Synergistic SERS Enhancement in GaN-Ag Hybrid System toward Label-Free and Multiplexed Detection of Antibiotics in Aqueous Solutions.

Noble metal-based surface-enhanced Raman spectroscopy (SERS) has enabled the simple and efficient detection of trace-amount molecules via significant electromagnetic enhancements at hot spots. However, the small Raman cross-section of various analytes forces the use of a Raman reporter for specific surface functionalization, which is time-consuming and limited to low-molecular-weight analytes. To tackle these issues, a hybrid SERS substrate utilizing Ag as plasmonic structures and GaN as charge transfer enhancement centers is presented. By the conformal printing of Ag nanowires onto GaN nanopillars, a highly sensitive SERS substrate with excellent uniformity can be fabricated. As a result, remarkable SERS performance with a substrate enhancement factor of 1.4 × 1011 at 10 fM for rhodamine 6G molecules with minimal spot variations can be realized. Furthermore, quantification and multiplexing capabilities without surface treatments are demonstrated by detecting harmful antibiotics in aqueous solutions. This work paves the way for the development of a highly sensitive SERS substrate by constructing complex metal-semiconductor architectures.

Effect of core and surface area toward hydrogen gas sensing performance using Pd@ZnO core-shell nanoparticles.

A versatile hydrogen gas sensor is fabricated using Pd@ZnO core-shell nanoparticles (CSNPs), which were synthesized through a hydrothermal route. Effect of oxidation behavior of Pd core to hydrogen sensing is also investigated for Pd@ZnO CSNPs. Accordingly, Pd@ZnO-2 sensor (core-shell sample was calcined in argon) demonstrates the best performance with respect to Pd@ZnO-1 (core-shell sample was calcined in air) and pure ZnO. It shows a much higher response (R = Ra/Rg = 22) than those of Pd@ZnO-1 (12) and pure ZnO (7) sensors with faster response and recovery times (1.4 and 7.8 min) to 100 ppm hydrogen at 350 °C. In addition, Pd@ZnO-2 sensor owns high selectivity to hydrogen among interfering target gases. Improvement can be attributed to the high content of metallic Pd0 species in CSNPs as calcined in argon. Thereby, a higher Pd metallic content (77%) still remains in Pd@ZnO-2 compared to Pd@ZnO-1 (56%), which in turn modulates the resistance of sensors as exposed to air and target gas, thus enhancing gas sensing activity. High BET surface area of core-shell materials provides plenty of active sites for accelerating the sensing reactions as well.

Triple phase boundary and power density enhancement in PEMFCs of a Pt/C electrode with double catalyst layers.

Exploring efficient approaches to design electrodes for proton exchange membrane fuel cells (PEMFCs) is of great advantage to overcome the current limitations of the standard platinum supported carbon (Pt/C) catalyst. Herein, a Pt/C electrode consisting of double catalyst layers (DCL) with low Pt loading of around 0.130 mgPt cm-2 is prepared using spray and electrophoresis (EPD) methods. The DCL electrode demonstrated a higher electrochemical surface area (ECSA-52.5 m2 gPt -1) and smaller internal resistance (133 Ω) as compared to single catalyst layer (SCL) sprayed (37.1 m2 gPt -1 and 184 Ω) or EPD (42.4 m2 gPt -1 and 170 Ω) electrodes. In addition, the corresponding DCL membrane electrode assembly (MEA), which consists of a Pt/C DCL electrode at the anode side and a Pt/C sprayed electrode at the cathode side, also showed improved PEMFC performance as compared to others. Specifically, the DCL MEA generated the highest power density of 4.9 W mgPt -1, whereas, the SCL MEAs only produced 3.1 and 3.8 W mgPt -1, respectively. The superior utilization of the Pt catalysts into the DCL MEA can originate from the enrichment of the triple phase boundary (TPB) presented on the Pt/C DCL electrode, which can strongly promote the adsorbed hydrogen intermediates' removal from the anode side, thus improving the overall PEMFC performance.