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Living bacteria therapies have been proposed as an alternative approach to treating a broad array of cancers. In this study, we developed a genetically encoded microbial encapsulation system with tunable and dynamic expression of surface capsular polysaccharides that enhances systemic delivery. Based on a small RNA screen of capsular biosynthesis pathways, we constructed inducible synthetic gene circuits that regulate bacterial encapsulation in Escherichia coli Nissle 1917. These bacteria are capable of temporarily evading immune attack, whereas subsequent loss of encapsulation results in effective clearance in vivo. This dynamic delivery strategy enabled a ten-fold increase in maximum tolerated dose of bacteria and improved anti-tumor efficacy in murine models of cancer. Furthermore, in situ encapsulation increased the fraction of microbial translocation among mouse tumors, leading to efficacy in distal tumors. The programmable encapsulation system promises to enhance the therapeutic utility of living engineered bacteria for cancer.

For the reason of rapid evolution of antibiotic resistance in Staphylococcus aureus, antivirulence therapy may be a promising alternative for effective control of spread of resistant pathogens. The Chinese Materia Medica has been widely used for treatment of disease and production of health food, and it remains a valuable resource for discovery of compounds possessing antivirule nce activity.Through a Caenorhabditis elegans infection model, EtOAc-soluble fraction of 80% EtOH extract of Salvia miltiorrhiza Bunge (SMEA) was found to possess potential anti-infective activity against S. aureus. Then, several in vitro assays indicated that SMEA had robust antivirulence activity at the dose of 400 μg/mL, reducing hemolytic activity and α-hemolysin expression in S. aureus. Furthermore, at 100 mg/kg, SMEA reduced abscess formation in the main organs of mice challenged with S. aureus. In order to identify the bioactive components of SMEA and investigate the mechanisms underlying the antivirulence activity, SMEA was separated using bioassay-guided fractionation. As a result, eight compounds were identified in SMEA. Among them, tanshinone IIB (TNB) showed strong antivirulence activity both in vitro and in vivo. Furthermore, at 24 μg/mL, TNB significantly reduced the expression of RNAIII and psmα, indicating that the mechanism underlying TNB activity was related to the accessory gene regulator quorum sensing system. Collectively, the antivirulence effect of TNB making it a promising candidate for the development of drugs used against S. aureus infections.

A ruthenium complex [Ru(phen)2(phen-5-amine)-C14] (Ru-C14) with broad-spectrum antibacterial activity was synthesized. Ru-C14 can target and image the cell membrane and can be used as a photosensitizer for photodynamic antimicrobial therapy under 465 nm light irradiation.

In order to understand the composition and accumulation characteristics of phthalates esters (PAEs) in agricultural soils in Gansu province, a total of 41 soil samples from four agricultural soils in Gansu province were collected, and the content of six PAEs compounds was analyzed using a gas chromatography-single quadrupole mass spectrometer (GC-MS). The results showed that the average value of PAEs compounds in agricultural soils in Gansu province was 432.4 μg·kg

Temporary cardiac pacemakers used in periods of need during surgical recovery involve percutaneous leads and externalized hardware that carry risks of infection, constrain patient mobility and may damage the heart during lead removal. Here we report a leadless, battery-free, fully implantable cardiac pacemaker for postoperative control of cardiac rate and rhythm that undergoes complete dissolution and clearance by natural biological processes after a defined operating timeframe. We show that these devices provide effective pacing of hearts of various sizes in mouse, rat, rabbit, canine and human cardiac models, with tailored geometries and operation timescales, powered by wireless energy transfer. This approach overcomes key disadvantages of traditional temporary pacing devices and may serve as the basis for the next generation of postoperative temporary pacing technology. A biodegradable pacemaker without external leads improves the safety of temporary cardiac pacing.

Although salinity stress is one of the principal abiotic stresses affecting crop yield, a suitable concentration of NaCl has proven to be useful for increasing crop quality. This study used low salinity (34 mmol/L NaCl) and high salinity (85 mmol/L) to cultivate purple sweetpotato. Using transcriptomics and metabolomics to profile the pathway indicated that glycometabolism, secondary metabolite biosynthesis and the starch catabolic process were the significant pathways under the salinity stress. Further research showed that purple sweetpotato could regulate genes related to the regulation of the cellular Na+, K+, and other ions concentration in response to the low salinity tolerance, but loses this ability under high salinity. Meanwhile, under low salinity, the activity of antioxidant enzymes and their related gene expression are maintained at a high level. The low salinity influences the monosaccharide composition as well as the content and regulation of genes related to starch synthesis. Quality analysis showed that the low salinity could increase the starch content and influence the amylopectin biosynthesis. It suggested that low salinity promotes substance accumulation. High salinity could increase the anthocyanins biosynthesis and low salinity had a significant impact on phenolic acid and flavonol. Finally, the gene expression levels also prove the low salinity could change the composition and content level of the purple sweetpotato. This study showed that an appropriate concentration of NaCl can be used as an elicitor for application in purple sweetpotato planting.

Due to the rapid evolution of antibiotic resistance in

Recent advances in therapeutic modulation of human microbiota have driven new efforts to engineer living microbial medicines using synthetic biology. However, a long-standing challenge for live bacterial therapies is balancing the high dose required to achieve robust efficacy with the potential for sepsis. Here, we developed a genetically encoded microbial encapsulation system with tunable and dynamic expression of surface capsular polysaccharides to enhance therapeutic delivery. Following a synthetic small RNA knockdown screen of the capsular biosynthesis pathway, we constructed synthetic gene circuits that regulate bacterial encapsulation based on sensing the levels of environmental inducer, bacterial density, and blood pH. The induced encapsulation system enabled tunable immunogenicity and survivability of the probiotic Escherichia coli, resulting in increased maximum tolerated dose and enhanced efficacy in murine cancer models. Furthermore, triggering in situ encapsulation was found to increase microbial translocation between mouse tumors, leading to efficacy in distal tumors. The programmable encapsulation system demonstrates a new approach to control microbial therapeutic profiles in vivo using synthetic biology.

A variety of chemical sensing materials and procedures for conveniently detecting mercuric ion (II) (Hg2+) have been extensively explored. The detection challenges for accomplishing a simple, fast, and low investment procedure at the ultrasensitive level are ongoing. Herein we report a quadrillionth level for detecting Hg2+ by the surface-enhanced Raman scattering (SERS) technique. There is an interaction of silver nanoparticles decorated on a zinc-oxide tetrapod structure and coated on FTO glass (Ag@ZnO-FTO) with an organic ligand. 4,4′-Dipyridyl (DPy) performed as being chemisorbed by Ag nanoparticles interacting with a pyridine ring to produce plasmonic hot spots for SERS. The morphology of the surface and porous structure of the tetrapod becomes the powerful platform for enhanced SERS performance of DPy detection. In the absence of the augmentative electrolyte, the enhancement factor for DPy is more than 107. The inhibiting of the aggregation between Ag and DPy was present following the appearance of Hg2+, demonstrated by the quenching of the SERS signal from the DPy molecules. The capability to reproduce and the selectivity of the sensing by DPy were both demonstrated. In addition, the applications for detecting Hg2+ in natural water and beverages were successfully detected. These results demonstrated the SERS sensors had the potential for detecting Hg2+ in practical use.

In this study we prepared six types of carbon nanodots (CNDs) from natural plant materials – through carbonization of two species of bamboo (Bamboo-I, Bamboo-II) and one type of wood (Wood), and through hydrothermal processing of the stem and root of the herb Mahonia oiwakensis Hayata (MO) and of the agricultural waste of two species of pineapple root (PA, PB). The resulting CNDs were spherical with dimensions on the nanoscale (3–7 nm); furthermore, CND-Bamboo I, CND-Wood, CND-Bamboo II, CND-MO, CND-PA, and CND-PB displayed fluorescence quantum yields of 9.63, 12.34, 0.90, 10.86, 0.35, and 0.71%, respectively. X-ray diffraction revealed that the carbon nanostructures possessed somewhat ordered and disordered lattices, as evidenced by broad signals at values of 2θ between 20 and 30°. CND-Bamboo I, CND-Wood, and CND-Bamboo II were obtained in yields of 2–3%; CND-MO, CND-PA, and CND-PB were obtained in yields of 17.64, 9.36, and 22.47%, respectively. Cytotoxicity assays for mouse macrophage RAW264.7 cells treated with the six types of CNDs and a commercial sample of Ag nanoparticles (NPs) revealed that each of our CNDs provided a cell viability of 90% at 2000 μg mL−1, whereas it was only 20% after treatment with the Ag NPs at 62.5 μg mL−1. The six types of CNDs also displayed low cytotoxicity toward human keratinocyte HacaT cells, human MCF-7 breast cancer cells, and HT-29 colon adenocarcinoma cells when treated at 500 μg mL−1. Moreover, confocal microscopic cell imaging revealed that the fluorescent CND-Bamboo I particles were located on the MCF-7 cell membrane and inside the cells after treatment for 6 and 24 h, respectively. We have thoroughly investigated the photoluminescence properties and carbon nanostructures of these highly dispersed CNDs. Because of the facile green synthesis of these six types of CNDs and their sourcing from abundant natural plants, herbs, and agriculture waste, these materials provide a cost-effective method, with low cytotoxicity and stable fluorescence, for biolabeling and for developing cell nanocarriers.

Rapid detection of the handiness of chiral molecules is an important topic for pharmaceutical industries because chiral drugs with opposing handiness sometimes exhibit unwanted side effects. In this research, a rapid optical method is proposed to determine the handiness of the chiral drug "Thalidomide". The platform is a large array of three-dimensional (3D) twisted metamaterials fabricated with a novel method by combining nanospherical-lens lithography (NLL) and hole-mask lithography (HML). The fabrication is high-throughput and the twisted metamaterials cover a large area. Strong circular dichroism (CD) response is observed in the near-infrared (NIR) region, which enables the chiral detection to be performed by a low-cost and portable spectroscope system. The proposed nanofabrication method significantly improves the capabilities of NLL and HML, which can be quickly adapted to fabricate various periodic 3D metamaterials. In addition, the results of this research pave the road for the rapid penetration of nanophotonics into the pharmaceutical industries.

Bioresorbable drug release platforms offer advanced treatment for hormone imbalances, malignant cancers, and diabetic conditions., Implantable drug release platforms that offer wirelessly programmable control over pharmacokinetics have potential in advanced treatment protocols for hormone imbalances, malignant cancers, diabetic conditions, and others. We present a system with this type of functionality in which the constituent materials undergo complete bioresorption to eliminate device load from the patient after completing the final stage of the release process. Here, bioresorbable polyanhydride reservoirs store drugs in defined reservoirs without leakage until wirelessly triggered valve structures open to allow release. These valves operate through an electrochemical mechanism of geometrically accelerated corrosion induced by passage of electrical current from a wireless, bioresorbable power-harvesting unit. Evaluations in cell cultures demonstrate the efficacy of this technology for the treatment of cancerous tissues by release of the drug doxorubicin. Complete in vivo studies of platforms with multiple, independently controlled release events in live-animal models illustrate capabilities for control of blood glucose levels by timed delivery of insulin.

Biologically and environmentally resorbable electronic devices support application possibilities that cannot be addressed with conventional technologies. This paper presents highly conductive, water-soluble composites that can be printed to form contacts, interconnects, antennas, and other important features that are essential to nearly all systems of this type. An optimized material formulation involves in situ polymerization to yield a polyanhydride containing a dispersion of molybdenum microparticles at appropriate concentrations. Comparisons of essential physical and electrical properties of these materials to those of composites formed with other polymers and other metal microparticles reveal the relevant considerations. Various functional demonstrations of screen-printed test structures and devices illustrate the suitability of these conductive inks for use in water-soluble electronic devices. A key advantage of the material introduced here compared to alternatives is its ability to maintain conductance over significant periods of time while immersed in relevant aqueous solutions. Studies involving live animal models establish the biocompatibility.

One new xanthone, (±) garciesculenxanthone C (

One new xanthone, (±) garciesculenxanthone C (1), two new biphenyls, garciesculenbiphenyls A (2) and B (3), together with two known compounds, doitungbiphenyl B (4) and morusignin D (5), were isolated from Garcinia esculenta. The structures of new compounds were elucidated by spectroscopic analysis, and the absolute configuration of (±) garciesculenxanthone C (1) was assigned by a modified Mosher′s method. All isolates were evaluated for their antistaphylococcal activities against Staphylococcus aureus Newman, USA300 LAC, USA400 MW2, and Mu50 strains. Among these, (±) garciesculenxanthone C (1) showed the best antistaphylococcal activity, and its effect was determined to be bactericidal by time-kill experiment.

The electrostatic charge distribution model and the finite-difference time-domain method were used to provide a physically intuitive interpretation of how the shape and the number of branches affect the localized surface plasmon resonances of 3D sea-urchin like nanoparticles. We consider both planner and spherical structures with pins of cylindrical, triangular and hexagonal shape. Better alignment between surface charges of opposite sign leads to higher resonant energy states. More pin numbers provide more surface distribution area to spread dipole charges which leads to worse charges alignment and redshift of dipole mode. However, as the pin number increases, the quadrupole surface charge was pushed toward the pin tip due to Coulomb repulsion. Better charge alignment caused the quadrupole blueshift. Other effects such as convex and concave shape and dielectric materials are also discussed. Our finding may provide a designing rule to synthesize multi-branch nanoparticles for bio-chemical sensing applications.

The circular dichroism (CD) performance of conjugated gammadion structure on the end facet of silicon waveguide in the mid-infrared regime is investigated theoretically. By engineering the orientation of the structure, the sign and value of its CD spectrum can be changed. For a fixed gammadion structure, different CD values can be obtained not only by changing the excitation wavelength but the excitation waveguide mode. This finding potentially provides an extra degree of freedom to design integrated chiral photonics chips.

Fructus Psoraleae (FP) causes cholestatic liver injury; however, its main toxic constituents that are responsible for causing hepatotoxicity remained undetermined in previous studies. In the present study, psoralen and isopsoralen, the two main constituents of FP, were administered orally to rats (80 and 40 mg/kg, respectively) and mice (320 and 160 mg/kg, respectively) for 28 days, followed by biochemical and histopathological examinations to evaluate their hepatotoxicity. The results showed that psoralen and isopsoralen could induce the toxic reactions of liver and other organs in rats, while mice were not sensitive to these two compounds. Furthermore, the corresponding results indicated that administration of psoralen and isopsoralen repressed the expression of CYP7A1, BSEP, MRP2 and SULT2A1 and increased the expression of FXR and MRP3 in the rat liver. In summary, the toxic reactions of psoralen and isopsoralen are different in different species. In this study, multiple organ toxicity, such as cholestatic liver injury, occurs in rats, but not in mice. Psoralen and isopsoralen are the two main toxic constituents of FP. In addition, psoralen and isopsoralen cause liver injury, possibly through inhibiting bile acid excretion in the liver, leading to the accumulation of toxin in hepatocytes.

Peripheral nerve injuries represent a significant problem in public health, constituting 2-5% of all trauma cases1. For severe nerve injuries, even advanced forms of clinical intervention often lead to incomplete and unsatisfactory motor and/or sensory function2. Numerous studies report the potential of pharmacological approaches (for example, growth factors, immunosuppressants) to accelerate and enhance nerve regeneration in rodent models3-10. Unfortunately, few have had a positive impact in clinical practice. Direct intraoperative electrical stimulation of injured nerve tissue proximal to the site of repair has been demonstrated to enhance and accelerate functional recovery11,12, suggesting a novel nonpharmacological, bioelectric form of therapy that could complement existing surgical approaches. A significant limitation of this technique is that existing protocols are constrained to intraoperative use and limited therapeutic benefits13. Herein we introduce (i) a platform for wireless, programmable electrical peripheral nerve stimulation, built with a collection of circuit elements and substrates that are entirely bioresorbable and biocompatible, and (ii) the first reported demonstration of enhanced neuroregeneration and functional recovery in rodent models as a result of multiple episodes of electrical stimulation of injured nervous tissue.

We investigated the effects of extracorporeal shockwave therapy (ESWT) on the rehabilitation of cervical spondylosis with nuchal ligament (NL) calcification under X-ray and ultrasound guidance. Sixty patients with cervical spondylosis and calcification of NL were selected and randomly assigned to three groups: A, B, and C. Patients in Group A received rehabilitation with 20 minutes of hot packs and underwent 15 minutes of intermittent cervical traction three times/week for 6 weeks. Patients in Group B received the same rehabilitation as those in Group A and ESWT (2000 impulses, 0.27 mJ/mm 2 ) over the calcified NL guided by X-ray image. Patients in Group C received the same treatment as those in Group B, but the ESWT was guided by musculoskeletal sonography. The therapeutic effects were evaluated by: changes in range of motion (ROM) of the cervical spine including flexion, extension, lateral bending, and rotation; visual analog pain scale; and Neck Disability Index before and after treatment and at follow up 3 months later. We found a significant reduction in pain in each treated group after treatment and at follow up. However, patients in Groups B and C showed more improvements in ROM and neck pain relief after treatment and a decrease in Neck Disability Index. Furthermore, patients in Group C showed better cervical ROM at follow up than Group B. ESWT is an adjuvant treatment in the management of cervical spondylosis with calcification of NL and ultrasound-guided ESWT results in more functional improvements.

Background AMP-activated protein kinase (AMPK), a principal intracellular energy sensor, plays a crucial role in cell growth, proliferation, apoptosis and autophagy. Imiquimod (IMQ) directly exhibits anti-tumor activity through the induction of apoptosis and autophagic cell death. Objective To evaluate the role of AMPK in IMQ-induced apoptosis and autophagy. Methods The phosphorylation of AMPK and its substrates was detected by immunoblotting. ATP contents were analyzed by an ATP bioluminescence assay. The upstream signaling for AMPK activation was dissected by examination of TLR7/8 expression, over-expression of TLR7/8, the addition of AMPK kinase inhibitors, and the genetic silencing of Myd88 and LKB1. The role of AMPK activation in IMQ-induced autophagy and apoptosis was assessed by inhibiting AMPK, genetically silencing AMPK and over-expressing AMPK dominant-negative mutants. Autophagy and apoptosis were evaluated by a DNA content assay, immunoblotting, EGFP-LC3 puncta detection and acridine orange staining. Results IMQ could activate AMPK and autophagy in cancer cells not expressing TLR7/8. IMQ caused ATP depletion and induced LKB1-mediated AMPK activation. The down-regulation of AMPK activity via pharmacological inhibition and genetic silencing resulted in reduced IMQ-induced apoptosis but did not influence autophagy, and this rescue effect was associated with the retention of translation factor activity and anti-apoptotic Bcl-2 family member Mcl-1 protein expression levels. Conclusion IMQ induces AMPK activation independent of TLR7/8 expression, resulting in translation inhibition and subsequent apoptosis through ATP depletion and LKB1 signaling, in skin tumor cells.

Air pollution has become a major threat today and the related respiration illnesses have deteriorated the wellness of many people. Herb, as one option of the medicine and also as diet, can provide very promising solution to the above threats. However, even though herbs are easily accessible in every cultures and areas, the knowledge of applying herbs on improving health is complicated and it takes quite lots of efforts to acquire the knowledge. In this paper, we design an ontology-based herb therapy recommendation web for respiration system health.

Dissection of qTGW1.2, a minor quantitative trait locus (QTL) for 1,000-grain weight located on the long arm of rice chromosome 1, was reported here. Six sets of near isogenic lines (NILs) were developed from six BC2F9 plants of the indica rice cross Zhenshan 973/Milyang 46, respectively, segregated in a sequential order covering the region for qTGW1.2. They were tested for 1,000-grain weight, grain length, grain width and heading date. The SAS procedure GLM was used to analyze the phenotype differences among three genotypic groups in each NIL set. The qTGW1.2 was separated into three QTLs, including qTGW1.2a located in the 933.6 kb interval RM11730–RM11762, qTGW1.2b in the 418.8 kb interval RM11781–RM11800, and qTGW1.2c in the 2.1 Mb interval RM11800–RM11885. While qTGW1.2a and qTGW1.2c displayed the genetic action mode of negatively partial dominance, qTGW1.2b appeared to have a positively dominance effect as large as its additive effect. In addition, the effects of the three QTLs were consistently detected in different NIL sets. It was also shown that the effects of qTGW1.2a and qTGW1.2b on grain weight were related more to grain length than grain width, and qTGW1.2c related more to grain width than grain length. Our results indicate that the effects of minor QTLs could be steadily detected in a highly isogenic background and suggest that dominance effects of minor QTLs might play an important role in the genetic control of heterosis in rice.

Power management has increased its significance in mobile communications along with the growing population of mobile users and wireless connectivity. In this paper we propose a smart scheduling algorithm in Android network kernel to increase power efficiency. As periodically-updating applications start sync with a DNS query packet, we defer the packets in order to make these applications synchronize from smaller time difference to finally simultaneously. To implement the idea, we design the algorithm for two or more applications in this paper. This algorithm is composed of several mechanisms: approaching, aligning, and maintaining. By experiments we show the practicability and the comparison between the energy saving ratios in different scenarios.

Graphical abstractDisplay Omitted HighlightsThe intrinsic parameter fluctuation is studied for the 16-nm-gate TiN/HfO2 bulk FinFETs.The fluctuation includes the random discrete dopant, the random interface trap, and the random work function, simultaneously.The full 3D simulated threshold voltage fluctuation is 26.2mV for the N-type bulk FinFET.The statistical sum of these fluctuations is 9.5% overestimation because independence assumption on these random variables is invalid.Compared with the planar MOSFET, more than 50% reduction on the threshold voltage fluctuation is estimated. In this work, based on the experimentally calibrated 3D device simulation, we for the first time estimate the impact of intrinsic parameter fluctuation on the electrical characteristic of 16-nm-gate TiN/HfO2 bulk FinFETs. The sources of intrinsic parameter fluctuation include the random discrete dopants, interface traps and work function differences, simultaneously. The full 3D simulated threshold voltage fluctuation, induced by the aforementioned random sources simultaneously, is 26.2mV for the N-type bulk FinFET (and is 55.5mV for the planar N-MOSFET). For the N-type bulk FinFET, the statistical sum of these fluctuations is 9.5% (and is 12.3% for the planar device) overestimation, compared with the full 3D simulation. One of the main reasons is the independence assumption on these random variables is destroyed owing to interactions to different extents among RDs, ITs and WKs. The coupled surface potentials cannot be simply estimated by using their statistical sum of individual random source. Under the same threshold voltage, compared with the result of the planar MOSFETs, more than 50% reduction on the threshold voltage fluctuation of the explored bulk FinFETs is observed owing to the benefit of 3D structural nature.

In this paper, the dynamic characteristics of the novel amorphous silicon thin-film transistor gate drive circuit applied on a 10.1-in. panel are optimized by using a multi-objective optimization method. Simultaneously, considering the multiple electrical characteristics of the tested circuit, the achieved results reveal interesting properties as well as good sensitivity of the optimized design parameters. The optimal specifications not only suppress the output ripple, but also reduce the dynamic and static power consumptions.

Compound C, a well-known inhibitor of the intracellular energy sensor AMP-activated protein kinase (AMPK), has been reported to cause apoptotic cell death in myeloma, breast cancer cells and glioma cells. In this study, we have demonstrated that compound C not only induced autophagy in all tested skin cancer cell lines but also caused more apoptosis in p53 wildtype skin cancer cells than in p53-mutant skin cancer cells. Compound C can induce upregulation, phosphorylation and nuclear translocalization of the p53 protein and upregulate expression of p53 target genes in wildtype p53-expressing skin basal cell carcinoma (BCC) cells. The changes of p53 status were dependent on DNA damage which was caused by compound C induced reactive oxygen species (ROS) generation and associated with activated ataxia-telangiectasia mutated (ATM) protein. Using the wildtype p53-expressing BCC cells versus stable p53-knockdown BCC sublines, we present evidence that p53-knockdown cancer cells were much less sensitive to compound C treatment with significant G2/M cell cycle arrest and attenuated the compound C-induced apoptosis but not autophagy. The compound C induced G2/M arrest in p53-knockdown BCC cells was associated with the sustained inactive Tyr15 phosphor-Cdc2 expression. Overall, our results established that compound C-induced apoptosis in skin cancer cells was dependent on the cell's p53 status.

In this study, effects of the thickness of a low temperature (LT) buffer and impurity incorporation on the characteristics of Nitrogen (N)-polar GaN are investigated. By using either a nitridation or thermal annealing step before the deposition of a LT buffer, three N-polar GaN samples with different thicknesses of LT buffer and different impurity incorporations are prepared. It is found that the sample with the thinnest LT buffer and a nitridation step proves to be the best in terms of a fewer impurity incorporations, strong PL intensity, fast mobility, small biaxial strain, and smooth surface. As the temperature increases at ~10 K, the apparent donor-acceptor-pair band is responsible for the decreasing integral intensity of the band-to-band emission peak. In addition, the thermal annealing of the sapphire substrates may cause more impurity incorporation around the HT-GaN/LT-GaN/sapphire interfacial regions, which in turn may result in a lower carrier mobility, larger biaxial strain, larger bandgap shift, and stronger yellow luminescence. By using a nitridation step, both a thinner LT buffer and less impurity incorporation are beneficial to obtaining a high quality N-polar GaN.