Collagen-coated agarose-chitosan scaffold used as a skin substitute.

A single biomaterial is disadvantageous for constructing skin in vitro, so a mixed biomaterial is more conducive to skin research. In this study, agarose-chitosan scaffolds with a final concentration of 4% were constructed by freeze-drying, in which the concentration ratios of agarose to chitosan were 1:3, 2:2, and 3:1. The scaffolds were coated with a 3 mg/ml collagen solution, and the mechanical properties were evaluated by studying density, porosity, swelling rate, and degradation rate. The results demonstrated that the agarose-chitosan scaffolds were porous, with porosity reaching 93%. Their densities ranged from 0.1 to 0.16 g/cm3 . Analysis of Young's modulus showed that the mechanical properties of the agarose-chitosan scaffolds were significantly enhanced when the agarose content in the agarose-chitosan scaffolds was increased. Moreover, the density and Young's modulus of the agarose-chitosan scaffolds of different concentration ratios were significantly different (p < 0.01). These scaffolds can withstand a certain amount of external pressure, such as that of human skin, making them more suitable for further skin replacement research. In addition, the results of thiazolyl blue tetrazolium bromide (MTT) cell assay and immunofluorescence staining showed that the collagen-coated agarose-chitosan scaffolds were conducive to keratinocyte proliferation and differentiation. The MTT results revealed significant differences between the agarose-chitosan scaffolds coated with collagen and the agarose-chitosan scaffolds without collagen (p < 0.05). This study provides the potential for in vitro skin research and applications.

Enhanced solar water splitting using plasmon-induced resonance energy transfer and unidirectional charge carrier transport.

Solar water splitting by photoelectrochemical (PEC) reactions is promising for hydrogen production. The gold nanoparticles (AuNPs) are often applied to promote the visible response of wideband photocatalysts. However, in a typical TiO2/AuNPs structure, the opposite transfer direction of excited electrons between AuNPs and TiO2 under visible light and UV light severely limits the solar PEC performance. Here we present a unique Pt/TiO2/Cu2O/NiO/AuNPs photocathode, in which the NiO hole transport layer (HTL) is inserted between AuNPs and Cu2O to achieve unidirectional transport of charge carriers and prominent plasmon-induced resonance energy transfer (PIRET) between AuNPs and Cu2O. The measured applied bias photon-to-current efficiency and the hydrogen production rate under AM 1.5G illumination can reach 1.5% and 16.4 µmol·cm-2·h-1, respectively. This work is original in using the NiO film as the PIRET spacer and provides a promising photoelectrode for energy-efficient solar water splitting.

Broadband and wide-angle light absorption of organic solar cells based on multiple-depths metal grating.

A silver grating containing three grooves with different depths in one period was proposed as the back electrode for improving light absorption in organic solar cells. We found that the broadband absorption enhancement of the active layer covering the visible and near-infrared bands can be obtained due to the excitation of surface plasmon resonance and the multiple resonances of cavity mode. The integrated absorption efficiency of the proposed structure under TM polarization between 350 nm to 900 nm is 57.4%, with consideration of the weight of AM 1.5G solar spectrum, and is increased by 13.4% with respect to the equivalent planar device. Besides, the wide-angle absorption in proposed structure can be observed in the range from 0 to 50 degrees. These findings are of great importance for rationally designing composite nanostructures of metal gratings-based absorbers for sensing and photon-detecting applications.

Zero-energy-state-oriented tunability of spin polarization in zigzag-edged bowtie-shaped graphene nanoflakes under an electric field.

A comprehensive first-principles study of the correlation between zero-energy states and the tunability of the spin-selective semiconducting properties of zigzag-edged bowtie-shaped graphene nanoflakes under an electric field is presented for the first time. We demonstrate that the spin degenerate semiconducting ground state can be lifted by the electric field. In particular, we find that the number of zero-energy states ('the nullity') defined by the structural configuration determines the complexity and efficiency of the tunability of spin polarization. The fine-tuning of spin-dependent properties by the electric field originates from the manipulation of spin-polarized molecular orbital energies. We expect this study to aid the design of more effective and controllable low-dimensional molecular spintronics.

Theoretical Analysis of an Optical Accelerometer Based on Resonant Optical Tunneling Effect.

Acceleration is a significant parameter for monitoring the status of a given objects. This paper presents a novel linear acceleration sensor that functions via a unique physical mechanism, the resonant optical tunneling effect (ROTE). The accelerometer consists of a fixed frame, two elastic cantilevers, and a major cylindrical mass comprised of a resonant cavity that is separated by two air tunneling gaps in the middle. The performance of the proposed sensor was analyzed with a simplified mathematical model, and simulated using finite element modeling. The simulation results showed that the optical Q factor and the sensitivity of the accelerometer reach up to 8.857 × 107 and 9 pm/g, respectively. The linear measurement range of the device is ±130 g. The work bandwidth obtained is located in 10-1500 Hz. The results of this study provide useful guidelines to improve measurement range and resolution of integrated optical acceleration sensors.

A Silicon-Based ROTE Sensor for High-Q and Label-Free Carcinoembryonic Antigen Detection.

This paper presents a biosensor based on the resonant optical tunneling effect (ROTE) for detecting a carcinoembryonic antigen (CEA). In this design, sensing is accomplished through the interaction of the evanescent wave with the CEA immobilized on the sensor's surface. When CEA binds to the anti-CEA, it alters the effective refractive index (RI) on the sensor's surface, leading to shifts in wavelength. This shift can be identified through the cascade coupling of the FP cavity and ROTE cavity in the same mode. Experimental results further show that the shift in resonance wavelength increases with the concentration of CEA. The biosensor responded linearly to CEA concentrations ranging from 1 to 5 ng/mL with a limit of detection (LOD) of 0.5 ng/mL and a total Q factor of 9500. This research introduces a new avenue for identifying biomolecules and cancer biomarkers, which are crucial for early cancer detection.

Synthesis of MoS2 Nanochains by Electrospinning for Ammonia Detection at Room Temperature.

MoS2 nanochains were successfully prepared via facile electrospinning and a hydrothermal process. The morphology of MoS2 nanochains was evaluated by field emission scanning electron microscopy and high-resolution transmission electron microscopy. A slurry composed of the MoS2 nanochains was coated on a silver electrode to detect ammonia. The detection range of ammonia was between 25 and 500 ppm. MoS2 nanochains offered outstanding sensing response, repeatable reproducibility, and excellent selectivity with a detection limit of 720 ppb. The responsiveness of MoS2 nanochains to ammonia remained unchanged for 1 week.

Biosensing Near the Exceptional Point Based on Resonant Optical Tunneling Effect.

Inspired by exceptional point (EP) sensing in non-Hermitian systems, in this work, a label-free biosensor for detecting low-concentration analytes is proposed, via a special multilayer structure: a resonant optical tunneling resonator. Due to the square root topology near the exceptional point, a recognized target analyte perturbs the system deviated from the exceptional point, leading to resolvable modes splitting in the transmission spectrum. The performance of the designed sensor is analyzed by the coupled-mode theory and transfer matrix method, separately. Here, the simulation results demonstrate that the obtained sensitivity is 17,120 nm/imaginary part unit of refractive index (IP) and the theoretical detection limit is 4.2 × 10-8 IP (regarding carcinoembryonic antigen (CEA), the minimum detection value is 1.78 ng). Instead of the typical diffusion manner, the liquid sample is loaded by convection, which can considerably improve the efficiency of sample capture and shorten the response time of the sensor. The sketched sensor may find potential application in the fields of biomedical detection, environment protection, and drinking water safety.

Enhancing plasmonic hot-carrier generation by strong coupling of multiple resonant modes.

Plasmon-induced hot carriers have recently attracted considerable interest, but the energy efficiency in visible light is often low due to the short lifetime of hot carriers and the limited optical absorption of plasmonic architectures. To increase the generation of hot carriers, we propose to exert multiple plasmonic resonant modes and their strong coupling using a metal-dielectric-metal (MDM) nanocavity that comprises an Au nanohole array (AuNHA), a TiO2 thin film and an Au reflector. Unlike common MDM structures, in addition to the Fabry-Pérot mode in the dielectric layer, AuNHA as the top layer is special because it excites the localized surface plasmon resonance (LSPR) mode in the Au nanoholes and launches the gap surface plasmon polariton (GSPP) mode in the Au reflector surface. The spatial field overlapping of the three resonance modes enables strong mode coupling by optimizing the TiO2 thickness, which leads to notably enhanced average IPCE (∼1.5%) and broadband photocurrent (170 µA·cm-2). This MDM structure would be useful for photochemistry and photovoltaics using sunlight.

One-pot synthesis of Cu2O/C@H-TiO2 nanocomposites with enhanced visible-light photocatalytic activity.

As an environment-friendly semiconductor, titanium dioxide (TiO2), which can effectively convert solar energy to chemical energy, is a crucial material in solar energy conversion research. However, it has several technical limitations for environment protection and energy industries, such as low photocatalytic efficiency and a narrow spectrum response. In this study, a unique mesoporous Cu2O/C@H-TiO2 nanocomposite is proposed to solve these issues. Polystyrene beads ((C8H8) n , PS) are utilized as templates to prepare TiO2 hollow microspheres. Cu2O nanocomposites and amorphous carbon are deposited by a one-pot method on the surface of TiO2 hollow spheres. After the heterojunction is formed between the two semiconductor materials, the difference in energy levels can effectively separate the photogenerated e--h+ pairs, thereby greatly improving the photocatalytic efficiency. Furthermore, due to the visible band absorption of Cu2O, the absorption range of the prepared nanocomposites is expanded to the whole solar spectrum. Amorphous carbon, as a Cu2O reduction reaction concomitant product, can further improve the electron conduction characteristics between Cu2O and TiO2. The structure and chemical composition of the obtained nanocomposites are characterized by a series of techniques (such as SEM, EDS, TEM, XRD, FTIR, XPS, DRS, PL, MS etc.). The experimental results of the degradation of methylene blue (MB) aqueous solution demonstrate that the degradation efficiency of Cu2O/C@H-TiO2 nanocomposites is about 3 times as fast as that of pure TiO2 hollow microspheres, and a more absolute degradation can be achieved. Herein, a recyclable photocatalyst with high degradation efficiency and a whole solar spectrum response is proposed and fabricated, and would find useful applications in environment protection, and optoelectronic devices.

Microfluidic Reactors for Plasmonic Photocatalysis Using Gold Nanoparticles.

This work reports a microfluidic reactor that utilizes gold nanoparticles (AuNPs) for the highly efficient photocatalytic degradation of organic pollutants under visible light. The bottom of microchamber has a TiO2 film covering a layer of AuNPs (namely, TiO2/AuNP film) deposited on the F-doped SnO2 (FTO) substrate. The rough surface of FTO helps to increase the surface area and the AuNPs enables the strong absorption of visible light to excite electron/hole pairs, which are then transferred to the TiO2 film for photodegradation. The TiO2 film also isolates the AuNPs from the solution to avoid detachment and photocorrosion. Experiments show that the TiO2/AuNP film has a strong absorption over 400-800 nm and enhances the reaction rate constant by 13 times with respect to the bare TiO2 film for the photodegradation of methylene blue. In addition, the TiO2/AuNP microreactor exhibits a negligible reduction of photoactivity after five cycles of repeated tests, which verifies the protective function of the TiO2 layer. This plasmonic photocatalytic microreactor draws the strengths of microfluidics and plasmonics, and may find potential applications in continuous photocatalytic water treatment and photosynthesis. The fabrication of the microreactor uses manual operation and requires no photolithography, making it simple, easy, and of low cost for real laboratory and field tests.

Continuous artificial synthesis of glucose precursor using enzyme-immobilized microfluidic reactors.

Food production in green crops is severely limited by low activity and poor specificity of D-ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) in natural photosynthesis (NPS). This work presents a scientific solution to overcome this problem by immobilizing RuBisCO into a microfluidic reactor, which demonstrates a continuous production of glucose precursor at 13.8 µmol g-1 RuBisCO min-1 from CO2 and ribulose-1,5-bisphosphate. Experiments show that the RuBisCO immobilization significantly enhances enzyme stabilities (7.2 folds in storage stability, 6.7 folds in thermal stability), and also improves the reusability (90.4% activity retained after 5 cycles of reuse and 78.5% after 10 cycles). This work mimics the NPS pathway with scalable microreactors for continuous synthesis of glucose precursor using very small amount of RuBisCO. Although still far from industrial production, this work demonstrates artificial synthesis of basic food materials by replicating the light-independent reactions of NPS, which may hold the key to food crisis relief and future space colonization.

Optofluidics Refractometers.

Refractometry is a classic analytical method in analytical chemistry and biosensing. By integrating advanced micro- and nano-optical systems with well-developed microfluidics technology, optofluidics are shown to be a powerful, smart and universal platform for refractive index sensing applications. This paper reviews recent work on optofluidic refractometers based on different sensing mechanisms and structures (e.g., photonic crystal/photonic crystal fibers, waveguides, whisper gallery modes and surface plasmon resonance), and traces the performance enhancement due to the synergistic integration of optics and microfluidics. A brief discussion of future trends in optofluidic refractometers, namely volume sensing and resolution enhancement, are also offered.

Cell Density Detector Based on Light Beam Focusing.

Although the lab-on-a-chip system has been successfully applied in a wide variety of fields, the goal of achieving a cell counter with simple operation, low cost, and high accuracy still attracts continuous research efforts. In this paper, the authors explore a cell counter based on light beam focusing to measure the density of adherent cells. In this sensor, the light emitted from the optical fibers is collimated by the collimating lens formed in polydimethylsiloxane (PDMS). The uniformly attached adherent cells act as a convex lens, focusing the collimated light propagated through them. The intensity of the focused light indicates the density of the adherent cells. For Hela cells, a detection limit of 8.3 × 104 cells/mL with a detection range from 0.1 × 106 cells/mL to 1.0 × 106 cells/mL is achieved. This sensor is particularly useful for drug screening, cell pathology analysis, and cancer pre-diagnosis.

A magnetoelastic biosensor based on E2 glycoprotein for wireless detection of classical swine fever virus E2 antibody.

A wireless magnetoelastic (ME) biosensor immobilized with E2 glycoprotein was first developed to detect classical swine fever virus (CSFV) E2 antibody. The detection principle is that a sandwich complex of CSFV E2 - rabbit anti-CSFV E2 antibody - alkaline phosphatase (AP) conjugated goat anti-rabbit IgG formed on the ME sensor surface, with biocatalytic precipitation used to amplify the mass change of antigen-antibody specific binding reaction, induces a significant change in resonance frequency of the biosensor. Due to its magnetostrictive feature, the resonance vibrations and resonance frequency can be actuated and wirelessly monitored through magnetic fields. The experimental results show that resonance frequency shift increases with the augmentation of the CSFV E2 antibody concentration. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and fluorescence microscopy analysis proved that the modification and detection process were successful. The biosensor shows a linear response to the logarithm of CSFV E2 antibody concentrations ranging from 5 ng/mL to 10 µg/mL, with a detection limit (LOD) of 2.466 ng/mL and the sensitivity of 56.2 Hz/µg·mL-1. The study provides a low-cost yet highly-sensitive and wireless method for selective detection of CSFV E2 antibody.

Highly Sensitive and Stretchable Strain Sensor Based on Ag@CNTs.

Due to the rapid development and superb performance of electronic skin, we propose a highly sensitive and stretchable temperature and strain sensor. Silver nanoparticles coated carbon nanowires (Ag@CNT) nanomaterials with different Ag concentrations were synthesized. After the morphology and components of the nanomaterials were demonstrated, the sensors composed of Polydimethylsiloxane (PDMS) and CNTs or Ag@CNTs were prepared via a simple template method. Then, the electronic properties and piezoresistive effects of the sensors were tested. Characterization results present excellent performance of the sensors for the highest gauge factor (GF) of the linear region between 0-17.3% of the sensor with Ag@CNTs1 was 137.6, the sensor with Ag@CNTs2 under the strain in the range of 0-54.8% exhibiting a perfect linearity and the GF of the sensor with Ag@CNTs2 was 14.9.

Optofluidic tunable lenses using laser-induced thermal gradient.

This paper reports a new design of optofluidic tunable lens using a laser-induced thermal gradient. It makes use of two straight chromium strips at the bottom of the microfluidic chamber to absorb the continuous pump laser to heat up the moving benzyl alcohol solution, creating a 2D refractive index gradient in the entrance part between the two hot strips. This design can be regarded as a cascade of a series of refractive lenses, and is distinctively different from the reported liquid lenses that mimic the refractive lens design and the 1D gradient index lens design. CFD simulation shows that a stable thermal lens can be built up within 200 ms. Experiments were conducted to demonstrate the continuous tuning of focal length from initially infinite to the minimum 1.3 mm, as well as the off-axis focusing by offsetting the pump laser spot. Data analyses show the empirical dependences of the focal length on the pump laser intensity and the flow velocity. Compared with previous studies, this tunable lens design enjoys many merits, such as fast tuning speed, aberration-free focusing, remote control, and enabling the use of homogeneous fluids for easy integration with other optofluidic systems.

Synthesis of p-Co3O4/n-TiO2 Nanoparticles for Overall Water Splitting under Visible Light Irradiation.

p-Co3O4/n-TiO2 nanoparticles (~400 nm) for photocatalysis were prepared via carbon assisted method and sol-gel method in this work. The paper also studied the application of visible light illuminated p-Co3O4/n-TiO2 nanocomposites cocatalyst to the overall pure water splitting into H2 and O2. In addition, the H2 evolution rate of the p-Co3O4/n-TiO2 nanocomposites is 25% higher than that of the pure Co3O4 nanoparticles. Besides, according to the results of the characterizations, the scheme of visible light photocatalytic water splitting is proposed, the Co3O4 of the nanocomposites is excited by visible light, and the photo-generated electrons and holes existing on the conduction band of Co3O4 and valence band of TiO2 have endowed the photocatalytic evolution of H2 and O2 with higher efficiency. The optimal evolution rate of H2 and O2 is 8.16 µmol/h·g and 4.0 µmol/h·g, respectively.

Portable microsystem integrates multifunctional dielectrophoresis manipulations and a surface stress biosensor to detect red blood cells for hemolytic anemia.

Hemolytic anemia intensity has been suggested as a vital factor for the growth of certain clinical complications of sickle cell disease. However, there is no effective and rapid diagnostic method. As a powerful platform for bio-particles testing, biosensors integrated with microfluidics offer great potential for a new generation of portable point of care systems. In this paper, we describe a novel portable microsystem consisting of a multifunctional dielectrophoresis manipulations (MDM) device and a surface stress biosensor to separate and detect red blood cells (RBCs) for diagnosis of hemolytic anemia. The peripheral circuit to power the interdigitated electrode array of the MDM device and the surface stress biosensor test platform were integrated into a portable signal system. The MDM includes a preparing region, a focusing region, and a sorting region. Simulation and experimental results show the RBCs trajectories when they are subjected to the positive DEP force, allowing the successful sorting of living/dead RBCs. Separated RBCs are then transported to the biosensor and the capacitance values resulting from the variation of surface stress were measured. The diagnosis of hemolytic anemia can be realized by detecting RBCs and the portable microsystem provides the assessment to the hemolytic anemia patient.

Detection system based on magnetoelastic sensor for classical swine fever virus.

In this paper, a magnetoelastic (ME) sensing system for the detection of classical swine fever virus (CSFV) is presented. The detection system comprises a test paper and a measurement circuit. The test paper consists mainly of an ME biosensor to detect the CSFV. Based on the impedance analysis technique, the measurement circuit is designed to measure the resonance frequency of the ME biosensor. The anti-CSFV IgG is immobilized onto the ME sensor surface to form the ME biosensor through a physical absorption approach. The experimental results show that the shift in the resonance frequency of the ME biosensor increases with the augmentation of the CSFV concentration. The effectiveness of the combination between the anti-CSFV IgG and CSFV is confirmed by the scanning electron microscopy (SEM) images, the sandwich-based enzyme-linked immunosorbent assay (ELISA) analysis, the interference study and the reference biosensor test method. The resonance frequency shift is linearly proportional to the concentration in the range from 0 to 2.5µg/ml, and becomes sub-linear at higher concentrations. The ME biosensor for CSFV detection has a sensitivity of about 95Hz/µg·ml(-1), with a detection limit of 0.6µg/ml.