Chip Design

Our chip designs

Introduction and first idea

Figure 1. First concept of microfluidic chip

One of the biggest challenges of detecting circulating tumor cells is their scarcity in the blood of patients. To overcome this problem, our first idea was to develop a microfluidic chip in order to perform single cell analysis. The biggest advantage of using a microfluidic chip is its ability to perform high-throughput cell biology. In order to do so, we wanted to produce water-in-oil emulsion droplets, that can then be sorted or analyzed by a machine analogous to FACS, (inspired from [Chiu 2015]). In the droplets, a mixture of bacteria and mammalian cells would be present. And the bacteria would express the green fluorescent protein only in the presence of cancer cells, exhibiting both increased lactate production rate and sensitivity to sTRAIL.

First Design

Figure 2. First design of microfluidic chip: On the figure, the orange layer represents the pressure control of the valves and the red layer represents the flow layer.

However, due to the complexity of this setup, we decided to first explore another design consisting of valves and chambers. Instead of having droplets to isolate single cells, we wanted to have a two-layer microfluidic chip. One of the layer would be the flow layer, where cells are flushed in. The other layer would consist of microfluidic valves, controlled by an external pressure source, and capable of occluding the flow layer. Thus, small chambers separating single cells could be formed. We drew the designs using AutoCAD.

Realistic and Final Design

Because of time constraints, we did not make the previous chip but instead we designed a "nano-well" plate which represents our proof of principle. Here, there is no flow going through the chip. Characteristics of the chip

• The volume of every well is 1nL.
• There are 4992 wells in our chip.

Figure 3. Final design of the microfluidic chip

Results and accomplishments

We implemented a testing system for single cell analysis in a nanowellplate and were able to detect lactate produced by singel mammalian cells. Also, we co-cultured bacteria and mammalian cells in the chip successfully.

Thanks to this experiment, we could show that we can introduce a coherent number of bacteria and mammalian cells into the chip. The aim was to obtain single mammalian cells in the chip with 1000 times more bacteria. The loading of the bacteria and mammalian cells is described elsewhere.

To visualize the mixture of cells, we used bacteria expressing RFP and 3T3 mouse fibroblast cells expressing GFP as a nuclear marker.

Results

We achieved to seed the cells in the desired ratio per chamber. We can see that 3T3s grow in the chip, even in the presence of bacteria (even over a couple of hours).

Figure 4. Picture of 3T3 (green fluorescence) co-cultured with bacteria (red fluorescence).