Biomedical Applications of Colloidal Nanocrystals

Because of the high affinity of the thiol groups to a metal such as gold and zinc, we can conjugate metal nanocrystals with chemical compounds which contain thiol such as cysteine, cyctein contained peptide, and thiol-modified nucleic acids including DNA. Among them, T. Pellegrino et al. investigated Gold-DNA conjugates in detail by a comprehensive gel-electrophoresis study based on 1200 gels. The investigation contains the following three results: firstly, the precise detection of relative changes in size upon binding of molecules, secondary, comparison of the specific attachment of DNA via gold-thiol bonds to Au nanoparticles with nonspecific adsorption of DNA, and thirdly, determination of the maximum number of DNA molecules bounded per particle. These data might be the essential information for designing a functional nanodevice such as for the nanometer-sized electric circuit and for the carrier for gene delivery system. A new ligand which readily binds itself to CdSe-ZnS core-shell QDs, via surface ligand exchange, was designed and synthesized by Kimihiro Susumu et al. from tetraethylene glycol (TEG) based bidentate ligand functionalized with dihydrolipoic acid (DHLA) and biotin (DHLA-TEG-biotin). Quantum dots capped with DHLA and DHLA-TEG-biotin or polyethylene glycol modified DHLA (DHLA-PEG600) are dispersed easily in aqueous buffer solutions. Homogenized buffer solutions of QDs capped with mixture of DHLA-PEG600 and DHLA-TEG-biotin are stable over broad pH range and showed specific interactions with NeutrAvidin in surface binding assays. The authors say " further studies of these surface functionalized QDs for coupling with a variety of bioreceptors and biological assays are in progress. " For the study on the ligand-receptor binding, we need fluorescent markers. Ligand conjugated quantum dots are reported here by Ian D. Tomlinson et al. for imaging GABAc receptor on the surface membrane of intact cell. They have already succeeded in developing serotonin-conjugated quantum dots and the method to reduce nonspecific binding using PEGylated quantum dots. Together with all these works, they have proceeded for imaging GABAc receptors heterologously expressed on Xenopus laevis oocytes. On the other hand, Dopamine conjugated quantum dots are known to be endocytozed by cells bearing dopamine receptors and not by cells without dopamine receptors. Rafael Khatchadourian et al. studied the tools of fluorescence intensity and intermittency for following dopamine biocon-jugate processing in living cells. In this special issue, we have three papers on quantum dots as for the use of Forster (or fluorescent) resonance energy transfer (FRET). The characters of quantum dots such as photostability, …