[Dental pulp stem cells in tooth regeneration: advancement and emerging directions]

Regenerating tissues similar to dental structure with normal function are putatively to be the aim in tooth regeneration filed. Currently, researchers preliminarily achieved tooth regeneration by applying dental pulp stem cells (DPSC) and stem cells from human exfoliated deciduous teeth (SHED). However, the regeneration efficiency remains unstable and needs further investigation. The development of single-cell RNA sequencing and organoid culture system provide potential of precise, targeted and controllable functional regeneration. This article reviews the current state of DPSC/SHED on tooth regeneration, and analyzes characteristics and hotspots of them, aiming to shed light on clinical translational application of stable and efficient tooth regeneration.

[A summary on surveillance system of occupational disease under the framework of National Health Insurance Informatization Project]

The surveillance of occupational disease has entered a new stage ofdevelopment, with the implementation of the national health informatization project. To improve the efficiency and quality of occupational disease monitoring information reporting in this paper, the system architecture and related management regulations, as long as the major changes and achievement of "surveillance system of occupational disease and health hazards information" under the framework of National Health Insurance Informatization Project were elaborated. The deficiencies existing in the system were analyzed, and expectation for the construction of the occupational disease surveillance system was addressed.

[Investigation and analysis of late reporting and under-reporting of occupational diseases from 2018 to 2020 in China]

Objective: To understand the late reporting and the under-reporting of occupational disease from 2018 to 2020 in China and analyze the causes, so as to provide scientific evidence for improving the quality of occupational disease reports in China, timely acquiring the incidence of occupational disease, and assessing the occupational hazards. Methods: From May to December 2021, A total of 320 occupational disease diagnostic institutions were selected for investigation. The original documents of occupational disease diagnosis cases from 2018 to 2020 were compared with the online reported cases, and late reported and under-reported cases of occupational disease were analyzed. Results: A total of 32207 diagnosed cases from 2018 to 2020 were investigated, including 28934 confirmed cases and 3273 cases without occupational disease. The overall late reported rate and under-reported rate of confirmed cases were 20.2% and 2.1%, respectively. There were significant differences in the rate of late reporting and under-reporting of occupational diseases in different regions and different types of diagnostic institutions (P<0.001). The southwest region had the highest rates of late reporting and under-reporting, 61.6% and 7.9% respectively. The late reported rate of all kinds of occupational diseases was about 15.0%, and the under-reported rate was from 1.5.0% to 5.0%. Conclusion: At present, the phenomenon of late reporting and under-reporting occupational diseases is still obvious. It is necessary to strengthen the inspection of occupational disease reporting, improve the quality of occupational disease reporting, and provide scientific basis for the formulation of occupational disease prevention and control policies.

Application of dendritic cells in tumor immunotherapy and progress in the mechanism of anti-tumor effect of Astragalus polysaccharide (APS) modulating dendritic cells: a review

Dendritic cells (DCs) are potent antigen-presenting cells (APCs) that are essential in mediating the body's natural and adaptive immune responses. The body can regulate the function of DCs in various ways to enhance their antitumor effects. In the tumour microenvironment (TME), antigen-specific T cell responses are initiated through DC processing and delivery of tumour-associated antigens (TAAs); conversely, tumour cells inhibit DC recruitment by releasing metabolites, cytokines and other regulatory TME and function. Different subpopulations of DCs exist in tumour tissues, and their functions vary. Insight into DC subgroups in TME allows assessment of the effectiveness of tumour immunotherapy. Astragalus polysaccharide (APS) is the main component of the Chinese herb Astragalus membranaceus. The study found that the antitumor effects of APS are closely related to DCs. APS can promote the expression of surface molecules CD80 and CD86, promote the maturation of DCs, and activate CTL to exert antitumor effects. We reviewed the application of DCs in tumor immunotherapy and the mechanism of modulation of DCs by Astragalus polysaccharide to provide new directions and strategies for tumor therapy and new drug development.

[Early histological changes detected by confocal microscopy in patients with advanced keratoconus receiving collagen cross-linking therapy]

Objective: To investigate the early histological changes by confocal microscopy of patients with advanced keratoconus receiving collagen cross-linking therapy. Methods: In this prospective case series study, confocal microscopy was used to observe 23 patients (32 eyes) who were diagnosed with advanced keratoconus and treated with collagen cross-linking at the Department of Ophthalmology, Chinese PLA General Hospital from September 2017 to March 2019, aged (26±10) year. All patients were examined before and at 1 week, 1 month and 3 months after the therapy. The tissue structure changes, the density of nerve fibers, stromal cells and endothelial cells, and the depth of the corneal stroma were recorded and compared. The overall differences at different times were compared by repeated measurement analysis of variance or Friedman test, and the pairwise comparison was corrected by LSD-t test or Bonferroni test. Results: One week after collagen cross-linking, the epithelial cells were in the repair stage, showing an increased nucleolar size and an enhanced reflection, and the activated cells could be detected under the epithelium. The superficial corneal stroma was swollen and spongiform, while the deep corneal stroma was patchy or cord-like, scattered and with a strong reflection. One month after the therapy, epithelial cells recovered, subepithelial nerves began to grow, the superficial corneal stroma still showed a spongy structure, and the reflection was further enhanced. The activation of the deep corneal stroma exhibited as thicker plaques or cord-like structure. Three months after the therapy, the continuous elongation of single nerve fibers could be detected occasionally. There was statistically significant difference in the density of nerve fibers before and early after the therapy (F=233.30, P<0.001). Compared with the preoperative value [(14.60±2.57) mm/mm²], the density of subepithelial nerve fibers decreased significantly in the early postoperative period, which was (0.51±0.31), (3.65±2.21) and (8.50± 4.02) mm/mm², respectively, at 1 week, 1 month and 3 months, and there were significant differences between different time points (all P<0.05). There was also statistically significant differences in the density of anterior stromal cells before and early after the therapy (χ²=92.48, P<0.001). Compared with the preoperative value [347.00(345.00,395.75) cells/mm²] the density of anterior stromal cells decreased significantly in the early postoperative period, which was 2.00(1.00,5.75), 2.50(1.00,5.75) and 79.00(64.25,94.00) cells/mm², respectively, at 1 week, 1 month and 3 months, and there were significant differences between different time points (all P<0.05). Within 3 months after the therapy, the depth of the corneal stroma observed by confocal microscopy ranged from 245 to 536 μm, with an average of (400.56±86.12) μm. Histologically, the depth of the corneal stroma ranged from 245 to 536 μm [average, (402.13±89.20) μm], from 251 to 527 μm [average, (399.88±85.92) μm] and from 259 to 530 μm [average, (399.69±85.94) μm] at 1 week, 1 month and 3 months, respectively, with no significant difference (F=0.797, P=0.455). There was no significant difference in the density of posterior stromal cells [(260.6±33.2) cells/mm² preoperatively, (264.4±44.5) cells/mm² at 1 week, (263.9±37.6) cells/mm² at 1 month and (266.3±40.2) cells/mm² at 3 months] and endothelial cells [(2 707±152.6) cells/mm² preoperatively, (2 704±148.5) cells/mm² at 1 week, (2 705±152.6) cells/mm² at 1 month and (2 704±150.1) cells/mm² at 3 months] between different time points (F=1.380, 1.011; P=0.259, 0.351). Conclusions: Confocal microscopy is able to clearly document the early morphological characteristics after collagen cross-linking in the treatment of keratoconus, including the epithelial and subepithelial nerve injury repair, the spongiform superficial corneal stroma, the patchy or cord-like deep corneal stroma, and the relatively stable stromal depth change.

An optical neural chip for implementing complex-valued neural network

Complex-valued neural networks have many advantages over their real-valued counterparts. Conventional digital electronic computing platforms are incapable of executing truly complex-valued representations and operations. In contrast, optical computing platforms that encode information in both phase and magnitude can execute complex arithmetic by optical interference, offering significantly enhanced computational speed and energy efficiency. However, to date, most demonstrations of optical neural networks still only utilize conventional real-valued frameworks that are designed for digital computers, forfeiting many of the advantages of optical computing such as efficient complex-valued operations. In this article, we highlight an optical neural chip (ONC) that implements truly complex-valued neural networks. We benchmark the performance of our complex-valued ONC in four settings: simple Boolean tasks, species classification of an Iris dataset, classifying nonlinear datasets (Circle and Spiral), and handwriting recognition. Strong learning capabilities (i.e., high accuracy, fast convergence and the capability to construct nonlinear decision boundaries) are achieved by our complex-valued ONC compared to its real-valued counterpart.

[Advances in esophageal microbiota and esophageal related diseases]

Esophagus, as the pipe connecting oral cavity and stomach, has unique anatomical structure and physiological functions. The related diseases including esophageal cancer and precancerous lesions are the ones of major public health problems in China. The pathogenesis of esophageal diseases is still not clear. The exploration of correlation between the changes of esophageal microbiota and esophageal diseases becomes a new breakthrough in the study of etiology. Previous studies have found enrichment of gram-positive bacteria in the normal esophagus, while a decrease in diversity of bacteria and a dominant gram-negative anaerobe in diseased esophagus. Although much progress has been made in the study of esophageal microbiota, the standard method of how to accurately and noninvasively collect esophageal microbiota is still lack, which is an important part of the esophageal microbial research.

[Changes of intestinal mucosal barrier in mice with chronic ulcerative colitis]

Objective: To study the damage and mechanism of intestinal mucosal barrier function in mice with ulcerative colitis induced by Dextran sulphate sodium (DSS). Methods: Mice models of chronic ulcerative colitis induced by DSS were established. The mice were completely randomized into normal control group and DSS group, 25 mice in each group. The body weight and colon length of the mice were monitored. The pathological examination of colon tissue was confirmed the success of the model and assessed the integrity of the colonic mucosal barrier; Evan's Blue's intestinal permeability analysis assessed the function of colon mucosal barrier; immunofluorescence staining and Western blot were used to evaluate the expression of intestinal mucosal barrier integrity-related proteins. Results: Compared with the normal control group, the DSS group had lower body weight [(25.6±0.7)g vs (23.5±0.7)g, t=2.14, P<0.05], and the colon length was shorter [(7.3±0.4)cm vs (5.6±0.2)cm, t=3.975, P<0.001]; colonic pathological results showed that the intestinal mucosa became thinner and part of the intestinal mucosa was defective; Evan's Blue instilled into the intestinal lumen was more abundant into the intestinal mucosa, and the optical density at 620 nm (OD(620))/colon tissue weight (g) was higher [(0.11±0.01) vs (0.15±0.01), t=4.174, P<0.05]; immunofluorescence and Western blot results showed lower expression of ZO-1, Claudin-1, and F-actin in colonic mucosa. Conclusion: The structure and function of intestinal mucosal barrier in DSS-induced chronic ulcerative colitis mice is impaired.

Sculpting nanoparticle dynamics for single-bacteria-level screening and direct binding-efficiency measurement

Particle trapping and binding in optical potential wells provide a versatile platform for various biomedical applications. However, implementation systems to study multi-particle contact interactions in an optical lattice remain rare. By configuring an optofluidic lattice, we demonstrate the precise control of particle interactions and functions such as controlling aggregation and multi-hopping. The mean residence time of a single particle is found considerably reduced from 7 s, as predicted by Kramer’s theory, to 0.6 s, owing to the mechanical interactions among aggregated particles. The optofluidic lattice also enables single-bacteria-level screening of biological binding agents such as antibodies through particle-enabled bacteria hopping. The binding efficiency of antibodies could be determined directly, selectively, quantitatively and efficiently. This work enriches the fundamental mechanisms of particle kinetics and offers new possibilities for probing and utilising unprecedented biomolecule interactions at single-bacteria level.

Optical trapping is a versatile tool for biomedical applications. Here, the authors use an optofluidic lattice to achieve controllable multi-particle hopping and demonstrate single-bacteria-level screening and measurement of binding efficiency of biological binding agents through particle-enabled bacteria hopping.

Haemolysis during sodium dimercaptosulphonate therapy for Wilson's disease in G6PD-deficient patients: First report of two cases

WHAT IS KNOWN AND OBJECTIVE

Wilson's disease (WD) is an inherited disorder in which defective biliary excretion of copper leads to its accumulation. Sodium dimercaptosulphonate (DMPS) is used as the primary therapy in China.

CASE DESCRIPTION

We report two cases, with WD and G6PD deficiency, who developed haemolysis on treatment with DMPS, without any other known risk. After withdrawal of DMPS and administration of dexamethasone and packed red blood cells, the patients recovered.

WHAT IS NEW AND CONCLUSION

Clinicians should keep in mind haemolysis as a potentially life-threatening side effect of DMPS in patients with G6PD.

Tunable Polarization Conversion and Rotation based on a Reconfigurable Metasurface

Polarization is an important property of electromagnetic (EM) wave and different polarization manipulations are required for varied optical applications. Here we report a reconfigurable metasurface which achieves both the polarization conversion and the polarization rotation in THz regime. The metasurface is reconfigured through the micro-electro-mechanical-systems (MEMS) actuation. The cross polarization transmittance from a linear polarized incidence is experimentally tuned from 0 to 28% at 2.66 THz. In addition, the polarization rotation angle is effectively changed from −12.8° to 13.1° at 1.78 THz. The tunable bi-functional metasurface for polarization conversion and the polarization rotation can be flexibly applied in various applications such as imaging, polarization microscopy and material analysis, etc.

High-resolution and multi-range particle separation by microscopic vibration in an optofluidic chip

An optofluidic chip is demonstrated in experiments for high-resolution and multi-range particle separation through the optically-induced microscopic vibration effect, where nanoparticles are trapped in loosely overdamped optical potential wells created with combined optical and fluidic constraints. It is the first demonstration of separating single nanoparticles with diameters ranging from 60 to 100 nm with a resolution of 10 nm. Nanoparticles vibrate with an amplitude of 3-7 μm in the loosely overdamped potential wells in the microchannel. The proposed optofluidic device is capable of high-resolution particle separation at both nanoscale and microscale without reconfiguring the device. The separation of bacteria from other larger cells is accomplished using the same chip and operation conditions. The unique trapping mechanism and the superb performance in high-resolution and multi-range particle separation of the proposed optofluidic chip promise great potential for a diverse range of biomedical applications.

[Effects of cell-to-cell communication and histone acetyltransferase on the change of osteogenic differentiation ability among single-cell clones from healthy periodontium with heterogeneity of osteogenic differentiation abilities]

Objective: To investigate the effect of cell-to-cell communication amongst single-cell clones from healthy periodontium with different osteogenic differentiation potentials on change of osteogenic differentiation capabilities and the role histone acetyltransferase partaken in this process. Methods: In order to research the change of osteogenic differentiation ability via cell-to-cell communication, indirect co-culture method was used by placing two single-cell clones with different osteogenesis potentials in each of the 6-well plates. Blank control, weak and strong osteogenic groups were set up, corresponding to Transwell chambers with blank, cells of weak osteogenesis ability and cells of strong osteogenesis ability, respectively. Each group was made in triplicate. After co-culture for four days, Transwell chamber was removed. Quantitative real-time PCR (qPCR) and alizarin red staining were employed to detect the change of osteogenic differentiation ability. The acetylation level of H3 was measured by using Western blotting. Histone acetyltransferases were detected by qPCR. Results: Single-cell clones were ensured from mesenchymal stem cells by flow cytometer, the positive expression of CD29, CD90, CD105, CD146 was (99.80±0.02)%, (99.36±0.18)%, (99.41±0.05)% and (95.10±2.11)%, respectively. And CD31 and CD34 expression were (0.29±0.11)% and (0.22±0.13)%, respectively. Alizarin red and oil red O staining confirmed that single-cell clones had the abilities of adipogenesis and osteogenesis. Alkaline phosphatase (ALP) and alizarin red staining indicated that different single-cell clones were heterogeneity in osteogenesis differentiation. Indirect co-culture indicated that the mRNA expression of osteocalcin (OCN) were 14.24±5.60 and 4.78±2.90, respectively and Runt-related transcription factor 2 (RUNX2) were 2.75±1.44 and 1.61±0.44, respectively, in strong and weak osteogenic groups. They were significantly higher compared to the blank group (the mRNA expression of OCN and RUNX2 were 1.00±0.47 and 1.00±0.39, respectively). The expression of OCN and RUNX2 were also higher in strong osteogenic group than that in weak osteogenic group (P<0.05). The mean gray level of the acetylation of H3 in strong osteogenic group (0.76±0.09) and weak osteogenic group (0.54±0.12) were also higher than that in the blank group (0.30±0.04)(P<0.05). qPCR results showed that KAT6A in strong osteogenic group exhibiting higher expression (P<0.05) compared to weak osteogenic group and the blank group, which were corresponding to the changes of acetylation levels. Conclusions: Single-cell clones from healthy periodontium showed heterogeneity in osteogenic differentiation abilities. Single-cell clones with strong osteogenesis abilities had an advantage over others by promoting others' osteogenesis differentiation and this change mediated by cell-to-cell communication might be caused by modulating KAT6A to affect the acetylation level of histone.

Correction: Optofluidic lens with low spherical and low field curvature aberrations

Correction for 'Optofluidic lens with low spherical and low field curvature aberrations' by H. T. Zhao et al., Lab Chip, 2016, 16, 1617-1624.

Optofluidic lens with low spherical and low field curvature aberrations

This paper reports an optofluidic lens with low spherical and low field curvature aberrations through the desired refractive index profile by precisely controlling the mixing between ethylene glycol and deionized water in an optofluidic chip. The experimental results demonstrate that the spherical aberration is reduced to 19.5 μm and the full width at half maximum of the focal point is 7.8 μm with a wide divergence angle of 35 degrees. In addition, the optofluidic lens can focus light at different off-axis positions on the focal plane with Δx' < 6.8 μm and at opposite transverse positions with |Δy - Δy'| < 5.7 μm. This is the first demonstration of a special optofluidic lens that significantly reduces both the spherical and field curvature aberrations, which enhances the focusing power and facilitates multiple light source illumination using a single lens. It is anticipated to have high potential for applications such as on-chip light manipulation, sample illumination and multiplexed detection.

Water's tensile strength measured using an optofluidic chip

In this paper, for the first time, the tensile strength of water is directly measured using an optofluidic chip based on the displacement of air-water interface deformation with homogeneous nucleation. When water in a microchannel is stretched dynamically via laser-induced shock reflection at the air-water interface, the shock pressures are determined by measuring the displacements of the deformed interface. Observation of the vapor bubbles is used as a probe to identify the cavitation threshold with a critical distance, and the tensile strength of water at 20 °C is measured to be -33.3 ± 2.8 MPa. This method can be extended to investigate the tensile strength of other soft materials such as glycerol, which is measured to be -59.8 ± 10.7 MPa at 20 °C.

Droplet generation via a single bubble transformation in a nanofluidic channel

Here we report the first demonstration on droplet generation from the transformation of a single bubble in a nanofluidic channel by a laser-induced jet. A viscous two-dimensional Rayleigh-Plesset-type model is derived to describe the bubble dynamics in the nanofluidic channel, which accounts for the effect of shear stresses from the channel wall. The droplet generation (number and volume) is investigated experimentally by controlling the jet velocity via laser energy and distance. This study expands the understanding of jetting in the nanofluidic channel and demonstrates a novel method for femtoliter-volume single or multiple droplet formation. It is envisioned that this work will open new doors in on-demand generation of nanodroplets.

Biological factors in plasma from diabetes mellitus patients enhance hyperglycaemia and pulsatile shear stress-induced endothelial cell apoptosis

People suffering from Diabetes Mellitus (DM) are prone to an array of vascular complications leading to end organ damage. The hallmark of these vascular complications is endothelium dysfunction, which is caused by endothelial cell (EC) apoptosis. Although the endothelial cell (EC) dysfunction induced by hyperglycaemia and fluid shear stress has been studied, the effects of biological factors in the blood of DM patients on EC integrity have not been reported in the in vitro models that mimic the physiological pulsatile nature of the vascular system. This study reports the development of a hemodynamic lab-on-a-chip system to investigate this issue. The pulsatile flow was applied to a monolayer of endothelial cells expressing a fluorescence resonance energy transfer (FRET)-based biosensor that changes colour from green to blue in response to caspase-3 activation during apoptosis. Plasma samples from healthy volunteers and DM patients were compared to identify biological factors that are critical to endothelial disruption. Three types of microchannels were designed to simulate the blood vessels under healthy and partially blocked pathological conditions. The results showed that EC apoptosis rates increased with increasing glucose concentration and levels of shear stress. The rates of apoptosis further increased by a factor of 1.4-2.3 for hyperglycaemic plasma under all dynamic conditions. Under static conditions, little difference was detected in the rate of EC apoptosis between experiments using plasma from DM patients and glucose medium, suggesting that the effects of hyperglycaemia and biological factors on the induction of EC apoptosis are all shear flow-dependent. A proteomics study was then conducted to identify biological factors, demonstrating that the levels of eight proteins, including haptoglobin and clusterin, were significantly down-regulated, while six proteins, including apolipoprotein C-III, were significantly up-regulated in the plasma of DM patients compared to healthy volunteers. This hemodynamic lab-on-a-chip system can serve as a high throughput platform to assess the risk of vascular complications of DM patients and to determine the effects of therapeutics or other interventions on EC apoptosis.

Droplet optofluidic imaging for λ-bacteriophage detection via co-culture with host cell Escherichia coli

Bacteriophages are considered as attractive indicators for determining drinking water quality since its concentration is strongly correlated with virus concentrations in water samples. Previously, bacteriophage detection was based on a plague assay that required a complicated labelling technique and a time-consuming culture assay. Here, for the first time, a label-free bacteriophage detection is reported by using droplet optofluidic imaging, which uses host-cell-containing microdroplets as reaction carriers for bacteriophage infection due to a higher contact ratio. The optofluidic imaging is based on the effective refractive index changes in the microdroplet correlated with the growth rate of the infected host cells, which is highly sensitive, i.e. can detect one E. coli cell. The droplet optofluidic system is not only used in drinking water quality monitoring, but also has high potential applications for pathogenic bacteria detection in clinical diagnosis and food industry.

A pseudo-planar metasurface for a polarization rotator

New demonstrations of effective interaction between light and artificially electromagnetic interface, or the metasurface, have stimulated intensive research interests on control of light to realize applications in beam steering, optical imaging and light focusing, etc. Here we reported a new type of planar metasurface of which every individual metamolecule is single metallic layer with stereo structure and the metasurface is name as Pseudo-Planar Metasurface (PPM). The metamolecule of the PPM is a chiral structure and therefore derives significant optical activity.

Study of endothelial cell apoptosis using fluorescence resonance energy transfer (FRET) biosensor cell line with hemodynamic microfluidic chip system

To better understand how hyperglycemia induces endothelial cell dysfunction under the diabetic conditions, a hemodynamic microfluidic chip system was developed. The system combines a caspase-3-based fluorescence resonance energy transfer (FRET) biosensor cell line which can detect endothelial cell apoptosis in real-time, post-treatment effect and with a limited cell sample, by using a microfluidic chip which can mimic the physiological pulsatile flow profile in the blood vessel. The caspase-3-based FRET biosensor endothelial cell line (HUVEC-C3) can produce a FRET-based sensor protein capable of probing caspase-3 activation. When the endothelial cells undergo apoptosis, the color of the sensor cells changes from green to blue, thus sensing apoptosis. A double-labeling fluorescent technique (yo pro-1 and propidium iodide) was used to validate the findings revealed by the FRET-based caspase sensor. The results show high rates of apoptosis and necrosis of endothelial cells when high glucose concentration was applied in our hemodynamic microfluidic chip combined with an exhaustive pulsatile flow profile. The two apoptosis detection techniques (fluorescent method and FRET biosensor) are comparable; but FRET biosensor offers more advantages such as real-time observation and a convenient operating process to generate more accurate and reliable data. Furthermore, the activation of the FRET biosensor also confirms the endothelial cell apoptosis induced by the abnormal pulsatile shear stress and high glucose concentration is through caspase-3 pathway. A 12% apoptotic rate (nearly a 4-fold increase compared to the static condition) was observed when the endothelial cells were exposed to a high glucose concentration of 20 mM under 2 h exhaustive pulsatile shear stress of 30 dyne cm(-2) and followed with another 10 h normal pulsatile shear stress of 15 dyne cm(-2). Therefore, the most important finding of this study is to develop a novel endothelial cell apoptosis detection method, which combines the microfluidic chip system and FRET biosensor. This finding may provide new insight into how glucose causes endothelial cell dysfunction, which is the major cause of diabetes-derived complications.

Microelectromechanical Maltese-cross metamaterial with tunable terahertz anisotropy

Dichroic polarizers and waveplates exploiting anisotropic materials have vast applications in displays and numerous optical components, such as filters, beamsplitters and isolators. Artificial anisotropic media were recently suggested for the realization of negative refraction, cloaking, hyperlenses, and controlling luminescence. However, extending these applications into the terahertz domain is hampered by a lack of natural anisotropic media, while artificial metamaterials offer a strong engineered anisotropic response. Here we demonstrate a terahertz metamaterial with anisotropy tunable from positive to negative values. It is based on the Maltese-cross pattern, where anisotropy is induced by breaking the four-fold symmetry of the cross by displacing one of its beams. The symmetry breaking permits the excitation of a Fano mode active for one of the polarization eigenstates controlled by actuators using microelectromechanical systems. The metamaterial offers new opportunities for the development of terahertz variable waveplates, tunable filters and polarimetry.

Single cell membrane poration by bubble-induced microjets in a microfluidic chip

This paper demonstrates membrane poration of a single suspension cell due to a fast liquid microjet. The jet is formed during the collapse of a laser induced bubble created at a variable stand-off distance from the target cell. The cell is trapped by a converging structure within a microfluidic chip. The asymmetrical growth and collapse of the cavitation bubble next to the cell lead to the microjetting, which deforms and porates the cell membrane. In the experiments, the membrane porations of myeloma cells are probed with the uptake of trypan blue. Time-resolved studies of the diffusion of trypan blue show a marked dependency on the bubble dynamics, i.e. the stand-off distance. The penetration length of the dye increases with shorter distances. Numerical simulations of the diffusion process agree with larger pores formed on the cell membrane. This method allows for a fast, repeatable, and localized rupture of membranes of individual cells in suspension.

Transformation optofluidics for large-angle light bending and tuning

Transformation optics is a new art of light bending by designing materials with spatially variable parameters for developing wave-manipulation devices. Here, we introduce a transformation optofluidic Y-branch splitter with large-angle bending and tuning based on the design of a spatially variable index. Differing from traditional splitters, the optofluidic splitter is achieved in an inhomogeneous medium by coordinate transformation. The designed bidirectional gradient index (GRIN) distribution can be achieved practically by the convection-diffusion process of liquid flowing streams. The transformation optofluidic splitter can achieve a much larger split angle with little bend loss than the traditional ones. In the experiments, a large tunable split angle up to 30° is achieved by tuning the flow rates, allowing optical signals to be freely transferred to different channels. Besides the symmetrical branch splitting, asymmetrical Y-branch splitting with approximately equal power splitting is also demonstrated by changing the composition of the liquids. The optofluidic splitter has high potential applications in biological, chemical and biomedical solution measurement and detection.

Force-induced optical nonlinearity and Kerr-like coefficient in opto-mechanical ring resonators

This paper demonstrates the optical nonlinearity in opto-mechanical ring resonators that consist of a bus waveguide and two ring resonators, which is induced by the optical gradient force and characterized by the Kerr-like coefficient. Each ring resonator has a free-hanging arc that is perpendicularly deformable by an optical gradient force and subsequently this deformation changes the effective refractive index (ERI) of the ring resonator. The change of the ERI induces optical nonlinearity into the system, which is described by an equivalent Kerr coefficient (Kerr-like coefficient). Based on the experimental results, the Kerr-like coefficient of the ring resonator system falls in the range from 7.64 × 10(-12) to 2.01 × 10(-10) m(2)W(-1), which is at least 6-order higher than the silicon's Kerr coefficient. The dramatically improved optical nonlinearity in the opto-mechanical ring resonators promises potential applications in low power optical signal processing, modulation and bio-sensing.

A nano-opto-mechanical pressure sensor via ring resonator

This paper reports a nano-opto-mechanical pressure sensor based on nano-scaled ring resonator. The pressure is measured through the output spectrum shift which is induced via mechanical deformation of the ring resonator. The sensitivity as high as 1.47 pm/kPa has been experimentally achieved which agrees with numerical prediction. Due to the strong variation of sensitivity with different ring radius and thickness of the diaphragm, the pressure sensor can be used to form an array structure to detect the pressure distribution in highly accurate measurement with low-cost advantages. The nano-opto-mechanical pressure sensor has potential applications such as shear stress displacement detection, pressure wave detector and pressure mapping etc.

Band gap opening of graphene by doping small boron nitride domains

Boron nitride (BN) domains are easily formed in the basal plane of graphene due to phase separation. With first-principles calculations, it is demonstrated theoretically that the band gap of graphene can be opened effectively around K (or K') points by introducing small BN domains. It is also found that random doping with boron or nitrogen is possible to open a small gap in the Dirac points, except for the modulation of the Fermi level. The surface charges which belong to the π states near Dirac points are found to be redistributed locally. The charge redistribution is attributed to the change of localized potential due to doping effects. The band opening induced by the doped BN domain is found to be due to the breaking of localized symmetry of the potential. Therefore, doping graphene with BN domains is an effective method to open a band gap for carbon-based next-generation microelectronic devices.

A tunable 3D optofluidic waveguide dye laser via two centrifugal Dean flow streams

This paper presents a tunable optofluidic waveguide dye laser utilizing two centrifugal Dean flows. The centrifugal Dean flow increases the light confinement of the dye laser by shaping a three-dimensional (3D) liquid waveguide from curved microchannels. The active medium with the laser dye is dissolved in the liquid core and pumped with an external pump laser to produce stimulated emission. The laser's Fabry-Pérot microcavity is formed with a pair of aligned gold-coated fiber facets to amplify the fluorescent emission. The advantage of the 3D optofluidic waveguide dye laser is its higher efficiency, thus to obtain lasing at a reduced threshold (60%) with higher output energy. The demonstrated slope efficiency is at least 3-fold higher than its traditional two-dimensional equivalent. In addition, the laser output energy can be varied on demand by tuning the flow rates of the two flows. This technique provides a versatile platform for high potential applications microfluidic biosensor and bioanalysis.

Fast on-demand droplet fusion using transient cavitation bubbles

A method for on-demand droplet fusion in a microfluidic channel is presented using the flow created from a single explosively expanding cavitation bubble. We test the technique for water-in-oil droplets, which are produced using a T-junction design in a microfluidic chip. The cavitation bubble is created with a pulsed laser beam focused into one droplet. High-speed photography of the dynamics reveals that the droplet fusion can be induced within a few tens of microseconds and is caused by the rapid thinning of the continuous phase film separating the droplets. The cavitation bubble collapses and re-condenses into the droplet. Droplet fusion is demonstrated for static and moving droplets, and for droplets of equal and unequal sizes. Furthermore, we reveal the diffusion dominated mixing flow and the transport of a single encapsulated cell into a fused droplet. This laser-based droplet fusion technique may find applications in micro-droplet based chemical synthesis and bioassays.

An optofluidic prism tuned by two laminar flows

This paper presents a tunable optofluidic prism based on the configuration of two laminar flow streams with different refractive indices in a triangular chamber. The chambers with 70° and 90° apex angles are designed based on simulation results, which provide the optimum working range and avoid recirculating flows in the chambers. In addition, a hydrodynamic model has been developed to predict the tuning of the prisms by the variation in the flow rates. Prisms with different refractive indices are realized using benzyl alcohol and deionized (DI) water as the inner liquids, respectively. The mixture of ethylene glycol and DI water with an effective refractive index matched to that of the microchannel is used as the outer liquid. The apex angle of the prism is tuned from 75° to 135° by adjusting the ratio of the two flow rates. Subsequently, the deviation angle of the output light beam is tuned from -13.5° to 22°. One of the new features of this optofluidic prism is its capability to transform from a symmetric to an asymmetric prism with the assistance of a third flow. Two optical behaviours have been performed using the optofluidic prism. First, parallel light beam scanning is achieved with a constant deviation angle of 10° and a tuning range of 60 μm using the asymmetric prism. The detected output light intensity is increased by 65.7%. Second, light dispersion is experimentally demonstrated using 488-nm and 633-nm laser beams. The two laser beams become distinguishable with a deviation angle difference of 2.5° when the apex angle of the prism reaches 116°.

Production of reactive oxygen species in endothelial cells under different pulsatile shear stresses and glucose concentrations

A hemodynamic Lab-on-a-chip system was developed in this study. This system has two unique features: (1) it consists of a microfluidic network with an array of endothelial cell seeding sites for testing them under multiple conditions, and (2) the flow rate and the frequency of the culture medium in the microchannel are controlled by a pulsation free pump to mimic the flow profile of the blood in the blood vessel under different physiological conditions. The investigated physiological conditions were: (1) the resting condition in a normal shear stress of 15 dyne cm(-2) with a normal heart rate of 70 bpm, (2) an exhaustive exercise condition with a high shear stress of 30 dyne cm(-2) and a fast heart rate of 140 bpm, and (3) a constant high shear stress of 30 dyne cm(-2). Two chemical conditions were investigated (10 mM and 20 mM glucose) to mimic hyperglycemic conditions in diabetes patients. The effects of various shear stresses either alone or in combination with different glucose concentrations on endothelial cells were examined using the developed hemodynamic Lab-on-a-chip system by assessing two parameters. One is the intracellular level of reactive oxygen species (ROS) determined by a fluorescent probe, H(2)DCFDA. Another is the mitochondrial morphology revealed with a fluorescent dye, MitoTracker Green FM. The results showed that ROS level was elevated nearly 4-fold after 60 min of exhaustive exercise. We found that the pulsatile nature of the fluid was the determination factor for causing ROS generation in the cells as almost no increase of ROS was detected in the constant shear stress condition. Similarly, much higher level of ROS was detected when 10 mM glucose was applied to the cells under normal or high pulsatile shear stresses compared with under a static condition. These results suggest that it is necessary to use pulsatile shear stress to represent the physiological conditions of the blood flow, and demonstrate the advantage of utilizing this newly developed hemodynamic Lab-on-a-chip system over the conventional non-pulsatile system in the future shear stress related studies.

First Report of Coleus blumei viroid 2 from Commercial Coleus in China

Coleus (Coleus blumei) is an ornamental plant that is susceptible to infection by several viroids of the genus Coleviroid, which is a member of the family Pospiviroidae. Coleus blumei viroid (CbVd) -1 was first reported in commercial yellow coleus fields in Brazil in 1989 (1). In addition, CbVd-2, CbVd-3, and CbVd-4 have only been detected from coleus in Germany in 1996 (4). CbVd-5 and CbVd-6 were recently identified in China (2). In March 2010, leaves were collected from 50 symptomless coleus plants from a commercial nursery in Hainan Province, China. Total RNA was extracted from the leaves (3). Reverse transcription (RT)-PCR using CbVd-2 specific primers (forward: 5'-AGCTTACCTGGGTTCCCT-3' and reverse: 5'-CTCTCCTCTATTTACTCTCTTCTC-3') corresponding to positions 76 to 93 and 52 to 75 on the CbVd-2 reference sequence, respectively (GenBank Accession No. NC003682). Amplification of a 301-bp product was obtained from one sample. This PCR product was then cloned into pMD18-T (Takara, Dalian, China). Twelve positive clones were sequenced and the results were subjected to BLAST analysis. Sequence analysis showed that two sequences (GenBank Accessions Nos. HQ727542 and HQ727544) shared 99% identity with the reference sequence of CbVd-2 (NC003682), and four sequences (HQ727541, HQ727543, HQ727545 and HQ727547) had 99.34% identity with the reference sequence of CbVd-2 (NC003682). The proposed secondary structures of these variants have approximately 75% paired nucleotides. Results suggested the presence of CbVd-2, which is a member of the Coleviroid genus, Pospoviroidae family. To our knowledge, this is the first report of CbVd-2 from commercial coleus in China. References: (1) M. E. N. Fonseca et al. Fitopatol. Bras. 14:94, 1989. (2) W. Y. Hou et al. Arch. Virol. 154:993, 2009. (3) S. F. Li et al. Ann. Phytopathol. Soc. Jpn. 61:381, 1995. (4) R. L. Spieker et al. J. Gen. Virol. 77:2839, 1996.

Tunable visual color filter using microfluidic grating

This paper reports a tunable visual color filter based on a microfluidic transmission grating. The grating lines are formed by the microflows in an array of evenly spaced straight microchannels. In experimental study, the transmission of white light measures a shift of visual color from red to blue in the zeroth order diffraction in response to a change of the refractive index from 1.3290 to 1.3782 in the microflows. The merit of large tunability of transmission peak (Δλ=408 nm) makes this grating potential for various applications in biological and chemical measurements, such as space- and time-resolving micropattern spectrophotometers and separation of the fluorescence from the excitation.

Pure angular momentum generator using a ring resonator

This paper reports a pure angular momentum generator using a ring resonator surrounded by a group of nano-rods. The evanescent waves of the circulating light in the ring are scattered by the nano-rods and generate a rotating electromagnetic field, which has only angular momentum but no linear momentum along the axis of rotation. The angular order is determined by the difference between the order of Whispering Gallery mode and the number of the rods, the rotating frequency is equal to the light frequency divided by the angular order. The maximum amplitude of the rotating electromagnetic fields can be 10 times higher than the amplitude of the input field when there are 36 rods (R(rod) = 120 nm, nr = 1.6). The pure angular momentum generator provides a new platform for trapping and rotation of small particles.

Microfluidic droplet grating for reconfigurable optical diffraction

This Letter presents a reconfigurable optical diffraction grating using multiphase droplets on a microfluidic chip. The uniform and evenly spaced circular droplets are generated by continuously dispersing two immiscible liquids into a T junction to produce plugs, which are then transformed into a circular shape at a sudden expansion of the microchannel. In experiments, the droplet grating shows a detection limit of ~6.3x10(-5) when used as an opto fl uidic refractometer and produces different colors as a color filter. Such a grating has the advantages of high stability and wide tunability in droplet size, grating period, and refractive index, making it promising for biochemical and biomaterial applications.

An optofluidic volume refractometer using Fabry-Pérot resonator with tunable liquid microlenses

This letter reports the development of an optofluidic Fabry-Pérot (FP) resonator, which consists of a microcavity and a pair of liquid microlenses. The microcavity forms part of the microchannel to facilitate sample injection. The liquid microlenses are used for efficient light coupling from the optical fiber to the microcavity. The liquid microlens collimates the diverging light from the optical fiber into the FP cavity, which provides real-time tuning to obtain the highest possible finesse up to 18.79. In volume refractive index measurement, a sensitivity of 960 nm per refractive index unit (RIU) and a detection range of 0.043 RIU are achieved.

A reconfigurable optofluidic Michelson interferometer using tunable droplet grating

This paper presents a novel optofluidic Michelson interferometer based on droplet microfluidics used to create a droplet grating. The droplet grating is formed by a stream of plugs in the microchannel with constant refractive index variation. It has a real-time tunability in the grating period through varying the flow rates of the liquids and index variation via different combinations of liquids. The optofluidic Michelson interferometer is highly sensitive and is suitable for the measurement of biomedical and biochemical buffer solutions. The experimental results show that it has a sensitivity of 66.7 nm per refractive index unit (RIU) and a detection range of 0.086 RIU.

Microchip system for monitoring microbial physiological behaviour under drug influences

Single-step real-time high-throughput monitoring of drug influences on bacterial cell behaviour has become important with growing interests in personalized therapy and medication. Conventional microchip assemblies to perform similar work do exist. However, most of these devices have complex set-ups incorporating micromixers, separators, pumps, or valves. These microcomponents can sometimes damage the entities being monitored because of the creation of unfavourable biological environments. This paper presents a microchip-based system that enables single-step mixing of two solutions in various ratios, without the need for additional microcomponents such as mixers and pumps, in order to screen effectively their combinatory effects on cell outcomes. In this work, in-vitro experiments were carried out using ampicillin at various concentrations to investigate their effects on Escherichia coli (E. coli). Results showed that the microchip provided effective screening, which yielded useful results such as effective dosages, ineffective dosages, and other possible outcomes; for instance, in this case, the occurrence of adaptive mutation of the bacteria at certain drug concentrations. Comparative microbiological laboratory tests were carried out as standard for confirmation of the results.

A micromachined tunable coupled-cavity laser for wide tuning range and high spectral purity

This paper presents the design and experimental study of a coupled-cavity laser based on the micromachining technology for wide tuning range and improved spectral purity. The core part of this design utilizes a deep-etched movable parabolic mirror to couple two identical Fabry-Pérot chips and thus allows the active adjustment of the cavity gap so as to optimize the mode selection and to increase the tuning range as well. In experiment, the laser achieves the single longitudinal mode output over 51.3 nm and an average side-mode-suppression ratio of 22 dB when the tuning current varies from 5.7-10.8 mA. The measured wavelength tuning speed is 1.2 micros and the single mode output is stable at any wavelength when the tuning current is varied within +/- 0.06 mA. Compared with the conventional fixed cavity gap coupled-cavity lasers, such design overcomes the phase mismatching and mode instability problems while maintaining the merit of high-speed wavelength tuning using electrical current.

Photonic bandgap crystal resonator enhanced, laser controlled modulations of optical interconnects for photonic integrated circuits

Ultrafast high-density photonic integrated circuit devices (PICDs) are not easily obtained using traditional index-guiding mechanisms. In this paper, photonic bandgap crystal resonator enhanced, laser-controlled modulations of optical interconnect PICDs were achieved in slab-type mix-guiding configuration - through developed CMOS-compatible processing technologies. The devices, with smallest critical dimensions of 90 nm have footprints of less than 5 x 5 microm(2). Quality-factors an order larger than previously realized was achieved. Through use of effective coupling structures; simultaneous alignment for probing and pumping laser beams, optical measurements of both instantaneous free carriers induced device modulations were obtained together with thermo-optical effects characterizations.

Investigation of resonant modes in thin microcavities by using electromagnetic theory

A biharmonic differential equation for 3D thin microcavities with uniform thickness is investigated by use of electromagnetic theory, whose exact solution is determined to govern the electromagnetic field distribution inside the thin microcavities. The resonant field patterns of a thin microdisk and thin rectangular microcavity are obtained accordingly. The governing equation can be verified by comparing the results of the thin microdisk presented with the approximate ones in the literature. The fourth-order partial differential equation and its exact solution should be useful in possible applications of the thin microcavities for optical resonators in laser optics and optical devices.

Modified step-theory for investigating mode coupling mechanism in photonic crystal waveguide taper

In this paper, the mathematical model of the modified step-theory is derived based on the platform of two-dimensional photonic crystal structure that is infinitely long in third dimension. The mode coupling mechanism of photonic crystal tapers is theoretically studied using the modified step-theory. The model is verified by comparing the transmission spectrum obtained for the input/output defect coupler where it shows a good match of less than 5% discrepancy. The modified step-theory is applied to different taper structures to investigate the power loss during the transmission. The power loss at the relative position of the taper provides an explanation as to which taper designs give the highest coupling efficiency.

Exact solution of resonant modes in a rectangular resonator

The resonant modes of rectangular two-dimensional optical resonators were analyzed exactly. Based on the characteristics of the Bessel function, the resonant frequencies of the rectangular microcavities are expressed in a simple way. In addition, a simple rule to judge when the finite length of a rectangular resonator can be considered infinite is given in realistic applications. The solution that is presented should be useful in possible applications of the rectangular resonators as filters for dense wavelength-division multiplexing.

Chaotic dynamics of a passively mode-locked soliton fiber ring laser

We report on the experimental and numerical studies of the chaotic dynamics of a soliton fiber ring laser passively mode-locked by using the nonlinear polarization rotation (NPR) technique. Period-doubling route to chaos on the soliton repetition rate of either the single pulse soliton or the bound solitons of the laser was experimentally observed. Based on a coupled complex Ginzburg-Landau equation model and also taking into account the laser cavity effect, we further show numerically that the period-doubling bifurcations and route to chaos are intrinsic properties of the laser, whose appearance is independent of the details of the laser cavity design and the laser soliton operation. Property of the solitons under the dynamical bifurcations is also numerically investigated.