Nitrogen‐doped graphene oxide quantum dots exhibit both p‐ and n‐type conductivities and catalyze overall water‐splitting under visible‐light irradiation. The quantum dots contain p‐n type ...photochemical diodes, in which the carbon sp2 clusters serve as the interfacial junction. The active sites for H2 and O2 evolution are the p‐ and n‐domains, respectively, and the reaction mimics biological photosynthesis.
The best of three worlds: Gold nanorods coated with poly(styrene‐alt‐maleic acid) (see picture; pink), the photosensitizer indocyanine green (black), and antibodies (green “Y”) serve not only as ...photodynamic therapy and hyperthermia agents to destroy malignant cells, but they also act as optical contrast agents to simultaneously to monitor cells by imaging in the near‐IR region.
Investigating quantum confinement in graphene under ambient conditions remains a challenge. In this study, we present graphene oxide quantum dots (GOQDs) that show excitation-wavelength-independent ...photoluminescence. The luminescence color varies from orange-red to blue as the GOQD size is reduced from 8 to 1 nm. The photoluminescence of each GOQD specimen is associated with electron transitions from the antibonding π (π*) to oxygen nonbonding (n-state) orbitals. The observed quantum confinement is ascribed to a size change in the sp2 domains, which leads to a change in the π*−π gap; the n-state levels remain unaffected by the size change. The electronic properties and mechanisms involved in quantum-confined photoluminescence can serve as the foundation for the application of oxygenated graphene in electronics, photonics, and biology.
Single‐molecule localization microscopy (SMLM) based on temporal‐focusing multiphoton excitation (TFMPE) and single‐wavelength excitation is used to visualize the three‐dimensional (3D) distribution ...of spontaneously blinking fluorophore‐labeled subcellular structures in a thick specimen with a nanoscale‐level spatial resolution. To eliminate the photobleaching effect of unlocalized molecules in out‐of‐focus regions for improving the utilization rate of the photon budget in 3D SMLM imaging, SMLM with single‐wavelength TFMPE achieves wide‐field and axially confined two‐photon excitation (TPE) of spontaneously blinking fluorophores. TPE spectral measurement of blinking fluorophores is then conducted through TFMPE imaging at a tunable excitation wavelength, yielding the optimal TPE wavelength for increasing the number of detected photons from a single blinking event during SMLM. Subsequently, the TPE fluorescence of blinking fluorophores is recorded to obtain a two‐dimensional TFMPE‐SMLM image of the microtubules in cancer cells with a localization precision of 18±6 nm and an overall imaging resolution of approximately 51 nm, which is estimated based on the contribution of Nyquist resolution and localization precision. Combined with astigmatic imaging, the system is capable of 3D TFMPE‐SMLM imaging of brain tissue section of a 5XFAD transgenic mouse with the pathological features of Alzheimer's disease, revealing the distribution of neurotoxic amyloid‐beta peptide deposits.
Temporal‐focusing multiphoton excitation single‐molecule localization microscopy (SMLM) provides the improvement in the utilization rate of the photon budget in three‐dimensional (3D) SMLM imaging through single‐wavelength, wide‐field, and axially‐confined two‐photon excitation of spontaneously blinking fluorophores and reveals the 3D distribution of neurotoxic amyloid‐β deposits in the brain tissue of a transgenic mouse of Alzheimer's disease.
Graphite oxide (GO) synthesized from the oxidation of graphite powders exhibits p-type conductivity and is active in photocatalytic H2 evolution from water decomposition. The p-type conductivity ...hinders hole transfer for water oxidation and suppresses O2 evolution. Treating GO with NH3 gas at room temperature tunes the electronic structure by introducing amino and amide groups to its surface. The ammonia-modified GO (NGO) exhibits n-type conductivity in photoelectrochemical analysis and has a narrower optical band gap than GO. Electrochemical analysis attributes the band gap reduction to a negative shift of the valence band. An NGO-film electrode exhibits a substantially higher incident photo-to-current efficiency in the visible light region than a GO electrode. Photoluminescence analyses demonstrate the above-edge emission characteristic of GO and NGO. NH3 treatment enhances the emission by removing nonirradiative epoxy and carboxyl sites on the GO. In half-reaction tests of water decomposition, NGO effectively catalyzes O2 evolution in an aqueous AgNO3 solution under mercury-lamp irradiation, whereas GO is inactive. NGO also effectively catalyzes H2 evolution in an aqueous methanol solution but shows less activity than GO. Under illumination with visible light (λ > 420 nm), NGO simultaneously catalyzes H2 and O2 evolutions, but with a H2/O2 molar ratio below 2. The n-type conductivity of NGO may hinder electron transfer and form peroxide species instead of H2 molecules. This study demonstrates that the functionality engineering of GO is a promising technique to synthesize an industrially scalable photocatalyst for overall water splitting.
Magnetic nano/micro-particles based on clinoptilolite-type of natural zeolite (CZ) were fabricated and were expected to act as carriers for controlled drug delivery/release, imaging and local heating ...in biological systems. Adsorption of rhodamine B, sulfonated aluminum phthalocyanine and hypericin by magnetic CZ nano/micro-particles was investigated, as was the release of hypericin. Using an alternating magnetic field, local temperature increase by 10 °C in animal tissue with injected magnetic CZ particles was demonstrated. In addition, the CZ-based particles have been found to exhibit an anti-amyloidogenic effect on the amyloid aggregation of insulin and lysozyme in a dose- and temperature-dependent manner. Therefore, the mesoporous structure of CZ particles provided a unique platform for preparation of multifunctional magnetic and optical probes suitable for optical imaging, MRI, thermo- and phototherapy and as effective containers for controlled drug delivery. We concluded that magnetic CZ nano/micro-particles could be evaluated for further application in cancer hyperthermia therapy and as anti-amyloidogenic agents.
This study elucidates how nitrogen functionalities influence the transition and transfer of photogenerated electrons in graphene‐based materials. Graphene oxide dots (GODs) and Nitrogen‐doped GODs ...(NGODs) are synthesized by thermally treating graphene oxide (GO) sheets in argon and ammonia, respectively, and then ultrasonically exfoliating the sheets in nitric acid. The nitrogen functionalities of NGODs are mainly quaternary/pyridinic/pyrrolic, and the nitrogen atoms in these functionalities are planar to the GO sheets and repair the vacancy defects on the sheets. Hydrothermal treatment of NGODs in ammonia yields ammonia‐treated NGODs (A‐NGODs), with some pyridinic/pyrrolic groups being converted to amino/amide groups. The nitrogen atoms in the amino/amide groups are not planar to the GO sheets and are prone to donate their lone pair electrons to resonantly conjugate with the aromatic π electrons. The promoted conjugation facilitates the relaxation of photogenerated electrons to the triplet states and prolongs the electron lifetime. When deposited with Pt as the co‐catalyst, the samples catalyze H2 production from an aqueous triethanolamine solution under 420 nm monochromatic irradiation at quantum yields of 7.3% (GODs), 9.7% (NGODs), and 21% (A‐NGODs). The high activity of A‐NGODs demonstrates that architecting nitrogen functionalities effectively mediate charge motion in carbon‐based materials for application to photoenergy conversion.
The nonplanar configuration of the nitrogen atoms in the amino/amide groups of ammonia‐treated nitrogen‐doped graphene oxide dots (A‐NGODs) promotes the conjugation of the nitrogen lone‐pair electrons with the aromatic π system, facilitating the singlet−triplet intersystem crossing transition of electrons. The photocatalytic H2 production from an aqueous solution suspending A‐NGODs reaches a quantum yield of 21% under 420 nm illumination.
Abstract Reactive oxygen species is the main contributor to photodynamic therapy. The results of this study show that a nitrogen-doped graphene quantum dot, serving as a photosensitizer, was capable ...of generating a higher amount of reactive oxygen species than a nitrogen-free graphene quantum dot in photodynamic therapy when photoexcited for only 3 min of 670 nm laser exposure (0.1 W cm-2 ), indicating highly improved antimicrobial effects. In addition, we found that higher nitrogen-bonding compositions of graphene quantum dots more efficiently performed photodynamic therapy actions than did the lower compositions that underwent identical treatments. Furthermore, the intrinsically emitted luminescence from nitrogen-doped graphene quantum dots and high photostability simultaneously enabled it to act as a promising contrast probe for tracking and localizing bacteria in biomedical imaging. Thus, the dual modality of nitrogen-doped graphene quantum dots presents possibilities for future clinical applications, and in particular multidrug resistant bacteria.
In this study, we extend on the three parameter analysis approach of utilizing a noninvasive dual-liquid-crystal-based polarization-resolved second harmonic generation (SHG) microscopy to facilitate ...the quantitative characterization of collagen types I and II in fracture healing tissues. The SHG images under various linear and circular polarization states are analyzed and quantified in terms of the peptide pitch angle (PA), SHG-circular dichroism (CD), and anisotropy parameter (AP). The results show that the collagen PA has a value of 49.26° after 2 weeks of fracture healing (collagen type II domination) and 49.05° after 4 weeks (collagen type I domination). Moreover, the SHG-CD and AP values of the different collagen types differ by 0.05. The change tendencies of the extracted PA, SHG-CD, and AP parameters over the healing time are consistent with the collagen properties of healthy nonfractured bone. Thus, the feasibility of the proposed dual-liquid-crystal-based polarization-SHG method for differentiating between collagen types I and II in bone fracture healing tissue is confirmed.
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