Mechanisms Underlying the Effect of Tea Extracts on In Vitro Digestion of Wheat Starch.

The effect of extracts from four types of tea made from Camelia sinensis (green, white, black, and oolong) on in vitro amylolysis of gelatinized starch and the underlying mechanisms were studied. Of the four extracts, black tea extract (BTE) gave the strongest inhibition of starch digestion and on α-amylase activity. Fluorescence quenching and surface plasmon resonance (SPR) showed compounds in BTE bound to α-amylase more strongly than those in the green, white, and oolong tea extracts. Individual testing of five phenolic compounds abundant in tea extracts showed that theaflavins had a greater inhibitory effect than catechins on α-amylase. SPR showed that theaflavins had much lower equilibrium dissociation constants and therefore bound more tightly to α-amylase than catechins. We conclude that BTE had a stronger inhibitory effect on in vitro enzymatic starch digestion than the other tea extracts, mainly due to the higher content of theaflavins causing stronger inhibition of α-amylase.

Nanobowls-assisted broadband absorber for unbiased Si-based infrared photodetection.

Hot electrons from the nonradiative decay of surface plasmons have drawn extensive attention due to the outstanding performance in realizing below-bandgap photodetection. However, the widely employed metallic nanostructures are normally complex and delicate with a great challenge in large-area fabrication, and there is a great limitation to achieve substantial photoresponse at relatively long wavelengths (e.g., 2000nm) with polarization- and incident-angle independence. In this study, we theoretically and experimentally demonstrate a broadband, omnidirectional, and polarization-insensitive absorber based on wafer-scale silicon honeycomb nanobowls with 20-nm-thick gold overlayer. The average absorption across the long wave near infrared band (LW-NIR, i.e., 1100-2500 nm) is higher than 82%, which is contributed from the random nature and multimode localized plasmonic resonances excited on the side walls of nanobowls. Benefitted from the well-connected thin Au film and relatively low Schottky barrier, the generated hot electrons have a high transport probability to reach Schottky interface and participate in the interfacial charge transfer process. As a result, the hot-electron photodetector under no bias realizes a broadband photodetection up to 2000nm wavelength with a responsivity of 0.145 mA/W, and its cutoff wavelength is predicted up to 3300 nm by fitting the experimental result with Fowler theory. Our proposed Au/Si nanobowls photodetector could open a pathway to further extend the detection wavelength of Si-based photodetectors with a large-area and low-cost fabrication process, which promotes practical hot-electron applications.

Understanding the varying mechanisms between the conformal interlayer and overlayer in the silicon/hematite dual-absorber photoanode for solar water splitting.

Dual-absorber photoelectrodes have been proved to have great potential in the photoelectrochemical (PEC) water splitting application due to their broadband absorption and suitable energy-band position, while the surface/interface issues are still not clearly resolved and understood. Here, during the preparation of a silicon/hematite dual-absorber photoanode achieved via synthesizing a Sn-doped hematite film on the silicon nanowire (SiNW) substrate, we separately introduced the conformal overlayer and interlayer of an Al2O3 thin film by atomic layer deposition. With the thickness-optimized interlayer (overlayer) of the Al2O3 thin film, the photocurrent density at 1.23VRHE can be enhanced from 0.85 mA cm-2 to 1.51 mA cm-2 (1.25 mA cm-2), and the on-set potential has a cathodic shift of ∼0.32 V. Although both the overlayer and interlayer modification can substantially improve the PEC performance, the underlying mechanisms are obviously different. The overlayer can only reduce the carrier recombination on the top surface and in the bulk of the hematite film; in contrast, the interlayer not only passivates the SiNW surface and bottom surface of the hematite film, but also the top surface of the photoanode due to Al3+ thermal diffusion from the bottom to the top surface of the hematite film and the resultant Al2O3 formation. This work deepens our understanding for the roles of the surface and interface engineering in the achievement of high-performance PEC systems based on dual or more absorbers.

In vitro digestibility of starches with different crystalline polymorphs at low α-amylase activity to substrate ratio.

In this study, potato, lotus seed and wheat starch samples with different degree of gelatinization (DG) were prepared and their in vitro digestibility at low α-amylase activity evaluated by measuring the release of reducing sugar. The hydrolysis rate (k) and the final equilibrium concentration (C∞) of the three starches increased with increasing DG. Kinetic analyses showed that the Michaelis-Menten constant (Km) and the catalytic efficiency (kcat/Km) increased with increasing DG, indicative of the increasing affinity and catalytic efficiency of α-amylase with all three starch samples. Of the three starches, lotus seed starch showed a much greater increase in k and kcat/Km than potato and wheat starches as the DG of starch increased. From this study, we concluded that at low activity of α-amylase, DG is a major determinant for the binding affinity and catalytic efficiency of α-amylase to starch and in turn the digestion rate of starch.

Tunable infrared hot-electron photodetection by exciting gap-mode plasmons with wafer-scale gold nanohole arrays.

Due to the strongly concentrated electromagnetic field and the ability to detect the below-bandgap photon energies, surface-plasmon-based photodetections have attracted considerable attention. However, the manipulation of plasmonic resonance is complicated with a high cost in fabrication; moreover, the performance of hot-electron photodetectors is generally unsatisfactorily low. Here, we demonstrated that a tunable absorption can be realized by using the nanohole patterned metal-spacer-metal (MSM) structure, which can be wafer-scale fabricated by the nanosphere lithography technology. The angle- and polarization-insensitive absorption is realized under the excitation of the gap-mode plasmons, which can be facilely manipulated in the near-infrared band by varying the thicknesses and material of the spacer as well as the diameter and period of the nanohole arrays. An asymmetrically bended electrical system is proposed to efficiently convert the highly absorbed photon energies into the photocurrent. Results show that the responsivity of the prepared MSM structure can be up to ∼2.82 mA/W at the wavelength of 1150 nm.

Tin and Oxygen-Vacancy Co-doping into Hematite Photoanode for Improved Photoelectrochemical Performances.

Hematite (α-Fe2O3) material is regarded as a promising candidate for solar-driven water splitting because of the low cost, chemical stability, and appropriate bandgap; however, the corresponding system performances are limited by the poor electrical conductivity, short diffusion length of minority carrier, and sluggish oxygen evolution reaction. Here, we introduce the in situ Sn doping into the nanoworm-like α-Fe2O3 film with ultrasonic spray pyrolysis method. We show that the current density at 1.23 V vs. RHE (Jph@1.23V) under one-sun illumination can be improved from 10 to 130 µA/cm2 after optimizing the Sn dopant density. Moreover, Jph@1.23V can be further enhanced 25-folds compared to the untreated counterpart via the post-rapid thermal process (RTP), which is used to introduce the defect doping of oxygen vacancy. Photoelectrochemical impedance spectrum and Mott-Schottky analysis indicate that the performance improvement can be ascribed to the increased carrier density and the decreased resistances for the charge trapping on the surface states and the surface charge transferring into the electrolyte. X-ray photoelectron spectrum and X-ray diffraction confirm the existence of Sn and oxygen vacancy, and the potential influences of varying levels of Sn doping and oxygen vacancy are discussed. Our work points out one universal approach to efficiently improve the photoelectrochemical performances of the metal oxide semiconductors.

Underlayer engineering into the Sn-doped hematite photoanode for facilitating carrier extraction.

A semiconductor underlayer(s) has been extensively used to improve the performance of photoelectrochemical (PEC) cells. Unfortunately, in many cases, the incorporation of underlayers leads to degraded system performances. A comprehensive study on the functions and manipulations of underlayers is therefore of high significance for achieving high-performance PEC cells. This study indicates that Sn-doped hematite photoanodes decorated with various underlayer materials show substantially distinguished photocurrent responses, leading to qualitatively different PEC cells. With an optimized TiO2 (ITO, Al2O3) underlayer, the photocurrent density at 1.23 V versus RHE can be enhanced from 0.25 to 0.71 (0.59, 0.42) mA cm-2, while it is decreased to 0.14 mA cm-2 by using NiO. Our further analysis reveals that the performance differences come mainly from the distinguished bulk and surface carrier recombination effects, i.e., (1) metal doping (i.e., Ti4+, In3+ and Al3+) from the underlayers improves the conductivity of hematite film and thus reduces the bulk recombination; (2) the underlayers of TiO2, ITO and Al2O3 can effectively suppress the carrier recombination at the bottom/top surfaces of the hematite layer, while the NiO underlayer leads to a higher surface recombination. Our work provides a basis for selecting an underlayer and a general guideline for the interface engineering for high performance photoelectrodes.

Self-improvement of solar water oxidation for the continuously-irradiated hematite photoanode.

Improving bulk- or surface-properties has been found as an effective route to regulate and enhance the photoelectrochemical (PEC) performances of some metal-oxide photoelectrodes. However, both bulk and surface self-improvement resulting from the photocharging (PC) effect is rarely reported and as a result the underlying mechanism of the PC effect is not fully understood. Here, we demonstrate that the hematite photoanode integrated with Sn doping and a TiO2 underlayer shows a substantial increase in the photocurrent density (i.e., from 0.69 to 1.12 mA cm-2 at 1.23 V relative to the standard hydrogen electrode) and a cathodic shift of the onset potential after being irradiated by a one-sun simulator for 12 h. The primary reasons for these can be categorized into two fundamental factors: (1) the enhanced bulk conductivity and the resulting decrease in carrier bulk recombination from the gradually increasing ratio of Fe2+ and Fe3+; (2) the reduced carrier surface recombination from the photogenerated passivation layer. Ultimately, both the bulk and surface electrical properties of the hematite photoanode are substantially self-improved under continuous irradiation. This work deepens the understanding of the PC effect and proves that it is a promising technique for the PEC-performance enhancement of the hematite photoanode.

Gap-mode excitation, manipulation, and refractive-index sensing application by gold nanocube arrays.

The challenges in fabricating two-dimensional metallic nanostructures over large areas, which normally involve expensive and time-consuming nanofabrication techniques, have severely limited the exploration of the related applications based on plasmon-induced effects. Here, we cost-efficiently prepared large-area Au nanocube arrays (NCAs) using only the electrostatic forces between colloidal Au nanocubes and polyelectrolyte layers. This method provides a flexible way for obtaining controlled Au NCAs with various fill fractions and single-cube sizes. When the Au NCAs were arranged to be coupled with a continuous Au film, the plasmonic gap mode could be excited and manipulated, leading to significant and tunable light absorbance from the visible to the near-infrared parts of the spectrum. Besides, the as-prepared Au NCAs were used to construct a prototype refractive-index (RI) sensor, which exhibited excellent stability and sensitivity over 560 nm per RI unit.

Regulating the Silicon/Hematite Microwire Photoanode by the Conformal Al2O3 Intermediate Layer for Water Splitting.

Dual-absorber photoelectrodes have been proved to possess greater potential than the single-absorber systems in the applications of photoelectrochemical (PEC) cells (e.g., solar-driven water splitting); however, the mismatching of the energy bands and substantial carrier recombinations at the two absorber interfaces are normally subsistent. Here, we introduce an intermediate layer of conformal Al2O3 into the silicon/hematite (Si/α-Fe2O3) microwire photoanode for enriching the understanding of the interaction among the interlayer, inner absorber, and outer absorber. Our results show that the Si/Al2O3/α-Fe2O3 microwire photoanode with the thickness-optimized Al2O3 can lead to a substantial increase in the photocurrent from 0.83 to 2.08 mA/cm2 at 1.23 VRHE (under 1 sun irradiation) and an obvious decrease in the onset potential relative to the counterpart without Al2O3. By analyzing the PEC responses under various monochromatic lights, PEC impedance spectroscopy, and intensity-modulated photocurrent spectroscopy, we ascribe the improvements to the fact that the suitable-thickness Al2O3 can passivate the Si microwire surfaces and the bottom surfaces of the α-Fe2O3 film and give rise to Al doping into the post-synthesized α-Fe2O3. These essential causes promote the carrier separation in α-Fe2O3, diminish the photoanode surface recombination rate, and then increase the surface charge-transfer efficiency.

Tunable light absorbance by exciting the plasmonic gap mode for refractive index sensing.

The tunable and narrowband optical response from the surface plasmon resonances usually requires periodic metal nanostructures; however, it is usually expensive and challenging to construct such macroscale and defect-free devices. Herein, we make it possible to obtain a characteristic and sharp absorbance via exciting the plasmonic gap mode, which can be obtained in a large-area sample prepared with relatively low cost. The resonant wavelength can be tuned via changing the bottom-facet area of the top structured metal or the spacer thickness. Furthermore, we design the hexagonal arrangement gold microholes atop the gold continuous film with a spacer, which possesses a sharp reflectance dip from the intense plasmonic gap mode. Numerical calculations show that the resonant wavelength is linearly changed with the varying environmental refractive index (RI). The sensitivity is up to ∼1287 nm per RI unit, and the figure of merit for an RI sensor is over 300.

[Preparation and characterization of monoclonal antibodies to rabies virus CVS-11 strain].

OBJECTIVE: To get the high specific and sensitive mononclonal antibodies against RV. METHODS: The myeloma cell line SP2/0 fused with the spleen cell of 6 - 8 weeks old BALB/c mice immunized with the CVS-11 virus antigen. The hybridized fusing cells were chosen by indirect ELISA detection and the positive hybridizing cells were amplified through mouse abdomen injection and the mouse McAbs ascites was purified by Protein A Sepharose 4 Fast Flow (Pharmacia Company). The specificity and sensitivity of the McAbs was identified by indirect ELISA and indirect DFA test. RESULTS: The cell fusion rate reachs 100% and the indirect ELISA results showed that the McAbs ascites titer were 1 x 10(4), 1 x 10(5), 1 x 10(4) and 1 x 10(5); The immunoglobulin G type McAbs show no cross reaction with other related viruses. CONCLUSION: The high specific and sensitive mononclonal antibodies of RV can be used for rapid RV diagnosis.