We report a simple, rapid approach to synthesize water-soluble and biocompatible fluorescent quantum dot (QD) micelles by encapsulation of monodisperse, hydrophobic QDs within surfactant/lipid micelles. Analyses of UV-vis and photo luminescence spectra, along with transmission electron microscopy, indicate that the water-soluble semiconductor QD micelles are monodisperse and retain the optical properties of the original hydrophobic QDs. The QD micelles were shown to be biocompatible and exhibited little or no aggregation when taken up by cultured rat hippocampal neurons.

The synthesis and self-assembly of nanocrystals (NCs) have gained much interest due to the NCs' unique size-dependent optical, electronic, and chemical properties and their potential applications in areas such as optics, electronics, catalysis, magnetic storage, and biological labeling and sensing. [1][2][3][4][5][6] To date, most work has focused on the synthesis and self-assembly of nanocrystals that are stabilized with alkane ligands (CH 3 (CH 2 ) n R, R = SH, NH 2 , PO, etc.). [3,7,8] Such NCs can be made at fairly high quality (narrow size distribution, preferred shapes such as rod, cube, etc., and large production). These NCs are hydrophobic, and their self-assembly is limited to organic solvents. However, there are many applications requiring hydrophilic or aqueous environments, such as biolabeling and surface-enhanced Raman spectroscopy (SERS)-based NC films or arrays for biosensing. [9][10][11][12] In addition, water-soluble NCs and their ordered arrays/films provide a great opportunity for further integration into inorganic ceramic frameworks that offer the chemical and mechanical robustness needed for enhanced device functionality. [13][14][15][16] Although some NC superlattices have been fabricated through aqueous media, [17][18][19] the methods are limited to spherical gold NCs.Here we report a facile route to prepare ordered NC arrays self-assembled from water-soluble NC-micelles. The method is simple, widely applicable to other materials, and can be used to prepare water-soluble NCs with different compositions and shapes, such as sphere, rod, and cube, as well as their ordered arrays. Our approach involves the synthesis of watersoluble gold-NC-micelles using our recently developed surfactant encapsulation techniques, [16,20] which were conducted in an interfacially driven water-in-oil microemulsion process. The whole process takes only ten minutes. Subsequent selfassembly of NC-micelles upon evaporation of a drop of NCmicelle aqueous solution on substrates, such as a transmission electron microscopy (TEM) grid, silicon wafer, glass, etc., leads to ordered two-and three-dimensional (2D and 3D) gold-NC superlattice films (Scheme 1). 1-Dodecanethiol (DT)-stabilized gold NCs were prepared using the method of Brust et al. [21] Heat treatment at 140°Cfor 30 min followed by size-selective precipitation using the solvent/non-solvent pair of toluene/ethanol was used to further narrow the size distribution to ∼ 7 %. The narrow size distribution of NCs is essential for formation of ordered NCmicelle arrays. In a typical NC-micelle synthesis procedure, a concentrated solution of monosized DT-stabilized gold NCs in chloroform was added to an aqueous solution of hexadecyltrimethylammonium bromide (C16TAB) under vigorous stirring to create an oil-in-water microemulsion. Chloroform evaporation during a heat course (40-80°C, ∼ 10 min) transfers the NCs into the aqueous phase (forming NC-micelle stock solution). This interfacial process is driven by the hydrophobic van der Waals interactions between the primary alka...

Supplemental figure 1 shows successive confocal images focusing down through the cells showing localization within the neurons.Supplemental figure 2 is a 3D reconstruction of supplemental figure 1 further confirming subcellular accumulation. Confocal images were obtained with a Nikon Eclipse TE2000-U inverted microscope with a CARV spinning disk confocal unit (Atto Biosciences) using a 40x oil objective (n.a. = 1.0). Optical sections were taken every micron. QDs were imaged using <460nm excitation and 585nm emission filter (Chroma Techology Corp) and FITC was imaged with a 484nm excitation filter and 518 nm emission filter (Chroma Technology Corp.).

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