The objective of this proposal is to develop novel photoluminescence (PL)-based sensors that are fully structurally integrated: The light source, the sensing element, and the photodetector (PD) and associated filter, are fabricated on transparent substrates and attached back-to-back. The resulting sensors could therefore be extremely compact, robust, selective, fast, autonomous, consume little power, and inexpensive. The proposal focuses on sensing oxygen, a key tool in medical, environmental, (bio)chemical, and food monitoring, and Bacillus anthracis toxin (anthrax).
The intellectual merit. The central concept is the novel total structural integration of the foregoing components. The light source is an array of organic light-emitting device (OLED) pixels. The sensing elements include porous films with an embedded dye, surface immobilized species whose PL is selectively analyte-sensitive, or microfluidic channels/wells with recognition elements in solution. The PD and filter are multilayer thin films of hydrogenated nanocrystalline Si, SiGe, and/or SiC. The geometry will be "back detection," i.e., the OLED and PD pixels are fabricated on the same side of the substrate. The array of long-pass filters and PD pixels is fabricated first, followed by the OLEDs in the gaps between the PD pixels. The sensing element is fabricated on a separate substrate and attached to the OLED/PD substrate. In the complete device, the electronic circuitry (including instruction receiver and data transmitter), readout, and battery will be positioned "behind" the PD. Hence the whole device would be ~2.5"x5"x1", far more compact and less costly than any sensors currently available. The work results in a new platform for PL-based sensors, which can be further developed to multianalyte sensor microarrays. Innovative elements are (i) the complete integration of all the sensor components, and (ii) the development of sensing elements utilizing microfluidic architectures and films/surfaces tailored for specific recognition molecules, which will enhance the sensitivity and shorten the response time. Moreover, the OLEDs will be operated in a pulsed mode, which will increase their lifetime and generate negligible heat, which is crucial for heat-sensitive recognition elements and agents. Oxygen will be monitored via the PL lifetime, thus eliminating the need for frequent calibration.
Different approaches will be evaluated to generate robust sensors for real-world applications. The oxygen sensor will be based on the dynamical quenching of the PL of oxygen-sensitive dyes, initially with a green OLED and Pt octaethyl porphyrin (PtOEP) dye. We will compare the sensors with dyes embedded in solid films with dyes solutions. The anthrax sensor will be based on the cleavage of certain peptides by anthrax lethal factor. Labeled peptides will be synthesized at the Protein Facility of Iowa State University (ISU), with a Forster resonance energy transfer donor and acceptor on either side of the cleavage site.
The broader impacts. The sensors for the two aforementioned agents will be ideal for a broad range of applications in areas such as homeland security, medical, environmental, biological, food/brewing, and health/safety. Beyond these impacts, the devices define a new sensor platform for chemical and biological agents, which could lead to extremely compact and inexpensive multianalyte sensor microarrays. The proposed work will serve as a basis for the development of this platform. It will also expand the basic knowledge in embedding/immobilizing recognition elements, sensor design, and sensor engineering. It will also have a broad educational impact, promoting the growth of the interdisciplinary biophysics program at ISU and training students in condensed matter physics, electrical engineering, biophysics, chemistry, and molecular biology. It will be integrated with teaching by developing new experimental course modules for graduate students. Significant participation of undergraduates, including minorities and women, is planned.
