Silica-Shelled Single Quantum Dot Micelles as Imaging Probes with Dual or Multimodality

Abstract

The present study describes a stabilization of single quantum dot (QD) micelles by a "hydrophobic" silica precursor and an extension of a silica layer to form a silica shell around the micelle using "amphiphilic" and "hydrophilic" silica precursors. The obtained product consists of approximately 92% single nanocrystals (CdSe, CdSe/ZnS, or CdSe/ZnSe/ZnS QDs) into the silica micelles, coated with a silica shell. The thickness of the silica shell varies, starting from 3-4 nm. Increasing the shell thickness increases the photoluminescence characteristics of QDs in an aqueous solution. The silica-shelled single CdSe/ZnS QD micelles possess a comparatively high quantum yield in an aqueous solution, a controlled small size, sharp photoluminescence spectra (fwhm approximately 30 nm), an absence of aggregation, and a high transparency. The surface of the nanoparticles is amino-functionalized and ready for conjugation. A comparatively good biocompatibility is demonstrated. The nanoparticles show ability for intracellular delivery and are noncytotoxic during long-term incubation with viable cells in the absence of light exposure, which makes them appropriate for cell tracing and drug delivery. The presence of the hydrophobic layer between the QD and silica-shell ensures an incorporation of other hydrophobic molecules with interesting properties (e.g., hydrophobic paramagnetic substances, hydrophobic photosensitizers, membrane stabilizers, lipid-soluble antioxidants or prooxidants, other hydrophobic organic dyes, etc.) in the close proximity of the nanocrystal. Thus, it is possible to combine the characteristics of hybrid materials with the priority of small size. The silica-shelled single QD micelles are considered as a basis for fabrication of novel hybrid nanomaterials for industrial and life science applications, for example, nanobioprobes with dual modality for simultaneous application in different imaging techniques (e.g., fluorescent imaging and functional magnetic resonance imaging).

Bioconjugated quantum dots for in vivo molecular and cellular imaging☆

“…To address these limitations, several research groups have led efforts to couple QD-based optical imaging with other imaging modalities that are not limited by penetration depth, such as MRI, positron emission tomography (PET) and single photon emission computed tomography (SPECT) [154][155][156][157][158]. For example, Mulder et al [154] developed a dual-modality imaging probe for both optical imaging and MRI by chemically incorporating paramagnetic gadolinium complexes in the lipid coating layer of QDs [154,155].…”

Chemical nature and structure of organic coating of quantum dots is crucial for their application in imaging diagnostics

“…21 Quantum dots were additionally coated with silica as described by Bakalova et al, 22 polyamidoamine (PAMAM) dendrimers as described by Wu et al 23 (with a slight modification of using the second-generation PAMAM-C12 dendrimer [Sigma-Aldrich, St Louis, MO] instead of octylaminemodified polyacrylic acid), and the second-generation PAMAM-C12 dendrimer (Sigma-Aldrich) crosslinked by a PAMAM-succinamic acid dendrimer (Sigma-Aldrich), with N-(3-dimethylaminopropyl)-N′-ethyl-carbodiimide hydrochloride used as a zero-length crosslinker.…”

Improved Biocompatibility and Pharmacokinetics of Silica Nanoparticles by Means of a Lipid Coating: A Multimodality Investigation

“…In addition to carrying contrastgenerating material for a single imaging modality, the ease of incorporation of different chemicals in silica makes it an excellent material for the integration of multiple properties to enable multimodality biomedical imaging. For example, combined FI and MRI have been shown in vitro [19][20][21][22][23] as well as in vivo. 24,25 Other promising, silica-based materials for combined FI and MRI, [26][27][28][29] combined FI and computed tomography (CT), 30 MRI and CT, 31 and even FI, MRI, and CT 32 have been reported but have not yet shown their applicability in vitro or in vivo.…”