Heavy metals such as mercury, lead, and copper are highly toxic and persistent contaminants that are not biodegradable and thus are retained in the ecosystem. The objective of this research is to develop a quantum dot-gold nanoparticle optical assay based on DNA hybridization. This nanosensor system is expected to be capable of simultaneously detecting multiple heavy metals with high sensitivity, selectivity and reliability. This nanosensor system is created by utilizing fluorescent (Föster) resonance energy transfer (FRET), whereby the luminescent emission of quantum dots (QDs) is quenched by the gold nanoparticles. Green, yellow and red QDs are employed to sense Hg2+, Cu2+ and Pb2+ ions, respectively. The target ions selectivity can be achieved by selected DNA sequences. Specifically, the thymine-thymine mismatching in the DNA double helixes is known to be a good base pair to selectively bind with Hg2+, while non-nature nucleobase hydroxypridone produce stable helixes through the cooperation with Cu2+. The guanine (G)-rich DNA-conjugated system can serve as an excellent binding sequence for Pb2+ during the formation of G-quartet quadruplexes.
This approach offers distinct advantages that will advance the state of the art in heavy metal detection. The QD-Au optical assay eliminates the photo-bleaching problem usually associated with the use of organic dyes. The high quantum yield of QDs enables the QD-Au assay to offer high sensitivity. Use of DNA as a molecular recognition probe is more stable in a non-physiological solution than enzymes, proteins and live microbes typically used as molecular recognition probes as well as enables sequence design for specific detection of different metal ions for high selectivity. Finally, the nanosensor system provides the capability of simultaneous and discriminative detection of several metal ions in a sample through tuning the optical emission of quantum dots at various wavelengths.
Broader impacts: The proposed nanosensor based on a DNA hybridization-driven quantum dot-gold nanoparticle optical assay effectively builds on prior work and significantly advances the state of the art for detection of toxic metal ions in water. If successful, the detection approach established through this work can be integrated to achieve portable, rapid monitoring of water quality for drinking, industrial and agricultural applications. The knowledge obtained from this project will reduce the risk of human and environment exposure to heavy metal pollutants. The inherently interdisciplinary nature of this project will provide us with an opportunity of integrating students? educational experience across diverse areas, including environment technology, nanotechnology, nanomaterials, organic and biochemistry. The educational activities to be carried out as an integral part of this grant include: i) training graduate and undergraduate students, ii) laboratory access for summer high school students, and iii) developing a course module for the new course in nanoscale science and engineering
