Emission Band Of Quantum Dots Research Articles

B-211 Quantum dot-DNA nanocomposite enhanced single-molecule flow (SiM-Flow) for ultrasensitive microRNA detection in metastatic castrate-resistant prostate cancer

Abstract Background MicroRNAs (miRs) like miR-375 and miR-1290 are associated with cancer progression and chemoresistance in metastatic castrate-resistant prostate cancer (mCRPC). However, these prognostic biomarkers are typically present in low abundance (0.1∼1 fM) in patient plasma, which is close to the detection limit of the current gold standard techniques, quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). Therefore, we tested a nanomaterial that incorporates quantum dots (QDs) and DNA amplicons for enhanced in-solution counting applications in plasma from a cohort of mCRPC patients. The QD-DNA nanocomposite increases the fluorescent intensity of an individual amplicon for ultrasensitive flow-counting and provides higher multiplex capacity due to the narrow emission band of QD for simple instrumentation. Methods QDs were synthesized with spectrally distinct emission bands by tuning the size or composition of CdSe core. QDs were then coated with multidentate polymer allowing further bioconjugations and better solubility in aqueous solution. The oligonucleotides complementary to amplicons generated from selected miR targets (prognostic biomarkers: miR-1290 and miR-375; normalization biomarkers: miR-16, miR-30a-5p, and cel-39) were then conjugated to QDs with optimized ratio. Total RNA was extracted from a screening cohort of 14 mCRPC patients from Huntsman Cancer Institute where platelet-poor plasma was uniformly processed with exogenous spike-in, cel-39, added in. qRT-PCR was performed using TaqMan miRNA assays, and SiM-Flow was conducted using a commercial flow cytometry to count QD barcoded enzymatic-extended miRs nanoparticles. The DNA template used for extending miRs was designed by our lab and purchased from IDT-DNA. Pearson correlation and interclass agreement analysis were applied to evaluate the concordance between the two assays. The mCRPC cohort was followed for clinical outcomes, and survival analysis for the time of progression from mCRPC to death/last follow-up was performed to determine the prognostic value of the QD-DNA nanoparticle counts. The Cox proportional hazards model was applied to linearly incorporate multiple hazard factors of patients for multivariate survival analysis. Results We demonstrated the multiplex ability of QDs with less than 5% false positive rate. The machine learning-guided optimized assay shows a 1000-time improved limit of detection of assay compared to the published literature. Interclass agreement > 0.9 and Pearson correlation of 0.94 between SiM-Flow and RT-qPCR on human plasma extracts suggest high specificity of SiM-Flow on miR detection. Also, miR-375 was identified among all the samples through SiM-Flow, although it was unidentified by qRT-PCR in 14 samples. Higher levels of miR-1290, miR-375, and prostate-specific antigen were significantly associated with poor overall survival (p=0.019) in the initial survival analysis. Survival analysis replication is ongoing in an independent mCRPC cohort. Conclusions SiM-Flow was able to detect target miRs in mCRPC patients’ plasma with a high agreement with qRT-PCR and lower detection limit and demonstrated multiplex ability with a simple optical set-up. This shows technological advancement in the detection of cancer-associated biomarkers and will aid in precision medicine therapeutic and point-of-care applications with both prognostic and predictive potential.

Printable Light-Emitting Metasurfaces with Enhanced Directional Photoluminescence.

Nanoimprint lithography is gaining popularity as a cost-efficient way to reproduce nanostructures in large quantities. Recent advances in nanoimprinting lithography using high-index nanoparticles have demonstrated replication of photonic devices, but it is difficult to confer special properties on nanostructures beyond general metasurfaces. Here, we introduce a novel method for fabricating light-emitting metasurfaces using nanoimprinting lithography. By utilizing quantum dots embedded in resin, we successfully imprint dielectric metasurfaces that function simultaneously as both emitters and resonators. This approach to incorporating quantum dots into metasurfaces demonstrates an improvement in photoluminescence characteristics compared to the situation where quantum dots and metasurfaces are independently incorporated. Design of the metasurface is specifically tailored to support photonic modes within the emission band of quantum dots with a large enhancement of photoluminescence. This study indicates that nanoimprinting lithography has the capability to construct nanostructures using functionalized nanoparticles and could be used in various fields of nanophotonic applications.

Energy-Transfer-Induced Enhanced Valley Splitting of Excitonic Emission of Inorganic CdTe@ZnS QDs in the Presence of Organic J-Aggregates: A Spectroscopic Insight into the Efficient Exciton (Inorganic)–Exciton (Organic) Coupling

An inorganic–organic nanohybrid material comprising an inorganic exciton (CdTe@ZnS) and an organic exciton (J-aggregates) has been synthesized, and subsequently investigations on exciton–exciton coupling between two components of the materials are carried out by employing various spectroscopic techniques. Analysis of the data has revealed very high Förster-type resonance energy transfer (FRET) from the donor quantum dots (QDs) to the acceptor J-aggregates. Interestingly, a clear splitting of the QD emission band during the FRET event is observed, indicating efficient coupling between inorganic and organic excitons. The observation of valley splitting of QD emission by organic J-aggregates, even in the absence of an external field, is new and exciting. More interestingly, the investigations have also shown that the valley splitting of the QD emission can be controlled by regulating the FRET process. In fact, a linear relationship between the energy separation value of the valley splitting and the FRET efficiency between QDs and J-aggregates is obtained. Moreover, in the present hybrid system, the presence of an organic moiety becomes advantageous in the sense that the valley splitting can also be controlled easily through chemical modification of the organic moiety. The outcome of the present investigation essentially demonstrates that the present nanohybrid system can be considered as a potential candidate for the fabrication of valleytronic materials.

Photoinduced charge carrier dynamics in a ZnSe quantum dot-attached CdTe system.

A new nanohybrid material is prepared by attaching CdTe nanoneedles (NNs) to surface-modified ZnSe quantum dots (QDs). The NNs and QDs are prepared by a colloidal synthesis method in an aqueous alkaline medium. The surface modification and the attachment of nanostructures are achieved by a bifunctional ligand 3-mercaptopropionic acid (3-MPA). The band gap of the ZnSe QDs is varied by controlling the size of the QDs in order to get the maximum overlap between the absorption band of the CdTe NNs and the emission band of the ZnSe QDs, which is a prerequisite for effective charge/energy transfer. The possibility of photoinduced charge transfer (PCT) and Förster resonance energy transfer (FRET) from the donor (QDs) to the acceptor (NNs) has been assessed. Very fast (less than 800 ps) PCT and FRET from QDs to NNs occur because the emission band of QDs overlaps with the absorption band of NNs. The calculated large value of the overlapping integral, J(λ) ∼4.5 × 1019 M-1 cm-1 nm4, of the donor and the acceptor bands proves the feasibility of energy transfer. These findings suggest that the ZnSe QDs can exchange photoinduced energy with the CdTe NNs effectively over a wide distance in a CdTe-ZnSe nanohybrid.

Size-Dependent Energy Transfer between CdSe/ZnS Quantum Dots and Gold Nanoparticles

This Letter deals with the effect of the particle size on the energy transfer from CdSe/ZnS quantum dots to the proximal gold nanoparticles with different sizes. The 3 nm sized gold nanoparticles have negligible localized surface plasmon resonance (LSPR) absorption and quench the fluorescence emission of the quantum dots with a 1/d4 distance-dependence, indicating the nanometal surface energy transfer (NSET) mechanism. The 15 and 80 nm sized gold nanoparticles have strong LSPR absorption bands that overlap with the emission band of the quantum dots. The energy transfer efficiency depends on the 1/d6 separation distance, which is dominated by the dipole–dipole interaction according to Förster resonance energy transfer (FRET). The 80 nm sized gold nanoparticle displays higher quenching efficiency due to the increased spectral overlap of the LSPR band with the emission band of quantum dots.

A novel strategy for selective detection of Ag+ based on the red-shift of emission wavelength of quantum dots

Selective determination of Ag(I) ion was accomplished based on the red-shift of the emission band of quantum dots (QDs). Under optimal conditions, a linear relationship does exist between the red-shift of the emission and the concentration of Ag(I) in the range from 1.0 × 10−7 to 1.5 × 10−5 mol L−1, with a detection limit of 5.0 × 10−8 mol L−1. The method has been successfully applied to the determination of Ag(I) ion in water samples. The possible reaction mechanism was investigated by ultraviolet–visible absorption, fluorescence, Raman spectroscopies and by high resolution transmission electron microscopy. The results suggest that the red-shift in emission be attributed to the stabilization of a charge-transfer state, but not due to the aggregation induced by AgI(I) ion.

Enhancement of emission from CdSe quantum dots induced by propagating surface plasmon polaritons

The influence on the emission property of CdSe quantum dots arising from propagating surface plasmon polaritons based on interconnected periodic gold nanoarrays with a large area of 1 cm2 is reported. Variation in the structural parameters allows us to tune the surface plasmon resonance to the emission band of quantum dots, which can result in an enhancement up to 54 times in the external quantum efficiency. Our strategy for the enhancement of luminescence efficiency from semiconductor quantum dots should be useful for the creation of high efficiency solid state emitters.

Propagation dynamics of exciton spins in a high‐density semiconductor quantum dot system

AbstractWe study propagation dynamics of exciton spins in a system composed of high‐density self‐assembled quantum dots (QDs) of CdSe and a diluted magnetic semiconductor (DMS) layer of ZnMnSe, where spin‐polarized excitons are generated in the DMS layer and are subsequently injected into the QDs. The degree of circular polarization, P, of excitonic photoluminescence at 5 T in the coupled QDs shows a rapid increase with increasing delay time after a linearly polarized pulsed excitation, indicating the exciton‐spin injection from the ZnMnSe to CdSe‐QDs. The P value tends to decay gradually because of the exciton‐spin relaxation in the QDs after the injection. The spin‐polarized excitons in the QD ensemble migrate simultaneously from the QDs with higher exciton energies to those with lower exciton energies, where the exciton‐spins relax inside each dot during the migration. Therefore, the observed P values in the QD emission band are affected by this feeding of the relaxed spins. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots of CdSe coupled with a diluted magnetic semiconductor layer ofZn0.80Mn0.20Se

We study the dynamics of exciton-spin injection, transfer, and relaxation in self-assembled quantum dots (QDs) of CdSe coupled with a diluted magnetic semiconductor (DMS) layer of ${\mathrm{Zn}}_{0.80}{\mathrm{Mn}}_{0.20}\mathrm{Se}$, where spin-polarized excitons can be injected from the DMS into the QDs. The degree of circular polarization $P$ of excitonic photoluminescence (PL) at $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ in the coupled QDs exhibits a rapid increase with increasing delay time, up to $+0.3$ at $25\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ after the pulse excitation of the DMS by a linearly polarized light. This development of a positive $P$ value directly reflects the spin-injection dynamics from the DMS, since the intrinsic polarization of the QD excitons due to Zeeman splitting is $P\ensuremath{\sim}\ensuremath{-}0.1$ when only the QDs are selectively excited. The $P$ value gradually decays with time after reaching its maximum, as a result of the exciton-spin relaxation with a time constant of $800\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ in the QDs. Time-resolved circularly polarized PL spectra immediately after the pulse excitation directly show the exciton-energy dependence of the spin-injection dynamics in the QD ensemble, where two-dimensional-like QDs with higher exciton energies show higher receptivity to the spin-polarized excitons than three-dimensional-like dots with lower exciton energies. A rate equation analysis reveals all time constants responsible for the spin-injection dynamics. We deduce a time constant of $10\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ for the spin injection. The spin-injection efficiency of 0.94 is also obtained, which corresponds to the ratio between the number of the spin-polarized excitons responsible for the rise of the positive $P$ value in the QD emission and the total number of the excitons injected from the DMS. Moreover, we observe that interdot exciton transfer significantly affects the $P$ value within the QD emission band after the fast spin injection, in addition to the spin relaxation within the QDs.

Dynamic quantum-confined stark effect in self-assembled InAs quantum dots

We present a detailed investigation of the carrier dynamics in a set of InAs/GaAs (N11) quantum dots (QD) by means of time-resolved photoluminesce (PL) techniques. A dynamical red shift of the PL bands when increasing the delay time after the pulse excitation is observed. We attribute this intrinsic optical nonlinearity to the photoinduced screening of internal built-in electric field. The value of the redshift of the QD emission band decays with the carrier population demonstrating the intrinsic nature of the built-in field. Its dependence on the substrate orientation and termination agrees with the expected piezoelectric induced quantum confined Stark effects of the QD optical transitions.

Time-space-resolved photoluminescence from (Zn,Cd)Se-based quantum structures

Spectroscopic technique which possesses both temporal and spacial resolution was developed by combining the pico-second pulsed laser system with the optical microscope. By using this technique, the time-resolved photoluminescence (TRPL) with micron spatial resolution was performed for the self-organized CdSe/ZnSe quantum dots (QDs) fabricated on GaAs(1 1 0) crystal surfaces. PL spectra of CdSe/ZnSe with 10 monolayer (ML) deposition thickness were composed of two emission bands peaking at 2.6 and 2.2 eV. These bands could be ascribed to the emissions from CdSe quantum wells (QWs) acting as wetting layers and QDs, respectively. With macroscopic excitation (spot size: 100 μm), temporal behavior of the emission band of QDs was characterized by multi-exponential decay. However, with microscopic excitation (spot size: 5 μm), it was found that both spectrum shapes and PL lifetimes have changed with sweeping the location of focus. Especially, the lifetimes were quite valuable and were well fitted by the single exponential decay. These results suggest that the radiative lifetime differs very much depending on the degree of exciton localization.