Quantum Dot Sensitizers Research Articles

Supersandwich Nanowire/Quantum Dots Sensitization Structure-Based Photoelectrochemical "Signal-On" Platform for Ultrasensitive Detection of Thrombin.

A new photoelectrochemical (PEC) "signal-on" sensing platform based on photoactive material Bi2O3-ZnO and CdS quantum dots (QDs) sensitizer was fabricated for ultrasensitive determination of thrombin by constructing supersandwich nanowires. The CdS/ZnO/Bi2O3 sensitization structure with excellent energy level arrangement remarkably improved photoelectric conversion efficiency because of the efficient separation of the electron-hole. Moreover, the DNA supersandwich nanowire is ingeniously synthesized in one step by simple dislocation hybridization, which could carry a large amount of sensitized material CdS QDs. More importantly, with Exonuclease III (Exo III)-assisted multiple amplification, the proposed "signal-on" platform demonstrated a detection range of 10 fM to 1 μM with the detection limit of 1.41 fM for thrombin. Impressively, the PEC platform can successfully detect human serum samples with good accuracy. Above all, the CdS/ZnO/Bi2O3 sensitization photoelectric biosensing platform by using DNA nanowire in combination with Exo III-multiple amplification opens new sensitized amplification paths for supersensitive biosensing and bioanalysis.

Noninvasive In Situ Ratiometric Imaging of Biometals Based on Self-Assembled Peptide Nanoribbon.

Development of probes for accurate sensing and imaging of biometals in situ is still a growing interest owing to their crucial roles in cellular metabolism, neurotransmission, and apoptosis. Among them, Zn2+ and Cu2+ are two important cooperative biometals closely related to Alzheimer's disease (AD). Herein, we developed a multifunctional probe based on self-assembling peptide nanoribbon for ratiometric sensing of Zn2+, Cu2+, or Zn2+ and Cu2+ simultaneously. Uniform peptide nanoribbon (AQZ@NR) was rationally designed by coassembling a Zn2+-specific ligand AQZ-modified peptide (AQZKL-7) with peptide KL-7. The nanoribbon further combined with Cu2+-sensitive near-infrared quantum dots (NIR QDs) and Alexa Fluor 633 as an inner reference molecule, which was endowed with the capability for ratiometric Zn2+ and Cu2+ imaging at the same time. The peptide-based probe exhibited good specificity to Zn2+ and Cu2+ without interference from other ions. Importantly, the nanoprobe was successfully applied for noninvasive Zn2+ and Cu2+ monitoring in both living cells and zebrafish via multicolor fluorescence imaging. This gives insights into the dynamic Zn2+ and Cu2+ distribution in an intracellular and in vivo mode, as well as understanding the neurotoxicity of high concentration of Zn2+ and Cu2+. Therefore, the self-assembled nanoprobe shows great promise in multiplexed detection of many other biometals and biomolecules, which will benefit the diagnosis and treatment of AD in clinical applications.

Quantum Dot-Based Sensitization System for Boosted Photon Absorption and Enhanced Second Near-Infrared Luminescence of Lanthanide-Doped Nanoparticle.

Efficient energy transfer is a promising strategy in overcoming the inherent limits of a narrow band and weak absorption of lanthanide ions due to the nature of 4f-4f transitions. Herein, we introduce a nanoparticle-sensitized nanoparticle system where a near-infrared-emitting quantum dot (QD) is used as a sensitizer with broadband photon absorption for a lanthanide-doped nanoparticle (LNP) to generate second near-infrared (NIR-II) emission. The NIR-II luminescence of Er3+-doped LNP by Ag2S QD sensitization displays an enhancement of ∼17-fold in intensity and ∼10-fold in brightness over bare LNP because of increased absorptivity and overall broadening of the absorption spectrum of LNP. Furthermore, a QD-sensitized LNP system exhibits excellent photostability and is able to improve the signal-to-noise ratio of tumor NIR-II imaging via in situ cross-linking of QD and LNP. The QD-sensitized LNP system for luminescence enhancement opens a potential avenue for efficient energy transfer in complex nanoparticle-nanoparticle systems.

Cascade Structured ZnO/TiO2/CdS quantum dot sensitized solar cell

Cascade structure of ZnO/TiO2/CdS quantum dot sensitized solar cell (QDSSC) using precursor solutions of CdS quantum dots having different concentrations such as 0.1 M, 0.2 M, 0.5 M and 0.8 M were synthesized on fluorine doped tin oxide (FTO) substrate, using the successive ionic layer absorption and reaction (SILAR) method. A polysulfide electrolyte was used as a redox mediator. The combination of ZnO/TiO2 used as a photoanode gives the best results and changes the mechanism of the QDSSC. The conventional Pt counter electrode was replaced by a low cost CuS counter electrode. Morphological and structural characterizations were carried out by field-emission scanning electron microscope (FESEM) & X-ray diffractometer, respectively. The optical characterizations were carried out by using ultraviolet–visible (UV–Vis) spectroscopy. Degree of porosity of prepared quantum dot (QD) sensitizers on TiO2/ZnO surface of different precursor concentrations 48.90%, 45.90%, 44.20% and 42.41% were observed. J-V characteristics and the performance of the prototype solar cell devices were evaluated by using a solar simulator, under illumination with an AM 1.5G spectrum having light intensity of 100 mWcm−2. The highest efficiency was obtained 2.44% at 0.1 M concentration and the lowest was 0.52% at 0.8 M concentration.

Electrochemical Performance of Photovoltaic Cells using HDA Capped-SnS Nanocrystal from bis (N-1,4-Phenyl-N-Morpho-Dithiocarbamato) Sn(II) Complexes.

Great consideration is placed on the choice of capping agents’ base on the proposed application, in order to cater to the particular surface, size, geometry, and functional group. Change in any of the above can influence the characteristics properties of the nanomaterials. The adoption of hexadecylamine (HDA) as a capping agent in single source precursor approach offers better quantum dots (QDs) sensitizer materials with good quantum efficiency photoluminescence and desirable particles size. Structural, morphological, and electrochemical instruments were used to evaluate the characterization and efficiency of the sensitizers. The cyclic voltammetry (CV) results display both reduction and oxidation peaks for both materials. XRD for SnS/HDA and SnS photosensitizers displays eleven peaks within the values of 27.02° to 66.05° for SnS/HDA and 26.03° to 66.04° for SnS in correlation to the orthorhombic structure. Current density–voltage (I–V) results for SnS/HDA exhibited a better performance compared to SnS sensitizers. Bode plot results indicate electrons lifetime (τ) for SnS/HDA photosensitizer have superiority to the SnS photosensitizer. The results connote that SnS/HDA exhibited a better performance compared to SnS sensitizers due to the presence of HDA capping agent.

Synthesis of SnSe quantum dots by successive ionic layer adsorption and reaction (SILAR) method for efficient solar cells applications

Quantum dots (QDs) are one of the promising materials in the development of third-generation photovoltaics. QDs have the advantage of multiple exciton generation (MEG), high absorption coefficient and tuneable bandgap, low cost and easy synthesis. The QDs act as analogues to dye molecules in QD sensitized solar cells (QDSSCs) when compared with traditional dye-sensitized solar cells (DSSCs). Extending the absorption range of quantum dots is one of potential solutions for enhancing photoconversion efficiencies. The sensitization of SnSe quantum dots on theTiO2 mesoporous layers is carried by a successive ionic layer adsorption and reaction (SILAR) method in a glove box. The advantages of SILAR method are a high loading rate and wide coverage of the TiO2 matrix by the quantum dots. The device has exhibited a photoconversion efficiency of 0.78% which is the known best among the SnSe quantum dot-based solar cells.

Effect of annealing temperature of MoO3 layer in MoO3/Au/MoO3 (MAM) coated PbS QDs sensitized ZnO nanorods/FTO glass solar cell

This research reports fabrication of MoO3/Au/MoO3 (MAM) coated PbS sensitized quantum dot solar cell. ZnO nanorod grown FTO glass substrates were sensitized by PbS quantum dots (PbS QDs/ZnO nanorods/FTO Glass), followed by (MoO3/Au/MoO3) coating. Hydrothermal process was used to grow ZnO nanorods, followed by the deposition of PbS QDs using Successive Ionic Layer Adsorption and Reaction (SILAR). Finally, (MoO3/Au/MoO3) layers were deposited for the back contact. Spin coating was used to deposit MoO3 layers while middle layer of Au was deposited by sputter coating. Three such devices were fabricated with three different annealing temperatures i.e. 100 °C, 150 °C and 200 °C for first MoO3 layer. Scanning Electron Microscopy (SEM) was used for surface morphology of the devices; Energy Dispersive Spectroscopy Analysis (EDS) and X-Ray Diffraction (XRD) techniques were used for elemental and structural analysis, Optical properties of the devices were determined using UV–Visible analysis. Power conversion efficiency (PCE) of all three devices was obtained to observe devices performance. Improved PCE of 4.617% was obtained by the device with the thermal treatment of 150 °C.

Origin of high photoluminescence yield and high SERS sensitivity of nitrogen-doped graphene quantum dots

Herein, we elucidate the origin of high photoluminescence quantum yield (PL QY) and high surface-enhanced Raman scattering (SERS) sensitivity of in-situ nitrogen-doped graphene quantum dots (N-GQDs). We show that the doping of heteroatoms in GQDs facilitates the excited-state charge transfer and improved recombination in N-GQDs yielding a PL QY of ∼34%. Our study reveals that growth of GQDs in dimethyformamide solvent enables the reduction of the nonradiative sites in N-GQDs and the rearrangement of the charge distribution in the graphitic plane. Further, we demonstrate N-GQDs as an efficient SERS substrate with an enhancement factor of 3.2 × 103 with 10−4 M RhB target, which is ∼7-fold higher than the previous reports. The comparative studies of the SERS for undoped and N- and S-doped GQDs allow us to assess the contribution of the Förster resonance energy transfer (FRET) and chemical enhancement (CM) factors. Further, by controlling the functional groups of N-GQDs with vacuum annealing, and with different laser excitations, we isolate the contributions of CM and FRET, for the first time. The optimized N-GQDs exhibits a SERS detection limit of 10−10 M for RhB. Finally, N-GQDs combined with RhB is utilized to demonstrate a white light emitter with a CIE coordinate (0.30, 0.34).

The role of the capping agent and nanocrystal size in photoinduced hydrogen evolution using CdTe/CdS quantum dot sensitizers.

Hydrogen production via light-driven water splitting is a key process in the context of solar energy conversion. In this respect, the choice of suitable light-harvesting units appears as a major challenge, particularly as far as stability issues are concerned. In this work, we report on the use of CdTe/CdS QDs as photosensitizers for light-assisted hydrogen evolution in combination with a nickel bis(diphosphine) catalyst (1) and ascorbate as the sacrificial electron donor. QDs of different sizes (1.7-3.4 nm) and with different capping agents (MPA, MAA, and MSA) have been prepared and their performance assessed in the above-mentioned photocatalytic reaction. Detailed photophysical studies have been also accomplished to highlight the charge transfer processes relevant to the photocatalytic reaction. Hydrogen evolution is observed with remarkable efficiencies when compared to common coordination compounds like Ru(bpy)32+ (where bpy = 2,2'-bipyridine) as light-harvesting units. Furthermore, the hydrogen evolution performance under irradiation is strongly determined by the nature of the capping agent and the QD size and can be related to the concentration of the surface defects within the semiconducting nanocrystal. Overall, the present results outline how QDs featuring large quantum yields and long lifetimes are desirable to achieve sustained hydrogen evolution upon irradiation and that a precise control of the structural and photophysical properties thus appears as a major requirement towards profitable photocatalytic applications.

The design of Mn2+&Co2+ co-doped CdTe quantum dot sensitized solar cells with much higher efficiency.

High quality Mn2+-doped CdTe quantum dots (QDs), Co2+-doped CdTe QDs and Mn2+&Co2+ co-doped CdTe QDs were successfully synthesized via an aqueous phase method with mercaptopropanoic acid (MPA) ligands. The doped QDs maintain the same zinc blende structure of CdTe by X-ray diffraction (XRD). The Mn2+-doped CdTe QDs and Co2+-doped CdTe QDs both show a red-shift on absorption and photoluminescence (PL) spectra compared to pure CdTe QDs. In addition, Mn2+-doped CdTe QDs show a significant increase in the PL lifetime due to an orbitally forbidden d–d transition, which is of benefit to the reduction of electron recombination loss. Co2+ doping has a more matched doping energy level. In view of this, Mn2+&Co2+ co-doped CdTe QDs were applied as sensitizers for quantum dot sensitized solar cells, resulting in a significantly enhanced efficiency.

Real‐Time Optical Response of Polysiloxane/Quantum Dot Nanocomposites under 2 MeV Proton Irradiation: Luminescence Enhancement of Polysiloxane Emission through Quantum Dot Sensitization

The growing interest toward the development of high‐Z–sensitized organic scintillators is related with the potential possibility to merge the advantages of organic materials with those of inorganics. In fact, organic plastic scintillators offer large‐area applications and fast response at a low cost, yet their performances for high‐energy photons and charged particles are limited by the poor stopping power related with low‐Z materials. The real‐time optical investigation in terms of steady‐state luminescence spectra of polysiloxane/quantum dot (QD) nanocomposite samples under 2 MeV proton irradiation is presented. Results show an increase in the light yield of the polysiloxane samples embedding QDs up to 8% in comparison with the undoped polymer, paving the way for high‐Z sensitization through QDs in polysiloxane‐based active radiation detection systems.

Pyridine functionalized carbon dots for specific detection of tryptophan in human serum samples and living cells

Tryptophan (Trp) serves as an essential amino acid in protein and peptide metabolism of human body. Sensitive detection and quantification of Trp is imperative for the early diagnosis and prevention of Trp-associated disease. Herein, a highly sensitive and selective carbon quantum dot (Py-CDs) was fabricated and synthesized by a high-efficiency, one-pot hydrothermal route utilizing pyridine (Py) derivative 3-aminoisonicotinic acid. The biosensor with superior optical and biological characteristics exhibited excellent water solubility, good photostability, high biocompatibility and great cellular imaging capability. The Py-CDs exhibited high sensitivity and selectivity toward Trp with low detection limits of 5.7 nM. The mechanism research of high selectivity revealed the surface pyridine ring of Py-CDs served as an active site and formed the table nonfluorescence composite with tryptophan within just 15 s. Meanwhile, the biosensor has realized tryptophan detection in human serum samples with satisfactory accuracy and recovery. Furthermore, the biosensor was also extended to efficient detection of intracellular Trp, which illustrated its bright prospect and great potential in practical application of tryptophan associated disease prevention and early clinical diagnosis.

Energy transfer kinetics in Basic Fuchsin dye sensitized CdS quantum dots

Sensitization of QDs (Quantum Dots) with a dye of good spectral overlap maximizes and extends the absorption range of incident photons. Interactions of Cadmium Sulfide Quantum Dots (CdS QDs) with Basic Fuchsin (BF) dye has been investigated in the present work using steady state and time resolved fluorescence emission techniques. The analysis has led to the inference that fluorescence resonance (Förster type) energy transfer (FRET) is the mechanism behind the fluorescence quenching of CdS QDs in the presence of dye molecules. An efficient energy transfer (~90%) from CdS donor to BF dye acceptor was observed and the FRET parameters such as Förster distance and spectral overlap integral were determined. The non-radiative energy transfer mechanism in QDs-dye binary mixtures holds great promise in analytical chemistry, biodetection system and in light harvesting systems.

Investigations of rare earth doped CdTe QDs as sensitizers for quantum dots sensitized solar cells

Gd doped CdTe (Gd:CdTe) QDs sensitized working electrodes were fabricated for QDSSC applications. In this fabrication process, mercapto succinic acid capped Gd:CdTe QDs were synthesized by colloidal method and used as the sensitizer. Improved optical properties of the prepared QDs were examined by optical absorption and emission spectral analysis. Fluorescence quantum yield measurement reveals that 10% Gd:CdTe QDs shows the highest quantum yield of 67%. XRD analysis confirms the cubic zinc blende crystalline structure of the prepared QDs and the dopant concentration dependent cell parameters and crystallite sizes were revealed. Performance of capping molecules over the prepared QDs was analyzed by FT-IR studies. Enhanced photovoltaic performance of prepared pure and doped QDs was analyzed through J-V characteristic curves, which show better photovoltaic response with an efficiency of 2.24% for 10% Gd:CdTe QDs.

CdSe Quantum Dot Sensitized Molecular Photon Upconversion Solar Cells

Incorporating photon upconversion, via triplet–triplet annihilation (TTA-UC), directly into a solar cell is an intriguing strategy for harnessing sub-band gap photons and surpassing the Shockley–Queisser limit. A majority of TTA-UC solar cells to date rely on difficult to synthesize and expensive platinum and/or palladium porphyrin sensitizers. Here, we present, as far as we know, the first TTA-UC solar cell that integrates quantum dot (QD) sensitizers directly into the photocurrent generation mechanism. The photoanodes are composed of a nanocrystalline TiO2 substrate, 4,4′-(anthracene-9,10-diyl)bis(4,1-phenylene)diphosphonic acid (A) as the annihilator molecule, and CdSe QDs as the sensitizer in an inorganic–organic-inorganic layered architecture (TiO2-A-QD). The TiO2-A-QD devices generate a photocurrent that is more than 1.4 times the sum of its parts and does so via a TTA-UC mechanism as demonstrated by intensity dependence, IPCE, and spectroscopic measurements. The maximum efficiency onset threshold (...

Conjugated molecular bridges: A new direction to escalate linker assisted QDSSC performance

Immobilizing quantum dots on an electron transport layer (ETL) is a very crucial step in the fabrication of quantum dot sensitized solar cells (QDSSC). Post-synthesis assembly of quantum dots (QDs) via aliphatic linkers has limited the device performance because of low and non-uniform coverage of QD sensitizers. This can result in intermediate surface trap states increasing the probability of exciton recombination. Therefore, we have designed a bi-phenyl aromatic linker 4′-mercapto-biphenyl-4′carboxylic acid (MBCA) that tethers QDs and ETL efficiently via SH and COOH groups respectively. The designed linker has enhanced the overall power conversion efficiency due to its interminable conjugation, and a favourable molecular orbital distribution inducing better electron injection rate. To enhance the photon collection efficiency and to apprehend the compatibility of QDs, cascading heterostructure of CdS/CdSe QDSSC devices were fabricated. The ligand linkage was confirmed via molecular spectroscopy (NMR and ATR-IR spectroscopy) and there performance studies like IV, IPCE, capacitance-voltage and impedance measurements were carried out. These studies clearly substantiates the augmentation of electron injection rate attributed to conjugated molecular bridges, assisting shift of fermi level of TiO2 and quick electron tunnelling.

Tailoring of graphene quantum dots for toxic heavy metals detection

The sensitivity of graphene quantum dots towards toxic heavy metals (THMs; Cd, Hg, Pb) can be improved through doping with nitrogen at the vacant site defects. Using density functional theory, we investigate the adsorption of THMs on the graphene quantum dots (GQDs) and nitrogen-coordinated defective GQDs (GQD@1N, GQD@2N, GQD@3N and GQD@4N) surfaces. Thermochemistry calculations reveal that the adsorption of Pb atom on the surfaces is more favorable than Cd and Hg adsorption. The decoration of the vacant defects with nitrogen on the GQD surface substantially increases the charge transfer and adsorption energy values of THMs on the GQD surface (GQD@4N > GQD@3N > GQD@1N > GQD@2N > GQD). The charge transfer and adsorption energy of lead on each of these surfaces are greater than those of cadmium and mercury (Pb > Cd > Hg). Quantum theory of atoms in molecules analysis and non-covalent interaction plots further validate this result while also confirming that Pb atom has a partially covalent and electrostatic nature of interaction at the nitrogen-coordinated vacant site defects. The electron density values—a criterion of bond strength—for the THM...N interactions are greater than for the THM…C interactions, confirming the observed adsorption energy trends of the THMs on the surfaces. The lowering of the HOMO–LUMO energy gap of the surfaces follows the order Pb > Cd > Hg and also results in increased electrical conductivity, which are consistent with the calculated adsorption energy trends. Significant changes in the energy gap and electric conductivity of the surfaces upon THMs adsorption make them promising sensors for metal detection. Finally, time-dependent density functional theory calculations showed that changes such as peak shifts, peak quenching and appearance of new peaks are seen in the UV–visible absorption spectra of the surfaces upon adsorption of THMs, wherein the shifts in peaks correspond to the magnitude of adsorption energy of THMs on the surfaces. These results should motivate the experimentalists towards using rational and systematic modulation of surfaces as sensors for heavy metal detection.

PbSe Quantum Dots Sensitized High-Mobility Bi2O2Se Nanosheets for High-Performance and Broadband Photodetection Beyond 2 μm.

As an emerging two-dimensional semiconductor, Bi2O2Se has recently attracted broad interests in optoelectronic devices for its superior mobility and ambient stability, whereas the diminished photoresponse near its inherent indirect bandgap (0.8 eV or λ = 1550 nm) severely restricted its application in the broad infrared spectra. Here, we report the Bi2O2Se nanosheets based hybrid photodetector for short wavelength infrared detection up to 2 μm via PbSe colloidal quantum dots (CQDs) sensitization. The type II interfacial band offset between PbSe and Bi2O2Se not only enhanced the device responsivity compared to bare Bi2O2Se but also sped up the response time to ∼4 ms, which was ∼300 times faster than PbSe CQDs. It was further demonstrated that the photocurrent in such a zero-dimensional-two-dimensional hybrid photodetector could be efficiently tailored from a photoconductive to photogate dominated response under external field effects, thereby rendering a sensitive infrared response >103 A/W at 2 μm. The excellent performance up to 2 μm highlights the potential of field-effect modulated Bi2O2Se-based hybrid photodetectors in pursuing highly sensitive and broadband photodetection.

Supersensitive Photoelectrochemical Aptasensor Based on Br,N-Codoped TiO2 Sensitized by Quantum Dots

Here, we fabricated a novel photoelectrochemical (PEC) aptasensor based on Br,N-codoped TiO2/CdS quantum dots (QDs) sensitization structure with excellent energy level arrangement for supersensitive detection of carcinoembryonic antigen (CEA). The prepared Br,N-codoped TiO2 could reduce the energy bandwidth of TiO2 from 3.2 to 2.88 eV, which could dramatically reduce the basic signal and obviously broaden the absorption of light (400-700 nm). In addition, the energy bandwidth of Br,N-codoped TiO2 (2.88 eV) matched well with that of CdS QDs (2.4 eV), making CdS QDs an ideal signal enhancer for amplifying the photocurrent signal of Br,N-codoped TiO2. More importantly, the constructed Br,N-codoped TiO2/CdS QDs sensitization structure with narrow energy level gradient enabled the effective promotion of electron-transfer capability and dramatic improvement of photoelectric conversion efficiency. Simultaneously, a small amount of the CEA was transformed into substantial single-chain DNA (T-DNA) via exonuclease III (Exo-III)-assisted cycle strategy. Under optimum conditions, the designed PEC aptasensor demonstrated a wide detection range from 1 fg/mL to 1 ng/mL and a low detection limit as 0.46 fg/mL for CEA assay. This strategy prepared a new photoactive material to markedly improve photoelectric conversion efficiency and initiated a new way to realize the highly sensitive PEC biomolecules detection.

Revealing antimicrobial and contrasting photocatalytic behavior of metal chalcogenide deposited P25-TiO2 nanoparticles

Quantum dot (QD)-sensitized P25-TiO2 based nanocomposites were developed using the pseudo-successive ionic layer adsorption and reaction (p-SILAR) technique and then applied in the photocatalytic degradation of an azo-type dye under visible and ultraviolet (UV) irradiation. The presence of PbS and CdS QDs on the P25-TiO2 nanoparticles facilitated visible light absorbance by P25-TiO2 and increased the photocatalytic activity under visible irradiation, whereas the efficacy of P25-TiO2 as a photocatalyst was reduced under UV light. We confirmed the successful deposition of PbS and CdS QDs on TiO2 under analogous QD sensitization conditions with p-SILAR, and showed that the PbS QD-sensitized TiO2 nanocomposite (TPbS) harvested more visible light than the CdS QD-sensitized TiO2 nanocomposite (TCdS), thereby resulting in greater dye degradation under visible light. In particular, TPbS degraded ˜57% of the dye acid orange-56 and TCdS degraded ˜16%. The nanocomposites exhibited antimicrobial activity against Bacillus subtilis (B. subtilis) where the most effective antimicrobial agent with the highest activity was TCdS.