PRELIMINARY ASSESSMENT OF A “MOLECULAR BEACON” BIOSENSOR FOR THE DETECTION OF ENVIRONMENTAL MERCURY CONTAMINATION

One environmental pollutant of particular relevance to the coal-generated power industry is mercury. Pennsylvania is reported to have the highest mercury air pollution in the nation, its older coal-fired power plants emitting up to ten times more mercury than newer plants. Rainfall monitored by eight field stations of the Mercury Deposition Network in Pennsylvania have detected regional and seasonal differences in mercury deposition patterns, the highest concentrations measured being ca.124 ng/L total mercury. Calls for increased mercury monitoring activities within the state have come from regional environmental groups concerned with environmental contamination and bioconcentration in fish. Likewise, the potential environmental benefits of reducing mercury emissions from existing power plants cannot be seriously evaluated without extensive environmental monitoring. Low environmental mercury concentrations and the expense of traditional laboratory analyses currently limit such routine and effective monitoring.

Microbial biosensors sensitive to mercury have been developed that quantitatively produce light in response to the amount of mercury (II) entering the cells. However, these sensors are often difficult to prepare, can have long lag times between initial mercury exposure and subsequent light emission, and are difficult to use in the field. In this paper, the use of a novel “molecular beacon” sensor for mercury (II) environmental screening is reported. An oligonucleotide sequence is used that changes its conformation upon binding with mercury (II) ions. The change in conformation causes a fluorophore at one end of the oligonucleotide sequence to come in proximity with a specific quencher molecule attached to the other end of the oligonucleotide. Enhanced fluorescence resonance energy transfer (FRET) results in a decrease in the intensity of fluorescence spectrum, which is correlated with the mercury concentration. The fluorescence spectrum generated by this sensor can be analyzed using a field spectrofluorometer, and applications employing fiber optic probes are envisioned. Data are presented that illustrate both the sensitivity of the oligonucleotide sensor under environmental conditions, as well as the potential benefits and shortcomings of this approach.