Amphiphilic Carbon Dots Research Articles

Nitrogen-rich carbon dots as the antisolvent additive for perovskite-based photovoltaic devices

Solution-processed perovskite solar cells (PSCs) have demonstrated a tremendous growth in power conversion efficiency (PCE). A high-quality, defect-free perovskite-based active layer is a key point to enhance PSC performance. Introduction of additives and interlayers have proved to be an effective tool to passivate surface defects, control crystal growth, and improve PSC stability. Antisolvent engineering has emerged recently as a new approach, which aims to adjust perovskite layer properties and enhance the PCE and stability of PSC devices. Here, we demonstrate that carbon dots (CDs) may serve as a prospective additive for antisolvent engineering. Nitrogen-rich amphiphilic CDs were synthesized from amines by a solvothermal method and used as an additive to chlorobenzene for a perovskite layer fabrication. The interaction between perovskite and functional groups in CDs promotes improved crystallization of an active perovskite layer and defects passivation, bringing higher PSCs efficiency, stability, and suppressed hysteresis. Under optimized CD concentration, the maximum PCE increased by 34% due to the improved short-circuit current and fill factor, and the device maintains 87% of its initial efficiency after 6 d of storage under ambient conditions.

Bio-Inspired Carbon Dots as Malondialdehyde Indicator for Real-Time Visualization of Lipid Peroxidation in Depression.

Brain lipidic peroxidation is closely associated with the pathophysiology of various psychiatric diseases including depression. Malondialdehyde (MDA), a reactive aldehyde produced in lipid region, serves as a crucial biomarker for lipid peroxidation. However, techniques enabling real-time detection of MDA are still lacking due to the inherent trade-off between recognition dynamics and robustness. Inspired by the structure of phospholipid bilayers, amphiphilic carbon dots named as CG-CDs targeted to cell membrane are designed for real-time monitoring of MDA fluctuations. The design principle relies on the synergy of dynamic hydrogen bonding recognition and cell membrane targetability. The latter facilitates the insertion of CG-CDs into lipid regions and provides a hydrophobic environment to stabilize the labile hydrogen bonding between CG-CDs and MDA. As a result, recognition robustness and dynamics are simultaneously achieved for CG-CDs/MDA, allowing for in situ visualization of MDA kinetics in cell membrane due to the instant response (<5 s), high sensitivity (9-fold fluorescence enhancement), intrinsic reversibility (fluorescence on/off), and superior selectivity. Subsequently, CG-CDs are explored to visualize nerve cell membrane impairment in depression models of living cells and zebrafish, unveiling the extensive heterogeneity of the lipid peroxidation process and indicating a positive correlation between MDA levels and depression.

Antibacterial behavior and mechanism of nitrogen, silicon-doped amphiphilic carbon dots

A new kind of amphiphilic carbon dots (CDs) was prepared with citric acid and silane coupling agent as raw materials. Due to the doping of nitrogen and silicon elements, the surface of CDs contains not only oxygen-containing functional groups, but also alkyl hydrophobic chains, showing amphiphilic characteristic. The micro molecular structure and elemental composition of CDs were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), and other tests. The antibacterial behavior of CDs against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was studied by the disk antibacterial method, plate colony, scanning electron microscopy (SEM) and other methods. The biocompatibility of CDs was evaluated by cytotoxicity and hemolysis in vitro. The results proved that CDs possessed the average particle size of 1.75 nm and the negative surface potential of −2.71 mV. For E. coli and S. aureus, the minimum bactericidal concentrations of CDs were 500 μg/mL and 400 μg/mL, respectively. These co-doped CDs also possessed the ability to inhibit biofilm formation. The antibacterial mechanism was mainly through the adsorption force to rupture the bacterial membrane and induce the generation of reactive oxygen species in bacterial cells. In addition, CDs exhibited excellent biocompatibility because of their low cytotoxicity and hemolysis, indicating that they can be used as a new material in the antibacterial field.

Red emissive fluorescent carbon dots based on ternary carbon source for imaging α-synuclein fibrils

The misfolding and aggregation of α-synuclein monomers usually cause the occurrence and development of Parkinson’s disease (PD). It is important to develop effective methods for detection of α-synuclein aggregates. Carbon dots (CDs) could be the potential fluorescence probe for this purpose owing to their appreciated optical properties. However, undefined structure of CDs and complicated three-dimensional structure of protein severely hindered the design of fluorescence probe towards protein aggregates. Herein, a red emissive fluorescent amphiphilic CD, named as CL-9, was designed with a high sensitivity to α-synuclein fibrils by a one-step heating process, using the ternary carbon source, including Congo red, l-tryptophan and urea. The CL-9 exhibited turn-on red emissive fluorescence towards α-synuclein fibril, but remained no change towards its monomer. Compared with the original Congo red dye, CL-9 exhibited stronger turn-on red fluorescence towards α-synuclein fibrils with better anti-photobleaching resistance, biocompatibility and signal-to-noise ratio. The CL-9 was successful as a fluorescent probe to image α-synuclein fibrils in NL-5901 C. elegans. The present study provided a feasible approach using the multiple carbon sources to construct the CDs based fluorescence probe targeting amyloid proteins.

Exploring the potential applications of amphiphilic carbon dots based nanocomposite hydrogel in liquid chromatographic separations

BackgroundDue to their excellent stability, low toxicity, flexible modification and adjustable functionality, carbon dots (CDs) have a promising application prospect in the field of chromatographic stationary phases. Hydrogels are new functional polymer materials with three-dimensional network structure that have excellent hydrophilicity, high porosity and unique mechanical properties, which are also good candidate materials for liquid chromatography. Nevertheless, a review of the literature reveals that CDs based nanocomposite hydrogels have not yet been reported as HPLC stationary phases. ResultsIn this work, amphiphilic CDs with multiple functional groups and polyacrylic acid hydrogel were grafted to the surface of silica gel by an in-situ polymerization method, and a CDs/polyacrylic acid nanocomposite hydrogel stationary phase (CDs/hydrogel@SiO2) was prepared. CDs act as the macroscopic cross-linking agents to form a cross-linked network with polyacrylic acid chains through physical cross-linking by hydrogen bonding and chemical cross-linking by amidation and esterification reactions, which not only improve the swelling property of the hydrogel but also increase its stability. Additionally, the introduction of CDs with multifunctional groups modulates the hydrophilic-hydrophobic balance of the hydrogel that also imparts good hydrophobicity to the composite hydrogel. Through the study of retention mechanism and influencing factors, it is certificate that the CDs/hydrogel@SiO2 has mixed-mode chromatographic performance. Furthermore, the CDs/hydrogel@SiO2 column shows great potential for the determination of organic contaminants in environmental water samples. SignificanceThis work confirms the potential application of CDs/hydrogel composite for the separation of various samples and provides the possibility of developing CDs based nanocomposite hydrogel in the field of liquid chromatography. Introducing CDs into hydrogel can open up a new way for nanocomposite hydrogels to be used in HPLC, which expands the advance of hydrogel and CDs in separation field.

Dynamic visualization monitoring of cell membrane damage using polarity-responsive amphiphilic carbon dots

Development of organelle-targeted fluorescent carbon dots (CDs) has attracted extensive attention recently, however, the application of CDs for monitoring cell membrane integrity is rarely reported. Herein, we propose a kind of amphiphilic CDs (∼2.84 nm) derived from o-phenylenediamine and urea (termed M-CDs). M-CDs display high-affinity capacity to polysaccharide structures, which allows the rapid (∼within 30 s), wash-free fluorescence (FL) imaging of microbes, including bacteria and fungi. For mammalian cells, M-CDs can selective bind to the intracellular cytoskeletal filaments when the cells undergo cytomembrane destruction. More interestingly, the FL feature of M-CDs is polarity-dependent that emits the maximum emission wavelength from 501 to 561 nm when the solvent polarity increases from 0.02 to 0.32, which offers the opportunity to detect the polarity microenvironment. We observe that the polarity increases significantly when M-CDs pass through the broken cytomembrane. M-CDs are finally adopted for the fast morphometric analysis of abnormal erythrocytes in haematuria, providing a novel avenue for the rapid test of membrane-related diseases.

Preparation of surface-active carbon dots with fluorocarbon and hydrocarbon hybrid chains via a one-pot solvothermal technique and their characterization and potential applications

Amphiphilic carbon dots (CDs) are new surface-active materials that exhibit several advantages over conventional small surfactants, such as improved stability and reduced toxicity. However, unlike for conventional small surfactants, amphiphilic CDs that simultaneously exhibit excellent surface and interfacial activities have never been achieved. Herein we prepare new amphiphilic CDs with fluorocarbon and hydrocarbon hybrid hydrophobic chains (FH-CDs) using a facile one-pot solvothermal technique. The obtained FH-CDs showed excellent surface and interfacial activities, and reduced the surface tension at critical micelle concentration and the oil-water interfacial tension to 16.7 and 2.2 mN/m, respectively. Comparison with control CDs bearing only non-hybrid hydrophobic chains demonstrated that decorating CDs with fluorocarbon and hydrocarbon hybrid chains contributed to the excellent interfacial activity, while only fluorocarbon chains contributed to good surface activity. The excellent surface and interfacial activities made FH-CDs good emulsifiers for the formation of stable water-in-oil emulsions and for the preparation of relatively uniform polystyrene spheres via emulsion polymerization. Moreover, FH-CD was a good wetting agent, whose aqueous solution could wet numerous different surfaces, including the commonly non-wettable amphiphobic polytetrafluoroethylene.

Solvent-controlled synthesis of hydrophilic and hydrophobic carbon dots.

Hydrophilicity and hydrophobicity are of paramount importance in surface chemistry. In this study, a solvent-controlled synthesis of hydrophilic and hydrophobic carbon dots (CDs) was prepared via a solvothermal process using pentafluorobenzyl alcohol as the carbon source in either deionized water or N,N-dimethylformamide (DMF) medium. By simply varying the reaction solvent to control the doping of nitrogen and fluorine elements, the hydrophilicity or hydrophobicity of the CDs could be regulated. Hydrophobic and hydrophilic CDs showed blue and green light under a UV lamp, respectively. Besides, we regulated the volume ratio of water/DMF (1 : 2, 1 : 1 and 2 : 1) in the reaction solvent to prepare amphiphilic CDs and further studied their hydrophilicity and hydrophobicity. Furthermore, the sensitivity of hydrophobic CDs to water was investigated. In water detection, the photoluminescent intensity of the blue peak and green peak showed high linearity within the water content of 4-80% and 10-80%, respectively (limit of detection = 0.08%, v/v, in DMF).

Interfacial properties, decompression, and augmented injection of amphiphilic carbon dots and surfactant mixtures

The mixing properties of amphiphilic carbon dots named C12-SCDs with a cationic surfactant (Dodecyl trimethyl ammonium bromide, DTAB) and an anionic surfactant (Sodium dodecyl sulfate, SDS) were investigated. Results indicated that surfactants DTAB and SDS show a synergistic effect in reducing surface tension with C12-SCDs. The synergistic effect of the DTAB/C12-SCDs mixture is more prominent than the SDS/C12-SCDs mixture, which may result from the electrostatic attraction between DTAB and C12-SCDs. Meanwhile, adding inorganic salts, the surface tension of these mixtures shows a trend of first decreasing slightly and then increasing. The DTAB/C12-SCDs mixture resists strong acids but not alkali environments. However, the surface tension of the SDS/C12-SCDs mixture gradually increases with the increase in pH. In addition, these mixtures have temperature-resistance properties. C12-SCDs and surfactants (DTAB and SDS) also have a synergistic effect in reducing the crude oil-water interfacial tension. Meanwhile, the DTAB/C12-SCDs and SDS/C12-SCDs mixtures have excellent wettability alternation performance. C12-SCDs and surfactants can form a mixed adsorption layer to promote the wettability alternation performance. The depressurization rates of DTAB, SDS, C12-SCDs, DTAB/ C12-SCDs mixture, and SDS/C12-SCDs mixture are 10.42 %, 11.54 %, 22.91 %, 26.32 %, and 24.75 %, respectively. The DTAB/C12-CDs and SDS/C12-CDs mixtures can effectively remove the oil film on the core surface, thus improving the channel of injected water. At the same time, these mixtures can be adsorbed on the surface of the hydrophilic core to form a hydrophobic surface, and the injection of water produces a hydrophobic slip effect. Finally, reducing the surface tension of water can also effectively reduce the injection pressure.

Spleen-Targeted mRNA Delivery by Amphiphilic Carbon Dots for Tumor Immunotherapy

In recent years, the application of mRNA vaccine-based tumor immunotherapy invigorated anti-tumor therapy. However, the low efficiency of mRNA delivery and the lack of targeting ability in vivo are the major obstacles to achieving highly efficient immunotherapy. In this work, we report a chemical library of amphiphilic carbon dots (ACDs) and the synthesized ACDs were applied to mRNA delivery, bio-imaging, and tumor immunotherapy. The ACDs can smoothly bind with mRNA to form ACDs@mRNA nanocomplexes, and the fluorescent properties of the ACDs afforded the nanoparticles with bio-imaging ability. By screening of the ACDs, O12-Tta-CDs were found to have optimal mRNA transfection efficiency and the ability of spleen-targeted delivery. In addition, O12-Tta-CDs can well transfect the immune cells and promote the maturation and antigen presentation of bone marrow-derived dendritic cells (BMDCs). Furthermore, O12-Tta-CDs@OVA-mRNA was successfully applied to inhibit tumor growth, and more specific T-cell infiltration was observed in spleen and tumors of mice after treatment in the E.G7-OVA tumor model. Besides, O12-Tta-CDs@OVA-mRNA also achieved a good therapeutic effect in tumor recurrence inhibition and tumor prophylactic experiments. This study provided a new direction for the design of mRNA vectors, which is promising in tumor immunotherapy.

Adsorptive Removal of Anthracene from Water by Biochar Derived Amphiphilic Carbon Dots Decorated with Chitosan

Adsorptive Removal of Anthracene from Water by Biochar Derived Amphiphilic Carbon Dots Decorated with Chitosan

Adsorptive Removal of Anthracene from Water by Biochar Derived Amphiphilic Carbon Dots Decorated with Chitosan

Adsorptive Removal of Anthracene from Water by Biochar Derived Amphiphilic Carbon Dots Decorated with Chitosan

Bright red fluorescent amphiphilic carbon dots as dualphase and visual sensor for selective detection of As3+ in aqueous environment

Increasing attention has been focused in the area of multi-mode sensing method for on-site application to avoid the false positive results and enhance the accuracy label measurements. This article reports the synthesis of bright red fluorescent amphiphilic carbon dots (C-dots) as dualphase fluorescent nanosensor for selective detection of As3+ in water. One-pot solvothermal approach was chosen for the C-dots synthesis with a maximum fluorescence quantum yield of 47%. Bright red fluorescence of the C-dots was selectively weakened upon the treatment with As3+, although the other competing ions showed infectivity. Static quenching was proved behind this fluorescence attenuation by absorbance and time-resolved fluorescence spectroscopy. The amphiphilicity of synthesized C-dots has been utilized to detect As3+ in both liquid and solid phase. Aqueous dispersion of C-dots showed a dramatic fluorescence quenching efficiency of maximum 80%. To fabricate solid phase sensor, C-dots were successfully coated and absorbed on silica beads and cotton buds. These fluorescent solid matrices also displayed a relative good quenching efficiency (70–80%) towards As3+ without any leaching out of the C-dots from the solid surface. In addition, these C-dots showed an adequate potentiality to detect this ion in real water sample analysis. These findings would enable a great potentiality in the environmental water contaminants sensing technology.

Understanding the aggregation of excitation wavelength independent emission of amphiphilic carbon dots for bioimaging and organic acid sensing

Herein, excitation wavelength-independent, tunable emissive and amphiphilic CDs with high quantum yield were synthesized by a low-temperature oxidation method employing banana peel waste as a carbon source. These CDs showed longer wavelength emissions (green to yellow) independent of the excitation wavelength when dispersed in different polar to non-polar solvents. The quantum yields of the same CDs were 9–32% in different solvent polarities for different emissions. On the other hand, a large stokes-shifted emission (∼9606 cm−1) was observed for CDs in the non-polar and weak polar solvents. The particle size of CDs increases from a hydrophobic to a hydrophilic environment with the change in emission colour from yellow to green. A polar and a non-polar host matrix were used to overcome the limitation of aggregation-caused quenching of CDs in the solid state to obtain bright emissions. These CDs were potentially used for naked-eye detection of trifluoroacetic acid (TFA) by changing the emission colour from yellow to orange under UV 365 nm. Sensing of TFA was also shown reversibly switch emission colour and average lifetime for multiple cycles. Additionally, the highly emissive CDs show negligible cytotoxicity in 3T3 fibroblast cells, indicating possible bioimaging applications in 3T3 cells.

Surface activity, micellization, and application of nano-surfactants—amphiphilic carbon dots

For nano-surfactants, a new class of surfactants, the unique surface properties, micellization, and application of amphiphilic carbon dots (CDs) have been investigated carefully. Amphiphilic CDs (C12-CDs and C12-SCDs) were synthesized under mild reaction conditions. These CDs exhibit higher surface activity than conventional surfactants (APG12 and SDBS), whereas hydrophilic CDs have negligible surface activity. Above the critical micelle concentration, C12-CDs aggregate into an irregular spherical structure like micelle with an average diameter of about 100 nm, whereas C12-SCDs do not form aggregates. The surface tension of C12-CDs and C12-SCDs reaches the minimum at pH = 3, which is close to the isoelectric point of CDs. As pH increases, the water solubility of CDs increases, and thus the surface tension increases. C12-CDs can still maintain high activity at cNaCl = 250 g/L, but their resistance to CaCl2 is poor. The addition of the sulfonate groups enhances the tolerance of CDs to both NaCl and CaCl2. At cNaCl = 360 g/L and cCaCl2 = 750 g/L, C12-SCDs still have high surface activity.The removal efficiency of oil film and contact angle experiments show that compared to the traditional surfactant SDBS, C12-CDs and C12-SCDs have an excellent wettability alternation due to their abundant hydroxyl, carboxyl, amine, and sulfonate groups. Among them, the wettability alternation of C12-SCDs is better than that of C12-CDs due to their hydrophilic sulfonate groups. Furthermore, the Pickering emulsions stabilized by C12-SCDs have rapid pH and CO2 response performance. In addition, compared to the traditional surfactants SDBS and APG12, CDs have an excellent dispersion performance to MWCNTs. Different from the dispersion mechanism of cationic surfactant CPC (strong electrostatic attraction), CDs are adsorbed on the surface of MWCNTs through their hydrophobic effect and π-π stacking effect to achieve effective dispersion. Among them, because the sulfonate groups have high steric resistance and electrostatic repulsion, the dispersion performance of C12-SCDs is better than that of C12-CDs.

Amphiphilic carbon dots as high-efficiency corrosion inhibitor for N80 steel in HCl solution: Performance and mechanism investigation

Three amphiphilic carbon dots (CDs, C6-CDs, C8-CDs, and C12-CDs) were synthesized and first adopted as a corrosion inhibitor for mild steel. The inhibition behavior of amphiphilic CDs for N80 steel in hydrochloric acid solution was studied via weight loss tests, surface characterization, and electrochemical measurements. Results confirmed that they could protect N80 steel effectively; the longer the carbon chain was, the better the inhibition effect was. Specifically, the inhibition efficiency of C12-CDs reached 92.9 % at 150 mg/L. Moreover, due to the fluorescence characteristics of CDs, the changes in adsorption film during corrosion could be directly observed under UV light. A dense adsorption film was formed through the electrostatic interaction with CDs and the metal surface. Long carbon chains formed a hydrophobic layer on the surface of N80 to isolate the corrosive medium.

Development of Highly Luminescent Water-Insoluble Carbon Dots by Using Calix[4]pyrrole as the Carbon Precursor and Their Potential Application in Organic Solar Cells.

Carbon dots (CDs) are carbon-based fluorescent nanomaterials that are of interest in different research areas due to their low cost production and low toxicity. Considering their unique photophysical properties, hydrophobic/amphiphilic CDs are powerful alternatives to metal-based quantum dots in LED and photovoltaic cell designs. On the other hand, CDs possess a considerably high amount of surface defects that give rise to two significant drawbacks: (1) causing decrease in quantum yield (QY), a crucial drawback that limits their utilization in LEDs, and (2) affecting the efficiency of charge transfer, a significant factor that limits the use of CDs in photovoltaic cells. In this study, we synthesized highly luminescent, water-insoluble, slightly amphiphilic CDs by using a macrocyclic compound, calix[4]pyrrole, for the first time in the literature. Calix[4]pyrrole-derived CDs (CP-DOTs) were highly luminescent with a QY of over 60% and size of around 4–10 nm with graphitic structure. The high quantum yield of CP-DOTs indicated that they had less amount of surface defects. Furthermore, CP-DOTs were used as an additive in the active layer of organic solar cells (OSC). The photovoltaic parameters of OSCs improved upon addition of CDs. Our results indicated that calix[4]pyrrole is an excellent carbon precursor to synthesize highly luminescent and water-insoluble carbon dots, and CDs derived from calix[4]pyrrole are excellent candidates to improve optoelectronic devices.

Remarkably boosting the lubricity of polyalphaolefin by loading amphiphilic carbon dots stabilized by Span-80

The amphiphilic carbon dots (A-CDs) derived from Tween-80 were used as the lubricant additives of polyalphaolefin (PAO4) with the aid of Span-80. The Span-80 (5.0 wt%) endowed A-CDs with super dispersibility in PAO4 by the hydrogen bond interactions between the hydrophilic head groups of Span-80 and the oxygen-containing groups on A-CDs. At the load of 50 N, the biggest friction and wear reductions for PAO4 triggered by the A-CDs (1.3 wt%) stabilized by Span-80 (5.0 wt%) were 45.4 and 69.8%, respectively. The distinguished tribological performance of A-CDs stabilized by Span-80 illustrated the co-lubrication effect of Span-80 and A-CDs. The wear scar surface analysis results revealed that the A-CDs stabilized by Span-80 distinctly alleviated the adhesive and abrasive wear of friction pair. The favorable smoothness and high O content on wear scar surface lubricated by A-CDs suspension reflected the A-CDs stabilized by Span-80 have participated in the formation of effective lubricating films. The reasonable lubrication mechanism of A-CDs stabilized by Span-80 was discussed based on the co-lubrication effect of Span-80 and A-CDs. The absorbing effect of Span-80 and the rolling and filling effects of A-CDs are all beneficial to the building of lubricating films, thereby tremendously boosting the lubricity of PAO4. The A-CDs stabilized by Span-80 are promising to become a kind of eco-friendly and high-performance lubricant additive for PAO.

Origin of solvent and excitation dependent emission in newly synthesized amphiphilic carbon dots

The present work demonstrates the synthesis of a new amphiphilic carbon dot from octylamine. Steady-state emission studies show excitation dependent emission features. Time-resolved emission studies show three different emission decay traces while exciting at 267 nm, 292–339 nm, and 374–445 nm regions. These excitation bands are assigned to the π–π*, n–π*, and surface group states respectively. It was further observed that only surface state exhibit excitation dependent emission behavior while both π–π* and n–π* states show marginal effect; the observation rarely discussed in the literature. Both growth and emission lifetime of π–π* is higher as compared to n–π* and surface group states suggesting the possibility of energy transfer from former to latter. The emission peak position was different in different solvents by exciting π–π* states however it was almost same when monitoring at the surface states which in contrast to the belief that π–π* states are embedded inside the shell and has the least exposure to the solvent. The study also suggests that in protic solvents both π–π* and n–π* states interact but not in other solvents. Moreover, the presence of multiple emission states is responsible for excitation dependent emission features from surface group states, each having its own lifetime.

One-step synthesized amphiphilic carbon dots for the super-resolution imaging of endoplasmic reticulum in live cells.

Stimulated emission depletion (STED) microscopy provides a powerful tool for visualizing the ultrastructure and dynamics of subcellular organelles, however, the photobleaching of organelle trackers have limited the application of STED imaging in living cells. Here, we report photostable and amphiphilic carbon dots (Phe-CDs) with bright orange fluorescence via a simple one-pot hydrothermal treatment of o-phenylenediamine and phenylalanine. The obtained Phe-CDs not only had high brightness (quantum yield ∼18%) but also showed excellent photostability under ultraviolet irradiation. The CDs can quickly penetrate into cells within 2 min and are specific for intracellular ER. The further investigations by Phe-CDs revealed the reconstitution process of ER from loosely spaced tubes into a continuously dense network of tubules and sheets during cell division. Importantly, compared with the standard microscopy, STED super-resolution imaging allowed the tracking of the ER ultrastructure with a lateral resolution less than 100 nm and the pores within the ER network are clearly visible. Moreover, the three dimensional (3D) structure of ER was also successfully reconstructed from z-stack images due to the excellent photostability of Phe-CDs.