Photoluminescence Lifetime Imaging Research Articles

Multiple pathways for lanthanide sensitization in self-assembled aqueous complexes

Lanthanide photoluminescence (PL) emission has attracted much attention for technological and bioimaging applications because of its particularly interesting features, such as narrow emission bands and very long PL lifetimes. However, this emission process necessitates a preceding step of energy transfer from suitable antennas. While biocompatible applications require luminophores that are stable in aqueous media, most lanthanide-based emitters are quenched by water molecules. Previously, we described a small luminophore, 8-methoxy-2-oxo-1,2,4,5-tetrahydrocyclopenta[de]quinoline-3-phosphonic acid (PAnt), which is capable of dynamically coordinating with Tb(III) and Eu(III), and its exchangeable behavior improved their performance in PL lifetime imaging microscopy (PLIM) compared with conventional lanthanide cryptate imaging agents. Herein, we report an in-depth photophysical and time-dependent density functional theory (TD–DFT) computational study that reveals different sensitization mechanisms for Eu(III) and Tb(III) in stable complexes formed in water. Understanding this unique behavior in aqueous media enables the exploration of different applications in bioimaging or novel emitting materials.

In-situ topotactic synthesis of decahedron BiVO4/2D networks Bi2S3 heterojunctions for efficient Cr(VI) reduction: Improved charge separation and imaged at the single-particle level

Epitaxial heterostructure has an optimized interfacial electronic structure compared to the traditional random heterostructures. However, accurately monitoring the interfacial charge transfer dynamics remains a grand challenge. We report here that single-particle spectroscopy techniques address this challenge by performing photoluminescence (PL) lifetime imaging and spectral fitting of interfacial micro/nano regions. A novel facet-selective BiVO4/2D nano-network Bi2S3 heterostructure is synthesized by a simple hydrothermal method. Single-particle PL spectroscopy shows that the PL emission at the oriented epitaxial heterojunction interface in BVO/S-O is weakened, and the PL lifetime increases by 213 % and 105 % compared to a single BiVO4 and random heterojunction particles, respectively, indicating that the topological heterojunction interface effectively promotes the separation of charge carriers. In addition, the possible mechanism of photocatalysis was also discussed in detail. Our work reveals the advantages of unique spatial structures and topological epitaxial interfaces in charge separation, which has great prospects for photocatalytic applications.

Superparamagnetic Nanoparticles with Phosphorescent Complexes as Hybrid Contrast Agents: Integration of MRI and PLIM

Two different hybrid nanosystems are prepared by loading highly crystalline, monodisperse magnetite nanocubes (MNCs) with phosphorescent Pt(II) complexes (PtCxs). One involves the encapsulation of the hydrophobic PtCx1 within an amphiphilic comb polymer (MNC@poly(maleic anhydride‐alt‐1‐octadecene) [PMAO]–PtCx1), whereas the other involves the direct binding of the hydrophilic PtCx2 to the surface of the MNC mediated by a ligand‐exchange procedure (MNC@OH–PtCx2). Both systems are evaluated as potential candidates for multimodal imaging in magnetic resonance imaging (MRI) and photoluminescence lifetime imaging micro(spectro)scopy (PLIM). PLIM measurements on agarose phantoms demonstrate significantly longer excited‐state lifetimes compared to the short‐lived autofluorescence of biological background. Additionally, both nanosystems perform as effective MRI contrast agents (CAs): the r2* values are 3–4 times higher than for the commercial CA ferucarbotran. MNC@PMAO–PtCx1 particles also cause significant increases in r2. While the ligand exchange procedure efficiently anchors PtCxs to the MNC surface, the polymeric encapsulation ensures higher colloidal stability, contributing to differences in PLIM and MRI outcomes. In these results, the successful integration of two complementary noninvasive imaging modalities within a single nanosystem is confirmed, serving as the impetus for further investigation of such systems as advanced multimodal–multiscale imaging agents with dual orthogonal readouts.

Photoluminescence lifetime engineering via organic resonant films with molecular aggregates

Abstract Manipulating the spontaneous emission rate of fluorophores is vital in creating bright incoherent illumination for optical sensing and imaging, as well as fast single-photon sources for quantum technology applications. This can be done via increasing the Purcell effect by using non-monolithic optical nanocavities; however, achieving the desired performance is challenging due to difficulties in fabrication, precise positioning, and frequency tuning of cavity-emitter coupling. Here, we demonstrate a simple approach to achieve a wavelength-dependent photoluminescence (PL) lifetime modification using monolithic organic molecular aggregates films. These single monolithic organic films are designed to have a Lorentzian dispersion, including epsilon-near-zero (ENZ) and epsilon-near-pole (ENP) spectral regions with increased and decreased photonic density of states, respectively. This dispersion leads to enhanced and depressed PL decay rates at different wavelengths. Both time-resolved photoluminescence (TRPL) and fluorescence lifetime imaging microscopy (FLIM) measurements are implemented to verify the validity of this approach. This approach offers a promising way to design dual-functional optical sources for a variety of applications, including bioimaging, sensing, data communications, and quantum photonics applications.

Short-wave Infrared Photoluminescence Lifetime Mapping of Rare-Earth Doped Nanoparticles Using All-Optical Streak Imaging.

The short-wave infrared (SWIR) photoluminescence lifetimes of rare-earth doped nanoparticles (RENPs) have found diverse applications in fundamental and applied research. Despite dazzling progress in the novel design and synthesis of RENPs with attractive optical properties, existing optical systems for SWIR photoluminescence lifetime imaging are still considerably restricted by inefficient photon detection, limited imaging speed, and low sensitivity. To overcome these challenges, SWIR photoluminescence lifetime imaging microscopy using an all-optical streak camera (PLIMASC) is developed. Synergizing scanning optics and a high-sensitivity InGaAs CMOS camera, SWIR-PLIMASC has a 1D imaging speed of up to 138.9kHz in the spectral range of 900-1700nm, which quantifies the photoluminescence lifetime of RENPs in a single shot. A 2D photoluminescence lifetime map can be acquired by 1D scanning of the sample. To showcase the power of SWIR-PLIMASC, a series of core-shell RENPs with distinct SWIR photoluminescence lifetimes is synthesized. In particular, using Er3+ -doped RENPs, SWIR-PLIMASC enables multiplexed anti-counterfeiting. Leveraging Ho3+ -doped RENPs as temperature indicators, this system is applied to SWIR photoluminescence lifetime-based thermometry. Opening up a new avenue for efficient SWIR photoluminescence lifetime mapping, this work is envisaged to contribute to advanced materials characterization, information science, and biomedicine.

Exchangeable Self-Assembled Lanthanide Antennas for PLIM Microscopy.

Lanthanides have unique photoluminescence (PL) emission properties, including very long PL lifetimes. This makes them ideal for biological imaging applications, especially using PL lifetime imaging microscopy (PLIM). PLIM is an inherently multidimensional technique with exceptional advantages for quantitative biological imaging. Unfortunately, due to the required prolonged acquisitions times, photobleaching of lanthanide PL emission currently constitutes one of the main drawbacks of PLIM. In this study, we report a small aqueous-soluble, lanthanide antenna, 8-methoxy-2-oxo-1,2,4,5-tetrahydrocyclopenta[de]quinoline-3-phosphonic acid, PAnt, specifically designed to dynamically interact with lanthanide ions, serving as exchangeable dye aimed at mitigating photobleaching in PLIM microscopy in cellulo. Thus, self-assembled lanthanide complexes that may be photobleached during image acquisition are continuously replenished by intact lanthanide antennas from a large reservoir. Remarkably, our self-assembled lanthanide complex clearly demonstrated a significant reduction of PL photobleaching when compared to well-established lanthanide cryptates, used for bioimaging. This concept of exchangeable lanthanide antennas opens new possibilities for quantitative PLIM bioimaging.

Exchangeable Self‐Assembled Lanthanide Antennas for PLIM Microscopy

AbstractLanthanides have unique photoluminescence (PL) emission properties, including very long PL lifetimes. This makes them ideal for biological imaging applications, especially using PL lifetime imaging microscopy (PLIM). PLIM is an inherently multidimensional technique with exceptional advantages for quantitative biological imaging. Unfortunately, due to the required prolonged acquisitions times, photobleaching of lanthanide PL emission currently constitutes one of the main drawbacks of PLIM. In this study, we report a small aqueous‐soluble, lanthanide antenna, 8‐methoxy‐2‐oxo‐1,2,4,5‐tetrahydrocyclopenta[de]quinoline‐3‐phosphonic acid, PAnt, specifically designed to dynamically interact with lanthanide ions, serving as exchangeable dye aimed at mitigating photobleaching in PLIM microscopy in cellulo. Thus, self‐assembled lanthanide complexes that may be photobleached during image acquisition are continuously replenished by intact lanthanide antennas from a large reservoir. Remarkably, our self‐assembled lanthanide complex clearly demonstrated a significant reduction of PL photobleaching when compared to well‐established lanthanide cryptates, used for bioimaging. This concept of exchangeable lanthanide antennas opens new possibilities for quantitative PLIM bioimaging.

An iridium complex-based probe for phosphorescent lifetime-elongated imaging of nitroreductase in living cells

Nitroreductase (NTR) is an important biomarker and often overexpressed in hypoxia tumors, thus the selective and precise detection of NTR is of great importance in the early diagnosis of tumors. Although various analytical methods have been constructed for NTR detection, there is still a lack of an effective photoluminescence probe for NTR using photoluminescence lifetime imaging (PLIM) within living cells. In this study, an iridium-based probe (Ir-NO2) decorated with p-nitrophenyl group has been designed and investigated for detection and imaging of NTR. Upon addition of NTR and nicotinamide adenine dinucleotide (NADH), the p-nitrophenyl group of Ir-NO2 underwent reduction and elimination, leading to generation of Ir-NH2. This transformation effectively blocked photoinduced electron transfer, resulting in an observable enhancement of phosphorescence intensity and an extension of phosphorescence lifetime during the detection process. The capability of Ir-NO2 to detect NTR at the cellular level was confirmed through PLIM analysis of hypoxia A549 cells.

Size-dependent sidewall defect effect of GaN blue micro-LEDs by photoluminescence and fluorescence lifetime imaging.

Sidewall defects play a key role in determining the efficiency of GaN-based micro-light emitting diodes (LEDs) for next generation display applications, but there still lacks direct observation of defects-related recombination at the affected area. In this Letter, we proposed a direct technique to investigate the recombination mechanism and size effect of sidewall defects for GaN blue micro-LEDs. The results show that mesa etching will produce stress release near the sidewall, which can reduce the quantum confinement Stark effect (QCSE) to improve the radiative recombination. Meanwhile, the defect-related non-radiative recombination generated by the sidewall defects plays a leading role under low-power injection. In addition, the effective area of the mesas affected by the sidewall defects can be directly observed according to the fluorescence lifetime imaging microscope (FLIM) characterization. For example, the effective area of the mesa with 80 µm is affected by 23% while the entire area of the mesa with 10 µm is almost all affected. This study provides guidance for the analysis and repair of sidewall defects to improve the quantum efficiency of micro-LEDs display at low current density.

Enhanced Photoluminescence and Prolonged Carrier Lifetime through Laser Radiation Hardening and Self-Healing in Aged MAPbBr3 Perovskites Encapsulated in NiO Nanotubes.

Organic-inorganic perovskites hold great promise as optoelectronic semiconductors for pure color light emitting and photovoltaic devices. However, challenges persist regarding their photostability and chemical stability, which limit their extensive applications. This paper investigates the laser radiation hardening and self-healing-induced properties of aged MAPbBr3 perovskites encapsulated in NiO nanotubes (MAPbBr3@NiO) using photoluminescence (PL) and fluorescence lifetime imaging (FLIM). After deliberately subjecting the MAPbBr3@ NiO to atmospheric conditions for two years, the sample remains remarkably stable. It exhibits no changes in PL wavelength during UV laser irradiation and self-healing. Furthermore, exposure to UV light at 375 nm enhances the PL of the self-healed MAPbBr3@NiO. FLIM analysis sheds light on the mechanism behind photodegradation, self-healing, and PL enhancement. The results indicate the involvement of many carrier-trapping states with low lifetime events and an increase in peak lifetime after self-healing. The formation of trapping states at the perovskite/nanotube interface is discussed and tested. This study provides new insights into the dynamics of photo-carriers during photodegradation and self-healing in organic-inorganic perovskites.

Investigation of CVD Growth of 2D MoS2 on MXene Structures with Photoluminescence Mapping and Fluorescence Lifetime Imaging Microscopy

Molybdenum disulfide (MoS2) and molybdenum carbide (Mo2C) are 2D materials with unique properties that make them suitable for electronic and optoelectronic applications. MoS2 is known for its high optical quantum yield and strong light–matter interaction, while Mo2C has metallic properties and is a member of the relatively new class of 2D materials called MXenes. In this research, a new heterostructure is obtained by growing MoS2 directly on Mo2C for the first time using chemical vapor deposition method. This novel hybrid structure changes the interlayer interaction and excited‐state dynamics, thereby increasing material diversity. The structure is characterized using Raman spectroscopy and atomic force microscopy, while photoluminescence (PL) and fluorescence lifetime imaging microscopy measurements are used to examine exciton motions. This study shows that the thickness of the hybrid structure is directly proportional to the frequency difference between the E2g and A1g modes, and inversely proportional to the PL intensities. The hybrid structure displays distinct exciton transitions due to the metallic effect and a longer fluorescence lifetime when compared to the bare monolayer of MoS2. The introduction of this novel hybrid structure with its optical properties holds great potential in opening up new avenues for optoelectronic device applications.

Imaging and micro-invasive analyses of black stains on the passepartout of Codex Atlanticus Folio 843 by Leonardo da Vinci

This paper accounts for the diagnostic campaign aimed at understanding the phenomenon of black stains appeared on the passepartout close to the margins of Folio 843 of Leonardo da Vinci’s Codex Atlanticus. Previous studies excluded microbiological deterioration processes. The study is based on a multi-analytical approach, including non-invasive imaging measurements of the folio, micro-imaging and synchrotron spectroscopy investigations of passepartout fragments at different magnifications and spectral ranges. Photoluminescence hyperspectral and lifetime imaging highlighted that black stains are not composed of fluorescent materials. μATR-FTIR imaging of fragments from the passepartout revealed the presence of a mixture of starch and PVAc glues localized only in the stained areas close to the margin of the folio. FE-SEM observations showed that the dark stains are localized inside cavities formed among cellulose fibers, where an accumulation of inorganic roundish particles (∅100–200 nm in diameter size), composed of Hg and S, was detected. Finally, by employing synchrotron μXRF, μXANES and HR-XRD analyses it was possible to identify these particles as metacinnabar (β-HgS). Further research is needed to assess the chemical process leading to the metacinnabar formation in the controlled conservation condition of Leonardo’s Codex.

Cellular imaging properties of phosphorescent iridium(III) complexes substituted with ester or amide groups.

Phosphorescent iridium(III) complexes have been extensively investigated as cellular imaging reagents and sensors. The intracellular localization of the complexes is known to be closely related to their formal charge, molecular size, lipophilicity, and bioactive pendants. Herein, we reported four phosphorescent iridium(III) complexes with the diimine ligands being modified with ester or amide groups as imaging reagents for living cells. The complexes have the same positive charge and very similar molecular size and weight. The lipophilicity of the complexes is similar ranging from 1.45 to 2.14. Upon internalization into living HeLa cells, while complexes 2-4, like most other iridium(III) complexes, were localized in the cytoplasm, complex 1 unexpectedly stained the whole cells including nuclei. The nuclear uptake of complex 1 was not observed when the cells were pretreated with chlorpromazine or nocodazole, suggesting that clathrin and microtubules mediated the nuclear uptake of complex 1. Additionally, the nuclear uptake efficiency is related to the cell division cycle. The complex was mainly concentrated in the nucleus when the cells were in mitosis, and distributed in whole cells when the cells were in the interphases. Furthermore, complex 1 exhibited a longer luminescence lifetime in the nucleus than in the cytoplasm as revealed by photoluminescence lifetime imaging microscopy (PLIM). Incubation of the cells in the hypoxia environment elongated the lifetime of the cytoplasmic complex, but hardly affected the luminescence properties of the intranuclear complex.

Fast wide-field upconversion luminescence lifetime thermometry enabled by single-shot compressed ultrahigh-speed imaging

Photoluminescence lifetime imaging of upconverting nanoparticles is increasingly featured in recent progress in optical thermometry. Despite remarkable advances in photoluminescent temperature indicators, existing optical instruments lack the ability of wide-field photoluminescence lifetime imaging in real time, thus falling short in dynamic temperature mapping. Here, we report video-rate upconversion temperature sensing in wide field using single-shot photoluminescence lifetime imaging thermometry (SPLIT). Developed from a compressed-sensing ultrahigh-speed imaging paradigm, SPLIT first records wide-field luminescence intensity decay compressively in two views in a single exposure. Then, an algorithm, built upon the plug-and-play alternating direction method of multipliers, is used to reconstruct the video, from which the extracted lifetime distribution is converted to a temperature map. Using the core/shell NaGdF4:Er3+,Yb3+/NaGdF4 upconverting nanoparticles as the lifetime-based temperature indicators, we apply SPLIT in longitudinal wide-field temperature monitoring beneath a thin scattering medium. SPLIT also enables video-rate temperature mapping of a moving biological sample at single-cell resolution.

Two-photon excited photoluminescence lifetime imaging studies on individual gelatin-coated gold nanorods

• Intrinsic TPE photoluminescence of different-sized gelatin-coated gold nanorods. • Combined fluorescence spectroscopy and FLIM assays on individual nanorods. • Single gold nanorod TPE photoluminescence overlaps the transverse LSPR band. • Effect of laser excitation power and wavelength on the TPE photoluminescence. The intriguing intrinsic photoluminescence (PL) properties of gold nanorods (AuNRs) have been intensively studied over the last years, not only in the linear but also in the non-linear optics regime, boosting their applicability in various fields of nanobiotechnology. In the present work, we investigate the two-photon excited (TPE) intrinsic PL of different-aspect ratio (AR) synthesized AuNRs, coated with gelatin (g@AuNRs), by performing innovative fluorescence spectroscopy - fluorescence lifetime imaging microscopy (FLIM) combined studies on individual g@AuNRs. In the first step, we employ Finite-difference time-domain (FDTD) simulations to confirm the optical response of AuNRs before and after coating with gelatin. While TPE FLIM assays performed under 800 nm excitation expose some interesting aspect regarding the AR-dependent TPE PL emission generated by individual g@AuNRs, spectroscopic measurements reveal that the TPE PL has a lifetime of around 100 ps and overlaps the corresponding transverse plasmonic band. Finally, we evaluate the effect of laser excitation power and wavelength on the TPE PL, pointing towards the important correlation between these parameters and the TPE PL performance of g@AuNR, as possible contrast agents for label-free TPE fluorescence imaging applications.

Ag-Diamond Core-Shell Nanostructures Incorporated with Silicon-Vacancy Centers.

Silicon-vacancy (SiV) centers in diamond have attracted attention as highly stable fluorophores for sensing and as possible candidates for quantum information science. While prior studies have shown that the formation of hybrid diamond-metal structures can increase the rates of optical absorption and emission, many practical applications require diamond plasmonic structures that are stable in harsh chemical and thermal environments. Here, we demonstrate that Ag nanospheres, produced both in quasi-random arrays by thermal dewetting and in ordered arrays using electron-beam lithography, can be completely encapsulated with a thin diamond coating containing SiV centers, leading to hybrid core-shell nanostructures exhibiting extraordinary chemical and thermal stability as well as enhanced optical properties. Diamond shells with a thickness on the order of 20-100 nm are sufficient to encapsulate and protect the Ag nanostructures with different sizes ranging from 20 nm to hundreds of nanometers, allowing them to withstand heating to temperatures of 1000 °C and immersion in harsh boiling acid for 24 h. Ultrafast photoluminescence lifetime and super-resolution optical imaging experiments were used to study the SiV properties on and off the core-shell structures, which show that the SiV on core-shell structures have higher brightness and faster decay rate. The stability and optical properties of the hybrid Ag-diamond core-shell structures make them attractive candidates for high-efficiency imaging and quantum-based sensing applications.

Conjugated Pt(II) Complexes as Luminescence-Switch-On Reporters Addressing the Microenvironment of Bacterial Biofilms.

In this work, the synthesis, structural and photophysical characterization of six phosphorescent H2O-soluble Pt(II) complexes are reported while addressing their emission maxima, photoluminescence quantum yields (ΦL), lifetimes (τ), aggregation tendency, and microenvironment sensitivity as a function of the substitution pattern on the main tridentate luminophore. Different ancillary ligands, namely, a trisulfonated phosphane and maltohexaose-conjugated pyridines (with or without amide bridges), were introduced and evaluated for the realization of switch-on-photoluminescent labels reporting on the microenvironment sensed in biofilms of Gram+ and Gram- models, namely, Staphylococcus aureus and Escherichia coli. With the aid of confocal luminescence micro(spectro)scopy, we observed that selected complexes specifically interact with the biofilms while leaving planktonic cells unlabeled. By using photoluminescence lifetime imaging microscopy, excited-state lifetimes within S. aureus biofilms were measured. The photoluminescence intensities were drastically boosted, and the excited state lifetimes were significantly prolonged upon binding to the viscous biofilm matrix, mainly due to the suppression of radiationless deactivation pathways upon shielding from physical quenching processes, such as interactions with solvent molecules and 3O2. The best performances were attained for non-aggregating complexes with maltohexaose targeting units and without amide bridges. Notably, in the absence of the maltodextrin, a hydrophobic adamantyl moiety suffices to attain a sizeable labeling capacity. Moreover, photoluminescence studies showed that selected complexes can also effectively interact with E. coli biofilms, where the bacterial cells are able to partially uptake the maltodextrin-based agents. In summary, the herein introduced concepts enable the development of specific biofilm reporters providing spatial resolution as well as lifetime- and spectrum-based readouts. Considering that most theragnostic agents reported so far mainly address metabolically active bacteria at the surface of biofilms but without reaching cells deeply immersed in the matrix, a new platform with a clear structure-property correlation is provided for the early detection of such bacterial arrays.

Real-Time Imaging of Short-Wave Infrared Luminescence Lifetimes for Anti-counterfeiting Applications.

Rare-earth doped nanoparticles (RENPs) have been widely used for anti-counterfeiting and security applications due to their light frequency conversion features: they are excited at one wavelength, and they display spectrally narrow and distinguished luminescence peaks either at shorter wavelengths (i.e., frequency/energy upconversion) or at longer wavelengths (frequency/energy downconversion). RENPs with a downconversion (DC) photoluminescence (PL) in short-wave infrared (SWIR) spectral range (~1,000–1,700 nm) have recently been introduced to anti-counterfeiting applications, allowing for multilevel protection based on PL imaging through opaque layers, due to a lesser scattering of SWIR PL emission. However, as the number and spectral positions of the discrete PL bands exhibited by rare-earth ions are well-known, it is feasible to replicate luminescence spectra from RENPs, which results in a limited anti-counterfeiting security. Alternatively, lifetime of PL from RENPs can be used for encoding, as it can be finely tuned in broad temporal range (i.e., from microseconds to milliseconds) by varying type of dopants and their content in RENPs, along with the nanoparticle morphology and size. Nevertheless, the current approach to decoding and imaging the RENP luminescence lifetimes requires multiple steps and is highly time-consuming, precluding practical applications of PL lifetime encoding for anti-counterfeiting. Herein, we report the use of a rapid lifetime determination (RLD) technique to overcome this issue and introduce real-time imaging of SWIR PL lifetime for anti-counterfeiting applications. NaYF4:20% Yb, x% Er (x = 0, 2, 20, 80)@NaYF4 core@shell RENPs were synthesized and characterized, revealing DC PL in SWIR region, with maximum at ~1,530 nm and PL lifetimes ranging from 3.2 to 6 ms. Imaging of the nanoparticles with different lifetimes was performed by the developed time-gated imaging system engaging RLD method and the precise manipulation of the delay between the excitation pulses and camera gating windows. Moreover, it is shown that imaging and decrypting can be performed at a high rate (3–4 fps) in a cyclic manner, thus allowing for real-time temporal decoding. We believe that the demonstrated RLD-based fast PL lifetime imaging approach can be employed in other applications of photoluminescent RENPs.

Dynamic Monitoring of Phase-Separated Biomolecular Condensates by Photoluminescence Lifetime Imaging.

The formation of biomolecular condensates is driven by liquid-liquid phase separation, which is prevalent in cells to govern crucial cellular functions. However, understanding the properties of phase-separated condensates remains very challenging for the lack of suitable techniques. Here, we report a photoluminescence lifetime imaging method for real-time monitoring of phase-separated condensates, both in vitro and in living cells, using a microsecond-scale photoluminescence lifetime probe based on iridium complex. The probe has a large Stokes shift, excellent cell permeability, and minimal cell autofluorescence interference. With this method, the dynamic process of phase separation of fused in sarcoma protein has been well explored, showing high spatiotemporal resolution and high throughput. Beginning with initial formation, the protein droplets get bigger and more viscous, and then a final maturation to solidified aggregates has been characterized. This study paves the path for a deeper understanding of the properties of phase-separated biomolecular condensates.

Controllable growth of Ga2O3 hexagonal prism with pyramid end and monitoring size-dependent electron transfer process in perylene/Ga2O3 conjugate system via FLIM

Hexagonal prisms with hexagonal pyramid end of Ga2O3 microstructures were successfully prepared on gallium arsenide substrate by double cell electrochemical etching method under various growth conditions. The field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and fluorescence lifetime imaging microscopy (FLIM) were used to characterize the hexagonal prisms. The EDS analysis confirmed that the prepared prisms were composed dominantly of gallium (Ga) and oxygen (O) with atomic ratio of ~ 2:3. The binding energy of the Ga 2p and Ga 3d XPS peaks revealed that the formation of Ga–O bonding with the highest oxidation state of Ga (Ga3+) and the formed hexagonal microstructures were Ga2O3. The PL spectra at room temperature under excitation at 290 nm exhibit a strong blue emission peak located at about 470 nm. The origin of this PL peak can be attributed to exciton recombination at different intrinsic defect sites such as O vacancies and Ga vacancies. Moreover, FLIM technique has been employed to probe time-resolved photoluminescence properties of individual Ga2O3 prisms with hexagonal tip. FLIM images provide two-dimensional spatial maps of the carrier recombination lifetime which considered the most critical parameter to improve the performance of optoelectronic devices. It has been concluded that the carrier recombination lifetime was strongly sensitive to the size of the hexagonal prism-shaped structures due to surface-related defects. Additionally, a quantitative analysis of a conjugate system prepared by functionalizing hexagonal Ga2O3 prisms with perylene organic dye molecules was reported in this work. The size-dependent electronic coupling between the conduction band level of gallium oxide and excited states of perylene molecules was investigated. We observed that highly efficient electron transfer process occurs for aggregated molecules due to excimer trap states. The grown prism structures seem to be interesting for applications in optoelectronic devices as well as to be used as an effective host medium for organic dye molecules in solar cell applications.