Methylene blue@silver nanoprisms conjugates as a strategy against Candida albicans isolated from balanoposthitis using photodynamic inactivation.

Balanoposthitis can affect men in immunocompromised situations, such as HIV infection and diabetes. The main associated microorganism is Candida albicans, which can cause local lesions, such as the development of skin cracks associated with itching. As an alternative to conventional treatment, there is a growing interest in the photodynamic inactivation (PDI). It has been shown that the association of photosensitizers with metallic nanoparticles may improve the effectiveness of PDI via plasmonic effect. We have recently shown that the association of methylene blue (MB), a very known photosensitizer, with silver prismatic nanoplatelets (AgNPrs) improved PDI of a resistant strain of Staphylococcus aureus. To further investigate the experimental conditions involved in PDI improvement, in the present study, we studied the effect of MB concentration associated with AgNPrs exploring spectral analysis, zeta potential measurements, and biological assays, testing the conjugated system against C. albicans isolated from a resistant strain of balanoposthitis. The AgNPrs were synthesized through silver anisotropic seed growth induced by the anionic stabilizing agent poly(sodium 4-styrenesulfonate) and showed a plasmon band fully overlapping the MB absorption band. MB and AgNPrs were conjugated through electrostatic association and three different MB concentrations were tested in the nanosystems. Inactivation using red LED light (660 nm) showed a dose dependency in respect to the MB concentration in the conjugates. Using the highest MB concentration (100 µmol⋅L-1) with AgNPr, it was possible to completely inactivate the microorganisms upon a 2 min irradiation exposure. Analyzing optical changes in the conjugates we suggest that these results indicate that AgNPrs are enhancers of MB photodynamic action probably by a combined mechanism of plasmonic effect and reduction of MB dimerization. Therefore, MBAgNPrs can be considered a suitable choice to be applied in PDI of resistant microorganisms.

UV Light as an Efficient Tool for Reducing Surface Defects of ZnSe-MSA Quantum Dots.

Defects in ZnSe quantum dots are responsible for increasing the trap states, which can lead to the drastic reduction of their fluorescence output, being one of the major drawbacks of these materials. As surface atoms become more relevant in these nanoscale structures, energy traps due to surface vacancies, play a very definite role in the final emission quantum yield. In the present study, we report the use of photoactivation procedures to decrease surface defects of ZnSe QDs stabilized with mercaptosuccinic acid (MSA), in order to improve the radiative pathways. We applied the colloidal precipitation procedure in a hydrophilic medium and evaluated the role of Zn/Se molar ratios as well as the Zn2+ precursors (nitrate and chloride salts) on their optical properties. Best results (i.e. increment of 400% of the final fluorescence intensity) were obtained for nitrate precursor and a Zn/Se = 1.2 ratio. Thus, we suggest that the chloride ions may compete more efficiently than nitrate ions with MSA molecules decreasing the passivation capability of this molecule. The improvement in ZnSe QDs fluorescence can potentialize their use for biomedical applications.

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-ß-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.

A Novel Strategy Based on Zn(II) Porphyrins and Silver Nanoparticles to Photoinactivate Candida albicans.

Background: Photodynamic inactivation (PDI) is an attractive alternative to treat Candida albicans infections, especially considering the spread of resistant strains. The combination of the photophysical advantages of Zn(II) porphyrins (ZnPs) and the plasmonic effect of silver nanoparticles (AgNPs) has the potential to further improve PDI. Here, we propose the novel association of polyvinylpyrrolidone (PVP) coated AgNPs with the cationic ZnPs Zn(II) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin or Zn(II) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin to photoinactivate C. albicans. Methods: AgNPs stabilized with PVP were chosen to allow for (i) overlap between the NP extinction and absorption spectra of ZnPs and (ii) favor AgNPs-ZnPs interaction; prerequisites for exploring the plasmonic effect. Optical and zeta potential (ζ) characterizations were performed, and reactive oxygen species (ROS) generation was also evaluated. Yeasts were incubated with individual ZnPs or their respective AgNPs-ZnPs systems, at various ZnP concentrations and two proportions of AgNPs, then irradiated with a blue LED. Interactions between yeasts and the systems (ZnP alone or AgNPs-ZnPs) were evaluated by fluorescence microscopy. Results: Subtle spectroscopic changes were observed for ZnPs after association with AgNPs, and the ζ analyses confirmed AgNPs-ZnPs interaction. PDI using ZnP-hexyl (0.8 µM) and ZnP-ethyl (5.0 µM) promoted a 3 and 2 log10 reduction of yeasts, respectively. On the other hand, AgNPs-ZnP-hexyl (0.2 µM) and AgNPs-ZnP-ethyl (0.6 µM) systems led to complete fungal eradication under the same PDI parameters and lower porphyrin concentrations. Increased ROS levels and enhanced interaction of yeasts with AgNPs-ZnPs were observed, when compared with ZnPs alone. Conclusion: We applied a facile synthesis of AgNPs which boosted ZnP efficiency. We hypothesize that the plasmonic effect combined with the greater interaction between cells and AgNPs-ZnPs systems resulted in an efficient and improved fungal inactivation. This study provides insight into the application of AgNPs in PDI and helps diversify our antifungal arsenal, encouraging further developments toward inactivation of resistant Candida spp.

Sensitive Zika biomarker detection assisted by quantum dot-modified electrochemical immunosensing platform.

We report the development of a new nanostructured electrochemical immunosensing platform for the detection of the Zika virus envelope protein (EP-ZIKV). For this, quantum dots (QDs) were explored in combination with screen-printed carbon electrodes (SPCEs) functionalized with a conductor polymeric film, formed from 2-(1H-pyrrol-1-yl)ethanamine (Pyam), and anti-EP DIII ZIKV antibodies. Carboxylated CdTe QDs were synthesized, characterized by optical and structural techniques, and covalently immobilized onto the SPCE/PPyam surface. Then, anti-EP ZIKV antibodies were also covalently conjugated to QDs. All stages of platform assembly were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The detection of EP-ZIKV was performed by differential pulse voltammetry (DPV). Results indicated that QDs were efficiently immobilized, and did not show oxidation, under the conditions evaluated, for at least 7 months. Anti-EP ZIKV antibodies were effectively immobilized on the PPyam/QDs surface, even after 2 months of electrode storage. The platform enabled the detection of EP-ZIKV with high sensitivity using minimal sample volumes (LOD = 0.1 ng mL-1 and LOQ = 0.4 ng mL-1). The platform was also able to detect EP-ZIKV in spiked serum samples. Moreover, the platform showed specificity, not detecting the EP-DENV 3 nor a mixture of four DENV serotypes antigens. Thus, the proposed combination favored the development of a sensitive immunosensing platform, promising for the detection of Zika in the viremic phase, which also holds potential for transposition to other arboviruses.

Photoinactivation of Yeast and Biofilm Communities of Candida albicans Mediated by ZnTnHex-2-PyP4+ Porphyrin.

Candida albicans is the main cause of superficial candidiasis. While the antifungals available are defied by biofilm formation and resistance emergence, antimicrobial photodynamic inactivation (aPDI) arises as an alternative antifungal therapy. The tetracationic metalloporphyrin Zn(II) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (ZnTnHex-2-PyP4+) has high photoefficiency and improved cellular interactions. We investigated the ZnTnHex-2-PyP4+ as a photosensitizer (PS) to photoinactivate yeasts and biofilms of C. albicans strains (ATCC 10231 and ATCC 90028) using a blue light-emitting diode. The photoinactivation of yeasts was evaluated by quantifying the colony forming units. The aPDI of ATCC 90028 biofilms was assessed by the MTT assay, propidium iodide (PI) labeling, and scanning electron microscopy. Mammalian cytotoxicity was investigated in Vero cells using MTT assay. The aPDI (4.3 J/cm2) promoted eradication of yeasts at 0.8 and 1.5 µM of PS for ATCC 10231 and ATCC 90028, respectively. At 0.8 µM and same light dose, aPDI-treated biofilms showed intense PI labeling, about 89% decrease in the cell viability, and structural alterations with reduced hyphae. No considerable toxicity was observed in mammalian cells. Our results introduce the ZnTnHex-2-PyP4+ as a promising PS to photoinactivate both yeasts and biofilms of C. albicans, stimulating studies with other Candida species and resistant isolates.

Silver nanoprisms as plasmonic enhancers applied in the photodynamic inactivation of Staphylococcus aureus isolated from bubaline mastitis.

Mastitis is a bacterial infection that affects all lactating mammals, and in dairy cattle, it leads to a reduction in their milk production and, in worse cases, it may lead to animal death. One viable therapeutic modality for overcoming bacterial resistance can be photodynamic inactivation (PDI), a therapeutic modality for bacterial infection treatment. One of the main factors that can lead to an efficient PDI process is the association of metallic nanoparticles in the close vicinity of photosensitizers, which has shown promising results due to localized surface plasmon resonance phenomena. In this work, methylene blue (MB) molecules were associated with Ag prismatic nanoplatelets (AgNPrs) to use as PDI photosensitizer against Staphylococcus aureus isolated from bubaline mastitis. The optical plasmonic activity of AgNPrs was tuned to the MB absorption region (600-700 nm) by inducing their growth into prismatic shapes by a seed-mediated procedure, using poly (sodium 4-styrene sulfonate) as the surfactant. A simulation on the plasmonic properties of the nanoprisms, applying particle size within the dimensions determined by TEM image analysis (d = 32 ± 6 nm), showed a 30 % increase of the incident field on the prismatic tips. Photodynamic results showed that the electrostatic AgNPr-MB conjugates promoted enhancement (ca. 15 %) of the reactive oxygen species production. Besides, PDI mediated by AgNPrs-MB led to the complete inactivation of the mastitis S. aureus strain after 6 min inactivation, in contrast to PDI mediated by MB, which reduced less than a 0.5 bacterial log. Thus, the results show this plasmonic enhanced photodynamic tool's potential to be applied in the inactivation of multi-resistant bacterial strains.

Efficient photodynamic inactivation of Leishmania parasites mediated by lipophilic water-soluble Zn(II) porphyrin ZnTnHex-2-PyP4.

BACKGROUND: Photodynamic inactivation (PDI) is emerging as a promising alternative for cutaneous leishmaniasis (CL). The chemotherapy currently used presents adverse effects and cases of drug resistance have been reported. ZnTnHex-2-PyP4+ is a porphyrin with a high potential as a photosensitizer (PS) for PDI, due to its photophysical properties, structural stability, and cationic/amphiphilic character that can enhance interaction with cells. This study aimed to investigate the photodynamic effects mediated by ZnTnHex-2-PyP4+ on Leishmania parasites. METHODS: ZnTnHex-2-PyP4+ stability was evaluated using accelerated solvolysis conditions. The photodynamic action on promastigotes was assessed by (i) viability assays, (ii) mitochondrial membrane potential evaluation, and (iii) morphological analysis. The PS-promastigote interaction was studied. PDI on amastigotes and the cytotoxicity on macrophages were also analyzed. RESULTS: ZnTnHex-2-PyP4+, under submicromolar concentration, led to immediate inactivation of more than 95% of promastigotes. PDI promoted intense mitochondrial depolarization, loss of the fusiform shape, and plasma membrane wrinkling in promastigotes. Fluorescence microscopy revealed a punctate PS labeling in the parasite cytoplasm. PDI also led to reductions of ca. 64% in the number of amastigotes/macrophage and 70% in the infection index after a single treatment session. No noteworthy toxicity was observed on mammalian cells. CONCLUSIONS: ZnTnHex-2-PyP4+ is stable against demetallation and more efficient as PS than the ethyl analogue ZnTE-2-PyP4+, indicating readiness for evaluation in in vivo studies as an alternative approach to CL. GENERAL SIGNIFICANCE: This report highlighted promising photodynamic effects mediated by ZnTnHex-2-PyP4+ on Leishmania parasites, opening up perspectives for applications in CL pre-clinical assays and PDI of other microorganisms.

Quantum Dots and Gd3+ Chelates: Advances and Challenges Towards Bimodal Nanoprobes for Magnetic Resonance and Optical Imaging.

The development of multimodal nanoprobes has been growing in recent years. Among these novel nanostructures are bimodal systems based on quantum dots (QDs) and low molecular weight Gd3+ chelates, prepared for magnetic resonance imaging (MRI) and optical analyses. MRI is a technique used worldwide that provides anatomic resolution and allows distinguishing of physiological differences at tissue and organ level. On the other hand, optical techniques are very sensitive and allow events to be followed at the cellular or molecular level. Thus, the association of these two techniques has the potential to achieve a more complete comprehension of biological processes. In this review, we present state-of-the-art research concerning the development of potential multimodal optical/paramagnetic nanoprobes based on Gd3+ chelates and QDs, highlighting their preparation strategies and overall properties.

Methods for Intracellular Delivery of Quantum Dots.

Quantum dots (QDs) have attracted considerable attention as fluorescent probes for life sciences. The advantages of using QDs in fluorescence-based studies include high brilliance, a narrow emission band allowing multicolor labeling, a chemically active surface for conjugation, and especially, high photostability. Despite these advantageous features, the size of the QDs prevents their free transport across the plasma membrane, limiting their use for specific labeling of intracellular structures. Over the years, various methods have been evaluated to overcome this issue to explore the full potential of the QDs. Thus, in this review, we focused our attention on physical and biochemical QD delivery methods-electroporation, microinjection, cell-penetrating peptides, molecular coatings, and liposomes-discussing the benefits and drawbacks of each strategy, as well as presenting recent studies in the field. We hope that this review can be a useful reference source for researches that already work or intend to work in this area. Strategies for the intracellular delivery of quantum dots discussed in this review (electroporation, microinjection, cell-penetrating peptides, molecular coatings, and liposomes).

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.

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.

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.

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 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.

Evaluation of the immunomodulatory effect against splenocytes of Balb/c mice of biflorin obtained from Capraria biflora by a new isolation method

Abstract Biflorin (6,9-dimethyl-3-(4-methylpent-3-en-1-yl) benzo[de]chromene-7,8-dione) is a promising substance that has been increasingly studied in the past decades due to its diverse pharmacological properties (i.e. antitumor, antioxidant, antiinflamatory, antimicrobial activity etc.). Aiming the comprehension of its antitumoral activity we investigated the cell proliferation and cytotoxicity habilities of biflorin against mice splenocytes Balb/c. Biflorin was able to stimulate mice splenocytes Balb/c in 48 h of incubation at a concentration of 20.2 µM. Its immunostimulation promoted the production of cytokines such as: TNF-α, IFN-γ, IL-2, IL-6 and IL-17, inducing the immune profile toward a Th1 response. Moreover, an original method which led to an excellent yield with less processing time compared to the methods described in the literature was developed to obtain biflorin, from sawdust of Capraria biflora L., Scrophulariaceae. This method shows a great potential of increasing the production of this pharmacological active compound.

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.

Quantum dots-based fluoroimmunoassay for anti-Zika virus IgG antibodies detection.

Zika virus (ZIKV) has been declared a public health emergency of international concern. ZIKV has been associated with some neurological disorders, and their long-term effects are not completely understood. The majority of the methods for ZIKV diagnosis are based on the detection of IgM antibodies, which are the first signs of immunological response. However, the detection of IgG antibodies can be an important approach for ZIKV past infection diagnosis, especially for pregnant women, helping the comprehension/treatment of this disease. There has been a growing interest in applying nanoparticles for efficient ZIKV or antibodies detection. Quantum dots (QD) are unique fluorescent semiconductor nanoparticles, highly versatile for biological applications. In the present study, we explored the special QD optical properties to develop an immunofluorescence assay for anti-ZIKV IgG antibodies detection. Anti-IgG antibodies were successfully conjugated with QDs and applied in a fluorescence sensing nanoplatform. After optimization using IgG antibodies, the conjugates were employed to detect anti-ZIKV IgG antibodies in polystyrene microplates sensitized with ZIKV envelope E protein. The nanoplatform was able to detect anti-ZIKV IgG antibodies in a concentration at least 100-fold lower than the amount expected for protein E immune response. Moreover, conjugates were able to detect the antibodies for at least 4 months. Thus, our results showed that this QDs-based fluoroimmunoplatform can be considered practical, simple and promising to detect Zika past infections and/or monitoring immune response in vaccine trials.

Hydrophilic Quantum Dots Functionalized with Gd(III)-DO3A Monoamide Chelates as Bright and Effective T1-weighted Bimodal Nanoprobes.

Magnetic resonance imaging (MRI) is a powerful non-invasive diagnostic tool that enables distinguishing healthy from pathological tissues, with high anatomical detail. Nevertheless, MRI is quite limited in the investigation of molecular/cellular biochemical events, which can be reached by fluorescence-based techniques. Thus, we developed bimodal nanosystems consisting in hydrophilic quantum dots (QDs) directly conjugated to Gd(III)-DO3A monoamide chelates, a Gd(III)-DOTA derivative, allowing for the combination of the advantages of both MRI and fluorescence-based tools. These nanoparticulate systems can also improve MRI contrast, by increasing the local concentration of paramagnetic chelates. Transmetallation assays, optical characterization, and relaxometric analyses, showed that the developed bimodal nanoprobes have great chemical stability, bright fluorescence, and high relaxivities. Moreover, fluorescence correlation spectroscopy (FCS) analysis allowed us to distinguish nanosystems containing different amounts of chelates/QD. Also, inductively coupled plasma optical emission spectrometry (ICP - OES) indicated a conjugation yield higher than 75%. Our nanosystems showed effective longitudinal relaxivities per QD and per paramagnetic ion, at least 5 times [per Gd(III)] and 100 times (per QD) higher than the r1 for Gd(III)-DOTA chelates, suitable for T1-weighted imaging. Additionally, the bimodal nanoparticles presented negligible cytotoxicity, and efficiently labeled HeLa cells as shown by fluorescence. Thus, the developed nanosystems show potential as strategic probes for fluorescence analyses and MRI, being useful for investigating a variety of biological processes.

Interactions of mannose binding-lectin with red blood cells by employing cationic quantum dots.

Mannose-binding lectin (MBL) plays important roles by interacting with specific molecular patterns on cell surfaces, triggering first-line host defense. We investigated the MBL interaction with healthy red blood cell membranes as well as its effects on the membrane rheology. We explored electrostatic interactions between cationic quantum dots (QDs) and negatively charged red blood cell surfaces to quantitatively evaluate membrane electrical charges as well as to investigate the MBL binding to healthy erythrocytes. Results showed that cationic QDs labeled efficiently red blood cells. However, the MBL interaction with erythrocytes prevents the QD labeling. We also observed that red blood cells treated with MBL are more resistant to lysis, suggesting a membrane-stabilizing effect. Moreover, we used a fluorescent anti-MBL antibody and Candida albicans cells to further study the MBL interaction with erythrocytes. Our results of this comparative labeling suggested that either this probe was not effective to detect MBL bound to healthy red blood cells (by its carbohydrate-recognition domain) or the MBL binding to those cells might be occurring via another portion. Thus, our results demonstrated the ability of MBL interacting with healthy red blood cells and pointed out to a new role of this protein as a membrane-stabilizing molecule.