Misun Cha

Biomolecular detection with a thin membrane transducer

We present a thin membrane transducer (TMT) that can detect nucleic acid based biomolecular reactions including DNA hybridization and protein recognition by aptamers. Specific molecular interactions on an extremely thin and flexible membrane surface cause the deflection of the membrane due to surface stress change which can be measured by a compact capacitive circuit. A gold-coated thin PDMS membrane assembled with metal patterned glass substrate is used to realize the capacitive detection. It is demonstrated that perfect match and mismatch hybridizations can be sharply discriminated with a 16-mer DNA oligonucleotide immobilized on the gold-coated surface. While the mismatched sample caused little capacitance change, the perfectly matched sample caused a well-defined capacitance decrease vs. time due to an upward deformation of the membrane by a compressive surface stress. Additionally, the TMT demonstrated the single nucleotide polymorphism (SNP) capabilities which enabled a detection of mismatching base pairs in the middle of the sequence. It is intriguing that the increase of capacitance, therefore a downward deflection due to tensile stress, was observed with the internal double mismatch hybridization. We further present the detection of thrombin protein through ligand-receptor type recognition with 15-mer thrombin aptamer as a receptor. Key aspects of this detection such as the effect of concentration variation are investigated. This capacitive thin membrane transducer presents a completely new approach for detecting biomolecular reactions with high sensitivity and specificity without molecular labelling and optical measurement.

Reversible Metal-Semiconductor Transition of ssDNA-Decorated Single-Walled Carbon Nanotubes

A field effect transistor (FET) measurement of a single-walled carbon nanotube (SWNT) shows a transition from a metallic one to a p-type semiconductor after helical wrapping of DNA. Water is found to be critical to activate this metal-semiconductor transition in the ssDNA-SWNT hybrid. Raman spectroscopy confirms the same change in electrical behaviors. According to our ab initio calculations, a band gap can open up in a metallic SWNT with wrapped ssDNA in the presence of water molecules due to charge transfer.

Cell response induced by internalized bacterial magnetic nanoparticles under an external static magnetic field.

Magnetic nanoparticles are widely used in bioapplications such as imaging and targeting tool. Their magnetic nature allows for the more efficient bioapplications by an external field gradient. However their combined effects have not yet been extensively characterized. Herein, we first demonstrate the biological effects of the communications between internalized bacterial magnetic nanoparticles (BMPs) and an external static magnetic field (SMF) on a standard human cell line. Combination of the BMPs and SMF act as the key factor leading to the alteration of cell structure and the enhanced cell growth. Also, their interaction reduced the apoptotic efficiency of human tumor cells induced by anticancer drugs. Microarray analysis suggests that these phenomena were caused by the alterations of GPCRs-mediated signal transduction originated in the interaction of internalized BMPs and the external SMF. Our findings may offer new approach for targeted cell therapy with the advantage of controlling cell viability by magnetic stimulation.

Single-crystal apatite nanowires sheathed in graphitic shells: synthesis, characterization, and application.

Vertically aligned one-dimensional hybrid structures, which are composed of apatite and graphitic structures, can be beneficial for orthopedic applications. However, they are difficult to generate using the current method. Here, we report the first synthesis of a single-crystal apatite nanowire encapsulated in graphitic shells by a one-step chemical vapor deposition. Incipient nucleation of apatite and its subsequent transformation to an oriented crystal are directed by derived gaseous phosphorine. Longitudinal growth of the oriented apatite crystal is achieved by a vapor-solid growth mechanism, whereas lateral growth is suppressed by the graphitic layers formed through arrangement of the derived aromatic hydrocarbon molecules. We show that this unusual combination of the apatite crystal and the graphitic shells can lead to an excellent osteogenic differentiation and bony fusion through a programmed smart behavior. For instance, the graphitic shells are degraded after the initial cell growth promoted by the graphitic nanostructures, and the cells continue proliferation on the bare apatite nanowires. Furthermore, a bending experiment indicates that such core-shell nanowires exhibited a superior bending stiffness compared to single-crystal apatite nanowires without graphitic shells. The results suggest a new strategy and direction for bone grafting materials with a highly controllable morphology and material conditions that can best stimulate bone cell differentiation and growth.

Magnetic manipulation of bacterial magnetic nanoparticle-loaded neurospheres

Specific targeting of cells to sites of tissue damage and delivery of high numbers of transplanted cells to lesion tissue in vivo are critical parameters for the success of cell-based therapies. Here, we report a promising in vitro model system for studying the homing of transplanted cells, which may eventually be applicable for targeted regeneration of damaged neurons in spinal cord injury. In this model system, neurospheres derived from human neuroblastoma SH-SY5Y cells labeled with bacterial magnetic nanoparticles were guided by a magnetic field and successfully accumulated near the focus site of the magnetic field. Our results demonstrate the effectiveness of using an in vitro model for testing bacterial magnetic nanoparticles to develop successful stem cell targeting strategies during fluid flow, which may ultimately be translated into in vivo targeted delivery of cells through circulation in various tissue-repair models.

Thin membrane transducer detectiing DNA hybridization on chip

We present a highly reliable ultra thin membrane transducer (TMT) - based chemo-mechanical sensing platform fabricated with MEMS process. This device is composed of 100 nm thick silicon nitride membrane and lower electrode for a capacitive detection. The counter electrode is integrated on a silicon substrate and the cavity side of the membrane is coated with thin gold film (30 nm) for molecular immobilization and reaction. Microfluidic flow cell is fabricated with PDMS and integrated with the chip. The TMT demonstrates the discrimination between perfect match and mismatch in hybridization with a well-defined time response due to a specific molecular recognition. The effect of concentration is investogated through the difference in response.

Cell Migration Driven by a Mechanical Stiffness Gradient

This paper reports the migration of cells along the gradient of mechanical stiffness when the cells are cultured on a flexible substrate with variable rigidity. The thickness difference of PDMS layer was used to create a stiffness gradient between a stiff (7 mum) and a soft (2 mum) region. A fabrication process was developed to minimize the effect of other factors such as height difference and surface chemistry variation that can affect the pattern of cell migration. A cultured embryonic carcinoma cells on the flexible substrate coated with fibronectin, and observed that most of cells were accumulated on the stiffer region. Patterns in various shapes and sizes with stiffness difference were tested to investigate the migratory behavior of the cells. The results suggest that our approach provides a key technology to study the mechanism of cell migration by durotaxis.

Effect of graphitic layers encapsulating single-crystal apatite nanowire on the osteogenesis of human mesenchymal stem cells.

An ideally designed scaffold for tissue engineering must be able to provide an environment that recapitulates the physiological conditions to control stem cell function. Here, we compared vertically aligned single-crystal apatite nanowires sheathed in graphitic layers (SANGs) with single-crystal apatite nanowires (SANs), which had the same geometric properties as--but differing nanotopographic surface chemistry than--SANGs, in order to evaluate the effect of the graphitic layer on the behavior of human mesenchymal stem cells (hMSCs). The difference in nanotopographic surface chemistry did not affect hMSC adhesion, growth, or morphology. However, hMSCs were more effectively differentiated into bone cells on SANGs through interaction with graphitic layers, which later degraded and thereby allowed the cells to continue differentiation on the bare apatite nanowires. Thus, SANGs provide an excellent microenvironment for the osteogenic differentiation of hMCS.

Effect of magnetic modulation of mitochondrial voltage-dependent anion channel 2 against beta-amyloid induced neurotoxicity

The magnetic capture of mitochondrial VDAC2 with bacterial magnetic particles (BMPs) conjugated VDAC2 antibody (BMPs–Ab) significantly decreased the expressed intracellular calcium levels and neurotoxicity induced by Aβ. This magnetic modulation of mitochondrial VDAC, playing a key role in various Ca2+ flux pathways, should provide attractive targets for the future development of AD treatments.

Cell manipulation systems using dielectrophoretic process for diagnostic sensors

This paper demonstrated the effectiveness of Dielectrophoresis (DEP) on microfluidic devices as part of diagnostic sensors. It was possible to focus bacterial cells into the intended area based on droplet evaporation on hydrophobic guide structure and DEP force with micro-patterned electrodes. Similarly, we dealt with separation of blood cells from whole blood so that plasma can be applied in many biomedical fields. The micro fluidic channels were attached on both sides of the device which includes electrodes for DEP and pore-array membrane. Micro-sized beads were experimented prior to realizing those two functions of DEP on biological cells.