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Three-dimensional (3D) spheroid cell cultures of fibroblast (L929) and tumor mammary mouse (4T1) were chosen as in vitro tissue models for tissue imaging of ternary AgInS/ZnS fraction quantum dots (QDs). We showed that the tissue-mimetic morphology of cell spheroids through well-developed cell-cell and cell-matrix interactions and distinct diffusion/transport characteristics makes it possible to predict the effect of ternary AgInS/ZnS fraction QDs on the vital activity of cells while simultaneously comparing with classical two-dimensional (2D) cell cultures. The AgInS/ZnS fractions, emitting in a wide spectral range from 635 to 535 nm with a mean size from ∼3.1 ± 0.8 to ∼1.8 ± 0.4 nm and a long photoluminescence lifetime, were separated from the initial QD ensemble by using antisolvent-induced precipitation. For ternary AgInS/ZnS fraction QDs, the absence of toxicity at different QD concentrations was demonstrated on 2D and 3D cell structures. QDs show a robust correlation between numerous factors: their sizes in biological fluids over time, penetration capabilities into 2D and 3D cell structures, and selectivity with respect to penetration into cancerous and healthy cell spheroids. A reproducible protocol for the preparation of QDs along with their unique biological properties allows us to consider ternary AgInS/ZnS fraction QDs as attractive fluorescent contrast agents for tissue imaging.

Luminescent carbon nanostructures (CNSs) have attracted great interest from the scientific community due to their photoluminescent properties, structural features, low toxicity, and a great variety of possible applications. Unfortunately, a few problems hinder their further development. These include the difficulties of separating a mixture of nanostructures after synthesis and the dependence of their properties on the environment and the aggregate state. The application of a silica matrix to obtain luminescent composite particles minimizes these problems and improves optical properties, reduces photoluminescence quenching, and leads to wider applications. We describe two methods for the formation of silica composites containing CNSs: inclusion of CNSs into silica particles and their grafting onto the silica surface. Moreover, we present approaches to the synthesis of multifunctional particles. They combine the unique properties of silica and fluorescent CNSs, as well as magnetic, photosensitizing, and luminescent properties via the combination of functional nanoparticles such as iron oxide nanoparticles, titanium dioxide nanoparticles, quantum dots (QDs), and gold nanoclusters (AuNCs). Lastly, we discuss the advantages and challenges of these structures and their applications. The novelty of this review involves the detailed description of the approaches for the silica application as a matrix for the CNSs. This will support researchers in solving fundamental and applied problems of this type of carbon-based nanoobjects.

A new bioanalytical labeling system based on alloyed quantum dots' (QDs) photoluminescence quenching caused by an enzymatic reaction has been developed and tested for the first time. The catalytic role of the enzyme provides high sensitivity and the possibility of varying detecting time to improve assay sensitivity. Alloyed luminescent QDs were chosen in view of their small size (5-7 nm) and the high sensitivity of their optical properties to physicochemical interactions. Here, we described the synthesis of alloyed luminescent QDs and demonstrated the possibility of using them as a luminescent turn-off substrate for enzymatic assay. Synthesized alloyed QDs were found to be a sensitive turn-off substrate for glucose oxidase in homogeneous and heterogeneous assay models. CdZnSeS and CdZnSeS/ZnS QDs covered with dihydrolipoic acid and 2-mercaptoethanol were tested. A glucose oxidase limit of detection of 6.6 nM for the heterogenous high-throughput model assay was reached., (© 2022. Springer-Verlag GmbH Germany, part of Springer Nature.)

Doxorubicin (DOX) is widely used in chemotherapy as an anti-tumor drug. However, DOX is highly cardio-, neuro- and cytotoxic. For this reason, the continuous monitoring of DOX concentrations in biofluids and tissues is important. Most methods for the determination of DOX concentrations are complex and costly, and are designed to determine pure DOX. The purpose of this work is to demonstrate the capabilities of analytical nanosensors based on the quenching of the fluorescence of alloyed CdZnSeS/ZnS quantum dots (QDs) for operative DOX detection. To maximize the nanosensor quenching efficiency, the spectral features of QDs and DOX were carefully studied, and the complex nature of QD fluorescence quenching in the presence of DOX was shown. Using optimized conditions, turn-off fluorescence nanosensors for direct DOX determination in undiluted human plasma were developed. A DOX concentration of 0.5 µM in plasma was reflected in a decrease in the fluorescence intensity of QDs, stabilized with thioglycolic and 3-mercaptopropionic acids, for 5.8 and 4.4 %, respectively. The calculated Limit of Detection values were 0.08 and 0.03 μg/mL using QDs, stabilized with thioglycolic and 3-mercaptopropionic acids, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photoluminescence enhancement of CdZnSeS/ZnS quantum dots (QDs) using thiol ligands. • Single-phase approach of ligand exchange without deprotonation agent. • Photoinduced one-pot ligand exchange in organic phase using dihydrolipoic acid (DHLA) as bidentate thiol. Most of the existing hydrophilization techniques for the semiconductor quantum dots (QDs) lead to degradation of photoluminescence (PL). Therefore, for the applying of QDs in the areas requiring their stability in water media (e.g. bio- and chemical analysis, labeling and sensing), it is often necessary to find a balance between high stability, good optical properties, and difficulty of acquiring. This article describes simple, fast, and easy scalable methods for alloyed CdZnSeS/ZnS QDs ligand exchange using 2-mercaptoethanol, thioglycolic, 3-mercaptorpopionic and dihydrolipoic acids. The proposed ligand exchange techniques provide the enhancement of the QDs photoluminescence intensity in contrast to most of other ligand exchange procedures on the QDs surface. In optimized conditions the twofold photoluminescence quantum yield increase compared to the initial hydrophobic CdZnSeS/ZnS QDs was achieved. Hydrophilized nanoparticles maintained colloidal stability for a period more than 13 months. The suggested mechanism of the PL increase is the passivation of the QDs surface with molecules containing a thiol group. The combination of the proposed effective CdZnSeS/ZnS QDs synthesis and modification methods shows the prospect of their implementation as basic luminescent material for a wide range of applications. [ABSTRACT FROM AUTHOR]

The new bioanalysis systems development is an important step to the quality of people life improving. A significant number of novel bioanalytical methods bases on quantum dots photoluminescent signal detection and determination. A separate class of that kind of analytical system is enzyme-based luminescent assays, in which the value of quantum dots photoluminescence change by the product of the enzymatic reaction is used for the analyte concentration determination. The advantageous attributes of the photoluminescence quenching based systems are the simple equipment requirements, inexpensiveness, availability to use by the non-professionals and using an only dilution of the samples before analysis without any other pretreatment. Described bioanalytical systems are applicable in health care, food analysis and agriculture for a large number of objects. The key aim of the review is to compile the shortcomings and disadvantages of the published detection systems preventing their commercial application and searching the possible solutions. • The comprehensive overview of the existed luminescent enzymatic QD-based immunoassays. • Types and modifications of QDs applicable in the luminescent enzymatic immunoassays. • Mechanisms of enzymatic quenching of QDs luminescence. • Further perspectives of the luminescence quenching based indicator systems. [ABSTRACT FROM AUTHOR]

Abstract This review targets valuable insight into the application of water dispersed luminescent quantum dots (QDs) for detection of microRNA (miRNA). Recently, considerable efforts have been devoted to obtain QDs for biosensing and bioimaging. Quantum dots with bright stable photoluminescence, synthesized directly in the water phase, offered an unparalleled advantage for the assay development involving small size, high colloidal stability, and presence of groups for bioconjugation. In this review we have delineated the fundamental principles guiding the rational design, synthesis, and application of photoluminescent water-dispersed QDs. Diverse analysis methods for miRNA detection based on the photoluminescence, electrochemiluminescence, Förster resonance energy transfer and electrochemiluminescence energy transfer with different enhancement strategies are discussed. Highlights • Water-dispersed QDs' application for micro-RNA detection is reviewed. • Special focus is made on the application of DNA-templated QDs. • QDs' synthesis routes are overviewed. • The principles of the generation of analytical signals are examined. [ABSTRACT FROM AUTHOR]

The luminescence of colloidal quantum dots (QDs) is often affected by the passivating layer, the stabilizing ligand, and the interactions in solution. The anthracycline antibiotic mitoxantrone (MTX) effectively quenches QDs luminescence while attaching to their surface in the aqua colloid. Careful selection of the architecture of QDs with significant luminescence quenching in the presence of MTX will make future for developing a simple and fast luminescence turn-off method to determine the concentration of MTX. To find the most sensitive QDs architecture to the presence of MTX, two types of nanoparticles were examined as detector systems: (i) a series of size-selected fractions of non-cadmium AgInS/ZnS QDs and (ii) alloyed CdZnSeS and CdZnSeS/ZnS QDs. All tested QDs in aqueous colloids were coated with thioglycolic acid as a surface stabilizing ligand. An examination of luminescence intensity and lifetime decreasing in the presence of MTX allowed us to evaluate the effect of the structure and composition of QDs on the efficiency of luminescence quenching by MTX. A detailed study demonstrates a predominantly static quenching mechanism, via the formation of complexes with high binding constants (∼106-107 M−1). The wide variability in the composition and size of QDs made it possible to achieve a low MTX detection limits (3 and 5 nM for the third fraction of AgInS/ZnS and CdZnSeS/ZnS QDs, respectively). Thus, the use of luminescent QDs as a direct detection system is promising for monitoring MTX concentrations [Display omitted] [ABSTRACT FROM AUTHOR]

The application of external electric field for verification of quantum dots (QDs) stability in aqueous medium was proposed. Hydrophilic CdSe core-shell nanocrystals were synthesized and used with three polymer-based organic stabilizers, two of which contain PEG chains. An increasing of the stability under applied electric field (EF) was shown for stabilizer containing higher amount of PEG chains and terminal amino-groups: introduction of additional PEG chains allowed reducing degradation of luminescence intensity for about 60%. The changes of QDs solutions after EF treatment were examined by dynamic light scattering measurements, luminescence and absorbance spectroscopy, and conductivity measurements and explained by decreasing of quantum yield of the samples due to degradation of stabilizer coating. [ABSTRACT FROM AUTHOR]