Application of Polymer Quantum Dot-Enzyme Hybrids in the Biosensor Development and Test Paper Fabrication

Both glutathione capped CdTe quantum dots (QDs) and enzymes were encapsulated with poly­(diallyldimethylammonium chloride) (PDDA) via electrostatic attraction to form hybrid films. The obtained PDDA QD-enzyme hybrids feature both high fluorescence and biorecognition. In the obtained hybrid materials, the fluorescence emission of the QDs was stable for at least 3 months, and the structure and activity of the enzyme was also well maintained as the Michaelis constant of tyrosinase was determined to be 0.90 mmol/L, which is just 2 times higher than that of free enzyme. This hybrid material was then utilized as a platform for the development of biosensors based on the quenching effects of the enzymatic products on the emission of the QDs with a kind of phenol (catechol) and glucose as example analytes. The detection limits of catechol and glucose were 1.0 × 10^–5 and 5.0 × 10^–6 mol/L, respectively. Moreover, this hybrid material was applied to the fabrication of test paper for these two analytes. The test paper was very stable with respect to the fluorescence of the QDs and the activity of the enzyme maintained for at least 1 month

Quantum-Dot-Based (Aero)gels: Control of the Optical Properties

In this work, we have developed novel hybrid quantum dot gels based on the controllable and reversible assembly of nanoparticles via metal–tetrazole complexation. Combining in one hybrid network nanocrystals of different semiconductors (ZnSe and CdTe) as well as quantum dots of different sizes (green and red emitting CdTe) with different band gaps, we have examined energy relations within these systems and act out a facile route to the color design of the resulting gels. Efficient energy pumping from donor quantum dots to acceptors leads to a remarkable enhancement of the emission intensity of the gel. Furthermore, by integrating three different quantum dot types into one network, we obtained a white-light-emitting aerogel

Penetration of Amphiphilic Quantum Dots through Model and Cellular Plasma Membranes

In this work we demonstrate progress in the colloidal synthesis of amphiphilic CdTe nanocrystals stabilized by thiolated PEG oligomers with the aim of facilitating cellular uptake of the particles. High-boiling, good coordinating solvents such as dimethylacetamide and dimethylformamide accelerate the growth of the nanoparticles yielding stable colloids of which photoluminescence maxima can be tuned to cover the region of 540–640 nm with quantum yields of up to 30%. The CdTe nanocrystals capped by thiolated methoxypolyethylene glycol are shown to penetrate through the lipid bilayer of giant unilamellar vesicles and giant plasma membrane vesicles which constitute basic endocytosis-free model membrane systems. Moreover, the penetration of amphiphilic particles through live cell plasma membranes and their ability to escape the endocytic pathway have been demonstrated

Aqueous-Based Cadmium Telluride Quantum Dot/Polyurethane/Polyhedral Oligomeric Silsesquioxane Composites for Color Enhancement in Display Backlights

Colloidal quantum dots (QDs) are gaining prominence in the lighting and display industry, due to their tunable and saturated emission colors. Their primary application is currently in optical enhancement films for large sized liquid crystal displays, improving the performance in terms of color reproduction and optical efficiency. While most current QD materials in this regard are synthesized and processed in organic media, this work introduces aqueous-based CdTe QDs as a viable alternative for display applications. After discussing relevant aspects of the aqueous synthesis, we demonstrate the fabrication of all-water processed free-standing CdTe QD/polyurethane films, with high flexibility and transparency. Additional introduction of polyhedral oligomeric silsesquioxane results in a better dispersion of the QDs in the polymer matrix and improves the optical properties and especially photo/thermal stabilities of the composites, which is crucial regarding their application in display backlights

Solid-State Anion Exchange Reactions for Color Tuning of CsPbX₃ Perovskite Nanocrystals

Herein, we report on a room-temperature anion exchange reaction of highly emitting, all-inorganic CsPbBr₃ nanocrystals (NCs) taking place entirely in the solid state. A fast exchange from Br to I and Br to mixed Br/Cl without exertion of additional energy is observed within minutes to hours, taking place by immobilization of the perovskite NCs on pure potassium halide salts (KCl, KBr, and KI). Via adjustment of the halide ratios of the embedding salt matrix, the bright fluorescence of the CsPbX₃ (X = Cl, Br, or I) NCs can be tuned over a wide spectral range (400–700 nm) while maintaining the initial photoluminescence quantum yields of ∼80% and narrow full widths at half-maximum. We found that combinations of different initial CsPbX₃ NCs and KX matrices result in different final halogen contents of the NCs. This is explained with a host-lattice limiting exchange mechanism. The anion exchange rate can be accelerated by pressing the soft, NC-loaded salts under pressure of 2.2 GPa. Because of the “cold flow” behavior of the potassium salts during the pressing, a complete embedding of the NCs into transparent salt pellets is achieved. This strategy allows for an easy adjustment of the NC loading as well as the form and thickness of the resulting composite. An encapsulation of the NC−salt pellets with silicone yields robustness and stability of the embedded NCs under ambient conditions. The ease of handling and the superior stability make the resulting perovskite composite materials attractive for various photonic and optoelectronic applications as demonstrated in a proof-of-concept color-converting layer for a light−emitting diode

Solid-State Anion Exchange Reactions for Color Tuning of CsPbX₃ Perovskite Nanocrystals

Herein, we report on a room-temperature anion exchange reaction of highly emitting, all-inorganic CsPbBr₃ nanocrystals (NCs) taking place entirely in the solid state. A fast exchange from Br to I and Br to mixed Br/Cl without exertion of additional energy is observed within minutes to hours, taking place by immobilization of the perovskite NCs on pure potassium halide salts (KCl, KBr, and KI). Via adjustment of the halide ratios of the embedding salt matrix, the bright fluorescence of the CsPbX₃ (X = Cl, Br, or I) NCs can be tuned over a wide spectral range (400–700 nm) while maintaining the initial photoluminescence quantum yields of ∼80% and narrow full widths at half-maximum. We found that combinations of different initial CsPbX₃ NCs and KX matrices result in different final halogen contents of the NCs. This is explained with a host-lattice limiting exchange mechanism. The anion exchange rate can be accelerated by pressing the soft, NC-loaded salts under pressure of 2.2 GPa. Because of the “cold flow” behavior of the potassium salts during the pressing, a complete embedding of the NCs into transparent salt pellets is achieved. This strategy allows for an easy adjustment of the NC loading as well as the form and thickness of the resulting composite. An encapsulation of the NC−salt pellets with silicone yields robustness and stability of the embedded NCs under ambient conditions. The ease of handling and the superior stability make the resulting perovskite composite materials attractive for various photonic and optoelectronic applications as demonstrated in a proof-of-concept color-converting layer for a light−emitting diode

Sodium Chloride Protected CdHgTe Quantum Dot Based Solid-State Near-Infrared Luminophore for Light-Emitting Devices and Luminescence Thermometry

Solid-state luminophores operating in the near-infrared (NIR) region may have applications in sensing, communication, and medicine. We report environmentally protected solid-state NIR-emitting luminophores fabricated by embedding CdHgTe colloidal quantum dots (QDs) into a NaCl matrix, with remarkable photo- and thermal stability and a photoluminescence quantum yield of 31% in the solid state, which is among the highest reported for solid-state NIR luminophores so far. We employed this luminophore as a down-conversion layer in a NIR-light-emitting device with a stable emission at 940 nm. Carrier recombination dynamics of the CdHgTe QDs@NaCl powders are examined as a function of temperature using steady-state and transient photoluminescence spectroscopy, and characteristic parameters such as the band gap, the temperature coefficient, the Debye temperature, the activation energy of thermal quenching, and radiative and nonradiative recombination rates are derived. Temperature-dependent changes of the spectral position and the photoluminescence lifetime of CdHgTe QDs@NaCl are shown to serve as a base for two temperature detection schemes, namely, luminescence spectral and luminescence lifetime thermometry, a versatile optical technique for the noninvasive, noncontact estimation of local temperature

Photoluminescence Quantum Yield and Matrix-Induced Luminescence Enhancement of Colloidal Quantum Dots Embedded in Ionic Crystals

The incorporation of colloidal quantum dots (QDs) into solid matrices, especially ionic salts, holds several advantages for industrial applications. Here, we demonstrated via absolute measurements of photoluminescence quantum yields (PL-QY) that the photoluminescence of aqueous CdTe QDs can be considerably increased upon incorporation into a salt matrix with a simple crystallization procedure. Enhancement factors of up to 2.8 and a PL-QY of 50 to 80%, both in NaCl crystals and incorporated in silicone matrices, were reached. The fact that the achievable PL enhancement factors depend strongly on PL-QY of the parent QDs can be described by the change of the dielectric surrounding and the passivation of the QD surface, modifying radiative and nonradiative rate constants. Time-resolved PL measurements revealed noncorrelating PL lifetimes and PL-QY, suggesting that weakly emissive QDs of the ensemble are more affected by the enhancement mechanism, thereby influencing PL-QY and PL lifetime in a different manner

Colloidal Nanocrystals Embedded in Macrocrystals: Robustness, Photostability, and Color Purity

The incorporation of colloidal quantum dots (QDs) into ionic crystals of various salts (NaCl, KCl, KBr, etc.) is demonstrated. The resulting mixed crystals of various shapes and beautiful colors preserve the strong luminescence of the incorporated QDs. Moreover, the ionic salts appear to be very tight matrices, ensuring the protection of the QDs from the environment and as a result providing them with extraordinary high photo- and chemical stability. A prototype of a white light-emitting diode (WLED) with a color conversion layer consisting of this kind of mixed crystals is demonstrated. These materials may also find applications in nonlinear optics and as luminescence standards

Macrocrystals of Colloidal Quantum Dots in Anthracene: Exciton Transfer and Polarized Emission

In this work, centimeter-scale macrocrystals of nonpolar colloidal quantum dots (QDs) incorporated into anthracene were grown for the first time. The exciton transfer from the anthracene host to acceptor QDs was systematically investigated, and anisotropic emission from the isotropic QDs in the anthracene macrocrystals was discovered. Results showed a decreasing photoluminescence lifetime of the donor anthracene, indicating a strengthening energy transfer with increasing QD concentration in the macrocrystals. With the anisotropy study, QDs inside the anthracene host acquired a polarization ratio of ∼1.5 at 0° collection angle, and this increases to ∼2.5 at the collection angle of 60°. A proof-of-concept application of these excitonic macrocrystals as tunable color converters on light-emitting diodes was also demonstrated