Bacteria-containing biosensor

Dr. Neil Canter, Contributing Editor | TLT Tech Beat January 2013

Undergraduate engineering students develop a field-deployable device that can quantitatively detect specific components.

KEY CONCEPTS
• A new field-deployable biosensor can detect arsenic down to 10 ppm in water used in processing oil sand in Northern Alberta.
• Cornell University students genetically engineered a metal-reduction pathway in the bacterium Shewanella oneidensis MR-1 to only activate in the presence of a specific component that is being measured.
• Initial work has been done on arsenic and naphthalene, but this technology can be modified for use to evaluate metals and inorganic anions that are present in water effluent generated by industrial plants.

DETERMINATION OF SPECIFIC PARAMETERS IN A LUBRICANT SYSTEM or detection of specific contaminants is becoming increasingly important in order to extend the optimum operating life of lubricants. Techniques are becoming more sophisticated as detection limits have been reduced and have become more accurate.

One other factor is the need for analytical equipment that is portable so that it can be used as a monitoring device on-site at the location of the lubricant system. This allows for real-life determination of specific parameters so that decisions can be made, if necessary, to treat the lubricant.

Sensors have become a valuable tool in providing prompt analytical data. In a previous TLT article, a sensor based on a block copolymer was developed that undergoes a change in color when in the presence of a specific stimulus (1). For example, the sensor can be used to determine changes in such parameters as pH, salt content, pressure and moisture. The value from a lubricant maintenance perspective is that the block copolymer can be incorporated into a coating on a surface that will change color so that a maintenance engineer can be alerted to a potential problem.

The problem with this type of sensor is that it cannot provide continuous, quantitative data on the concentration of a specific parameter of interest. Jim Mathew, an undergraduate chemical engineering student at Cornell University in Ithaca, N.Y., says, “A type of sensor we have been looking at is a biosensor, which detects a specific component or parameter, either through the use of a specific living microorganism or else at the molecular level through the use of biomolecules such as an enzyme.”

Biosensors use similar techniques such as color changes and fluorescence to detect specific parameters in a system. Mathew says, “These types of biosensors have limitations such as problems with light contamination in the case of using fluorescence. In addition, a cumbersome photodiode will also be required to enable the sensor to operate properly.” Such sensors are also not easily adaptable to a field-deployable device for continuous monitoring.

There is need for a new type of biosensor that uses a different detection approach. Such a biosensor is now in the process of being developed.

METAL-REDUCTION PATHWAY
A team of 22 undergraduate engineering students formed the Cornell University Genetically Engineered Machines to develop a new type of biosensor that can quantitatively detect specific components. Mathew, co-team leader, says, “We received an opportunity from the Oil Sands Leadership Initiative, which is a cooperative effort by the companies operating in the Canadian Oil Sands in Northern Alberta, to develop a sensor to monitor specific pollutants that can be found in the water used in processing oil sand.”

The team already had the concept in mind for developing a biosensor, according to Mathew. He says, “We had known that the bacterium Shewanella oneidensis MR-1 can create an electronic current using a well-known metal-reduction pathway. In this fashion, this bacterium can transfer electrons to inorganic solids and generate current in solid-state electrodes.”

Acting in a similar fashion to a switch, production of the membrane protein MTRB completes a biological circuit in the bacteria, allowing current to flow from the cell to a measuring electrode. The team determined how to genetically engineer this pathway to only activate in the presence of a specific component that is present in the environment.

MtrB is used in this metal-reduction pathway to enable the bacterium to conduct respiration, which is essential for its survival. Mathew says, “Two of the components we were asked to detect using this biosensor are arsenic and naphthalene. We have done extensive work evaluating the capability of analyzing arsenic in the wastewater. Our initial experiments have demonstrated a detection limit in the range of 10 ppm.”

The team is still working to evaluate the ability of the biosensor to detect naphthalene.

A bioreactor shown in Figure 3 was designed in which the bacteria are able to detect a specific component, as the water is pumped through a chamber where they reside. Mathew says, “We have not been able to test the actual bioreactor, but have tested the various mechanical and electrical components.”


Figure 3. A biosensor can be used in the field to analyze trace amounts of specific components in wastewater streams. Initial work was done with water used in processing oil sand. (Courtesy of Cornell University)

One very helpful aspect of this system is that results for the level of the component detected can be sent over a wireless network to another office. From a lubricant standpoint, this is exceptionally valuable because it enables the results in the field to be quickly provided to those individuals involved in managing a specific lubricant system.

The team hopes to lower the detection limit for arsenic down to the ppb range. Mathew adds, “This is a relatively young technology, so we need to determine an operations curve for both arsenic and naphthalene.”

When asked about other components that can be detected by this approach, Mathew mentioned that metals such as cadmium, chromium, iron and mercury can all be analyzed in this fashion.

Other potential components that can be analyzed include a myriad of organic compounds and inorganic anions such as nitrates, nitrites and phosphates.

The team is looking for other applications for this biosensor beyond the water stream used in oil-sand processing. Additional information can be found at the Website or by contacting Mathew at james.r.mathew@gmail.com.

REFERENCES
1. Canter, N. (2008), “A Color Changing Sensor,” TLT, 64 (4), pp. 10-11.


Neil Canter heads his own consulting company, Chemical Solutions, in Willow Grove, Pa. Ideas for Tech Beat items can be sent to him at neilcanter@comcast.net.