Hardware

Background

This year, Links-China is genetically engineering yeasts to produce MAAs, a kind of molecule that can protect organisms from UV, and hence we would want to select the fastest-growing engineered yeasts so that we can perform directed evolution, which will ultimately enables us to obtain the yeasts with the highest MAAs yield rate. However, we realize that most standard equipments use for measuring and comparing yeast's growth rate are very expensive and often not commonly-avaible in many places. However, we also know that directed revolution can be immensely helpful and important for a lot of iGEM projects. Thus, this year, we decide to build a hardware to use cleverly addresses a common problem for many iGEM teams: how to accurately identify the fastest-growing yeasts for directed evolution without having to buy and use expensive not-commonly-available equipments. We document the design graphs of all three main parts of our hardware in great detail, and all the components can be easily bought, thus making our hardware reproducible.

Design

Overview

Our hardware contains three main parts. The first part is a glass microfluidic chip with 20 channels narrow enough to only allow approximately one yeast cell per channel to flow out at a time. The second part is an acrylic container beneath the microfluidic chip that will be filled with flowing liquid when we want to collect the yeasts. The flowing liquid will wash the yeast cells that grow the fastest under UV-thus the ones most effective at producing MAAs-into a collecting culture flask through a flexible plastic tranport tube. The third part is an astable multivibrator PCB board with UV light beads molded onto it that enable the light to automatically and periodically turn on and off for a set amount of time so that the heat released by the UV light bead will not affect yeast growth.

Our device. From left to right are the needle, the acrylic container, the microfluidic chip, and the transport tube.

Microfluidic chip

Our microfluidic chips has 20 channels, and each channel is 8 micrometer deep, 20 micrometer wide, and 5 millimeter long. We want the channels to be as narrow as possible so that only one yeast can grow out of a channel at a time, but we also don't want the channel to be so narrow as to severly limiting the movement of yeast due to capillary action.

You can download our microfluidic chip here.

Because glass microfluidic chips at the level of precision we want are quite expensive and we wish to minimize the cost of our hardware, we also investigated the possibility of using much cheaper PDMS microfluidic chips. However, we realized that there is comparatively few studies that use PDMS to grow yeasts. Hence, in order to save time, we ultimately still chose to design and purchase glass microfluidic chips.

Container

Design for the acrylic container

PCB

Initially, we want to assemble an astable multivibrator PCB board using an NE555 chip with UV light beads molded onto it so that the UV light can automatically and periodically turn on and off for a set amount of time. In doing so, we can ensure that the possible heat released by the UV light bead will not affect yeast growth.

Design for PCB

However, after we have designed, purchased, and received the PCB board, we realized that although most LED only requrie a forward current rating of about 10 to 30 mA, the 3535LED that we bought require 200mA. This can be solved by purchasing an additional transistor, which can amplify current. Although transistors are commonly available, due to the lack of time, we were unable to purchase the additional transistors. However, fortunately, we realized that we can use the UV light box that was designed by Links-China 2021 team. Thus, we did the initial testing of our hardware using the UV light box.