Many of us, at least in developed countries, have CD players rusting in our homes. So why not turning them into something useful? A very short note by the American Chemical Society (ACS) says that Spanish researchers have adapted this now venerable technology into home health monitoring systems. This means that CD technology could be used for tests ranging from the measurement of environmental toxins to at-home disease diagnosis and even laboratory-based testing. The researchers don't give any clues about the availability of such a product, but I think they've got a brilliant idea.
You can see above (A) a schematic representation of the detection system. "The set of servo systems (spindle and stepper motors) of the CD drive keeps the laser beam focused on the spiral track, allowing disc rotation and laser scanning. The transmitted light through the disc is transformed by the photodiode into an analog electrical signal. At the same time, the photosensor detects the trigger footprints, starting the data collection on disc. [...] The CD drive is controlled by software and connected to the computer by USB2.0 interface." You also can see a picture of the CD player used in this work (B). (Credit: Universidad Politecnica de Valencia, Spain)
This research project has been done at the Institute of Applied Molecular Chemistry and the Valencia Nanophotonics Technology Center at the Universidad Politécnica de Valencia (UPV) by Sergi Morais, Javier Carrascosa, David Mira, Rosa Puchades, and Angel Maquieira.
This research work is published online by Analytical Chemistry, an ACS Publication, under the title "Microimmunoanalysis on Standard Compact Discs To Determine Low Abundant Compounds" (Online publication: September 14, 2007; Printed edition: October 15, 2007. Here is a link to the abstract. "High-density competitive indirect microimmunoassays were performed in both sides of compact discs by direct absorption of immunoreagents on polycarbonate surface, using gold- or enzyme-labeled immunoglobulins as tracers for displaying the immunoreaction. The operational principle is based on the use of a low-reflectivity compact disc as analytical platform that allows the reflection/transmission (30/70%) of the CD reader laser beam (lambda 780 nm). The reflected light is used to scan the disc track keeping it in movement. The transmitted light is detected by a planar photodiode integrated on the CD drive. The variation of the optical transmission of the light caused by the immunoreaction products is related to the sample concentration. As a proof of concept, low abundant compounds, commonly used as pesticides, were detected in a 60-min total assay time, with a limit of detection ranging from 0.02 to 0.62 mug/L for 2,4,5-TP, chlorpyriphos, and metolachlor. The obtained results show the enormous prospective of compact discs in combination with CD players for multiresidue and drug discovery applications."
The full text of this article is available online, both in HTML format or in PDF format (8 pages, 311 KB). The above illustration has been extracted from this paper.
Here are some of the conclusions of the researchers. "The use of a low-reflectivity compact disc and an adapted CD drive as the detector is a suitable methodology to sense low abundant molecules in a high-density format with microgram per liter level sensitivity. The detection setup fully uses all the servo systems of a CD drive, improving and implementing the former detection CD-based analytical methodologies. Sensing on the top side of standard compact discs resulted in a good imaging resolution to readily detect as small as 13-m-diameter spots. The response capacity of the CD drive is huge. In the current configuration, up to 2560 spots of 500 m in diameter in 7 min can be detected. Furthermore, considering that the active surface of a disc is a circular band of 3 cm width and a track pitch of 200 m (center-to-center distance between spots), a total of 300 000 spots of 100-m diameter could be deposited on the disc and detected by the CD reader in a few minutes. Also, the automation of the printing step (for instance, the use of inkjet CD printers, robot stampers adapted to the CD platform, etc.) would permit us to set up a quicker, less expensive, more precise, and higher throughput technique."
Finally, here is how they summarize their project. "In summary, the herein developed methodology is sensitive, versatile, portable, low cost, and easy to operate and could become a very advantageous system for a simultaneous multiresidue and real-time high-throughput technique of general application in molecular recognition-based biochemical methods at the point of need for home health monitoring or in situ analysis."
Sources: American Chemical Society's Weekly PressPac, September 19, 2007; and various websites
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