Semiconductor Quantum Dots for Electrochemical Biosensors

Abstract

IntroductionQuantum dot s ( QD s) or semiconductor nanoparticles are colloidal nanocrystalline semiconductors made of group II -VI or III -V elements. With diameters of between 1 and 100 nm, QDs demonstrate interesting optical and electronic properties. The unique photophysical properties of QDs, such as high fl uorescence, quantum yield stability against photobleaching, and size -controlled luminescence properties, enable them to be utilized as optical labels for bioanalysis [1] . The photoexcitation of semiconductor QDs can result in the transfer of an electron from the valence band to the conduction band, thus yielding an electron hole pair. When the photoexcited QDs were confi ned to electrode surfaces, the cathodic photocurrent could be formed by the ejection of the conduction band electrons to an electron acceptor in the electrolyte solution, followed by the supply of electrons from the electrode to neutralize the valence -bound holes. By comparison, the anodic photocurrent can be yielded by transferring the conduction band electrons to the electrode with the transfer of electrons from an electron donor in the solution [2] . These photoelectrochemical properties of QDs can be used for developing light -to -electrical energy conversion systems. The optical and electrophotochemical applications of QDs for bioanalysis were reviewed by Zayats and Willner [2] .It is known that the surfaces of QDs can be chemically modifi ed by a functional capping monolayer, which allows a tethering of the biomacromolecules for bioanalysis applications [3] . When biomacromolecules are immobilized on the surface of QDs, the semiconductor QDs also can promote direct electron transfer between the biomolecules and electrode surface, and improve the performance of the biosensor. Recently, QDs were incorporated with redox proteins by covalent bonding or electrostatic interaction to realize the direct electrochemistry of the biosensor. Electrochemical immunosensors or immunoassays for DNA and proteins have developed dramatically over the past two decades because of their high sensitivity, inherent simplicity, low cost, and miniaturization. Nanomaterials -based electrochemical immunoassays and immunosensors have attracted considerable interest, since they can enhance the sensitivity via the signal amplifi cation. Of the various

Evidence for a Through-Space Pathway for Electron Transfer from Quantum Dots to Carboxylate-Functionalized Viologens

“…Chemically tuning the electronic coupling between redox-active ligands and inorganic QDs provides a handle by which we can tune the rates of charge transfer across the QD-ligand interface in order to (i) generate (and inhibit the recombination of) mobile charge carriers within photovoltaic materials, (ii) initiate redox chemistry within photocatalytic materials in the production of solar fuels, or (iii) regulate photoluminescence of the QDs in redox-based ion or biomolecule detection schemes . The conformation of ligands adsorbed to surfaces of QDs is determined by complex and dynamic interactions between the ligand and the surface of the QD, the neighboring ligands, and the solvent molecules.…”

Nanomaterials based microarray platforms for biodetection

“…they have a wide excitation spectra. 24,25 Because of their properties QDs are used in biosensing as either fluorescent probes 26,27 or labels for electrochemical detection 28 .…”

“…In fact, as an oxygenated lattice of donor/acceptor molecules exposed in a planar surface, GO enables unprecedented optical biosensing strategies to detect DNA, cancer biomarkers, viruses, and more. It has excellent capabilities for direct wiring with biomolecules, heterogeneous chemical and electronic structures, the ability to be solution-processed, and the ability to be tuned as either an insulator, semiconductor or semi-metal (published in Advanced Materials, see pages [19][20][21][22][23][24][25][26][27][28][29][30].…”