Overcoming the Cut‐Off Charge Transfer Bandgaps at the PbS Quantum Dot Interface

Light harvesting from large size of semiconductor PbS quantum dots (QDs) with a bandgap of less than 1 eV is one of the greatest challenges precluding the development of PbS QD‐based solar cells because the interfacial charge transfer (CT) from such QDs to the most commonly used electron acceptor materials is very inefficient, if it occurs at all. Thus, an alternative electron‐accepting unit with a new driving force for CT is urgently needed to harvest the light from large‐sized PbS QDs. Here, a cationic porphyrin is utilized as a new electron acceptor unit with unique features that bring the donor–acceptor components into close molecular proximity, allowing ultrafast and efficient electron transfer for QDs of all sizes, as inferred from the drastic photoluminescence quenching and the ultrafast formation of the porphyrin anionic species. The time‐resolved results clearly demonstrate the possibility of modulating the electron transfer process between PbS QDs and porphyrin moieties not only by the size quantization effect but also by the interfacial electrostatic interaction between the positively charged porphyrin and the negatively charged QDs. This approach provides a new pathway for engineering QD‐based solar cells that make the best use of the diverse photons making up the Sun's broad irradiance spectrum.     

Engineering Immunological Tolerance Using Quantum Dots to Tune the Density of Self‐Antigen Display

Treatments for autoimmunity—diseases where the immune system mistakenly attacks self‐molecules—are not curative and leave patients immunocompromised. New studies aimed at more specific treatments reveal that development of inflammation or tolerance is influenced by the form in which self‐antigens are presented. Using a mouse model of multiple sclerosis (MS), it is shown for the first time that quantum dots (QDs) can be used to generate immunological tolerance by controlling the density of self‐antigen on QDs. These assemblies display dense arrangements of myelin self‐peptide associated with disease in MS, are uniform in size (<20 nm), and allow direct visualization in immune tissues. Peptide‐QDs rapidly concentrate in draining lymph nodes, colocalizing with macrophages expressing scavenger receptors involved in tolerance. Treatment with peptide‐QDs reduces disease incidence tenfold. Strikingly, the degree of tolerance—and the underlying expansion of regulatory T cells—correlates with the density of myelin molecules presented on QDs. A key discovery is that higher numbers of tolerogenic particles displaying lower levels of self‐peptide are more effective for inducing tolerance than fewer particles each displaying higher densities of peptide. QDs conjugated with self‐antigens can serve as a new platform to induce tolerance, while visualizing QD therapeutics in tolerogenic tissue domains.     

A Polyallylamine Anchored Amine‐Rich Laser‐Ablated Graphene Platform for Facile and Highly Selective Electrochemical IgG Biomarker Detection

Current immunosensors have an insufficient number of binding sites for the recognition of biomolecules, which leads to false positive or negative results. In this research, a facile, cost‐effective, disposable, and highly selective electrochemical immunosensing platform is developed based on cationic polyelectrolyte polyallylamine (PAAMI) anchored laser‐ablated graphene (LAG). Here, for the first time, PAAMI is introduced to stabilize LAG flakes, while retaining the intrinsic thermal and electronic properties of the substrate by noncovalent π–π interaction and electrostatic physical absorption. The sensing platform offers a suitable number of anchoring sites for the immobilized antibodies by providing ? NH₂ functional groups. The proper grafting of PAAMI is confirmed through X‐ray photoelectron spectroscopy and Raman spectroscopy. The immunosensing platform is applied to detect immunoglobulin (IgG) biomarkers as a proof of concept. Under optimized conditions, the sensing platform exhibits a linear range of 0.012–15 and 15–352 ng mL^?1 with a limit of detection of 6 pg mL^?1 for IgG detection with high selectivity. Based on the analysis, the developed immunosensing platform can be used for point‐of‐care detection of IgG in clinical diagnostic centers. Furthermore, the developed strategy is well suited for the detection of other cancer biomarkers after immobilizing the relevant antibodies.     

Origins of Low Quantum Efficiencies in Quantum Dot LEDs

The promise for next generation light‐emitting device (LED) technologies is a major driver for research on nanocrystal quantum dots (QDs). The low efficiencies of current QD‐LEDs are often attributed to luminescence quenching of charged QDs through Auger‐processes. Although new QD chemistries successfully suppress Auger recombination, high performance QD‐LEDs with these materials have yet to be demonstrated. Here, QD‐LED performance is shown to be significantly limited by the electric field. Experimental field‐dependent photoluminescence decay studies and tight‐binding simulations are used to show that independent of charging, the electric field can strongly quench the luminescence of QD solids by reducing the electron and hole wavefunction overlap, thereby lowering the radiative recombination rate. Quantifying this effect for a series of CdSe/CdS QD solids reveals a strong dependence on the QD band structure, which enables the outline of clear design strategies for QD materials and device architectures to improve QD‐LED performance.     

Controlled Fabrication of PbS Quantum‐Dot/Carbon‐Nanotube Nanoarchitecture and its Significant Contribution to Near‐Infrared Photon‐to‐Current Conversion

A solution‐processed nanoarchitecture based on PbS quantum dots (QDs) and multi‐walled carbon nanotubes (MWCNTs) is synthesized by simply mixing the pre‐synthesized high‐quality PbS QDs and oleylamine (OLA) pre‐functionalized MWCNTs. Pre‐functionalization of MWCNTs with OLA is crucial for the attachment of PbS QDs and the coverage of QDs on the surface of MWCNTs can be tuned by varying the ratio of PbS QDs to MWCNTs. The apparent photoluminescence (steady‐state emission and fluorescence lifetime) “quenching” effect indicates efficient charge transfer from photo‐excited PbS QDs to MWCNTs. The as‐synthesized PbS‐QD/MWCNT nanoarchitecture is further incorporated into a hole‐conducting polymer poly(3‐hexylthiophene)‐(P3HT), forming the P3HT:PbS‐QD/MWCNT nanohybrid, in which the PbS QDs act as a light harvester for absorbing irradiation over a wide wavelength range of the solar spectrum up to near infrared (NIR, ≈1430 nm) range; whereas, the one‐dimensional MWCNTs and P3HT are used to collect and transport photoexcited electrons and holes to the cathode and anode, respectively. Even without performing the often required “ligand exchange” to remove the long‐chained OLA ligands, the built nanohybrid photovoltaic (PV) device exhibits a largely enhanced power conversion efficiency (PCE) of 3.03% as compared to 2.57% for the standard bulk hetero‐junction PV cell made with P3HT and [6,6]‐Phenyl‐C₆₁‐Butyric Acid Methyl Ester (PCBM) mixtures. The improved performance of P3HT:PbS‐QD/MWCNT nanohybrid PV device is attributed to the significantly extended absorption up to NIR by PbS QDs as well as the effectively enhanced charge separation and transportation due to the integrated MWCNTs and P3HT. Our research results suggest that properly integrating QDs, MWCNTs, and polymers into nanohybrid structures is a promising approach for the development of highly efficient PV devices.     

Luminescent Graphene Oxide with a Peptide‐Quencher Complex for Optical Detection of Cell‐Secreted Proteases by a Turn‐On Response

Graphene oxide (GO) is an emerging luminescent nanomaterial with photostable and unique photoluminescence (PL) in the visible and near‐infrared region. Herein, a GO PL‐based optical biosensor consisting of a luminescent GO donor covalently linked with a peptide‐quencher complex is reported for the simple, rapid, and sensitive detection of proteases. To this end, the quenching efficiency of various candidate quenchers of GO fluorescence, such as metalloprotoporphyrins and QXL₅₇₀, are examined and their quenching mechanisms investigated. A fluorescence resonance energy transfer‐based quencher, QXL₅₇₀, is found to be much more effective for quenching the intrinsic fluorescence of GO than other charge transfer‐based quenchers. The designed GO–peptide–QXL system is then able to sensitively detect specific proteases—chymotrypsin and matrix metalloproteinase‐2—via a “turn‐on” response of quenched GO fluorescence after proteolytic cleavage of the quencher. Finally, the GO–peptide–QXL hybrid successfully detects MMP‐2 secreted from living cells—human hepatocytes HepG2—with high sensitivity.     

Magnetic/Fluorescent Barcodes Based on Cadmium‐Free Near‐Infrared‐Emitting Quantum Dots for Multiplexed Detection

Magnetic/fluorescent barcodes, which combine quantum dots (QDs) and superparamagnetic nanoparticles in micrometer‐sized host microspheres, are promising for automatic high‐throughput multiplexed biodetection applications and “point of care” biodetection. However, the fluorescence intensity of QDs sharply decreases after addition of magnetic nanoparticles (MNPs) due to absorption by MNPs, and thus, the encoding capacity of QDs becomes more limited. Furthermore, the intrinsic toxicity of cadmium‐based QDs, the most commonly used QD in barcodes, has significant risks to human health and the environment. In this work, to alleviate fluorescence quenching and intrinsic toxicity, cadmium‐free NIR‐emitting CuInS₂/ZnS QDs and Fe₃O₄ MNPs are successfully incorporated into poly(styrene‐co‐maleic anhydride) microspheres by using the Shirasu porous glass membrane emulsification technique. A “single‐wavelength” encoding model is successfully constructed to guide the encoding of NIR QDs with wide emission spectra. Then, a “single‐wavelength” encoding combined with size encoding is used to produce different optical codes by simply changing the wavelength and the intensity of the QDs as well as the size of the barcode microspheres. 48 barcodes are easily created due to the greatly reduced energy transfer between the NIR‐emitting QDs and MNPs. The resulting bifunctional barcodes are also combined with a flow cytometer using one laser for multiplexed detection of five tumor markers in one test. Assays based on these barcodes are significantly more sensitive than non‐magnetic and traditional ELISA assays. Moreover, validating experiments also show good performance of the bifunctional barcodes‐based suspension array when dealing with patient serum samples. Thus, magnetic/fluorescent barcodes based on NIR‐emitting CuInS₂/ZnS QDs are promising for multiplexed bioassay applications.     

Synthesis of Highly Luminescent SnO2 Nanocrystals: Analysis of their Defect‐Related Photoluminescence Using Polyoxometalates as Quenchers

Colloidal semiconductor nanocrystals (NCs), called quantum dots (QDs), have been intensively studied because of their excellent photoluminescence (PL) quantum yields. However, commercial QDs such as CdSe and InP contain toxic or expensive rare elements, limiting their sustainable use. This study focuses on nontoxic, stable, and cheap tin oxides, and synthesized luminescent SnO₂ NCs of ≈2 nm in size by a heating‐up method. Tin precursors and diols in a high‐boiling point solvent with oleylamine as the surfactant are heated at 240 °C. SnO₂ NCs show defect‐related photoluminescence at 400–460 nm by excitation at 370 nm, achieving a high quantum yield of more than 60%. The PL intensity is stable even when the NCs are stored in atmospheric air at room temperature for over 1 year. The defect‐related emissions of the SnO₂ NCs are studied using polyoxometalates (POMs) as the PL quencher. POMs efficiently quench the PL emissions by extracting excited electrons from the conduction band and shallow surface defects. The results reveal that PL emissions from SnO₂ NCs are associated with radiative charge recombination via shallow defect levels on the surface and in the bulk, demonstrating the effectiveness of the PL quenching technique using POMs in studying the PL emission mechanism in QDs.     

Photoluminescence Detection of Biomolecules by Antibody‐Functionalized Diatom Biosilica

Diatoms are single‐celled algae that make microscale silica shells called “frustules”, which possess intricate nanoscale features imbedded within periodic two‐dimensional pore arrays. In this study, antibody‐functionalized diatom biosilica frustules serve as a microscale biosensor platform for selective and label‐free photoluminescence (PL)‐based detection of immunocomplex formation. The model antibody rabbit immunoglobulin G (IgG) is covalently attached to the frustule biosilica of the disk‐shaped, 10‐µm diatom Cyclotella sp. by silanol amination and crosslinking steps to a surface site density of 3948 ± 499 IgG molecules µm^?2. Functionalization of the diatom biosilica with the nucleophilic IgG antibody amplifies the intrinsic blue PL of diatom biosilica by a factor of six. Furthermore, immunocomplex formation with the complimentary antigen anti‐rabbit IgG further increases the peak PL intensity by at least a factor of three, whereas a non‐complimentary antigen (goat anti‐human IgG) does not. The nucleophilic immunocomplex increases the PL intensity by donating electrons to non‐radiative defect sites on the photoluminescent diatom biosilica, thereby decreasing non‐radiative electron decay and increasing radiative emission. This unique enhancement in PL emission is correlated to the antigen (goat anti‐rabbit IgG) concentration, where immunocomplex binding follows a Langmuir isotherm with binding constant of 2.8 ± 0.7 × 10^?7 M .     

Human Platelet Membrane Functionalized Microchips with Plasmonic Codes for Cancer Detection

The possibility of functional roles played by platelets in close alliance with cancer cells has inspired the design of new biomimetic systems that exploit platelet–cancer cell interactions. Here, the role of platelets in cancer diagnostics is leveraged to design a microfluidic platform capable of detecting cancer‐derived extracellular vesicles (EVs) from ultrasmall volumes (1 µL) of human plasma samples. Further, the captured EVs are counted by direct optical coding of plasmonic nanoprobes modified with EV‐specific antibodies. Owing to the inherent properties of platelets for multifaceted interaction with cancer cells, the microfluidic chip equipped with a biologically interfaced platelet membrane‐cloaked surface (denoted “PLT‐Chip”) can capture a significantly higher number of EVs from multiple types of cancer cell lines (prostate, lung, bladder, and breast) than the normal cell‐derived EVs. Furthermore, this chip allows the monitoring of the growth of tumor spheroids (100 µm–2.5 mm) and clearly distinguishes the plasma of cancer patients from that of normal healthy controls. This robust, multifaceted, and cancer‐specific binding affinity, coupled with excellent biocompatibility, is a unique feature of platelet membrane‐cloaked surfaces, which therefore represent promising alternatives to antibodies for application in EVs‐based cancer theranostics.     

Decoupling Theranostics with Rare Earth Doped Nanoparticles

Theranostic nanoagents targeted for personalized medicine provide a unified platform for therapeutics and diagnostics. To be able to discretely control each individually, allows for safer, more precise, and truly multifunctional theranostics. Rare earth doped nanoparticles can be rationally tailored to best match this condition with the aid of core/shell engineering. In such nanoparticles, the light‐mediated theranostic approach is functionally decoupled—therapeutics or diagnostics are prompted on‐demand, by wavelength‐specific excitation. These decoupled rare earth nanoparticles (dNPs) operate entirely under near‐infrared (NIR) excitation, for minimized light interference with the target and extended tissue depth action. Under heating‐free 806 nm irradiation, dNPs behave solely as high‐contrast NIR‐to‐NIR optical markers and nanothermometers, visualizing and probing the area of interest without prompting the therapeutic effect beforehand. On the contrary, 980 nm NIR irradiation is upconverted by the dNPs to UV/visible light, which triggers secondary photochemical processes, e.g., generation of reactive oxygen species by photosensitizers coupled to the dNPs, causing damage to cancer cells. Additionally, integration of NIR nanothermometry helps to control the temperature in the vicinity of the dNPs avoiding possible overheating and quenching of upconversion (UC) emission, harnessed for photodynamic therapy. Overall, a new direction is outlined in the development of state‐of‐the‐art rare earth based theranostic nanoplatforms.     

Sub‐kilogram‐Scale One‐Pot Synthesis of Highly Luminescent and Monodisperse Core/Shell Quantum Dots by the Successive Injection of Precursors

The one‐pot synthesis of core/shell quantum dots (QDs) represents an attractive alternative to conventional synthesis techniques, where the core CdSe QDs are first purified and then an epitaxial shell of the desired thickness is obtained by the slow addition of shell precursors to a solution of the purified QDs at high temperature. We have developed a one‐pot synthesis procedure involving the successive injection of deliberately selected core‐ and shell‐forming reagents at appropriate temperatures. Sub‐kilogram quantities of highly luminescent and monodisperse core/shell QDs with desirable optical properties (full width at half maximum of photoluminescence (PL) band is ca. 30 nm) have been produced by the sequential growth of the core and shell in a controlled manner. This one‐pot method has also been extended to form water‐soluble core/double‐shell CdSe/ZnSe/ZnS QDs exhibiting high PL efficiency and stability.     

BIOMEDICAL MATERIALS: Compact and Stable Quantum Dots with Positive,Negative, or Zwitterionic Surface: Specific Cell Interactions and Non‐Specific Adsorptions by the Surface Charges (Adv. Funct. Mater. 9/2011)

A new type of quantum dot (QD) ligand chemistry is introduced that can provide positive, negative, or zwitterionic surface QDs. CdSe/CdZnS core‐shell QDs are decorated with ligands, and the non‐specific and specific interactions of the QDs through their surface charge are investigated with the focus on cellular adsorptions and endocytosis. Zwitterionic QDs are compact with a ligand hydrodynamic thickness of less than 2 nm, they are colloidally very stable over a broad pH range and even in saturated NaCl solution, and they show minimal non‐specific adsorptions. Positive and negative QDs show a very different behavior for cellular adsorption and subsequent incorporation, suggesting mostly energy‐independent pathways for positive QDs and exclusively adenosine triphosphate (ATP)‐dependent pathways for negative QDs. The zwitterionic QD surface ligands can also be used in conjunction with other functional groups, which allows simple conjugations for highly specific targeting whereas retaining the advantages of a zwitterionic QD surface. This QD surface chemistry can provide highly specific and very sensitive imaging with very low background level. Using the mixed QD surface ligand system, we demonstrated streptavidin and antibody QD conjugates that show a signal‐to‐noise ratio that is over 4000 times higher than the unconjugated mixture, which was used as a control case. The QD chemistry reported herein can be easily extended to other functional groups, such as alkynes, azides, or other amines, and can be further used in many future applications, including single‐QD level experiments, sensitive assays, or in vivo applications using anti‐fouling QD probes.     

3D Printed Bioelectronic Microwells

The in-house and on-demand fabrication of electrochemical integrated biosensors is a great challenge, especially in the field of modern point-of-care diagnostics. 3D printing technology allows the production of specialized electronic devices adapted to the required conditions, and 3D printed thermoplastic electrodes have shown hopeful achievements mainly in enzymatic bioassays. This work describes a novel configuration of integrated all-3D-printed electrochemical microtitration wells (e-wells) for direct quantum dot-based (QDs) and enzymatic bioassays. The e-wells enable the in situ development of complete bioassays, that is, from sample addition to biomarker detection, without the need for external equipment other than a micropipette and a detector. The bioanalytical capability of the 3D e-wells is demonstrated through the voltammetric bioassay of C-reactive protein employing biotinylated reporter antibody and streptavidin-conjugated CdSe/ZnS QDs. In addition, in order to extend their scope to enzymatic biosensing, e-wells are applied to the amperometric determination of hydrogen peroxide by-products, demonstrating their universal applicability in electrochemical bioassays.     

多层In_(0.55)Al_(0.45)As/A_(0.5)Ga_(0.5)As量子点的变温光致发光研究

测量了自组织多层In0.55Al0.45As/Al0.5Ga0.5As量子点的变温光致发光谱,同时观察到来自浸润层和量子点的发光,首次直接观察到了浸润层和量子点之间的载流子热转移.分析发光强度随温度的变化发现浸润层发光的热淬灭包括两个过程:低温时浸润层的激子从局域态热激发到扩展态,然后被量子点俘获;而温度较高时则通过势垒层的X能谷淬灭.利用速率方程模拟了激子在浸润层和量子点间的转移过程,计算结果与实验符合得很好     

Organometal Halide Perovskite Quantum Dot Light‐Emitting Diodes

Organometal halide perovskites quantum dots (OHP‐QDs) with bright, color‐tunable, and narrow‐band photoluminescence have significant advantages in display, lighting, and laser applications. Due to sparse concentrations and difficulties in the enrichment of OHP‐QDs, production of large‐area uniform films of OHP‐QDs is a challenging task, which largely impedes their use in electroluminescence devices. Here, a simple dip‐coating method has been reported to effectively fabricate large‐area uniform films of OHP‐QDs. Using this technique, multicolor OHP‐QDs light‐emitting diodes (OQ‐LEDs) emitting in blue, blue‐green, green, orange, and red color have been successfully produced by simply tuning the halide composition or size of QDs. The blue, green, and red OQ‐LEDs exhibited, respectively, a maximum luminance of 2673, 2398, and 986 cd m^?2 at a current efficiency of 4.01, 3.72, and 1.52 cd A^?1, and an external quantum efficiency of 1.38%, 1.06%, and 0.53%, which are much better than most LEDs based on OHP films. The packaged OQ‐LEDs show long‐term stability in air (humidity ≈50%) for at least 7 d. The results demonstrate the great potential of the dip‐coating method to fabricate large‐area uniform films for various QDs. The high‐efficiency OQ‐LEDs also demonstrate the promising potential of OHP‐QDs for low‐cost display, lighting, and optical communication applications.     

Functionalized Self‐Assembled InAs/GaAs Quantum‐Dot Structures Hybridized with Organic Molecules

Low‐dimensional III–V semiconductors have many advantages over other semiconductors; however, they are not particularly stable under physiological conditions. Hybridizing biocompatible organic molecules with advanced optical and electronic semiconductor devices based on quantum dots (QDs) and quantum wires could provide an efficient solution to realize stress‐free and nontoxic interfaces to attach larger functional biomolecules. Monitoring the modifications of the optical properties of the hybrid molecule–QD systems by grafting various types of air‐stable diazonium salts onto the QD structures surfaces provides a direct approach to prove the above concepts. The InAs/GaAs QD structures used in this work consist of a layer of surface InAs QDs and a layer of buried InAs QDs embedded in a wider‐bandgap GaAs matrix. An enhancement in photoluminescence intensity by a factor of 3.3 from the buried QDs is achieved owing to the efficient elimination of the dangling bonds on the surface of the structures and to the decrease in non‐radiative recombination caused by their surface states. Furthermore, a narrow photoluminescence band peaking at 1620 nm with a linewidth of 49 meV corresponding to the eigenstates interband transition of the surface InAs QDs is for the first time clearly observed at room temperature, which is something that has rarely been achieved without the use of such engineered surfaces. The experimental results demonstrate that the hybrid molecule–QD systems possess a high stability, and both the surface and buried QDs are very sensitive to changes in their surficial conditions, indicating that they are excellent candidates as basic sensing elements for novel biosensor applications.     

Graphene Enabled Low-Noise Surface Chemistry for Multiplexed Sepsis Biomarker Detection in Whole Blood

Affinity-based electrochemical (EC) sensors offer a potentially valuable approach for point-of-care (POC) diagnostics applications, and for the detection of diseases, such as sepsis, that require simultaneous detection of multiple biomarkers, but their development has been hampered due to biological fouling and EC noise. Here, an EC sensor platform that enables detection of multiple sepsis biomarkers simultaneously by incorporating a nanocomposite coating composed of crosslinked bovine serum albumin containing a network of reduced graphene oxide nanoparticles that prevents biofouling while maintaining electroconductivity is described. Using nanocomposite coated planar gold electrodes, a sensitive procalcitonin (PCT) sensor is constructed and validated in undiluted serum, which produced an excellent correlation with a conventional ELISA (adjusted r²  = 0.95) using clinical samples. A single multiplexed platform containing sensors for three different sepsis biomarkers—PCT, C-reactive protein, and pathogen-associated molecular patterns—is also developed, which exhibits specific responses within the clinically significant range without any cross-reactivity. This platform enables sensitive simultaneous EC detection of multiple analytes in human whole blood, and it can be applied to detect any target analyte with an appropriate antibody pair. Thus, this nanocomposite-enabled EC sensor platform may offer a potentially valuable tool for development of a wide range of clinical POC diagnostics.     

Compact and Stable Quantum Dots with Positive,Negative, or Zwitterionic Surface: Specific Cell Interactions and Non‐Specific Adsorptions by the Surface Charges

A new type of quantum dot (QD) ligand chemistry is introduced that can provide positive, negative, or zwitterionic surface QDs. CdSe/CdZnS core‐shell QDs are decorated with ligands, and the non‐specific and specific interactions of the QDs through their surface charge are investigated with the focus on cellular adsorptions and endocytosis. Zwitterionic QDs are compact with a ligand hydrodynamic thickness of less than 2 nm, they are colloidally very stable over a broad pH range and even in saturated NaCl solution, and they show minimal non‐specific adsorptions. Positive and negative QDs show a very different behavior for cellular adsorption and subsequent incorporation, suggesting mostly energy‐independent pathways for positive QDs and exclusively adenosine triphosphate (ATP)‐dependent pathways for negative QDs. The zwitterionic QD surface ligands can also be used in conjunction with other functional groups, which allows simple conjugations for highly specific targeting whereas retaining the advantages of a zwitterionic QD surface. This QD surface chemistry can provide highly specific and very sensitive imaging with very low background level. Using the mixed QD surface ligand system, we demonstrated streptavidin and antibody QD conjugates that show a signal‐to‐noise ratio that is over 4000 times higher than the unconjugated mixture, which was used as a control case. The QD chemistry reported herein can be easily extended to other functional groups, such as alkynes, azides, or other amines, and can be further used in many future applications, including single‐QD level experiments, sensitive assays, or in vivo applications using anti‐fouling QD probes.     

Improved nanocrystal formation,quantum confinement and carrier transport properties of doped Si quantum dot superlattices for third generation photovoltaics

An all‐Si tandem solar cell has the potential to achieve high conversion efficiency at low cost. However, the selection and synthesis of candidate material remain challenging. In this work, we show that the conventional ‘Si quantum dots (Si QDs) in SiO₂ matrix’ approach can lead to the formation of over‐sized Si nanocrystals especially when doped with phosphorous, making the size‐dependent quantum confinement less effective. Also, our investigation has shown that the high resistivity of this material has become the performance bottleneck of the solar cell. To resolve these matters, we propose a new design based on Si QDs embedded in a SiO₂/Si₃N₄ hybrid matrix. By replacing the SiO₂ tunnel barriers by the Si₃N₄ layers, the new material manages to constrain the growth of doped Si QDs effectively and enhances the apparent band gap, as shown in X‐ray diffraction, Raman, photoluminescence and optical spectroscopic measurements. Besides, electrical characterisation on Si QD/c‐Si heterointerface test structures indicates the new material possesses improved vertical carrier transport properties. Copyright © 2011 John Wiley & Sons, Ltd.