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We demonstrate GaAs pillar array-based light emitting diodes (LEDs) with axial p-i-n junctions fabricated using a room-temperature metal-assisted chemical etching (MacEtch) method. Variations in vertical etch rates for all three doping types of GaAs are investigated as a function of etching temperature, oxidant/acid concentration ratio, and dilution of the etching solution. Control over nanopillar morphologies is demonstrated, simply through modification of the etching conditions. Optical emission enhancement from the MacEtched p-i-n GaAs nanopillar LED is observed, relative to the non-etched planar counterpart, through room-temperature photoluminescence and electroluminescence characterization.

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In this work, a surface plasmon resonance (SPR) biosensor based on two-dimensional transition metal dichalcogenides (TMDCs) is proposed to improve the biosensor’s sensitivity. In this sensor, different kinds of two-dimensional TMDCs are coated on both surfaces of metal film. By optimizing the structural parameters, the angular sensitivity can reach as high as 315.5 Deg/RIU with 7-layers WS2 and 36 nm Al thin film, which is 3.3 times of the conventional structure based on single Al thin film. We also obtain maximum phase sensitivity (3.85 × 106 Deg/RIU) with bilayer WS2 and 35 nm Al thin film. The phase sensitivity can be further improved by employing Ag and removing air layer. The proposed configuration is of great potential for biochemical sensing.

Metallic films with subwavelength apertures, integrated into a semiconductor by metal-assisted chemical etch (MacEtch), demonstrate enhanced transmission when compared to bare semiconductor surfaces. The resulting "buried" metallic structures are characterized spectroscopically and modeled using rigorous coupled wave analysis. These composite materials offer potential integration with optoelectronic devices, for simultaneous near-uniform electrical contact and strong optical coupling to free space.

The demand for rapid and sensitive bacterial detection is continuously increasing due to the significant requirements of various applications. In this study, a terahertz (THz) biosensor based on rolling circle amplification (RCA) was developed for the isothermal detection of bacterial DNA. The synthetic bacterium-specific sequence of 16S rDNA hybridized with a padlock probe (PLP) that contains a sequence fully complementary to the target sequence at the 5' and 3' ends. The linear PLP was circularized by ligation to form a circular PLP upon recognition of the target sequence; then the capture probe (CP) immobilized on magnetic beads (MBs) acted as a primer to initialize RCA. As DNA molecules are much less absorptive than water molecules in the THz range, the RCA products on the surface of the MBs cause a significant decrease in THz absorption, which can be sensitively probed by THz spectroscopy. Our results showed that 0.12 fmol of synthetic bacterial DNA and 0.05 ng μL of genomic DNA could be effectively detected using this assay. In addition, the specificity of this strategy was demonstrated by its low signal response to interfering bacteria. The proposed strategy not only represents a new method for the isothermal detection of the target bacterial DNA but also provides a general methodology for sensitive and specific DNA biosensing using THz spectroscopy.

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