Investigation of Sulfur Doping in Mn–Co Oxide Nanotubes on Surface-Enhanced Raman Scattering Properties

Doping engineering is an efficient strategy to manipulate the optoelectronic properties of metal oxides for sensing, catalysis, and energy applications. Herein, we have demonstrated the fabrication of sulfur (S)-doped Mn–Co oxides to regulate their band and surface electronic structures, which is beneficial to enhancing the charge transfer (CT) between the metal oxides and their adsorbed molecules. As expected, significantly enhanced SERS signals are achieved on S-doped Mn–Co oxide nanotubes, and the minimum detection concentration can reach as low as 10–8 M. Furthermore, the change in the electronic structure caused by S-doping provides different microelectric fields to influence the orientation of the interaction between the probe molecules and the substrate. Additionally, the evaluation of the oxidase-like catalytic activity of the substrate proved that, with an increase in the ratio of Co2+/Co3+ content, the number of electrons on the substrate increases, which promotes the CT process and further increases the degree of CT. The nonmetallic doping route in semiconducting metal oxides can provide effective and stable SERS activity; moreover, it provides a new strategy for exploring the relationship between CT in catalysis and SERS performance of semiconductors

In Situ Growth of Laser-Induced Graphene on Flexible Substrates for Wearable Sensors

Advances in healthcare monitoring, human–machine interfaces, and soft robots require the development of wearable sensors that are efficient, scalable, and facile to prepare. Although laser-induced graphene (LIG) has recently attracted considerable attention in the fabrication of patterned graphene-based wearable sensors, the transfer process is inevitable due to the limited stretchability of carbon precursors. In this work, we proposed a strategy for in situ growth, transfer-free LIG on various flexible substrates (poly(dimethylsiloxane) (PDMS), poly(ethylene terephthalate) (PET), and paper). This was achieved by coating a biobased liquid carbon precursor (PGE-fa) on target substrates followed by laser irradiation under ambient conditions. After encapsulation, the fabricated flexible sensors were obtained. Based on the advantage of LIG in patterning, designs with different shapes and geometrical parameters were systematically investigated to optimize the sensing performance. The resulting LIG/PDMS sensor had a wide working range of ∼30% and demonstrated an ultrahigh sensitivity of 68,238.5 as well as outstanding stability over 10,000 cycles. Additionally, the sensor responded well to external stimuli at different bending angles. The potential applications of the sensor were further demonstrated by monitoring human motions, from subtle signals, including vocal cords, to large movements of the fingers and elbow joints

DHA-induced apoptosis is caused by ROS.

<p>(A) Apoptosis of pancreatic cancer cells. BxPC-3 and PANC-1 cells were treated with DHA (50 µmol/L) and Apo2L/TRAIL (100 ng/ml) as indicated. Flow cytometry was performed to measure apoptosis rates (%). A significant increase in the apoptosis rate compared with the control is denoted by “*” (<i>P</i><0.05), a significant increase compared with DHA- or Apo2L/TRAIL-treated cells is denoted by “†” (<i>P</i><0.01), and a significant decrease compared with DHA+Apo2L/TRAIL-treated cells is denoted by “‡” (<i>P</i><0.01). Representative histograms from cytometrically analyzed BxPC-3 and PANC-1 cells treated with control, DHA, Apo2L/TRAIL, DHA+Apo2L/TRAIL or NAC (10 mM). (B) Laser scanning confocal microscopy of cells. Representative photographs were taken of the control BxPC-3 and PANC-1 cells and of BxPC-3 and PANC-1 cells treated with DHA+Apo2L/TRAIL and DHA+Apo2L/TRAIL+NAC. (C) Levels of intracellular ROS measured in vitro. BxPC-3 and PANC-1 cells were treated with DHA (50 µmol/L), Apo2L/TRAIL (100 ng/ml), DHA+Apo2L/TRAIL, or pretreated with NAC (10 mM) and then treated with DHA+Apo2L/TRAIL for 6 h. Untreated cells served as the control. The cells were incubated with DCFHDA and then subjected to flow cytometry to measure the levels of intracellular ROS, as represented by DCF fluorescence. A significant increase in DCF fluorescence compared with the control is denoted by “*” (<i>P</i><0.05), a highly significant difference compared with the control is denoted by “**” (<i>P</i><0.01), and a significant reduction compared with the DHA+Apo2L/TRAIL treatment is denoted by “†” (<i>P</i><0.05). (D) Representative photographs are shown for DCFHDA-stained cells observed using laser scanning confocal microscopy. The green fluorescence represents intracellular ROS. (E) The mean fluorescence intensity was measured for the DCFHDA-stained cells, and the respective 3-dimensional horizontal plane images were produced by laser scanning confocal microscopy. A significant difference from the control is denoted by “*” (<i>P</i><0.01), and a significant difference from the DHA+Apo2L/TRAIL treatment is denoted by “†” (<i>P</i><0.05).</p

The expression of apoptosis-related genes.

<p>BxPC-3 and PANC-1 cells were treated with various concentrations of DHA (0, 25, 50, 100 µmol/L) and pretreated with NAC followed by DHA (100 µmol/L) for 72 h. Whole cell extracts were prepared and analyzed by western blotting using antibodies against Bcl-2, Bax, surviving, caspase-3, caspase-8, and caspase-9. DHA significantly up-regulated the expression of Bax, caspase-3, caspase-8 and caspase-9, and down-regulated the expression of Bcl-2. However, DHA had little influence on the expression of survivin. DHA with NAC (10 mM) pretreatment did not up-regulate the expression of caspase-8, Bax, caspase-9, and caspase-3. β-actin served as an internal control.</p

Effects of knockdown of DR5 expression on DHA-induced cytotoxicity and cell apoptosis of Apo2L/TRAIL.

<p>BxPC-3 and PANC-1 cells were transfected with DR5 siRNA and control siRNA, either alone or in combination. After 48 h, the cells were treated with 50 µmol/L DHA for 24 h, and whole cell extracts were subjected to western blotting to test for the expression of DR5. Transfection of cells with siRNA targeting DR5 specifically silenced the expression of DR5. The cells were seeded on a chamber slide and transfected with siRNAs. After 48 h, the cells were treated with 50 µmol/L DHA, 100 ng/mL Apo2L/TRAIL, either alone or in combination, and incubated at 37°C for 72 h. The viability of the cells was assessed using the MTT method, and the viability index (%) was calculated. Silencing of DR5 by siRNA reduced the cytotoxic effect of the combination of DHA and Apo2L/TRAIL but not of DHA alone. Significant differences are denoted by “*” (<i>P</i><0.01).</p

Up-regulation of DR5 by DHA was mediated by ROS.

<p>(A) BxPC-3 and PANC-1 cells were treated with the indicated doses of DHA for 48 h. Whole cell extracts were prepared and analyzed for DR5 expression using western blotting. DHA had dose-dependent effects on the expression of DR5. The DHA-induced increase in DR5 levels was significantly blocked by pretreatment with 10 mM NAC. β-actin served as an internal control. (B) The cells were collected and analyzed using flow cytometry. A gradual increase in fluorescence was observed in cells treated with 25, 50 and 100 µmol/L DHA, respectively, indicating a dose-dependent increase in the production of ROS in response to DHA treatment in the two cell lines. The production of ROS was markedly inhibited by pretreating the cells with NAC (10 mM). (C) The cells were treated with DHA (50 µmol/L) alone, Apo2L/TRAIL (100 ng/ml) alone or a combination of the two agents. The cells were also treated with NAC (10 mM) alone or pretreated with NAC and incubated at 37°C for 72 h. The viability of the cells was assessed using the MTT method and the viability index (%) was calculated. Significant differences are denoted by “*” (<i>P</i><0.01).</p

Tumor growth, tumor gene expression, tumor proliferation and apoptosis <i>in vivo</i>.

<p>(A) BxPC-3 tumors were established subcutaneously in mice. When the tumors reached approximately 120 mm³ in volume, the mice were randomly assigned to control, DHA, Apo2L/TRAIL, or DHA+Apo2L/TRAIL groups and treated as described in the methods section. The sizes (measured in mm³) of the tumors were monitored and recorded. A significant difference in tumor volume from the control is denoted by “*” (<i>P</i><0.05), and a significant reduction compared to the DHA or Apo2L/TRAIL-treated tumors is denoted by “**” (<i>P</i><0.01). (B) Representative animals and tumors are shown for each group. (C) Tumors from control mice and from mice treated with DHA, Apo2L/TRAIL, and DHA+Apo2L/TRAIL were homogenized and subjected to western blot analysis to detect the expression of caspase-3 and caspase-8. β-actin served as an internal control. (D) Analysis of proliferation marker PCNA by immunohistochemistry and apoptotic status of tumor cells by in situ TUNEL assay. PCNA positive (E) and TUNEL-positive (F) cells were also counted under microscope to calculate the proliferation index and apoptotic index, respectively. “*”: <i>P</i><0.05, compared with control. “**”: <i>P</i><0.01, compared with single agent.</p

DHA synergistically enhances Apo2L/TRAIL-induced cell death in BxPC-3 cells.

<p>(A) Cells were treated with DHA alone, Apo2L/TRAIL alone or a combination of the two agents and incubated at 37°C for 72 h. The viability of the cells was assessed using the MTT method. Combination index (CI) versus fraction affected (Fa) plots obtained from median-effect analysis of Chou-Talalay. A CI>1 indicates antagonism,  = 1 indicates additivity, and <1 indicates synergy. (B) The clonogenic assay was performed as described in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037222#s4" target="_blank">Materials and Methods</a> section. The cells were treated with DHA (50 µmol/L) alone, Apo2L/TRAIL (100 ng/ml) alone or the combination of the two drugs for 24 h and washed with PBS. The cells were then incubated for an additional 7 d and stained with crystal violet. (C) Clonogenic survival is presented as the percentage of surviving colonies formed in drug-treated cells with respect to untreated cells.</p