Micromachines2015, 6(5), 648-659; doi:10.3390/mi6050648 (registering DOI) - published 22 May 2015 Show/Hide Abstract
Abstract: We propose a system that transports oocytes and measures their mechanical characteristics in an open environment using a robot integrated microfluidic chip (chip). The cells are transported through a micropillar array in the chip, and their characteristics are measured by a mechanical probe and a force sensor. Because the chip has an open microchannel, important cells such as oocytes are easily introduced and collected without the risk for losing them. In addition, any bubbles trapped in the chip, which degrade the measurement precision, are easily removed. To transport the oocytes through the open microchannel, we adopt a transportation technique based on a vibration-induced flow. Under this flow, oocytes arrive at the measurement point, where their mechanical characteristics are determined. We demonstrate the introduction, transportation, measurement of mechanical characteristics, and collection of oocytes using this system.
Micromachines2015, 6(5), 634-647; doi:10.3390/mi6050634 (registering DOI) - published 22 May 2015 Show/Hide Abstract
Abstract: Flow cytometry is a well-established diagnostic tool for cell counting and characterization. It utilizes fluorescence and scattered excitation light simultaneously emitted from cells passing an excitation laser focus to discriminate various cell types and estimate cell size. Here, we apply the principle of spatially modulated emission (SME) to fluorescently stained SUP-B15 cells as a model system for cancer cells and Marinococcus luteus as model for bacteria. We demonstrate that the experimental apparatus is able to detect these model cells and that the results are comparable to those obtained by a commercially available CASY® TT Counter. Furthermore, by examining the velocity distribution of the cells, we observe clear relationships between cell condition/size and cell velocity. Thus, the cell velocity provides information comparable to the scatter signal in conventional flow cytometry. These results indicate that the SME technique is a promising method for simultaneous cell counting and viability characterization.
Micromachines2015, 6(5), 622-633; doi:10.3390/mi6050622 (registering DOI) - published 21 May 2015 Show/Hide Abstract
Abstract: This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic channels. Droplet, core and shell dimensions were controlled by varying the flow rates of each phase. When the organic solvent was released from the organic phase shell, the environmental conditions changed the shape of the solidified polymer shell to either a hollow capsule or a microlens. A uniform solvent release process produced polymeric capsules with nanoliter gas core volumes and a membrane thickness of approximately 3 μm. Alternatively physical rearrangement of the core and shell allowed for the formation of polymeric microlenses. On-demand formation of the polymer lenses in wells and through-holes polydimethylsiloxane (PDMS) structures was achieved. Optical properties of the lenses were controlled by changing the dimension of these structures.
Micromachines2015, 6(5), 611-621; doi:10.3390/mi6050611 - published 19 May 2015 Show/Hide Abstract
Abstract: Tribology of SU-8 polymer is increasingly relevant due to bursting use of this material in a variety of applications. This study is directed towards introduction and investigation of a novel self-lubricating composite of an ionic liquid (IL) in SU-8. The new material can be utilized for fabrication of lubricating polymer coating with tunable surface properties or SU8-made elements for microelectromechanical systems (MEMS) with enhanced tribological performance. It is shown that addition of IL drastically alters water affinity of the composite while UV patternability remains unmodified. A lower coefficient of friction and wear has been obtained for two investigated compositions with 4 and 10 wt % ionic liquid.
Micromachines2015, 6(5), 600-610; doi:10.3390/mi6050600 - published 13 May 2015 Show/Hide Abstract
Abstract: To manipulate liquid matter at the nanometer scale, we have developed a robotic assembly equipped with a hollow atomic force microscope (AFM) cantilever that can handle femtolitre volumes of liquid. The assembly consists of four independent robots, each sugar cube sized with four degrees of freedom. All robots are placed on a single platform around the sample forming a nano-workbench (NWB). Each robot can travel the entire platform and has a minimum position resolution of 5 nm both in-plane and out-of-plane. The cantilever chip was glued to the robotic arm. Dispensing was done by the capillarity between the substrate and the cantilever tip, and was monitored visually through a microscope. To evaluate the performance of the NWB, we have performed three experiments: clamping of graphene with epoxy, mixing of femtolitre volume droplets to synthesize gold nanoparticles and accurately dispense electrolyte liquid for a nanobattery.
Micromachines2015, 6(5), 592-599; doi:10.3390/mi6050592 - published 12 May 2015 Show/Hide Abstract
Abstract: This paper presents the design of terahertz 2× and 4× sub-harmonic down-mixers using Schottky Barrier Diodes fabricated in standard 0.13 μm SiGe BiCMOS technology. The 340 GHz sub-harmonic mixers (SHMs) are designed based on anti-parallel-diode-pairs (APDPs). With the 2nd and 4th harmonic, local oscillator (LO) frequencies of 170 GHz and 85 GHz are used to pump the two 340 GHz SHMs. With LO power of 7 dBm, the 2× SHM exhibits a conversion loss of 34.5–37 dB in the lower band (320–340 GHz) and 35.5–41 dB in the upper band (340–360 GHz); with LO power of 9 dBm, the 4× SHM exhibits a conversion loss of 39–43 dB in the lower band (320–340 GHz) and 40–48 dB in the upper band (340–360 GHz). The measured input 1-dB conversion gain compression point for the 2× and 4× SHMs are −8 dBm and −10 dBm at 325 GHz, respectively. The simulated LO-IF (intermediate frequency) isolation of the 2× SHM is 21.5 dB, and the measured LO-IF isolation of the 4× SHM is 32 dB. The chip areas of the 2× and 4× SHMs are 330 μm × 580 μm and 550 μm × 610 μm, respectively, including the testing pads.