Optical tweezers can control the position and orientation of individual colloidal particles in solution. Such control is often desirable but challenging for single-particle spectroscopy and microscopy, especially at the nanoscale. Functional nanoparticles that are optically trapped and manipulated in a three-dimensional (3D) space can serve as freestanding nanoprobes, which provide unique prospects for sensing and mapping the surrounding environment of the nanoparticles and studying their interactions with biological systems. In this perspective, we will first describe the optical forces underlying the optical trapping and manipulation of microscopic particles, then review the combinations and applications of different spectroscopy and microscopy techniques with optical tweezers. Finally, we will discuss the challenges of performing spectroscopy and microscopy on single nanoparticles with optical tweezers, the possible routes to address these challenges, and the new opportunities that will arise.

Constructing graphdiyne-supported transition metal double-atom catalysts to address the challenges of activity and selectivity in the electrochemical nitrogen reduction reaction.

Single-atom-sized Ni–N4 sites embedded in three-dimensional and hierarchically structured carbon exhibit a high catalytic activity for the ORR.

This work reports a plasmonic surface-enhanced Raman scattering (SERS) biosensor that allows for quantitative analysis of hematin in erythrocytes without the need of separating it from hemoglobin (Hb). The biosensor exploits the tunable localized surface plasmon resonance (LSPR) characteristics of multibranched gold nanoparticles (M-AuNPs) and the strong plasmon coupling between an Au thin film and a flexible substrate consisting of M-AuNPs embedded in polydimethylsiloxane (PDMS) (i.e., M-AuNP-embedded PDMS substrate). In the assay, the hematin (or hematin-containing erythrocyte hemolysate) was deposited on Au film surface and covered with M-AuNP-embedded PDMS. Strong SERS signals were generated under excitation at 785 nm; the signals were sensitive to hematin concentration but not to several common coexisting biological substances. The intensities of the SERS signal (at 1623 cm-1) displayed a wide linear range using hematin concentrations in a range of at least ∼1.5 nM-1.1 μM; the limit of detection (LOD) was ∼0.03 ± 0.01 nM at a signal/noise (S/N) of 3. This assay is simple and sensitive without tedious separation procedures, thereby saving time and enhancing efficiency. This biosensor can be used to determine hematin concentration in human erythrocyte cytosols giving concentrations of ∼18.5 ± 4.5 (by averaging eight samples) and 51.5 ± 6.2 μM (by averaging three samples) for healthy and sickle erythrocytes, respectively, making it a potential application in clinical detection.

Discriminative identification of homologous miRNAs in miRNA family with high specificity and sensitivity is crucial for accurate classification, diagnosis and prognosis of breast cancer. Herein, we report a reliable, sensitive, and selective assay by coupling fluorescence resonance energy transfer (FRET) with cascade signal amplification. The strategy is developed by designing two programmable DNA probes that can be triggered to shift from "off" to "on" state in a cascade hybridization reaction in the presence of target miRNA let-7a, leading to the generation of an amplified signal. The assay can detect concentrations as low as ∼3.0 pM let-7a and discriminate let-7a from other highly homologous members in the let-7 miRNA family. Moreover, it can also be used to determine let-7a levels at single-cell resolution and evaluate the drug efficacy of let-7a expression among various molecular types of breast cancer cell lines. The advantage of this assay is a combined result of signal generation and amplification triggered by target miRNA, which can satisfy an assay of analogous miRNA in a downregulated manner with high specificity. It has promising potential as a selective assay for homologous miRNAs in precision medicine.

A molecular signaling pathway of apoptosis induced by photothermal therapy was revealed by surface-enhanced Raman spectroscopy.

A molecular signaling pathway of apoptosis induced by photothermal therapy was revealed by surface-enhanced Raman spectroscopy.

We report a facile and new method to tune the electron transport (ETp) band gaps of proteins (bovine serum albumin, BSA) via doping with other molecules (cyanocobalamin, Vb12). The results indicated that doping with Vb12 can enhance the ETp ability of BSA and reduce its conduction band (CB) and valence band (VB) energy levels, thereby achieving the goal of tuning protein ETp band gaps.

In order to study the flow force characteristics of a new-type submerged spur dike, a 3D mathematical model is developed by using the fluid calculation software Fluent to study the flow force characteristics of the new-type spur dike with tooth-shaped structures under the conditions of different flow velocities, water depths and dike lengths based on the finite volume method and the free surface capture method. Meanwhile, a physical model with the scale of 1∶ 50 is also designed to make a supplementary verification of the flow force of the new spur dike under the conditions of different dike lengths. The numerical simulation results are in good agreement with the model test results. The distribution laws of the flow velocity and water depth of the spur dike's flow field are obtained, and the flow force response laws of the new-type spur dike with tooth-shaped structures under the conditions of different flow velocities, water depths and dike lengths are analyzed, and the response laws of relative dike lengths and the critical submergence degree to the flow force coefficients via dimensional process are further analyzed. And the sensitivity of relative dike lengths and the critical submergence degree to the flow force coefficients are respectively discussed by means of independent analysis. The research results will provide certain technical supports and scientific guidance for the location of the new-type submerged spur dikes in the 12.5 m deep waterway regulation works in the lower reaches of the Yangtze River from Nanjing.

大型混凝土齿形丁坝首次应用于深水航道整治工程中,其与水流相互作用的影响并不清晰.通过理论分析与数值模拟的方法对新型丁坝的壅水特性进行研究,并通过与其它坝型结构对比分析了新型丁坝对过坝水流的影响,进而通过阻挡流量的表征方法对新型丁坝的水流力计算方法进行探讨.研究发现新型丁坝壅水公式能够较为合理地预测其壅水值,且由于基床的存在,新型丁坝对过坝水流的影响较小,同时,通过阻挡流量表征的水流力计算公式形式更为简便.新型丁坝的引入对长江沿岸水沙及生态平衡起到保护作用,其研究成果可为新型丁坝的设计及应用提供科学的理论指导,也对其他新型结构设计具有借鉴价值.

Multibranched gold nanoparticles (M-AuNPs) can serve as photothermal agents for near-infrared (NIR) photothermal therapy (PTT) of cancer, but a major shortcoming is that they tend to strongly scatter NIR light, causing a significant reduction in absorption. This work addresses this issue, based on theoretical simulations and experimental determinations, to enhance the absorption and reduce the scattering of these materials by screening their structural parameters. Our finite-difference time-domain simulations predict that M-AuNPs with a core size of similar to 25 nm, a tip number of 5, and a tip height of similar to 40 nm (i.e., an aspect ratio of similar to 2) are optimal for trapping NIR light and yielding the highest light-to-heat conversion efficiency (eta) and for trapping NIR light of various polarization and incident directions. The predicted M-AuNPs were synthesized by a seed-mediated growth method, and the measured optical properties agreed well with the simulation results. The M-AuNPs were further used as photothermal agents for in vitro killing of MCF-7 cells and in vivo ablation of tumors constructed on nude mice. Nearly all cells died after they were incubated with M-AuNPs and irradiated under an 808 nm laser at a 1.0 W cm(-2) for 10 min. The tumors on the nude mice were also effectively ablated without regrowth during the observation period (20 days) after PTT.

Sediment concentration is one of the main targets of the river and harbor physical model experiments.With narrow measuring range, large measurement error and low repeatability of faults, the existing sedimentconcentration technology restricts the test range and accuracy of physical model experiments. This paper introduces anew wireless real?time sediment concentration measuring instrument. It adopts photoelectric measuring principle,which realizes real?time online sediment concentration measurement by converting light signals into electricalsignals. This paper mainly introduces the basic principle and hardware system design of the sediment concentrationmeasuring instrument. The connection among transmission intensity, scattering intensity, optical power andsediment concentration is studied, and a method is proposed for measuring sediment concentration by combiningtransmission and 90° scattering light. In order to achieve the requirement that the relative error of the sedimentcontent is less than 5%, the algorithm and implementation through multiple experimental studies are realized. Thereliability of the newly developed instrument based on the uncertainty analysis method is analyzed. The experimentdata show that the uncertainly of the sediment concentration measuring instrument is less than 0. 4.

Single-atom-sized catalysts (often called single atom catalysts) are highly desired for maximizing the efficiency of metal atom use. However, their synthesis is a major challenge that largely depends on finding an appropriate supporting substrate to achieve a well-defined and highly dispersed single atom. This work demonstrates, based on density functional theory (DFT) predictions and experimental validations, that graphdiyne is a good substrate for anchoring Fe atoms through the formation of covalent Fe-C bonds to produce graphdiyne-supported single-atom-sized Fe catalysts (Fe-graphdiyne catalysts); moreover, this catalyst shows high catalytic activity to oxygen reduction reactions (ORRs) similar to or even slightly better than the precious metal benchmark (commercial 20 wt % Pt/C catalyst). DFT predicts that the O-2 molecule can bind with an Fe atom, and the electron transformation process of ORRs occurs through a 4e(-) pathway. To validate the theoretical predictions, the Fe-graphdiyne catalyst was then synthesized by a reduction of Fe3+ ions adsorbed on a graphdiyne surface in aqueous solution, and its electrocatalytic activities toward ORR were experimentally evaluated in alkaline electrolytes (0.1 M KOH). The electrochemical measurements indicate that the Fe-graphdiyne catalyst can facilitate the 4e(-) ORR while limiting the 2e(-) transfer reaction, showing a high 4e(-) selectivity for ORRs and a good agreement with DFT predictions. The results presented here demonstrate that graphdiyne can provide a unique platform for synthesizing well-defined and uniform single-atom-sized metal catalysts with high catalytic activity toward ORRs.

The knowledge of the bed shear stress under breaking waves is essential for understanding the sediment transport and beach morphology in the surf zone.The turbulence and vortexes generated by breaking waves have a significant effect on the bed shear stress.Application tests of the bed shear stress measurement under breaking waves by the MEMS flexible hot-film shear stress sensor are conducted in a wave flume.The experimental results show that the sensor can be applied to the measurement of the bed shear stress under breaking waves.Before the breaking point, the direction of the bed shear stress can be determined by the near-bed velocity.The change of the bed shear stress is gentle before wave breaking.The fluctuations and the peak value of the bed shear stress increase after wave breaking.The extreme value of the average maximum bed shear stress along the slope appears after the plunging point.

The appearance of new wall shear stress sensors provides new methods for measuring the underwater bed shear stress in estuarine and coastal engineering.The thermal wall shear stress sensor is affected by the ambient temperature significantly.The relevant research and application of these sensors are inseparable from the accurate calibration.Based on the relationship between the wall shear stress and the pressure gradient along the duct with high aspect ratio, a static calibration device for underwater wall shear stress sensor with temperature control is developed.This device can produce wall shear stress for calibration at different water temperature.The calibration device can provide a maximum water temperature of 35℃.A static calibration experiment of the MEMS flexible hot-film wall shear stress sensor is conducted using the device, and the calibration coefficients under different water temperature conditions are determined.The linear relation between the calibration coefficient B and the water temperature is found.

The movement of sediment at estuary and coast is directly restricted by the bed shear stress.Therefore, the basic research on the influence of the bed shear stress on the sediment movement is important.However, there is no available method for measuring and computing the bed shear stress under a complicated dynamic condition like the wave current.This paper conducts the measurement and test research on the bed shear stress in a long launder of direct current by the new thermal shearometer based on micro-nanotechnology.As the research results show, the thermal shearometer has high response frequency and strong stability.The measuring result reflects the basic law of the bed shear stress with the wave and wave-current effect, and confirms that the method of measuring bed shear stress under wave-current condition with the thermal shearometer is feasible.Meanwhile, a preliminary method to compute the shear stress compounded by wave-current is put forward.It benefits further research on the basic theory of the sediment movement with complicated dynamic effects.

Although bed shear stress is one of the important ways to research the basic theory of sediment movement under the action of complex hydrodynamic force, the effective method for measurement of bed shear stress hasn’t formed yet. By application of the new micro-nanotechnology-based thermal shear stress gauge, this paper experimentally researches the bed shear stress measurement in wave flume. The research shows that the thermal shear stress gauge is with high response frequency and good stability and, the measurement results present the basic laws of variation of bed shear stresses under wave action and confirm the feasibility of measuring bed shear stress with thermal shear stress gauge on condition of complex hydrodynamic force.

Nitrogen-doped graphene quantum dots (N-GQDs) are synthesized at low temperature as a new catalyst allowing electrochemical detection of 2,4,6-trinitrotoluene (TNT). N-GQDs are made by an oxidative ultrasonication of graphene oxide (GO) forming nanometer-sized species, which are then chemically reduced and nitrogen doped by reacting with hydrazine. The as-synthesized N-GQDs have an average diameter of ∼2.5 nm with an N/C atomic ratio of up to ∼6.4%. To detect TNT, TNT is first accumulated on N-GQDs modified glassy carbon (N-GQDs/GC) electrode by holding the electrode at a 0 V versus Ag/AgCl for 150 s in an aqueous TNT solution. Next, the N-GQDs/GC electrode with accumulated TNT is transferred to a fresh PBS solution (0.1 M, pH 7.0, without TNT), where the TNT reduction current at -0.36 V versus Ag/AgCl in a linear scan voltammogram (LSV) shows a linear response to TNT concentration in the aqueous solution from 1 to 400 ppb, with a correlation coefficient of 0.999, a detection limit of 0.2 ppb at a signal/noise (S/N) of 3, and a detection sensitivity of 363 ± 7 mA mM(-1) cm(-2). The detection limit of 0.2 ppb of TNT for this new method is much lower than 2 ppb set by the U.S. Environmental Protection Agency for drinking water. Therefore, N-GQDs allow an electrochemical method for assaying TNT in drinking water to determine if levels of TNT are safe or not.