Scientists at the US Department of Energy’s Ames Laboratory, in collaboration with scientists at the University of Michigan have developed and demonstrated a fluorescence-based chemical sensor that is reportedly more compact, versatile and less expensive than existing technology of its kind.
The new sensor holds promise for applications such as monitoring oxygen or volatile organic compounds. Within the field of molecular diagnostics for biomedical and biochemical research, the sensor could be used for point-of-care medical testing, high-throughput drug discovery, and the detection of pathogens.
The new sensor is said to have grown out of a basic research effort by Ames Laboratory senior physicist Joseph Shinar and members of his group to study the photophysics of luminescent organic thin films and organic light-emitting devices (OLEDs). The University of Michigan researchers, led by chemist Raoul Kopelman, were interested in developing fluorescent sensors. The collaboration resulted in the creation of an integrated OLED/optical chemical sensor.
Shinar explained that fluorescence-based chemical sensing devices, in general, include a light source that excites the sensing element, the sensing element that produces the fluorescence (usually a fluorescent dye that is used to tag the sample under investigation), and a photodetector that responds to the fluorescence of the sensor. Conventional sensors use lasers or inorganic light emitting devices as light sources, but they present problems in that they are expensive, bulky and cannot be integrated with the other sensor components.
Shinar’s and Kopelman’s OLED/optical chemical sensor is said to be unique because the detector and the OLED light source that excites the fluorescence integrated so simply. ‘This is a real advantage,’ said Shinar. ‘With this kind of geometry, called ‘back detection,’ we should be able to use the sensor for in vivo biological applications.’
Explaining the back-detection design, Shinar said, ‘Let’s say you have some solution on a glass substrate – blood, urine, whatever – that has lots of compounds in it that you want to detect. Your sensor is in contact with the biological solution on the substrate, and your OLED light source is behind the substrate. It’s like a sandwich: sample solution, sensor, substrate and OLED. As the OLED light source excites the sensor, the sensor fluoresces. ‘When the sensor detects the compound of interest in the sample solution, its fluorescence changes, and the change is picked up by a photodetector positioned behind the OLED light source.’
Early in 2001, Shinar and his collaborators successfully demonstrated an oxygen-sensor prototype in which the OLED was integrated with the oxygen-sensor film. ‘We got really good results on the oxygen sensor,’ he said. ‘The response of the sensor to oxygen was very fast.’
Shinar said they had used front detection instead of back detection with the oxygen-sensor prototype. Now they’re trying to demonstrate the back-detection capability. In addition, he anticipates that the Ames Lab research team and the University of Michigan collaborators will be able to develop a prototype for a glucose sensor in the near future. ‘The recipe is there, but we’re wrestling with the stability of the glucose enzyme, which has a drastic effect on the uptake of oxygen by glucose,’ he said.
The versatility, flexibility and cost-effectiveness of OLEDs are said to offer excellent opportunities for developing OLED/optical chemical sensor arrays and high-density microarrays. Such systems, in principle, could contain up to 256 sensors on a single, one-square-millimetre chip.
They would be able to discriminate between multiple compounds in complex biological samples, such as blood, urine, saliva or airborne particles, creating what Shinar described as a very low-cost, compact and versatile optoelectronic ‘nose’ or ‘tongue’ suitable for in vivo measurements.