Encapsulating of single quantum dots into polymer particles

Single semiconductor quantum dots were embedded into polymer particles with diameters below 0.1 μm by an emulsion polymerization procedure or via a secondary dispersion approach. The photoluminescence properties of the nanocrystals are retained upon encapsulation, as demonstrated by fluorescence confocal microscopy.

Highly luminescent biocompatible carbon quantum dots by encapsulation with an amphiphilic polymer

Highly luminescent, water-soluble and biocompatible Carbon Quantum Dots (aqCQDs) were prepared by encapsulating the parent hydrophobic CQDs in an amphiphilic polymer. The resulting aqCQDs were non-toxic to living cells, and were found to cross the cell membrane and localise primarily in the cytosol.     

Efficient incorporation of quantum dots into porous microspheres through a solvent-evaporation approach

Quantum dot (QD)-encoded microspheres play an important role in suspension arrays by acting as supports for various reactions between biomolecules. With regard to QD-encoded microspheres utilized in suspension arrays, three key requirements are controllable size, abundant surface functional groups, and especially excellent fluorescence properties. In this paper, narrowly dispersed poly(styrene-co-divinylbenzene-co-methylacrylic acid) (PSDM) microspheres with specific size, surface carboxyl groups, and porous structures were synthesized by seeded copolymerization. In order to improve the incorporation efficiency of QDs within microspheres, we developed a swelling-evaporation approach in which the swelling process was combined with gradual evaporation of the solvent and thus gradual concentration of QDs in the dispersion solution. This approach was demonstrated to be an efficient method for improving the fluorescence intensity of resultant microspheres compared with the use of swelling alone. Moreover, the porous structure was shown to aid the penetration of QDs into the interiors of the microspheres. Through this approach, microspheres encoded with either single or multiple wavelength-emitting QDs were fabricated effectively. The suspension immunoassays were then founded based on the QD-encoded microspheres, by coating mouse antihuman chorionic gonadotropin as the probe for goat antimouse IgG detection. The positive results determined by Luminex 100 and the low cytotoxicity of the QD-encoded microspheres demonstrated their great potential in suspension arrays.     

Organosilane micellization for direct encapsulation of hydrophobic quantum dots into silica beads with highly preserved fluorescence

Effective silica coating on hydrophobic quantum dots (QDs) was achieved by ultrasonic fragmentation of lipophilic silane-QDs precusor into water-soluble micelles and subsequent silicate deposition. This method allowed high retention of QD fluorescent properties and an easy scaling over the size and loading amount of silica beads.     

Design and evaluation of polymer matrices for the encapsulation of CdSe/ZnS quantum dots in photonic nanocomposite thin films

A systematic approach and a new scheme for the evaluation of the as–is encapsulation of CdSe/ZnS core/shell quantum dots into polymer matrices is proposed, aiming to the implementation of thin film photonic integrated structures. Work focuses on quantum dots capped by hexadecylamine and trioctylphosphine oxide with no ligand exchange or other intermediate processing steps involved. The polymers studied include poly(methyl–methacrylate) (PMMA), polystyrene and acrylic polymers incorporating long alkyl chains, which are expected to promote the compatibility of the quantum dot ligands to that of the polymer chains. In this approach, the variation of photoluminescence properties of the nanocomposite thin films is measured versus increased concentration of the quantum dots, so as to evaluate the suitability of each polymer structure as an efficient host. Furthermore, the refractive index of the quantum dots/polymer nanocomposite thin films are also estimated using white light reflectance spectroscopy data, as appropriate for the integration of photonic devices. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 552–560     

Stabilization and encapsulation of human immunoglobulin G into biodegradable microspheres

The instability of protein during preparation, storage, and release has become a major concern in recent years in the encapsulation of proteins into biodegradable polymers for controlled release systems. The present investigation was performed to study the mechanism of degradation of human immunoglobulin G (IgG) in double emulsion and solid-in-oil-in-water (S/O/W) encapsulation processes. The stabilizing effects of various excipients during the period of protein atomization using spray freeze-drying and subsequent encapsulation into polylactide-co-glycolide (PLGA) microspheres were explored. The size-exclusion high-performance liquid chromatography (SEC-HPLC) results showed that ultrasonication did not change the primary structure of IgG significantly. However, enzyme-linked immunosorbent assay (ELISA) revealed that the subsequent double-emulsion solvent evaporation process denatured nearly 80% of the total amount of IgG. This was possibly due to the adsorption, unfolding, and aggregation of IgG at the water/organic solvent interface. Both mannitol and trehalose could stabilize IgG during spray freeze-drying, with over 90% retention of its molecular integrity and immunoactivity, which were verified using SEC-HPLC and ELISA. Solid protein microparticles were further entrapped into monolithic-type microspheres of PLGA using the S/O/W method. FTIR results suggested that the incomplete release that is often observed in the formulation of controlled protein release systems may be due to the degradation or aggregation of protein in the solid polymer matrix.     

Photoluminescence of cadmium selenide quantum dots in polymer solutions

The effect of solvent on the photoluminescence of cadmium selenide quantum dots stabilized by oleic acid is examined with the example of two organic solvents: toluene and THF. It is found that THF favors desorption of ligands and formation of surface defects to a greater extent than toluene; as a result, the maximum of the photoluminescence band shifts to the red spectral region and its intensity decreases. The addition of polymers to the solution of quantum dots causes changes in the efficiency of photoluminescence and in the kinetics of its quenching. In the range of low concentrations (≤2 wt %) of quantum dots in polymer solutions, the intensity of luminescence first grows and then passes through a maximum and decreases. This effect may be explained both by the increasing number of surface defects and by quenching via energy transfer to polymers, especially in the case of polymers containing aromatic groups.     

An insight into the surface engineering of colloidal PbSe quantum dots for polymer hybrid photovoltaic applications

Journal of Sol-Gel Science and Technology - In this article, the beneficial effect of surface passivation rendered by the amalgamation of co-ordinating tri-n-octylphophine (TOP), oleylamine (OLA),...     

The encapsulation of an amphiphile into polystyrene microspheres of narrow size distribution

ABSTRACT: Encapsulation of compounds into nano- or microsized organic particles of narrow size distribution is of increasing importance in fields of advanced imaging and diagnostic techniques and drug delivery systems. The main technology currently used for encapsulation of molecules within uniform template particles while retaining their size distribution is based on particle swelling methodology, involving penetration of emulsion droplets into the particles. The swelling method, however, is efficient for encapsulation only of hydrophobic compounds within hydrophobic template particles. In order to be encapsulated, the molecules must favor the hydrophobic phase of an organic/aqueous biphasic system, which is not easily achieved for molecules of amphiphilic character.The following work overcomes this difficulty by presenting a new method for encapsulation of amphiphilic molecules within uniform hydrophobic particles. We use hydrogen bonding of acid and base, combined with a pseudo salting out effect, for the entrapment of the amphiphile in the organic phase of a biphasic system. Following the entrapment in the organic phase, we demonstrated, using fluorescein and (antibiotic) tetracycline as model molecules, that the swelling method usually used only for hydrophobes can be expanded and applied to amphiphilic molecules.     

In-situ synthesis of stable perovskite quantum dots in core-shell nanofibers via microfluidic electrospinning

Perovskite quantum dots (PQDs) possess remarkable optical properties, such as tunable photoluminescence (PL) emission spectra, narrow full width at half maximum (FWHM) and high PL quantum yield (QY), endowing the PQDs great application prospects. However, the inherent structural instability of PQDs has seriously hindered the application of PQDs in various photoelectric devices. In this work, a microfluidic electrospinning method was used to fabricate color-tunable fluorescent formamidinium lead halogen (FAPbX₃, X = Cl, Br, I) PQDs/polymer core-shell nanofiber films. The core-shell spinning nanofiber not only supplies the interspace for the in-situ formation of PQDs, but also significantly reduces the permeability of moisture and oxygen in the air, which greatly improves the stability of PQDs. After adjusting the composition of precursors, the blue-emissive polystyrene (core) and polymethyl methacrylate (shell) coated FAPbCl₃ QDs (abbreviated as PS/FAPbCl₃/PMMA, hereinafter), green-emissive PS/FAPbBr₃/PMMA and red-emissive PS/FAPbI₃/PMMA nanofiber films were fabricated with the highest PL QY of 82.3%. Moreover, the PS/FAPbBr₃/PMMA nanofiber film exhibits great PL stability under blue light irradiation, long-term storage in the air and water resistance test. Finally, the green- and red-emissive nanofiber films were directly applied as light conversion films to fabricate wide-color-gamut display with the color gamut of 125%, indicating their tremendous potentials in optoelectronic applications.     

Preparation of quantum dots encoded microspheres by electrospray for the detection of biomolecules

In this paper, a novel method based on the electrospray technique has been developed for preparation of quantum dot (QD)-encoded microspheres for the fist time. By electrospraying the mixture of polymer solution and quantum dots solution (single-color QDs or multi-color QDs), it is accessible to obtain a series of composite microspheres containing the functional nanoparticle. Poly(styrene-acrylate) was utilized as the electrospray polymer materials in order to obtain the microsphere modified with carboxyl group on the surface. Moreover, to test the performance of the QD-encoded microsphere in bioapplication, it is carried out that immunofluorescence analysis between antigens of mouse IgG immobilized on the functional microsphere and FITC labeled antibodies of goat-anti-mouse IgG in experiment. To the best of our knowledge, this is the first report of QD-encoded microspheres prepared by electrospray technology. This technology can carry out the one-pot preparation of different color QD-encoded microspheres with multiple intensities. This technology could be also suitable for encapsulating other optical nanocrystals and magnetic nanoparticles for obtaining multifunctional microspheres. All of the results in this paper show that the fluorescence beads made by electrospray technique can be well applied in multiplex analysis. These works provide a good foundation to accelerate application of preparing microspheres by electrospray technique in practice.     

Self-selective recovery of photoluminescence in amphiphilic polymer encapsulated PbS quantum dots

Self-selected recovery of the photoluminescence (PL) of amphiphilic polymer encapsulated PbS quantum dots (QDs) was observed in water for the first time and possible mechanisms were proposed based on investigations by means of transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and fluorescence spectroscopy. Water-soluble PbS QDs were synthesized by transferring monodispersed QDs capped with hydrophobic ligands of oleylamine from an organic solvent into water via amphiphilic polymers poly(maleic anhydride-alt-1-octadecene-co-poly(ethylene glycol)). The water transfer process leads to a double size distribution (5.6 ± 0.9 nm and 2.7 ± 0.4 nm), attributed to ligand etching together with Ostwald ripening, as well as the fast decay of PL. The automatic recovery of the PL in PbS QDs stored in water in the dark for 3 months was only observed for the subset of smaller QDs and is largely due to the removal of surface defects with aging, as evidenced by the decreased percentage of unpassivated surface atoms from XPS studies. In contrast, the PL of the subset of larger QDs in the same sample does not self-recover in water and can only be slightly recovered by transferring them into environments with less external quenches. The results strongly suggest that it is the surface defect in the larger QDs themselves, introduced during Ostwald ripening, that is primarily responsible for their non-emitting status or rather low PL intensity under different conditions. The increase of unpassivated Pb atoms in larger PbS QDs after the 3 month aging has been confirmed by XPS, which explains their non-recovery behavior in water. The PL-recovered QD sample in water is very stable and shows comparable photostability to the initial QDs dispersed in an organic phase.     

One-pot synthesis, encapsulation, and solubilization of size-tuned quantum dots with amphiphilic multidentate ligands

We report one-pot synthesis, encapsulation, and solubilization of high-quality quantum dots (QDs) based on the use of amphiphilic and multidentate polymer ligands. In this "all-in-one" procedure, the resulting QDs are first capped by the multidentate ligand and are then spontaneously encapsulated and solubilized by a second layer of the same multidentate polymer upon exposure to water. In addition to providing better control of nanocrystal nucleation and growth kinetics (including resistance to Ostwald ripening), this procedure allows for in situ growth of an inorganic passivating shell on the nanocrystal core, enabling one-pot synthesis of both type-I and type-II core-shell QDs with tunable light emission from visible to near-infrared wavelengths.     

Minimizing the hydrodynamic size of quantum dots with multifunctional multidentate polymer ligands

We report a new strategy to minimize the hydrodynamic size of quantum dots (QDs) and to overcome their colloidal stability and photobleaching problems based on the use of multifunctional and multidentate polymer ligands. A novel finding is that a balanced composition of thiol (-SH) and amine (-NH 2) coordinating groups grafted to a linear polymer chain leads to highly compact nanocrystals with exceptional colloidal stability, a strong resistance to photobleaching, and high fluorescence quantum yields. In contrast to the standing brushlike conformation of PEGylated dihydrolipoic acid molecules, mutlidentate polymer ligands can wrap around the QDs in a closed "loops-and-trains" conformation. This structure is highly stable thermodynamically and is responsible for the excellent colloidal and optical properties. We have optimized this process for the preparation of ultrastable CdTe nanocrystals and have found the strategy to be broadly applicable to a wide range of nanocrystalline materials and heterostructures. This work has led to a new generation of bright and stable QDs with small hydrodynamic diameters between 5.6 and 9.7 nm with tunable fluorescence emission from the visible (515 nm) to the near-infrared (720 nm). These QDs are well suited for molecular and cellular imaging applications in which the nanoparticle hydrodynamic size must be minimized.     

Preparation and characterization of monodisperse CdS quantum dot‐polymer microspheres

A novel and effective method for the preparation of monodisperse CdS quantum dot‐polymer microspheres was proposed. The monodisperse hollow polymer microspheres were firstly swelled in chloroform. Then, the reaction precursor composed of CdO and sulfur, was impregnated into the hollow polymer microspheres. Subsequently, the CdS quantum dots were synthesized directly within the polymer microspheres by thermal decomposition. The morphology, structure, and fluorescence properties of CdS quantum dot‐polymer microspheres were studied by scanning electron microscope, transmission electron microscope, fluorescence microscope, and flow cytometry. The results indicate that the fluorescent CdS quantum dots are successfully synthesized in the monodisperse hollow polymer microspeheres, which provide very strong fluorescence intensity, and offer excellent photostability due to the compact structure of the polymer matrix. These CdS quantum dot‐polymer microspheres have potential applications in biotechnology and biomedicine. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 751–755, 2010     

Thermo-sensitive imprinted polymer coating CdTe quantum dots for target protein specific recognition

A thermo-sensitive imprinted polymer coating CdTe quantum dots was developed to prepare fluorescent thermo-sensitive protein-affinity materials, which exhibited high specific recognition ability towards target proteins.     

pH-sensitive quantum dots

We have designed organic ligands able to adsorb on the surface of CdSe-ZnS core-shell quantum dots and switch the luminescence of the inorganic nanoparticles in response to hydroxide anions. These compounds incorporate a [1,3]oxazine ring within their molecular skeleton, which reacts with the nucleophilic hydroxide anion to generate a 4-nitrophenylazophenolate chromophore. The chromogenic transformation activates an energy transfer pathway from the quantum dot to the adsorbed chromophores. As a result, the luminescence intensity of the coated nanoparticles decreases significantly in the presence of hydroxide anions. In fact, this mechanism can be exploited to probe the pH of aqueous solutions. Indeed, an increase in pH from 7.1 to 8.5 translates into a 35% decrease in the luminescence intensity of the sensitive quantum dots. Thus, our operating principles for luminescence switching can efficiently transduce a chemical stimulation into a change in the emissive response of semiconductor nanoparticles. In principle, this protocol can be extended from hydroxide anions to other target analytes with appropriate adjustments in the molecular design of the chromogenic ligands. It follows that luminescent chemosensors, based on the unique photophysical properties of semiconductor quantum dots, can eventually evolve from our design logic and choice of materials.     

Caged quantum dots

Photoactivatable organic fluorophores and fluorescent proteins have been widely adopted for cellular imaging and have been critical for increasing temporal and spatial resolution, as well as for the development of superresolution microscopy techniques. At the same time, semiconducting nanocrystal quantum dots (QDs) have shown superior brightness and photostability compared to both organic fluorophores and proteins. As part of our efforts to develop nanoparticles with novel optical properties, we have synthesized caged quantum dots, which are nonluminescent under typical microscopic illumination but can be activated with stronger pulses of UV light. We show that ortho-nitrobenzyl groups efficiently quench QDs of different compositions and emissions and can be released from the nanoparticle surface with UV light, both in solution and in live cells. This caging is dependent on the emission of the QD, but it is effective through the visible spectrum into the nIR, offering a large array of new colors for photoactivatable probes. Like organic and protein-based photoactivatable probes, caged QDs can confer increased spatial and temporal resolution, with the added brightness and photostability of QDs.     

Pulsed field gradient NMR studies of polymer adsorption on colloidal CdSe quantum dots

Pulsed field gradient nuclear magnetic resonance (PFG NMR) experiments have been used to examine ligand exchange between poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMA) (Mn = 12,000, Mw/Mn = 1.20, Nn = 78) and trioctylphosphine oxide (TOPO) bound to the surface of CdSe/TOPO quantum dots (QDs). We show that PFG 1H NMR can quantify the displacement of TOPO by PDMA through its ability to differentiate signals due to TOPO bound to the QDs versus those from TOPO molecules free in solution. For CdSe QDs with a band edge absorption maximum at 558 nm (diameter 2.7 nm by transmission electron microscopy), we determined that, at saturation, 8 polymer chains on average displace greater than 90% of the surface TOPO groups. At partial saturation, with an average of 6 polymer chains/QD, each TOPO displaced requires 28 DMA repeat units. Assuming that one Me2N- group binds to a surface Cd2+ for each TOPO displaced, we infer that only about 3% of the DMA units are directly bound to the surface. The remaining groups are present as loops or tails that protrude into the solvent and increase the hydrodynamic diameter of the particles.