Enhancement of Intracellular Delivery of CdTe Quantum Dots (QDs) to Living Cells by Tat Conjugation

Advancement and application of novel cell-penetrating peptide in cancer management

Cell-penetrating peptides (CPPs) are small amino acid sequences with the potential to enter cell membranes. Along with nucleic acids, large proteins, and other chemical compounds, they can deliver several bioactive cargos inside cells. Numerous CPPs have been extracted from natural or synthetic materials since the discovery of the first CPP. In the past few decades, a significant variety of studies have shown the potential of CPPs to cure different diseases. The low toxicity in peptide compared to other drug delivery carriers is a significant benefit of CPP-based therapy, in addition to the high efficacy brought about by swift and effective delivery. A significant tendency for intracellular DNA delivery may also be observed when nanoparticles and the cell penetration peptide are combined. CPPs are frequently used to increase intracellular absorption of nucleic acid, and other therapeutic agents inside the cell. Due to long-term side effects and possible toxicity, its implementation is restricted. The use of cell-permeating peptides is a commonly used technique to increase their intracellular absorption. Additionally, CPPs have lately been sought for application in vivo, following their success in cellular studies. This review will go through the numerous CPPs, the chemical modifications that improve their cellular uptake, the various means for getting them across cell membranes, and the biological activity they acquire after being conjugate with specific chemicals.

Cell-penetrating peptides (CPPs): an overview of applications for improving the potential of nanotherapeutics

In the field of nanotherapeutics, gaining cellular entry into the cytoplasm of the target cell continues to be an ultimate challenge. There are many physicochemical factors such as charge, size and molecular weight of the molecules and delivery vehicles, which restrict their cellular entry. Hence, to dodge such situations, a class of short peptides called cell-penetrating peptides (CPPs) was brought into use. CPPs can effectively interact with the cell membrane and can assist in achieving the desired intracellular entry. Such strategy is majorly employed in the field of cancer therapy and diagnosis, but now it is also used for other purposes such as evaluation of atherosclerotic plaques, determination of thrombin levels and HIV therapy. Thus, the current review expounds on each of these mentioned aspects. Further, the review briefly summarizes the basic know-how of CPPs, their utility as therapeutic molecules, their use in cancer therapy, tumor imaging and their assistance to nanocarriers in improving their membrane penetrability. The review also discusses the challenges faced with CPPs pertaining to their stability and also mentions the strategies to overcome them. Thus, in a nutshell, this review will assist in understanding how CPPs can present novel possibilities for resolving the conventional issues faced with the present-day nanotherapeutics.

Synergistic Enhancement of Antitumor Efficacy by PEGylated Multi-walled Carbon Nanotubes Modified with Cell-Penetrating Peptide TAT

In the present study, a cell-penetrating peptide, the transactivating transcriptional factor (TAT) domain from HIV, was linked to PEGylated multi-walled carbon nanotubes (MWCNTs) to develop a highly effective antitumor drug delivery system. FITC was conjugated on MWCNTs-polyethylene glycol (PEG) and MWCNTs-PEG-TAT to provide fluorescence signal for tracing the cellular uptake of the nanocarrier. After loaded with an anticancer agent, doxorubicin (DOX) via π - π stacking interaction, the physicochemical characteristics, release profile and biological evaluation of the obtained nano-sized drug carrier were investigated. The DOX loaded MWCNTs-PEG and MWCNTs-PEG-TAT drug carriers both displayed appropriate particle size, excellent stability, high drug loading, and pH-dependent drug release profile. Nevertheless, compared with DOX-MWCNTs-PEG, DOX-MWCNTs-PEG-TAT showed improved cell internalization, intracellular distribution and potentiated anticancer efficacy due to the TAT-mediated membrane translocation, endosomal escape and nuclear targeting. Furthermore, the therapeutic efficacy of DOX was not compromised after being conjugated with MWCNTs-PEG-TAT and the proposed nanocarrier was also confirmed to have a good biocompatibility. In conclusion, our results suggested that the unique combination of TAT and MWCNTs as a multifunctional drug delivery system might be a powerful tool for improved anticancer drug development.

Quantum dots: bright and versatile in vitro and in vivo fluorescence imaging biosensors

Colourful cells and tissues: semiconductor quantum dots and their versatile applications in multiplexed bioimaging research.

Cell-penetrating peptides for nanomedicine – how to choose the right peptide

More than two decades ago, a group of peptides, now known as cell-penetrating peptides, sparked the hope that the ultimate carrier molecules have been found. The high expectations for these peptides, which are reflected in their bold name, led to many disappointments due to the controversial results their utilization entailed and nowadays even their effectiveness has been called into question. In this review, we discuss the uptake mechanism and application of cell penetrating peptides as mediators for organelle specific delivery of nanocarriers, pointing out the possibilities as well as strategies of their successful utilization. Additionally, we provide an overview of the conjugation techniques usually employed for the attachment of cell penetrating peptides to quantum dots, as well as silver and gold nanoparticles, and we address the various aspects that need to be considered for the successful implementation of cell penetrating peptides for organelle-specific delivery of nanoparticles into cells.

Cell penetrating peptides: efficient vectors for delivery of nanoparticles, nanocarriers, therapeutic and diagnostic molecules

Efficient delivery of therapeutic and diagnostic molecules to the cells and tissues is a difficult challenge. The cellular membrane is very effective in its role as a selectively permeable barrier. While it is essential for cell survival and function, also presents a major barrier for intracellular delivery of cargo such as therapeutic and diagnostic agents. In recent years, cell-penetrating peptides (CPPs), that are relatively short cationic and/or amphipathic peptides, received great attention as efficient cellular delivery vectors due to their intrinsic ability to enter cells and mediate uptake of a wide range of macromolecular cargo such as plasmid DNA (pDNA), small interfering RNA (siRNAs), drugs, and nanoparticulate pharmaceutical carriers. This review discusses the various uptake mechanisms of these peptides. Furthermore, we discuss recent advances in the use of CPP for the efficient delivery of nanoparticles, nanocarriers, DNA, siRNA, and anticancer drugs to the cells. In addition, we have been highlighting new results for improving endosomal escape of CPP-cargo molecules. Finally, pH-responsive and activable CPPs for tumor-targeting therapy have been described.

Fluorescence lifetime imaging and FRET-induced intracellular redistribution of Tat-conjugated quantum dot nanoparticles through interaction with a phthalocyanine photosensitiser

The interaction of Tat-conjugated PEGylated CdSe/ZnS quantum dots (QD) with the amphiphilic disulfonated aluminium phthalocyanine photosensitiser is investigated in aqueous solution and in a human breast cancer cell line. In aqueous solution, the QDs and phthalocyanine form stable nanocomposites. Using steady-state and time-resolved fluorescence measurements combined with singlet oxygen detection, efficient Förster resonance energy transfer (FRET) is observed with the QDs acting as donors, and the phthalocyanine photosensitiser, which mediates production of singlet oxygen, as acceptors. In cells, the Tat-conjugated QDs localise in lysosomes and the QD fluorescence lifetimes are close to values observed in aqueous solution. Strong FRET-induced quenching of the QD lifetime is observed in cells incubated with the nanocomposites using fluorescence lifetime imaging microscopy (FLIM). Using excitation of the QDs at wavelengths where phthalocyanine absorption is negligible, FRET-induced release of QDs from endo/lysosomes is confirmed using confocal imaging and FLIM, which is attributed to photooxidative damage to the endo/lysosomal membranes mediated by the phthalocyanine acceptor.

Endocytic Trafficking of Nanoparticles Delivered by Cell-penetrating Peptides Comprised of Nona-arginine and a Penetration Accelerating Sequence

Cell-penetrating peptides (CPPs) can traverse cellular membranes and deliver biologically active molecules into cells. In this study, we demonstrate that CPPs comprised of nona-arginine (R9) and a penetration accelerating peptide sequence (Pas) that facilitates escape from endocytic lysosomes, denoted as PR9, greatly enhance the delivery of noncovalently associated quantum dots (QDs) into human A549 cells. Mechanistic studies, intracellular trafficking analysis and a functional gene assay reveal that endocytosis is the main route for intracellular delivery of PR9/QD complexes. Endocytic trafficking of PR9/QD complexes was monitored using both confocal and transmission electron microscopy (TEM). Zeta-potential and size analyses indicate the importance of electrostatic forces in the interaction of PR9/QD complexes with plasma membranes. Circular dichroism (CD) spectroscopy reveals that the secondary structural elements of PR9 have similar conformations in aqueous buffer at pH 7 and 5. This study of nontoxic PR9 provides a basis for the design of optimized cargo delivery that allows escape from endocytic vesicles.

Intracellular delivery of nanoparticles and DNAs by IR9 cell-penetrating peptides

Cell-penetrating peptides (CPPs) comprised of basic amino residues are able to cross cytoplasmic membranes and are able to deliver biologically active molecules inside cells. However, CPP/cargo entrapment in endosome limits biomedical utility as cargoes are destroyed in the acidic environment. In this study, we demonstrate protein transduction of a novel CPP comprised of an INF7 fusion peptide and nona-arginine (designated IR9). IR9 noncovalently interacts with quantum dots (QDs) and DNAs to form stable IR9/QD and IR9/DNA complexes which are capable of entering human A549 cells. Zeta-potentials were a better predictor of transduction efficiency than gel shift analysis, emphasizing the importance of electrostatic interactions of CPP/cargo complexes with plasma membranes. Mechanistic studies revealed that IR9, IR9/QD and IR9/DNA complexes may enter cells by endocytosis. Further, IR9, IR9/QD and IR9/DNA complexes were not cytotoxic at concentrations below 30, 5 and 20.1 µM, respectively. Without labor intensive production of fusion proteins from prokaryotes, these results indicate that IR9 could be a safe carrier of genes and drugs in biomedical applications.

Quantum dots: heralding a brighter future for clinical diagnostics

Quantum dots (QDs) are semiconductor nanocrystals that possess unique optical properties including broad-range excitation, size-tunable narrow emission spectra and high photostability, giving them considerable value in various biomedical applications. The size and composition of QDs can be varied to obtain the desired emission properties and make them amenable to simultaneous detection of multiple targets. Furthermore, numerous surface functionalizations can be used to adapt QDs to the needed application. The successful use of QDs has been reported in the areas of in vitro diagnostics and imaging. There is also potential for multimodal applications for simultaneous imaging. Toxicity issues are still a prime concern with regards to in vivo applications on account of the toxic constituents of QDs.

Quantum dots: synthesis, bioapplications, and toxicity

This review introduces quantum dots (QDs) and explores their properties, synthesis, applications, delivery systems in biology, and their toxicity. QDs are one of the first nanotechnologies to be integrated with the biological sciences and are widely anticipated to eventually find application in a number of commercial consumer and clinical products. They exhibit unique luminescence characteristics and electronic properties such as wide and continuous absorption spectra, narrow emission spectra, and high light stability. The application of QDs, as a new technology for biosystems, has been typically studied on mammalian cells. Due to the small structures of QDs, some physical properties such as optical and electron transport characteristics are quite different from those of the bulk materials.

Enabling biomedical research with designer quantum dots

Quantum Dots (QDs) are a new class of semiconductor nanoparticulate luminophores, which are actively researched for novel applications in biology and nanomedicine. In this review, the recent progress in the design and applications of QD labels for in vitro and in vivo imaging of cells is presented. Surface chemical engineering of hydrophobic QDs is required to render them water soluble and biocompatible. Further surface modification and attachment of bioactive molecules to the surface of QDs, such as peptides, aptamers, or antibodies are intensively explored for targeted imaging of living cells, and disease states in animals. Specially designed surface coatings can drastically decrease nonspecific interactions between QDs and cells, minimize degradation of QDs under in vivo physiological conditions, reduce the cytotoxicity of QDs, and prolong circulation lifetimes in animals. New generations of QD probes are also promising for imaging cellular processes at the single-molecule level. Ultimately, QDs as components of complex therapeutic nanosystems are poised to contribute significantly to the field of personalized medicine.

In Vivo Stability and Biodistribution of Quantum Dots by Inductively Coupled Plasma-Atomic Emission Spectrometry

Here we studied in vivo stability and biodistribution of quantum dots. Their distribution in vivo at various time points were determined by measuring the amount of cadmium ions and selenium ions in various organs by inductively coupled plasma-atomic emission spectrometry. The amount of cadmium ions was higher in liver than in other organs at all times. The amount of cadmium ions in kidney and spleen were increased gradually in time-dependent. There are also obviously increased cadmium ions in lung and heart at all times compared to the control. However the amount of selenium ions was high in all organs except for brain before the 3rd day.

Beauty is skin deep: a surface monolayer perspective on nanoparticle interactions with cells and bio-macromolecules

Surface recognition of biosystems is a critical component in the development of novel biosensors and delivery vehicles, and for the therapeutic regulation of biological processes. Monolayer-protected nanoparticles present a highly versatile scaffold for selective interaction with bio-macromolecules and cells. Through the engineering of the monolayer surface, nanoparticles can be tailored for surface recognition of biomolecules and cells. This review highlights recent progress in nanoparticle-bio-macromolecule/cellular interactions, emphasizing the effect of the surface monolayer structure on the interactions with proteins, DNA, and cell surfaces. The extension of these tailored interactions to hybrid nanomaterials, biosensing platforms, and delivery vehicles is also discussed.

Substance P conjugated to CdTe quantum dots triggers cytosolic calcium concentration oscillations and induces quantum dots internalization in the pancreatic carcinoma cell line AR4-2J

Highly fluorescent CdTe quantum dots (QDs) stabilized by 3-mercaptopropionic acid were prepared by an aqueous solution approach and used as a fluorescent label to link substance P (SP) in studying the interaction of SP with NK-1 receptor, which was expressed on the AR4-2J cell line. Nonspecific adsorptions of CdTe QDs on the AR4-2J cell membrane were observed, whereas the QD-SP conjugates successfully crossed the cell membrane and entered the cytosol. SP is a neurotransmitter, and neurotransmitter-induced calcium concentration oscillation is a common phenomenon in diverse cells especially of secretory type. Cytosolic calcium concentration responses were studied in the AR4-2J cell line during stimulation with SP and QD-SP conjugates. The oscillations triggered by SP and QD-SP conjugates were dose-dependent and very similar. Such QD-SP conjugates readily internalized into the cytosol as would be expected of an active NK-1 ligand. Therefore QD-SP conjugates could be used successfully to study ligand and NK-1 receptor interactions in live cells. Our research may provide a meaningful reference for congener research.

Cellular uptake, intracellular trafficking, and cytotoxicity of nanomaterials

The interactions of nanoparticles with the soft surfaces of biological systems like cells play key roles in executing their biomedical functions and in toxicity. The discovery or design of new biomedical functions, or the prediction of the toxicological consequences of nanoparticles in vivo, first require knowledge of the interplay processes of the nanoparticles with the target cells. This article focusses on the cellular uptake, location and translocation, and any biological consequences, such as cytotoxicity, of the most widely studied and used nanoparticles, such as carbon-based nanoparticles, metallic nanoparticles, and quantum dots. The relevance of the size and shape, composition, charge, and surface chemistry of the nanoparticles in cells is considered. The intracellular uptake pathways of the nanoparticles and the cellular responses, with potential signaling pathways activated by nanoparticle interactions, are also discussed.

Intracellular delivery of quantum dots mediated by a histidine- and arginine-rich HR9 cell-penetrating peptide through the direct membrane translocation mechanism

Functional peptides that transfer biomaterials, such as semiconductor quantum dots (QDs), into cells in biomaterial research have been developed in recent years. Delivery of QDs conjugated with cell-penetrating peptides (CPPs) into cells by the endocytic pathway was problematic in biomedical applications because of lysosomal trapping. Here, we demonstrate that histidine- and arginine-rich CPPs (HR9 peptides) stably and noncovalently combined with QDs are able to enter into cells in an extremely short period (4 min). Interrupting both F-actin polymerization and active transport did not inhibit the entry of HR9/QD complexes into cells, indicating that HR9 penetrates cell membrane directly. Subcellular colocalization studies indicated that QDs delivered by HR9 stay in cytosol without any organelle capture. Dimethyl sulphoxide, ethanol and oleic acid, but not pyrenebutyrate, enhanced HR9-mediated intracellular delivery of QDs by promoting the direct membrane translocation pathway. HR9 and HR9/QDs were not cytotoxic. These findings suggest that HR9 could be an efficient carrier to deliver drugs without interfering with their therapeutic activity.

Conjugation reactions in the preparations of quantum dot-based immunoluminescent probes for analysis of proteins by capillary electrophoresis

A number of biologically important molecules, such as DNA, proteins, and antibodies, are routinely conjugated with fluorescent tags for high-sensitivity analyses. Here, the application of quantum dots in the place of bright and size-tunable luminophores is studied. Several selected bioconjugation reactions via zero-length cross-linkers, long-chain linkers, and oriented methods for linking of quantum dots with proteins were tested. Anti-ovalbumin, anti-proliferating cell nuclear antigen, anti-hemagglutinin, and anti-CD3 membrane protein as model antibodies and annexin V were used as high-specificity selectors. The reaction yield and efficiency of the prepared immunoluminescent probes were tested by capillary zone electrophoresis with laser-induced fluorescence detection.

Nona-arginine facilitates delivery of quantum dots into cells via multiple pathways

Semiconductor quantum dots (QDs) have recently been used to deliver and monitor biomolecules, such as drugs and proteins. However, QDs alone have a low efficiency of transport across the plasma membrane. In order to increase the efficiency, we used synthetic nona-arginine (SR9), a cell-penetrating peptide, to facilitate uptake. We found that SR9 increased the cellular uptake of QDs in a noncovalent binding manner between QDs and SR9. Further, we investigated mechanisms of QD/SR9 cellular internalization. Low temperature and metabolic inhibitors markedly inhibited the uptake of QD/SR9, indicating that internalization is an energy-dependent process. Results from both the pathway inhibitors and the RNA interference (RNAi) technique suggest that cellular uptake of QD/SR9 is predominantly a lipid raft-dependent process mediated by macropinocytosis. However, involvement of clathrin and caveolin-1 proteins in transducing QD/SR9 across the membrane cannot be completely ruled out.

Study on effect of peptide-conjugated near-infrared fluorescent quantum dots on the clone formation, proliferation, apoptosis, and tumorigenicity ability of human buccal squamous cell carcinoma cell line BcaCD885

Quantum dots (QDs) have shown great development potential in noninvasive imaging and monitoring of cancer cells in vivo because of their unique optical properties. However, the key issue of whether or not QDs-labeled cancer cells affect the proliferation, apoptosis and in vivo tumorigenicity ability has not been reported. The primary issue is if the results obtained from the noninvasive visualization of QDs-labeled tumors are scientific. Here, we applied peptide-linked near-conjugated fluorescent QDs to label human buccal squamous cell carcinoma cell line (BcaCD885). We performed in vivo tumorigenicity ability assays, tumorigenic cells proliferation, and apoptotic capability assays detected by flow cytometry and plate clone formation experiment, and found that peptide-linked near-conjugated fluorescent QDs labeling did not affect the growth, proliferation, apoptosis, and tumorigenicity ability of those cancer cells. Our study provides scientific foundation to support the application of near-infrared fluorescent QDs in noninvasive imaging and monitoring of cancer cells in vivo.

Study on the intracellular fate of Tat peptide-conjugated quantum dots by spectroscopic investigation

The photoluminescence (PL) spectrum of water-soluble thiol-capped CdTe quantum dots (QDs) conjugated with Tat peptide in solution showed a remarkable redshift as compared to that of unconjugated QDs. After cellular uptake of the Tat-QDs conjugates, the micro-PL spectrum of Tat-QDs in lysosomes showed a spectral blueshift, which was most probably due to the fact that Tat peptide was digested by the enzymes, leaving the Tat-detached QDs in lysosomes. The reasons for the spectral changes have been discussed in detail.

Probing the dynamic effect of cys-CdTe quantum dots toward cancer cells in vitro

The application of quantum dots (QDs) in various biomedical areas requires detailed studies of their toxicity. We report a new strategy for probing the biocompatibility of these nanocrystals, namely, a dynamic investigation of cellular uptake images, cell growth curves, metabolic activity changes, and apoptosis aspects of cadmium telluride QDs capped with cysteamine (Cys-CdTe QDs) on human hepatocellular carcinoma SMMC-7721 cells. We used a real-time cell electronic sensing (RT-CES) system in combination with fluorescence microscopy, 3-(4,5-dimethyl-thiazol-zyl)-2,5-diphenyltetrazolium bromide assay, and flow cytometry (FCM) analysis. As observed from fluorescence images and RT-CES system results, Cys-CdTe QDs can readily bind on the cell plasma membrane and then enter into the cancer cell, causing decreased adherence of cancer cells during the initial 6-12 h, while the metabolic activity apparently decreased. After 24 h, the metabolic activity of the cancer cells was significantly reduced, with continued reduction in metabolic activity observed at even longer incubation times. Moreover, FCM observation and DNA fragmentation analysis clearly indicate apoptosis-related phenomena when SMMC-7721 cells were treated with the Cys-CdTe QDs. Thus, our study reveals details of the cellular aging and death process induced by Cys-CdTe QDs.

Effect of surface properties on nanoparticle-cell interactions

The interaction of nanomaterials with cells and lipid bilayers is critical in many applications such as phototherapy, imaging, and drug/gene delivery. These applications require a firm control over nanoparticle-cell interactions, which are mainly dictated by surface properties of nanoparticles. This critical Review presents an understanding of how synthetic and natural chemical moieties on the nanoparticle surface (in addition to nanoparticle shape and size) impact their interaction with lipid bilayers and cells. Challenges for undertaking a systematic study to elucidate nanoparticle-cell interactions are also discussed.

TAT-based drug delivery system--new directions in protein delivery for new hopes?

There has been great progress in the use of TAT-based drug delivery systems for the delivery of different macromolecules into cells in vitro and in vivo, thus circumventing the bioavailability barrier that is a problem for so many drugs. There are many advantages to using this system, such as the ability to deliver these cargoes into all types of cells in culture and into all organs in vivo. This system can even deliver cargoes into the brain across the blood-brain barrier. In addition, the ability to target specific intracellular sub-localizations such as the nuclei, the mitochondria and lysosomes further expands the possibilities of this drug delivery system to the development of sub-cellular organelle-targeted therapy. The therapeutic applications seem almost unlimited, and the use of the TAT-based delivery system has extended from proteins to a large variety of cargoes such as oligonucleotides, imaging agents, low molecular mass drugs, nanoparticles, micelles and liposomes. In this review the most recent advances in the use of the TAT-based drug delivery system will be described, mainly discussing TAT-mediated protein delivery and the use of the TAT system for enzyme replacement therapy.

Thiol-capped CdTe quantum dots with two-photon excitation for imaging high autofluorescence background living cells

To effectively image living cells with quantum dots (QDs), particularly for those cells containing high content of native fluorophores, the two-photon excitation (TPE) with a femto-second 800 nm laser was employed and compared with the single-photon excitations (SPE) of 405 nm and 488 nm in BY-2 Tobacco (BY-2-T) and human hepatocellular carcinoma (QGY) cells, respectively. The 405 nm SPE produced the bright photoluminescence (PL) signals of cellular QDs but also induced a strong autofluorescence(AF) from the native fluorophores like flavins in cells. The AF occupied about 30% and 13% of the total signals detected in QD imaging channel in the BY-2-T and QGY cells, respectively. With the excitation of 488 nm SPE, the PL signals were lower than those excited with the 405 nm SPE, although the AF signals were also reduced. The 800 nm TPE generated the best PL images of intracellular QDs with the highest signal ratio of PL to AF, because the two-photon absorption cross section of QDs is much higher than that of the native fluorophores. By means of the TPE, the reliable cellular imaging with QDs, even for the cells having the high AF background, can be achieved.

Hyaluronic acid-quantum dot conjugates for in vivo lymphatic vessel imaging

A simple and novel electrostatic coupling method is reported, which provides a hyaluronic acid-quantum dot conjugate (HA-QD) that is colloidally stable and size-tunable from 50 to 120 nm. The HA-QDs show cancer targeting efficiency, which suggests diagnostic and imaging applications. The conjugates are also demonstrated for the fluorescence staining capability for lymphatic vessels in vitro and in vivo. Using the HA-QDs in a small animal model, lymphatic vessels are visualized real-time in vivo for days. Comprehensive cytotoxicity evaluations are made for the conjugates and the unconjugated counterpart. The HA-QDs showcase the potentials toward cancer imaging and real-time visualization of changes in lymphatic vessels such as lymphangiogenesis.

Fluorescent immunolabeling of cancer cells by quantum dots and antibody scFv fragment

Semiconductor quantum dots (QDs) coupled with cancer-specific targeting ligands are new promising agents for fluorescent visualization of cancer cells. Human epidermal growth factor receptor 2/neu (HER2/neu), overexpressed on the surface of many cancer cells, is an important target for cancer diagnostics. Antibody scFv fragments as a targeting agent for direct delivery of fluorophores offer significant advantages over full-size antibodies due to their small size, lower cross-reactivity, and immunogenicity. We have used quantum dots linked to anti-HER2/neu 4D5 scFv antibody to label HER2/neu-overexpressing live cells. Labeling of target cells was shown to have high brightness, photostability, and specificity. The results indicate that construction based on quantum dots and scFv antibody can be successfully used for cancer cell visualization.

Transfection of aqueous CdS quantum dots using polyethylenimine

In this study, we have examined the transfection of aqueous CdS quantum dots (QDs) in the cytoplasm of PC12 neuronal cells using polyethylenimine (PEI) as carrier. The CdS QDs were prepared using a unique aqueous synthesis method, at 5 nm in size and capped with 3-mercaptopropyltrimethoxysilane (MPS). They exhibited a quantum yield of 7.5% and a zeta potential of -25 mV. With PEI they formed complexes by electrostatic attraction. At PEI/QD number ratios of>100, the PEI-QD complexes obtained exhibited a saturated size of about 24 nm and a zeta potential of about 15 mV. Confocal microscopy showed that PEI-QD complexes of a PEI/QD number ratio of 200 were successfully internalized and uniformly distributed inside the cells, indicating that the PEI-QD complexes were able to rupture the vesicles to enter the cytoplasm without aggregation. In addition, we showed that the presence of the PEI did not reduce the photoluminescence of the QDs and only mildly reduced the mitochondrial activity of the transfected cells-with no apparent reduction at a PEI/QD ratio of <40 to about 30% reduction at a PEI/QD number ratio of 200.

Transmembrane delivery of the cell-penetrating peptide conjugated semiconductor quantum dots

Conjugation of the cell-penetrating peptide derived from the human immunodeficiency virus-1 transactivator protein (TAT) to semiconductor quantum dots (QDs) is an effective way to enhance transmembrane delivery of QDs for intracellular and molecular imaging. In this work, the internalization pathway of TAT-QDs was studied systematically in living cells. Cellular uptake of TAT-QDs, under different endocytosis-inhibiting conditions, was compared by fluorescence imaging and flow cytometry. The results suggest TAT-QDs internalize through lipid-raft-dependent macropinocytosis, which is different from that of FITC-labeled TAT. They also provide new information for better understanding of the TAT-mediated cell uptake mechanism.

Delivering quantum dots into cells: strategies, progress and remaining issues

The use of semiconductor quantum dots (QDs) in biological sensing and labeling continues to grow with each year. Current and projected applications include use as fluorescent labels for cellular labeling, intracellular sensors, deep-tissue and tumor imaging agents, sensitizers for photodynamic therapy, and more recently interest has been sparked in using them as vectors for studying nanoparticle-mediated drug delivery. Many of these applications will ultimately require the QDs to undergo targeted intracellular delivery, not only to specific cells, but also to a variety of subcellular compartments and organelles. It is apparent that this issue will be critical in determining the efficacy of using QDs, and indeed a variety of other nanoparticles, for these types of applications. In this review, we provide an overview of the current methods for delivering QDs into cells. Methods that are covered include facilitated techniques such as those that utilize specific peptide sequences or polymer delivery reagents and active methods such as electroporation and microinjection. We critically examine the benefits and liabilities of each strategy and illustrate them with selected examples from the literature. Several important related issues such as QD size and surface coating, methods for QD biofunctionalization, cellular physiology and toxicity are also discussed. Finally, we conclude by providing a perspective of how this field can be expected to develop in the future.

Intracellular delivery of nanoparticles via the HIV-1 tat peptide

Functionalized nanoparticles are heralded as part of the future with regards to targeted cell and nuclear delivery. However, direct intracellular and intranuclear delivery has, until recently, been difficult to achieve owing to the impermeable nature of the plasma and nuclear membranes. During the past 15 years, a range of peptides, termed cell-penetrating peptides (CPPs), which have the ability to translocate into living cells, have been discovered. Thus, in more recent years, the combination of CPPs with nanoparticles, enabling CPP-mediated cell delivery, has opened up many avenues of research. This review discusses the use of various CPPs, focusing on tat peptide, to functionalize nanoparticles and the possible move from the laboratory to the clinic.