Houxiao Wang

Bifunctional electro-optical nanoprobe to real-time detect local biochemical processes in single cells

A bifunctional electro-optical nanoprobe with integrated nanoring electrode and optical nanotip was fabricated and investigated to simultaneously detect both electrical and optical signals in real-time with high spatial resolution. Concurrent measurements of the oxidant generation and the intracellular antioxidant levels in single cells correlate the stronger oxidant generation with an altered initial antioxidant response in the breast cancer cells in comparison to the normal ones suggesting that the cell malignancy is associated with the strength of oxidative stress, and the higher antioxidant level may be the cause of the drug resistance. While the optical detection indicates the fluctuation of the intracellular redox homeostasis, the chronoamperometric signals allow quantitative real-time detection of the H₂O₂ release and decay. Furthermore, the nanoscale probe enables localized simultaneous detections thus discovering that activated enzymes responsible for the oxidative stress target at specific membrane regions. This method promises applications in study of the dynamics of important physiological processes, and provides the opportunity to unravel the interplay of various signaling pathways.

Focused ion beam assisted interface detection for fabricating functional plasmonic nanostructures

Plasmonic nanoscale devices/structures have gained more attention from researchers due to their promising functions and/or applications. One important technical focus on this rapidly growing optical device technology is how to precisely control and fabricate nanostructures for different functions or applications (i.e., patterning end points should locate at/near the interface while fabricating these plasmonic nanostructures), which needs a systematic methodology for nanoscale machining, patterning, and fabrication when using the versatile nanoprecision tool focused ion beam (FIB), that is, the FIB-assisted interface detection for fabricating functional plasmonic nanostructures. Accordingly, in this work, the FIB-assisted interface detection was proposed and then successfully carried out using the sample-absorbed current as the detection signal, and the real-time patterning depth control for plasmonic structure fabrication was achieved via controlling machining time. Besides, quantitative models for the sample-absorbed currents and the ion beam current were also established. In addition, some nanostructures for localized surface plasmon resonance biosensing applications were developed based on the proposed interface detection methodology for FIB nanofabrication of functional plasmonic nanostructures. It was shown that the achieved methodology can be conveniently used for real-time control and precise fabrication of different functional plasmonic nanostructures with different geometries and dimensions.

Focused Ion Beam Nano-Precision Machining for Analyzing Photonic Structures in Butterfly

Nano-precision machining using focused ion beam (FIB) is widely applied in many fields. So far, FIB-based nanofabrication for specific nanoscale applications has become an interesting topic to realize more diversities for nano-construction. Through FIB machining, we can easily achieve the required nano- and micro-scale patterning, device fabrication, and preparation of experimental samples. Nowadays, there is an increasing trend to learn from nature to design novel multi-functional materials and devices. Thus, more interestingly, another advantage of FIB is that it can be conveniently used to analyze the natural photonic structures, e.g., those in the butterfly which exhibits amazing optical phenomena due to sub-wavelength structural color. Accordingly, in the present study, structural analyses for butterfly wings were carried out using FIB. It is found that the photonic structures for the backside and frontside of the butterfly wing studied differ considerably. The difference accounts for the different colors on the dorsal and ventral sides of butterfly wings.

Influence of assist gases on pulsed laser drilling of nickel-based superalloy

Assist gases, including combustion-supporting gas and shielding gas, can greatly affect laser drilling process and drilled hole quality. In this study, oxygen and argon were used for assisting pulsed laser drilling of nickel-based superalloy plates. Influential mechanisms for oxygen and argon on pulsed laser drilling processes were discussed. Effects of oxygen and argon on drilled microhole entry, hole wall quality (defects, morphology, surface roughness), and drilling efficiency were analyzed. It was shown that oxygen-assisted laser drilling could achieve higher drilling efficiency (threshold of pulse number for argon-assisted laser drilling is relatively high). Different from argon-assisted laser drilling, the melted material might combust with oxygen during oxygen-assisted laser drilling process, leading to some black brittle oxides around the drilled hole wall/entry (these oxides could be easily removed due to their poor adhesion to hole entry surface). When using oxygen-assisted laser drilling, many microscale depressions and cracks were found around the drilled microhole wall. Moreover, compared with oxygen-assisted laser drilling (on the same other conditions), surface roughness and microcracks of the microhole wall drilled using argon-assisted pulsed laser were obviously reduced.

Butterfly-Inspired 2D periodic tapered-staggered subwavelength gratings designed based on finite difference time domain method

The butterfly-inspired 2D periodic tapered-staggered subwavelength gratings were developed mainly using finite difference time domain (FDTD) method, assisted by using focused ion beam (FIB) nanoscale machining or fabrication. The periodic subwavelength structures along the ridges of the designed gratings may change the electric field intensity distribution and weaken the surface reflection. The performance of the designed SiO2 gratings is similar to that of the corresponding Si gratings (the predicted reflectance can be less than around 5% for the bandwidth ranging from 0.15 µm to 1 µm). Further, the antireflection performance of the designed x-unspaced gratings is better than that of the corresponding x-spaced gratings. Based on the FDTD designs and simulated results, the butterfly-inspired grating structure was fabricated on the silicon wafer using FIB milling, reporting the possibility to fabricate these FDTD-designed subwavelength grating structures.