Microwave-assisted one-pot synthesis of hybrid nanosystems based on CdS quantum dots functionalized with organic chromophores: effect of the chromophore nature on the nanosystem composition

Quantum dot/organic dye nanosystems were synthesised via a one-pot technique. Different dependences of the nanosystem composition on the synthetic conditions for different dyes were observed.

Thioglycolic Acid-Capped CdS Quantum Dots Conjugated to α-Amylase as a Fluorescence Probe for Determination of Starch at Low Concentration

In the present research, water soluble thioglycolic acid-capped CdS quantum dots (QDs) were synthesized by chemical precipitation method. The characteristics of prepared quantum dots were determined using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The obtained results revealed that CdS QDs have 5.60 nm crystallite size, hexagonal wurtzite structure and spherical morphology with less than 10 nm diameter. The photoluminescence (PL) spectroscopy was performed in order to study the effect of the presence of starch solutions. Blue emission peaks were positioned at 488 nm and its intensity quenched by increasing the concentration of starch solutions. The result of PL quenches in range of studied concentrations (0-100 ppm) was best described by Michaelis-Menten model. The amount of Michaelis constant (Km) for immobilized α-amylase in this system was about 68.08 ppm which showed a great tendency of enzyme to hydrolyze the starch as substrate. Finally, the limit of detection (LOD) was found to be about 2.24 ppm.

Nanoparticles and DNA - a powerful and growing functional combination in bionanotechnology

Functionally integrating DNA and other nucleic acids with nanoparticles in all their different physicochemical forms has produced a rich variety of composite nanomaterials which, in many cases, display unique or augmented properties due to the synergistic activity of both components. These capabilities, in turn, are attracting greater attention from various research communities in search of new nanoscale tools for diverse applications that include (bio)sensing, labeling, targeted imaging, cellular delivery, diagnostics, therapeutics, theranostics, bioelectronics, and biocomputing to name just a few amongst many others. Here, we review this vibrant and growing research area from the perspective of the materials themselves and their unique capabilities. Inorganic nanocrystals such as quantum dots or those made from gold or other (noble) metals along with metal oxides and carbon allotropes are desired as participants in these hybrid materials since they can provide distinctive optical, physical, magnetic, and electrochemical properties. Beyond this, synthetic polymer-based and proteinaceous or viral nanoparticulate materials are also useful in the same role since they can provide a predefined and biocompatible cargo-carrying and targeting capability. The DNA component typically provides sequence-based addressability for probes along with, more recently, unique architectural properties that directly originate from the burgeoning structural DNA field. Additionally, DNA aptamers can also provide specific recognition capabilities against many diverse non-nucleic acid targets across a range of size scales from ions to full protein and cells. In addition to appending DNA to inorganic or polymeric nanoparticles, purely DNA-based nanoparticles have recently surfaced as an excellent assembly platform and have started finding application in areas like sensing, imaging and immunotherapy. We focus on selected and representative nanoparticle-DNA materials and highlight their myriad applications using examples from the literature. Overall, it is clear that this unique functional combination of nanomaterials has far more to offer than what we have seen to date and as new capabilities for each of these materials are developed, so, too, will new applications emerge.

Multimodal Mn-doped I-III-VI quantum dots for near infrared fluorescence and magnetic resonance imaging: from synthesis to in vivo application

The development of sensitive multimodal contrast agents is a key issue to provide better global, multi-scale images for diagnostic or therapeutic purposes. Here we present the synthesis of Zn-Cu-In-(S, Se)/Zn(1-x)Mn(x)S core-shell quantum dots (QDs) that can be used as markers for both near-infrared fluorescence imaging and magnetic resonance imaging (MRI). We first present the synthesis of Zn-Cu-In-(S, Se) cores coated with a thick ZnS shell doped with various proportions of Mn. Their emission wavelengths can be tuned over the NIR optical window suitable for deep tissue imaging. The incorporation of manganese ions (up to a few thousand ions per QD) confers them a paramagnetic character, as demonstrated by structural analysis and electron paramagnetic resonance spectroscopy. These QDs maintain their optical properties after transfer to water using ligand exchange. They exhibit T1-relaxivities up to 1400 mM(-1) [QD] s(-1) at 7 T and 300 K. We finally show that these QDs are suitable multimodal in vivo probes and demonstrate MRI and NIR fluorescence detection of regional lymph nodes in mice.

Single CdSe/ZnS nanocrystals in an ion trap: charge and mass determination and photophysics evolution with changing mass, charge, and temperature

We report measurements of fluorescence intermittency (blinking) and spectral behavior for single semiconductor nanocrystal quantum dots (QDs) isolated in the gas phase and discuss the effects on fluorescence of the QD charge state and heating to the point of sublimation. Core-shell CdSe/ZnS QDs were trapped in a quadrupole ion trap and detected by laser-induced fluorescence. The mass (M) and charge (Q) were determined nondestructively, and both were followed continuously over the course of hours or days. Emission spectra of the trapped QDs are significantly red-shifted relative to the solution-phase emission from the same particles. The temperature of the trapped QDs is determined by the balance between laser heating and collisional cooling and thermal emission, and it is possible to heat the particles to remove ligands or to the point of sublimation. QDs are observed to be emissive during sublimation, for up to 85% mass loss, with emission intensity roughly proportional to the surface area. Eventually, the fluorescence quantum yield drops suddenly, and the QDs begin to blink. The method used is versatile and will allow studies of quantum dot optical properties as a function of size, ligand removal, heating, surface oxidation, and other manipulations, where these properties are continuously correlated with the mass and charge.

Revisiting the principles of preparing aqueous quantum dots for biological applications: the effects of surface ligands on the physicochemical properties of quantum dots

Aqueous CdSe/CdS/ZnS quantum dots with different surface ligands were prepared through ligand exchange and extensively characterized for biological applications.

Processing and characterization of stable, pH-sensitive layer-by-layer modified colloidal quantum dots

Quantum Dots (QDs) stabilized with dihydrolipoic acid (DHLA) were used as a template for layer-by-layer (LbL) modification to study the effect on the QD optical properties. We studied several different polyelectrolytes to determine that large quantities of monodisperse DHLA-QDs could only be obtained with the weak polyelectrolyte pair of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). The key to this success was the development of a two-step method to split the LbL process into adsorption and centrifugation phases, which require different pH solutions for optimum success. Solution pH is highlighted as an important factor to achieve sufficient QD surface coverage and QD recovery during wash cycles. We optimized the process to scale up synthesis by introducing a solvent precipitation step before ultracentrifugation that, when coupled with the correct pH conditions, results in a mean QD recovery of 86-90% after three wash cycles. We found that adsorption of PAH had a negligible effect on the quantum yield and lifetime but an additional layer of PAA resulted in a substantial decrease in both quantum yield and lifetime that could not be recovered by the addition of more layers. The PAH coating provides a protective coating that extends DHLA-QDs stability, prevents photo-oxidation mediated aggregation, alleviates concerns over batch variability, and results in pH-dependent emission.

Highly enhanced affinity of multidentate versus bidentate zwitterionic ligands for long-term quantum dot bioimaging

High colloidal stability in aqueous conditions is a prerequisite for fluorescent nanocrystals, otherwise known as "quantum dots", intended to be used in any long-term bioimaging experiment. This essential property implies a strong affinity between the nanoparticles themselves and the ligands they are coated with. To further improve the properties of the bidentate monozwitterionic ligand previously developed in our team, we synthesized a multidentate polyzwitterionic ligand, issued from the copolymerization of a bidentate monomer and a monozwitterionic one. The nanocrystals passivated by this polymeric ligand showed an exceptional colloidal stability, regardless of the medium conditions (pH, salinity, dilution, and biological environment), and we demonstrated the affinity of the polymer exceeded by 3 orders of magnitude that of the bidentate ligand (desorption rates assessed by a competition experiment). The synthesis of the multidentate polyzwitterionic ligand proved also to be easily tunable and allowed facile functionalization of the corresponding quantum dots, which led to successful specific biomolecules targeting.