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Biological Electronics and Sensors for Medical Applications

10.23.2007: Electronic Polymers in Biosensors

SPEAKER: Timothy M. Swager, PhD: MIT

MODERATOR: Jay Schnitzer, MD, PhD: MGH

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Experts discuss biological electronics and sensors

Two researchers discussed the topic of “Biological electronics and sensors for medical applications” at the CIMIT Forum on Oct. 23 at Simches Research Center at Massachusetts General Hospital.

Presenting were Luke Theogarajan, PhD, of MIT, and Timothy Swager, PhD, John D. MacArthur Professor and Department Head, Department of Chemistry, MIT.

Dr. Theogarajan’s topic was “Electronic and ionic neural interfaces.” He said that neural prostheses are being developed around the world to alleviate various debilitating conditions. The key component of any neural prosthesis is the biotic-abiotic interface. He discussed the conventional electronic coupling to neurons that has been successful in areas like cochlear prosthesis.

 “The main objective is to enable the design of efficient interfaces so that we can build devices to alleviate some of the debilitating conditions that arise from neural damage like blindness, Parkinson's disease etc. I am not with the clinic at MGH though I work with surgeons at MEEI and in the context of the Boston Retinal Implant project at the Veterans Administration, Boston. I am always looking for collaborations with like-minded people.”

Dr. Swager’s subject was “Electronic polymers and biosensors.” He focused on the applications of conjugated (electronic) polymers to detect molecules of biological origin and develop systems that can be used to measure biological activity. The mechanisms discussed will make use of optical detection and the ability of electronic polymers to amplify.”

He said, “My research program is broad and we are working on many applications in sensors (environmental, national security, and miscellaneous industries).  The road to the clinic for new technologies is a difficult and slow one. I suspect if all goes well, in 5-10 years we could have something out there.”

In many biological assays, detecting the presence of small molecules is crucial.  Researchers led by Timothy J. Swager of MIT are designing polymers capable of spectroscopically sensing small metabolites.  Electrons in the highly conjugated polymers occupy either valence orbitals or slightly more energetic conduction orbitals.  Light can excite electrons from valence orbitals into conduction orbitals, and when these excited electrons fall back into valence orbitals, they emit usually photons.  The polymers can be designed so that if the excited electrons in the conduction orbitals come near another specific molecule, known as an analyte, they drop back into valence orbitals without emitting photons.  In this case, the analyte quenches the polymer’s fluorescence, and this quenching can be observed by measuring the photons emitted by the polymer. 

The polymers may soon provide biologists with a valuable research tool, and Swager’s group is currently experimenting with polymer-coated microspheres.  At the center of these microspheres, different fluorescent molecules provide a baseline that allows investigators to make quantitative measurements of quenching.  The microspheres, however, have not been perfected.  Proteins and other undesirable macromolecules tend to stick to the microspheres’ surfaces, preventing analytes from binding.  Swager’s group is attempting to circumvent this problem by encasing the microspheres in a hydrogel that macromolecules can’t penetrate.  In the future, microspheres, or nanospheres, may become part of new biological assays, and this technology might even lead to particles that could be introduced into the human body to track down metabolites associated with tumors and other problems. 



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