Folic acid modified gelatine coated quantum dots as potential reagents for in vitro cancer diagnostics

High-quantum yield alloy-typed core/shell CdSeZnS/ZnS quantum dots for bio-applications

Background

Quantum dots (QDs) have been used as fluorophores in various imaging fields owing to their strong fluorescent intensity, high quantum yield (QY), and narrow emission bandwidth. However, the application of QDs to bio-imaging is limited because the QY of QDs decreases substantially during the surface modification step for bio-application.

Results

In this study, we fabricated alloy-typed core/shell CdSeZnS/ZnS quantum dots (alloy QDs) that showed higher quantum yield and stability during the surface modification for hydrophilization compared with conventional CdSe/CdS/ZnS multilayer quantum dots (MQDs). The structure of the alloy QDs was confirmed using time-of-flight medium-energy ion scattering spectroscopy. The alloy QDs exhibited strong fluorescence and a high QY of 98.0%. After hydrophilic surface modification, the alloy QDs exhibited a QY of 84.7%, which is 1.5 times higher than that of MQDs. The QY was 77.8% after the alloy QDs were conjugated with folic acid (FA). Alloy QDs and MQDs, after conjugation with FA, were successfully used for targeting human KB cells. The alloy QDs exhibited a stronger fluorescence signal than MQD; these signals were retained in the popliteal lymph node area for 24 h.

Conclusion

The alloy QDs maintained a higher QY in hydrophilization for biological applications than MQDs. And also, alloy QDs showed the potential as nanoprobes for highly sensitive bioimaging analysis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01227-2.

Exploiting the biomimetic and luminescence properties of multivalent dendrimer-semiconductor nanohybrid materials in the ultra-low level determination of folic acid

In view of the enhanced generation of folate receptors in cancerous cells and diseases linked to the deficiency of folic acid, such as anemia, mental devolution, congenital malformation, etc., the development of a simple method for the ultra-sensitive determination of folic acid remains a long-standing issue for practical applications in medicine and biotechnology. Thus, the proposed luminescence based strategy involving multifunctional poly(amidoamine) (PAMAM) dendrimer encapsulated quantum dots (QDs) as a probe provides a simple, fast and efficient method for the selective determination of folic acid at the nano-molar level. Absorption and Fourier transform infra-red (FTIR) spectroscopy provide evidence of the binding of folic acid with dendrimer amine groups. The emission quenching of dendrimer encapsulated CdS QDs follows a linear Stern-Volmer plot with an exceedingly high value of the Stern-Volmer constant (K_SV = 8.4 × 10⁶ M^-1) facilitating a higher detection efficiency. Similar quenching analysis with dendrimer-ZnS QDs showed a slightly lower Stern-Volmer constant (K_SV = 2.29 × 10⁶ M^-1). The lower probing efficiency of the protein or amino acid capping of QDs has been explained through zeta potential measurements. The solvent polarity dependence suggests a charge transfer process responsible for the emission quenching of CdS QDs, which is static in nature as revealed by lifetime measurements. The determination of folic acid at this low level is not affected by possible interfering molecules, such as vitamin C, vitamin B₁₂ and uric acid. Calorimetric measurements showed that the exothermic binding of folic acid with a dendrimer follows enthalpy-entropy compensation. The detailed mechanistic aspect of interactions of folic acid with the QD probe helps in a better understanding of the detection process, which in turn can assist in developing a dendrimer based material for image analysis and drug delivery in folate receptor rich cells.

The anticoagulant properties of cadmium telluride quantum dots

The size-dependent optical properties of quantum dots (QDs) are frequently exploited for use in medical imaging and labelling applications. Similarly, presented here, they also elicit profound size-dependent anticoagulant properties. Cadmium telluride quantum dot (QDs) (3.2 nm) were shown to have a dramatic anticoagulant effect centred on around the intrinsic coagulation pathway, compared to their 3.6 nm counterparts. Several clinically relevant diagnostic tests were carried out over a concentration range of the QDs and demonstrated that the 3.2 nm QDs elicited their response on the intrinsic pathway as a whole, yet the activity of the individual intrinsic coagulation factors was not affected. The mechanism appears also to be strongly influenced by the concentration of calcium ions and not cadmium ions leached from the QDs. Static and shear-based primary haemostasis assays were also carried out, demonstrating a profound anticoagulant effect which was independent of platelets and phospholipids. The data presented here suggest that the physical-chemical properties of the QDs may have a role in the modulation of haemostasis and the coagulation cascade, in a yet not fully understood mechanism. This study has implications for the use of similar QDs as diagnostic or therapeutic tools in vivo, and for the occupational health and safety of those working with such materials.

Semiconductorversusgraphene quantum dots as fluorescent probes for cancer diagnosis and therapy applications

This review provides a comparison of optical, chemical and biocompatibility properties of graphene and semiconductor quantum dots as fluorescent probes.

Application of semiconductor quantum dots in bioimaging and biosensing

In this review we present new concepts and recent progress in the application of semiconductor quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing.

The effect of "Jelly" CdTe QD uptake on RAW264.7 monocytes: immune responses and cell fate study

Encapsulation of Quantum Dots (QDs) has become an essential factor which regulates particles cytotoxicity, as well as physical and chemical stability. Negatively charged cellular membranes have a great affinity to nanoparticles with surface molecules carrying positive charge, hence creating perfect conditions for fast and aggressive intracellular penetration. The preference for non-charged outer shells is topical in QD design and various applications. In the current paper we develop gelatination as a prominent coating approach to create neutrally passivated QDs with improved biocompatibility. We have revealed the trends in particle's uptake, accumulation, intracellular localisation and retaining time as well as RAW264.7 monocyte cell fate and immune responses. Also the difference in particle endocytosis kinetics and dynamics has been shown to depend on the QD core size. The intracellular QD content along with cell responses at the population level was quantified by flow cytometry.

Non-Cytotoxic Quantum Dot-Chitosan Nanogel Biosensing Probe for Potential Cancer Targeting Agent

Quantum dot (Qdot) biosensors have consistently provided valuable information to researchers about cellular activity due to their unique fluorescent properties. Many of the most popularly used Qdots contain cadmium, posing the risk of toxicity that could negate their attractive optical properties. The design of a non-cytotoxic probe usually involves multiple components and a complex synthesis process. In this paper, the design and synthesis of a non-cytotoxic Qdot-chitosan nanogel composite using straight-forward cyanogen bromide (CNBr) coupling is reported. The probe was characterized by spectroscopy (UV-Vis, fluorescence), microscopy (Fluorescence, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Dynamic Light Scattering. This activatable (“OFF”/“ON”) probe contains a core–shell Qdot (CdS:Mn/ZnS) capped with dopamine, which acts as a fluorescence quencher and a model drug. Dopamine capped “OFF” Qdots can undergo ligand exchange with intercellular glutathione, which turns the Qdots “ON” to restore fluorescence. These Qdots were then coated with chitosan (natural biocompatible polymer) functionalized with folic acid (targeting motif) and Fluorescein Isothiocyanate (FITC; fluorescent dye). To demonstrate cancer cell targetability, the interaction of the probe with cells that express different folate receptor levels was analyzed, and the cytotoxicity of the probe was evaluated on these cells and was shown to be nontoxic even at concentrations as high as 100 mg/L.

Facile synthesis of fluorescent Au/Ce nanoclusters for high-sensitive bioimaging

Background

Tumor-target fluorescence bioimaging is an important means of early diagnosis, metal nanoclusters have been used as an excellent fluorescent probe for marking tumor cells due to their targeted absorption. We have developed a new strategy for facile synthesis of Au/Ce nanoclusters (NCs) by doping trivalent cerium ion into seed crystal growth process of gold. Au/Ce NCs have bright fluorescence which could be used as fluorescent probe for bioimaging.

Results

In this study, we synthesized fluorescent Au/Ce NCs through two-step hydrothermal reaction. The concentration range of 25–350 μM, Au/Ce NCs have no obvious cell cytotoxicity effect on HeLa, HepG2 and L02 cells. Furthermore, normal cells (L02) have no obvious absorption of Au/Ce NCs. Characterization of synthesized Au/Ce NCs was done by using TEM, EDS and XPS. Then these prepared Au/Ce NCs were applied for in vitro/in vivo tumor-target bioimaging due to its prolonged fluorescence lifetime and bright luminescence properties.

Conclusions

The glutathione stabilized Au/Ce NCs synthesized through hydrothermal reaction possess stable and bright fluorescence that can be readily utilized for high sensitive fluorescence probe. Our results suggest that Au/Ce NCs are useful candidate for in vitro/in vivo tumor bioimaging in potential clinical application.

The interaction of QDs with RAW264.7 cells: nanoparticle quantification, uptake kinetics and immune responses study

Exposure to small QDs in high concentration in continuous cell culture results in cell death by apoptosis and necrosis co-existing within the same cell population.

Physicochemical and in vitro biocompatibility evaluation of water-soluble CdSe/ZnS core/shell

Group II-VI semiconductor quantum dots (Q-dots) have found various applications in biomedical field during last decade. In this study, we have synthesized CdSe Q-dots and CdSe/ZnS core/shell (CS) by wet chemical route and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FT-IR) and Photoluminescence (PL) spectroscopy. CS formation was confirmed by red shift as well as enhancement in the luminescence peak compared to bare Q-dots. Processing parameters such as core and sulfur concentrations were optimized at maximum luminescence efficiency during the shell preparation. Effects of dialysis, aging and cell culture medium on the properties of the Q-dots and CS were also studied by luminescence and DLS techniques. DLS data showed Q-dots and CS to be stable, and there was no effect on the integrity of the Q-dots and CS after various modifications. CS was found to be hemocompatible and cytocompatible for human umbilical vein endothelial cells even at a high concentration of 0.1 mg/ml up to 48 h indicating high potential for CS in various biomedical applications.

Self-assembly of folate onto polyethyleneimine-coated CdS/ZnS quantum dots for targeted turn-on fluorescence imaging of folate receptor overexpressed cancer cells

Folate receptor (FR) can be overexpressed by a number of epithelial-derived tumors, but minimally expressed in normal tissues. As folic acid (FA) is a high-affinity ligand to FR, and not produced endogenously, development of FA-conjugated probes for targeted imaging FR overexpressed cancer cells is of significance for assessing cancer therapeutics and for better understanding the expression profile of FR in cancer. Here we report a novel turn-on fluorescence probe for imaging FR overexpressed cancer cells. The probe was easily fabricated via electrostatic self-assembly of FA and polyethyleneimine-coated CdS/ZnS quantum dots (PEI-CdS/ZnS QDs). The primary fluorescence of PEI-CdS/ZnS QDs turned off first upon the electrostatic adsorption of FA onto PEI-CdS/ZnS QDs based on electron transfer to produce negligible fluorescence background. The presence of FR expressed on the surface of cancer cells then made FA desorb from PEI-CdS/ZnS QDs due to specific and high affinity of FA to FR. As a result, the primary fluorescence of PEI-CdS/ZnS QDs adhering to the cells turned on due to the inhibition of electron transfer. The most important merits of the developed probe are its simplicity and the effective avoidance of the false positive results due to the simple electrostatic self-assembly of FA onto the surface of PEI-CdS/ZnS QDs and the involved fluorescence "off-on" mechanism. The probe was demonstrated to be sensitive and selective for targeted imaging of FR overexpressed cancer cells in turn-on mode.

Preparation of multifunctional nanoparticles and their assemblies

This article describes the synthesis of multifunctional nanoparticulate systems and a range of organic reactions for modifying the surface functionalities of these particles and their composites. The reactions include surface silanization, amine-azide conversion, azide-alkyne 'click' chemistry, thiol and amine click chemistry and amide coupling. In addition, we discuss a number of relevant nanoparticle preparations to exemplify the interrelationship of these reactions. This system can readily be adapted to produce a wide range of composites with different features, such as fluorescence, magnetism, plasmon resonance and multiple biofunctionalities.

The Invasion and Reproductive Toxicity of QDs-Transferrin Bioconjugates on Preantral Follicle in vitro

The toxicity of QD has been extensively studied over the past decade. However, the potential toxicity of QDs impedes its use for clinical research. In this work, we established a preantral follicle in vitro culture system to investigate the effects of QD-Transferrin (QDs-Tf) bioconjugates on follicle development and oocyte maturation. The preantral follicles were cultured and exposed to CdTe/ZnTe QDs-Tf bioconjugates with various concentrations and the reproductive toxicity was assessed at different time points post-treatment. The invasion of QDs-Tf for oocytes was verified by laser scanning confocal microscope. Steroid production was evaluated by immunoassay. C-band Giemsa staining was performed to observe the chromosome abnormality of oocytes. The results showed that the QDs-Tf bioconjugates could permeate into granulosa cells and theca cells, but not into oocyte. There are no obvious changes of oocyte diameter, the mucification of cumulus-oocyte-complexes and the occurrence of aneulpoidy as compared with the control group. However, delay in the antrum formation and decrease in the ratio of oocytes with first polar body were observed in QDs-Tf-treated groups. The matured oocytes with first polar body decreased significantly by ~16% (from 79.6±10 % to 63±2.9 %) when the concentration of QDs-Tf bioconjugates exceeded 2.89 nmol·L^-1 (P < 0.05). Our results implied that the CdTe/ZnTe QDs-Tf bioconjugates were reproductive toxic for follicle development, and thus also revealed that this in vitro culture system of preantral follicle is a highly sensitive tool for study on the reproductive toxicity of nanoparticles.