Engineering Monovalent Quantum Dot−Antibody Bioconjugates with a Hybrid Gel System

Precise control methods of the physicochemical properties of nanoparticles for personalized medicine

Biomedical applications of nanoparticles (NPs) have attracted much attention. With the advancement of personalized medicine, researchers are now proposing the concept that the design of NPs needs to be optimized according to the individual patient. To realize this concept, an important question is how precisely we can tailor the physicochemical properties of NPs, such as size, shape, and surface chemistry, using current technology. This review discusses recent advances and challenges in the precise control of the size, shape, and surface chemistry of NPs. While control methods have advanced significantly over the past 20 years, the size, shape, and surface chemistry of currently available NPs vary by type, requiring careful selection based on the targeted disease, organ, and patient.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

Quantum dots combined with a fluorescence-linked immunosorbent assay for detecting the metabolic balance of DT-13 excretion in rats

Saponin monomer 13 of the dwarf lilyturf tuber (DT-13) is a steroidal saponin component isolated from the tuber of Liriope muscari (Decne.) Bailey that exhibits multiple pharmacological activities. We used a liquid chromatography-tandem mass spectrometry method and MetaboLynx XS software to investigate the metabolites of DT-13 in vivo and obtained potential metabolites and changes in functional groups during the formation of metabolites from the substrate. The main metabolites obtained had the ruscogenin (RUS) backbone structure. We also report a competitive fluorescence-linked immunosorbent assay (FLISA) based on monoclonal antibodies (MABS) conjugated with quantum dots (QDs) for rapid and sensitive quantitative analysis of DT-13 and its metabolite levels in biological samples. Using this method, the DT-13 levels detected in rat urine and feces displayed a good linear relationship within the corresponding linear ranges. The DT-13 recovery rate ranged from 85.28 to 101.40%, with a relative standard deviation of 2.96-9.26%. The method was successfully applied to study the distribution of DT-13 excretion in rats after oral administration. DT-13 was primarily excreted in the urine after metabolism. This study provides a new tool for pharmacokinetic studies of DT-13 and other active substances for which the analysis efficacy does not match the bioavailability or that are difficult to study using isotope labeling.

Tracking Single Molecules in Biomembranes: Is Seeing Always Believing?

The spatial organization of molecules in cell membranes and their dynamic interactions play a central role in regulating cell functions. Single-particle tracking (SPT), a technique in which single molecules are imaged and tracked in real time, has led to breakthrough discoveries regarding these spatiotemporal complexities of cell membranes. There are, however, emerging concerns about factors that might produce misleading interpretations of SPT results. Here, we briefly review the application of SPT to understanding the nanoscale heterogeneities of plasma membranes, with a focus on the unique challenges, pitfalls, and limitations that confront the use of nanoparticles as imaging probes for tracking the dynamics of single molecules in cell membranes.

Compact Quantum Dots for Quantitative Cytology

In this chapter, we describe the preparation of fluorescent quantum dots for imaging and measuring protein expression in cells. Quantum dots are nanocrystals that have numerous advantages for biomolecular detection compared with organic dyes and fluorescent proteins, but their large size has been a limiting factor. We describe the synthesis of nanoparticles smaller than 10 nm (smaller than an antibody), their attachment to monoclonal antibodies through click chemistry, characterization of the conjugates, and use for labeling of cellular antigens. We further discuss the unique advantages and challenges associated with this approach compared with conventional immunofluorescence techniques.

Ligand density on nanoparticles: A parameter with critical impact on nanomedicine

Nanoparticles modified with ligands for specific targeting towards receptors expressed on the surface of target cells are discussed in literature towards improved delivery strategies. In such concepts the ligand density on the surface of the nanoparticles plays an important role. How many ligands per nanoparticle are best for the most efficient delivery? Importantly, this number may be different for in vitro and in vivo scenarios. In this review first viruses as "biological" nanoparticles are analyzed towards their ligand density, which is then compared to the ligand density of engineered nanoparticles. Then, experiments are reviewed in which in vitro and in vivo nanoparticle delivery has been analyzed in terms of ligand density. These results help to understand which ligand densities should be attempted for better targeting. Finally synthetic methods for controlling the ligand density of nanoparticles are described.

Counting growth factors in single cells with infrared quantum dots to measure discrete stimulation distributions

The distribution of single-cell properties across a population of cells can be measured using diverse tools, but no technology directly quantifies the biochemical stimulation events regulating these properties. Here we report digital counting of growth factors in single cells using fluorescent quantum dots and calibrated three-dimensional deconvolution microscopy (QDC-3DM) to reveal physiologically relevant cell stimulation distributions. We calibrate the fluorescence intensities of individual compact quantum dots labeled with epidermal growth factor (EGF) and demonstrate the necessity of near-infrared emission to overcome intrinsic cellular autofluoresence at the single-molecule level. When applied to human triple-negative breast cancer cells, we observe proportionality between stimulation and both receptor internalization and inhibitor response, reflecting stimulation heterogeneity contributions to intrinsic variability. We anticipate that QDC-3DM can be applied to analyze any peptidic ligand to reveal single-cell correlations between external stimulation and phenotypic variability, cell fate, and drug response.

Measuring growth factors in single cells at physiologically relevant stimulation doses is challenging. Here the authors use fluorescent quantum dots and calibrated three-dimensional deconvolution microscopy to digitally count growth factors in single cells and reveal stimulation distributions in cancer cells.

The synthesis and oligomerization of a monofunctional bottlebrush-shaped polymer terminated with an azide group

A monofunctional bottlebrush-shaped polymer terminated with an azide group and its oligomers (dimer, trimer) were synthesized in a controlled manner and directly visualized.

Inorganic Nanoparticles as Donors in Resonance Energy Transfer for Solid-Phase Bioassays and Biosensors

Bioassays for the rapid detection and quantification of specific nucleic acids, proteins, and peptides are fundamental tools in many clinical settings. Traditional optical emission methods have focused on the use of molecular dyes as labels to track selective binding interactions and as probes that are sensitive to environmental changes. Such dyes can offer good detection limits based on brightness but typically have broad emission bands and suffer from time-dependent photobleaching. Inorganic nanoparticles such as quantum dots and upconversion nanoparticles are photostable over prolonged exposure to excitation radiation and tend to offer narrow emission bands, providing a greater opportunity for multiwavelength multiplexing. Importantly, in contrast to molecular dyes, nanoparticles offer substantial surface area and can serve as platforms to carry a large number of conjugated molecules. The surface chemistry of inorganic nanoparticles offers both challenges and opportunities for the control of solubility and functionality for selective molecular interactions by the assembly of coatings through coordination chemistry. This report reviews advances in the compositional design and methods of conjugation of inorganic quantum dots and upconversion nanoparticles and the assembly of combinations of nanoparticles to achieve energy exchange. Our interest is the exploration of configurations where the modified nanoparticles can be immobilized to solid substrates for the development of bioassays and biosensors that operate by resonance energy transfer (RET).

A Novel Fluoroimmunoassay for Detecting Ruscogenin with Monoclonal Antibodies Conjugated with CdSe/ZnS Quantum Dots

Ruscogenin (RUS) is a steroidal sapogenin found in Ruscus aculeatus and Ophiopogon japonicus with several pharmacological activities. In the work reported herein, a novel method termed competitive fluorescence-linked immunosorbent assay (cFLISA) based on monoclonal antibodies (mAbs) coupled with quantum dots (QDs) was developed for the quick and sensitive determination of RUS in biological samples. The mAbs against RUS were conjugated with CdSe/ZnS QDs by the crossing-linking reagents and an indirect cFLISA method was developed. There was a good linear relationship between inhibition efficiency and logarithm concentration of RUS which was varied from 0.1 to 1000 ng/mL. The IC₅₀ and limit of detection (LOD) were 9.59 ng/mL and 0.016 ng/mL respectively, which much lower than the enzyme-linked immunosorbent assay (ELISA) method. The recoveries in plasma and tissues were ranged from 82.3% to 107.0% and the intra- and inter-day precision values were below 15%. The developed cFLISA has been successfully applied to the measurement of the concentrations of RUS in biological samples of rats, and showed great potential for the tissue distribution study of RUS. The cFLISA method may provide a valuable tool for the analysis of small molecules in biological samples and such an approach could be applied to other natural products.

Tumor Microenvironment-Triggered Aggregation of Antiphagocytosis 99m Tc-Labeled Fe3 O4 Nanoprobes for Enhanced Tumor Imaging In Vivo

A tumor microenvironment responsive nanoprobe is developed for enhanced tumor imaging through in situ crosslinking of the Fe₃ O₄ nanoparticles modified with a responsive peptide sequence in which a tumor-specific Arg-Gly-Asp peptide for tumor targeting and a self-peptide as a "mark of self" are linked through a disulfide bond. Positioning the self-peptide at the outmost layer is aimed at delaying the clearance of the nanoparticles from the bloodstream. After the self-peptide is cleaved by glutathione within tumor microenvironment, the exposed thiol groups react with the remaining maleimide moieties from adjacent particles to crosslink the particles in situ. Both in vitro and in vivo experiments demonstrate that the aggregation substantially improves the magnetic resonance imaging (MRI) contrast enhancement performance of Fe₃ O₄ particles. By labeling the responsive particle probe with ^99m Tc, single-photon emission computed tomography is enabled not only for verifying the enhanced imaging capacity of the crosslinked Fe₃ O₄ particles, but also for achieving sensitive dual modality imaging of tumors in vivo. The novelty of the current probe lies in the combination of tumor microenvironment-triggered aggregation of Fe₃ O₄ nanoparticles for boosting the T₂ MRI effect, with antiphagocytosis surface coating, active targeting, and dual-modality imaging, which is never reported before.

Evaluation of fluorophores to label SNAP-tag fused proteins for multicolor single-molecule tracking microscopy in live cells

Single-molecule tracking has become a widely used technique for studying protein dynamics and their organization in the complex environment of the cell. In particular, the spatiotemporal distribution of membrane receptors is an active field of study due to its putative role in the regulation of signal transduction. The SNAP-tag is an intrinsically monovalent and highly specific genetic tag for attaching a fluorescent label to a protein of interest. Little information is currently available on the choice of optimal fluorescent dyes for single-molecule microscopy utilizing the SNAP-tag labeling system. We surveyed 6 green and 16 red excitable dyes for their suitability in single-molecule microscopy of SNAP-tag fusion proteins in live cells. We determined the nonspecific binding levels and photostability of these dye conjugates when bound to a SNAP-tag fused membrane protein in live cells. We found that only a limited subset of the dyes tested is suitable for single-molecule tracking microscopy. The results show that a careful choice of the dye to conjugate to the SNAP-substrate to label SNAP-tag fusion proteins is very important, as many dyes suffer from either rapid photobleaching or high nonspecific staining. These characteristics appear to be unpredictable, which motivated the need to perform the systematic survey presented here. We have developed a protocol for evaluating the best dyes, and for the conditions that we evaluated, we find that Dy 549 and CF 640 are the best choices tested for single-molecule tracking. Using an optimal dye pair, we also demonstrate the possibility of dual-color single-molecule imaging of SNAP-tag fusion proteins. This survey provides an overview of the photophysical and imaging properties of a range of SNAP-tag fluorescent substrates, enabling the selection of optimal dyes and conditions for single-molecule imaging of SNAP-tagged fusion proteins in eukaryotic cell lines.

Semiconducting polymer dots with monofunctional groups

This communication describes an approach for preparing monovalent semiconducting polymer dots (mPdots) with a size of 5 nm where each mPdot was composed of precisely a single active functional group.

Monofunctional polymer nanoparticles prepared through intramolecularly cross-linking the polymer chains sparsely grafted on the surface of sacrificial silica spheres

Polymeric monofunctional nanoparticles with exactly one functional group on the surface of each nanoparticle are prepared.

Discrete nanoparticle-BSA conjugates manipulated by hydrophobic interaction

Nanoparticle-protein conjugates are promising probes for biological diagnostics as well as versatile building blocks for nanotechnology. Here we demonstrate a facile method to prepare nanoparticles bearing discrete numbers of BSA simply by physical adsorption and electrophoretic isolation, in which the specific amphiphilic properties of BSA play important roles and the number of adsorbed BSA molecules can also be manipulated by tuning the coating extent of nanoparticles by amphiphilic polymer.

Solid-phase bioconjugation of heterobifunctional adaptors for versatile assembly of bispecific targeting ligands

High-throughput generation of bispecific molecules promises to expedite the discovery of new molecular therapeutics and guide engineering of novel multifunctional constructs. However, high synthesis complexity and cost have hampered the discovery of bispecific molecules in drug development and biomedical research. Herein we describe a simple solid-phase bioconjugation procedure for preparation of Protein A(G,L)-PEG-Streptavidin heterobifunctional adaptors (with 1:1:1 stoichiometry), which enable self-assembly of unmodified antibodies and biotinylated molecules into bispecific targeting ligands in a versatile mix-and-use manner. Utility of such adaptors is demonstrated by assembly of anti-CD3 and anti-Her2 antibodies into bispecific CD3xHer2 targeting ligands, which efficiently drive T-cell-mediated lysis of Her2-positive cancer cells. In comparison to bioconjugation in solution, the solid-phase procedure described here offers precise stoichiometry control, ease of purification, and high yield of functional conjugates. Simplicity and versatility should prove this methodology instrumental for preparation of bispecific ligands, as well as for high-throughput screening of bispecific combinations, before proceeding to synthesis of lead candidates via recombinant engineering or chemical cross-linking.

Rapid and quantitative detection of prostate specific antigen with a quantum dot nanobeads-based immunochromatography test strip

Convenient and fast testing using an immunochromatography test strip (ICTS) enables rapid yes/no decisions regarding a disease to be made. However, the fundamental limitations of an ICTS, such as a lack of quantitative and sensitive analysis, severely hampers its application in reliable medical testing for the early detection of cancer. Herein, we overcame these limitations by integrating an ICTS with quantum dot nanobeads (QD nanobeads), which were fabricated by encapsulating QDs within modified poly(tert-butyl acrylate-co-ethyl acrylate-co-methacrylic acid) and served as a robust signal-generating reagent for the ICTS. Prostate specific antigen (PSA) was used as a model analyte to demonstrate the performance of the QD nanobeads-based ICTS platform. Under optimized conditions, the concentration of PSA could be determined within 15 min with high sensitivity and specificity using only 40 μL of sample. The detection limit was enhanced by ∼12-fold compared with that of an ICTS that used QDs encapsulated by commercial 11-mercaptoundecanoic acid (QDs@MUA) as the signal-generating reagent. At the same time, the possible clinical utility of this approach was demonstrated by measurements recorded from PSA-positive patient specimens. Our data suggest that the QD nanobeads-based ICTS platform is not only rapid and low-cost but also highly sensitive and specific for use in quantitative point-of-care diagnostics; thus, it holds promise for becoming a part of routine medical testing for the early cancer of detection.

Bitargeting and ambushing nanotheranostics

The main problem in cancer chemotherapy is the cytotoxic side effects of therapeutics on healthy tissues and cells. The targeted drug delivery and nanotechnology are intensively investigated area to find new ways to solve, at least to reduce, these problems. Hereby, we have reported a new method inspired from both conventional military strategies and biorecognition in the body. In this respect, we have produced two fluorescent nano-drug systems with bitargeting and biorecognition properties, recognizing cancer cells and each other. The multiplexed nanostructures were interacted with HL-60 cells to show their efficiency for bitargeting, ambushing, timed, and double-controlled cancer cell apoptosis.

Electrophoretic study of peptide-mediated quantum dot-human immunoglobulin bioconjugation

The bioconjugation of quantum dots (QDs) is a key process in their application for bioanalysis as well as imaging. The coupling of QDs with biologically active molecules such as peptides, nucleic acids, and/or antibodies enables their fluorescent labeling, and therefore, selective and sensitive tracking during the bioanalytical process, however, the efficiency of the labeling and preservation of the biological activity of the bioconjugate have to be considered. In this study, a new approach of the bioconjugation of CdTe-QDs and human immunoglobulin employing a small peptide is described. The heptapeptide (HWRGWVC) was synthesized and characterized by mass spectrometry, liquid chromatography, and capillary electrophoresis. Moreover, the peptide was used as a capping agent for QDs synthesis. The CdTe-QDs were synthesized by microwave synthesis (600 W, 20 min) using 3.2 mM CdCl2 and 0.8 mM Na2TeO3. The bioconjugation of QDs capped by this peptide with immunoglobulin was investigated by capillary electrophoresis and magnetic immunoextraction coupled with electrochemical detection by differential pulse voltammetry. Furthermore, the applicability of prepared bioconjugates for fluorescent immunodetection was verified using immobilized goat antihuman IgG antibody.

Surface engineering of inorganic nanoparticles for imaging and therapy

Many kinds of inorganic nanoparticles (NPs) including semiconductor, metal, metal oxide, and lanthanide-doped NPs have been developed for imaging and therapy applications. Their unique optical, magnetic, and electronic properties can be tailored by controlling the composition, size, shape, and structure. Interaction of such NPs with cells and/or in vivo compartments is critically determined by the surface properties, and sophisticated control over the NP surface is essential to control their fate in biological environments. We review NP surface coating strategies using the categories of small surface ligand, polymer, and lipid. Use of small ligand molecules has the advantage of maintaining the minimal hydrodynamic (HD) size. Polymers can be advantageous in NP anchoring by combining multiple affinity groups. Encapsulation of NPs in polymers, lipids or surfactants can preserve the as-synthesized NPs. NP surface properties and reaction conditions should be carefully considered to obtain a bioconjugate that maintains the physicochemical properties of NP and functionalities of the conjugated biomolecules. We highlight how the surface properties of NPs impact their interactions with cells and in vivo compartments, especially focused on the important surface design parameters such as HD size, surface charge, and targeting. Typically, maximal cellular uptake can take place in the intermediate NP size range of 40-60nm. Clearance of NPs from blood circulation is largely dependent on the degree of uptake by reticuloendothelial system when they are larger than 10nm. When the HD size is below 10nm, NPs show broad distribution over many organs. Reduction of HD size below the limit of renal barrier can achieve fast clearance of NPs. For maximal tumor accumulation, NPs should have long blood circulation time and should be large enough to prevent rapid penetration. NPs are also desired to rapidly clear out from the body after the mission before they cause toxic side effects. However, efficient clearance from the body to avoid side effects may result in the reduction in residence time required for accumulation in target tissues. Smart design of NP surface coating that can meet the conflicting demands can open a new avenue of NP applications. Surface charge and hydrophobicity need to be carefully considered for NP surface design. Positively charged NPs more adsorb on cell membranes and consequently show higher level of internalizations when compared with negatively charged or neutral NPs. NPs encounter a large variety of biomolecules in vivo, where non-specific adsorptions can potentially alter the physicochemical properties of the NPs. For optimal performance, NPs are suggested to have neutral surface charge at physiological conditions, small HD size, and minimal non-specific adsorption levels. Zwitterionic NP surface coating by small surface ligands can be a promising approach. Toxicity is one of most critical issues, where proper control of the NP surface can significantly reduce the toxicities.

Semiconductor quantum dots for biomedicial applications

Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed analysis of immunocomplexes or DNA hybridization processes, cell sorting and tracing, in vivo imaging and diagnostics in biomedicine. Meanwhile, QDs can be used as labels for the electrochemical detection of DNA or proteins. This article reviews the synthesis and toxicity of QDs and their optical and electrochemical bioanalytical applications. Especially the application of QDs in biomedicine such as delivering, cell targeting and imaging for cancer research, and in vivo photodynamic therapy (PDT) of cancer are briefly discussed.