2 February 2012 Design and study of activatable ("OFF/ON") quantum dots (Qdots): ligand selection for Qdot surface modification for controlling Qdot fluorescence quenching and restoration
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We report design and synthesis of a series of activatable "OFF/ON" CdS:Mn/ZnS quantum dot (Qdot) based sensing probes. The Qdot "OFF" state represent the "quenched state" where the Qdot fluorescence is quenched by ligands attached to Qdot surface. Fluorescence quenching is likely due to ligand assisted electron transfer process. Qdot fluorescence is restored when the electron transfer process is stopped. Using this activatable Qdots, we have successfully demonstrated usefulness of these Qdot probes for reliable detection of toxic cadmium ions in solution, selective detection of glutathione and sensitive detection of intracellular cancer drug release event. In this paper, we will discuss a simple but robust method of making water-soluble CdS:Mn/ZnS Qdots at the room-temperature. Two different water-soluble biomolecules, the N-acetyl cysteine (NAC) and the glutathione (GSH) were used as surface coating ligands. This is a singlestep, one-pot synthesis where the Qdot nanocrystals were grown in the presence of the biomolecules. These Qdots were characterized by fluorescence spectroscopy. Stability of the GSH coated Qdots and the NAC coated Qdots were studied by treating with ethylenediaminetetraacetic acid (EDTA, a strong chelating agent for Zn and Cd ions). Our results show that fluorescence properties of Qdots are affected by the type of surface coated ligands. In comparison to the GSH coated Qdots, the NAC coated Qdots show broad but strong emission towards near infra-red region. When treated with EDTA, fluorescence property of the GSH coated Qdot was affected less than the NAC coated Qdots. This preliminary study shows that NAC coated Qdots could potentially be used to develop activatable ("OFF/ON") probes for potential deep-tissue imaging applications. Similarly, the GSH coated Qdots could be applied for probing desired analytes or for bioimaging purposes in environmentally harsh conditions.
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Andrew Teblum, Andrew Teblum, Srijita Basumallick, Srijita Basumallick, Rikhav Shah, Rikhav Shah, Rajendra Narayan Mitra, Rajendra Narayan Mitra, Subhash Banerjee, Subhash Banerjee, Swadeshmukul Santra, Swadeshmukul Santra, } "Design and study of activatable ("OFF/ON") quantum dots (Qdots): ligand selection for Qdot surface modification for controlling Qdot fluorescence quenching and restoration", Proc. SPIE 8232, Colloidal Nanocrystals for Biomedical Applications VII, 82321H (2 February 2012); doi: 10.1117/12.912799; https://doi.org/10.1117/12.912799

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