Increase the photostability of aqueous dispersed QDs using surfactants as stabilizing agent under long- time UV-light irradiation

Abstract

Quantum dots (QDs) have attracted a great deal of attention over the past two decades because of their unique photochemical and photo physical properties. Colloidal semiconductor quantum dots (QDs) have great potential as a new class of fluorophores for biological and biomedical imaging because of high brightness, long-term photostability and single-light source excitation for multicolored QDs.1,2 The syntheses of monodispersed fluorescent QDs are generally performed in organic solvents with surface passivation by alkyl phosphine oxides such as trioctylphosphine oxide (TOPO).3,4 The resulting QDs are soluble only in nonpolar solvents that making them difficult to use for biological application. So far, many synthetic methodologies for the preparation of water-soluble QDs have been developed by surface modifications with amphiphilic compounds including thiols1,2,5–8 polymers,9,10 phpholipids.11 In recent years, there has been great progress in synthetic methods of quantum dot production, which made large scale preparation of QDs with high quality and narrow size distribution possible. Luminescent QDs have been successfully attached to protein, sugar, and other biologically active agents.9,12–14 Among the various types of modified QDs have been studied most thoroughly due to their possible applications in biological disciplines. However, consideration of QDs behavior at biological interfaces, e.g., cell membranes, is one of the most important issues requiring further study prior to implementation in real applications. Currently, few studies have been conducted regarding surface chemistry properties of quantum dots at biological interfaces. Quantum dots synthesized in organic solvents are insoluble in water. Hence a challenge is how to make the highquality hydrophobic quantum dots soluble in water and also active in bioconjugate reactions. Ligand exchange inevitably alters the chemical and physical states of the quantum dot surface atoms and in most cases dramatically decreases the quantum efficiency of the quantum dots, thiol-based molecules (e.g.,mercaptocarbonic acids) may form disulfides over time and come off from the quantum dot surface and finally the quantum dots aggregate and precipitate out of water. Surface functionalization of quantum dots can improve the solubility but reduce the quantum efficiency.