Home > Nanotechnology Columns > Magda Carvalho PhD, JD > Bioelectronics: Biosensors and G Protein-Coupled Receptor
The field of bioelectronics exploits biology in conjunction with electronics. A patent application describing a real-time nano-biosensor used as an analytical device of a sensing mechanism—olfactory—captures a new concept of nano-bioelectronic noses.
July 16th, 2009
Bioelectronics: Biosensors and G Protein-Coupled Receptor
Bioelectronics joins the principles of electronics to biotechnology/medicine in at least three areas of research and development: biosensors, molecular electronics, and neuronal interfaces. Biosensors are analytical devices that measure biological analytes and/or exploit biological recognition as part of the sensing mechanism.
The animal olfactory system can identify and discriminate thousands of odors with very low thresholds. Using olfactory receptors as sensing elements leads to a new generation of bioelectronic noses at the nanoscale level.
Receptor proteins are proteins which have specific affinity for biologically active compounds. Receptors are responsible for opening and closing of membrane channels for transport of specific metabolites. Olfactory receptors undergo a conformational change induced by odorant binding.
G-protein coupled receptors (GPCR) include receptors for sensing processes: visual and smell. GPCRs are integral membrane proteins that possess seven membrane-spanning domains or transmembrane helices. The extracellular parts of the receptor can be glycosylated. These extracellular loops also contain two highly conserved cysteine residues which build disulfide bonds to stabilize the receptor structure. The ligands of GPCRs typically bind within the transmembrane domain. The ligands bind and activate GPCRs. One such ligand is an odor (or smell) which is a volatilized chemical compound perceived by the sense of olfaction at very low concentration.
Patent Application 2009/0156427 — Bio-Sensing Nanodevice.
The invention relates to bio-sensing nanodevices which detect the presence, absence or quality of specific odoriferous chemical/biological compounds such as illegal and controlled substances, pathogens, toxins or human odors. The nanodevice comprises a biologically-derived G-protein coupled receptor, a real time receptor-ligand binding detection method, an odorant delivery system and an odorant recognition program. The novelty relies on the real time bio-sensing nanodevice with improved speed, precision and sensitivity. The "real time" means that a certain state is substantially simultaneously displayed in another form.
In one embodiment, the GPCR is of the type that falls into the cAMP system. This GPCR is coupled with trimeric G-protein and produces cAMP as the second messenger and the inositol phospholipid transmitter system producing inositol-1,4,5-triphosphate or diacyl glycerol as the second messenger. The cAMP can activate some pathways in single or parallel. In some types of nerve cells, such as olfactory-receptor nerve cells, cAMP-dependent ion-channels are opened, the cellular membrane is depolarized, and calcium enters the cell through the channel, transiently increasing intracellular concentration of it. cAMP activates cAMP-dependent kinase , phosphorylates serine and/or threonine residues of function-protein, and modifies its activity. On the other hand, inositol-1,4,5-triphosphate binds to its receptors on the endoplasmic reticulum and accelerates the release of calcium into the cell. Diacyl glycerol activates protein kinase C promoting the action of hormones.
In the preferred embodiment the G-protein coupled receptor is an olfactory receptor. It is stabilized by mixing it with a surfactant such as peptides. The surfactants and the olfactory receptor form a new self-assembled nanostructure including liposomes, lamellar phase, and hexagonal, cubic or tubular structures. The GPCRs are immobilized on a support made of organic or inorganic material including any material capable of forming a solid surface. A solid support can take the form of a plate, a microwell, chip, glass slide, or the like. Immobilization of the GPCR onto the support can be achieved by several methods, for example attaching the self GPCR to the metal oxide nanowires.
The reading devices to detect the "real-time" of the binding receptor-ligand include Surface Plasmon Resonance (label free) used to show binding of a known ligand, ultraviolet-visible absorption and fluorescence resonant energy transfer, among others. Devices that utilizes optical sensors for fluorescence or luminescence were preferred since they have the ability to detect emitted light of very low intensity at specific wavelengths and the ability to block light at other wavelengths which can interfere with the signal being detected. The optical sensors can be used in either conventional or "contact" imaging configuration. The "contact" imaging configuration generates a representation of a specimen directly coupled to the surface of the chip.
The odorant delivery system can be either passive exposure to air or microfluidic bubble logic operation. The microfluidic bubble logic operation includes micron-sized droplets and bubbles of chemical in a microfluidic chip. The "bubble logic" employs nano-liters volume of droplets and bubbles of chemicals to mimic the actions of the electrons moving through the circuits of a microprocessor. Thus, bubbles traveling in a microfluidic channel can carry a variety of gas samples to precise locations on a chip. The system can be first "trained" to recognize known odorants and form a database of signatures so that it will match unknown or combinations of odorants.
In summary, this patent application relating to odorant detector devices utilizing nanoscale sensing elements bearing GCPR olfactory receptors highlights a new notion of bioelectronic noses.
Literature of Interest:
US Patent Application 20090156427. Inventors Zhang, Shuguang; Mershin, Andreas; Kaiser, Liselotte; Cook, Brian; Graveland-Bikker, Johanna F.; Prakash, Manu; Kong, David; Maguire, Yael, for Bio-Sensing Nanodevice. (June 18 2009)
Pennetta, C., Akimov, V., Alfinito, E., Reggiani, L., Gorojankina, T., Minic, J., Pajot-Augy, E., Persuy, M. A., Salesse, R., Casuso, I., Errachid, A., Gomila, G., Ruiz, O., Samitier, J., Hou, Y., Jaffrezic, N., Ferrari, G., Fumagalli, L., and Sampietro, M. (2006). Towards the realization of nanobiosensors based on G protein-coupled receptors. In C. S. S. R. Kumar (Ed.), Nanodevices for the life sciences (series: Nanotechnologies for the life sciences) (Vol. 4, pp. 217-240) Wiley-VCH.
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