NIR quantum dot construction of a fluorescence anisotropy signal amplification biosensor for sensitive, rapid and separation-free detection of dopamine in serum.

Dopamine (DA) is an important small-molecule neurotransmitter, which is closely related to the development of many neurological diseases and has received increasing attention in the diagnosis of neurological diseases. Currently, the assays of the detection of dopamine such as electrochemical and colorimetric methods have low sensitivity, poor selectivity and susceptibility to interference, which limit the accurate quantification of dopamine. Fluorescence anisotropy immunoassay is a traditional analytical method in which the quantification is based on the change in fluorescence anisotropy values observed when fluorescence molecules are bound to a certain volume and mass of the material. Since dopamine is a small molecule with small volume and mass, we took advantage of the good photostability of the second near-infrared window (NIR-II) quantum dots (QDs) and the low spontaneous interference of the substrate, and designed a biosensor dopamine fluorescence anisotropy probe streptavidin biosensor (DFAP-SAB) based on the NIR-II QDs combined with streptavidin signal amplification to achieve rapid and separation-free detection of dopamine in human serum. The detection signal has a good linearity between 50 nM and 3000 nM with a detection limit of 11.2 nM. The application of NIR-II QDs provides the possibility of biosensor applications for complex samples. The construction of the streptavidin signal amplification device provides a new idea for small molecule detection.

NIR-II fluorescent Ag2Se polystyrene beads in a lateral flow immunoassay to detect biomarkers for breast cancer.

Fluorescent lateral flow immunoassay (LFA), one tool in point of care testing (POCT) systems for breast cancer, has attracted attention because it is quick, simple, and convenient. However, samples and the constituent material exhibit autofluorescence in the visible region, which is a very large obstacle in the development of fluorescent LFAs. The autofluorescence of biological samples is scarcely found in the second near-infrared (NIR-II) range and samples scatter and absorb less NIR-II light than visible light. Here, we report an NIR-II QD-LFA platform using the NIR-II fluorescent Ag2Se quantum dots (QDs) with 1020 nm emission encapsulated into polystyrene beads as fluorescent probes. The NIR-II LFA platform was established to detect breast cancer tumour markers (CEA and CA153) within 15 min with a low limit of detection (CEA: 0.768 ng mL-1, CA153: 1.192 U mL-1), high recoveries (93.7% ~ 108.8%), and relative standard deviations (RSDs) of less than 10%. This study demonstrated the potential of NIR-II Ag2Se polystyrene beads as a fluorescent probe in LFA for rapid and accurate identification of biomarkers. They are suited for use in professional situations.

Ultrasmall Pb:Ag2 S Quantum Dots with Uniform Particle Size and Bright Tunable Fluorescence in the NIR-II Window.

Ag2 S quantum dots (QDs) are well-known near-infrared fluorophores and have attracted great interest in biomedical labeling and imaging in the past years. However, their photoluminescence efficiency is hard to compete with Cd-, Pb-based QDs. The high Ag+ mobility in Ag2 S crystal, which causes plenty of cation deficiency and crystal defects, may be responsible mainly for the low photoluminescence quantum yield (PLQY) of Ag2 S QDs. Herein, a cation-doping strategy is presented via introducing a certain dosage of transition metal Pb2+ ions into Ag2 S nanocrystals to mitigate this intrinsic shortcoming. The Pb-doped Ag2 S QDs (designated as Pb:Ag2 S QDs) present a renovated crystal structure and significantly enhanced optical performance. Moreover, by simply adjusting the levels of Pb doping in the doped nanocrystals, Pb:Ag2 S QDs with bright emission (PLQY up to 30.2%) from 975 to 1242 nm can be prepared without altering the ultrasmall particle size (≈2.7-2.8 nm). Evidently, this cation-doping strategy facilitates both the renovation of crystal structure of Ag2 S QDs and modulation of their optical properties.

Near-Infrared Fluorescent Ag2 Se-Cetuximab Nanoprobes for Targeted Imaging and Therapy of Cancer.

Theranostic nanoprobes integrated with diagnostic imaging and therapy capabilities have shown great potential for highly effective tumor therapy by realizing imaging-guided drug delivery and tumor treatment. Developing novel high-performance nanoprobes is an important basis for tumor theranostic application. Here, near-infrared (NIR) fluorescent and low-biotoxicity Ag2 Se quantum dots (QDs) have been coupled with cetuximab, a clinical antiepidermal growth factor receptor antibody drug for tumor therapy, via a facile bioconjugation strategy to prepare multifunctional Ag2 Se-cetuximab nanoprobes. Compared with the Ag2 Se QDs alone, the Ag2 Se-cetuximab nanoprobes display faster and more enrichment at the site of orthotopic tongue cancer, and thus present better NIR fluorescence contrast between the tumor and the surrounding regions. At 24 h postinjection, the NIR fluorescence of Ag2 Se-cetuximab nanoprobes at the tumor site is still easily detectable, whereas no fluorescence is observed for the Ag2 Se QDs. Moreover, the Ag2 Se-cetuximab nanoprobes have also significantly inhibited the tumor growth and improved the survival rate of orthotopic tongue cancer-bearing nude mice from 0% to 57.1%. Taken together, the constructed multifunctional Ag2 Se-cetuximab nanoprobes have achieved combined targeted imaging and therapy of orthotopic tongue cancer, which may greatly contribute to the development of nanotheranostics.

Exploring sialic acid receptors-related infection behavior of avian influenza virus in human bronchial epithelial cells by single-particle tracking.

Human respiratory tract epithelial cells are the portals of human infection with influenza viruses. However, the infection pathway of individual avian influenza viruses in human respiratory cells remains poorly reported so far. The single-particle tracking technique (SPT) is a powerful tool for studying the transport mechanism of biomolecules in live cells. In this work, we use quantum dots to label avian influenza H9N2 virus and elaborate on the infection mechanism of the virus in human bronchial epithelial (HBE) cells using a three-dimensional SPT technique. We have found that the H9N2 virus can infect HBE cells directly and the virus infection follows an actin filament- and microtubule-dependent process with a three-stage pattern. The transport behaviors show a high degree of consistency between the sialic acid receptors and the influenza virus. Real-time SPT provides dynamic evidence of the sialic acid receptors-related infection behavior of the avian influenza virus in live cells. The study of the influence of sialic acid receptors on virus infection may contribute to a better understanding of the cross-species transmission of the avian influenza virus.

Evaluation of nonspecific interactions between quantum dots and proteins.

A method based on the AFM and colloidal probe techniques was proposed to directly measure nonspecific interactions between QDs and different proteins with respective sizes and isoelectric points. Results indicated that van der Waals forces were the leading force, while electrostatic interactions also played an important role in nonspecific interactions.

One-step sensitive detection of Salmonella typhimurium by coupling magnetic capture and fluorescence identification with functional nanospheres.

Sensitive, rapid, and reliable detection of bacteria has always been pursued due to the great threat of the bacteria to human health. In this study, a convenient one-step strategy for detecting Salmonella typhimurium was developed. Immunomagnetic nanospheres (IMNS) and immunofluorescent nanospheres (IFNS) were used to specifically capture and recognize S. typhimurium simultaneously. After magnetic separation, the sandwich immune complexes (IMNS-bacteria-IFNS) were detected under a fluorescence microscope with a detection limit as low as ca. 10 CFU/mL. When they were detected by fluorescence spectrometer, a linear range was exhibited at the concentration from 10(5) to 10(7) CFU/mL with R(2) = 0.9994. Compared with the two-step detection strategy, in which the bacteria were first captured with the IMNS and subsequently identified with the IFNS, this one-step strategy simplified the detection process and improved the sensitivity. Escherichia coli and Shigella flexneri both showed negative results with this method, indicating that this method had excellent selectivity and specificity. Moreover, this method had strong anti-interference ability, and it had been successfully used to detect S. typhimurium in synthetic samples (milk, fetal bovine serum, and urine), showing the potential application in practice.

Electrochemical methods--important means for fabrication of fluorescent nanoparticles.

Fluorescent nanoparticles have attracted much attention over the last two decades. Due to the size- and composition-dependent optical and electrical properties, fluorescent nanoparticles have been emphasized in electronic, optical and biomedical applications. Till now, many kinds of methods have been developed to fabricate diverse fluorescent nanoparticles, which include pyrolysis, template synthesis, hydrothermal synthesis, microemulsion, electrochemical methods and so on. Among them, electrochemical methods are favored for relatively good controllability, ease of operation and mild reaction conditions. By adjusting the applied potential, current, components of the electrolyte and other relevant parameters, the fluorescent nanoparticles could be electrochemically manufactured with tunable sizes, compositions and surface structure, which allows for the modification of electronic and optical properties. Therefore, electrochemical methods are regarded as important means in preparing fluorescent nanoparticles. This review focuses on the recent progress in electrochemical fabrications of fluorescent nanoparticles (together with their optical properties and some applications in optoelectronics and biomedicine).

Detection of Epstein-Barr virus infection in gastric carcinomas using quantum dot-based fluorescence in-situ hybridization.

Quantum dots were proposed as new fluorochromes for use in fluorescence in-situ hybridization. EBV-encoded small RNA, the most abundant viral product in latently infected cells, was detected by quantum dot fluorescence in-situ hybridization in paraffin-embedded tissue sections of gastric carcinoma. An indirect FISH approach using quantum dots streptavidin conjugates as secondary reporters and digoxigenin labeled EBV-encoded small RNA oligonucleotide probes as detectable molecules was employed. Quantum dot fluorescence in-situ hybridization offered a slightly higher sensitivity in detecting EBV-encoded small RNA in gastric carcinoma than chromogenic in-situ hybridization. Statistical analyses showed that the detected EBV-associated gastric carcinoma was not associated with any clinicopathological parameters of the Chinese gastric carcinoma patients investigated in this study.

Recapitulating Developmental Condensation and Constructing Self-organised Cartilaginous Tissue for Cartilage Regeneration.

OBJECTIVE: To develop a novel chondrocyte condensation culture strategy recapitulating developmental condensation and construct self-organised cartilaginous tissue for cartilage regeneration. METHODS: Cell-condensation aggregate (CCA) was generated using the condensation culture method by sequential cell seeding. The chondrification capacities and biocompatibilities of CCA were assessed by comparison with the cell-scaffold complex (CSC), which was constructed by cell-scaffold coculture. Preclinical studies including implantation into nude mice subcutaneously and cartilage defect repair in rabbits were performed. RESULTS: CCA constructed by condensation culture exhibited a morphology of self-organised cartilaginous tissue. Meanwhile, the condensation culture inhibited or abolished expression of HOX genes including HOXC4 and HOXD8, which was partially consistent with developmental HOX gene expression patterns and associated with enhanced regeneration capacities. Compared with CSC, CCA showed a higher capacity for chondrification and regeneration of rabbit cartilage defects. CONCLUSION: The therapeutic assessments indicate that CCA is an efficient therapeutic tool for cartilage regeneration, providing a new strategy for tissue engineering by mimicking developmental events.

A near-infrared-II fluorescence anisotropy strategy for separation-free detection of adenosine triphosphate in complex media.

Fluorescence anisotropy (FA) has been widely applied for detecting and monitoring special targets in life sciences. However, matrix autofluorescence restricted its further application in complex biological samples. Herein, we report a near-infrared-II (NIR-II) FA strategy for detecting adenosine triphosphate (ATP) in human serum samples and breast cancer cell lysate, which employed NIR-II fluorescent Ag2Se quantum dots (QDs) as tags to reduce matrix autofluorescence effect and applied graphene oxide (GO) to enhance fluorescence anisotropy signals. In the presence of ATP, the recognition between NIR-II Ag2Se QDs labeled aptamer (QD-pDNA) and ATP led to the release of QD-pDNA from GO, resulting in the obvious decrease of FA values. ATP could be quantitatively detected in concentrations ranged from 3 nM to 2500 nM, with a detection limit down to 1.01 nM. This study showed that the developed NIR-II FA strategy could be applied for detecting targets in complex biological samples and had great potential for monitoring interactions between biomolecules in biomedical research.

Target-modulated sensitization of upconversion luminescence by NIR-emissive quantum dots: a new strategy to construct upconversion biosensors.

We herein used Ag2Se quantum dots (QDs) as a target-modulated sensitizer for upconversion nanoparticles (UCNPs) and the target thrombin as the sensitizing switch to construct a biosensor, circumventing the limited luminescence resonance energy transfer (LRET) efficiency of UCNPs, with enhanced signal-to-background ratio (SBR) and assay sensitivity.

Color-tunable fluorescent-magnetic core/shell multifunctional nanocrystals.

We have developed a convenient strategy for preparing color-tunable fluorescent-magnetic core/shell multifunctional nanocrystals, which exhibit excellent photoluminescence (PL) properties (fluorescing tunably from 550 nm to 630 nm by modifying the shell thickness) and ferromagnetic material properties (a magnetization of 4.4 emu g(-1) and a coercivity of 95 Oe).

Controlled and reversible binding of positively charged quantum dots to lambda DNA.

Biomacromolecules/Nanomaterials bioconjugate complexes have many applications in the interdisciplinary research fields. Accessible and easy synthesis methods of these complexes are the key roles for these applications. High quality water-soluble surface-charged quantum dots (QDs) were successfully prepared via surface modification by amphiphilic surfactants. The positively charged QDs can interact with deoxyribonucleic acid (DNA) molecules to form QDs/DNA bioconjugates via self-targeting electrostatic force. The stability of these QDs/DNA bioconjugates is influenced by ionic strength and concentration of negative or neutral surfactants in the solution. High ionic concentration or ca. 10(-3) mol/L surfactants can break the interaction between the QDs and DNA molecules (Lambda DNA/Hind III Marker segments) and controllably release DNA molecules from these bioconjugates. The conformation of DNA molecules has little change during the binding and releasing process. The condensation of lambda DNA molecules can be induced by positively charged QDs. High resolution transmission electron microscopy experiments have revealed the different stages of DNA condensation process, showing the fine structures of QDs/DNA bioconjugates at biomolecular scale. A long chain DNA molecule starts to self-enwind and condense to a porous globule when it is exposing to positively charged QDs but there is no direct interaction between QDs and DNA at early stages of condensation. After the DNA molecule becomes a compact globule, QDs stick onto its surface via electrostatic force. The coil conformation of the DNA molecules can be recovered from globule structure after DNA molecules are controllably released from bioconjugate complexes. These QDs/DNA bioconjugates have great potential applications for gene delivery and at the same time the fluorescence of QDs can be utilized to monitor the DNA releasing process.

[Correlations between SNP of LALBA gene and economic traits in Inner Mongolian white cashmere goat].

PCR-SSCP and DNA sequencing methods were conducted to detect single nucleotide polymorphism of alpha-lactalbumin (LALBA) gene in 452 Inner Mongolian white cashmere goats (IMWC). Correlations between SNP of goat LALBA gene and economic traits, e.g., cashmere yield, cashmere thickness, length and weight, were analyzed. The SSCP in P2 primer locus, which was caused by the point mutation M63868:g.1897T>C in the exon 3 of LALBA gene was detected. At this locus, the genotype TT and allele T were predominant in the IMWC population, which agreed with Hardy-Weinberg equilibrium. Moreover, there was a significant correlation between polymorphism of goat M63868:g.1897 locus and cashmere yield of IMWC (P=0.017). The individuals with genotype TC had more cashmere yield than those with geontype TT. Hence, genotype TC of LALBA gene can be used as a molecular marker for breeding superior cashmere yield in goat marker-assisted selection.

Gd-DTPA-coupled Ag2Se quantum dots for dual-modality magnetic resonance imaging and fluorescence imaging in the second near-infrared window.

Near-infrared (NIR) fluorescent quantum dots (QDs) are ideal platforms to fabricate multifunctional contrast agents for multimodal imaging. Herein, second near-infrared window fluorescent (NIR-II) Ag2Se QDs were coupled with gadopentetate dimeglumine injection (Gd-DTPA) for dual-modality T1-weighted magnetic resonance (MR) imaging and fluorescence imaging. In vitro experiments suggested that the prepared Ag2Se-Gd QDs exhibit low cytotoxicity, remarkable T1-weighted MR imaging, and fluorescence imaging contrast properties. In vivo experiment results showed that Ag2Se-Gd QDs were the preferred contrast agents for dual-modality T1-weighted MR imaging and fluorescence imaging with high spatial resolution. Moreover, excellent temporal resolution and high tissue penetration depth were also achieved by fluorescence imaging. These results indicate the potential of Ag2Se-Gd QDs as multifunctional contrast agents for multimodal imaging in clinical diagnosis and research.

Real-Time Dissection of Distinct Dynamin-Dependent Endocytic Routes of Influenza A Virus by Quantum Dot-Based Single-Virus Tracking.

Entry is the first critical step for the infection of influenza A virus and of great significance for the research and development of antiflu drugs. Influenza A virus depends on exploitation of cellular endocytosis to enter its host cells, and its entry behaviors in distinct routes still need further investigation. With the aid of a single-virus tracking technique and quantum dots, we have realized real-time and multicolor visualization of the endocytic process of individual viruses and comprehensive dissection of two distinct dynamin-dependent endocytic pathways of influenza A virus, either dependent on clathrin or not. Based on the sequential progression of protein recruitment and viral motility, we have revealed the asynchronization in the recruitments of clathrin and dynamin during clathrin-dependent entry of the virus, with a large population of events for short-lived recruitments of these two proteins being abortive. In addition, the differentiated durations of dynamin recruitment and responses to inhibitors in these two routes have evidenced somewhat different roles of dynamin. Besides promoting membrane fission in both entry routes, dynamin also participates in the maturation of a clathrin-coated pit in the clathrin-dependent route. Collectively, the current study displays a dynamic and precise image of the entry process of influenza A virus and elucidates the mechanisms of distinct entry routes. This quantum dot-based single-virus tracking technique is proven to be well-suited for investigating the choreographed interactions between virus and cellular proteins.

Controllable synthesis of nanocrystals in droplet reactors.

In recent years, a broad range of nanocrystals have been synthesized in droplet-based microfluidic reactors which provide obvious advantages, such as accurate manipulation, better reproducibility and reliable automation. In this review, we initially introduce general concepts of droplet reactors followed by discussions of their main functional regions including droplet generation, mixing of reactants, reaction controlling, in situ monitoring, and reaction quenching. Subsequently, the enhanced mass and heat transport properties are discussed. Next, we focus on research frontiers including sequential multistep synthesis, intelligent synthesis, reliable scale-up synthesis, and interfacial synthesis. Finally, we end with an outlook on droplet reactors, especially highlighting some aspects such as large-scale production, the integrated process of synthesis and post-synthetic treatments, automated droplet reactors with in situ monitoring and optimizing algorithms, and rapidly developing strategies for interfacial synthesis.

Dissecting the Factors Affecting the Fluorescence Stability of Quantum Dots in Live Cells.

Labeling and imaging of live cells with quantum dots (QDs) has attracted great attention in the biomedical field over the past two decades. Maintenance of the fluorescence of QDs in a biological environment is crucial for performing long-term cell tracking to investigate the proliferation and functional evolution of cells. The cell-penetrating peptide transactivator of transcription (TAT) is a well-studied peptide to efficiently enhance the transmembrane delivery. Here, we used TAT peptide-conjugated QDs (TAT-QDs) as a model system to examine the fluorescence stability of QDs in live cells. By confocal microscopy, we found that TAT-QDs were internalized into cells by endocytosis, and transported into the cytoplasm via the mitochondria, Golgi apparatus, and lysosomes. More importantly, the fluorescence of TAT-QDs in live cells was decreased mainly by cell proliferation, and the low pH value in the lysosomes could also lower the fluorescence intensity of intracellular QDs. Quantitative analysis of the amount of QDs in the extracellular region and whole cells indicated that the exocytosis was not the primary cause of fluorescence decay of intracellular QDs. This work facilitates a better understanding of the fluorescence stability of QDs for cell imaging and long-term tracking in live cells. Also, it provides insights into the utility of TAT for transmembrane transportation, and the preparation and modification of QDs for cell imaging and tracking.

Purification of quantum dot-based bioprobes via high-performance size exclusion chromatography.

Due to excellent optical properties, quantum dots (QDs) have been widely applied to sensing, labeling, and imaging. For the fabrication of QD-based bioprobes, purification is usually the crucial step. Hydrophilic octylamine grafted polyacrylic acid modified QDs (OPA-QDs) were prepared, and purified by high-performance size exclusion chromatography (HPSEC) to remove excess OPA and aggregated QDs. The percentage of suspended agglomerates of OPA-QDs in the unpurified OPA-QDs increases from 4% to 31% through a year, but the purified OPA-QDs of the same batch possess excellent colloidal stability for at least one year. Subsequently, QD-based bioprobes were fabricated by the conjugation between QDs and streptavidin (SA) or antibody (IgG), generating QD-SA and QD-IgG, respectively, which were purified via HPSEC. Finally, the resulting QD-SA and QD-IgG were adopted to detect tumour markers on slices and showed specific positive signals without nonspecific adsorption, which was contrary to the unpurified QD-IgG. Thus, the HPSEC-coupled system proposed in the current work is potent and universal for the generation of purified and monodisperse QD-based bioprobes, which is promising in the nanobiodetection field.