Project Overview

Inspired by the need for a simple, inexpensive, and portable means of toxin detection, Brown University’s Team Toxipop wanted to create a biosensor that utilizes a novel method to detect the presence of a toxin in a solution of bacteria. After a great deal of brainstorming and research, our team finalized on a design for our project that interfaces both biological and electrical systems. Our design is primarily based on a list that our team compiled of ideal bio-sensor guidelines:

Biological

• Uses minimal biological machinery
• Direct induction of system by inducer creates a sensitive system
• Versatile construct

Engineering

• Compact and user-friendly system for sample analysis
• Economically feasible

Minimal biological machinery

Our biological construct consists of three interacting proteins under the control of a single promoter. Such a simple construct increases efficiency and minimizes sources of error in the system.

Direct induction of system by inducer optimizes sensitivity

The triggering of the lysis gene cassette is directly influenced by inducer presence, creating a sensitive system that should maintain a constant gain.

Versatile construct

The simplicity of our construct lends to its versatility. The promoter controlling the lysis cassette can easily be interchanged, optimizing our system's potential to detect several different types of toxins and other substances. For example, a mercury-induced, arsenic-induced, or lead-induced promoter, all of which have been introduced by iGEM teams in the past, could be placed in control of the lysis cassette, creating three separate and specific toxin detection systems.

Compact and user-friendly

The physical bio-sensor envisioned by our team would be hand-held, consisting of a small compartment of bacterial cells with electrical probes fixed in this compartment. The probes feed information to a simple circuit within the sensor which monitors conductance of the bacterial solution and outputs an increase in conductance via a simple LED light signal (See the "Application" below for more details). This set-up would enable any person with little or no knowledge of the machinery of the bio-sensor to utilize it effectively.

Economically feasible

E. coli bacteria, which provide the main machinery of the bio-sensor, are inexpensive to obtain, grow, and store. Additionally, after consultation with mechanical engineers, we discovered that the circuit required for our proposed system would be simple to create and inexpensive to produce, in the range of a few dollars.

Application

The proposed biosensor

Current Water Contamination Machinery

The proposed prototype for Team Toxipop's biosensor is pictured on above on the left. It would be inexpensive to produce, portable, and user-friendly compared to a current water detection system, as pictured above on the right.

• The Toxipop biosensor consists of a small box with a compartment containing lyophilized E.coli bacterial cells, engineered with the lysis cassette under the control of a specific toxin-inducible promoter. Two graphite electrical probes are fixed on either side of this compartment (white arrows) which detect relative changes in current and feed that information to a small circuit board within the sensor. This circuit board, receiving a constant voltage from a battery source, will compute relative changes in resistance (or conductance) and will report that information via an LED light signal.

• The following protocol could be proposed for the Toxipop system:

1. Re-constitute lyohphilized cells with cell growth media.
2. Apply a few drops of the water sample with potential toxin into specified compartment.
3. Allow cells to to sit for approximately two hours. If lysis occurs after this time