Fluorescent Semiconductor Nanorods for the Solid-Phase Polymerase Chain Reaction-Based, Multiplexed Gene Detection of Mycobacterium tuberculosis.

The spread of infectious diseases with significantly high mortality rates can wreak devastating damage on global health systems and economies, underscoring the need for better disease diagnostic platforms. Solid-phase polymerase chain reaction (SP-PCR) potentially combines the advantages of conventional PCR-based diagnostics with the capability of multiplexed detection, given that the spatial separation between primers circumvents unwanted primer-primer interactions. However, the generally low efficiency of solid-phase amplification results in poor sensitivity and limits its use in detection schemes. We present an SP-PCR-based, multiplexed pulldown fluorescence assay for the detection of Mycobacterium tuberculosis (MTB), utilizing highly fluorescent oligonucleotide-functionalized CdSe/CdS and CdSe1-xSx/CdS nanorods (NRs) as multicolor hybridization probes. The large surface area of the NRs allows for their easy capture and pulldown, but without contributing significantly to the interparticle photon reabsorption when clustered at the pulldown sites. The NR nanoprobes were specifically designed to target the hotspot regions of the rpoB gene of MTB, which have been implicated in resistance to standard rifampicin treatment. The implementation of the semiconductor NRs as photostable multicolor fluorophores in a multiplexed SP-PCR-based detection scheme allowed for the identification of multiple hotspot regions with sub-picomolar levels of sensitivity and high specificity in artificial sputum. While this work demonstrates the utility of semiconductor NRs as highly fluorescent chromophores that can enable SP-PCR as a sensitive and accurate technique for multipathogen diagnostics, the flexible surface chemistry of the NRs should allow them to be applicable to a wide variety of detection motifs.

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.

Reversible Electrochemical Gelation of Metal Chalcogenide Quantum Dots.

The ability to dictate the assembly of quantum dots (QDs) is critical for their integration into solid-state electronic and optoelectronic devices. However, assembly methods that enable efficient electronic communication between QDs, facilitate access to the reactive surface, and retain the native quantum confinement characteristics of the QD are lacking. Here we introduce a universal and facile electrochemical gelation method for assembling metal chalcogenide QDs (as demonstrated for CdS, ZnS, and CdSe) into macroscale 3-D connected pore-matter nanoarchitectures that remain quantum confined and in which each QD is accessible to the ambient. Because of the redox-active nature of the bonding between QD building blocks in the gel network, the electrogelation process is reversible. We further demonstrate the application of this electrogelation method for a one-step fabrication of CdS gel gas sensors, producing devices with exceptional performance for NO2 gas sensing at room temperature, thereby enabling the development of low-cost, sensitive, and reliable devices for air quality monitoring.

Synthesis of pH Sensitive Dual Capped CdTe QDs: Their Optical Properties and Structural Morphology.

We herein report five different types of thiol dual capped cadmium tellurite quantum dots (CdTe QDs) namely glutathione-mercapto-propanoic acid (QD 1), glutathione-thiolglycolic acid (QD 2), L-cysteine-mercapto-propanoic acid (QD 3), L-cysteine- thiol-glycolic acid (QD 4) and mercapto-propanoic acid-thiol-glycolic (QD 5). Dual-capped CdTe QDs were prepared using a one pot synthetic method. Cadmium acetate and sodium tellurite were respectively used as cadmium and tellurium precursors. Photo-physical properties of the synthesized QDs were examined using UV-Vis and photoluminescence spectroscopy while structural characterization was performed by means of transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The influence of pH on QD characteristics (fluorescence intensity) was studied using phosphate and citrate buffers and continuous titration with HCl (0.1 N). UV-vis and photoluminescence spectra exhibited sharp absorption band edge with high intensities and improved colloidal stability. All the QDs were found to be in nano-size rang. TEM analysis revealed the presence of spherical nanoparticles while FTIR evidenced successful dual-capping of QDs. Upon pH changes, QDs 3 and 4 demonstrated more remarkable variations in fluorescence intensity than QDs 1 and 2. The pH-sensitivity of these QDs represents a promising feature for further development of potential theranostic nano-devices.

Enzymatic Preparation of Plasmonic-Fluorescent Quantum Dot-Gold Hybrid Nanoprobes for Sensitive Detection of Glucose and Alkaline Phosphatase and Dual-Modality Cell Imaging.

Herein, we develop a route to prepare bifunctional plasmonic-fluorescent quantum dot-gold (QD-Au) hybrid nanoprobes by use of enzymatic reactions. Two bioenzymes, glucose oxidase (GOx) and alkaline phosphatase (ALP) were chosen for the enzymatic preparation of core-satellite or core-shell type CdSe/ZnS@Au hybrid nanostructures. The enzymatic products, H2O2 and l-ascorbic acid, of the two enzymes were exploited as mild reducing agents for controlled Au deposition on QD surfaces. The polymer multilayers by layer-by-layer assembly were used to adjust the separation between QD core and plasmonic Au, which can effectively reduce the quenching effect of the Au on QDs. The as-prepared QD@Au hybrid nanostructures are excellent dual-modality imaging nanoprobes, and can be used for fluorescence and dark-field scattering dual-imaging of MCF-7 cells. More importantly, the two enzymatic reaction systems can be explored for sensitive and selective detection of glucose and alkaline phosphatase, respectively, by monitoring the fluorescence spectra change of QD@Au hybrid nanoparticles, which is very useful for the glucose- and ALP-related disease diagnosis.

Cleaning Matters!

Translation of a manual process to high throughput for research and development requires special consideration. One important and often unreported aspect is the establishment of an efficient cleaning routine. This becomes significant, as precious time and, in particular, material would be lost, that is, when low-quality high-throughput experimentation is involved. We present a fully automated cleaning routine of the challenging synthesis of cadmium selenide quantum dots. Manual, semiautomated, and fully automated cleaning protocols were executed and compared in terms of spectral similarities of the synthesized colloids. Only the fully automated protocol enabled true 24/7 operation.

Three-Dimensional CdS@Carbon Fiber Networks: Innovative Synthesis and Application as a General Platform for Photoelectrochemical Bioanalysis.

This Letter reports a novel synthetic methodology for the fabrication of three-dimensional (3D) nanostructured CdS@carbon fiber (CF) networks and the validation of its feasibility for applications as a general platform for photoelectrochemical (PEC) bioanalysis. Specifically, 3D architectures are currently attracting increasing attention in various fields due to their intriguing properties, while CdS has been most widely utilized for PEC bioanalysis applications because of its narrow band gap, proper conduction band, and stable photocurrent generation. Using CdS as a representative material, this work realized the innovative synthesis of 3D CdS@CF networks via a simple solvothermal process. Exemplified by the sandwich immunoassay of fatty-acid-binding protein (FABP), the as-fabricated 3D CdS@CF networks exhibited superior properties, and the assay demonstrated good performance in terms of sensitivity and selectivity. This work features a novel fabrication of 3D CdS@CF networks that can serve as a general platform for PEC bioanalysis. The methodology reported here is expected to inspire new interest for the fabrication of other 3D nanostructured Cd-chalcogenide (S, Se, Te)@CF networks for wide applications in biomolecular detection and beyond.

Synthesis and characterization of cadmium selenide quantum dots doped by europium and investigation of their chemiluminescence properties and antibacterial activities.

Nanoparticles of cadmium selenide (CdSe) doped with europium, were synthesized as stabilizing agents using thioglycolic acid ligand. This method is based on the enhancing effect of CdSe quantum dots (QDs) doped with europium on chemiluminescence (CL) emission. This emission was generated by mixing CdSe QDs with manganese (II), iron (II) and chrome (II) sulfates as catalysts in the presence of hydrogen peroxide (H2 O2 ). The structural characteristics and morphology of these nanoparticles were investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible absorption spectroscopy, X-ray pattern and dynamic light scattering methods. The CdSe QDs doped with europium were used as the sensitizer in a luminol-hydrogen peroxide CL system. The sensitized CdSe QDs were analyzed for antibacterial activity against Gram-positive or Gram-negative bacteria. The results showed that the CdSe QDs are effective against all the studied bacteria, effectiveness was especially higher for Bacillus subtilis.

Synthesis and characterization of novel bithiazolidine derivatives-capped CdTe/CdS quantum dots used as a novel Hg2+ fluorescence sensor.

In the present study, (E)-2,2'-(4,4'-dioxo-2,2'-dithioxo-2H,2'H-[5,5'-bithiazolylidene]-3,3'(4H,4'H)-diyl) bis(3-mercaptopropanoic acid) (DTM) as a new derivative of thiazolidine was synthesis and characterized for the detrtmination of Hg2+ ions. Then, the CdTe@CdS QDs and DTM capped CdTe@CdS QDs were produced. The DTM-CdTe@CdS/QDs used as an effective fluorescence sensing material due to the selective interaction of DTM with Hg (II). The results indicated that the DTM-CdTe@CdS/QDs shows strong fluorescence emissions in the absence of mercury ions and efficiently quenched in presence of Hg2, with the formation of a strong and stable complex between Hg2+ and DTM. Experimental results showed that under optimal conditions, Hg2+ could be detected with a detection limit of 0.08 nM in a linear range from 0.3 nM to 21 nM. The constructed aptasensor illustrated the high selectivity for mercury ions even in the presence of the other interfering metal ions when their concentration ratio was more than 300 times. The satisfactory results illustrated that the designed fluorescence sensor as a sensitive, reliable and easy to use approach could be applied for the facile and rapid determination of Hg2+ in tap water.

Rapid and green synthesis of cadmium telluride quantum dots with low toxicity based on a plant-mediated approach after microwave and ultrasonic assisted extraction: Synthesis, characterization, biological potentials and comparison study.

In this work, a quick, facile and efficient approach was presented for green synthesis of cadmium telluride quantum dots (CdTe QDs) based on an aqueous extract of the Ficus johannis plant. Two extraction methods involving microwave assisted extraction (MWAE; 90 and 270 w; 15 min) and ultrasonic assisted extraction (USAE; 15 min; 45 °C) were performed as eco-friendly, effective, green and fast techniques for the extract preparation of the fruit's plant. The as-prepared plant extracts were used as natural stabilizing precursors in the synthesis of CdTe QDs. The synthesized QDs were characterized using various techniques. The average particle size of the QDs from the X-ray diffraction patterns was calculated to be 1.2 nm. UV-Vis absorption and fluorescence spectroscopic studies show a wide absorption band from 400 to 425 nm and a maximum emission peak around 470 nm, which confirmed the successful synthesis of CdTe QDs via the applied synthetic method. After synthesis and characterization of the samples, the antimicrobial properties, genotoxicity, toxicity and antifungal activities of the as-prepared CdTe QDs were investigated. In addition, antioxidant properties of the samples (QDs and extracts), were evaluated by different antioxidant assays. The results indicate the significant antimicrobial activity of the extract and CdTe QDs samples, with negligible toxicity and genotoxicity impacts.

Ultrasensitive detection of glibenclamide based on its enhancing effect on the fluorescence emission of CdTe quantum dots.

Glibenclamide (GB), as a sulfonylurea-based medication is commonly prescribed for the treatment of type 2 diabetes. Due to its increasing consumption, there is a need to develop a simple, fast, and reliable detection method to follow its concentration in pharmaceutical and biological samples. Herein, a novel fluorometric method is developed for the sensitive measurement of GB. The method is based on the enhancing effect of GB on the fluorescence emission of mercaptopropionic acid (MPA) capped cadmium telluride quantum dots (CdTe QDs). QDs were synthesized in aqueous solution and were characterized by fluorescence spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Fluorescence intensity of QDs was enhanced by adding GB in a very low concentration. The effect of operative factors such as pH, buffer, contact time and concentration of CdTe QDs were investigated and in the optimized condition, a linear increase was achieved for the emission intensity of QDs by increasing GB concentration in the range 49-345 ng mL-1 , with a detection limit of 17.84 ng mL-1 . The offered method has an acceptable precision (relative standard deviations were < 2.8%) and was satisfactorily applied for the determination of GB in pharmaceutical products and human urine samples.

Host-guest supramolecular assembly directing beta-cyclodextrin based nanocrystals towards their robust performances.

Fluorescent CdTe nanocrystals (NCs) capped with beta-cyclodextrin (ß-CD) are successfully synthesized by host-guest supramolecular assembly of the hydrophobic alkyl chains of N-acetyl-l-cysteine (NAC) on the surface of CdTe NCs and eco-friendly ß-CD via the promising simple hydrothermal method in our experiments. The as-prepared NCs display better stability and lower toxicity compared with traditional those only capped with NAC. Specially, cytotoxicity experiments to human umbilical vein endothelial cells in vitro and zebrafish embryo toxicological tests in vivo are performed to determine the toxicity of CdTe NCs. For their practical applications, the promising red-luminescent NCs are employed as stable and low poison red phosphors to fabricate white light-emitting diodes (WLEDs) with remarkable color-rendering index (CRI) being 91.6. This research offers significance for solving the difficulty in toxicity and instability of heavy metal based NCs, which has potential applications in future optoelectronic devices and biomarkers.

The essentialness of glutathione reductase GorA for biosynthesis of Se(0)-nanoparticles and GSH for CdSe quantum dot formation in Pseudomonas stutzeri TS44.

Pseudomonas stutzeri TS44 was able to aerobically reduce Se(IV) into SeNPs and transform Se(IV)/Cd(II) mixture into CdSe-QDs. The SeNPs and CdSe-QDs were systematically characterized by surface feature analyses, and the molecular mechanisms of SeNPs and CdSe-QD formation in P. stutzeri TS44 were characterized in detail. In vivo, under 2.5 mmol/L Se(IV) exposure, GorA was essential for catalyzing of Se(IV) reduction rate decreased by 67% when the glutathione reductase gene gorA was disrupted, but it was not decreased in the glutathione synthesis rate-limiting gene gshA mutated strain compared to the wild type. The complemented strains restored the phenotypes. While under low amount of Se(IV) (0.5 mmol/L), GSH played an important role for Se(IV) reduction. In vitro, GorA catalyzed Se(IV) reduction with NADPH as the electron donor (Vmax of 3.947 ± 0.1061 µmol/min/mg protein under pH 7.0 and 28℃). In addition, CdSe-QDs were successfully synthesized by a one-step method in which Se(IV) and Cd(II) were added to bacterial culture simultaneously. GSH rather than GorA is necessary for CdSe-QD formation in vivo and in vitro. In conclusion, the results provide new findings showing that GorA functions as a selenite reductase under high amount Se(IV) and GSH is essential for bacterial CdSe-QD synthesis.

Synthesis, characterization and optical property investigation of CdS nanoparticles.

Microwave-assisted routes have attracted much attention for nanoparticle synthesis because of minimal solvent use and rapid, high efficiency and controlled morphology. Cadmium sulphide (CdS) nanoparticles form the line between bulk and molecular states of materials and show variation in their physical and chemical properties. Cadmium sulphate and thiourea were used as precursors during this synthesis. These are included in the category of practical semiconductor metal sulphides, which are extensively used as catalysts and optical materials. X-ray diffraction (XRD) patterns confirmed that CdO nanoparticles are crystalline and have a hexagonal phase with crystal sizes that agree with transmission electron microscopy (TEM) data. UV-visible spectroscopy and photoluminescence (PL) spectroscopy were used to evaluate optical properties using band gap energy measurements.

Identifying reactive organo-selenium precursors in the synthesis of CdSe nanoplatelets.

In the synthesis of CdSe nanoplatelets, the selenium-to-selenide reduction pathway is unknown. We study solvent-free growth of CdSe nanoplatelets and identify bis(acyl) selenides as key reactive intermediates. Based on our findings, we prepare a series of bis(acyl) selenides that provide useful precursors with tailored reactivity for liquid-phase syntheses of nanoplatelets.

A facile synthesis of biocompatible, glycol chitosan shelled CdSeS/ZnS QDs for live cell imaging.

We here report a facile synthesis of chitosan shelled quantum dot (QD/fGC) that holds essential properties requisite for biological applications, such as excellent water solubility, super colloidal stability, and low nonspecific adsorption as well as ease of functionalization. In this method, the amphiphilic glycol chitosan fragment (MW 1.0-1.7 kDa) was assembled on the top of CdSeS/ZnS nanocrystal through hydrophobic interaction in aqueous solution, without displacing the native coordinating ligands, which result in a higher quantum yield of about 0.26, 46% of the uncoated CdSeS/ZnS QDs in chloroform (0.57). In addition, the prepared QD/fGC composes an individual semiconductor core and presents an extremely small size of about 6.03 ± 1.50 nm (n = 399) in diameter. By conjugation with bioactive amines via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-based hydroxyl activation approach, the functionalized QD/fGC presented excellent recognition of specific cells in fluorescent imaging. Our work provides a new general method of chitosan modification of hydrophobic nanoparticles for biomedical applications.

Chiral ligand-induced photoluminescence intermittence difference of CdTe quantum dots.

Semiconductor quantum dots (QDs) are a new nano-material, and their unique optical properties have become a focal point of research in both academia and industry. In this study, we studied photoluminescence (PL) intermittence (or 'blinking') behaviors of individual QDs prepared with different chiral ligands by using single molecule microscopy and single molecule fluorescence correlation spectroscopy (FCS). We found that the chirality of N-isobutyryl-d/l-cysteine (D/L-NIC) as surface stabilizers significantly influences PL blinking behaviors of cadmium telluride (CdTe) QDs synthesized in aqueous solution. The 'on time' distribution and the power-law exponent analyses show that the D-NIC more efficiently suppresses the blinking of QDs over L-NIC. Ensemble spectroscopies verfied that the remarkably-different blinking behaviors of QDs induced by ligand chirality were attributed to the different number of chiral ligands bound in the surface of QDs.

Preparation of Microkernel-Based Mesoporous (SiO2-CdTe-SiO2)@SiO2 Fluorescent Nanoparticles for Imaging Screening and Enrichment of Heat Shock Protein 90 Inhibitors from Tripterygium Wilfordii.

The currently utilized ligand fishing for bioactive molecular screening from complex matrixes cannot perform imaging screening. Here, we developed a new solid-phase ligand fishing coupled with an in situ imaging protocol for the specific enrichment and identification of heat shock protein 90 (Hsp 90) inhibitors from Tripterygium wilfordii, utilizing a multiple-layer and microkernel-based mesoporous nanostructure composed of a protective silica coating CdTe quantum dot (QD) core and a mesoporous silica shell, i.e., microkernel-based mesoporous (SiO2-CdTe-SiO2)@SiO2 fluorescent nanoparticles (MMFNPs) as extracting carries and fluorescent probes. The prepared MMFNPs showed a highly uniform spherical morphology, retention of fluorescence emission, and great chemical stability. The fished ligands by Hsp 90α-MMFNPs were evaluated via the preliminary bioactivity based on real-time cellular morphology imaging by confocal laser scanning microscopy (CLSM) and then identified by mass spectrometry (MS). Celastrol was successfully isolated as an Hsp 90 inhibitor, and two other specific components screened by Hsp 90α-MMFNPs, i.e., demecolcine and wilforine, were preliminarily identified as potential Hsp 90 inhibitors through the verification of strong affinity to Hsp 90 and antitumor bioactivity. The approach based on the MMFNPs provides a strong platform for imaging screening and discovery of plant-derived biologically active molecules with high efficiency and selectivity.

One-pot synthesis and characterization CdTe:Zn2+ quantum dots and its molecular interaction with calf thymus DNA.

Tremendous research efforts have been dedicated to fabricating high-quality Zn-doped CdTe quantum dots (QDs) for any potential biomedical applications. In particular, the correlation of issues regarding how QDs interact with DNA is of greatest importance. Herein, a pH-responsive study of the interactions between CdTe:Zn2+ quantum dots with 4 different sizes and calf thymus DNA (ctDNA) was conducted using multispectroscopic techniques and electrochemical investigation. Fluorescence studies revealed that this interaction process is predominantly a static process and groove binding was the main binding mode for CdTe:Zn2+ QDs to ctDNA. The calculated negative values of enthalpy (-45.06 kJ mol-1 ) and entropy (-133.62 J mol-1  K-1 ) with temperature changes indicated that the hydrogen bonds and van der Waals interactions played major roles in the reaction. Furthermore, circular dichroism spectroscopy and Fourier transform infrared spectrometry analyses indicate that the normal conformation of ctDNA is discombobulated by CdTe:Zn2+ QDs. In addition, the electrochemical behavior of the affinity of CdTe:Zn2+ QDs for ctDNA agreed well with the results obtained from fluorescence experiments. This study might be meaningful for understanding the molecular binding mechanism of QDs for DNA and provides a basis for QD-labeled systems.

Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures.

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be covalently and site-specifically linked via their end facets, resulting in polymer-like linear or branched chains. The linking procedure begins with a cation-exchange process in which the end facets of the cadmium chalcogenide NCs are first converted to silver chalcogenide. This is followed by the selective removal of ligands at their surface. This results in cadmium chalcogenide NCs with highly reactive silver chalcogenide end facets that spontaneously fuse upon contact with each other, thereby establishing an interparticle facet-to-facet attachment. Through the judicious choice of precursor concentrations, an extensive network of linked NCs can be produced. Structural characterization of the linked NCs is carried out via low- and high-resolution transmission electron microscopy (TEM), as well as energy-dispersive X-ray spectroscopy, which confirm the presence of silver chalcogenide domains between chains of cadmium chalcogenide NCs.