II Temperature control module

 Temperature control module provide constant temperature environment in the chip for two reasons:1.E.coil need constant temperature environment when they restore activity from freeze-dried state;2.E. coli have the best growth and metabolism state in constant temperature environment.

2.1 Design:

  Temperature control module consists of four parts, namely: alumina ceramic, heating piece, temperature sensor module and it’s supporting control module.The alumina ceramic is the base of the chip, and the chip is connected to it. The rest of the temperature control board is located on the instrument, and the chip is placed on it when used.The alumina ceramic allow the chips to heat evenly.The control module control the work of the heater piece.The temperature sensor provide temperature information of microfluidic chip to the microcontroller at real-time.

2.2 Material:

  Alumina ceramic piece’s thermal conductivity is 23W/(m^2*K), and the size is 45 * 30 mm. Heating piece’s rated voltage is 5V, the power is 10W, and the size is 40 x 40mm. Temperature sensor’s accuracy is 0.1 ° C.

2.3Working Process:

  Its working process is very simple:When the chip temperature is higher than 37 degrees, the control module control the heating piece to stop heating;when the temperature is higher than 37 degrees, the heating piece works again.

Demonstrate

1.Biological part

Introduction

In our project, the chip is the carrier of biological reactions, its most basic function is to provide a growth environment for engineering bacteria. In order to be used smoothly as a biological carrier in our project, the chip needs to meet the following conditions:
①:The freeze-drying and recovery of engineering bacteria can be finished in the chip.And the engineering bacteria needs to keep a relatively high activity after recovery process.
②:The engineering bacteria can survive in the chip for the short period between recovery and finishing a detection.

Experiments

In order to characterize the biological properties of the chip, we conducted a series of experiments on the basis of measurement of OD600 and the fluorescence intensity:

1.1Experiment about investigating the Growth and Metabolism status’s change of E.coli inside and outside the Microfluidic Chip.

1.1.1 Experimental purpose

Our project aims to achieve fast detection of biomarks on the chip, and we need to use E.coil in the detection process.That means we need verify whether the affinity of E. coil with our chip can meet our requirements. And we designed an experiment to cultivate E. coil to verify this problem.

1.1.2 Method

First, we selected E.coli that was imported into BBa_K876070 plasmid as the strain of the experiment.Second,we cleaned the chip with anhydrous ethanol and PBS as preprocessing, to make the chip environment more conducive to microbial growth.Third,we injected E. coli into chamber II, put the chip in 37 degree incubator, and measured its OD:600 every two hours, and last draw its growth curve.

1.1.3 Experimental results

According to the growth curve (Figure 1.1)of E. Coli inside Microfluidic chip, the growth of E. coil was somewhat inhibited. But in the short time, the inhibition is weak. And our project aimed at detecting quickly, so the affinity of E. coil with our chip can meet our projects’ requirements. By analyzing the process and principles of the experiment, we think maybe the hypoxic environment in the chip inhibits the growth of E. coil in the chip. So, we use the PCR tube filled with E. coli bacteria to simulate the chip inside environment and re-measure the growth curve of E. Coli inside Microfluidic chip. Compare these two similarities growth curves, we basically confirm the hypoxic environment inhibits the growth of E. coil in the chip.

1.1.4Discussion

To improve the hypoxic environment in the chip, let the strain of the experiment grow better, we have some ideas. And we are still studying it, here to discuss with you.
①: Transform microchip structure
Leave some vent hole on one side of the chamber, adhere a pellicle which has good air permeability and waterproofness. This will help chamber take gas exchange with air, and solve the hypoxic problem.
②: Add oxygen carrier
Process microchip with some oxygen carrier like hemoglobin, some of them will remain in the inner surface of chamber. They will release some oxgyen when the environment is hypoic. But we don’t know how much oxgyen they will release and whether oxygen carrier will influence E. coil. So, there still need more experiments and study.
③: Reserve oxygen in the chamber
When injecting E. coli bacteria, we can reserve some oxygen in chamber. But the chamber is tiny, we must have enough E. coli bacteria to achieve out detection, so there won’t have much room for oxygen. And the gas we reserve maybe will influence other parts of detection, so there still need more experiments and study.