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Polymerase chain reaction (PCR) has been considered as the gold standard for detecting nucleic acids. The simple PCR system is of great significance for medical applications in remote areas, especially for the developing countries. Herein, we proposed a low-cost self-assembled platform for microchamber PCR. The working principle is rotating the chamber PCR microfluidic chip between two heaters with fixed temperature to solve the problem of low temperature variation rate. The system consists of two temperature controllers, a screw slide rail, a chamber array microfluidic chip and a self-built software. Such a system can be constructed at a cost of about US$60. The micro chamber PCR can be finished by rotating the microfluidic chip between two heaters with fixed temperature. Results demonstrated that the sensitivity of the temperature controller is 0.1℃. The relative error of the duration for the microfluidic chip was 0.02 s. Finally, we successfully finished amplification of the target gene of Porphyromonas gingivalis in the chamber PCR microfluidic chip within 35 min and on-site detection of its PCR products by fluorescence. The chip consisted of 3200 cylindrical chambers. The volume of reagent in each volume is as low as 0.628 nL. This work provides an effective method to reduce the amplification time required for micro chamber PCR. [ABSTRACT FROM AUTHOR]

Aims: Plant stoichiometry is known to influence ecological processes and element cycles in ecosystems, which in turn can all be affected by ongoing climate change. While previous studies mainly focused on warming, drought or species invasion, effects of changing water supply on plant stoichiometry have not been well explored. Methods: To study how water supply affects plant stoichiometry (here C:N, N:P), and whether such effects differ among plant species, a manipulative experiment was conducted in which four grass species (Leymus chinensis, Stipa grandis, Artemisia frigida and Potentilla acaulis) dominant in the Inner Mongolia steppe were subjected to a gradient of water supply via changes in growing-season rainfall. Results: Water supply significantly impacted C:N and N:P, and these effects differed among grass species. Specifically, while C:N of A. frigida and P. acaulis was unaffected by water supply, C:N of L. chinensis and S. grandis increased with increasing precipitation. Furthermore, N:P of A. frigida showed a unimodal pattern along the imposed precipitation gradient. Whereas aboveground and belowground N:P showed similar trends (but different patterns) with changing water supply, this was not the case for aboveground and belowground C:N. As a result, plant stoichiometry between aboveground and belowground parts followed an allometric pattern. Conclusions: Changes in water supply can significantly modulate plant stoichiometry. These results could improve our understanding of the dynamics of grasslands under climate change. [ABSTRACT FROM AUTHOR]

There are growing demands for multimaterial three-dimensional (3D) printing to manufacture 3D object where voxels with different properties and functions are precisely arranged. Digital light processing (DLP) is a high-resolution fast-speed 3D printing technology suitable for various materials. However, multimaterial 3D printing is challenging for DLP as the current multimaterial switching methods require direct contact onto the printed part to remove residual resin. Here we report a DLP-based centrifugal multimaterial (CM) 3D printing method to generate large-volume heterogeneous 3D objects where composition, property and function are programmable at voxel scale. Centrifugal force enables non-contact, high-efficiency multimaterial switching, so that the CM 3D printer can print heterogenous 3D structures in large area (up to 180 mm × 130 mm) made of materials ranging from hydrogels to functional polymers, and even ceramics. Our CM 3D printing method exhibits excellent capability of fabricating digital materials, soft robots, and ceramic devices. Multimaterial 3D printing using digital light processing (DLP) is challenging because multimaterial switching methods require direct contact onto the printed part to remove residual resin. Here, the authors report a DLP-based centrifugal multimaterial 3D printing method to generate large-volume heterogeneous 3D objects where composition, property and function are programmable at voxel scale. [ABSTRACT FROM AUTHOR]

Materials capable of extracting gold from complex sources, especially electronic waste (e-waste), are needed for gold resource sustainability and effective e-waste recycling. However, it remains challenging to achieve high extraction capacity and precise selectivity if only a trace amount of gold is present along with other metallic elements. Here we report an approach based on reduced graphene oxide (rGO) which provides an ultrahigh capacity and selective extraction of gold ions present in ppm concentrations (>1000 mg of gold per gram of rGO at 1 ppm). The excellent gold extraction performance is accounted to the graphene areas and oxidized regions of rGO. The graphene areas spontaneously reduce gold ions to metallic gold, and the oxidized regions allow good dispersibility of the rGO material so that efficient adsorption and reduction of gold ions at the graphene areas can be realized. By controlling the protonation of the oxidized regions of rGO, gold can be extracted exclusively, without contamination by the other 14 co-existing elements typically present in e-waste. These findings are further exploited to demonstrate recycling gold from real-world e-waste with good scalability and economic viability, as exemplified by using rGO membranes in a continuous flow-through process. High extraction capacity with precise selectivity to trace amounts of gold over a wide range of co-existing elements remains a challenge for effective e-waste recycling. Here, authors demonstrate the excellent performance of rGO for gold extraction from e-waste leachate, even at minute concentrations. [ABSTRACT FROM AUTHOR]

Based on differential pulse voltammetry technology, we developed a portable and affordable instrument for on-site detection of trace heavy metal pollutants in liquid through a disposable plastic pipette. It mainly consists of a six-electrode electrochemical sensor which is integrated in the instrument. The pipette chip is equipped with a pump valve, and thus, it can avoid contamination. We have analyzed the sensitivity and specificity of the electrochemical sensor for heavy metal detection. Experimental results demonstrated that the limit of detection for Pb, Hg, Cu, and Zn was 2.2 ng/mL, 2.5 ng/mL, 15.5 ng/mL, and 10 ng/mL, respectively. The limit of quantification for them was 10 ng/mL, 25 ng/mL, 25 ng/mL, and 14 ng/mL, respectively. The correlation coefficient between peak current and the target heavy metal concentration was above 0.96. Finally, we have tested the analytical performance of the self-build instrument by measuring heavy metal ions in industrial wastewater and rainwater, respectively. Such an instrument is user-friendly for all users even for the common people, and we can envision its wide application in future heavy metal pollutant detection in groundwater, tap water, and supernatant of soil solution. [ABSTRACT FROM AUTHOR]

Metal-semiconductor ohmic contacts are required to reduce the energy dissipation for two-dimensional (2D) electronic devices, and phase engineering of 2D transition-metal dichalcogenides (TMDCs) is a promising approach for building ohmic contacts. Here, 2D in-plane 1T′-2H MoTe2 homojunctions were prepared by direct epitaxy via vapor deposition. The interface properties of in-plane 1T′-2H MoTe2 homojunction were investigated in detail by combining experiments, calculations and theories. The ohmic contact properties of 1T′-2H MoTe2 homojunction were proved according to Kelvin force probe microscopy and density functional theory calculations. The charge carriers robust transport in in-plane 1T′-2H MoTe2 homojunction without Fermi-level pinning can be well described by Poisson equation and band alignment. These results indicate that phase engineering of 2D TMDCs is promising to construct ohmic contacts for device applications. [ABSTRACT FROM AUTHOR]

Fluorescent microspheres (FMs) are widely employed in diagnostics and life sciences research; here, we investigated the effect of capillary coating, polymer concentration, electric field strength, and sample concentration on the separation performance of 1.0 μm FMs in hydroxyethyl cellulose (HEC) by capillary electrophoresis (CE). Results showed that (1) capillary coating could enhance the fluorescence signal. (2) For HEC with the same molecular weight, the higher HEC concentration is, the later the first peak appears in the electropherogram. (3) When FMs are diluted, increasing the electric field strength can enhance the migration speed and reduce the aggregation of FMs. (4) The number of FMs calculated is close to the theoretical value when it is diluted 10,000 times. The optimum conditions for CE were as follows: 6 cm/8 cm of effective length and total length of the coated capillary, 0.3% HEC (1300 k), and 300 V/cm of electric field strength. Such a study is helpful for the development of a FM counting system. [ABSTRACT FROM AUTHOR]

The reasons for restricting continuous flow polymerase chain reaction (CF-PCR) microfluidic chip from lab to application are that it is not portable and requires costly external precision pumps for sample injection. Herein, we employed water as the substitute for PCR solution, and investigated the effect of the cross-section, width-to-depth ratio, and the length ratio for three temperature zones of the micro channel on the thermal and flow distribution of fluid in micro tube by finite element analysis. Results show that the central velocity is uniform and stable velocity occupies the most if the cross-section is rectangular. The deviation between predefined temperature and theoretical temperature is slight and the fluid flux is the most if width-to-depth ratio is 1:1. It is suitable for the short DNA replication if the high temperature zone Wh is larger than the low temperature zone Wl, and vice versa. Then a portable CF-PCR microfluidic chip was fabricated and an automatic sample injection system was developed. As an application, we have successfully amplified the DNA of Treponema denticola in the chip within 8 min. Such a study may offer new insight into the design of CF-PCR microfluidic chip and promote it from lab-scale research to full-scale application. [ABSTRACT FROM AUTHOR]

Aims: Soil heterogeneity is a primary mechanism explaining plant species diversity. Yet, controlled experiments yield inconsistent soil heterogeneity-diversity (SHD) relationships, ranging from positive, neutral to negative.Methods: Here we investigated the SHD relationship by experimentally alternating nutrient-rich and nutrient-poor substrate in three dimensions, creating four levels of soil configurational heterogeneity (cell sizes 0, 12, 24 and 48 cm). Across each mesocosm, a mixture of species with high and low nitrogen requirements was evenly sown.Results: Contrary to earlier experimental findings, this approach yielded a unimodal SHD relationship, peaking at cell size 12 cm. This pattern originated mainly from increased plant diversity of species with high nitrogen requirement. Diversity increases with configurational heterogeneity were not due to greater variation in light niches, and diversity decreases were not due to success of fast growing species. Strikingly, plant density increased monotonically with increasing configurational heterogeneity, indicating that not only more species but also more individuals could coexist.Conclusions: This study provides experimental evidence for unimodal SHD curves in plant communities, which has hitherto only been predicted by models. Our results carry a striking similarity with other unimodal response patterns of plant species diversity, notably in diversity-disturbance and diversity-productivity relationships. [ABSTRACT FROM AUTHOR]

Stem cell therapy is a promising approach to treat myocardial infarction. However, direct delivery of stem cells into hearts experiences poor cell engraftment and differentiation, due to ischemic conditions (low nutrient and oxygen) in the infarct hearts. Development of suitable cell carriers capable of supporting cell survival and differentiation under these harsh conditions is critical for improving the efficacy of current stem cell therapy. In this work, we created a family of novel cell carriers based on thermosensitive hydrogels and insulin-like growth factor 1 (IGF-1), and investigated if these cell carriers can improve cell survival and differentiation under ischemic conditions. The thermosensitive hydrogels were synthesized from N-isopropylacrylamide, acrylic acid, acrylic acid N-hydroxysuccinicimide ester, and 2-hydroxyethyl methacrylate-oligo(hydroxybutyrate). The hydrogel solutions can be readily injected through 26G needles, and can quickly solidify at 37 °C to form highly flexible hydrogels. IGF-1 was immobilized into the hydrogels in order to support long-term cell survival and differentiation. Different amount of IGF-1 was immobilized by using hydrogels with different content of N-hydroxysuccinicimide ester groups. Cardiosphere derived cells were encapsulated in the hydrogels and cultured under ischemic conditions. The results demonstrated that a significant improvement of cell survival and differentiation was achieved after IGF-1 immobilization. These IGF-1 immobilized hydrogels have the potential to improve cell survival and differentiation in infarct hearts. [ABSTRACT FROM AUTHOR]

This study reports improved pulsed field capillary electrophoresis (PFCE) for separation of large DNA ladders. Important analytical conditions, including gel polymer concentration, ratio of forward to backward pulse duration, and separation potential, were investigated for their effects on the separation performance of DNA ranging in size from 0.1 to 10.0 kilo base pairs (kbp). Results show that DNA fragments from 0.1 to 8.0 kbp can be resolved with high resolution, simultaneously, in a short time. The ratio of forward to backward pulse duration affects the separation performance for DNA fragments greater than 1.5 kbp, and 3 or 4 is the optimum value of the ratio for separation of DNA up to 10 kbp. Furthermore, the separations that were obtained with 74-19,329 bp λ-DNA restriction fragments clearly demonstrate a dramatic improvement in the separation time and resolution over the conventionally used square-wave PFCE. The inversion field capillary electrophoresis reported here may help enable future DNA analysis studies to be performed quickly and effectively. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We studied the distribution pattern, species diversity and life-form spectra of plant communities along an altitudinal gradient in the mid-section of the northern slopes of Qilianshan Mountains by means of multivariate analyses. Two data sets (167 species × 75 plots, 10 environmental variables × 75 plots), originated from the fieldworks in 1998–1999, were subjected to TWINSPAN and DCCA, resulting in 8 major plant communities: 1) Asterothamnus centraliasiaticus–Halogeton arachnoideus desert grassland on azonal substrates from 1450 to 1600 m and 2) zonal Reaumuria soogorica desert grassland on gravels from 1470 to 1900 m; 3) Stipa przewalskii–Stipa purpurea montane grassland from 2200 to 2900 m; 4) Polygonum viviparum alpine grassland from 2900 to 3700 m; 5) Caragana stenophylla–Ajania fruticulosa dry-warm shrubland from 2350 to 2800 m; 6) Sabina przewalskii mid-wet warm forest from 2700 to 3300 m; 7) Picea crassifolia cold coniferous forest from 2450 to 3200 m; 8) Caragana jubata wet-cold alpine shrubland from 3100 to 3700 m. Species diversity and species richness of both grasslands and forests peaked at the intermediate portion of the elevational gradient. Evenness might be strongly influenced by either biotic or abiotic factors at a local scale, while seems quite independent of an elevational gradient at landscape scales. Beta-diversity decreased from 1500 to 3700 m, indicating that species turnover declined with increased elevation. Both richness of life-form and total species richness in a given altitudinal belt (gamma-diversity) peaked at intermediate elevations, while relative species richness of different life-form varied differently along the altitudinal gradient. [ABSTRACT FROM AUTHOR]

There is no final conclusion yet on the uplifting mechanism and epoch of the Tibetan Plateau, which is a hot point of the geological research. This paper discusses the epoch and scales of the hydrothermal activities based on the ESR ages of hot-spring sediments. The ESR ages show that hydrothermal activities mainly happened in four periods: 50×104a, 50×104–47×104, 40×104–35×104, 27×104–20×104 and 10×104—0 aB.P. This conclusion is supported by the geophysical data and the inner plateau and surrounding sediments. Through analyzing the constraints of the deep restraint mechanism and uplift tensile function of the plateau, the uplifting processes of the Tibetan Plateau since 50×104a B.P. is elucidated. [ABSTRACT FROM AUTHOR]

Gaps play a crucial role in maintaining species diversity, yet how community structure and composition influence gap formation is still poorly understood. We apply a spatially structured community model to predict how species diversity and intraspecific aggregation shape gap patterns emerging after climatic events, based on species-specific mortality responses. In multispecies communities, average gap size and gap-size diversity increased rapidly with increasing mean mortality once a mortality threshold was exceeded, greatly promoting gap recolonization opportunity. This result was observed at all levels of species richness. Increasing interspecific difference likewise enhanced these metrics, which may promote not only diversity maintenance but also community invasibility, since more diverse niches for both local and exotic species are provided. The richness effects on gap size and gap-size diversity were positive, but only expressed when species were sufficiently different. Surprisingly, while intraspecific clumping strongly promoted gap-size diversity, it hardly influenced average gap size. Species evenness generally reduced gap metrics induced by climatic events, so the typical assumption of maximum evenness in many experiments and models may underestimate community diversity and invasibility. Overall, understanding the factors driving gap formation in spatially structured assemblages can help predict community secondary succession after climatic events. [ABSTRACT FROM AUTHOR]