The theme for the issue is, “Water Quality and Health.” Click here to download a copy. Here’s an excerpt:
Many situations exist in which water practitioners want to know the concentrations of organic chemicals in water, including evaluating whether a site is characterized as contaminated and/or whether a water treatment process is effective. But obtaining this informa- tion has traditionally involved collecting a water sample and analyzing it in a laboratory, usually off-site. Laboratory analyses involve various steps before the sample is analyzed in a gas chromatograph or similar instrument, and thus results are expensive and not readily available. Undesired outcomes of this situation include cases in which relatively few data are available to make important decisions (e.g., about the design of a remediation system), and that poorly functioning treatment systems are not corrected quickly.
About 15 years ago, my [Ken Reardon] laboratory at CSU began to develop biosensors to make it easier to measure this aspect of water quality. Our goals were to develop sensors that could provide continuous measurements of an organic chemical concentration and that could be placed directly in the water to be measured. The ability to take the sensor to the water (rather than removing a sample of water) is important, because sampling can skew the results in several ways.
A biosensor is a device that contains a biological detection element, usually an enzyme or antibody, as well as components that allow the biological detection event to be converted into a useable signal or number. We used our knowledge of the ways in which bacteria break down pollutants to develop enzymatic biosensors, and we chose to interface this with an optical method to produce a signal, since that approach often is more sensitive and has less environmental interference than electrical methods. These sensor systems consist of three parts: an optical- electronic hardware unit, one or more biosensor tips, and optical fiber connectors. Sensing is done using a two-layer detection element immobilized on the end of the biosensor tip (Figure 2). One layer is a fluorescent dye, and the other layer contains specific enzymes. The enzymes catalyze a reaction with the chemical of interest (the analyte), and the products of that reaction change the fluorescence properties of the dye. Those changes in fluorescence are detected and correlated to the analyte concentration. We recently started OptiEnz Sensors LLC to commercialize this technology.
Important features of the biosensor system are:
• Versatility: By matching enzymes and fluorescent dyes, biosensors for a wide range of organic chemicals can be constructed. The biosensors can also be designed to cover different concentration ranges.
• Ease of use: Measurements with these biosensors are simple and require no reagent or pretreatment. The tip of the biosensor is simply placed in the sample to be measured, and the analysis time is on the order of minutes.
• Ability to measure continuously, in place and online: These biosensors can be placed in a process vessel or in a process flow and can provide continuous, real-time measurements of the analyte concentration. Such information can then be used for process control or quality assurance/control.
• Low detection limits: Detection limits in the biosensors developed to date range from μg/L to sub-ng/L.
• Small size: The biosensors are based on plastic optical fiber that is about one millimeter in diameter, and can thus easily be placed in small wells.
• Multiplexing: Our optical-electronic hardware unit can monitor up to eight biosensors simultaneously, meaning that several contaminants can be measured.