CdTe quantum dots conjugated to concanavalin A as potential fluorescent molecular probes for saccharides detection in Candida albicans

Quantum dots as a fluorescent labeling tool for live-cell imaging of Leptospira

Leptospirosis is a global public health problem caused by Gram-negative pathogenic bacteria belonging to the genus Leptospira. The disease is transmitted through the urine of infected animals, which contaminates water and soil, leading to the infection of other animals and humans. Currently, several approaches exist to detect these bacteria; however, a new sensitive method for the live-cell imaging of Leptospira is required. In this study, we report the green synthesis of cadmium telluride quantum dots (CdTe QDs) which are unique fluorescent nanocrystals with a high fluorescence quantum yield capable of modifying cell surfaces and are biocompatible with cells. The fabrication of QDs with concanavalin A (ConA), a carbohydrate-binding lectin and known biological probe for Gram-negative bacteria, produced ConA-QDs which can effectively bind on Leptospira and exhibit strong fluorescence under simple fluorescence microscopy, allowing the live-cell imaging of the bacteria. Overall, we performed the simple synthesis of ConA-QDs and demonstrated their potential use as versatile fluorescent probes for the live-cell imaging of Leptospira. This technique could be further applied to track leptospiral cells and study the infection mechanism, contributing to a more thorough understanding of leptospirosis and how to control it in the future.

Comparison of Toxicity and Cellular Uptake of CdSe/ZnS and Carbon Quantum Dots for Molecular Tracking Using Saccharomyces cerevisiae as a Fungal Model

Plant resource sharing mediated by mycorrhizal fungi has been a subject of recent debate, largely owing to the limitations of previously used isotopic tracking methods. Although CdSe/ZnS quantum dots (QDs) have been successfully used for in situ tracking of essential nutrients in plant-fungal systems, the Cd-containing QDs, due to the intrinsic toxic nature of Cd, are not a viable system for larger-scale in situ studies. We synthesized amino acid-based carbon quantum dots (CQDs; average hydrodynamic size 6 ± 3 nm, zeta potential -19 ± 12 mV) and compared their toxicity and uptake with commercial CdSe/ZnS QDs that we conjugated with the amino acid cysteine (Cys) (average hydrodynamic size 308 ± 150 nm, zeta potential -65 ± 4 mV) using yeast Saccharomyces cerevisiae as a proxy for mycorrhizal fungi. We showed that the CQDs readily entered yeast cells and were non-toxic up to 100 mg/L. While the Cys-conjugated CdSe/ZnS QDs were also not toxic to yeast cells up to 100 mg/L, they were not taken up into the cells but remained on the cell surfaces. These findings suggest that CQDs may be a suitable tool for molecular tracking in fungi (incl. mychorrhizal fungi) due to their ability to enter fungal cells.

A fluorescent glyconanoprobe based on quantum dots and thiolated glucose: Applications in monolayers and spheroids of cancer cells

The differential energy metabolism of cancer cells has stimulated the development of tools that can be applied to better understand the complex biological interaction involved in the uptake of glucose analogs at the cellular level in this disease. Herein, we explored the outstanding optical properties of quantum dots (QDs) to develop a new fluorescent glyconanoprobe using the 1-thio-β-d-glucose (Glc). Then, monolayers and spheroids of HeLa cells were applied to probe the biological interaction with the conjugate through fluorescence techniques. Spheroids have been gaining prominence for better mimicking the tumor microenvironment. The Glc-QDs conjugate was prepared by a facile and direct procedure based on the affinity of the Glc thiol group by the QD semiconductor surface. The conjugation was evaluated and confirmed by Zeta potential (ζ) measurements, FTIR spectroscopy, and fluorescence correlation spectroscopy (FCS). Moreover, a biological assay using Candida albicans yeasts coated with concanavalin A, by exploring the lectin-carbohydrate affinity, was also developed to further confirm the conjugation, which corroborated the previous analyses. The hanging drop method was used to prepare the spheroids. The fluorescence microscopy analyses indicated an intracellular labeling by the glyconanoprobe, in both cell culture models. Flow cytometry assays revealed effective uptake of the conjugate (above ca. 76%), even by cells cultivated as spheroids, applying short incubation time. Therefore, a new fluorescent glyconanoprobe was developed, which showed potential to be applied for investigating mechanisms involved in the uptake of glucose analogs, both by simpler and complex cancer biological models, as monolayers and spheroids.

Fluorescent nanoprobes based on quantum dots conjugated to cramoll to assess surface carbohydrates of Aeromonas spp

The association of quantum dots (QDs) to carbohydrate-binding proteins - lectins - has revealed novel biotechnological strategies for glycobiology studies. Herein, carboxyl-coated QDs were conjugated by adsorption to Cramoll, a glucose/mannose lectin obtained from Cratylia mollis seeds. Then, the conjugates were optically characterized and used to evaluate the surface carbohydrate profiles of four Aeromonas species isolated from the tambaqui fish (Colossoma macropomum). All the Aeromonas cells were labeled by the conjugate. Inhibition assays with methyl-α-D-mannopyranoside and mannan were performed to confirm the labeling specificity. Cramoll-QDs conjugates presented high brightness and showed similar absorption and emission profiles compared to bare QDs. According to the labeling pattern of Aeromonas spp. by the conjugate, results suggested that A. jandaei and A. dhakensis strains may harbor a higher content of more complex glucose/mannose surface glycans, with more available sites for Cramoll-QDs interaction, than A. hydrophila and A. caviae. Noteworthy, the Cramoll-QDs conjugates demonstrated to be a potential tool for bacterial characterization based on superficial carbohydrate detection.

Nanoparticle-Based Photodynamic Inhibition of Candida albicans Biofilms with Interfering Quorum Sensing

Biofilm formation is a critical event in the pathogenesis and virulence of fungal infections caused by Candida albicans, giving rise to about a 1000-fold increase in the resistance to antifungal agents. Although photodynamic treatment (PDT) has been excellently implicated in bacterial infections, studies on its potential against fungal infection through the clearance of fungal biofilm formation remain at its infancy stage. Here, we have designed photodynamic nanoparticles with different sizes, modifications, and the ability of generating reactive oxygen species (ROS) to examine their effects on inhibiting biofilm formation and destructing mature biofilms of C. albicans. We found that the nanoparticles modified with oligo-chitosan exhibited a better binding efficiency for planktonic cells, leading to stronger inhibitory efficacy of the filamentation and the early-stage biofilm formation. However, for mature biofilms, the nanoparticles with the smallest size (∼15 nm) showed the fastest penetration speed and a pronounced destructing effect albeit conferring the lowest ROS-producing capability. The inhibitory effect of photodynamic nanoparticles was dependent on the disruption of fungal quorum sensing (QS) by the upregulation of QS molecules, farnesol and tyrosol, mediated through the upregulation of ARO 8 and DPP 3 expression. Our findings provide a powerful strategy of nanoparticulate PDT to combat fungal infections through the inhibition of both hyphal and biofilm formation by disrupting QS.

Asian Sand Dust Particles Enhance the Development of Aspergillus fumigatus Biofilm on Nasal Epithelial Cells

Background: Asian sand dust (ASD) and Aspergillus fumigatus are known risk factors for airway mucosal inflammatory diseases. Bacterial and fungal biofilms commonly coexist in chronic rhinosinusitis and fungus balls. We evaluated the effects of ASD on the development of A. fumigatus biofilm formation on nasal epithelial cells. Methods: Primary nasal epithelial cells were cultured with A. fumigatus conidia with or without ASD for 72 h. The production of interleukin (IL)-6, IL-8, and transforming growth factor (TGF)-β1 from nasal epithelial cells was determined by the enzyme-linked immunosorbent assay. The effects of ASD on A. fumigatus biofilm formation were determined using crystal violet, concanavalin A, safranin staining, and confocal scanning laser microscopy. Results: ASD and A. fumigatus significantly enhanced the production of IL-6 and IL-8 from nasal epithelial cells. By coculturing A. fumigatus with ASD, the dry weight and safranin staining of the fungal biofilms significantly increased in a time-dependent manner. However, the increased level of crystal violet and concanavalin A stain decreased after 72 h of incubation. Conclusions: ASD and A. fumigatus induced the production of inflammatory chemical mediators from nasal epithelial cells. The exposure of A. fumigatus to ASD enhanced the formation of biofilms. The coexistence of ASD and A. fumigatus may increase the development of fungal biofilms and fungal inflammatory diseases in the sinonasal mucosa.

Mannose-binding lectin conjugated to quantum dots as fluorescent nanotools for carbohydrate tracing

Quantum dots (QDs) have stood out as nanotools for glycobiology due to their photostability and ability to be combined with lectins. Mannose-binding lectin (MBL) is involved in the innate immune system and plays important roles in the activation of the complement cascade, opsonization, and elimination of apoptotic and microbial cells. Herein, adsorption and covalent coupling strategies were evaluated to conjugate QDs to a recombinant human MBL (rhMBL). The most efficient nanoprobe was selected by evaluating the conjugate ability to labelCandida albicansyeasts by flow cytometry. The QDs-rhMBL conjugate obtained by adsorption at pH 6.0 was the most efficient, labelingca.100% of cells with the highest median fluorescence intensity. The conjugation was also supported by Fourier transform infrared spectroscopy, zeta potential, and size analyses.C. albicanslabeling was calcium-dependent; 12% and <1% of cells were labeled in buffers without calcium and containing EDTA, respectively. The conjugate promoted specific labeling (based on cluster effect) since, after inhibition with mannan, there was a reduction of 80% in cell labeling, which did not occur with methyl-α-D-mannopyranoside monosaccharide. Conjugates maintained colloidal stability, bright fluorescence, and biological activity for at least 8 months. Therefore, QDs-rhMBL conjugates are promising nanotools to elucidate the roles of MBL in biological processes.

Synthesis and Characterization of CdTe QDs Capped with Branched 3MB3MP Ligand and Fluorescent Switching Detection of H2O2

Owing to the possibility for modification with various multifunctional ligand groups , and thereby attaining selective and sensitive detection; water soluble quantum dots (QDs) always attract scientific attention, in the...

Quantum dots conjugated to lectins from Schinus terebinthifolia leaves (SteLL) and Punica granatum sarcotesta (PgTeL) as potential fluorescent nanotools for investigating Cryptococcus neoformans

This study reports the development of conjugates based on quantum dots (QD)s and lectins from Schinus terebinthifolia leaves (SteLL) and Punica granatum sarcotesta (PgTeL). Cryptococcus neoformans cells were chosen to evaluate the efficiency of the conjugates. Lectins were conjugated to QDs via adsorption, and the optical parameters (emission and absorption) were monitored. Lectin stability in the conjugates towards denaturing agents was investigated via fluorometry. The conjugation was evaluated using fluorescence microplate (FMA) and hemagglutination (HA) assays. The labeling of the C. neoformans cell surface was quantified using flow cytometry and observed via fluorescence microscopy. The QDs-SteLL and QDs-PgTeL conjugates, obtained at pH 7.0 and 8.0, respectively, showed the maintenance of colloidal and optical properties. FMA confirmed the conjugation, and the HA assay indicated that the lectin carbohydrate-binding ability was preserved after conjugation. SteLL and PgTeL showed stability towards high urea concentrations and heating. Conjugates labeled over 90% of C. neoformans cells as observed via flow cytometry and confirmed through fluorescence microscopy. C. neoformans labeling by conjugates was inhibited by glycoproteins, suggesting specific interactions through the lectin carbohydrate-binding site. Thus, an effective protocol for the conjugation of SteLL or PgTeL with QDs was proposed, yielding new nanoprobes useful for glycobiological studies.

A brief insight to the role of glyconanotechnology in modern day diagnostics and therapeutics

Carbohydrate-protein and carbohydrate-carbohydrate interactions are very important for various biological processes. Although the magnitude of these interactions is low compared to that of protein-protein interaction, the magnitude can be boosted by multivalent approach known as glycocluster effect. Nanoparticle platform is one of the best ways to present diverse glycoforms in multivalent manner and thus, the field of glyconanotechnology has emerged as an important field of research considering their potential applications in diagnostics and therapeutics. Considerable advances in the field have been achieved through development of novel techniques, use of diverse metallic and non-metallic cores for better efficacy and application of ever-increasing number of carbohydrate ligands for site-specific interaction. The present review encompasses the recent developments in the area of glyconanotechnology and their future promise as diagnostic and therapeutic tools.

Quantum dots functionalized with 3-mercaptophenylboronic acids as novel nanoplatforms to evaluate sialic acid content on cell membranes

Sialic acids (SAs) modulate essential physiological and pathological conditions, including cell-cell communication, immune response, neurological disorders, and cancer. Besides, SAs confer negative charges to cell membranes, also contributing to hemorheology. Phenylboronic acids, called as mimetic lectins, have been highlighted to study SA profiles. The association of these interesting molecules with the optical properties of quantum dots (QDs) can provide a deeper/complementary understanding of mechanisms involving SAs. Herein, we explored the thiol affinity to the QD surface to develop a simple, fast and direct attachment procedure to functionalize these nanocrystals with 3-mercaptophenylboronic acids (MPBAs). The functionalization was confirmed by fluorescence correlation spectroscopy and inductively coupled plasma spectrometry. The conjugate specificity/efficiency was proved in experiments using red blood cells (RBCs). A labeling >90% was found for RBCs incubated with conjugates, which reduced to 17% after neuraminidase pretreatment. Moreover, QDs-MPBA conjugates were applied in a comparative study using acute (KG-1) and chronic (K562) myelogenous leukemia cell lines. Results indicated that KG-1 membranes have a greater level of SA, with 100% of cells labeled and a median of fluorescence intensity of ca. 2.5-fold higher when compared to K562 (94%). Therefore, this novel QDs-MPBA conjugate can be considered a promising nanoplatform to evaluate SA contents in a variety of biological systems.

Evaluating internalization and recycling of folate receptors in breast cancer cells using quantum dots

Folic acid (FA) regulates metabolic activities essential to the human body. FA receptor (FR) overexpression has been reported for many cancers, but there are still few or conflicting data about FRs in breast cancer cells. Quantum dots (QDs) have arisen as tools to elucidate aspects on FRs, due to their unique physicochemical properties. Herein, QDs conjugated to FA were explored to study the internalization and recycling of FRs in breast cancer cells, using HeLa as an out-group control. QDs were covalently conjugated to FA under different conditions. The best conjugate was applied to study FRs in HeLa, MCF7, MDA-MB231, and T47D cells applying confocal microscopy and flow cytometry analyses. The conjugation efficiency and specificity were evaluated, respectively, using fluorescence correlation spectroscopy (FCS) and saturation assays. FCS confirmed the effectiveness of the conjugation. HeLa and T47D had/internalized a higher amount of FRs (95% and 90% of labeling, respectively) than MDA-MB231 cells (68%). MCF7 cells seem to have very low functional FRs (3%). Saturation assays proved the specificity of QD-FA conjugates and suggested that FR recycling rate is low in the majority of cells studied, except for T47D. QD-FA conjugates were successfully developed. Therapies targeting FRs may be more effective for HeLa, T47D, and MDA-MB231.

Anionic Quantum Dots reveal actin-microridges in zebrafish epidermis

Enhancement of hydrophilicity and functionalization of CdTe QDs (Quantum Dots) via surface modifications have made them suitable to be used as specific probes for cell imaging. Applications for targeting cell surfaces have been widely demonstrated in vitro but their use in animal models is not trivial. Here, we reported the interaction of mercaptosuccinic-coated (MSA) CdTe QDs with the epidermis of living and Carnoy-fixed zebrafish embryos. QDs concentrate along adherent junctions and reveal the characteristic pattern of actin microridges at the apical surface of the enveloping layer. In our study, labeling with anionic QDs is attained within few minutes at submicromolar concentrations in whole mounted Carnoy-fixed zebrafish embryos, providing a faster approach compared with immunodetection or standard Phalloidin staining of actin for visualization by fluorescence microscopy.

Concanavalin A-Rose Bengal bioconjugate for targeted Gram-negative antimicrobial photodynamic therapy

Photodynamic therapy (PDT) is considered a very promising therapeutic modality for antimicrobial therapy. Although several studies have demonstrated that Gram-positive bacteria are very sensitive to PDT, Gram-negative bacteria are more resistant to photodynamic action. This difference is due to a different cell wall structure. Gram-negative bacteria have an outer cell membrane containing lipopolysaccharides (LPS) that hinder the binding of photosensitizer molecules, protecting the bacterial cells from chemical attacks. Combination of the lipopolysaccharides-binding activity of Concanavalin A (ConA) with the photodynamic properties of Rose Bengal (RB) holds the potential of an innovative protein platform for targeted photodynamic therapy against Gram-negative bacteria. A ConA-RB bioconjugate was synthesized and characterized. Approximately 2.4 RB molecules were conjugated per ConA monomer. The conjugation of RB to ConA determines a decrease of the singlet oxygen generation and an increase of superoxide and peroxide production. The photokilling efficacy of the ConA-RB bioconjugate was demonstrated in a planktonic culture of E. coli. Irradiation with white light from a LED lamp produced a dose-dependent photokilling of bacteria. ConA-RB conjugates exhibited a consistent improvement over RB (up to 117-fold). The improved uptake of the photosensitizer explains the enhanced PDT effect accompanying increased membrane damages induced by the ConA-RB conjugate. The approach can be readily generalized (i) using different photo/sonosensitizers, (ii) to target other pathogens characterized by cell membranes containing lipopolysaccharides (LPS).

Quantum Dot Labelling of Tepary Bean (Phaseolus acutifolius) Lectins by Microfluidics

Lectins are bioactive proteins with the ability to recognize cell membrane carbohydrates in a specific way. Diverse plant lectins have shown diagnostic and therapeutic potential against cancer, and their cytotoxicity against transformed cells is mediated through the induction of apoptosis. Previous works have determined the cytotoxic activity of a Tepary bean (Phaseolus acutifolius) lectin fraction (TBLF) and its anti-tumorigenic effect on colon cancer. In this work, lectins from the TBLF were additionally purified by ionic-exchange chromatography. Two peaks with agglutination activity were obtained: one of them was named TBL-IE2 and showed a single protein band in two-dimensional electrophoresis; this one was thus selected for coupling to quantum dot (QD) nanoparticles by microfluidics (TBL-IE2-QD). The microfluidic method led to low sample usage, and resulted in homogeneous complexes, whose visualization was achieved using multiphoton and transmission electron microscopy. The average particle size (380 nm) and the average zeta potential (-18.51 mV) were determined. The cytotoxicity of the TBL-IE2 and TBL-IE2-QD was assayed on HT-29 colon cancer cells, showing no differences between them (p ≤ 0.05), where the LC50 values were 1.0 × 10-3 and 1.7 × 10-3 mg/mL, respectively. The microfluidic technique allowed control of the coupling between the QD and the protein, substantially improving the labelling process, providing a rapid and efficient method that enabled the traceability of lectins. Future studies will focus on the potential use of the QD-labelled lectin to recognize tumor tissues.

Resazurin-Based Assay to Evaluate Cell Viability After Quantum Dot Interaction

The increasing applications of quantum dots (QDs) as optic tools in life science have stimulated researchers to evaluate the effects of these nanoprobes in cell viability using a variety of methods, especially colorimetric ones. One of the most applied tests is the MTT assay. In comparison to MTT, for example, the resazurin-based method has the main advantage of not evaluating the cells directly, thus eliminating false-positive results that may arise from the overlap of the absorbances of the QD with the colorimetric compound. Therefore, herein, we describe the resazurin assay as an alternative, simple, quick, sensitivity, reproducible, and nontoxic test to evaluate the in vitro cell viability after QD exposure. Moreover, this test presents an additional advantage; the cells remain viable for complementary experimental procedures, such as cell migration or adhesion.

Evaluating viscoelastic properties and membrane electrical charges of red blood cells with optical tweezers and cationic quantum dots - applications to β-thalassemia intermedia hemoglobinopathy

Biomechanical and electrical properties are important to the performance and survival of red blood cells (RBCs) in the microcirculation. This study proposed and explored methodologies based on optical tweezers and cationic quantum dots (QDs) as biophotonic tools to characterize, in a complementary way, viscoelastic properties and membrane electrical charges of RBCs. The methodologies were applied to normal (HbA) and β-thalassemia intermedia (Hbβ) RBCs. The β-thalassemia intermedia disease is a hereditary hemoglobinopathy characterized by a reduction (or absence) of β-globin chains, which leads to α-globin chains precipitation. The apparent elasticity (μ) and membrane viscosity (η_m) of RBCs captured by optical tweezers were obtained in just a single experiment. Besides, the membrane electrical charges were evaluated by flow cytometry, exploring electrostatic interactions between cationic QDs, stabilized with cysteamine, with the negatively charged RBC surfaces. Results showed that Hbβ RBCs are less elastic, have a higher η_m, and presented a reduction in membrane electrical charges, when compared to HbA RBCs. Moreover, the methodologies based on optical tweezers and QDs, here proposed, showed to be capable of providing a deeper and integrated comprehension on RBC rheological and electrical changes, resulting from diverse biological conditions, such as the β-thalassemia intermedia hemoglobinopathy.

Studies on Toxicity of Suspensions of CdTe Quantum Dots to Biomphalaria glabrata Mollusks

Quantum dots have generated great interest because of their optical properties, both to life sciences and electronics applications. However, possible risks to the environment associated with these nanoparticles are still under investigation. The present study aimed to evaluate the toxicity of suspensions of cadmium telluride (CdTe) quantum dots to Biomphalaria glabrata mollusks, a very sensitive aquatic environmental bioindicator for physical and chemical agents. Toxicity was examined by using embryos and adult mollusks as well as hemocytes. The distribution of cadmium in the organs of adults was also assessed. Effects of the stabilizing agent of the quantum dots were also evaluated. Animals were exposed to suspensions of quantum dots for 24 h, at concentrations varying from 1.2 to 20 nM for embryos and from 50 to 400 nM for adult mollusks. Results showed that suspensions of quantum dots induced malformations and mortality in embryos and mortality in adults, depending on the concentration applied. In the cytotoxicity study, hemocyte apoptosis was observed in adults exposed to the highest concentration of quantum dots applied as well as to the stabilizing agent. Cell binucleation and micronucleus frequencies were not significative. Bioaccumulation evaluation revealed that quantum dots targeted the digestive gland (hepatopancreas). Taken together, outcomes suggested that specific nano-effects related directly not only to composition but also to the aggregation of quantum dots may be mediating the observed toxicity. Thus B. glabrata was determined to be a very sensitive species for interpreting possible nano-effects in aquatic environments. Environ Toxicol Chem 2019;38:2128-2136. © 2019 SETAC.

Evaluating glucose and mannose profiles in Candida species using quantum dots conjugated with Cramoll lectin as fluorescent nanoprobes

Glycoconjugates found on cell walls of Candida species are fundamental for their pathogenicity. Laborious techniques have been employed to investigate the sugar composition of these microorganisms. Herein, we prepared a nanotool, based on the fluorescence of quantum dots (QDs) combined with the specificity of Cramoll lectin, to evaluate glucose/mannose profiles on three Candida species. The QDs-Cramoll conjugates presented specificity and bright fluorescence emission. The lectin preserved its biological activity after the conjugation process mediated by adsorption interactions. The labeling of Candida species was analyzed by fluorescence microscopy and quantified by flow cytometry. Morphological analyses of yeasts labeled with QDs-Cramoll conjugates indicated that C. glabrata (2.7 μm) was smaller when compared to C. albicans (4.0 μm) and C. parapsilosis sensu stricto (3.8 μm). Also, C. parapsilosis population was heterogeneous, presenting rod-shaped blastoconidia. More than 90% of cells of the three species were labeled by conjugates. Inhibition and saturation assays indicated that C. parapsilosis had a higher content of exposed glucose/mannose than the other two species. Therefore, QDs-Cramoll conjugates demonstrated to be effective fluorescent nanoprobes for evaluation of glucose/mannose constitution on the cell walls of fungal species frequently involved in candidiasis.

Highly Photostable and Two-Photon Active Quantum Dot-Polymer Multicolor Hybrid Coacervate Droplets

Fabrication and precise control of the physicochemical properties of multifunctional organic-inorganic hybrid nanocomposites find great importance in various research fields. Herein, we report the fabrication of a new class of luminescent hybrid coacervate droplets from CdTe quantum dots (QDs) and a poly(diallyldimethylammonium chloride) (PDADMAC) aqueous mixture. The colloidal stability of these droplets has been explored over wide ranges of composition, pH, and ionic strength. Although these hybrid droplets are quite stable in a low-ionic-strength medium (<100 mM NaCl) and neutral/basic pH (pH >6.5), they are unstable in a higher-ionic-strength medium (>100 mM NaCl) and acidic pH (pH <5.5). Our findings indicate specific electrostatic interactions between negatively charged QDs and positively charged PDADMAC behind the observed coacervation. They exhibit the preferential sequestration of organic dyes and serum albumins. The intrinsic luminescent properties of these hybrid droplets have been explored using confocal laser scanning microscopy (CLSM) and epifluorescence microscopy. CLSM reveals the formation of intrinsically luminescent hybrid droplets. In addition, mixed two-color luminescent droplets have been fabricated by simultaneously mixing green- and red-emitting QDs with PDADMAC aqueous solution. Epifluorescence imaging reveals highly photostable and nonbleaching photoluminescence (PL) from individual droplets as a consequence of efficient surface passivation by polymeric chains of PDADMAC. Moreover, using two-photon (2P) confocal imaging we have shown that these hybrid droplets are ideal candidates for 2P confocal imaging applications. The present study can be easily extended to fabricate a wide range of hybrid droplets with various inorganic counterparts having unique optoelectronic properties, which will further expand their applicability in nanocatalysis, bioimaging, and biosensing.

Evaluating the glycophenotype on breast cancer tissues with quantum dots-Cramoll lectin conjugates

During carcinogenesis, changes in the glycosylation can modulate many biological processes. Thus, the interest in exploring and understanding the roles of carbohydrates as cancer biomarkers has been increasing. Lectins have been applied as useful tools in glycobiology, especially when associated with fluorescent reporters. Therefore, to take advantage of the physicochemical properties of quantum dots (QDs), herein, we conjugated Cramoll, a lectin that recognizes glucose/mannose residues, with those nanoparticles. We applied the conjugates to investigate the glycocode of normal, fibroadenoma (FB), and invasive ductal carcinoma (IDC) human breast tissues. Additionally, we proposed a method to quantitatively evaluate the tissue labeling intensity by a fluorescence microplate assay (FMA). Conjugates showed intense fluorescence and specificity. The lectin activity and secondary structure were also preserved after the conjugation with QDs. Moreover, fluorescence images showed that ductal cells of normal and FB tissues were preferentially labeled by conjugates, whereas both cells and stroma were strongly labeled in IDC. FMA showed in a quantitative, practical, and sensitive way that the level of exposed glucose/mannose residues increased accordingly to the sample malignancy degree. In conclusion, QDs-Cramoll conjugates can be considered effective, specific, and versatile probes to evaluate glycan profiles in normal and transformed tissues, by fluorescence microscopy as well as FMA quantification. Furthermore, FMA showed to be a potential method that can be applied with other fluorescent conjugates.

Canavalia ensiformis-derived lectin inhibits biofilm formation of enterohemorrhagic Escherichia coli and Listeria monocytogenes

AIM

A lectin Concanavalin A (ConA) derived from Canavalia ensiformis (jack bean) exhibits high-binding affinity to carbohydrates on bacterial cell surfaces. The objective of this study was to inhibit the biofilm formation of the foodborne pathogens enterohemorrhagic Escherichia coli and Listeria monocytogenes using ConA prepared by a membrane-based extraction method.

METHODS AND RESULTS

ConA was extracted using a simple and inexpensive membrane method instead of a chromatography approach. The extracted ConA was effective in inhibiting biofilms of E. coli by 30-fold and L. monocytogenes by 140-fold. In addition, ConA decreased the swimming motility of enterohemorrhagic E. coli EDL933 (EHEC) by 37%, resulting in low biofilm formation, as ConA binding to the bacterial cell surfaces might cause a reduced capability to adhere due to low cellular motility. We confirmed that the extracted ConA contains active components at less than 10 kDa as well as ConA multimers (>30 kDa) that repress EHEC biofilms. Additionally, noncell-based mannose reduced the activity of ConA in inhibiting biofilms.

CONCLUSIONS

ConA extracted using the membrane-based method is active in inhibiting the biofilm formation by E. coli and L. monocytogenes via the mannose-binding affinity of ConA.

SIGNIFICANCE AND IMPACT OF THE STUDY

ConA can be used as a promising anti-adherent and antibiofilm agent in inhibiting biofilm formation by enterohemorrhagic E. coli and L. monocytogenes. The membrane-based extraction approach may be applied for the economic production of biologically active lectins.

Tracing Tellurium and Its Nanostructures in Biology

Tellurium (Te) is a semimetal rare element in nature. Together with oxygen, sulfur (S), and selenium (Se), Te is considered a member of chalcogen group. Over recent decades, Te applications continued to emerge in different fields including metallurgy, glass industry, electronics, and applied chemical industries. Along these lines, Te has recently attracted research attention in various fields. Though Te exists in biologic organisms such as microbes, yeast, and human body, its importance and role and some of its potential implications have long been ignored. Some promising applications of Te using its inorganic and organic derivatives including novel Te nanostructures are being introduced. Before discovery and straightforward availability of antibiotics, Te had considered and had been used as an antibacterial element. Antilishmaniasis, antiinflammatory, antiatherosclerotic, and immuno-modulating properties of Te have been described for many years, while the innovative applications of Te have started to emerge along with nanotechnological advances over the recent years. Te quantum dots (QDs) and related nanostructures have proposed novel applications in the biological detection systems such as biosensors. In addition, Te nanostructures are used in labeling, imaging, and targeted drug delivery systems and are tested for antibacterial or antifungal properties. In addition, Te nanoparticles show novel lipid-lowering, antioxidant, and free radical scavenging properties. This review presents an overview on the novel forms of Te, their potential applications, as well as related toxicity profiles.

Quantitative and multiplexed detection for blood typing based on quantum dot-magnetic bead assay

Background

Accurate and reliable blood grouping is essential for safe blood transfusion. However, conventional methods are qualitative and use only single-antigen detection. We overcame these limitations by developing a simple, quantitative, and multiplexed detection method for blood grouping using quantum dots (QDs) and magnetic beads.

Methods

In the QD fluorescence assay (QFA), blood group A and B antigens were quantified using QD labeling and magnetic beads, and the blood groups were identified according to the R value (the value was calculated with the fluorescence intensity from dual QD labeling) of A and B antigens. The optimized performance of QFA was established by blood typing 791 clinical samples.

Results

Quantitative and multiplexed detection for blood group antigens can be completed within 35 min with more than 10⁵ red blood cells. When conditions are optimized, the assay performance is satisfactory for weak samples. The coefficients of variation between and within days were less than 10% and the reproducibility was good. The ABO blood groups of 791 clinical samples were identified by QFA, and the accuracy obtained was 100% compared with the tube test. Receiver-operating characteristic curves revealed that the QFA has high sensitivity and specificity toward clinical samples, and the cutoff points of the R value of A and B antigens were 1.483 and 1.576, respectively.

Conclusion

In this study, we reported a novel quantitative and multiplexed method for the identification of ABO blood groups and presented an effective alternative for quantitative blood typing. This method can be used as an effective tool to improve blood typing and further guarantee clinical transfusion safety.

Glucose modulates antimicrobial photodynamic inactivation of Candida albicans in biofilms

Candida albicans biofilm is a main cause of infections associated with medical devices such as catheters, contact lens and artificial joint prosthesis. The current treatment comprises antifungal chemotherapy that presents low success rates. Photodynamic inactivation (PDI) involves the combination of a photosensitizing compound (PS) and light to generate oxidative stress that has demonstrated effective antimicrobial activity against a broad-spectrum of pathogens, including C. albicans. This fungus senses glucose inducing an upregulation of membrane transporters that can facilitate PS uptake into the cell. The aim of this study was to evaluate the effects of glucose on methylene blue (MB) uptake and its influence on PDI efficiency when combined to a red LED with central wavelength at λ=660nm. C. albicans biofilms were grown on hydrogel disks. Prior to PDI assays, MB uptake tests were performed with and without glucose-sensitization. In this system, the optimum PS administration was determined as 500μM of MB in contact with the biofilm during 30min before irradiation. Irradiation was performed during 3, 6, 9, 12, 15 and 18min with irradiance of 127.3mW/cm². Our results showed that glucose was able to increase MB uptake in C. albicans cells. In addition, PDI without glucose showed a higher viability reduction until 6min; after 9min, glucose group demonstrated a significant decrease in cell viability when compared to glucose-free group. Taken together, our data suggest that glucose is capable to enhance MB uptake and modulate photodynamic inactivation of C. albicans biofilm.

Blood group antigen studies using CdTe quantum dots and flow cytometry

New methods of analysis involving semiconductor nanocrystals (quantum dots [QDs]) as fluorescent probes have been highlighted in life science. QDs present some advantages when compared to organic dyes, such as size-tunable emission spectra, broad absorption bands, and principally exceptional resistance to photobleaching. Methods applying QDs can be simple, not laborious, and can present high sensibility, allowing biomolecule identification and quantification with high specificity. In this context, the aim of this work was to apply dual-color CdTe QDs to quantify red blood cell (RBC) antigen expression on cell surface by flow cytometric analysis. QDs were conjugated to anti-A or anti-B monoclonal antibodies, as well as to the anti-H (Ulex europaeus I) lectin, to investigate RBCs of A₁, B, A₁B, O, A₂, and A_weak donors. Bioconjugates were capable of distinguishing the different expressions of RBC antigens, both by labeling efficiency and by flow cytometry histogram profile. Furthermore, results showed that RBCs from A_weak donors present fewer amounts of A antigens and higher amounts of H, when compared to A₁ RBCs. In the A group, the amount of A antigens decreased as A₁ > A₃ > A_X = A_el, while H antigens were A_X = A_el > A₁. Bioconjugates presented stability and remained active for at least 6 months. In conclusion, this methodology with high sensibility and specificity can be applied to study a variety of RBC antigens, and, as a quantitative tool, can help in achieving a better comprehension of the antigen expression patterns on RBC membranes.

Fast synthesis of fluorescent SiO2@CdTe nanoparticles with reusability in detection of H2O2

In this study, highly fluorescent core/shell SiO₂@CdTe nanoparticles (NPs) were synthesized conveniently and efficiently via a hydrothermal method. The as-prepared SiO₂@CdTe NPs were uniform with good fluorescence preservation. The SiO₂@CdTe NPs could be used for the rapid detection of H₂O₂ with good sensitivity within several minutes. Excellent linear relationships existed between the quenching degrees of the SiO₂@CdTe NPs and the concentration of H₂O₂ in the range of 0.005 mM to 0.1 mM. The limit of detection (LOD) for H₂O₂ was 10 nM. Furthermore, it was proved that SiO₂@CdTe NPs could be used repeatedly for H₂O₂ detection due to their easy separation, which is an important feature. The excellent performance of SiO₂@CdTe NPs should facilitate their applications in chemistry or biology for detection of H₂O₂.

Comparative Study on the Efficiency of the Photodynamic Inactivation of Candida albicans Using CdTe Quantum Dots, Zn(II) Porphyrin and Their Conjugates as Photosensitizers

The application of fluorescent II-VI semiconductor quantum dots (QDs) as active photosensitizers in photodymanic inactivation (PDI) is still being evaluated. In the present study, we prepared 3 nm size CdTe QDs coated with mercaptosuccinic acid and conjugated them electrostatically with Zn(II) meso-tetrakis (N-ethyl-2-pyridinium-2-yl) porphyrin (ZnTE-2-PyP or ZnP), thus producing QDs-ZnP conjugates. We evaluated the capability of the systems, bare QDs and conjugates, to produce reactive oxygen species (ROS) and applied them in photodynamic inactivation in cultures of Candida albicans by irradiating the QDs and testing the hypothesis of a possible combined contribution of the PDI action. Tests of in vitro cytotoxicity and phototoxicity in fibroblasts were also performed in the presence and absence of light irradiation. The overall results showed an efficient ROS production for all tested systems and a low cytotoxicity (cell viability >90%) in the absence of radiation. Fibroblasts incubated with the QDs-ZnP and subjected to irradiation showed a higher cytotoxicity (cell viability <90%) depending on QD concentration compared to the bare groups. The PDI effects of bare CdTe QD on Candida albicans demonstrated a lower reduction of the cell viability (~1 log10) compared to bare ZnP which showed a high microbicidal activity (~3 log10) when photoactivated. The QD-ZnP conjugates also showed reduced photodynamic activity against C. albicans compared to bare ZnP and we suggest that the conjugation with QDs prevents the transmembrane cellular uptake of the ZnP molecules, reducing their photoactivity.