Prompted by a study of traumatic brain injury (TBI) in a model system of cultured astrocytes, we
discovered that low level laser illumination (LLL) at 660nm elevates the level of intracellular Ca<sup>2+</sup>. The coherence
of the illumination was not essential since incoherent red light also worked. For cells bathed in low Ca<sup>2+</sup> saline so
that influx was suppressed, the Ca<sup>2+</sup> level rose with no significant latency following illumination and consistent
with a slow leak of Ca<sup>2+</sup> from storage such as from the endoplasmic reticulum and/or mitochondria. When the cells
were bathed in normal Ca<sup>2+</sup> saline, the internal Ca<sup>2+</sup> rose, but with a latency of about 17 seconds from the beginning
of illumination. Pharmacologic studies with ryanodine inhibited the light effect. Testing the cells with fluid shear
stress as used in the TBI model showed that mechanically induced elevation of cell Ca<sup>2+</sup> was unaffected by
In this paper we have designed and built a microfluidic thermal chip that provides rapid temperature changes in
the solution combined with accurate temperature control. The thermal chip was designed to facilitate the patch-clamp to
study temperature dependent activities of ion channels. The device consists of a fluid channel for perfusing solution
connected to an accessible reservoir for making patch-clamp measurements on individual cells. A thin film platinum
heater was used to generate rapid temperature change and the temperature was monitored using a thin film resistor. The
thermal chip was constructed using SU-8 materials on glass wafer to minimize the heat loss to the substrate and channel
walls. The chip was characterized for various flow rates ranging from 0.0093 mL/min to 0.0507 mL/min with heater
power ranging from 2.7 to 19.4 mW. The heating element is capable of alternating the temperature ranging from bath
temperature (20°C) to 90°C at maximum heating rate of 1°C/10 ms. Using the chip, patch clamp recordings were made
on cultured HEK cells as the temperature was rapidly varied. The results demonstrated that the thermal chip could be
used as a thermal clamp for many thermosensitive ion channel studies.
Rapid identification and detection of bacteria is an important issue in environmental and food science. We have
developed an impedance-based method to simultaneously identify and detect bacteria in a derivatized microfluidic
chamber with monoclonal antibodies. The presence of bacteria in the solution can be selectively recognized and fixed
on the chamber wall and detected via impedance change in real time. The optimum reaction time between antibody and
bacteria has been estimated using a simple model and evaluated experimentally. Various concentrations of cultured <i>E.
coli</i> cells ranging from 10<sup>5</sup> to 10<sup>8</sup> CFU/ml were tested using the biosensor. By taking the advantage of a microfluidic
system, the bacteria can be concentrated and accumulated on the chamber wall by continuously perfusing the chamber
with bacterial suspension, therefore, enhancing the detection limit of the sensor. Using this approach, the biosensor was
able to detect 10<sup>6</sup> CFU/ml <i>E. coli </i>(BL21(<i>DE3</i>)) via five consecutive perfusions. The selectivity of the sensor is
demonstrated by testing the antibody reaction for two bacteria stains, <i>E. coli </i>and <i>M. catarrhalis</i>. By derivatizing the
chamber walls with specific antibodies, we can clearly identify the bacteria that are specific to the antibodies in the
detection chamber. The simplicity of the technique also makes the device portable and ideal for clinical and field
In this paper we demonstrate an integration approach for making high-density microfluidic systems. A complex microfluidic system including both sensors and actuators was constructed on silicon chip. Electrically addressable bubble-based valves were used to regulate the fluid flow. A number of electrolytic bubble sensors were placed in parallel channels (sensing limb) connected with the main flow channel for measurements of open channel pressure in real-time. All the fluidic components were made using a single microfabrication process. The pressure dependence of the bubble-based sensor was systematically investigated by applying an inlet pressure ranging from 101 kPa to 133 kPa, while keeping the outlet pressure at atmosphere. The results show that open flow pressure can be accurately measured using the bubble-based sensor located in an adjacent sensing limb. The bubble-shrinking rate can also serve as a measurable parameter for the pressure in main fluidic channel. The experimental data validated with 3D numerical simulation results. The electrolytic bubble-based approach provides an ability to integrate a large number of microfluidic components on a monolithic lab-chip.
The elasticity and anelasticity of Ni<SUB>50</SUB>Ti<SUB>50</SUB> films deposited on Si substrates was studied yielding information on the damping and modulus softening. It was found that the transformation behavior strongly depends on the film thickness and approaches bulk Ni<SUB>50</SUB>Ti<SUB>50</SUB> behavior as the film becomes a few micrometers thick. For the same film thickness, the transformation depends on the film/substrate adhesion. In films with good adhesion cross sectional transmission electron microcopy (TEM) reveals a thin parent phase layer which does not transform while the bulk part of the Ni<SUB>50</SUB>Ti<SUB>50</SUB> film transforms. It is thus proposed that interface constraints stabilize the B2 structure. A microscopic interpretation in terms of transformation strains at the interface is given.