Dextran-Functionalized Semiconductor Quantum Dot Bioconjugates for Bioanalysis and Imaging

Natural Food Components as Biocompatible Carriers: A Novel Approach to Glioblastoma Drug Delivery

Efficient drug delivery methods are crucial in modern pharmacotherapy to enhance treatment efficacy, minimize adverse effects, and improve patient compliance. Particularly in the context of glioblastoma treatment, there has been a recent surge in interest in using natural dietary components as innovative carriers for drug delivery. These food-derived carriers, known for their safety, biocompatibility, and multifunctional properties, offer significant potential in overcoming the limitations of conventional drug delivery systems. This article thoroughly overviews numerous natural dietary components, such as polysaccharides, proteins, and lipids, used as drug carriers. Their mechanisms of action, applications in different drug delivery systems, and specific benefits in targeting glioblastoma are examined. Additionally, the safety, biocompatibility, and regulatory considerations of employing food components in drug formulations are discussed, highlighting their viability and future prospects in the pharmaceutical field.

Bait and Cleave: Exosite-Binding Peptides on Quantum Dots Selectively Accelerate Protease Activity for Sensing with Enhanced Sensitivity

The advantageous optical properties of quantum dots (QDs) motivate their use in a wide variety of applications related to imaging and bioanalysis, including the detection of proteases and their activity. Recent studies have shown that surface chemistry on QDs is able to modulate protease activity, but only nonspecifically. Here, we present a strategy to selectively accelerate the activity of a particular target protease by as much as two orders of magnitude. Exosite-binding "bait" peptides were derived from proteins that span a range of biological roles─substrate, receptor, and inhibitor─and were used to increase the affinity of the QD-peptide conjugates for either thrombin or factor Xa, resulting in increased rates of proteolysis for coconjugated substrates. Unlike effects from QD surface chemistry, the acceleration was specific to the target protease with negligible acceleration of other proteases. Benefits of this "bait and cleave" sensing approach included detection limits that improved by more than an order of magnitude, reenabled detection of target protease against an overwhelming background of nontarget proteolysis, and mitigation of the action of inhibitors. The cumulative results point to a generalizable strategy, where the mechanism of acceleration, considerations for the design of bait peptides and conjugates, and routes to expanding the scope of this approach are discussed. Overall, this research represents a major step forward in the rational design of nanoparticle-based enzyme sensors that enhance sensitivity and selectivity.

Assessing the Steric Impact of Surface Ligands on the Proteolytic Turnover of Quantum Dot-Peptide Conjugates

Proteases are important biomarkers and targets for the diagnosis and treatment of disease. The advantageous properties of semiconductor quantum dots (QDs) have made these nanoparticles useful as probes for protease activity; however, the effects of QD surface chemistry on protease activity are not yet fully understood. Here, we present a systematic study of the impact of sterics on the proteolysis of QD-peptide conjugates. The study utilized eight proteases (chymotrypsin, trypsin, endoproteinase Lys C, papain, endoproteinase Arg C, thrombin, factor Xa, and plasmin) and 41 distinct surface chemistries. The latter included three molecular weights of each of three macromolecular ligands derived from dextran and polyethylene glycol, as well as anionic and zwitterionic small-molecule ligands, and an array of mixed coatings of macromolecular and small-molecule ligands. These surface chemistries spanned a diversity of thicknesses, densities, and packing organization, as characterized by gel electrophoresis, capillary electrophoresis, dynamic light scattering, and infrared spectroscopy. The macromolecular ligands decreased the adsorption of proteases on the QDs and decelerated proteolysis of the QD-peptide conjugates via steric hindrance. The properties of the QD surface chemistry, rather than the protease properties, were the main factor in determining the magnitude of deceleration. The broad scope of this study provides insights into the many ways in which QD surface chemistry affects protease activity, and will inform the development of optimized nanoparticle-peptide conjugates for sensing of protease activity and resistance to unwanted proteolysis.

Multifunctional polysaccharide nanoprobes for biological imaging

Imaging and tracking biological targets or processes play an important role in revealing molecular mechanisms and disease states. Bioimaging via optical, nuclear, or magnetic resonance techniques enables high resolution, high sensitivity, and high depth imaging from the whole animal down to single cells via advanced functional nanoprobes. To overcome the limitations of single-modality imaging, multimodality nanoprobes have been engineered with a variety of imaging modalities and functionalities. Polysaccharides are sugar-containing bioactive polymers with superior biocompatibility, biodegradability, and solubility. The combination of polysaccharides with single or multiple contrast agents facilitates the development of novel nanoprobes with enhanced functions for biological imaging. Nanoprobes constructed with clinically applicable polysaccharides and contrast agents hold great potential for clinical translations. This review briefly introduces the basics of different imaging modalities and polysaccharides, then summarizes the recent progress of polysaccharide-based nanoprobes for biological imaging in various diseases, emphasizing bioimaging with optical, nuclear, and magnetic resonance techniques. The current issues and future directions regarding the development and applications of polysaccharide nanoprobes are further discussed.

Tetrameric Antibody Complexes and Affinity Tag Peptides for the Selective Immobilization and Imaging of Single Quantum Dots

Colloidal semiconductor quantum dots (QDs) are of widespread interest as fluorescent labels for bioanalysis and imaging applications. Single-particle measurements have proven to be a very powerful tool for better understanding the fundamental properties and behaviors of QDs and their bioconjugates; however, a recurring challenge is the immobilization of QDs in a solution-like environment that minimizes interactions with a bulk surface. Immobilization strategies for QD-peptide conjugates are particularly underdeveloped within this context. Here, we present a novel strategy for the selective immobilization of single QD-peptide conjugates using a combination of tetrameric antibody complexes (TACs) and affinity tag peptides. A glass substrate is modified with an adsorbed layer of concanavalin A (ConA) that binds a subsequent layer of dextran that minimizes nonspecific binding. A TAC with anti-dextran and anti-affinity tag antibodies binds to the dextran-coated glass surface and to the affinity tag sequence of QD-peptide conjugates. The result is spontaneous and sequence-selective immobilization of single QDs without any chemical activation or cross-linking. Controlled immobilization of multiple colors of QDs is possible using multiple affinity tag sequences. Experiments confirmed that this approach positions the QD away from the bulk surface. The method supports real-time imaging of binding and dissociation, measurements of Förster resonance energy transfer (FRET), tracking of dye photobleaching, and detection of proteolytic activity. We anticipate that this immobilization strategy will be useful for studies of QD-associated photophysics, biomolecular interactions and processes, and digital assays.

Dextran-Functionalized Super-nanoparticle Assemblies of Quantum Dots for Enhanced Cellular Immunolabeling and Imaging

Colloidal semiconductor quantum dots (QDs) are a popular material for applications in bioanalysis and imaging. Although individual QDs are bright, some applications benefit from the use of even brighter materials. One approach to achieve higher brightness is to form super-nanoparticle (super-NP) assemblies of many QDs. Here, we present the preparation, characterization, and utility of dextran-functionalized super-NP assemblies of QDs. Amphiphilic dextran was synthesized and used to encapsulate many hydrophobic QDs via a simple emulsion-based method. The resulting super-NP assemblies or "super-QDs" had hydrodynamic diameters of ca. 90-160 nm, were characterized at the ensemble and single-particle levels, had orders-of-magnitude superior brightness compared to individual QDs, and were non-blinking. Additionally, binary mixtures of red, green, and blue (RGB) colors of QDs were used to prepare super-QDs, including colors difficult to obtain from individual QDs (e.g., magenta). Tetrameric antibody complexes (TACs) enabled simple antibody conjugation for selective cellular immunolabeling and imaging with both an epifluorescence microscope and a smartphone-based platform. The technical limitations of the latter platform were overcome by the increased per-particle brightness of the super-QDs, and the super-QDs outperformed individual QDs in both cases. Overall, the super-QDs are a very promising material for bioanalysis and imaging applications where brightness is paramount.

Organic quantum dots: An ultrasmall nanoplatform for cancer theranostics

Tumours are the second leading cause of death globally, generating alterations in biological interactions and, as a result, malfunctioning of crucial genetic traits. Technological advancements have made it possible to identify tumours at the cellular level, making transcriptional gene variations and other genetic variables more easily investigated. Standard chemotherapy is seen as a non-specific treatment that has the potential to destroy healthy cells while also causing systemic toxicity in individuals. As a result, developing new technologies has become a pressing necessity. QDs are semiconductor particles with diameters ranging from 2 to 10 nanometers. QDs have grabbed the interest of many researchers due to their unique characteristics, including compact size, large surface area, surface charges, and precise targeting. QD-based drug carriers are well known among the many nanocarriers. Using QDs as a delivery approach enhances solubility, lengthens retention time, and reduces the harmful effects of loaded medicines. Several varieties of quantum dots used in drug administration are discussed in this article, along with their chemical and physical characteristics and manufacturing methods. Furthermore, it discusses the role of QDs in biological, medicinal, and theranostic applications.

Polysaccharide peptide conjugates: Chemistry, properties and applications

The intention of this publication is to give an overview on research related to conjugates of polysaccharides and peptides. Dextran, chitosan, and alginate were selected, to cover four of the most often encountered functional groups known to be present in polysaccharides. These groups are the hydroxyl, the amine, the carboxyl, and the acetal functionality. A collection of the commonly used chemical reactions for conjugation is provided. Conjugation results into distinct properties compared to the parent polysaccharide, and a number of these characteristics are highlighted. This review aims at demonstrating the applicability of said conjugates with a strong emphasis on biomedical applications, drug delivery, biosensing, and tissue engineering. Some suggestions are made for more rigorous chemistries and analytics that could be investigated. Finally, an outlook is given into which direction the field could be developed further. We hope that this survey provides the reader with a comprehensive summary and contributes to the progress of works that aim at synthetically combining two of the main building blocks of life into supramolecular structures with unprecedented biological response.

Prototype Smartphone-Based Device for Flow Cytometry with Immunolabeling via Supra-nanoparticle Assemblies of Quantum Dots

Methods for the detection, enumeration, and typing of cells are important in many areas of research and healthcare. In this context, flow cytometers are a widely used research and clinical tool but are also an example of a large and expensive instrument that is limited to specialized laboratories. Smartphones have been shown to have excellent potential to serve as portable and lower-cost platforms for analyses that would normally be done in a laboratory. Here, we developed a prototype smartphone-based flow cytometer (FC). This compact 3D-printed device incorporated a laser diode and a microfluidic flow cell and used the built-in camera of a smartphone to track immunofluorescently labeled cells in suspension and measure their color. This capability was enabled by high-brightness supra-nanoparticle assemblies of colloidal semiconductor quantum dots (SiO₂@QDs) as well as a support vector machine (SVM) classification algorithm. The smartphone-based FC device detected and enumerated target cells against a background of other cells, simultaneously and selectively counted two different cell types in a mixture, and used multiple colors of SiO₂@QD-antibody conjugates to screen for and identify a particular cell type. The potential limits of multicolor detection are discussed alongside ideas for further development. Our results suggest that innovations in materials and engineering should enable eventual smartphone-based FC assays for clinical applications.

Quantum dots conjugated to lectins from Schinus terebinthifolia leaves (SteLL) and Punica granatum sarcotesta (PgTeL) as potential fluorescent nanotools for investigating Cryptococcus neoformans

This study reports the development of conjugates based on quantum dots (QD)s and lectins from Schinus terebinthifolia leaves (SteLL) and Punica granatum sarcotesta (PgTeL). Cryptococcus neoformans cells were chosen to evaluate the efficiency of the conjugates. Lectins were conjugated to QDs via adsorption, and the optical parameters (emission and absorption) were monitored. Lectin stability in the conjugates towards denaturing agents was investigated via fluorometry. The conjugation was evaluated using fluorescence microplate (FMA) and hemagglutination (HA) assays. The labeling of the C. neoformans cell surface was quantified using flow cytometry and observed via fluorescence microscopy. The QDs-SteLL and QDs-PgTeL conjugates, obtained at pH 7.0 and 8.0, respectively, showed the maintenance of colloidal and optical properties. FMA confirmed the conjugation, and the HA assay indicated that the lectin carbohydrate-binding ability was preserved after conjugation. SteLL and PgTeL showed stability towards high urea concentrations and heating. Conjugates labeled over 90% of C. neoformans cells as observed via flow cytometry and confirmed through fluorescence microscopy. C. neoformans labeling by conjugates was inhibited by glycoproteins, suggesting specific interactions through the lectin carbohydrate-binding site. Thus, an effective protocol for the conjugation of SteLL or PgTeL with QDs was proposed, yielding new nanoprobes useful for glycobiological studies.

Pharmaceutical Applications of Quantum Dots

Nanotechnology has been utilized in developing novel drug formulations with minimal adverse effects. Nanoparticles in a lower size range with great surface area, increased potency, and easy permeability could be an approach for the treatment of cancer and other diseases. Unlike other nanoparticles, quantum dots have specific functional groups, have charges over their surface, and are extremely small in size (2-10nm), which makes them more permeable through tight junctions. Quantum dots are interesting materials that offer diagnosis and treatment concurrently. Quantum dots are reported to have several applications in pharmaceuticals as well as drug delivery, diagnosis, immunolabeling, and cell labeling tools. However, the existence of heavy metals in quantum dots such as cadmium poses a potential challenge for future medical applications, where quantum dots may be deliberately injected into the body. In this review, we are focusing on various pharmaceutical applications of quantum dots. Graphical Abstract.

A brief insight to the role of glyconanotechnology in modern day diagnostics and therapeutics

Carbohydrate-protein and carbohydrate-carbohydrate interactions are very important for various biological processes. Although the magnitude of these interactions is low compared to that of protein-protein interaction, the magnitude can be boosted by multivalent approach known as glycocluster effect. Nanoparticle platform is one of the best ways to present diverse glycoforms in multivalent manner and thus, the field of glyconanotechnology has emerged as an important field of research considering their potential applications in diagnostics and therapeutics. Considerable advances in the field have been achieved through development of novel techniques, use of diverse metallic and non-metallic cores for better efficacy and application of ever-increasing number of carbohydrate ligands for site-specific interaction. The present review encompasses the recent developments in the area of glyconanotechnology and their future promise as diagnostic and therapeutic tools.

Preparation and Characterization of Quantum Dot-Peptide Conjugates Based on Polyhistidine Tags

Quantum dots (QDs) offer bright and robust photoluminescence among several other advantages in comparison to fluorescent dyes. In order to leverage the advantageous properties of QDs for applications in bioanalysis and imaging, simple and reliable methods for bioconjugation are required. One such method for conjugating peptides to QDs is the use of polyhistidine tags, which spontaneously bind to the surface of QDs. We describe protocols for assembling polyhistidine-tagged peptides to QDs and for characterizing the resultant QD-peptide conjugates. The latter include both electrophoretic and FRET-based protocols for confirming successful peptide assembly, estimating the maximum peptide loading capacity, and measuring the assembly kinetics. Sensors for protease activity and intracellular delivery are briefly noted as prospective applications of QD-peptide conjugates.

Affinity Immobilization of Semiconductor Quantum Dots and Metal Nanoparticles on Cellulose Paper Substrates

Colloidal semiconductor quantum dots (QDs), metal nanoparticles, and cellulose paper are materials with numerous applications in bioanalysis and beyond. The functional properties of QDs and metal NPs are substantially different than those of cellulose, such that their integration with cellulose paper is potentially enabling for many applications. Here, we characterize and evaluate multiple chemistries that modify cellulose paper substrates for the affinity-based immobilization of QDs, gold nanoparticles (Au NPs), and platinum nanoparticles (Pt NPs). These chemistries include grafting of cellulose fibers with imidazole and dithiol groups, as well as the aminosilanization of cellulose fibers (both with and without subsequent grafting with dithiol groups). Cellulose modifications and nanoparticle immobilization are characterized by multiple techniques, including, but not limited to, X-ray photoelectron spectroscopy, scanning electron microscopy, and optical imaging, extinction, and fluorescence measurements. We demonstrate the on-paper immobilization of color-tuned mixtures of QDs, on-paper patterning of QDs by microcontact printing, and post-immobilization enhancement of energy transfer and model assays of protease activity. The robustness of QD photoluminescence is also evaluated between immobilization chemistries. Paper-immobilized Au NPs and Pt NPs are evaluated as potential substrates for SERS and as supported catalysts for a model decolorization reaction. Our cumulative results indicate that there may not be a one-size-fits-all immobilization chemistry. Instead, the immobilization chemistry should be tailored and optimized for the downstream application.

Fully Self-Assembled Silica Nanoparticle-Semiconductor Quantum Dot Supra-Nanoparticles and Immunoconjugates for Enhanced Cellular Imaging by Microscopy and Smartphone Camera

There is a growing need for brighter luminescent materials to improve the detection and imaging of biomarkers. Relevant contexts include low-abundance biomarkers and technology-limited applications, where an example of the latter is the emerging use of smartphones and other nonoptimal but low-cost and portable devices for point-of-care diagnostics. One approach to achieving brighter luminescent materials is incorporating multiple copies of a luminescent material into a larger supra-nanoparticle (supra-NP) assembly. Here, we present a facile method for the preparation and immunoconjugation of supra-NP assemblies (SiO₂@QDs) that comprised many quantum dots (QDs) around a central silica nanoparticle (SiO₂ NP). The assembly was entirely driven by spontaneous affinity interactions between the constituent materials, which included imidazoline-functionalized silica nanoparticles, ligand-coated QDs, imidazole-functionalized dextran, and tetrameric antibody complexes (TACs). The physical and optical properties of the SiO₂@QDs were characterized at both the ensemble and single-particle levels. Notably, the optical properties of the QDs were preserved upon assembly into supra-NPs, and single SiO₂@QDs were approximately an order of magnitude brighter than single QDs and nonblinking. In proof-of-concept applications, including selective immunolabeling of breast cancer cells, the SiO₂@QDs provided higher sensitivity and superior signal-to-background ratios whether using research-grade fluorescence microscopy or smartphone-based imaging. Overall, the SiO₂@QDs are promising materials for enhanced bioanalysis and imaging.