Design, fabrication, and characterization of a multidimensional prism.

In this research, a novel multidimensional prism with three distinct 45°, 135°, and 225° inclined optical surfaces were realized by using inclined exposure technology and SU-8 polymer. To obtain a smooth surface, the solvent loss percentage and temperature of post-exposure bake (PEB) are two key factors that need to be well controlled during fabrication. The experimental results showed that surface roughness can achieve 42.9±7.6 nm, which is one-tenth of high-precision machining or molding processes, under the processes parameter combinations of PEB temperature, and solvent loss percentage is 95°C and 82.86%, respectively. The surface reflectivity of the prism was measured by using a He-Ne laser, and reflectivity of the prism surface without and with aluminum metal film was 90.8% and 91.8%, respectively. The slight difference of reflectivity means that a prism with a high-quality inclined surface can be realized. The functionality of the prism for three lasers was also verified with RGB lasers, and it successfully demonstrated the feasibility of application of a multidimensional prism on the optical system. Finally, the utilization of inclined exposure technology not only monolithically integrates three 45° inclined surfaces into one prism without precision assembly but also greatly simplifies the fabrication processes to further reduce the cost. This component and technology can also be applied to medical endoscope systems if the SU-8 is replaced by PDMS or other biocompatible materials using a molding process. These results provide the potential for mass manufacturing, which is of considerable value to the optical markets.

Fabrication and Characterization of a High-Performance Multi-Annular Backscattered Electron Detector for Desktop SEM.

Scanning electron microscopy has been developed for topographic analysis at the nanometer scale. Herein, we present a silicon p-n diode with multi-annular configuration to detect backscattering electrons (BSE) in a homemade desktop scanning electron microscope (SEM). The multi-annular configuration enables the enhancement of the topography contrast of 82.11 nA/µm as compared with the commercial multi-fan-shaped BSE detector of 40.08 nA/µm. Additionally, we integrated it with lateral p-n junction processing and aluminum grid structure to increase the sensitivity and efficiency of the multi-annular BSE detector that gives higher sensitivity of atomic number contrast and better surface topography contrast of BSE images for low-energy detection. The responsivity data also shows that MA-AL and MA p-n detectors have higher gain value than the MA detector does. The standard deviation of measurements is no higher than 1%. These results verify that MA p-n and MA-AL detectors are stable and can function well in SEM for low-energy applications. It is demonstrated that the multi-annular (MA) detectors are well suited for imaging in SEM systems.

Inhibition of peroxisome proliferator-activated receptor gamma prevents the melanogenesis in murine B16/F10 melanoma cells.

The purpose of this study was to investigate if PPARγ plays a role in the melanogenesis. B16/F10 cells were divided into five groups: control, melanin stimulating hormone (α-MSH), α-MSH+retinol, α-MSH+GW9662 (PPARγ antagonist), and GW9662. Cells in the control group were cultured in the Dulbecco's modified Eagle's medium (DMEM) for 48 hrs. To initiate the melanogenesis, cells in all α-MSH groups were cultured in medium containing α-MSH (10 nM) for 48 hrs. Cells were treated simultaneously with retinol (5 µM) in the α-MSH+retinol group. Instead of retinol, GW9662 (10 µM) was cocultured in the α-MSH+GW9662 group. Cells in the final group were cultured in the DMEM with GW9662. All the analyses were carried out 48 hours after treatments. The α-MSH was able to increase cell number, melanin production, and the activity of tyrosinase, the limiting enzyme in melanogenesis. These α-MSH-induced changes were prevented either by retinol or by GW9662. Further analyses of the activities of antioxidant enzymes including glutathione, catalase, and the superoxide dismutase (SOD) showed that α-MSH treatment raised the activity of SOD which was dependent on PPARγ level. According to our results, the α-MSH-induced melanogenesis was PPARγ dependent, which also modulated the expression of SOD.

Self-aligned wet-cell for hydrated microbiology observation in TEM.

This paper describes a Self-Aligned Wet (SAW) cell suitable for direct-cell or bacteria incubation and observation in a wet environment inside a transmission electron microscope. This SAW cell is fabricated by a bulk-micromachining process and composed of two structurally complementary counterparts (an out-frame and an in-frame), where each contain a silicon nitride film based observation window. The in- and out-frames can be self-aligned via a mechanism of surface tension from a bio-sample droplet without the aid of positioning stages. The liquid chamber is enclosed between two silicon nitride membranes that are thin enough to allow high energy electrons to penetrate while also sustaining the pressure difference between the TEM vacuum and the vapor pressure within the liquid chamber. A large field of view (150 µm × 150 µm) in a SAW cell is favored and formed from a larger sized observation window in the out-frame, which is fabricated using a unique circular membrane formation process. In this paper, we introduce a novel design to circumvent the challenges of charging/heating problems in silicon nitride that arise from interactions with an electron beam. This paper also demonstrates TEM observations of D. Radiodurans growth in a liquid environment within a thicker chamber (20 µm) within a SAW cell.

Microfluidic systems for biosensing.

In the past two decades, Micro Fluidic Systems (MFS) have emerged as a powerful tool for biosensing, particularly in enriching and purifying molecules and cells in biological samples. Compared with conventional sensing techniques, distinctive advantages of using MFS for biomedicine include ultra-high sensitivity, higher throughput, in-situ monitoring and lower cost. This review aims to summarize the recent advancements in two major types of micro fluidic systems, continuous and discrete MFS, as well as their biomedical applications. The state-of-the-art of active and passive mechanisms of fluid manipulation for mixing, separation, purification and concentration will also be elaborated. Future trends of using MFS in detection at molecular or cellular level, especially in stem cell therapy, tissue engineering and regenerative medicine, are also prospected.

A gold-nanoparticle-enhanced immune sensor based on fiber optic interferometry.

A method using gold nanoparticles (GNPs) to enhance fiber optic interferometry (GNPFOI) for immune-sensing is reported in this paper. It is suggested that an enlarged index mismatch and an elongated optical path by GNPs conjugated on recognition proteins will contribute most to signal enhancement in the interference fringe shift. Theoretical and experimental results show that the interference fringe shift is linearly related to both the amount and size of the GNPs binding on the sensor surface. The detected signal for 30 nm GNPs can reach a lowest detection limit of 18 pM (10(10) particles ml(-1)). Immune-sensing for rabbit IgG as the antigen to anti-rabbit IgG has been demonstrated and a detection cycle has been completed by elution buffer for surface regeneration. The repeatability of the immune-sensing on one GNPFOI sensor has also been verified by three identical cycles, and the detection limit for 13 nm GNPs conjugated anti-rabbit IgG reaches 0.17 nM (∼25.5 ng ml(-1)). The sensory mechanism has the potential to be engineered on the tip of a needle-type micro-device, which would allow it to monitor immune recognition signals in the future.

Micro-patternable nanoporous polymer integrated with microstructures for molecular filtration.

This paper proposes a facile method to fabricate nanoporous microstructures by a photo-patternable SU-8 photoresist, to serve as a molecular filter in microfluidic systems. The fabrication process involves solvent-controlled nanoporous structure formation combined with standard photolithography steps for microstructure fabrication. The self-formed nanoporous morphology embedded inside the microstructure exhibits a sufficient mechanical strength and eliminates complex processes or protocols for integration/assembly of nano- and microstructures. Field emission gun scanning electronic microscopy (FEGSEM) images showed the fabricated nanoporous morphologies with embedded nanogaps of about 6-10 nm. Atomic force microscopy (AFM) images also depicted a clear difference on the degree of porosity between the solvent-controlled SU-8 and the standard resist. Fluorescent dyes, namely Rhodamine-B and Rhodamine-6G, were employed to estimate the diffusivity of the fabricated SU-8 based nanofilter and demonstrated that the Rhodamine based fluorescent molecules can penetrate these nanosized filtration structures. The fabricated nanofilter was capable of providing a molecular weight cut-off range up to 70 kDa, estimated roughly for a molecule with a diameter of 6-10 nm. This simple process provides a novel way to integrate the nanofiltration capability into microstructures while maintaining a sufficient mechanical strength for molecular level filtration in lab-on-chip (LOC) systems.

Self-masked high-aspect-ratio polymer nanopillars.

In this paper, a simple, cost effective, and potentially universal method is proposed for the formation of high-aspect-ratio nanopillars on various polymers. Our method involves direct reactive ion etching (RIE) using self-formed nanomasks oriented from a dummy material (cover glass). The mechanism is evaluated using nanopillar characterization and surface analysis results from x-ray photoelectron microscopy (XPS) and Auger electron microscopy (AES). By varying the dummy material configuration and modifying the RIE etching time, the distribution and dimensions of the nanopillars can be manipulated to meet a range of requirements. The maximum structural aspect ratio of 60 (6.7 microm high and 112 nm thick nanopillars) can be easily prepared using a 60 min self-masked high-aspect-ratio polymer nanopillars fabrication (SMHAR) process on poly(monochloro-p-xylylene) (Parylene C). Furthermore, nanopillars can also be generated using the same SMHAR process on poly(dimethylsiloxane) (PDMS) and SU-8 photoresist, creating nanostructured PDMS or SU-8 materials in lab-on-a-chip (LOC) or nano/micro-electromechanical systems (N/MEMS).