Time-resolved Methods Research Articles

New strokes to the portrait of inactivated actin

In addition to the well-known monomeric and polymeric forms of actin there is another unique thermodynamically stable state of this protein, called "inactivated actin" (I-actin). I-actin is formed at moderate concentration of a denaturant, release of Ca2+ ions and /or ATP, or after heating. This state is a monodisperse associate and it has the same spectral characteristics regardless of the method of preparation. The interest in I-actin arises from the discovery of similar-sized short oligomers of actin in the cell nucleus, which structurally differ from polymeric actin. In this work, we investigated the intramolecular mobility of I-actin using the time-resolved anisotropy method. Our findings indicate that its tryptophan residues participate in structural oscillations, although their correlation time is significantly longer than that of native actin. Using the dynamic light scattering, we demonstrated that I-actin obtained by heating possesses the same dimensions as I-actin in 1.8 M GdnHCl. Using the fluorescent probe ANS, it was shown that I-actin has a unique structure with hydrophobic pockets on the surface and tryptophan residues in the polar internal regions of the structure.

A fluorescence immunochromatography method for detection of human papillomavirus type 16 E6 and L1 proteins

This study aims to establish a time-resolved fluorescence immunochromatography method for simultaneous determination of human papillomavirus (HPV) type 16 E6 and L1 protein concentrations. The amount of lanthanide microsphere-labeled antibodies, the concentration of coated antibodies, and the reaction time were optimized, and then a test strip for the simultaneous determination of the protein concentrations was prepared. The performance of the detection method was evaluated based on the concordance of the results from clinical practice. The optimal conditions were 8 μg and 10 μg of HPV16 L1 and E6-labeled antibodies, respectively, 1.5 mg/mL coated antibodies, and reaction for 10 min. The detection with the established method for L1 and E6 proteins showed the linear ranges of 5-320 ng/mL and 2-64 ng/mL and the lowest limits of detection of 1.78 ng/mL and 1.09 ng/mL, respectively. There was no cross reaction with human immunodeficiency virus (HIV), treponema pallidum (TP), or HPV18 E6 and L1 proteins. The average recovery rate of the established method was between 97% and 107%. The test strip prepared in this study showed the sensitivity, specificity, and diagnostic accuracy of 97.46%, 90.57%, and 95.32%, respectively, in distinguishing patients with cervical cancer and precancerous lesions from healthy subjects, with the area under the curve (AUC) of 0.980 1 and 95% Confidence Interval (CI) of 0.956 5 to 1.000 0. The time-resolved fluorescence immunochromatography combined with the test strips prepared in this study showed high sensitivity, high accuracy, simple operation, and rapid reaction in the quantitation of HPV16 E6 and L1 proteins. It thus can be used as an auxiliary method for the diagnosis and early screening of cervical cancer and precancerous lesions and the assessment of disease course.

The Development of an Electron Pulse Dilation Photomultiplier Tube Diagnostic Instrument

A new pulse-dilated photomultiplier tube (PD-PMT) with sub-20 ps temporal resolution and associated drivers have been developed for use detection and signal amplification in the inertial confinement fusion (ICF) community. The PD-PMT is coupled to a transmission line output in order to provide a continuous time history of the input signal. Electron pulse dilation provides high-speed detection capabilities by converting incoming signals into a free-electron cloud and manipulating the electron signal with electric and magnetic fields. This velocity dispersion is translated into temporal separation after the electrons transit into a drift space. The free electrons are then detected by using conventional time-resolved methods and the effective temporal resolution is improved about 12 times. In order to accurately obtain the actual device input signal, we experimentally investigated the relationship between microchannel plate (MCP) gain and electron energy during the first collision. We report the measurements with the PD-PMT, and the error source of the amplitude of the compressed signal is analyzed, which provides a reference for subsequent accurate construction.

Development of a time-resolved laser-induced fluorescence fingerprinting method for detecting low-level adulteration in extra virgin olive oil

Adulteration identification in extra virgin olive oil (EVOO) is a significant concern in the olive oil industry. This study aimed to detect low-level adulteration of EVOO with other edible oils by using a novel time-resolved laser-induced fluorescence (TRLIF) fingerprinting method. Five EVOO brands were first analyzed to assess its potential for classification based on their differing fluorophore content. The developed method effectively reduces the effects associated with the optical path length and excitation light intensity. Subsequently, three sets of binary mixtures were tested: EVOO adulterated with refined olive oil, soybean oil, and sunflower oil. Quantitative analysis was performed using parallel factor analysis, which achieved a cross-validation coefficient of determination (R2) exceeding 0.90, with a prediction error < 1.40 %. These findings demonstrate that this method has the potential to determine the purity and quality of EVOO.

Time-resolved observation of DHR123 nano-clay radio-fluorogenic gel dosimeters by photoluminescence-detected pulse radiolysis

The importance of real-time dose evaluation has increased for recent advanced radiotherapy. However, conventional methods for real-time dosimetry using gel dosimeters face challenges owing to the delayed dose response caused by the slow completion of radiation-induced chemical reactions. In this study, a novel technique called photoluminescence-detected pulse radiolysis (PLPR) was developed, and its potential to allow real-time dose measurements using nano-clay radio-fluorogenic gel (NC-RFG) dosimeters was investigated. PLPR is a time-resolved observation method, and enables time-resolved fluorescence measurement. NC-RFG dosimeters were prepared, typically consisting of 100 μM dihydrorhodamine 123 (DHR123) and 2.0 wt.% nano-clay, along with catalytic and dissolving additives. We successfully achieved time-resolved observation of the increase in fluorescence intensity upon irradiation of the dosimeter. Dose evaluation was possible at 1 s after irradiation. The dose-rate effect was not observed for the deoxygenated dosimeter, but was observed for the aerated dosimeter. Besides the dose-rate effect, linear dose responses were obtained for both conditions. Furthermore, we made a novel observation of a decay in the fluorescence intensity over time in the early stages which named fluorescence secondary loss (FSL) and elucidated the conditions under which this phenomenon occurs.

Photothermal Infrared Radiometry and Thermoreflectance-Unique Strategy for Thermal Transport Characterization of Nanolayers.

Thermal transport properties for the isotropic and anisotropic characterization of nanolayers have been a significant gap in the research over the last decade. Multiple studies have been close to determining the thermal conductivity, diffusivity, and boundary resistance between the layers. The methods detailed in this work involve non-contact frequency domain pump-probe thermoreflectance (FDTR) and photothermal radiometry (PTR) methods for the ultraprecise determination of in-plane and cross-plane thermal transport properties. The motivation of one of the works is the advantage of the use of amplitude (TR signal) as one of the input parameters along with the phase for the determination of thermal parameters. In this article, we present a unique strategy for measuring the thermal transport parameters of thin films, including cross-plane thermal diffusivity, in-plane thermal conductivity, and thermal boundary resistance as a comprehensively reviewed article. The results obtained for organic and inorganic thin films are presented. Precise ranges for the thermal conductivity can be across confidence intervals for material measurements between 0.5 and 60 W/m-K for multiple nanolayers. The presented strategy is based on frequency-resolved methods, which, in contrast to time-resolved methods, make it possible to measure volumetric-specific heat. It is worth adding that the presented strategy allows for accurate (the signal in both methods depends on cross-plane thermal conductivity and thermal boundary resistance) and precise measurement.

Insights into Ultrafast Relaxation Dynamics of Electronically Excited Furfural and 5-Methylfurfural.

The ultrafast relaxation dynamics of furfural and 5-methylfurfural following excitation in the ultraviolet range is investigated using the femtosecond time-resolved photoelectron spectroscopy method. Specifically, the pump wavelength-dependent decay dynamics of electronically excited furfural and 5-methylfurfural is discussed on the basis of a detailed analysis of our measured time-resolved photoelectron spectroscopy spectra. Irradiation at all pump wavelengths prepares both furfural and 5-methylfurfural molecules with different vibrational levels in the first optically bright S2 (1ππ*) state, the lifetime of which is measured to be at least hundreds of femtoseconds. Besides the prominent deactivation channels of ring-opening and ring-puckering pathways for the S2(1ππ*) state, we propose that there is a minor decay channel of internal conversion from the initially prepared S2(1ππ*) state to the S1(1nπ*) state. The wavepacket decays out of the Franck-Condon region on the S2(1ππ*) state potential energy surface and bifurcates into different parts somewhere. A small fraction of the wavepacket funnels down to the S1(1nπ*) state via internal conversion. The subsequently populated S1(1nπ*) state contains large vibrational excess energy and decays over a lifetime of 2.5-2.8 ps. One of the deactivation channels of the S1(1nπ*) state is intersystem crossing to the 3ππ* triplet state. In addition, methyl substitution effects on the excited-state dynamics of furfural are also discussed. This experimental study provides new insights into the excitation energy-dependent decay dynamics of photoexcited furfural and 5-methylfurfural.

Nanosecond-Lived Excimer Observation in a Crystal of a Rhodium(I) Complex via Time-Resolved X-ray Laue Diffraction.

The rare observation of transient Rh···Rh excimer formation in a single crystal is reported. The estimated excited-state lifetime at 100 K is 2 ns, which makes it the shortest-lived small-molecule species caught experimentally using the laser-pump/X-ray-probe time-resolved Laue method. Upon excitation with 390 nm laser light, the intermolecular Rh···Rh distance decreases from 3.379(4) to 3.19(1) Å, and the metal-metal contact gains more bonding character. On the basis of the experimental results and theoretical modeling, the structural changes determined with 100 ps time resolution reflect principally the S0 → S1 electronic transition.

Phase volume correlation approach for overcoming decorrelation in three-dimensional phase-sensitive optical coherence elastography.

The dynamic measurement range in phase-sensitive optical coherence elastography (PhS-OCE) is limited for the phase decorrelation induced by pixel-level displacements in precision measurement, where the consideration of the time-resolved incremental method and in-plane pixels tracking method is insufficient to recover the phase holistically. This work presented a phase volume correlation (PVC) approach to handle the phase decorrelation in three-dimensional PhS-OCE. By utilizing the ability of the discontinuous source diagram to quantify voxel phase correlation levels, the PVC establishes a wrapped phase-matching equation aimed at optimizing the number of volumetric source distributions. The three-dimensional pixel-level motions in the deformed phase space can be evaluated by solving the optimization model for phase matching, thereby enabling the reconstruction of the volumetric phase variation corrupted by decorrelation. The large deformations experiments including diffident loadings, i.e., stretching, three-point bending, and light-cured, verified the proposed PPVC approach's of feasibility, reliability, and stability. The contribution of this work can dramatically enhance the dynamic measuring range in three-dimensional PhS-OCE.

Photochemistry of a proton relay – system with triple fluorescence

The excited state of proton transfer and the dynamics of the excited states of three 3-carboxy substituted bis-salicylidenes (H4L1-3) have been studied by combining steady state and time-resolved absorption and emission methods, and with quantum chemical calculations. The 3-carboxy substituted bis-salicylidenes contain two coupled intramolecular hydrogen bonds of the OH…OH…N type. This system has two proton transfer sites. The compounds have excitation – dependent emission and a high sensitivity to the solvent polarity. ESIPT and deprotonation result in the co-existence of enol, keto, anionic and zwitterionic species with or without quinoid structure, whose emission bands are located from the blue to the yellowish-green region. The photophysical processes in the nano-to-microseconds timescale have been linked to the intermolecular interactions with the solvent, where hydrogen bonding leads to the formation of a cyclic 1:2 solute − solvent complex. Transient absorption spectroscopy revealed that the generation of charged structures of H4L1-3 occurs through a solvent-assisted proton transfer along the chain of two solvent molecules, which act as a proton-relay system. The computational study of the energy profiles and of the enol-to-keto tautomerization with explicit solvent molecules has been performed for the first time for this kind of ESIPT system.

Unsteady vane-rotor secondary flow interaction of the endwall region in a 1.5-stage variable-geometry turbine

Variable-geometry turbines present significant improvements in both off-design cycle efficiency and enhanced engine responsiveness for future adaptive cycle engines. The adjustable vanes regulate the through-flow capacity by varying the installation angle and thus unavoidably require endwall clearance, resulting in profound implications for vane and downstream blade rows. Unsteady numerical simulations are carried out to investigate the vane-rotor flow interaction under the zero and partial clearance type of the adjustable vane in a 1.5-stage variable-geometry turbine. First, specific vortical structures and loss characteristics of upstream adjustable vane leakage flow at turning angles of −5°, 0°, and +5° are described. Then, the basic mechanisms of vane-rotor secondary flow interaction between acquired upstream leakage flow and downstream blade rows secondary flow is explored by the time-resolved method and quantitative detailed analysis method. The results show that adjustable vane vortex core area is the primary cause of internal loss within the vortex, and the mixing and interaction between the leakage vortex and other vortex systems contribute to secondary loss in the vane. Due to the downstream blade shear action caused by different flow velocity on the suction and pressure surfaces, the vane leakage flow fragments upon entering the R1 blade passage and develops downstream of the endwall region. Compared to the vane with zero clearance case at same turning angle, the intensity of the R1 tip leakage vortex at the design turning angle and open turning angle is reduced by 47.4 % and 23.66 % with the upstream partial clearance, respectively. The unsteady vane-rotor secondary flow interaction under different turning angles has large influence on the flow structure and loss characteristics of the downstream blade rows, and results in significant differences in the variation pattern and trend direction of the turbine performance.

Branched Polymeric Prenucleation Assemblies Initiate Calcium Phosphate Precipitation.

The formation of crystalline calcium phosphate (CaP) has recently gained ample attention as it does not follow the classic nucleation-and-growth mechanism of solid formation. Instead, the precipitation mechanisms can involve numerous intermediates, including soluble prenucleation species. However, structural features, stability, and transformation of such solution-state precursors remain largely undisclosed. Herein, we report a detailed and comprehensive characterization of the sequential events involved in calcium phosphate crystallization starting from the very early prenucleation stage. We integrated an extensive set of time-resolved methods, including NMR, turbidimetry, SAXS, cryo-TEM, and calcium-potentiometry to show that CaP nucleation is initiated by the transformation of "branched" polymeric prenucleation assemblies into amorphous calcium phosphate spheres. Such a mineralization process starts with the spontaneous formation of so-called nanometric prenucleation clusters (PNCs) that later assemble into those branched polymeric assemblies without calcium ion uptake from the solution. Importantly, the branched macromolecular species are invisible to many techniques (NMR, turbidity, calcium-potentiometry) but can readily be evidenced by time-resolved SAXS. We find that these polymeric assemblies constitute the origin of amorphous calcium phosphate (ACP) precipitation through an unexpected process: spontaneous dissolution is followed by local densification of 100-200 nm wide domains leading to ACP spheres of similar size. Finally, we demonstrate that the timing of the successive events involved in the CaP mineralization pathway can be kinetically controlled by the Ca2+/Pi molar ratio, such that the lifetime of the soluble transient species can be increased up to hours when decreasing it.

Doping of Colloidal Nanocrystals for Optimizing Interfacial Charge Transfer: A Double-Edged Sword.

Doping of colloidal nanocrystals offers versatile ways to improve their optoelectronic properties, with potential applications in photocatalysis and photovoltaics. However, the precise role of dopants on the interfacial charge transfer properties of nanocrystals remains poorly understood. Here, we use a Cu-doped InP@ZnSe quantum dot as a model system to investigate the dopant effects on both the intrinsic photophysics and their interfacial charge transfer by combining time-resolved transient absorption and photoluminescent spectroscopic methods. Our results revealed that the Cu dopant can cause the generation of the self-trapped exciton, which prolongs the exciton lifetime from 48.3 ± 1.7 to 369.0 ± 4.3 ns, facilitating efficient charge separation to slow electron and hole acceptors. However, hole localization into the Cu site alters their energetic levels, slowing hole transfer and accelerating charge recombination loss. This double-edged sword role of dopants in charge transfer properties is important in the future design of nanocrystals for their optoelectronic and photocatalytic applications.

Dynamic Evolution of Copper Nanowires during CO2 Reduction Probed by Operando Electrochemical 4D-STEM and X-ray Spectroscopy.

Nanowires have emerged as an important family of one-dimensional (1D) nanomaterials owing to their exceptional optical, electrical, and chemical properties. In particular, Cu nanowires (NWs) show promising applications in catalyzing the challenging electrochemical CO2 reduction reaction (CO2RR) to valuable chemical fuels. Despite early reports showing morphological changes of Cu NWs after CO2RR processes, their structural evolution and the resulting exact nature of active Cu sites remain largely elusive, which calls for the development of multimodal operando time-resolved nm-scale methods. Here, we report that well-defined 1D copper nanowires, with a diameter of around 30 nm, have a metallic 5-fold twinned Cu core and around 4 nm Cu2O shell. Operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM) showed that as-synthesized Cu@Cu2O NWs experienced electroreduction of surface Cu2O to disordered (spongy) metallic Cu shell (Cu@CuS NWs) under CO2RR relevant conditions. Cu@CuS NWs further underwent a CO-driven Cu migration leading to a complete evolution to polycrystalline metallic Cu nanograins. Operando electrochemical four-dimensional (4D) STEM in liquid, assisted by machine learning, interrogates the complex structures of Cu nanograin boundaries. Correlative operando synchrotron-based high-energy-resolution X-ray absorption spectroscopy unambiguously probes the electroreduction of Cu@Cu2O to fully metallic Cu nanograins followed by partial reoxidation of surface Cu during postelectrolysis air exposure. This study shows that Cu nanowires evolve into completely different metallic Cu nanograin structures supporting the operando (operating) active sites for the CO2RR.

Effective and robust quantum state tomography of electron-nuclear spins in diamond by time-resolved fluorescence

Quantum state tomography (QST) of electron-nuclear spins of nitrogen-vacancy (NV) center in diamond commonly requires a sequence of population flipping operations and frequent calibration of basis states by fluorescence photon-counting. Here, we realize an effective and robust quantum state tomography of electron-nuclear spins based on time-resolved fluorescence, which can enhance the signal-to-noise ratio between different basis states up to 29.6% compared to the photon-counting method. Meanwhile, our method can directly obtain the population of four basis states with only one measurement, which significantly improves the efficiency of tomography. Furthermore, the photon count rate fluctuation of time-resolved fluorescence can be reduced to the standard quantum limit by normalization operation, indicating that the time-resolved method is calibration-free. This method could be easily applied to multi-nuclear spins of NV center in diamond and extended to other solid-state spin systems.

(Invited) Exciton Dynamics for Spin Qubits

Singlet fission (SF) can generate exchange-coupled triplet pairs. This may lead to realizations of quantum manipulation and quantum sensing using entangled multiple qubits. However, direct manipulation of the quantum coherence has been limited in the triplet pairs. Here we show that the quantum coherence of SF-derived, weakly coupled spin correlated triplet pair (T+T) in biphenyl linked tetracece oligomer systems by using time-resolved pulsed electron paramagnetic resonance method.

(Invited) Comprehensive Analysis of Exciton Diffusion with Time-Resolved Fluorescence Spectroscopy, Anisotropy and Imaging

Excitons produced in materials play a crucial role in photo-energy conversion such as photovoltaics and electroluminescence devices. The temporal and spatial diffusion of excitons is a key factor for dominating the fundamental performance of optoelectronic materials. In this context, analysis of the exciton diffusion dynamics is an important issue for obtaining the rational design of the materials. Excitons diffusing in materials can be characterized by several parameters such as the energy level, orientation of the transition dipole moment and spatial distribution, and the detection of these properties is required for the comprehensive analysis. In the present study, we show time-resolved fluorescence methods for detecting the above relevant properties of excitons.First, time-resolved fluorescence spectroscopy is a basic technique for analyzing the exciton diffusion dynamics. Fluorescence intensity is detected as functions of observation wavelength and time, and the spectral intensity and shift of fluorescence bands provide information on the population of excitons and their energy level. For example, dynamic Stokes shift indicates downhill energy migration and excitons are trapped by the defective site in molecular aggregates. Second, fluorescence anisotropy can be a good indicator for tracking the exciton diffusion in amorphous materials. Fluorescence anisotropy is sensitive to orientation change in transition dipole moments (TDMs) between absorption and fluorescence. In systems where the relative orientation of adjacent molecules is different from each other, such as amorphous solids, the exciton diffusion is accompanied with the change in TDM. Thus, appropriate modeling of molecular alignment enables quantitative estimation of the exciton diffusion coefficient and diffusion length from the anisotropy signal. Finally, time-resolved imaging is a combination of time-resolved spectroscopy and super-resolution microscopy, and an emergent technique for visualizing real-space propagation of excitons in materials. The diffraction-limited excitation beam produces excitons in several hundreds of nanometers and the subsequent exciton diffusion is evaluated by the spatial width of the fluorescence spot. The temporal broadening of the fluorescence spot directly reflects the exciton distribution and we can intuitively obtain the diffusion coefficient and length. Unlike the conventional methods for bulk materials, the advantage of the time-resolved imaging is the applicability to materials with nano- and meso-scale heterogeneous structure and it enables site-selective evaluation of the exciton transport capability. In the conference site, we will also show the application of the above methods to supramolecular polymers and thermally activated delayed fluorescence materials. Figure 1

An assessment of analytical performance using the six sigma scale in second-trimester maternal prenatal screening practices in China

ObjectivesWe aimed to evaluate the analytical performance of second-trimester maternal serum screening in China, and to compare if there are differences in sigma levels across different methods and months. MethodsA retrospective study was conducted to assess the analytical quality levels of laboratories by calculating the Sigma metrics with prenatal screening biomarkers: AFP, Total β-hCG, free β-hCG, uE3. Data from 591 laboratories were selected. Sigma metrics were computed using the formula: Sigma metrics(σ) = (%TEa - |%Bias|)/%CV. The Friedman test and Mann-Whitney test were used to compare differences across various methods and different months. The Hodges–Lehmann was used for determining 95 % confidence intervals of pseudo-medians. ResultsOnly uE3 showed significant monthly variations in sigma calculations. However, around 8 % of laboratories across all four analytes demonstrated sigma levels both above 6 and below 3 in different months. Laboratories utilizing time-resolved fluorescence methods significantly outperformed those using chemiluminescence in sigma level. For AFP, the pseudo-median difference between these methods lies within a 95 % confidence interval of (−3.22, −1.93), while for uE3, it is at (−2.30, −1.40). Notably, the median sigma levels for all analytes reached the 4-sigma threshold, with free β-hCG even attaining the 6-sigma level. ConclusionWith current standards, China's second-trimester maternal serum screening is of relatively high analytical quality, and variations in sigma levels exist across different months and methods.

Lanthanide metal-organic frameworks as ratiometric fluorescent probes for real-time monitoring of PFOA photocatalytic degradation process

The assessment of perfluorooctanoic acid (PFOA) photocatalytic degradation usually involves tedious pre-treatment and sophisticated instrumentation, making it impractical to evaluate the degradation process in real-time. Herein, we synthesized a series of lanthanide metal-organic frameworks (Ln-MOFs) with outstanding fluorescent sensing properties and applied them as luminescent probes in the photocatalytic degradation reaction of PFOA for real-time evaluation. As the catalytic reaction proceeds, the fluorescence color changes significantly from green to orange-red due to the different interaction mechanisms between the electron-deficient PFOA and smaller radius F− with the ratiometric fluorescent probe MOF-76 (Tb: Eu = 29:1). The limit of detection (LOD) was calculated to be 0.0127 mM for PFOA and 0.00746 mM for F−. In addition, the conversion rate of the catalytic reaction can be read directly based on the chromaticity value by establishing a three-dimensional relationship graph of G/R value-conversion rate-time (G/R indicates the ratio between green and red luminance values in the image.), allowing for real-time and rapid tracking of the PFOA degradation. The recoveries of PFOA and F− in the actual water samples were 99.3–102.7% (RSD = 2.2–4.4%) and 100.7–105.3% (RSD = 3.9–6.8%), respectively. Both theoretical calculations and experiments reveal that the detection mechanism was attributed to the photoinduced electron transfer and energy transfer between the analytes and the probe. This method simplifies the sample analysis process and avoids the use of bulky instruments, and thus has great potential on the design and development of quantitative time-resolved visualization methods to assess catalytic performance and reveal mechanisms.

Charge transport dynamics and emission response in quantum-dot light-emitting diodes for next-generation high-speed displays

Inorganic quantum-dot light-emitting diodes (QD-LEDs) have gained significant attention as optoelectronic devices for next-generation display systems due to their superior colour properties. A comprehensive understanding of the charge transport dynamics and transient emission responses of the QD-LED is crucial to achieving high motion picture quality next-generation QD-LED display systems. In this study, we investigated the transient emission response of QD-LED devices through an advanced charge transport simulation model tailored to the quantum-dots (QDs). The dynamic response of the QD-LED devices is evaluated using the time-resolved electroluminescence measurement method for both cadmium-based and cadmium-free red, green, and blue QD-LEDs. The QD-LED devices exhibit notable emission drops during pulse voltage application. The charge transport simulation quantitatively reveals that the on and off switching speeds and the emission drops are intricately influenced by the electron and hole injection balance and a combination of carrier recombination factors within the QD layer. The charge transport simulation also shows that space-charge accumulation, due to the combined effects of charge imbalance and Auger recombination, quantitatively explains a potential device degradation mechanism. Therefore, the QD-specified charge transport model provides a crucial approach in designing and optimizing QD-LED devices for next-generation high-speed QD-LED displays with ultimate colour quality and long lifetimes.