The optical cross section and absolute size of a photosynthetic unit

The concepts of a photosynthetic unit (PSU) and of an optical cross section are defined. The various estimates of sizes of photosynthetic units are described, and it is shown how an unambiguous measurement of the size of a unit can be obtained by measurement of its optical cross section via the saturation response to a single turnover light flash. The Emerson-Arnold unit must be divided by the quantum requirement for oxygen to obtain the true size of the unit. The size so obtained is the average number of chlorophylls per trap or reaction center. The effects of escape from open and closed traps are considered and it is shown that when these escape probabilities are equal, their effect on the saturation curve vanishes, leaving the simple cumulative one hit Poisson distribution.     

Rhizopus stolonifer mediated biosynthesis of biocompatible cadmium chalcogenide quantum dots

We report an efficient method to biosynthesize biocompatible cadmium telluride and cadmium sulphide quantum dots from the fungus Rhizopus stolonifer. The suspension of the quantum dots exhibited purple and greenish-blue luminescence respectively upon UV light illumination. Photoluminescence spectroscopy, X-ray diffraction, and transmission electron microscopy confirms the formation of the quantum dots. From the photoluminescence spectrum the emission maxima is found to be 424 and 476 nm respectively. The X-ray diffraction of the quantum dots matches with results reported in literature. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability evaluation carried out on 3-days transfer, inoculum 3 × 10⁵ cells, embryonic fibroblast cells lines shows that more than 80% of the cells are viable even after 48 h, indicating the biocompatible nature of the quantum dots. A good contrast in imaging has been obtained upon incorporating the quantum dots in human breast adenocarcinoma Michigan Cancer Foundation-7 cell lines.     

Biofabrication of ZnS:Mn luminescent nanocrystals using histidine,hexahistidine, and His-tagged proteins: A comparison study

The ubiquitous hexahistidine purification tag has been used to conjugate proteins to the shell of CdSe:ZnS quantum dots (QDs) due to its affinity for surface-exposed Zn²⁺ ions but little attention has been paid to the potential of His-tagged proteins for mineralizing luminescent ZnS nanocrystals. Here, we compare the ability of free histidine, a His tag peptide, His-tagged thioredoxin (TrxA, a monomeric protein), and N- and C-terminally His-tagged versions of Hsp31 (a homodimeric protein) to support the synthesis of Mn-doped ZnS nanocrystals from aqueous precursors under mild conditions of pH (8.2) and temperature (37 °C). We find that: (1) it is possible to produce poor quality QDs when histidine is used at high (8 mM) concentration; (2) an increase in local histidine concentration through repetition of the amino acid as a His tag decreases the amount of needed reagent ≈10-fold and improves optical properties; (3) fusion of the same His tag to TrxA allows for ZnS:Mn QDs mineralization at micromolar concentrations; and (4) doubling the local hexahistidine concentration by exploiting Hsp31 dimerization further improves nanocrystal luminescence with the brightest particles obtained when His tags are spatially co-localized at the Hsp31 N-termini. Although hexahistidine tracts are not as efficient as combinatorially selected ZnS binding peptides at QD synthesis, it should be possible to use the large number of available His-tagged proteins and the synthesis approach described herein to produce luminescent nanoparticles whose protein shell carries a broad range of functions.     

Cancer Detection and Treatment: The Role of Nanomedicines

Nanotechnology is a field which has been at the forefront of research over the past two decades. The full potential of nanotechnology has yet to be fully realized. One subset of nanotechnology that has emerged is nanomedicine, which has been able to exploit the unique properties of nano-sized particles for therapeutics. Nanomedicine has the potential to increase the specific treatment of cancer cells while leaving healthy cells intact through the use of novel nanoparticles to seek and treat cancer in the human body. However, there are undoubtedly toxicities, which have not yet been fully elucidated. Various nano-carriers such as nanoshells, nanocrystals, nanopolymers, quantum dots, and dendrimers, and their role in early cancer detection and treatment have been discussed in this article.     

Quantitative In Situ Detection of Phosphoproteins in Fixed Tissues Using Quantum Dot Technology

Detection and quantitation of phosphoproteins (PPs) in fixed tissues will become increasingly important as additional inhibitors of protein kinases enter clinical use and new disease entities are defined by molecular changes affecting PP levels. We characterize fixation conditions suitable for accurate PP quantitation that are achievable in a clinical laboratory and illustrate the utility of in situ quantitation of PPs by quantum dot (QD) nanocrystals in two models: (1) a therapeutic model demonstrating effects of a targeted therapeutic (quantitative reduction of phospho-GSK3β) in xenografts treated with enzastaurin; and (2) a diagnostic model that identifies elevated levels of nuclear phospho-STAT5 in routine bone marrow biopsies from patients with acute myeloid leukemia based on the presence of the activating FLT3-ITD mutation. Finally, we document production of a well-characterized tissue microarray of widely available cell lines as a multilevel calibrator for validating numerous phosphoprotein assays. QD immunofluorescence is an ideal method for in situ quantitation of PPs in fixed samples, providing valuable cell type–specific and subcellular information about pathway activation in primary tissues. (J Histochem Cytochem 57:701–708, 2009)     

Quantum dot-based HIV capture and imaging in a microfluidic channel

Globally, over 33.2 million people who mostly live in developing countries with limited access to the appropriate medical care suffer from the human immunodeficiency virus (HIV) infection. We developed an on-chip HIV capture and imaging method using quantum dots (Qdots) from fingerprick volume (10 μl) of unprocessed HIV-infected patient whole blood in anti-gp120 antibody-immobilized microfluidic chip. Two-color Qdots (Qdot525 and Qdot655 streptavidin conjugates) were used to identify the captured HIV by simultaneous labeling the envelope gp120 glycoprotein and its high-mannose glycans. This dual-stain imaging technique using Qdots provides a new and effective tool for accurate identification of HIV particles from patient whole blood without any pre-processing. This on-chip HIV capture and imaging platform creates new avenues for point-of-care diagnostics and monitoring applications of infectious diseases.     

Simultaneous and sensitive determination of multiplex chemical residues based on multicolor quantum dot probes

Biotinylated denatured bovine serum albumin (Bt-dBSA)-coated cadmium telluride (CdTe) quantum dot (QD) conjugates were prepared and used to develop the multiplexed fluoroimmunoassay for the simultaneous determination of five chemical residues. An immune complex was formed using avidin as the bridge to link the Bt-dBSA-QDs with the antibodies. Primarily, individual quantitative determinations of five representative chemical residues were carried out based on the different emission properties of the QDs. Five antibodies were then conjugated with the corresponding QDs to establish the indirect competition fluorescent-linked immunosorbent assay (ic-FLISA) for the simultaneous detection of five chemicals in one well of a microplate. The linear range for dexamethason (DEX) was from 0.33 μg/kg to 10 μg/kg, 0.28 μg/kg to 10 μg/kg for gentamicin (GM), 0.16 μg/kg to 25 μg/kg for clonazepam (CZP), 0.17 μg/kg to 10 μg/kg for medroxyprogesterone acetate (MPA) and 0.32 μg/kg to 25 μg/kg for ceftiofur (CEF), respectively. The limit of detection (LOD) for the simultaneous determination of DEX, GM, CZP, MPA and CEF were as low as 0.13 μg/kg, 0.16 μg/kg, 0.07 μg/kg, 0.06 μg/kg and 0.14 μg/kg, respectively. This detection method was used to analyze samples of pork muscle and the recoveries ranged from 61.3% to 80.3% for DEX and from 74.0% to 87.2% for MPA. Further more, good correlation between the novel ic-FLISA and traditional ELISA was demonstrated during the determination of DEX and MPA residues in real samples. The QD-based protocol described here is less time consuming than the classical method and it may be sufficiently flexible to be used in other systems for the simultaneous multicolor detection of the drugs.     

Quantum dot binding to DNA: Single-molecule imaging with atomic force microscopy

The interaction between nanoparticles (NPs) and DNA is of significance for both application and implication research of NPs. In this study, a single-molecule imaging technique based on atomic force microscopy (AFM) was employed to probe the NP-DNA interactions with quantum dots (QDs) as model NPs. Reproducible high-quality images of single DNA molecules in air and in liquids were acquired on mica by optimizing sample preparation conditions. Furthermore, the binding of QDs to DNA was explored using AFM. The DNA concentration was found to be a key factor influencing AFM imaging quality. In air and liquids, the optimal DNA concentration for imaging DNA molecules was approximately 2.5 and 0.25 μg/mL, and that for imaging DNA binding with QDs was 0.5 and 0.25 μg/mL, respectively. In the presence of QDs, the DNA conformation was altered with the formation of DNA condensates. Finally, the fine conformation of QD-DNA binding sites was examined to analyze the binding mechanisms. This work will benefit investigations of NP-DNA interactions and the understanding of the structure of NP-DNA bioconjugates. See accompanying article by Wang DOI: 10.1002/biot.201200309     

Triple density molecular quantum similarity measures: A general connection between theoretical calculations and experimental results

A newquantum similarity measure is defined. It is proposed as a way to project density functions from infinite dimensional spaces, where density functions belong, to finite dimensional ones. The procedure allows the representation of a given molecule initially described in terms ofnth order density functions as a point in a finite dimensional Euclidean space: apoint-molecule. Further manipulation of the obtained information permits the representation of a molecular set as a cloud of points: amolecular point cloud, in a variety of graphical manners. A previous experience in the field is compared with this new approach.A contribution of the Grup de Química Quàntica del Institut d'Estudis Catalans.     

Quantum dot immunoassays in renewable surface column and 96-well plate formats for the fluorescence detection of botulinum neurotoxin using high-affinity antibodies

A fluorescence sandwich immunoassay using high-affinity antibodies and quantum dot (QD) reporters has been developed for detection of botulinum neurotoxin serotype A (BoNT/A) using a nontoxic recombinant fragment of the holotoxin (BoNT/A-H_C-fragment) as a structurally valid simulant for the full toxin molecule. The antibodies used, AR4 and RAZ1, bind to nonoverlapping epitopes present on both the full toxin and on the recombinant fragment. In one format, the immunoassay is carried out in a 96-well plate with detection in a standard plate reader using AR4 as the capture antibody and QD-coupled RAZ1 as the reporter. Detection to 31 pM with a total incubation time of 3 h was demonstrated. In a second format, the AR4 capture antibody was coupled to Sepharose beads, and the reactions were carried out in microcentrifuge tubes with an incubation time of 1 h. The beads were subsequently captured and concentrated in a rotating rod “renewable surface” flow cell equipped with a fiber optic system for fluorescence measurements. In PBS buffer, the BoNT/A-H_C-fragment was detected to concentrations as low as 5 pM using the fluidic measurement approach.