Instrumentation

Instrumentation was a vital aspect of our project in the development of the kit. It includes the mechanical, electrical and software components that allow the incorporation of our multiple independent modules into a working kit.

Mechanical chassis

The mechanical chassis prototype was made using foam, due to the ease of its manipulation, and aluminium due to its excellent strength to weight ratio. The chassis includes a rotary mechanism (central metal axon connected to cuvette holder cylinder) that is driven in steps by an electric motor.

The purpose is that our self-developed sensor, which was made using two photoresistors, an orange and a blue theatrical filter, takes multiple readings from different biosensors, each found in a different cuvette. It should be noted that each cuvette holder is coated on the inside with highly reflective mylar film. In this way, most of the light produced by the bacteria is concentrated for more accurate sensor measurements.

The system, as illustrated (below), is made up of a sensor, a motor, an arduino and a breadboard. A Bluetooth modem (Bluesmirf) can also act as an addition to allow the communication with mobile devices (e.g. Android tablets). The sensor is made up of two light dependent resistors that sit in a potential divider circuit allowing for a direct ratiometric output without further calculations needing to be made in the software. There is also a circuit for running a DC motor, which will turn the rotating parts of our device. The whole system has been incorporated into the mechanical chassis for an attractive, ergonomic overall design. A pre-set C++ code is loaded onto the arduino to handle both the data taken from the sensor as well as driving the motor. The code is found 'here'.

Bluesmirf Bluetooth Modem

Cuvette holder coated inside with mylar film

Arduino circuitry

Android application start page

Python program for PC

The software is being developed for both computers and android devices for extra flexibility whatever the final application of the product is. The computer software is written in the free open-source language python with cross-platform wxWidgets used to implement a GUI. The current idea is to develop a fully functional GUI for collecting sensor data from all six inputs and display these as line graphs and in a final bar chart. The data above was recorded by moving luciferase-producing E.coli being moved towards and away from the sensor. To the right is a screengrab of the GUI under development and testing its ratiometric ability. The higher values are when one sensor is covered, the lower for the other and no change is observed when both are illuminated equally. The android GUI was made in Java using Eclipse based on Amarino open-source code. The first screen (shown below) asks for the MAC address of the Arduino device and the application can successfully connect, read real-time data and plot them in any Android phone/tablet.

The code (for programmers) as well as a ready application to be downloaded (for non-programmers) can be found 'here'. The aim of the instrumentation is to show how different biological constructs can be used quite effectively together once the right hardware and software is made. We aimed for everything to be open-sourced (hardware designs, electrical designs, software code), always in the spirit of iGEM.