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Special Issue "Sensing with Quantum Dots"

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A special issue of Sensors (ISSN 1424-8220).

Deadline for manuscript submissions: closed (30 August 2011)

Special Issue Editors

Guest Editor
Dr. Igor Medintz (Website)

Laboratory for Biosensors and Biomaterials, Center for Biomolecular Science & Engineering, United States Naval Research Laboratory, Washington, D.C. USA
Fax: +1 202 7679594
Interests: nanoparticle-biological interface, energy transfer, FRET, biosensing, enzymatic catalysis at a nanoparticle interface, nanoparticle-based cellular imaging
Guest Editor
Prof. Dr. Niko Hildebrandt (Website)

NanoBioPhotonics, Institut d’Electronique Fondamentale, Université Paris-Sud 91405 Orsay Cedex, France
Interests: FRET; spectroscopy; imaging; diagnostics; immunoassays; multiplexing; biosensing; lanthanides; quantum dots; time-gating
Guest Editor
Dr. Thomas Pons

Laboratoire Physique et Etude des Matériaux, ESPCI-CNRS-UPMC UMR8213 10, rue Vauquelin, 75005 Paris, France
Interests: quantum dot synthesis, nanoparticle-biological interface, biological sensing with nanoparticles, FRET, cellular imaging, in vivo imaging

Special Issue Information

Dear Colleagues,

Interest in utilizing quantum dots (QDs) within all types of sensing and imaging applications continues to grow nearly unabated. We have been generously asked by Sensors to guest edit a special issue that focuses on and reflects the vibrant research ongoing in this area.

We invite manuscripts for this forthcoming special issue that describe all aspects pertinent to sensing with quantum dots. This includes reviews that provide a current or critical overview of the state of the art in a particular QD application such as immunoassays, imaging, and the like or alternatively a signal transduction modality such as FRET, direct fluorescence or electrochemical detection. Reviews that focus on many related topics such as synthesizing QDs for sensing along with bioconjugation and characterization of QD sensor assemblies are also welcomed. Similarly, original research papers that describe all aspects of utilizing QDs in sensing whether the targets are biological (protein, DNA) or abiotic (ions or physical parameters such as temperature) are also of interest. If you have a preliminary idea or suggestion you would like to discuss beforehand, please feel free to contact us. We look forward to and welcome your participation in this special issue.

Prof. Dr. Niko Hildebrandt
Dr. Igor Medintz
Dr. Thomas Pons
Guest Editors

Published Papers (18 papers)

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Research

Jump to: Review

Open AccessArticle Time-Resolved Fluorescence Immunoassay for C-Reactive Protein Using Colloidal Semiconducting Nanoparticles
Sensors 2011, 11(12), 11335-11342; doi:10.3390/s111211335
Received: 24 August 2011 / Revised: 18 October 2011 / Accepted: 14 November 2011 / Published: 28 November 2011
Cited by 5 | PDF Full-text (207 KB) | HTML Full-text | XML Full-text
Abstract
Besides the typical short-lived fluorescence with decay times in the nanosecond range, colloidal II/VI semiconductor nanoparticles dispersed in buffer also possess a long-lived fluorescence component with decay times in the microsecond range. Here, the signal intensity of the long-lived luminescence at microsecond [...] Read more.
Besides the typical short-lived fluorescence with decay times in the nanosecond range, colloidal II/VI semiconductor nanoparticles dispersed in buffer also possess a long-lived fluorescence component with decay times in the microsecond range. Here, the signal intensity of the long-lived luminescence at microsecond range is shown to increase 1,000-fold for CdTe nanoparticles in PBS buffer. This long-lived fluorescence can be conveniently employed for time-gated fluorescence detection, which allows for improved signal-to-noise ratio and thus the use of low concentrations of nanoparticles. The detection principle is demonstrated with a time-resolved fluorescence immunoassay for the detection of C-reactive protein (CRP) using CdSe-ZnS nanoparticles and green light excitation. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessArticle Simplistic Attachment and Multispectral Imaging with Semiconductor Nanocrystals
Sensors 2011, 11(11), 10557-10570; doi:10.3390/s111110557
Received: 14 September 2011 / Revised: 26 October 2011 / Accepted: 26 October 2011 / Published: 7 November 2011
Cited by 5 | PDF Full-text (4356 KB) | HTML Full-text | XML Full-text
Abstract
Advances in spectral deconvolution technologies are rapidly enabling researchers to replace or enhance traditional epifluorescence microscopes with instruments capable of detecting numerous markers simultaneously in a multiplexed fashion. While significantly expediting sample throughput and elucidating sample information, this technology is limited by [...] Read more.
Advances in spectral deconvolution technologies are rapidly enabling researchers to replace or enhance traditional epifluorescence microscopes with instruments capable of detecting numerous markers simultaneously in a multiplexed fashion. While significantly expediting sample throughput and elucidating sample information, this technology is limited by the spectral width of common fluorescence reporters. Semiconductor nanocrystals (NC’s) are very bright, narrow band fluorescence emitters with great potential for multiplexed fluorescence detection, however the availability of NC’s with facile attachment chemistries to targeting molecules has been a severe limitation to the advancement of NC technology in applications such as immunocytochemistry and immunohistochemistry. Here we report the development of simple, yet novel attachment chemistries for antibodies onto NC’s and demonstrate how spectral deconvolution technology enables the multiplexed detection of 5 distinct NC-antibody conjugates with fluorescence emission wavelengths separated by as little as 20 nm. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
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Open AccessArticle Fabrication and Characterization of Electrospun Semiconductor Nanoparticle—Polyelectrolyte Ultra-Fine Fiber Composites for Sensing Applications
Sensors 2011, 11(11), 10372-10387; doi:10.3390/s111110372
Received: 27 September 2011 / Revised: 21 October 2011 / Accepted: 24 October 2011 / Published: 31 October 2011
Cited by 8 | PDF Full-text (1151 KB) | HTML Full-text | XML Full-text
Abstract
Fluorescent composite fibrous assembles of nanoparticle-polyelectrolyte fibers are useful multifunctional materials, utilized in filtration, sensing and tissue engineering applications, with the added benefits of improved mechanical, electrical or structural characteristics over the individual components. Composite fibrous mats were prepared by electrospinning aqueous [...] Read more.
Fluorescent composite fibrous assembles of nanoparticle-polyelectrolyte fibers are useful multifunctional materials, utilized in filtration, sensing and tissue engineering applications, with the added benefits of improved mechanical, electrical or structural characteristics over the individual components. Composite fibrous mats were prepared by electrospinning aqueous solutions of 6 wt% poly(acrylic acid) (PAA) loaded with 0.15 and 0.20% v/v, carboxyl functionalized CdSe/ZnS nanoparticles (SNPs). The resulting fluorescent composite fibrous mats exhibits recoverable quenching when exposed to high humidity. The sensor response is sensitive to water concentration and is attributed to the change in the local charges around the SNPs due to deprotonation of the carboxylic acids on the SNPs and the surrounding polymer matrix. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
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Open AccessCommunication Following Glucose Oxidase Activity by Chemiluminescence and Chemiluminescence Resonance Energy Transfer (CRET) Processes Involving Enzyme-DNAzyme Conjugates
Sensors 2011, 11(11), 10388-10397; doi:10.3390/s111110388
Received: 26 September 2011 / Revised: 24 October 2011 / Accepted: 25 October 2011 / Published: 31 October 2011
Cited by 18 | PDF Full-text (705 KB) | HTML Full-text | XML Full-text
Abstract
A hybrid consisting of glucose oxidase-functionalized with hemin/G-quadruplex units is used for the chemiluminescence detection of glucose. The glucose oxidase-mediated oxidation of glucose yields gluconic acid and H2O2. The latter in the presence of luminol acts as substrate [...] Read more.
A hybrid consisting of glucose oxidase-functionalized with hemin/G-quadruplex units is used for the chemiluminescence detection of glucose. The glucose oxidase-mediated oxidation of glucose yields gluconic acid and H2O2. The latter in the presence of luminol acts as substrate for the hemin/G-quadruplex-catalyzed generation of chemiluminescence. The glucose oxidase/hemin G-quadruplex hybrid was immobilized on CdSe/ZnS quantum dots (QDs). The light generated by the hybrid, in the presence of glucose, activated a chemiluminescence resonance energy transfer process to the QDs, resulting in the luminescence of the QDs. The intensities of the luminescence of the QDs at different concentrations of glucose provided an optical means to detect glucose. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
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Open AccessArticle Enzyme-Polymers Conjugated to Quantum-Dots for Sensing Applications
Sensors 2011, 11(10), 9951-9972; doi:10.3390/s111009951
Received: 22 September 2011 / Revised: 11 October 2011 / Accepted: 17 October 2011 / Published: 21 October 2011
Cited by 27 | PDF Full-text (1139 KB) | HTML Full-text | XML Full-text
Abstract
In the present research, the concept of developing a novel system based on polymer-enzyme macromolecules was tested by coupling carboxylic acid functionalized poly(vinyl alcohol) (PVA-COOH) to glucose oxidase (GOx) followed by the bioconjugation with CdS quantum-dots (QD). The resulting organic-inorganic nanohybrids were [...] Read more.
In the present research, the concept of developing a novel system based on polymer-enzyme macromolecules was tested by coupling carboxylic acid functionalized poly(vinyl alcohol) (PVA-COOH) to glucose oxidase (GOx) followed by the bioconjugation with CdS quantum-dots (QD). The resulting organic-inorganic nanohybrids were characterized by UV-visible spectroscopy, infrared spectroscopy, Photoluminescence spectroscopy (PL) and transmission electron microscopy (TEM). The spectroscopy results have clearly shown that the polymer-enzyme macromolecules (PVA-COOH/GOx) were synthesized by the proposed zero-length linker route. Moreover, they have performed as successful capping agents for the nucleation and constrained growth of CdS quantum-dots via aqueous colloidal chemistry. The TEM images associated with the optical absorption results have indicated the formation of CdS nanocrystals with estimated diameters of about 3.0 nm. The “blue-shift” in the visible absorption spectra and the PL values have provided strong evidence that the fluorescent CdS nanoparticles were produced in the quantum-size confinement regime. Finally, the hybrid system was biochemically assayed by injecting the glucose substrate and detecting the formation of peroxide with the enzyme horseradish peroxidase (HRP). Thus, the polymer-enzyme-QD hybrid has behaved as a nanostructured sensor for glucose detecting. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
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Open AccessArticle Terbium to Quantum Dot FRET Bioconjugates for Clinical Diagnostics: Influence of Human Plasma on Optical and Assembly Properties
Sensors 2011, 11(10), 9667-9684; doi:10.3390/s111009667
Received: 1 September 2011 / Revised: 29 September 2011 / Accepted: 30 September 2011 / Published: 12 October 2011
Cited by 18 | PDF Full-text (359 KB) | HTML Full-text | XML Full-text
Abstract
Förster resonance energy transfer (FRET) from luminescent terbium complexes (LTC) as donors to semiconductor quantum dots (QDs) as acceptors allows extraordinary large FRET efficiencies due to the long Förster distances afforded. Moreover, time-gated detection permits an efficient suppression of autofluorescent background leading [...] Read more.
Förster resonance energy transfer (FRET) from luminescent terbium complexes (LTC) as donors to semiconductor quantum dots (QDs) as acceptors allows extraordinary large FRET efficiencies due to the long Förster distances afforded. Moreover, time-gated detection permits an efficient suppression of autofluorescent background leading to sub-picomolar detection limits even within multiplexed detection formats. These characteristics make FRET-systems with LTC and QDs excellent candidates for clinical diagnostics. So far, such proofs of principle for highly sensitive multiplexed biosensing have only been performed under optimized buffer conditions and interactions between real-life clinical media such as human serum or plasma and LTC-QD-FRET-systems have not yet been taken into account. Here we present an extensive spectroscopic analysis of absorption, excitation and emission spectra along with the luminescence decay times of both the single components as well as the assembled FRET-systems in TRIS-buffer, TRIS-buffer with 2% bovine serum albumin, and fresh human plasma. Moreover, we evaluated homogeneous LTC-QD FRET assays in QD conjugates assembled with either the well-known, specific biotin-streptavidin biological interaction or, alternatively, the metal-affinity coordination of histidine to zinc. In the case of conjugates assembled with biotin-streptavidin no significant interference with the optical and binding properties occurs whereas the histidine-zinc system appears to be affected by human plasma. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessArticle A Fusion-Spliced Near-Field Optical Fiber Probe Using Photonic Crystal Fiber for Nanoscale Thermometry Based on Fluorescence-Lifetime Measurement of Quantum Dots
Sensors 2011, 11(9), 8358-8369; doi:10.3390/s110908358
Received: 18 July 2011 / Revised: 22 August 2011 / Accepted: 22 August 2011 / Published: 29 August 2011
Cited by 3 | PDF Full-text (1871 KB) | HTML Full-text | XML Full-text
Abstract
We have developed a novel nanoscale temperature-measurement method using fluorescence in the near-field called Fluorescence Near-field Optics Thermal Nanoscopy (Fluor-NOTN). Fluor-NOTN enables the temperature distributions of nanoscale materials to be measured in vivo/in situ. The proposed method measures temperature [...] Read more.
We have developed a novel nanoscale temperature-measurement method using fluorescence in the near-field called Fluorescence Near-field Optics Thermal Nanoscopy (Fluor-NOTN). Fluor-NOTN enables the temperature distributions of nanoscale materials to be measured in vivo/in situ. The proposed method measures temperature by detecting the temperature dependent fluorescence lifetimes of Cd/Se Quantum Dots (QDs). For a high-sensitivity temperature measurement, the auto-fluorescence generated from a fiber probe should be reduced. In order to decrease the noise, we have fabricated a novel near-field optical-fiber probe by fusion-splicing a photonic crystal fiber (PCF) and a conventional single-mode fiber (SMF). The validity of the novel fiber probe was assessed experimentally by evaluating the auto-fluorescence spectra of the PCF. Due to the decrease of auto-fluorescence, a six- to ten-fold increase of S/N in the near-field fluorescence lifetime detection was achieved with the newly fabricated fusion-spliced near-field optical fiber probe. Additionally, the near-field fluorescence lifetime of the quantum dots was successfully measured by the fabricated fusion-spliced near-field optical fiber probe at room temperature, and was estimated to be 10.0 ns. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessArticle Optimizing Two-Color Semiconductor Nanocrystal Immunoassays in Single Well Microtiter Plate Formats
Sensors 2011, 11(8), 7879-7891; doi:10.3390/s110807879
Received: 25 April 2011 / Revised: 29 July 2011 / Accepted: 1 August 2011 / Published: 11 August 2011
Cited by 14 | PDF Full-text (720 KB) | HTML Full-text | XML Full-text
Abstract
The simultaneous detection of two analytes, chicken IgY (IgG) and Staphylococcal enterotoxin B (SEB), in the single well of a 96-well plate is demonstrated using luminescent semiconductor quantum dot nanocrystal (NC) tracers. The NC-labeled antibodies were prepared via sulfhydryl-reactive chemistry using a [...] Read more.
The simultaneous detection of two analytes, chicken IgY (IgG) and Staphylococcal enterotoxin B (SEB), in the single well of a 96-well plate is demonstrated using luminescent semiconductor quantum dot nanocrystal (NC) tracers. The NC-labeled antibodies were prepared via sulfhydryl-reactive chemistry using a facile protocol that took Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
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Open AccessArticle FRET-Based Quantum Dot Immunoassay for Rapid and Sensitive Detection of Aspergillus amstelodami
Sensors 2011, 11(6), 6396-6410; doi:10.3390/s110606396
Received: 14 April 2011 / Revised: 10 June 2011 / Accepted: 13 June 2011 / Published: 16 June 2011
Cited by 21 | PDF Full-text (472 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a fluorescence resonance energy transfer (FRET)-based quantum dot (QD) immunoassay for detection and identification of Aspergillus amstelodami was developed. Biosensors were formed by conjugating QDs to IgG antibodies and incubating with quencher-labeled analytes; QD energy was transferred to the [...] Read more.
In this study, a fluorescence resonance energy transfer (FRET)-based quantum dot (QD) immunoassay for detection and identification of Aspergillus amstelodami was developed. Biosensors were formed by conjugating QDs to IgG antibodies and incubating with quencher-labeled analytes; QD energy was transferred to the quencher species through FRET, resulting in diminished fluorescence from the QD donor. During a detection event, quencher-labeled analytes are displaced by higher affinity target analytes, creating a detectable fluorescence signal increase from the QD donor. Conjugation and the resulting antibody:QD ratios were characterized with UV-Vis spectroscopy and QuantiT protein assay. The sensitivity of initial fluorescence experiments was compromised by inherent autofluorescence of mold spores, which produced low signal-to-noise and inconsistent readings. Therefore, excitation wavelength, QD, and quencher were adjusted to provide optimal signal-to-noise over spore background. Affinities of anti-Aspergillus antibody for different mold species were estimated with sandwich immunoassays, which identified A. fumigatus and A. amstelodami for use as quencher-labeled- and target-analytes, respectively. The optimized displacement immunoassay detected A. amstelodami concentrations as low as 103 spores/mL in five minutes or less. Additionally, baseline fluorescence was produced in the presence of 105 CFU/mL heat-killed E. coli O157:H7, demonstrating high specificity. This sensing modality may be useful for identification and detection of other biological threat agents, pending identification of suitable antibodies. Overall, these FRET-based QD-antibody biosensors represent a significant advancement in detection capabilities, offering sensitive and reliable detection of targets with applications in areas from biological terrorism defense to clinical analysis. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessArticle Interfacial Chemistry and the Design of Solid-Phase Nucleic Acid Hybridization Assays Using Immobilized Quantum Dots as Donors in Fluorescence Resonance Energy Transfer
Sensors 2011, 11(6), 6214-6236; doi:10.3390/s110606214
Received: 26 April 2011 / Revised: 26 May 2011 / Accepted: 7 June 2011 / Published: 9 June 2011
Cited by 22 | PDF Full-text (602 KB) | HTML Full-text | XML Full-text
Abstract
The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of [...] Read more.
The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of these systems. In this work, we identify several strategies based on the design of interfacial chemistry for improving sensitivity, obtaining lower limits of detection (LOD) and enabling the regeneration and reuse of solid-phase QD-FRET hybridization assays. FRET-sensitized emission from acceptor dyes associated with hybridization events at immobilized QD donors provides the analytical signal in these assays. The minimization of active sensing area reduces background from QD donor PL and allows the resolution of smaller amounts of acceptor emission, thus lowering the LOD. The association of multiple acceptor dyes with each hybridization event can enhance FRET efficiency, thereby improving sensitivity. Many previous studies have used interfacial protein layers to generate selectivity; however, transient destabilization of these layers is shown to prevent efficient regeneration. To this end, we report a protein-free interfacial chemistry and demonstrate the specific detection of as little as 2 pmol of target, as well as an improved capacity for regeneration. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
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Open AccessArticle Observing GLUT4 Translocation in Live L6 Cells Using Quantum Dots
Sensors 2011, 11(2), 2077-2089; doi:10.3390/s110202077
Received: 30 November 2010 / Revised: 29 December 2010 / Accepted: 6 February 2011 / Published: 10 February 2011
Cited by 1 | PDF Full-text (725 KB) | HTML Full-text | XML Full-text
Abstract
The glucose transporter 4 (GLUT4) plays a key role in maintaining whole body glucose homeostasis. Tracking GLUT4 in space and time can provide new insights for understanding the mechanisms of insulin-regulated GLUT4 translocation. Organic dyes and fluorescent proteins were used in previous [...] Read more.
The glucose transporter 4 (GLUT4) plays a key role in maintaining whole body glucose homeostasis. Tracking GLUT4 in space and time can provide new insights for understanding the mechanisms of insulin-regulated GLUT4 translocation. Organic dyes and fluorescent proteins were used in previous studies for investigating the traffic of GLUT4 in skeletal muscle cells and adipocytes. Because of their relative weak fluorescent signal against strong cellular autofluorescence background and their fast photobleaching rate, most studies only focused on particular segments of GLUT4 traffic. In this study, we have developed a new method for observing the translocation of GLUT4 targeted with photostable and bright quantum dots (QDs) in live L6 cells. QDs were targeted to GLUT4myc specifically and internalized with GLUT4myc through receptor-mediated endocytosis. Compared with traditional fluorescence dyes and fluorescent proteins, QDs with high brightness and extremely photostability are suitable for long-term single particle tracking, so individual GLUT4-QD complex can be easily detected and tracked for long periods of time. This newly described method will be a powerful tool for observing the translocation of GLUT4 in live L6 cells. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)

Review

Jump to: Research

Open AccessReview Sensing with Superconducting Point Contacts
Sensors 2012, 12(5), 6049-6074; doi:10.3390/s120506049
Received: 14 March 2012 / Revised: 6 April 2012 / Accepted: 20 April 2012 / Published: 10 May 2012
Cited by 1 | PDF Full-text (515 KB) | HTML Full-text | XML Full-text
Abstract
Superconducting point contacts have been used for measuring magnetic polarizations, identifying magnetic impurities, electronic structures, and even the vibrational modes of small molecules. Due to intrinsically small energy scale in the subgap structures of the supercurrent determined by the size of the [...] Read more.
Superconducting point contacts have been used for measuring magnetic polarizations, identifying magnetic impurities, electronic structures, and even the vibrational modes of small molecules. Due to intrinsically small energy scale in the subgap structures of the supercurrent determined by the size of the superconducting energy gap, superconductors provide ultrahigh sensitivities for high resolution spectroscopies. The so-called Andreev reflection process between normal metal and superconductor carries complex and rich information which can be utilized as powerful sensor when fully exploited. In this review, we would discuss recent experimental and theoretical developments in the supercurrent transport through superconducting point contacts and their relevance to sensing applications, and we would highlight their current issues and potentials. A true utilization of the method based on Andreev reflection analysis opens up possibilities for a new class of ultrasensitive sensors. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessReview Exploring Transduction Mechanisms of Protein Transduction Domains (PTDs) in Living Cells Utilizing Single-Quantum Dot Tracking (SQT) Technology
Sensors 2012, 12(1), 549-572; doi:10.3390/s120100549
Received: 30 November 2011 / Revised: 30 December 2011 / Accepted: 31 December 2011 / Published: 5 January 2012
Cited by 9 | PDF Full-text (1211 KB) | HTML Full-text | XML Full-text
Abstract
Specific protein domains known as protein transduction domains (PTDs) can permeate cell membranes and deliver proteins or bioactive materials into living cells. Various approaches have been applied for improving their transduction efficacy. It is, therefore, crucial to clarify the entry mechanisms and [...] Read more.
Specific protein domains known as protein transduction domains (PTDs) can permeate cell membranes and deliver proteins or bioactive materials into living cells. Various approaches have been applied for improving their transduction efficacy. It is, therefore, crucial to clarify the entry mechanisms and to identify the rate-limiting steps. Because of technical limitations for imaging PTD behavior on cells with conventional fluorescent-dyes, how PTDs enter the cells has been a topic of much debate. Utilizing quantum dots (QDs), we recently tracked the behavior of PTD that was derived from HIV-1 Tat (TatP) in living cells at the single-molecule level with 7-nm special precision. In this review article, we initially summarize the controversy on TatP entry mechanisms; thereafter, we will focus on our recent findings on single-TatP-QD tracking (SQT), to identify the major sequential steps of intracellular delivery in living cells and to discuss how SQT can easily provide direct information on TatP entry mechanisms. As a primer for SQT study, we also discuss the latest findings on single particle tracking of various molecules on the plasma membrane. Finally, we discuss the problems of QDs and the challenges for the future in utilizing currently available QD probes for SQT. In conclusion, direct identification of the rate-limiting steps of PTD entry with SQT should dramatically improve the methods for enhancing transduction efficiency. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessReview Semiconductor Quantum Dots for Biomedicial Applications
Sensors 2011, 11(12), 11736-11751; doi:10.3390/s111211736
Received: 2 November 2011 / Revised: 6 December 2011 / Accepted: 13 December 2011 / Published: 16 December 2011
Cited by 56 | PDF Full-text (457 KB) | HTML Full-text | XML Full-text
Abstract
Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed [...] Read more.
Semiconductor quantum dots (QDs) are nanometre-scale crystals, which have unique photophysical properties, such as size-dependent optical properties, high fluorescence quantum yields, and excellent stability against photobleaching. These properties enable QDs as the promising optical labels for the biological applications, such as multiplexed analysis of immunocomplexes or DNA hybridization processes, cell sorting and tracing, in vivo imaging and diagnostics in biomedicine. Meanwhile, QDs can be used as labels for the electrochemical detection of DNA or proteins. This article reviews the synthesis and toxicity of QDs and their optical and electrochemical bioanalytical applications. Especially the application of QDs in biomedicine such as delivering, cell targeting and imaging for cancer research, and in vivo photodynamic therapy (PDT) of cancer are briefly discussed. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessReview CdTe and CdSe Quantum Dots Cytotoxicity: A Comparative Study on Microorganisms
Sensors 2011, 11(12), 11664-11678; doi:10.3390/s111211664
Received: 27 October 2011 / Revised: 26 November 2011 / Accepted: 9 December 2011 / Published: 15 December 2011
Cited by 17 | PDF Full-text (1649 KB) | HTML Full-text | XML Full-text
Abstract
Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or [...] Read more.
Quantum dots (QDs) are colloidal semiconductor nanocrystals of a few nanometers in diameter, being their size and shape controlled during the synthesis. They are synthesized from atoms of group II–VI or III–V of the periodic table, such as cadmium telluride (CdTe) or cadmium selenium (CdSe) forming nanoparticles with fluorescent characteristics superior to current fluorophores. The excellent optical characteristics of quantum dots make them applied widely in the field of life sciences. Cellular uptake of QDs, location and translocation as well as any biological consequence, such as cytotoxicity, stimulated a lot of scientific research in this area. Several studies pointed to the cytotoxic effect against micoorganisms. In this mini-review, we overviewed the synthesis and optical properties of QDs, and its advantages and bioapplications in the studies about microorganisms such as protozoa, bacteria, fungi and virus. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessReview Overview of Stabilizing Ligands for Biocompatible Quantum Dot Nanocrystals
Sensors 2011, 11(12), 11036-11055; doi:10.3390/s111211036
Received: 12 October 2011 / Revised: 21 November 2011 / Accepted: 22 November 2011 / Published: 28 November 2011
Cited by 57 | PDF Full-text (908 KB) | HTML Full-text | XML Full-text
Abstract
Luminescent colloidal quantum dots (QDs) possess numerous advantages as fluorophores in biological applications. However, a principal challenge is how to retain the desirable optical properties of quantum dots in aqueous media while maintaining biocompatibility. Because QD photophysical properties are directly related to [...] Read more.
Luminescent colloidal quantum dots (QDs) possess numerous advantages as fluorophores in biological applications. However, a principal challenge is how to retain the desirable optical properties of quantum dots in aqueous media while maintaining biocompatibility. Because QD photophysical properties are directly related to surface states, it is critical to control the surface chemistry that renders QDs biocompatible while maintaining electronic passivation. For more than a decade, investigators have used diverse strategies for altering the QD surface. This review summarizes the most successful approaches for preparing biocompatible QDs using various chemical ligands. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessReview Surface X-Ray Diffraction Results on the III-V Droplet Heteroepitaxy Growth Process for Quantum Dots: Recent Understanding and Open Questions
Sensors 2011, 11(11), 10624-10637; doi:10.3390/s111110624
Received: 16 September 2011 / Revised: 25 October 2011 / Accepted: 2 November 2011 / Published: 8 November 2011
Cited by 3 | PDF Full-text (2009 KB) | HTML Full-text | XML Full-text
Abstract
In recent years, epitaxial growth of self-assembled quantum dots has offered a way to incorporate new properties into existing solid state devices. Although the droplet heteroepitaxy method is relatively complex, it is quite relaxed with respect to the material combinations that can [...] Read more.
In recent years, epitaxial growth of self-assembled quantum dots has offered a way to incorporate new properties into existing solid state devices. Although the droplet heteroepitaxy method is relatively complex, it is quite relaxed with respect to the material combinations that can be used. This offers great flexibility in the systems that can be achieved. In this paper we review the structure and composition of a number of quantum dot systems grown by the droplet heteroepitaxy method, emphasizing the insights that these experiments provide with respect to the growth process. Detailed structural and composition information has been obtained using surface X-ray diffraction analyzed by the COBRA phase retrieval method. A number of interesting phenomena have been observed: penetration of the dots into the substrate (“nano-drilling”) is often encountered; interdiffusion and intermixing already start when the group III droplets are deposited, and structure and composition may be very different from the one initially intended. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)
Open AccessReview Biosensing with Quantum Dots: A Microfluidic Approach
Sensors 2011, 11(10), 9732-9763; doi:10.3390/s111009732
Received: 1 September 2011 / Revised: 4 October 2011 / Accepted: 17 October 2011 / Published: 18 October 2011
Cited by 24 | PDF Full-text (12900 KB) | HTML Full-text | XML Full-text
Abstract
Semiconductor quantum dots (QDs) have served as the basis for signal development in a variety of biosensing technologies and in applications using bioprobes. The use of QDs as physical platforms to develop biosensors and bioprobes has attracted considerable interest. This is largely [...] Read more.
Semiconductor quantum dots (QDs) have served as the basis for signal development in a variety of biosensing technologies and in applications using bioprobes. The use of QDs as physical platforms to develop biosensors and bioprobes has attracted considerable interest. This is largely due to the unique optical properties of QDs that make them excellent choices as donors in fluorescence resonance energy transfer (FRET) and well suited for optical multiplexing. The large majority of QD-based bioprobe and biosensing technologies that have been described operate in bulk solution environments, where selective binding events at the surface of QDs are often associated with relatively long periods to reach a steady-state signal. An alternative approach to the design of biosensor architectures may be provided by a microfluidic system (MFS). A MFS is able to integrate chemical and biological processes into a single platform and allows for manipulation of flow conditions to achieve, by sample transport and mixing, reaction rates that are not entirely diffusion controlled. Integrating assays in a MFS provides numerous additional advantages, which include the use of very small amounts of reagents and samples, possible sample processing before detection, ultra-high sensitivity, high throughput, short analysis time, and in situ monitoring. Herein, a comprehensive review is provided that addresses the key concepts and applications of QD-based microfluidic biosensors with an added emphasis on how this combination of technologies provides for innovations in bioassay designs. Examples from the literature are used to highlight the many advantages of biosensing in a MFS and illustrate the versatility that such a platform offers in the design strategy. Full article
(This article belongs to the Special Issue Sensing with Quantum Dots)

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