The idea I want to present is how to cure a blindness causing genetic disorder, retinitis pigmentosa (RP), by making use of nanotechnology, namely quantum dot technology. Recently it was found that cone cells die by necrosis in RP while cone cells die by another mechanism that mainly involves membrane rupture and cell enlargement, but the exact cause of RP is yet to be elucidated. Genetic mutations of pigments of photoreceptor cells were also shown to produce certain forms of RP.
The retina of the human eye contains millions of photoreceptor cells (PC) that transform light into electro-chemical signals that are processed by the brain to produce the image we finally perceive. For example, the human eye contains about 130 million rods and about 7 million cones. Rod cells mediate black-and-white vision while cone cells mediate color vision. It is known that in RP the loss of color vision due to cone cell death is the most debilitating part of this disease.
Having briefly introduced the anatomy of the anterior part of the retina we will review the technology of semiconductor quantum dots. Quantum dots (QD) are geometrical structures of semiconductor crystals. A subclass of QDs are the optically active quantum dots (OAQDs) and they represent only those QDs that can interact with light quanta (photons). A photon creates an exciton i.e. an electron-hole pair, where by hole we understand a vacancy in the valence band of the semiconductor. Then an applied field along the QD may disintegrate the exciton via electron and hole quantum tunneling into electron and hole reservoirs. This in turn gives rise to a measurable photocurrent. Briefly, light can be converted to current using OAQD. It is important to mention that OAQDs can be made biocompatible and used in vivo.
The solution of QDs will target the damaged PC cells in the retina if inserted in the human body. When the compunds arrive at the place of the ruptured membrane of the PC they insert themselves into the plasmalema at the place where rhodopsin pigments are to be found. Then the bias of chemical potentials between the extracellular fluid and the intracellular fluid transforms the impinging light quanta (coming from the outside world) into an electrical current, a photocurrent. This in turn gives rise to a graded action potential along the PC thus restoring the function of the previously unhealthy cell.
We mention that there are three types of anti-bodies for the three types of rhodopsin found in a cone cell. They facilitate the binding to the pigment with the right color. In order to make the process complete QDs must be grown in three sizes, depending on the detected wavelength of the absorbed photon.
The proposed idea is a cure of retinitis involving the restauration of the dead photoreceptor cells of the inflicted retina. OAQDs made of ZnS are coated with hidrophylic chains of chitosans and then conjugated with streptavidin, biotin and anti-bodies that target the rhodopsin pigments in retinal cone cells. Then the membrane surface of an unhealthy cell is bathed in the injected solution of colloidal OAQDs. Once bound to the specific rhodopsin molecule in the PC the OAQD starts to function in the transport regime in which photons are converted to electrical signals that regenerate the lost action potential needed for the well functioning of the retina. We hope that the solution presented would present better prospects for rehabilitation of a patient who suffers from retinitis pigmentosa.
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