In microfluidic filtration systems, one of the leading obstacles to efficient, continuous operation is clogging of the filters. Here, we introduce a lateral flow microfluidic sieving (μ-sieving) technique to overcome clogging and to allow continuous operation of filter based microfluidic separation. A low frequency mechanical oscillation was added to the fluid flow, which made possible the release of aggregated unwanted polystyrene (PS) particles trapped between the larger target PS particles in the filter demonstrating continuous μ-sieving operation. We achieved collection of the target PS particles with 100% separation efficiency. Also, on average, more than 98% of the filtered target particles were retrieved after the filtration showing high retrieval rates. Since the oscillation was applied to the fluid but not to the microfluidic filter system, mechanical stresses to the system was minimized and no additional fabrication procedures were necessary. We also applied the μ-sieving technique to the separation of cancer cells (MDA-MB-231) from whole blood and showed that the fluidic oscillations prevented the filters from being blocked by the filtered cancer cells allowing continuous microfluidic separation with high efficiency.

We report on a method which allows direct patterning of density controlled carbon nanotube network (NTN) devices during network formation. By lithographically patterning photoresist on the filter membrane, the nanotubes in suspension were guided to the exposed pattern areas of the filter surface during vacuum filtration allowing in situ device formation. The NTNs were transferred to an elastomer substrate by directly curing polydimethylsiloxane on its surface. We compared electrical characteristics of NTN patterns fabricated simultaneously using this method and found that the different NTNs with equal nanotube density showed reproducible characteristics.

The separation of circulating tumor cells (CTCs) from the peripheral blood is an important issue that has been highlighted because of their high clinical potential. However, techniques that depend solely on tumor-specific surface molecules or just the larger size of CTCs are limited by tumor heterogeneity. Here, we present a slanted weir microfluidic device that utilizes the size and deformability of CTCs to separate them from the unprocessed whole blood. By testing its ability using a highly invasive breast cancer cell line, our device achieved a 97% separation efficiency, while showing an 8-log depletion of erythrocytes and 5.6-log depletion of leukocytes. We also developed an image analysis tool that was able to characterize the various morphologies and differing deformability of the separating cells. From the results, we believe our system possesses a high potential for liquid biopsy, aiding future cancer research.

The doping effect on graphene by photoresists were studied in this article. Polymethyl methacrylate (PMMA) is the usual choice for graphene transfer, but it is known to leave a significant amount of residue. PMMA results in strong hole doping and reduction of mobility of the graphene devices. Not only PMMA, but photoresists also leave residues during the lithographic steps and dope the graphene in strong hole-doping states along with water and oxygen molecules. In this article, we tested three types of photoresists for their effects on graphene’s electrical properties. It was found that a specific photoresist can significantly reduce the amount of hole-doping of the graphene transistor more than other photoresists. The use of hydrophobic substrates and additional thermal treatment can help reducing the hole-doping further.

We report on a stable and sensitive biochemical sensor based on amorphous indium-gallium-zinc-oxide (a-IGZO) thinfilm transistors (TFTs) with a versatile extended-gate electrode used as the sensing membrane. The extended-gate allows the active transistor channel not to be exposed to the ionic analyte and the gate surface may be modified with chemicals or affinity reagents without affecting the operation of the active sensor. The extendedgate a-IGZO TFT was able to detect the pH levels of various solutions based on protonation and deprotonation at the surface of the indium-tin-oxide (ITO) extended-gate electrode achieving a pH dependent threshold voltage shift of 22.8 mV/pH. Highly sensitive and specific protein sensing was achieved for both electrical polarities according to pH values of solutions using the biotin-streptavidin interaction. The extended-gate TFT sensor demonstrated a detection limit for streptavidin down to 10 fM, using the biotin-streptavidin binding on the extended-gate surface. It was also possible to detect changes in the streptavidin concentration in real-time with specificity and repeatability. Since the extended-gate can be easily replaced without affecting the performance of the a-IGZO TFT, this sensor configuration may be utilized for future multifunctional biomolecular sensing and analysis.

In this article, we report on a biomimetic tactile sensor that has a surface kinetic interface (SKIN) that imitates human epidermal fingerprint ridges and the epidermis. The SKIN is composed of a bilayer polymer structure with different elastic moduli. We improved the tactile sensitivity of the SKIN by using a hard epidermal fingerprint ridge and a soft epidermal board. We also evaluated the effectiveness of the SKIN layer in shear transfer characteristics while varying the elasticity and geometrical factors of the epidermal fingerprint ridges and the epidermal board. The biomimetic tactile sensor with the SKIN layer showed a detection capability for surface structures under 100 μm with only 20-μm height differences. Our sensor could distinguish various textures that can be easily accessed in everyday life, demonstrating that the sensor may be used for texture recognition in future artificial and robotic fingers.