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Nanoscale sensing arrays utilizing the unique properties of the optical protein bacteriorhodopsin and colloidal semiconductor quantum dots are being developed for toxin detection applications. This paper describes an innovative method to activate bacteriorhodopsin-based electrodes with the optical output of quantum dots, producing an enhanced electrical response from the protein. Results show that the photonic emission of CdSe/ZnS quantum dots is absorbed by the bacteriorhodopsin retinal and initiates the proton pumping sequence, resulting in an electrical output from a bacteriorhodopsin-based electrode. It is also shown that activated quantum dots in sub-10 nm proximity to bacteriorhodopsin further amplify the photovoltaic response of the protein by approximately 23%, compared to without attached quantum dots, suggesting direct energy transfer mechanisms beyond photonic emission alone. The ability of quantum dots to activate nanoscale regions on bacteriorhodopsin-based electrodes could allow sub-micron sensing arrays to be created due to the ability to activate site-specific regions on the array.

The unique energy transfer interaction between the optical Utilizing the direct energy transfer mechanism existing between semiconductor quantum dots and the hydrogen ion protein pump bacteriorhodopsin, a multi-functional bioelectronics platform is demonstrated. Fluorescence resonance energy transfer coupled QD-bR systems have been proven in both aqueous and dried film states, allowing for the vast QD optical absorbance range to directly contribute energy to the bR proton pumping sequence. A nanoscale deposition technique was employed to construct hybrid QD-bR electrodes capable of harnessing the FRET phenomena and enhancing the bR electrical output by nearly 300%. A biosensing prototype system was created where the target molecule disrupts the QD-bR FRET relationship and is signaled by an altered bR electrical output. With an integrated TiO 2 electron generating substrate, the QD-bR hybrid functions as a sensitizer in a thin film bio solar cell design, which will be presented in more detail at the conference and in the full paper.

Harnessing the energy transfer interactions between the optical protein bacteriorhodopsin (bR) and CdSe/ZnS quantum dots (QDs) could provide a novel bio-nano electronics substrate with a variety of applications. In the present study, a polydimethyldiallyammonium chloride based I-SAM technique has been utilized to produce bilayers, trilayers and multilayers of alternating monolayers of bR, PDAC and QD's on a conductive ITO substrate. The construction of multilayer systems was directly monitored by measuring the unique A570 nm absorbance of bR, as well as QD fluorescence emission. Both of these parameters displayed a linear relationship to the number of monolayers present on the ITO substrate. The photovoltaic response of bilayers of bR/PDAC was observed over a range of 3 to 12 bilayers and the ability to efficiently create an electrically active multilayered substrate composed of bR and QDs has been demonstrated for the first time. Evaluation of QD fluorescence emission in the multilayer system strongly suggests that FRET coupling is occurring and, since the I-SAM technique provide a means to control the bR/QD separation distance on the nanometer scale, this technique may prove highly valuable for optimizing the distance dependent energy transfer effects for maximum sensitivity to target molecule binding by a biosensor. Finally, preliminary studies on the production of a sensor protein/bR hybrid gene construct are presented. It is proposed that the energy associated with target molecule binding to a hybrid sensor protein would provide a means to directly modulate the electrical output from a sensor protein/bR biosensor platform.

Nanoscale sensing arrays utilizing the unique properties of the optical protein bacteriorhodopsin and colloidal semiconductor quantum dots are being developed to detect minute concentrations of airborne toxins. This paper describes an innovative method to activate bacteriorhodopsin-based sensors with the optical output of quantum dots, producing a measurable electrical response from the protein. The ability of quantum dots to activate nanoscale regions on bacteriorhodopsin-based electrodes allows sub-micron sensing arrays to be created due to the ability to activate site-specific regions on the array. A novel method to modulate the sensor's electrical output to obtain both "on" and "off" states is also achieved utilizing the fluorescence resonance energy transfer characteristics of a bacteriorhodopsin/quantum dot system. Apart from applying this technology to toxin detection arrays, the ability to readily manipulate the protein's electrical and optical characteristics could have implications in other areas of nanobiotronics.