Application of functional quantum dot nanoparticles as fluorescence probes in cell labeling and tumor diagnostic imaging

Cytotoxicity of Quantum Dots in Receptor-Mediated Endocytic and Pinocytic Pathways in Yeast

Despite the promising applications of the use of quantum dots (QDs) in the biomedical field, the long-lasting effects of QDs on the cell remain poorly understood. To comprehend the mechanisms underlying the toxic effects of QDs in yeast, we characterized defects associated with receptor-mediated endocytosis (RME) as well as pinocytosis using Saccharomyces cerevisiae as a model in the presence of cadmium selenide/zinc sulfide (CdSe/ZnS) QDs. Our findings revealed that QDs led to an inefficient RME at the early, intermediate, and late stages of endocytic patch maturation at the endocytic site, with the prolonged lifespan of GFP fused yeast fimbrin (Sac6-GFP), a late marker of endocytosis. The transit of FM1-43, a lipophilic dye from the plasma membrane to the vacuole, was severely retarded in the presence of QDs. Finally, QDs caused an accumulation of monomeric red fluorescent protein fused carbamoyl phosphate synthetase 1 (mRFP-Cps1), a vacuolar lumen marker in the vacuole. In summary, the present study provides novel insights into the possible impact of CdSe/ZnS QDs on the endocytic machinery, enabling a deeper comprehension of QD toxicity.

Recent Applications of Quantum Dots in Pharmaceutical Analysis

Nanotechnology has emerged as one of the most potential areas for pharmaceutical analysis. The need for nanomaterials in pharmaceutical analysis is comprehended in terms of economic challenges, health and safety concerns. Quantum dots (QDs)or colloidal semiconductor nanocrystals are new groups of fluorescent nanoparticles that bind nanotechnology to drug analysis. Because of their special physicochemical characteristics and small size, QDs are thought to be promising candidates for the electrical and luminescent probes development. They were originally developed as luminescent biological labels, but are now discovering new analytical chemistry applications, where their photo-luminescent properties are used in pharmaceutical, clinical analysis, food quality control and environmental monitoring. In this review, we discuss QDs regarding properties and advantages, advances in methods of synthesis and their recent applications in drug analysis in the recent last years.

Novel Förster Resonance Energy Transfer probe with quantum dot for a long-time imaging of active caspases inside individual cells

With the goal to investigate biological phenomena at a single-cell level, we designed, synthesized and tested a molecular probe based on Förster resonance energy transfer (FRET) between a highly luminescent quantum dot (QD) as a donor and a fluorophore or fluorescence quencher as an acceptor linked by a specific peptide. In principle, QD luminescence, effectively dissipated in the probe, is switched on after the cleavage of the peptide by a protease and the release of the quencher. We proposed a novel synthesis strategy of a probe. A two-step synthesis consists of: (i) Conjugation of CdTe QDs functionalized by -COOH groups of succinic acid on the nanoparticle surface with the designed specific peptide (GTADVEDTSC) using a ligand-exchange approach; (ii) A fast, high-yield reaction of amine-reactive succinimidyl group on the BHQ-2 quencher with N-terminal of the peptide. This way, any crosslinking between individual nanoparticles and any nonspecific conjugation bonds are excluded. The analysis of the product after the first step proved a high reaction yield and nearly no occurrence of unreacted QDs, a prerequisite of the specificity of our luminescent probe. Its parameters evaluated as Michaelis-Menten description of enzymatic kinetics are similar to products published by other groups. Our research is focused on the fluorescence microscopy analyses of biologically active molecules, such as proteolytic active caspases, playing important roles in cell signaling regulations in normal and diseased states. Consequently, they are attractive targets for clinical diagnosis and medical therapy. The ultimate goal of our work was to synthesize a new QD luminescent probe for a long-time quantitative monitoring of active caspase-3/7 distribution in apoptotic osteoblastic MC3T3-E1 cells treated with camptothecin. As a result of comparison, our synthetized luminescent probe provides longer imaging times of caspases than commercial products. The probe proved the stability of the luminescence signal inside cells for more than 14 days.

Microcavity- and Microlaser-Based Optical Barcoding: A Review of Encoding Techniques and Applications

Optical microbarcodes have recently received a great deal of interest because of their suitability for a wide range of applications, such as multiplexed assays, cell tagging and tracking, anticounterfeiting, and product labeling. Spectral barcodes are especially promising because they are robust and have a simple readout. In addition, microcavity- and microlaser-based barcodes have very narrow spectra and therefore have the potential to generate millions of unique barcodes. This review begins with a discussion of the different types of barcodes and then focuses specifically on microcavity-based barcodes. While almost any kind of optical microcavity can be used for barcoding, currently whispering-gallery microcavities (in the form of spheres and disks), nanowire lasers, Fabry-Pérot lasers, random lasers, and distributed feedback lasers are the most frequently employed for this purpose. In microcavity-based barcodes, the information is encoded in various ways in the properties of the emitted light, most frequently in the spectrum. The barcode is dependent on the properties of the microcavity, such as the size, shape, and the gain materials. Various applications of these barcodes, including cell tracking, anticounterfeiting, and product labeling are described. Finally, the future prospects for microcavity- and microlaser-based barcodes are discussed.

Surface-engineered nanoparticles in cancer immune response and immunotherapy: Current status and future prospects

Cancer immunotherapy is a therapeutic strategy to inhibit tumor growth and metastasis by intervening in the immune response process. Strategies applied to cancer immunotherapy mainly include blocking immune checkpoints, adoptive transfer of engineered immune cells, cytokine therapy, cancer vaccines, and oncolytic virus infection. However, many factors, such as off-target side effects, immunosuppressive cell infiltration and/or upregulation of immune checkpoint expression, cancer cell heterogeneity, and lack of antigen presentation, affect the therapeutic effect of immunotherapy on cancer. To improve the efficacy of targeted immunotherapy and reduce off-target effects, over the past two decades, nanoparticle delivery platforms have been increasingly used in tumor immunotherapy. However, nanoparticles are still subject to biological barriers and biodistribution challenges, which limit their overall clinical potential. This has prompted a series of engineered nanoparticles to overcome specific obstacles and transfer the accumulation of payloads to tumor-infiltrating immune cells. In recent years, new techniques and chemical methods have been employed to modify or functionalize the surfaces of nanoparticles. This review discusses the recent progress of surface-engineered nanoparticles in inducing tumor immune responses and immunotherapy, as well as future directions for the development of next-generation nanomedicines.

Rapid-format recombinant antibody-based methods for the diagnosis of Clostridioides difficile infection: Recent advances and perspectives

Clostridioides difficile, the most common cause of nosocomial diarrhea, has been continuously reported as a worldwide problem in healthcare settings. Additionally, the emergence of hypervirulent strains of C. difficile has always been a critical concern and led to continuous efforts to develop more accurate diagnostic methods for detection of this recalcitrant pathogen. Currently, the diagnosis of C. difficile infection (CDI) is based on clinical manifestations and laboratory tests for detecting the bacterium and/or its toxins, which exhibit varied sensitivity and specificity. In this regard, development of rapid diagnostic techniques based on antibodies has demonstrated promising results in both research and clinical environments. Recently, application of recombinant antibody (rAb) technologies like phage display has provided a faster and more cost-effective approach for antibody production. The application of rAbs for developing ultrasensitive diagnostic tools ranging from immunoassays to immunosensors, has allowed the researchers to introduce new platforms with high sensitivity and specificity. Additionally, DNA encoding antibodies are directly accessible in these approaches, which enables the application of antibody engineering to increase their sensitivity and specificity. Here, we review the latest studies about the antibody-based ultrasensitive diagnostic platforms for detection of C. difficile bacteria, with an emphasis on rAb technologies.

Engineering nanosystems to overcome barriers to cancer diagnosis and treatment

Over the past two decades, multidisciplinary investigations into the development of nanoparticles for medical applications have continually increased. However, nanoparticles are still subject to biological barriers and biodistribution challenges, which limit their overall clinical potential. This has motivated the implementation of innovational modifications to a range of nanoparticle formulations designed for cancer imaging and/or cancer treatment to overcome specific barriers and shift the accumulation of payloads toward the diseased tissues. In recent years, novel technological and chemical approaches have been employed to modify or functionalize the surface of nanoparticles or manipulate the characteristics of nanoparticles. Combining these approaches with the identification of critical biomarkers provides new strategies for enhancing nanoparticle specificity for both cancer diagnostic and therapeutic applications. This review discusses the most recent advances in the design and engineering of nanoparticles as well as future directions for developing the next generation of nanomedicines.

Renal cell carcinoma management: A step to nano-chemoprevention

Renal cell carcinoma (RCC) is one of the most common kidney cancers, responsible for nearly 90 % of all renal malignancies. Despite the availability of many treatment strategies, RCC still remains to be an incurable disease due to its resistivity towards conventional therapies. Nanotechnology is an emerging field of science that offers newer possibilities in therapeutics including cancer medicine, specifically by targeted delivery of anticancer drugs. Several phytochemicals are known for their anti-cancer properties and have been regarded as chemopreventive agents. However, the hydrophobic nature of many phytochemicals decreases its bioavailability and distribution, thus showing limited therapeutic effect. Application of nanotechnology to enhance chemoprevention is an effective strategy to increase the bioavailability of phytochemicals and thereby its therapeutic efficacy. The present review focuses on the utility of nanotechnology in RCC treatment and chemopreventive agents of RCC. We have also visualized the future prospects of nanomolecules in the prevention and cure of RCC.

Nanotechnology Advances in the Detection and Treatment of Cancer: An Overview

Over the last few years, progress has been made across the nanomedicine landscape, in particular, the invention of contemporary nanostructures for cancer diagnosis and overcoming complexities in the clinical treatment of cancerous tissues. Thanks to their small diameter and large surface-to-volume proportions, nanomaterials have special physicochemical properties that empower them to bind, absorb and transport high-efficiency substances, such as small molecular drugs, DNA, proteins, RNAs, and probes. They also have excellent durability, high carrier potential, the ability to integrate both hydrophobic and hydrophilic compounds, and compatibility with various transport routes, making them especially appealing over a wide range of oncology fields. This is also due to their configurable scale, structure, and surface properties. This review paper discusses how nanostructures can function as therapeutic vectors to enhance the therapeutic value of molecules; how nanomaterials can be used as medicinal products in gene therapy, photodynamics, and thermal treatment; and finally, the application of nanomaterials in the form of molecular imaging agents to diagnose and map tumor growth.

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.

Advances in quantum dots as diagnostic tools

Quantum dots (QDs) are crystalline inorganic semiconductor nanoparticles a few nanometers in size that possess unique optical electronic properties vs those of larger materials. For example, QDs usually exhibit a strong and long-lived photoluminescence emission, a feature dependent on size, shape and composition. These special optoelectronic properties make them a promising alternative to conventional luminescent dyes as optical labels in biomedical applications including biomarker quantification, biomolecule targeting and molecular imaging. A key parameter for use of QDs is to functionalize their surface with suitable (bio)molecules to provide stability in aqueous solutions and efficient and selective tagging biomolecules of interest. Researchers have successfully developed biocompatible QDs and have linked them to various biomolecule recognition elements, i.e., antibodies, proteins, DNA, etc. In this chapter, QD synthesis and characterization strategies are reviewed as well as the development of nanoplatforms for luminescent biosensing and imaging-guided targeting. Relevant biomedical applications are highlighted with a particular focus on recent progress in ultrasensitive detection of clinical biomarkers. Finally, key future research goals to functionalize QDs as diagnostic tools are explored.

The Application of Nanoparticles in Diagnosis and Treatment of Kidney Diseases

Nanomedicine is currently showing great promise for new methods of diagnosing and treating many diseases, particularly in kidney disease and transplantation. The unique properties of nanoparticles arise from the diversity of size effects, used to design targeted nanoparticles for specific cells or tissues, taking renal clearance and tubular secretion mechanisms into account. The design of surface particles on nanoparticles offers a wide range of possibilities, among which antibodies play an important role. Nanoparticles find applications in encapsulated drug delivery systems containing immunosuppressants and other drugs, in imaging, gene therapies and many other branches of medicine. They have the potential to revolutionize kidney transplantation by reducing and preventing ischemia-reperfusion injury, more efficiently delivering drugs to the graft site while avoiding systemic effects, accurately localizing and visualising the diseased site and enabling continuous monitoring of graft function. So far, there are known nanoparticles with no toxic effects on human tissue, although further studies are still needed to confirm their safety.

The State of the Art of Theranostic Nanomaterials for Lung, Breast, and Prostate Cancers

The synthesis and engineering of nanomaterials offer more robust systems for the treatment of cancer, with technologies that combine therapy with imaging diagnostic tools in the so-called nanotheranostics. Among the most studied systems, there are quantum dots, liposomes, polymeric nanoparticles, inorganic nanoparticles, magnetic nanoparticles, dendrimers, and gold nanoparticles. Most of the advantages of nanomaterials over the classic anticancer therapies come from their optimal size, which prevents the elimination by the kidneys and enhances their permeation in the tumor due to the abnormal blood vessels present in cancer tissues. Furthermore, the drug delivery and the contrast efficiency for imaging are enhanced, especially due to the increased surface area and the selective accumulation in the desired tissues. This property leads to the reduced drug dose necessary to exert the desired effect and for a longer action within the tumor. Finally, they are made so that there is no degradation into toxic byproducts and have a lower immune response triggering. In this article, we intend to review and discuss the state-of-the-art regarding the use of nanomaterials as therapeutic and diagnostic tools for lung, breast, and prostate cancer, as they are among the most prevalent worldwide.

Quantum Dots Based Fluorescent Probe for the Selective Detection of Heavy Metal Ions

Heavy metal ions are one of the primary causes of environmental pollution. A marshal effect of heavy metal ions is a paramount ultimatum to humans, aquatic animals and other organisms present in nature. Multitude arrays of materials have been proclaimed for sensing of heavy metal ions and also many methodologies are applied for heavy metal ion sensing. Due to their toxicity and non-biodegradability, it is required to be perceived immediately prior to its manifestation of harmful effects. Quantum Dots (QDs) are zero-dimensional nanomaterial particles and owing to their distinctive optical and electronic properties, they are utilized as nanosensors. QDs have enriched fluorescence properties which includes broad excitation spectrum, narrow emission spectrum and photostability. QDs offer eclectic and sensitive detection of heavy metal ions due to presence of discrete capping agents and different functional groups present on the surface of the QDs. These capping layers and functional groups attune the sensing capability of the QDs, which leverages the interactions of QDs with various analytes by different mechanisms. This review, comprising of papers from 2011 to 2020,focuses on heavy metal ions sensing potential of various quantum dots and its applicability as a nanosensor for on field heavy metal ions detection in water. Quantum Dots (QDs) based Heavy Metal Detection.

Head and Neck Cancer Treatments from Chemotherapy to Magnetic Systems: Perspectives and Challenges

BACKGROUND

Cancer is one of the diseases causing society's fears as a stigma of death and pain. Head and Neck Squamous Cell Carcinoma (HNSCC) is a group of malignant neoplasms of different locations in this region of the human body. It is one of the leading causes of morbidity and mortality in Brazil, because these malignant neoplasias, in most cases, are diagnosed in late phases. Surgical excision, chemotherapy and radiotherapy encompass the forefront of antineoplastic therapy; however, the numerous side effects associated with these therapeutic modalities are well known. Some treatments present enough potential to help or replace conventional treatments, such as Magnetic Hyperthermia and Photodynamic Therapy. Such approaches require the development of new materials at the nanoscale, able to carry out the loading of their active components while presenting characteristics of biocompatibility mandatory for biomedical applications.

OBJECTIVE

This work aims to make a bibliographical review of HNSCC treatments. Recent techniques proven effective in other types of cancer were highlighted and raised discussion and reflections on current methods and possibilities of enhancing the treatment of HNSCC.

METHOD

The study was based on a bibliometric research between the years 2008 and 2019 using the following keywords: Cancer, Head and Neck Cancer, Chemotherapy, Radiotherapy, Photodynamic Therapy, and Hyperthermia.

RESULTS

A total of 5.151.725 articles were found, 3.712.670 about cancer, 175.470 on Head and Neck Cancer, 398.736 on Radiotherapy, 760.497 on Chemotherapy, 53.830 on Hyperthermia, and 50.522 on Photodynamic Therapy.

CONCLUSION

The analysis shows that there is still much room for expanding research, especially for alternative therapies since most of the studies still focus on conventional treatments and on the quest to overcome their side effects. The scientific community needs to keep looking for more effective therapies generating fewer side effects for the patient. Currently, the so-called alternative therapies are being used in combination with the conventional ones, but the association of these new therapies shows great potential, in other types of cancer, to improve the treatment efficacy.

An enzyme-mediated controlled release system for curcumin based on cyclodextrin/cyclodextrin degrading enzyme

In this study, an enzyme-triggered system based on β-cyclodextrin (β-CD) has been developed to achieve controlled release of hydrophobic drugs in the presence of maltogenic amylase (MAase). The inclusion complex formation of curcumin (CUR), as a model anticancer compound, with β-CD was characterized by fluorescence and Fourier transform infrared (FTIR) spectroscopy. CUR was loaded into β-CD with an encapsulation efficiency of approximately 30 %. The in vitro profiles of CUR release from β-CD showed that 100 % of the drug was released after one hour incubation in the presence of MAase with cyclodextrin degrading activity. Fluorescence microscopy images indicate a significantly greater cellular uptake of CUR using β-CD-CUR/MAase system compared to β-CD-CUR inclusion complex without MAase. The β-CD-CUR/MAase system exhibited lower IC₅₀ values and greater anti-proliferative effects in comparison with free CUR and β-CD-CUR in MCF-7 and Huh-7 cancer cells. The results from fluorescence microscopy and flow cytometric assay using the acridine orange/ethidium bromide and Annexin V-PE/7-AAD staining suggest that the β-CD-CUR/MAase system exhibited higher cytotoxic and apoptotic effects on cancer cells compared to other formulations. This triggered release of CUR in the presence of MAase is owing to the β-CD degradation by MAase resulting ring opening and chain scission in β-CD. We demonstrate that this enzyme-mediated controlled release system has a potential application for controlled release of poorly water-soluble drugs or hydrophobic compounds such as CUR.

Superior Properties and Biomedical Applications of Microorganism-Derived Fluorescent Quantum Dots

Quantum dots (QDs) are fluorescent nanocrystals with superb photo-physical properties. Applications of QDs have been exponentially increased during the past decade. They can be employed in several disciplines, including biological, optical, biomedical, engineering, and energy applications. This review highlights the structural composition and distinctive features of QDs, such as resistance to photo-bleaching, wide range of excitations, and size-dependent light emission features. Physical and chemical preparation of QDs have prominent downsides, including high costs, regeneration of hazardous byproducts, and use of external noxious chemicals for capping and stabilization purposes. To eliminate the demerits of these methods, an emphasis on the latest progress of microbial synthesis of QDs by bacteria, yeast, and fungi is introduced. Some of the biomedical applications of QDs are overviewed as well, such as tumor and microRNA detection, drug delivery, photodynamic therapy, and microbial labeling. Challenges facing the microbial fabrication of QDs are discussed with the future prospects to fully maximize the yield of QDs by elucidating the key enzymes intermediating the nucleation and growth of QDs. Exploration of the distribution and mode of action of QDs is required to promote their biomedical applications.

Silanized Luminescent Quantum Dots for the Simultaneous Multicolor Lateral Flow Immunoassay of Two Mycotoxins

A critical point for the successful development of a fluorescent quantum dot (QD)-based immunoassay is maintaining the high fluorescence quantum yield of QDs during hydrophilization and bioconjugation. In this paper, we carefully designed CdSe/CdS and CdSe/CdS/ZnS core-shell heterostructures and extended them with silica coating of different surface composition allowing preservation of fluorescence quantum yield as high as 70% in aqueous media. The silanized QDs containing epoxy and carboxy surface groups were bioconjugated with monoclonal antibodies. The synthesized fluorescent conjugates were used in a multicolor lateral flow immunoassay for simultaneous determination of two mycotoxins. Zearalenone and deoxynivalenol were chosen as a proof of concept. Cutoff levels for the zearalenone and deoxynivalenol detection were adjusted to be at 40 and 400 μg kg^-1, respectively, complying with the European Commission regulation. Validation of the developed test was performed by analysis of 34 naturally contaminated maize and wheat samples; as a confirmatory method, LC-MS/MS was used.

The Biological Activity Research of the Nano-Drugs Based on 5-Fluorouracil-Modified Quantum Dots

PURPOSE

Over the past decades, quantum dots (QDs) have shown the broad application in diverse fields, especially in intracellular probing and drug delivery, due to their high fluorescence intensity, long fluorescence lifetime, strong light-resistant bleaching ability, and strong light stability. Therefore, we explore a kind of therapeutic potential against cancer with fluorescent imaging.

METHODS

In the current study, a new type of QDs (QDs@L-Cys-TAEA-5-FUA) capped with L-cysteine (L-Cys) and tris(2-aminoethyl)amine (TAEA) ligands, and conjugated with 5-fluorouracil-1-acetic acid (5-FUA) has been synthesized. Ligands were characterized by electrospray ionization mass spectrometry and H-nuclear magnetic resonance (1H NMR) spectroscopy. The modified QDs were characterized by transmission electron microscopy, ultraviolet and visible spectrophotometry (UV-Vis), and fluorescence microscopy. And the biological activity of modified QDs was explored by using MTT assay with HeLa, SMMC-7721 HepG2, and QSG-7701 cells. The fluorescence imaging of modified QDs was obtained by fluorescence microscope.

RESULTS

The modified QDs are of controllable sizes in the range of 4-5 nm and they possess strong optical emission properties. UV-Vis and fluorescence spectra demonstrated that the L-Cys-TAEA-5-FUA was successfully incorporated into QD nanoparticles. The MTT results demonstrated that L-Cys-TAEA-5-FUA modified QDs could efficiently inhibit the proliferation of cancer cells as compared to the normal cells, illustrating their antitumor efficacy. The mechanistic studies revealed that the effective internalization of modified QDs inside cancer cells could inhibit their proliferation, through excessive production of intracellular reactive oxygen species, leading to apoptosis process.

CONCLUSION

The present study suggests that modified QDs can enter cells efficiently and could be employed as therapeutic agents for the treatment of various types of cancers with fluorescent imaging.

A Multiparametric Evaluation of Quantum Dot Size and Surface-Grafted Peptide Density on Cellular Uptake and Cytotoxicity

Despite the progress in nanotechnology for biomedical applications, great efforts are still being employed in optimizing nanoparticle (NP) design parameters to improve functionality and minimize bionanotoxicity. In this study, we developed CdSe/CdS/ZnS core/shell/shell quantum dots (QDs) that are compact ligand-coated and surface-functionalized with an HIV-1-derived TAT cell-penetrating peptide (CPP) analog to improve both biocompatibility and cellular uptake. Multiparametric studies were performed in different mammalian and murine cell lines to compare the effects of varying QD size and number of surface CPPs on cellular uptake, viability, generation of reactive oxygen species, mitochondrial health, cell area, and autophagy. Our results showed that the number of cell-associated NPs and their respective toxicity are higher for the larger QDs. Meanwhile, increasing the number of surface CPPs also enhanced cellular uptake and induced cytotoxicity through the generation of mitoROS and autophagy. Thus, here we report the optimal size and surface CPP combinations for improved QD cellular uptake.

Quantum Dot Bioconjugates for Diagnostic Applications

Quantum dots (QDs) are a special type of engineered nanomaterials with outstanding optoelectronic properties that make them as a very promising alternative to conventional luminescent dyes in biomedical applications, including biomolecule (BM) targeting, luminescence imaging and drug delivery. A key parameter to ensure successful biomedical applications of QDs is the appropriate surface modification, i.e. the surface of the nanomaterials should be modified with the appropriate functional groups to ensure stability in aqueous solutions and it should be conjugated with recognition elements capable of ensuring an efficient tagging of the BMs of interest. In this review we summarize the most relevant strategies used for surface modification of QDs and for their conjugation to BMs in preparation of their application in nanoplatforms for luminescent BM sensing and imaging-guided targeting. The applications of conjugations of photoluminescent QDs with different BMs in both in vitro and in vivo chemical sensing, immunoassays or luminescence imaging are reviewed. Recent progress in the application of functionalized QDs in ultrasensitive detection in bioanalysis, diagnostics and imaging strategies are reported. Finally, some key future research goals in the progress of bioconjugation of QDs for diagnosis are identified, including novel synthetic approaches, the need for exhaustive characterization of bioconjugates and the design of signal amplification schemes.

Nanoparticle-Mediated Visualization and Control of Cellular Membrane Potential: Strategies, Progress, and Remaining Issues

The interfacing of nanoparticle (NP) materials with cells, tissues, and organisms for a range of applications including imaging, sensing, and drug delivery continues at a rampant pace. An emerging theme in this area is the use of NPs and nanostructured surfaces for the imaging and/or control of cellular membrane potential (MP). Given the important role that MP plays in cellular biology, both in normal physiology and in disease, new materials and methods are continually being developed to probe the activity of electrically excitable cells such as neurons and muscle cells. In this Review, we highlight the current state of the art for both the visualization and control of MP using traditional materials and techniques, discuss the advantageous features of NPs for performing these functions, and present recent examples from the literature of how NP materials have been implemented for the visualization and control of the activity of electrically excitable cells. We conclude with a forward-looking perspective of how we expect to see this field progress in the near term and further into the future.

Fluorescence Intensity Enhancement of Green Carbon Dots: Synthesis, Characterization and Cell Imaging

The hydrothermal treatment of green carbon dots (CDs) is an appropriate fluorescent probe synthesis method. CDs are exploited as biological staining agents, especially for cellular detection and imaging. The nitrogen-doped green carbon dots (N-CDs) formation can improve the fluorescence intensity property in a one-step process. Here, we report two N-CDs from lemon and tomato extraction in the presence of hydroxylamine. Lemon and tomato N-CDs showed the blue fluorescence under ultraviolet radiation of about 360 nm. The characterization of CDs and N-CDs showed the presence of N-H and C-N bonds which enhanced the fluorescence efficiency. The mean size of lemon and tomato N-CDs were about 2 and 3 nm with an increased quantum yield (QY) of 5% and 3.38%, respectively. The CDs and N-CDs cytotoxicity assay exhibited high cell viability approximately 85% and 73%, respectively. N-CDs show superior fluorescent intensity in different solvents and significant stability under long-time UV irradiation, different PH and high ionic strength. Our results indicated that the use of N-CDs in cell imaging can lead to fluorescence intensity enhancement as well as proper biocompatibility. Therefore, the safe and high fluorescence intensity of green N-CDs can be utilized for fluorescent probes in biolabeling and bioimaging applications.

A Lysosome-Targetable Fluorescence Probe Based on L-Cysteine-Polyamine-Morpholine-Modified Quantum Dots for Imaging in Living Cells

PURPOSE

Quantum dots (QDs) are used as fluorescent probes due to their high fluorescence intensity, longevity of fluorescence, strong light-resistant bleaching ability and high light stability. Therefore, we explore a more precise probe that can target an organelle.

METHODS

In the current study, a new class of fluorescence probes were developed using QDs capped with 4 different L-cysteine-polyamine-morpholine linked by mercapto groups. Ligands were characterised by Electrospray ionization mass spectrometry (ESI-MS), H-Nuclear Magnetic Resonance (1H NMR) spectroscopy, and 13C NMR spectroscopy. Modified QDs were characterized by Transmission Electron Microscope (TEM), Ultraviolet and visible spectrophotometry (UV-Vis), and fluorescence microscopy. And the biological activity of modified QDs was explored by using MTT assay with HeLa, SMMC-7721 and HepG2 cells. The fluorescence imaging of modified QDs was obtained by confocal laser scanning fluorescence microscopy (CLSM).

RESULTS

Synthesized QDs ranged between 4 to 5 nm and had strong optical emission properties. UV-Vis and fluorescence spectra demonstrated that the cysteine-polyamine-morpholine were successfully incorporated into QD nanoparticles. The MTT results demonstrated that modified QDs had lesser cytotoxicity when compared to unmodified QDs. In addition, modified QDs had strong fluorescence intensity in HeLa cells and targeted lysosomes of HeLa cells.

CONCLUSION

This study demonstrates the modified QDs efficiently entered cells and could be used as a potential lysosome-targeting fluorescent probe.

Polyamine-Modified Gold Nanoparticles Readily Adsorb on Cell Membranes for Bioimaging

The surface modification of nanoparticles (NPs) can enhance cellular and intracellular targeting. A new type of polyamine-modified gold NPs (AuNPs) are designed and synthesized, which can be selectively absorbed onto the cell membrane. AuNPs with an average diameter of 4.0 nm were prepared and modified with polyamine (R-4C) through amidation. In order to detect the distribution of NPs within cells by fluorescence imaging, AuNP@MPA-R-4C was functionalized with fluorescein isothiocyanate (FITC). The fluorescence-labled NPs AuNP@MPA-R-4C-FITC demonstrated minimal cytotoxicity in several cell lines. Both confocal laser scanning microscopy and transmission electron microscopy demonstrated that AuNP@MPA-R-4C-FITC was distributed on the cell membrane. Compared with the free organic dye, the modified AuNPs showed significantly increased accumulation on the cell membrane after treatment for only 10 min. These results suggested that AuNP@MPA-R-4C-FITC can be used as a bioprobe targeting the cell membrane for various biological applications.

Chemical Synthesis and Characterization of Poly(poly(ethylene glycol) methacrylate)-Grafted CdTe Nanocrystals via RAFT Polymerization for Covalent Immobilization of Adenosine

This paper describes the functionalization of poly(poly(ethylene glycol) methacrylate) (PPEGMA)-grafted CdTe (PPEGMA-g-CdTe) quantum dots (QDs) via surface-initiated reversible addition–fragmentation chain transfer (SI-RAFT) polymerization for immobilization of adenosine. Initially, the hydroxyl-coated CdTe QDs, synthesized using 2-mercaptoethanol (ME) as a capping agent, were coupled with a RAFT agent, S-benzyl S′-trimethoxysilylpropyltrithiocarbonate (BTPT), through a condensation reaction. Then, 2,2′-azobisisobutyronitrile (AIBN) was used to successfully initiate in situ RAFT polymerization to generate PPEGMA-g-CdTe nanocomposites. Adenosine-above-PPEGMA-grafted CdTe (Ado-i-PPEGMA-g-CdTe) hybrids were formed by the polymer shell, which had successfully undergone bioconjugation and postfunctionalization by adenosine (as a nucleoside). Fourier transform infrared (FT-IR) spectrophotometry, energy-dispersive X-ray (EDX) spectroscopy, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy results indicated that a robust covalent bond was created between the organic PPEGMA part, cadmium telluride (CdTe) QDs, and the adenosine conjugate. The optical properties of the PPEGMA-g-CdTe and Ado-i-PPEGMA-g-CdTe hybrids were investigated by photoluminescence (PL) spectroscopy, and the results suggest that they have a great potential for application as optimal materials in biomedicine.

Biocompatible quantum dot-antibody conjugate for cell imaging, targeting and fluorometric immunoassay: crosslinking, characterization and applications

Quantum dots (QDs) are important fluorescent probes that offer great promise for bio-imaging research due to their superior optical properties. However, QDs for live cell imaging and the tracking of cells need more investigation to simplify processing procedures, improving labeling efficiency, and reducing chronic toxicity. In this study, QDs were functionalized with bovine serum albumin (BSA) via a chemical linker. Anti-human immunoglobulin antibodies were oxidized by sodium periodate to create reactive aldehyde groups for a spontaneous reaction with the amine groups of BSA-modified QDs. An antibody-labeled QD bioconjugate was characterized using agarose gel electrophoresis, dynamic light scattering, and zeta potential. Using fluorescence spectroscopy, we found that the fluorescence of QDs was retained after multiple conjugation steps. The cell-labeling function of the QD bioconjugate was confirmed using an image analyzer and confocal microscopy. The QD bioconjugate specifically targeted human immunoglobulin on the membrane surface of recombinant cells. In addition, the QD bioconjugate applied in fluorometric immunoassay was effective for the quantitative analysis of human immunoglobulin in an enzyme-linked immunosorbent assay. The developed QD bioconjugate may offer a promising platform to develop biocompatible tools to label cells and quantify antibodies in the immunoassay.

A layer-by-layer covalent strategy is developed including the modification of QDs using BSA as a stabilizing agent and then anti-human immunoglobulin antibody as a targeting moiety.

Advantages and Limitations of Current Techniques for Analyzing the Biodistribution of Nanoparticles

Nanomedicines are typically submicrometer-sized carrier materials (nanoparticles) encapsulating therapeutic and/or imaging compounds that are used for the prevention, diagnosis and treatment of diseases. They are increasingly being used to overcome biological barriers in the body to improve the way we deliver compounds to specific tissues and organs. Nanomedicine technology aims to improve the balance between the efficacy and the toxicity of therapeutic compounds. Nanoparticles, one of the key technologies of nanomedicine, can exhibit a combination of physical, chemical and biological characteristics that determine their in vivo behavior. A key component in the translational assessment of nanomedicines is determining the biodistribution of the nanoparticles following in vivo administration in animals and humans. There are a range of techniques available for evaluating nanoparticle biodistribution, including histology, electron microscopy, liquid scintillation counting (LSC), indirectly measuring drug concentrations, in vivo optical imaging, computed tomography (CT), magnetic resonance imaging (MRI), and nuclear medicine imaging. Each technique has its own advantages and limitations, as well as capabilities for assessing real-time, whole-organ and cellular accumulation. This review will address the principles and methodology of each technique and their advantages and limitations for evaluating in vivo biodistribution of nanoparticles.

Functionalization of stable fluorescent nanodiamonds towards reliable detection of biomarkers for Alzheimer's disease

Background

Stable and non-toxic fluorescent markers are gaining attention in molecular diagnostics as powerful tools for enabling long and reliable biological studies. Such markers should not only have a long half-life under several assay conditions showing no photo bleaching or blinking but also, they must allow for their conjugation or functionalization as a crucial step for numerous applications such as cellular tracking, biomarker detection and drug delivery.

Results

We report the functionalization of stable fluorescent markers based on nanodiamonds (NDs) with a bifunctional peptide. This peptide is made of a cell penetrating peptide and a six amino acids long β-sheet breaker peptide that is able to recognize amyloid β (Aβ) aggregates, a biomarker for the Alzheimer disease. Our results indicate that functionalized NDs (fNDs) are not cytotoxic and can be internalized by the cells. The fNDs allow ultrasensitive detection (at picomolar concentrations of NDs) of in vitro amyloid fibrils and amyloid aggregates in AD mice brains.

Conclusions

The fluorescence of functionalized NDs is more stable than that of fluorescent markers commonly used to stain Aβ aggregates such as Thioflavin T. These results pave the way for performing ultrasensitive and reliable detection of Aβ aggregates involved in the pathogenesis of the Alzheimer disease.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0385-7) contains supplementary material, which is available to authorized users.

Interface formation during silica encapsulation of colloidal CdSe/CdS quantum dots observed by in situ Raman spectroscopy

We investigate the encapsulation of CdSe/CdS quantum dots (QDs) in a silica shell by in situ Raman spectroscopy and find a distinct shift of the CdS Raman signal during the first hours of the synthesis. This shift does not depend on the final silica shell thickness but on the properties of the initial core-shell QD. We find a correlation between the Raman shift rate and the speed of the silica formation and attribute this to the changing configuration of the outermost layers of the QD shell, where an interface to the newly formed silica is created. This dependence of Raman shift rate on the speed of silica formation process will give rise to many possible studies concerning the growth mechanism in the water-in-oil microemulsion, rendering in situ Raman a valuable instrument in monitoring this type of reaction.

Quantum dot-decorated semiconductor micro- and nanoparticles: A review of their synthesis, characterization and application in photocatalysis

Quantum dot (QD)-decorated semiconductor micro- and nanoparticles are a new class of functional nanomaterials that have attracted considerable interest for their unique structural, optical and electronic properties that result from the large surface-to-volume ratio and the quantum confinement effect. In addition, because of QDs' excellent light-harvesting capacity, unique photoinduced electron transfer, and up-conversion behaviour, semiconductor nanoparticles decorated with quantum dots have been used widely in photocatalytic applications for the degradation of organic pollutants in both the gas and aqueous phases. This review is a comprehensive overview of the recent progress in synthesis methods for quantum dots and quantum dot-decorated semiconductor composites with an emphasis on their composition, morphology and optical behaviour. Furthermore, various approaches used for the preparation of QD-based composites are discussed in detail with respect to visible and UV light-induced photoactivity. Finally, an outlook on future development is proposed with the goal of overcoming challenges and stimulating further research into this promising field.

Lysyl oxidase activates cancer stromal cells and promotes gastric cancer progression: quantum dot-based identification of biomarkers in cancer stromal cells

Purpose

Semiconductor quantum dots (QDs) are a promising alternative to organic fluorescent dyes for multiplexed molecular imaging of cancer stroma, which have great advantages in holistically analyzing the complex interactions among cancer stromal components in situ.

Patients and methods

A QD probe-based multiplexed spectral molecular imaging method was established for simultaneous imaging. Three tissue microarrays (TMAs) including 184 gastric cancer (GC) tissues were constructed for the study. Multispectral analyses were performed for quantifying stromal biomarkers, such as lysyl oxidase (LOX). The stromal status including infiltrating of immune cells (high density of macrophages), angiogenesis (high density of microvessel density [MVD], low neovessel maturation) and extracellular matrix (ECM) remodeling (low density of type IV collagen, intense expression of matrix metalloproteinase 9 [MMP-9]) was evaluated.

Results

This study compared the imaging features of the QD probe-based single molecular imaging method, immunohistochemistry, and organic dye-based immunofluorescent methods, and showed the advantages of the QD probe-based multiple molecular imaging method for simultaneously visualizing complex components of cancer stroma. The risk of macrophages in high density, high MVD, low neomicrovessel maturation, MMP-9 expression and low type IV collagen was significantly increased for the expression of LOX. With the advantages of the established QD probe-based multiplexed molecular imaging method, the spatial relationship between LOX and stromal essential events could be simultaneously evaluated histologically. Stromal activation was defined and then evaluated. Survival analysis showed that the stromal activation was correlated with overall survival and disease-free survival (P<0.001 for all). The expression of LOX was significantly increased in the intense activation subgroup (P<0.001).

Conclusion

Quantifying assessment of the stroma indicates that the LOX may be a stromal marker for GC and stromal activation, which is not only responsible for the ECM remodeling morphologically, but also for the formation of invasive properties and recurrence. These results support the possibility to integrate morphological and molecular biomarker information for cancer research by the biomedical application of QDs.

Quantum-dot nanoprobes and AOTF based cross talk eliminated six color imaging of biomolecules in cellular system

Primary cell cultures mimic the physiology and genetic makeup of in-vivo tissue of origin, nonetheless, a complication in the derivation and propagation of primary cell culture limits its use in biological research. However, in-vitro models using primary cells might be a complement model to mimic in vivo response. But, conventional techniques such as western blot and PCR employed to study the expression and activation of proteins requires a large number of cells, hence repeated establishment and maintenance of primary culture are unavoidable. Quantum dot (Q-dot) and acousto-optic tunable filters (AOTF) based multiplex imaging system is a viable alternative choice to evaluate multiple signaling molecules by using a small number of cells. Q-dots have broad excitation and narrow emission spectra, which allows to simultaneously excite multiple Q-dots by using single excitation wavelength. The use of AOTF in the fluorescence detection system enables to scan the fluorescence emission intensity of a Q-dot at their central wavelength, this phenomenon effectively avoids spectral overlap among the neighboring Q-dots. When Q-dots are conjugated with antibodies it acts as effective sensing probes. To validate this, the expression pattern of p-JNK-1, p-GSK3β, p-IRS1ser, p-IRS1tyr, p-FOXO1, and PPAR-γ, involved in the insulin resistance were concurrently monitored in adipocyte and HepG2 co-cell culture model. The observed results clearly indicate that PPAR-γ is the critical component in the development of insulin resistance. Moreover, the results proved that developed Q-dot based AOTF imaging methodology is a sensible choice to concurrently monitor multiple signaling molecules with limited cell population.

Coating of Quantum Dots strongly defines their effect on lysosomal health and autophagy

In the last decade the interest in autophagy got an incredible boost and the phenomenon quickly turned into an extensive research field. Interestingly, dysfunction of this cytoplasmic clearance system has been proposed to lie at the root of multiple diseases including cancer. We therefore consider it crucial from a toxicological point of view to investigate if nanomaterials that are developed for biomedical applications interfere with this cellular process. Here, we study the highly promising 'gradient alloyed' Quantum Dots (QDs) that differ from conventional ones by their gradient core composition which allows for better fluorescent properties. We carefully examined the toxicity of two identical gradient alloyed QDs, differing only in their surface coatings, namely 3-mercaptopropionic (MPA) acid and polyethylene glycol (PEG). Next to more conventional toxicological endpoints like cytotoxicity and oxidative stress, we examined the influence of these QDs on the autophagy pathway. Our study shows that the cellular effects induced by QDs on HeLa cells were strongly dictated by the surface coat of the otherwise identical particles. MPA-coated QDs proved to be highly biocompatible as a result of lysosomal activation and ROS reduction, two cellular responses that help the cell to cope with nanomaterial-induced stress. In contrast, PEGylated QDs were significantly more toxic due to increased ROS production and lysosomal impairment. This impairment next results in autophagy dysfunction which likely adds to their toxic effects. Taken together, our study shows that coating QDs with MPA is a better strategy than PEGylation for long term cell tracking with minimal cytotoxicity.

STATEMENT OF SIGNIFICANCE

Gradient alloyed Quantum Dots (GA-QDs) are highly promising nanomaterials for biomedical imaging seeing they exhibit supremely fluorescent properties over conventional QDs. The translation of these novel QDs to the clinic requires a detailed toxicological examination, though the data on this is very limited. We therefore applied a systematic approach to examine the toxicity of GA-QDs coated with two commonly applied surface ligands, this while focusing on the autophagy pathway. The impact of QDs on this pathway is of importance since it has been connected with various diseases, including cancer. Our data accentuates that the coating defines the impact on autophagy and therefore the toxicity induced by QDs on cells: while MPA coated QDs were highly biocompatible, PEGylated QDs were toxic.

Synthesis and Cell Imaging of a Near-Infrared Fluorescent Magnetic "CdHgTe-Dextran-Magnetic Layered Double Hydroxide-Fluorouracil" Composite

In this article, a water-soluble near-infrared quantum dots of CdHgTe were prepared and subsequently combined with the drug delivery system "dextran-magnetic layered double hydroxide-fluorouracil" (DMF) to build a new nanostructure platform in form of CdHgTe@DMF, in which the fluorescent probe function of quantum dots and the magnetic targeting transport and slow-release curative effect of DMF were blended availably together. The luminescent property particle size, and internal structure of the composite were characterized using fluorescence spectrophotometer, ultraviolet spectrophotometer, laser particle size distribution, TEM, X-ray diffraction, and Fourier transform infrared. The experimental study on fluorescent tags effect and magnetic targeting performance of the multifunctional platform were performed by fluorescent confocal imaging. The results showed that the CdHgTe could be grafted successfully onto the surface of DMF by electrostatic coupling. The CdHgTe@DMF composite showed super-paramagnetic and photoluminescence property in the near-infrared wavelength range of 575-780 nm. Compared with CdHgTe, the CdHgTe@DMF composite could significantly improve the cell imaging effect, the label intensity increased with the magnetic field intensity, and obeyed the linear relationship Dmean = 1.758 + 0.0075M under the conditions of magnetic field interference. It can be implied that the CdHgTe@DMF may be an effective multifunction tool applying to optical bioimaging and magnetic targeted therapy.

General Bioluminescence Resonance Energy Transfer Homogeneous Immunoassay for Small Molecules Based on Quantum Dots

Here, we describe a general bioluminescence resonance energy transfer (BRET) homogeneous immunoassay based on quantum dots (QDs) as the acceptor and Renilla luciferase (Rluc) as the donor (QD-BRET) for the determination of small molecules. The ratio of the donor-acceptor that could produce energy transfer varied in the presence of different concentrations of free enrofloxacin (ENR), an important small molecule in food safety. The calculated Förster distance (R0) was 7.86 nm. Under optimized conditions, the half-maximal inhibitory concentration (IC50) for ENR was less than 1 ng/mL and the linear range covered 4 orders of magnitude (0.023 to 25.60 ng/mL). The cross-reactivities (CRs) of seven representative fluoroquinolones (FQs) were similar to the data obtained by an enzyme-linked immunosorbent assay (ELISA). The average intra- and interassay recoveries from spiked milk of were 79.8-118.0%, and the relative standard deviations (RSDs) were less than 10%, meeting the requirement of residue detection, which was a satisfactory result. Furthermore, we compared the influence of different luciferase substrates on the performance of the assay. Considering sensitivity and stability, coelenterazine-h was the most appropriate substrate. The results from this study will enable better-informed decisions on the choice of Rluc substrate for QD-BRET systems. For the future, the QD-BRET immunosensor could easily be extended to other small molecules and thus represents a versatile strategy in food safety, the environment, clinical diagnosis, and other fields.