Fluorescence Properties Of Quantum Dots Research Articles

Fluorescent Switchable Surfaces Based on Quantum Dots Modified With Redox‐Active Molecules

AbstractBy combining the switching ability of redox molecules with the unique fluorescence properties of quantum dots (QDs), a robust electrochemical fluorescence switch is developed here. This is realized by grafting CdSe/ZnS QDs on transparent indium tin oxide (ITO) substrates and, subsequently, modifying them with a Ferrocene (Fc) molecular monolayer. The application of oxidation/reduction voltage pulses to tune the Fc redox state leads to the tuning of the surface fluorescence output. Interestingly, the ON/OF ratio can be enhanced by reducing the distance between the redox active unit and the QD due to a more efficient electronic coupling. Remarkably, by defining a mixed‐valence state, a ternary switch has also been achieved. It is highlighted that the QD surface immobilization is key to realize this switch to avoid aggregation and fluorescence quenching in suspension. Hence, an efficient and versatile novel route to fabricate robust fluorescent redox switches is demonstrated, opening a wide avenue of possibilities to be explored in the field of sensing and information storage.

Multifunctional natural derived carbon quantum dots from Withania somnifera (L.) – Antiviral activities against SARS-CoV-2 pseudoviron

Natural carbon dots (NCQDs) are expediently significant in the photo-, nano- and biomedical spheres owing to their facile synthesis, optical and physicochemical attributes. In the present study, three NCQDs are prepared and optimized from Withania somnifera (ASH) by one-step hydrothermal (bottom-up) method: HASHP (without dopant), nitrogen doped HASHNH3 (surface passivation using ammonia) and HASHEDA (surface passivation with ethylenediamine). The HR-TEM images reveal that HASHP, HASNH3, HASHEDA are spherically shaped with 2.5 ± 0.5 nm, 4 ± 1 nm and 5 ± 2 nm particle size, respectively, whereas FTIR confirms the aqueous solubility and nitrogen doping. The XRD patterns ensure that the NCQDs are amorphous and graphitic in nature. Comparatively, HASHNH3 (32.5%) and HASHEDA (27.6%) portray better fluorescence quantum yield than HASHP (5.6%). The increase in quantum yield for the doped NCQDs can be attributed to the surface passivation using ammonia and ethylenediamine. Surface passivation plays a crucial role in enhancing the fluorescence properties of quantum dots. The introduction of nitrogen through ammonia and ethylenediamine provides additional electronic states, possibly reducing non-radiative recombination sites and hence boosting the QY. In addition, an antiviral study unveils the striking potential of surface passivated NCQDs to curb Covid-19 crises with around 85% inhibition of SARS-CoV pseudoviron cells, which is better in comparison to the non-doped NCQDs. Hence, to understand the paramount efficacy of these NCQDs, a hypothesis on their possible mechanism of action against Covid-19 is discussed.

Fluorescent Quantum Dots and Its Composites for Highly Sensitive Detection of Heavy Metal Ions and Pesticide Residues: A Review

Quantum dots nanomaterials have attracted extensive interest for fluorescence chemical sensors due their attributes, such as excellent optical characteristics, quantum size effects, interface effects, etc. Moreover, the fluorescence properties of quantum dots can be adjusted by changing their structure, size, morphology, composition, doping, and surface modification. In recent years, quantum dots nanomaterials have been considered the preferred sensing materials for the detection of heavy metal ions and pesticide residues by the interactions between quantum dots and various analytes, showing excellent sensitivity, selectivity, and interference, as well as reducing the cost of equipment compared with traditional measurement methods. In this review, the applications and sensing mechanisms of semiconductor quantum dots and carbon-based quantum dots are comprehensively discussed. The application of semiconductor quantum dots, carbon quantum dots, graphene quantum dots, and their nanocomposites that are utilized as fluorescence sensors are discussed in detailed, and the properties of various quantum dots for heavy metal ion and pesticide residue determination are also presented. The recent advances in and application perspectives regarding quantum dots and their composites are also summarized.

Establishment of a Ca(II) ion-quantum dots fluorescence signal amplification sensor for high-sensitivity biomarker detection

Quantum dots (QDs) have been considered as the promising fluorescent labeling material, which is expected to meet the requirement of high-sensitivity detection in clinical diagnostics. Some common metal ions are known to affect the stability and fluorescence properties of QDs, but scarcely any systematic research has been done about their impacts on QD-based bio-detection. By evaluating the effect of Ca2+ metal ions on the properties of aqueous QDs, a new metal ion-QD fluorescence signal amplification sensor (i.e., Ca2+-QD-fluorescence-linked immunosorbent assay, Ca2+-QD-FLISA) has been developed for the detection of inflammatory biomarkers with high sensitivity. Compared with the common QD-FLISA, the detection sensitivity for CRP of Ca2+-QD-FLISA was improved by a 4-fold of magnitude to 0.23 ng/mL, and this assay showed good selectivity, high accuracy, and excellent repeatability. The versatility of the QD-FLISA method were also validated by using different metal ion-QD probes (Ca2+, Mg2+, Ba2+, Fe2+, and Mn2+) to detect CRP, serum amyloid A (SAA), and procalcitonin (PCT). The significant improvement in detection sensitivity was achieved due to the crosslinking of aqueous QDs by Ca2+ ions to enhance fluorescence and at the same time promote antigen-antibody binding efficiency. The present study illustrates the versatility of metal ion-QD-FLISA as a simple and effective method to detect a wide range of biomarkers with high sensitivity and accuracy.

QD:Puf Nanohybrids Are Compatible with Studies in Cells.

Colloidal semiconductor quantum dots (QD), as well as other nanoparticles, are useful in cell studies as fluorescent labels. They may also be used as more active components in various cellular assays, serving as sensors or effectors. However, not all QDs are biocompatible. One of the main problems is their outer coat, which needs to be stable and to sustain hydrophilicity. Here we show that purpose-designed CdSe QDs, covered with a Puf protein, can be efficiently accumulated by HeLa cells. The uptake was measurable after a few hours of incubation with nanoparticles and most of the fluorescence was localised in the internal membrane system of the cell, including the endoplasmic reticulum and the Golgi apparatus. The fluorescence properties of QDs were mostly preserved, although the maximum emission wavelength was slightly shifted, and the fluorescence lifetime was shortened, indicating partial sensitivity of the QDs to the cell microenvironment. QD accumulation resulted in a decrease in cell viability, which was attributed to disturbance of endoplasmic reticulum performance.

Dual recognition strategy for ultra-sensitive fluorescent detection of Hg2+ at femto-molar level based on aptamer functionalized sulfur quantum dots

In the present study, a dual recognition strategy for ultrasensitive detection of Hg 2+ was successfully developed for the first time based on aptamer functionalized sulfur quantum dots (Apt-SQDs). The developed Apt-SQDs not only retained the good fluorescence properties of quantum dots but also overcame the problem of poor selectivity of SQDs for heavy metal ions. This system used the dual recognition strategy, including the combination of S x 2− and Hg 2+ and T-Hg 2+ -T structures to excellently identify and capture Hg 2+ , and an ultrahigh sensitivity fluorescent aptasensor was fabricated. The fluorescent aptasensor had a good response to Hg 2+ at concentrations ranging of 10 −15 to 10 −7 M with an ultralow limit of detection of 0.3 fM, and the response to other metal ions was far less than that to Hg 2+ . It was successfully applied to detect Hg 2+ in nearby environmental water samples (tap water, lake water and river water) with a good recovery rate. Moreover, portable test papers that would be useful for Hg 2+ monitoring in environmental water were designed. The dual recognition strategy not only achieves ultrasensitive fluorescent detection of Hg 2+ but also provides a new insight into the further expansion of the application of SQDs.

PH-Dependent Photophysical Properties of Metallic Phase MoSe2 Quantum Dots.

Fluorescence properties of quantum dots (QDs) are critically affected by their redox states, which is important for practical applications. In this study, we investigated the optical properties of MoSe2-metallic phase quantum-dots (MoSe2-mQDs) depending on the pH variation, in which the MoSe2-mQDs were dispersed in water with two sizes (Φ~3 nm and 12 nm). The larger MoSe2-mQDs exhibited a large red-shift and broadening of photoluminescence (PL) peak with a constant UV absorption spectra as varying the pH, while the smaller ones showed a small red-shift and peak broadening, but discrete absorption bands in the acidic solution. The excitation wavelength-dependent photoluminescence shows that the PL properties of smaller MoSe2-mQDs are more sensitive to the pH change compared to those of larger ones. From the time-resolved PL spectroscopy, the excitons dominantly decaying with an energy of ~3 eV in pH 2 clearly show the shift of PL peak to the lower energy (~2.6 eV) as the pH increases to 7 and 11 in the smaller MoSe2-mQDs. On the other hand, in the larger MoSe2-mQDs, the exciton decay is less sensitive to the redox states compared to those of the smaller ones. This result shows that the pH variation is more critical to the change of photophysical properties than the size effect in MoSe2-mQDs.

Graphene Quantum Dots enable digital communication through biological fluids

A method of communication through biological fluids is herein presented. This bioinspired approach does not use electromagnetic waves but rather the exchange of chemical systems – a method known as Molecular Communication (MC). In the example herein outlined, communication is achieved by exploiting the fluorescence properties of quantum dots which are then analysed in the domain of the Fourier transform. The problem is studied from a theoretical point of view by numerically solving the differential equation that governs the phenomenon. The theoretical results are exploited to develop a prototype MC platform that enables the communication of infection-induced temperature variations via biological fluids to a receiver that has the task of releasing an antibiotic drug.

Nanotechnology based therapeutic application in cancer diagnosis and therapy.

Due to the lack of early diagnosis, cancer remains as one of the leading cause of human mortality. Inability to translate research into clinical trials and also inability of chemotherapeutics delivery to targeted tumor sites are major drawbacks in cancer therapeutics. With the emergence of nanomedicine, several nanoprobes (conjugated with targeting ligands and chemotherapeutic drugs) are developed. It can interact with biological system and thus sense and monitor the biological events with high efficiency and accuracy along with therapy application. Nanoparticles like gold and iron oxide are frequently used in the computed tomography and magnetic resonance imaging applications, respectively. Moreover, enzymatic activity of gold and iron oxide nanoparticles enables the visible colorimetric diagnostic of cancer cells, whereas, fluorescence property of quantum dots and upconversion nanoparticles helps in in vivo imaging application. Other than this, drug conjugation with nanoparticles also reduces the systemic toxic effect of chemotherapeutic drugs. Due to their several unique intrinsic properties, nanoparticles itself can also be employed as therapeutics in cancer treatment by photothermal therapy (PTT) and photodynamic therapy (PDT). Thus, the main focus of this review is to emphasize on current progress in diagnostic and therapeutic application of nanoprobes in cancer.

English

Cadmium selenide quantum dots (CdSe QDs) were synthesized by using Providencia vermicola BGRW, which has discriminatory ability to resist many metals such as Selenium, Cadmium, Silver, Zinc, Copper, Lead, Nickel, Cobalt and Bismuth metals. BGRW was able to grow in the presence of 6 mM of CdCl2. The best conditions for extra/intracellular CdSe QDs synthesis were 0.1 mM SeO2: 0.9 mM CdCl2, 37°C, pH 9 within 24 h. The biosynthesis of CdSe QDs was monitored by UV–Visible spectrum that showed surface plasmon resonance (SPR) peaks at 388 nm. Depending on fluorescence property of quantum dots, photoluminescence characteristics of the biogenic CdSe QDs were at 385 nm. Further characterization of synthesized CdSe QDs was carried out using the X-ray Diffraction (XRD), Transmission Electron Microscope (TEM) and Fourier Transform Infrared (FTIR) spectroscopy. TEM and XRD analysis revealed that CdSe QDs was cubic in shape with a size range of ∼2 to 4 nm. EDS analysis confirmed the composition of QDs from cadmium and selenium ions. FTIR spectroscopy confirmed the presence of proteins as the stabilizing agent surrounding the quantum dots. Key words: Quantum dots, cadmium selenide quantum dots, capping agent, transmission electron microscope, fluorescence spectroscopy, X-ray and FTIR analysis.

Synthesis of AgInS2 QDs in droplet microreactors: Online fluorescence regulating through temperature control

For the synthesis of AgInS2 quantum dots (QDs), a suitable temperature is extremely important for control of the size, shape and fluorescence properties of QDs. Most of synthesis methods for AgInS2 QDs are based on batch reactors, which bring uneven distribution of temperature, affecting their fluorescence properties and size uniformity. Here we designed a droplet microreactor with a temperature-controllable region, and successfully synthesized water-soluble AgInS2 QDs. By accurately controlling temperature, we also studied how the reaction temperature affected the fluorescence properties of AgInS2 QDs. The results showed that with the increasing of reaction temperature, the QDs size increased and the fluorescence peak constantly red-shifted along with enhanced fluorescence intensity. Based on the droplet microreactor, we could achieve more appropriate reaction condition to synthesize AgInS2 QDs with higher fluorescence quantum yield (QY) and intensity.

Clicking Hydrazine and Aldehyde: The Way to Labeling of Viruses with Quantum Dots.

Real-time tracking of fluorophore-tagged viruses in living cells can help uncover virus infection mechanisms. Certainly, the indispensable prerequisite for virus-tracking is to label viruses with some bright and photostable beacons such as quantum dots (QDs) via an appropriate labeling strategy. Herein, we devise a convenient hydrazine-aldehyde based strategy to label viruses with QDs through the conjugation of 4-formylbenzoate (4FB) modified QDs to 6-hydrazinonicotinate acetone hydrazone (HyNic) modified viruses under mild conditions. On the basis of this strategy, viruses can be successfully labeled with QDs with high selectivity, stable conjugation, good reproducibility, high labeling efficiency of 92-93% and maximum retention of both fluorescence properties of QDs and infectivity of viruses, which is very meaningful to tracking and statistical analysis of virus infection processes. By further comparing with the most widely used labeling strategy based on the Biotin-SA system, this new strategy has advantages of both high labeling efficiency and good retention of virus infectivity, thus offering a promising alternative for virus-labeling. Moreover, due to the ubiquitous presence of exposed amino groups on the surface of various viruses, this selective, efficient, reproducible and biofriendly strategy should have good universality for labeling both enveloped and nonenveloped viruses.

The engineering of doxorubicin-loaded liposome-quantum dot hybrids for cancer theranostics

Many studies have recently attempted to develop multifunctional nanoconstructs by integrating the superior fluorescence properties of quantum dots (QD) with therapeutic capabilities into a single vesicle for cancer theranostics. Liposome-quantum dot (L-QD) hybrid vesicles have shown promising potential for the construction of multifunctional nanoconstructs for cancer imaging and therapy. To fulfil such a potential, we report here the further functionalization of L-QD hybrid vesicles with therapeutic capabilities by loading anticancer drug doxorubicin (Dox) into their aqueous core. L-QD hybrid vesicles are first engineered by the incorporation of TOPO-capped, CdSe/ZnS QD into the lipid bilayers of DSPC:Chol:DSPE-PEG2000, followed by Dox loading using the pH-gradient technique. The loading efficiency of Dox into L-QD hybrid vesicles is achieved up to 97%, comparable to liposome control. All these evidences prove that the incorporation of QD into the lipid bilayer does not affect Dox loading through the lipid membrane of liposomes using the pH-gradient technique. Moreover, the release study shows that Dox release profile can be modulated simply by changing lipid composition. In conclusion, the Dox-loaded L-QD hybrid vesicles presented here constitute a promising multifunctional nanoconstruct capable of transporting combinations of therapeutic and diagnostic modalities.

Doubly and Triply Coupled Nanowire Antennas

Nanoantenna is one of the most important optical components for light harvesting. In this study, we show experimental evidence of interactions between coupled nanowires by comparing the fluorescence properties of quantum dots on single nanowire as well as doubly and triply coupled nanowire arrays. Because of the localized surface plasmon mode, there are strong polarization dependences in this photon–plasmon–exciton conversion process. It is interesting that both the polarization-dependent enhancement and the degree of fluorescence polarization are more pronounced for triply coupled nanowires than that of doubly coupled nanowire, while the case of single nanowire is weakest. Our theoretical analysis indicates the above phenomena can be ascribed to the coupled plasmon from the nanowire antennas. Our investigations demonstrate a potential method to control the polarization of emitters using coupled nanowire arrays.

Quantum dot–aptamer nanoprobes for recognizing and labeling influenza A virus particles

The fluorescence labeling of viruses is a useful technology for virus detection and imaging. By combining the excellent fluorescence properties of quantum dots (QDs) with the high affinity and specificity of aptamers, we constructed a QD-aptamer probe. The aptamer A22, against the hemagglutinin of influenza A virus, was linked to QDs, producing the QD-A22 probe. Fluorescence imaging and transmission electron microscopy showed that the QD-A22 probe could specifically recognize and label influenza A virus particles. This QD labeling technique provides a new strategy for labeling virus particles for virus detection and imaging.

Composite of CdTe quantum dots and molecularly imprinted polymer as a sensing material for cytochrome c

A newly designed molecularly imprinted polymer (MIP) material was fabricated and successfully utilized as recognition element to develop a quantum dots (QDs) based MIP-coated composite for selective recognition of the template cytochrome c (Cyt). The composites were synthesized by sol–gel reaction (imprinting process). The imprinting process resulted in an increased affinity of the composites toward the corresponding template. The fluorescence of MIP-coated QDs was stronger quenched by the template versus that of non-imprinted polymer (NIP)-coated QDs, which indicated the composites could recognize the corresponding template. The results of specific experiments further exhibited the recognition ability of the composites. Under optimum conditions, the linear range for Cyt is from 0.97 μM to 24 μM, and the detection limit is 0.41 μM. The new composites integrated the high selectivity of molecular imprinting technology and fluorescence property of QDs and could convert the specific interactions between imprinted cavities and corresponding template to the obvious changes of fluorescence signal. Therefore, a simple and selective sensing system for protein recognition has been realized.

Using quantum dots as fluorescence probe to evaluate the immune complex deposits in paraffin-embedded sections

To detect the immune complex deposits in IgA nephropathy (IgAN) by using quantum dots (QDs)-labeled immunofluorescence technology and to evaluate its significance. Using the fluorescence property of QDs and indirect immunofluorescence methods to detect the IgA and complement C3 in formalin-fixed paraffin-embedded (FFPE) tissues of IgAN. Minimal change disease (MCD) was used as a control. Immunoglobulin and a complement were significantly detected in IgAN and manifested as special distribution of intensive salmon pink fluorescence. Compared with fluorescein isothiocyanate (FITC) tagging, QD signal showed better specificity and signal to noise ratio, and QD signal was not significantly quenched after 60 min of excitation. QDs can be used to label subcellular proteins and have obvious advantages compared with the traditional organic fluorophores. QDs-tagged fluorescence can be applied as a new method for clinical labeling detection in renal pathology.

Optical memory based on photo-activated fluorescence of core/shell CdSe/CdS quantum dots embedded in poly(butylmethacrylate)

This work presents the observation of a photo-activated fluorescence from core/shell quantum dots of CdSe/CdS incorporated in a poly(butylmethacrylate) matrix. Upon illumination with UV-light, the intensity of fluorescence from the quantum dots increases as seen by naked eyes at ambient conditions. This allows its utilization in optical memory media based on thin films of CdSe/CdS polymer nanocomposites suitable for practical application. The quantum dots are synthesized by the hot-injection method and embedded in poly(butylmethacrylate) matrix by radical polymerization with 1,1′-azobis-(cyclohexanecarbonitrile). The fluorescence of quantum dots quenched during the polymerization process, but appeared again after illumination of the nanocomposite material with UV-light. The fluorescence properties of quantum dots are governed by the presence of trioctylphosphine oxide in the matrix, which allows control of the optical memory effect.

Sugar−Quantum Dot Conjugates for a Selective and Sensitive Detection of Lectins

One-pot synthesized neoglycoconjugates with a reactive thiol group are introduced here for functionalization with carbohydrates for solubilization and stabilization of CdSe-ZnS quantum dots in aqueous solution. Three different sizes of quantum dots (QDs) with lactose, melibiose, and maltotriose on their surface have been utilized, for the first time, for lectin detection through agglutination assay. The sugar-QDs thus synthesized were characterized by transmission election microscopy (TEM), fluorescence, and absorption spectroscopy. Agglutination of sugar-QDs by three different lectins occurred through specific multivalent carbohydrate-lectin interactions and was studied extensively by monitoring the scattered light at 600 nm. This assay was very selective, which has been demonstrated by a more selective binding of soybean agglutinin (SBA) with melibiose-QD, as compared to lactose-QD, and specific deagglutination caused by alpha-d-galactose, while alpha-d-mannose did not show any effect. The detection sensitivity of the maltotriose-QD was tested with Concanavalin A (ConA), and as little as 100 nM of the lectin was detected using light scattering. The detection sensitivity of this protocol has been enhanced considerably by the fluorescence properties of QDs. This agglutination process seems to occur through formation of smaller soluble aggregates, which further associate to form larger aggregates.