattern and daily life habit with cognitive function.
Compared with participants in the lowest quartile of lifestyle score, those in the highest quartile had a lower risk of cognitive impairment after controlling for all covariates (OR = 0.52, 95% confidence interval (CI), 0.41-0.65, P < 0.001). Higher lifestyle score was associated with better cognitive function (β = 0.74, 95% CI, 0.55-0.93, P < 0.001). Participants with top quartile of dietary pattern had a lower risk of cognitive impairment (OR = 0.65, 95% CI, 0.51-0.81, P < 0.001). Similar trends were observed in daily life habit, showing that more exercises, moderate alcohol consumption, and non-smoking were associated with improved cognition status (OR = 0.64, 95% CI, 0.53-0.77, P < 0.001).
Our findings suggest that maintaining a healthy dietary pattern and carrying out outdoor exercises is associated with a lower risk of cognitive impairment among Chinese old people.
The rapid increase in global energy demand and the need to replace carbon dioxide (CO2)-emitting fossil fuels with renewable sources have driven interest in chemical storage of intermittent solar and ...wind energy1,2. Particularly attractive is the electrochemical reduction of CO2 to chemical feedstocks, which uses both CO2 and renewable energy3-8. Copper has been the predominant electrocatalyst for this reaction when aiming for more valuable multi-carbon products9-16, and process improvements have been particularly notable when targeting ethylene. However, the energy efficiency and productivity (current density) achieved so far still fall below the values required to produce ethylene at cost-competitive prices. Here we describe Cu-Al electrocatalysts, identified using density functional theory calculations in combination with active machine learning, that efficiently reduce CO2 to ethylene with the highest Faradaic efficiency reported so far. This Faradaic efficiency of over 80 per cent (compared to about 66 per cent for pure Cu) is achieved at a current density of 400 milliamperes per square centimetre (at 1.5 volts versus a reversible hydrogen electrode) and a cathodic-side (half-cell) ethylene power conversion efficiency of 55 ± 2 per cent at 150 milliamperes per square centimetre. We perform computational studies that suggest that the Cu-Al alloys provide multiple sites and surface orientations with near-optimal CO binding for both efficient and selective CO2 reduction17. Furthermore, in situ X-ray absorption measurements reveal that Cu and Al enable a favourable Cu coordination environment that enhances C-C dimerization. These findings illustrate the value of computation and machine learning in guiding the experimental exploration of multi-metallic systems that go beyond the limitations of conventional single-metal electrocatalysts.
A very basic pathway from CO2 to ethyleneEthylene is an important commodity chemical for plastics. It is considered a tractable target for synthesizing renewable resources from carbon dioxide (CO2). ...The challenge is that the performance of the copper electrocatalysts used for this conversion under the required basic reaction conditions suffers from the competing reaction of CO2 with the base to form bicarbonate. Dinh et al. designed an electrode that tolerates the base by optimizing CO2 diffusion to the catalytic sites (see the Perspective by Ager and Lapkin). This catalyst design delivers 70% efficiency for 150 hours.Science, this issue p. 783; see also p. 707Carbon dioxide (CO2) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO2 to ethylene with 70% faradaic efficiency at a potential of −0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at −0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.
The electrochemical reduction of carbon monoxide is a promising approach for the renewable production of carbon-based fuels and chemicals. Copper shows activity toward multi-carbon products from CO ...reduction, with reaction selectivity favoring two-carbon products; however, efficient conversion of CO to higher carbon products such as n-propanol, a liquid fuel, has yet to be achieved. We hypothesize that copper adparticles, possessing a high density of under-coordinated atoms, could serve as preferential sites for n-propanol formation. Density functional theory calculations suggest that copper adparticles increase CO binding energy and stabilize two-carbon intermediates, facilitating coupling between adsorbed *CO and two-carbon intermediates to form three-carbon products. We form adparticle-covered catalysts in-situ by mediating catalyst growth with strong CO chemisorption. The new catalysts exhibit an n-propanol Faradaic efficiency of 23% from CO reduction at an n-propanol partial current density of 11 mA cm
.
Optical trapping has widely affected both the physical and life sciences. Past approaches to optical trapping of nanoscale objects required large optical intensities, often above their damage ...threshold. To achieve more than an order of magnitude reduction in the local intensity required for optical trapping, we present a self-induced back-action (SIBA) optical trap, where the trapped object has an active role in enhancing the restoring force. We demonstrate experimentally trapping of a single 50 nm polystyrene sphere using a SIBA optical trap on the basis of the transmission resonance of a nanoaperture in a metal film. SIBA optical trapping shows a striking departure from previous approaches, which we quantify by comprehensive calculations. The SIBA optical trap enables new opportunities for non-invasive immobilization of a single nanoscale object, such as a virus or a quantum dot. PUBLICATION ABSTRACT
Electrochemical reduction of carbon dioxide (CO^sub 2^) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity1-7. ...Unfortunately, the reaction suffers from slow kinetics7,8 owing to the low local concentration of CO^sub 2^ surrounding typical CO^sub 2^ reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species9,10, but the effect is restricted by the solubility of relevant salts. Large applied electrode potentials can also enhance CO^sub 2^ adsorption11, but this comes at the cost of increased hydrogen (H^sub 2^) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO^sub 2^ close to the active CO^sub 2^ reduction reaction surface. Simulations reveal tenfold higher electric fields associated with metallic nanometre-sized tips compared to quasi-planar electrode regions, and measurements using gold nanoneedles confirm a field-induced reagent concentration that enables the CO^sub 2^ reduction reaction to proceed with a geometric current density for CO of 22 milliamperes per square centimetre at -0.35 volts (overpotential of 0.24 volts). This performance surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxidederived noble metal catalysts. Similarly designed palladium nanoneedle electrocatalysts produce formate with a Faradaic efficiency of more than 90 per cent and an unprecedented geometric current density for formate of 10 milliamperes per square centimetre at -0.2 volts, demonstrating the wider applicability of the field-induced reagent concentration concept.
Conversion of CO2 to CO powered by renewable electricity not only reduces CO2 pollution but also is a means to store renewable energy via chemical production of fuels from CO. However, the kinetics ...of this reaction are slow due its large energetic barrier. We have recently reported CO2 reduction that is considerably enhanced via local electric field concentration at the tips of sharp gold nanostructures. The high local electric field enhances CO2 concentration at the catalytic active sites, lowering the activation barrier. Here we engineer the nucleation and growth of next-generation Au nanostructures. The electroplating overpotential was manipulated to generate an appreciably increased density of honed nanoneedles. Using this approach, we report the first application of sequential electrodeposition to increase the density of sharp tips in CO2 electroreduction. Selective regions of the primary nanoneedles are passivated using a thiol SAM (self-assembled monolayer), and then growth is concentrated atop the uncovered high-energy planes, providing new nucleation sites that ultimately lead to an increase in the density of the nanosharp structures. The two-step process leads to a new record in CO2 to CO reduction, with a geometric current density of 38 mA/cm2 at −0.4 V (vs reversible hydrogen electrode), and a 15-fold improvement over the best prior reports of electrochemical surface area (ECSA) normalized current density.
Abstract
Copper-based materials are promising electrocatalysts for CO
2
reduction. Prior studies show that the mixture of copper (I) and copper (0) at the catalyst surface enhances multi-carbon ...products from CO
2
reduction; however, the stable presence of copper (I) remains the subject of debate. Here we report a copper on copper (I) composite that stabilizes copper (I) during CO
2
reduction through the use of copper nitride as an underlying copper (I) species. We synthesize a copper-on-nitride catalyst that exhibits a Faradaic efficiency of 64 ± 2% for C
2+
products. We achieve a 40-fold enhancement in the ratio of C
2+
to the competing CH
4
compared to the case of pure copper. We further show that the copper-on-nitride catalyst performs stable CO
2
reduction over 30 h. Mechanistic studies suggest that the use of copper nitride contributes to reducing the CO dimerization energy barrier—a rate-limiting step in CO
2
reduction to multi-carbon products.
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