Bioimaging Tools Based on Polyelectrolyte Microcapsules Encoded with Fluorescent Semiconductor Nanoparticles: Design and Characterization of the Fluorescent Properties

Abstract

Fluorescent imaging is a widely used technique for detecting and monitoring the distribution, interaction, and transformation processes at molecular, cellular, and tissue level in modern diagnostic and other biomedical applications. Unique photophysical properties of fluorescent semiconductor nanocrystals “quantum dots” (QDs) make them advanced fluorophores for fluorescent labeling of biomolecules or optical encoding of microparticles to be used as bioimaging and theranostic agents in targeted delivery, visualization, diagnostics, and imaging. This paper reports on the results of development of an improved approach to the optical encoding of polyelectrolyte microcapsules with stable, covered with the multifunctional polyethyleneglycol derivatives water-soluble QDs, as well as characterization of the optical properties, morphological and structural properties of the encoded microcapsules. The embedding of QDs into the polymer microcapsule membrane through layer-by-layer deposition on a preliminarily formed polymeric polyelectrolyte shell makes it possible to obtain bright fluorescent particles with an adapted charge and size distribution that are distinctly discernible by flow cytometry as individual homogeneous populations. The fluorescent microcapsules developed can be used in further designing bioimaging and theranostic agents sensitive to various external stimuli along with photoexcitation.

Biofunctionalized Polyelectrolyte Microcapsules Encoded with Fluorescent Semiconductor Nanocrystals for Highly Specific Targeting and Imaging of Cancer Cells

“…The microcapsules were labelled with the prepared water-soluble QDs via adsorption of the QDs onto the calcium carbonate microparticles preliminarily coated with the PAH/PSS/PAH/PSS/PAH layers as described elsewhere [17,18]. The layer of adsorbed QDs was then coated with additional polyelectrolyte layers in the order PAH/PSS/PAH/PSS/PAH/PSS.…”

“…Each cycle of polyelectrolyte and QD deposition was characterized by flips in the surface charge of the microparticles, which varied from −26 mV to +15 mV. Flips of surface charges by layer-by-layer coating were examined by zeta-potential measurements using a ZetaSizer Nano ZS (Malvern Instruments, Worcestershire, UK) and were presented in our previous studies [17,18]. The resultant microcapsules were characterized by the size and shape similar to those of the template microbeads used.…”

“…The microphotograph of the QD-encoded microcapsules demonstrates their bright fluorescence determined by the QDs (Figure 1b). The QD localization pattern within the polyelectrolyte shell was already investigated in microcapsule sections using fluorescence microscopy, where the highly homogeneous distribution of QDs fluorescence within the shell was observed [18]. The loading of QDs on microparticles was quantified earlier [17].…”

“…This fact shows a multilayer character of QD adsorption during their layer-by-layer deposition on the microcapsule surface. The fluorescence properties of the final microparticles, including the fluorescence spectra and lifetimes of embedded QDs, have been examined and described in our previous studies [17,18].…”

“…For that purpose, we prepared samples of BSA-coated microcapsules without Abs. BSA was used as a back-coating agent in bioconjugation to block activated areas of the microcapsule surface and make it more inert to the microenvironment and more biocompatible [18]. As shown in Figure 5, the interaction of the conjugates with EGFR-negative cells was almost negligible.…”