Two-Dimensional Electrochemiluminescence on Porous Silicon Platform for Explosive Detection and Discrimination

This work established a rapid and sensitive explosive detection and recognition technique. We report a two-dimensional electrochemiluminescence (2-D ECL) method based on porous silicon (pSi) by monitoring the dynamic change in peak position and peak intensity of pSi-ECL. Gold nanoparticles (AuNPs) were deposited on the pSi surface to promote the electrochemical reaction and electron transfer efficiency at the pSi–electrolyte interface. The 2-D ECL can effectively detect and discriminate different classes of explosives including nitro compounds, peroxides with nitrogen atoms, and peroxides without nitrogen atoms due to their different oxidation and electron transfer ability

Rapid Antibiotic Susceptibility Testing in a Microfluidic pH Sensor

For appropriate selection of antibiotics in the treatment of pathogen infection, rapid antibiotic susceptibility testing (AST) is urgently needed in clinical practice. This study reports the utilization of a microfluidic pH sensor for monitoring bacterial growth rate in culture media spiked with different kinds of antibiotics. The microfluidic pH sensor was fabricated by integration of pH-sensitive chitosan hydrogel with poly­(dimethylsiloxane) (PDMS) microfluidic channels. For facilitating the reflectometric interference spectroscopic measurements, the chitosan hydrogel was coated on an electrochemically etched porous silicon chip, which was used as the substrate of the microfluidic channel. Real-time observation of the pH change in the microchannel can be realized by Fourier transform reflectometric interference spectroscopy (FT-RIFS), in which the effective optical thickness (EOT) was selected as the optical signal for indicating the reversible swelling process of chitosan hydrogel stimulated by pH change. With this microfluidic pH sensor, we demonstrate that confinement of bacterial cells in a nanoliter size channel allows rapid accumulation of metabolic products and eliminates the need for long-time preincubation, thus reducing the whole detection time. On the basis of this technology, the whole bacterial growth curve can be obtained in less than 2 h, and consequently rapid AST can be realized. Compared with conventional methods, the AST data acquired from the bacterial growth curve can provide more detailed information for studying the antimicrobial behavior of antibiotics during different stages. Furthermore, the new technology also provides a convenient method for rapid minimal inhibition concentration (MIC) determination of individual antibiotics or the combinations of antibiotics against human pathogens that will find application in clinical and point-of-care medicine

<i>rsa1-1</i> plants are hypersensitive to NaCl, and RSA1 is involved in Na⁺ homeostasis under salt stress.

<p>(A)–(C) Five-d-old wild-type and <i>rsa1-1</i> seedlings grown on MS medium were transferred to MS medium supplemented with different levels of NaCl and allowed to grow for an additional 8 d. Root elongation or shoot fresh weight was measured and is shown as a percentage relative to growth on normal MS medium. (D) Two-week-old wild-type and <i>rsa1-1</i> plants grown in soil were irrigated with 300 mM NaCl for 0 or 14 d. (E) Survival rate of wild-type and <i>rsa1-1</i> plants as shown in (D). (F) Seed germination of wild type and <i>rsa1-1</i> in response to various NaCl levels. There were 80–150 seeds per genotype per biological replicate. Seeds in which the radical had emerged through the seed coat were considered germinated. (G) Na⁺ content in soil-grown wild-type and <i>rsa1-1</i> plants. DW, dry weight. (H) K⁺ content in soil-grown wild-type and <i>rsa1-1</i> plants. (I) Ratio of Na⁺ to K⁺ accumulation in soil-grown wild-type and <i>rsa1-1</i> plants. WT, wild type. Error bars indicate the standard deviation (n = 30–40). The experiments in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003755#pgen-1003755-g001" target="_blank">Figure 1</a> were repeated at least five times with similar results, and data from one representative experiment are presented.</p

2D Hybrid Nanomaterials for Selective Detection of NO₂ and SO₂ Using “Light On and Off” Strategy

In order to distinguish NO₂ and SO₂ gas with one sensor, we designed a paper chip assembled with a 2D g-C₃N₄/rGO stacking hybrid fabricated via a layer-by-layer self-assembly approach. The g-C₃N₄/rGO hybrid exhibited a remarkable photoelectric property due to the construction of a van der Waals heterostructure. For the first time, we have been able to selectively detect NO₂ and SO₂ gas using a “light on and off” strategy. Under the “light off” condition, the g-C₃N₄/rGO sensor exhibited a p-type semiconducting behavior with a low detection limit of 100 ppb of NO₂, but with no response toward SO₂. In contrast, the sensor showed n-type semiconducting behavior which could detect SO₂ at concentration as low as 2 ppm under UV light irradiation. The effective electron transfer among the 2D structure of g-C₃N₄ and rGO nanosheets as well as highly porous structures could play an important role in gas sensing. The different sensing mechanisms at “light on and off” circumstances were also investigated in detail

<i>ritf1</i> mutant plants are sensitive to salt and oxidative stresses, and overexpression of <i>RITF1</i> increases plant tolerance to salt and oxidative stresses.

<p>(A) Seed germination of wild type and <i>ritf1</i> in response to various NaCl levels. There were 80–150 seeds per genotype per biological replicate. (B) Fresh weight of wild-type and <i>ritf1</i> seedlings under salt stress. Five-d-old seedlings grown on MS medium were transferred to MS medium containing 0 or 100 mM NaCl and allowed to grow for an additional 7 d. (C) Growth responses of wild-type and <i>ritf1</i> seedlings to oxidative stress-inducing reagents H₂O₂ and methyl viologen (MV). (D) and (E) Fresh weight of seedlings grown on MS medium containing various levels of H₂O₂ (D) or MV (E) as shown in (C). (F) Salt tolerance of <i>RITF1</i> overexpression plants. Five-d-old seedlings grown on MS medium were transferred to MS medium containing 0 or 100 mM NaCl and allowed to grow for an additional 10 d. (G) and (H) Fresh weight of wild-type and <i>RITF1</i> overexpression plants grown on MS medium containing various levels of H₂O₂ (G) or MV (H). In (C)–(E), (G), and (H), seeds were sown directly on MS medium supplemented with various levels of H₂O₂ or MV and allowed to grow for an additional 10 d. Error bars represent the standard deviation (n = 8 in [A], 40 in [B], [D]–[H]). One-way ANOVA (Tukey-Kramer test) was performed, and statistically significant differences are indicated by different lowercase letters (p<0.05). The experiments in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003755#pgen-1003755-g005" target="_blank">Figure 5</a> were repeated at least four times with similar results, and data from one representative experiment are presented.</p

Low Power Consumption Gas Sensor Created from Silicon Nanowires/TiO₂ Core–Shell Heterojunctions

Silicon nanowires/TiO₂ (SiNWs/TiO₂) array with core–shell nanostructure was created by sol–gel and drop-casting methods. The hybrid material displayed excellent sensing performance for CH₄ detection at room temperature. The chemiresistor sensor has a linear response toward CH₄ gas in the 30–120 ppm range with a detection limit of 20 ppm, which is well below most CH₄ sensors reported before. The enhanced gas sensing performance at room temperature was attributed to the creation of heterojunctions that form a depletion layer at the interface of SiNWs and TiO₂ layer. Adsorption of oxygen and corresponding gas analyte on TiO₂ layer could induce the change of depletion layer thickness and consequently the width of the SiNWs conductive channel, leading to a sensitive conductive response toward gas analyte. Compared to conventional metal oxide gas sensors, the room temperature gas sensors constructed from SiNWs/TiO₂ do not need an additional heating device and work at power at the μW level. The low power consumption feature is of great importance for sensing devices, if they are widely deployed and connected to the Internet of Things. The innovation of room temperature sensing materials may push forward the integration of gas sensing element with wireless device

A working model for RSA1 and RITF1 function under salt stress.

<p>The calcium-binding protein RSA1 senses salt-induced changes in nuclear free calcium and interacts with a bHLH transcription factor, RITF1. RITF1 may be phosphorylated by nuclear-localized MAPKs. The RSA1-RITF1 complex controls expression of genes important for detoxification of salt-induced ROS and for Na⁺ homeostasis under salt stress. Some RITF1 target genes may play a role in salt tolerance with so far unknown mechanisms. The calcium-binding protein SOS3 senses salt-induced cytosolic calcium increases and interacts with SOS2, a protein kinase. The SOS3-SOS2 protein kinase complex then phosphorylates and thereby activates the plasma membrane-localized Na⁺/H⁺ antiporter SOS1.</p

RSA1 interacts with RITF1.

<p>(A) RSA1 interacts with RITF1 as determined by yeast two-hybrid assays. Yeast strain AH109 co-transformed with RSA1-pDEST32 (bait) and RITF1-pDEST22 (prey) was subjected to x-gal assay. AH109 cells co-transformed with RSA1-pDEST32/pDEST22 (empty vector) or RITF1-pDEST22/pDEST32 (empty vector) were used as negative controls. Yeast cells grown on SD medium-L-W or SD medium-L-W-H+3-AT are shown. 3-AT, 3-amino-1,2,4-triazole. L, W, H, symbols for amino acids leucine, tryptophan, and histidine, respectively. SD, yeast minimal media. (B) Localization of RITF1-GFP in <i>Arabidopsis</i> protoplasts. Bar = 25 µm. (C) RSA1 interacts with RITF1 <i>in vivo</i> as determined by BiFC assays in tobacco leaf epidermal cells. Bars = 25 µm in (a), and 50 µm in (b) and (c). YFP images were detected at an approximate frequency of 4.04% (101 out of 2,501 tobacco leaf epidermal cells analyzed exhibited BiFC events). (D) RSA1 interacts with RITF1 <i>in vivo</i> as determined by Split-LUC assays. (E) RSA1 interacts with RITF1 <i>in vivo</i> as determined by Co-IP assays. (F) <i>RITF1</i> expression under salt stress. The qRT-PCR analysis was carried out with 14-d-old wild-type seedlings grown for 6 h on MS medium containing 0, 100, or 150 mM NaCl. Error bars represent the standard deviation (n = 20 in [D], 4 in [F]). The experiments in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003755#pgen-1003755-g004" target="_blank">Figure 4</a> were performed at least three times with similar results, and data from one representative experiment are presented.</p

Drug-Porous Silicon Dual Luminescent System for Monitoring and Inhibition of Wound Infection

Wound monitoring and curing is of great importance in biomedical research. This work created a smart bandage that can simultaneously monitor and inhibit wound infection. The main components of the smart bandage are luminescent porous silicon (LuPSi) particles loaded with ciprofloxacin (CIP). This dual luminescent system can undergo accelerated fluorescent color change from red to blue upon the stimulation of reactive oxygen species (ROS) and elevated pH, which are main biomarkers in the infected wound. The mechanism behind the chemical-triggered fluorescent color change was studied in detail. <i>In vitro</i> experiment showed that the ratiometric fluorescent intensity (<i>I</i>_Red/<i>I</i>_Blue) of CIP-LuPSi particles decreased from 10 to 0.03 at pH 7.5 after 24 h, while the value deceased from 10 to 2.15 at pH 7.0. Strong correlation can be also found between the <i>I</i>_Red/<i>I</i>_Blue value and ROS concentration ranging from 0.1 to 10 mM. In addition, the oxidation of LuPSi also simultaneously triggered the release of CIP molecules, which exhibited bacterial inhibition activity. Therefore, the ratiometric fluorescent intensity change at red and blue channels can indicate not only the wound infection status but also the release of antibiotics. <i>In vivo</i> test proved that the smart bandage could distinguish infected wounds from acute wounds, just relying on the naked eyes or a cell phone camera. On the basis of the Si nanotechnology established in this work, theranostic wound care will be realized in future

Tip-Enhanced Photoinduced Electron Transfer and Ionization on Vertical Silicon Nanowires

Nanostructured semiconductors are one of the most potent candidates for matrix-free laser desorption/ionization mass spectrometric (LDI-MS) analysis of low-molecular-weight molecules. Herein, the enhanced photoinduced electron transfer and LDI on the tip of a vertical silicon nanowire (SiNW) array were investigated. Theoretical simulation and LDI detection of indigo and isatin molecules in negative ion mode revealed that the electric field can be enhanced on the tip end of SiNWs, thereby promoting the energy and electron transfer to the analytes adsorbed on the tip of SiNWs. On the basis of this finding, a tip-contact sampling method coupled with LDI-MS detection was established. In this strategy, the tip of SiNWs can be regarded as microextraction heads for the sampling of molecules when they come in contact with analytes. Impression of skin, tissue, and pericarp on the vertical SiNW array can effectively transfer endogenous metabolites or exogenous substances onto the tip. Upon laser irradiation, the adsorbed molecules on the SiNW tip can be efficiently ionized and detected in negative ion mode because of the tip-enhanced electron transfer and LDI effect. We believe this work may significantly expand the application of LDI-MS in various fields