We report an automated microdroplet platform for chemostat culture of bacterial cell, and continuous detection of optical density of microdroplet. The microdroplets, divided by air bubbles, are continuously injected into PMMA micro-fluidic chip using injection pump controlled by PC. Microdroplets are divided or merged via microchannels on the chip. On the top side of michochannels, optical detector is applied to acquire optical density of luminescent light. This platform is used to study chemostat continuous culture Escherichia coli on the chip, while concentration of bacterial cell can be online detected after tracer solution is merged into microdroplet. This system has several key characteristics: small (<100 μL, typically 2 μL) samples of liquids and suspensions of bacteria that are introduced directly into the chip; a sequence of droplets with compositions can controlled by injection speed and time; dividing and merging procedures can be easily programmed by user according experimental requirement; the droplets are detected with an in-line homemade optic spectrophotometer that measures cell growth, which detection limit reach 0.01 in 637nm wavelength. The E. coli detection experiment for water sanitary is on the way, while positive result can be expected.

It is becoming clear that bacteria exist primarily as members of surface-adhered social communities, called biofilms, rather than as free-living individuals. These communities are encased in an extracellular matrix that provides protection from harsh environmental conditions, predation, enables resource sharing, and facilitates intercellular communication. Depending on the local conditions bacteria will transition between these two states and this interplay is fundamental to the ecology and biology of bacteria. The biofilm lifestyle colors all aspects of bacterial interactions with their environment whether attached to a rock in a stream, as an aggregate in activated sludge, or in an infection. To begin understanding biofilm development we visualize the initial encounter bacteria have with surfaces. Here, bacteria undergo a fundamental change in lifestyle, becoming surface-bound. We use cell tracking to link surface motility to surface exploration and colonization. As biofilms mature, growing three-dimensional, we utilize laser scanning confocal microscopy as well as label free imaging techniques to visualize phenotypic changes that occur within biofilms over time and space.

Advances in the microfabrication of microfluidic and biochip devices have made polydimethylsiloxane (PDMS) the material of choice for biomedical, analytical and biotechnological applications.^1-3 And a variety of bonding technologies have been developed to seal the micro-channels on PDMS. But, most technologies aim for small and single chip functions. It is still a challenge to investigate new technologies for large-size and high-throughput PDMS microfluidic chip fabrication.

This paper reports a new bonding method for large size PDMS-based microfluidic chip fabrication, which is based on display technology. The fabrication process combines a process of first polaroid bonding commonly used in liquid crystal display (LCD) manufacturing production and then thermal bonding. Polaroid bonding provides specific advantages to the large size microchip including good alignment and bubble free. Thermal bonding is applied to improve the bonding strength between PDMS and glass.

 The microchannel design of the PDMS microfluidic chip is shown in Fig 1a. And Fig.1b is the photo of a large sized PDMS chip obtained by the new bonding method. Fig. 2a and 2b respectively shows the polaroid bonding machine used in this study and the schematic illustration of the machine’s working principle. The bonding strength of the PDMS chip obtained by different method is shown in Fig. 3. Leakage tests are another method to assess the adhesion strength of the large size PDMS-glass microchip. Fig. 4 exhibits the results of the leak tests.The maximum pressure between PDMS and the glass substrate is 739 Kpa, which is comparable to interference-assisted thermal bonding method.⁴ The new bonding method can also be used for 6×6 inch microchip bonding procedure. This provides an efficient method for manufacturing large size and high throughput PDMS microfluidic chip.

Refractive index sensing method based on silicon ring resonator is used to build the sensing platform, for its potential to be CMOS compatible and can be easily integrated with other sensors and control elements [1]. An integrated volatile organic compounds (VOC) sensor is presented in this paper. Current device is tested with acetone vapor, and the detection limit reached 200 ppm, which is lower than the human safety level [2]. By making a ring resonator array, the proposed sensor has a potential to detect and distinguish different gas species. 

Figure 1(a) shows the sensing platform with silicon ring resonator as the key component. A straight waveguide is used to couple laser into the ring structure. The width and height of the waveguide and the ring is 450 and 220 nm, respectively. The ring structure is coated by a thin absorption layer and covered in a microfluidic channel, acting as the main sensing unit. Figure 1(b) shows the SEM image of one of the sensing ring.

After light passing through the resonator, resonance peaks can be seen on the output spectrum. As shown in Figure 2(a), the linewidth of each peak is less than 30 pm, which offers a Q-factor of more than 5×10⁴. This resonance peak, however, is very sensitive to the refractive index and thickness of the absorption layer. Gas absorb inside the layer will affect the resonance peak position. Figure 2(b) shows the mode distribution in the waveguide after the absorption layer coating. The strong light field in the absorption layer will make the device sensitive to refractive index and thickness change.

To demonstrate this sensing performance, a 20-nm polydimethylsiloxane is spin coated on top of the device to absorb VOC vapor. Acetone is chosen as the target gas. Gas is injected to the chip surface via a microfluidic channel. Figure 3(a) shows the monitored peak position as a function of time. The periods with white background represents the condition when pure N₂ gas is injected to the channel. On the other hand, the periods with gray background represents the condition when different concentrations of acetone vapor are injected in the channel. Stable performance and fast response is observed. The response time constant is about 20 s. Figure 3(b) indicates a linear relationship between acetone concentration and resonance peak position. Based on the experimental results, the sensitivity is 1.7 pm/1000 ppm and the detection limit is 200 ppm.

In conclusion, a gas sensor for VOC based on silicon photonics ring resonator system is presented in this paper. Sensitivity of 1.7 pm/1000 ppm and detection limit of 200 ppm are achieved, which is lower than the human safety level. This makes it a potential application for indoor air quality detection and monitoring.

Heart failure is a major international health issue. Myocardial mass loss and lack of contractility are precursors to heart failure. Although, the treatment of cardiac injury is severely limited, cardiac tissue engineering is considered to be a promising approach [1]. In native heart tissue, the cardiac muscle cells are assembled in a conductive network, so the materials selected for cardiac tissue engineering should also be conductive. In the last decades, some conductive polymers(e.g., polythiophene (PT), polyaniline, polypyrrole, metals particles, carbontube (CNT), etc.) have been developed for the cardiac tissue engineering[2].However, these material are more or less defective, such as some of them are not conductive and soft enough. In this paper we make a kind of graphene foam with size controllable holes, primary rats myocardial cells are seeded in the foam. As we know, graphene is a good conductive material, and here we make it to a unique foam structure, so cells growth in a three-dimensional space (needn't worry about the material breaking when the cells are beating) and demonstrate higher cell attachment, spreading and tissue function.

The SEM images showed in Fig.1 are the structure of graphene foam, and primary rats myocardial cells are seeded in interior holes of the graphene foam. Fig.2 shows the cell state after they have been cultured in graphene foam for several days. Our study provides a method for preparing graphene material, which can be used to study myocardial tissue engineering in vitro.