Hequn Zhang

High‐Order Non‐Linear Optical Effects in Organic Luminogens with Aggregation‐Induced Emission

2,3-bis(4-(phenyl(4-(1,2,2-triphenylvinyl)phenyl)amino)phenyl)fumaronitrile (TTF) shows unique aggregation-induced emission (AIE) characteristics. Under the excitation of a 1560 nm femtosecond laser, simultaneous three-photon-excited luminescence (3PL) and third-harmonic-generation signals can be observed from its nanoaggregate and the solid state. TTF is further encapsulated with DSPE-mPEG (a type of amphiphilic polymer) to form AIE-active nanoparticles. 3PL brain imaging of mice is achieved based on the nanoparticles.

Real‐Time and High‐Resolution Bioimaging with Bright Aggregation‐Induced Emission Dots in Short‐Wave Infrared Region

Fluorescence imaging in the spectral region beyond the conventional near-infrared biological window (700-900 nm) can theoretically afford high resolution and deep tissue penetration. Although some efforts have been devoted to developing a short-wave infrared (SWIR; 900-1700 nm) imaging modality in the past decade, long-wavelength biomedical imaging is still suboptimal owing to the unsatisfactory materials properties of SWIR fluorophores. Taking advantage of organic dots based on an aggregation-induced emission luminogen (AIEgen), herein microscopic vasculature imaging of brain and tumor is reported in living mice in the SWIR spectral region. The long-wavelength emission of AIE dots with certain brightness facilitates resolving brain capillaries with high spatial resolution (≈3 µm) and deep penetration (800 µm). Owning to the deep penetration depth and real-time imaging capability, in vivo SWIR microscopic angiography exhibits superior resolution in monitoring blood-brain barrier damage in mouse brain, and visualizing enhanced permeability and retention effect in tumor sites. Furthermore, the AIE dots show good biocompatibility, and no noticeable abnormalities, inflammations or lesions are observed in the main organs of the mice. This work will inspire new insights on development of advanced SWIR techniques for biomedical imaging.

Toxicity assessment and long-term three-photon fluorescence imaging of bright aggregation-induced emission nanodots in zebrafish

Aggregation-induced emission (AIE) luminogen displays bright fluorescence and has photobleaching resistance in its aggregation state. It is an ideal fluorescent contrast agent for bioimaging. Multiphoton microscopy is an important tool for bioimaging since it possesses the ability to penetrate deep into biological tissues. Herein, we used AIE luminogen together with multiphoton microscopy for long-term imaging of zebrafish. A typical AIE luminogen, 2,3-bis(4-(phenyl(4- (1,2,2-triphenylvinyl) phenyl)amino)phenyl) fumaronitrile (TPE-TPA-FN or TTF), was encapsulated with 1,2-distearoyl-sn-glycero-3-phosphoethanola-mine-N-[methoxy(polyethylene glycol)-2000] (DSPE-mPEG2000) to form nanodots that exhibited bright three-photon fluorescence under 1,560 nm-femtosecond (fs) laser excitation. The TTF-nanodots were chemically stable in a wide range of pH values and showed no in vivo toxicity in zebrafish according to a series of biological tests. The TTF-nanodots were microinjected into zebrafish embryos, and the different growth stages of the labeled embryos were monitored with a three-photon fluorescence microscope. TTF-nanodots could be traced inside the zebrafish body for as long as 120 hours. In addition, the TTF-nanodots were utilized to target the blood vessel of zebrafish, and three-photon fluorescence angiogram was performed. More importantly, these nanodots were highly resistant to photobleaching under 1,560 nm-fs excitation, allowing long-term imaging of zebrafish.

The role of band alignment in p-type conductivity of Na-doped ZnMgO: Polar versus non-polar

We investigate the electrical properties of polar and non-polar ZnMgO:Na films that have been fabricated on c-plane and r-plane sapphire substrates using intervened ZnO layers (10–30 nm thick) by pulsed laser deposition. Hall-effect measurements indicate that the a-plane ZnMgO:Na film exhibits p-type conductivity with a carrier concentration of about 3.5 × 1016 cm−3, while the polar film shows a compensatory conductivity. Meanwhile, the dependence of the band alignment on the orientation of the ZnMgO/ZnO heterojunctions has been investigated using photoelectron spectroscopy. The heterojunctions form in the type-I straddling alignment with valence band offsets of 0.07 (0.02) eV for the (non-)polar heterojunction. The difference in valence band offsets is primarily attributed to the spontaneous polarization effect. We propose that the smaller valence band offsets and larger conduction band offsets would reduce the NaZn acceptor level and enhance the relative intrinsic donor levels. Such effects consequently...

Biocompatible aggregation-induced emission nanoparticles with red emission for in vivo three-photon brain vascular imaging

Three-photon luminescence (3PL) imaging with near-infrared (NIR) excitation is quite promising for its deep penetration, high resolution, and good signal-to-noise ratio (SNR). In this report, a type of red emissive fluorophore TPEPT with aggregation-induced emission (AIE) properties was synthesized, and it was found to possess a large three-photon absorption (3PA) cross-section of 6.33 × 10-78 cm6 s2 under 1550 nm femtosecond laser excitation. TPEPT was then encapsulated with mPEG5000-DSPE to form AIE nanoparticles, and the chemical stability, optical properties and toxicity were studied afterwards. TPEPT nanoparticles were then applied for 3PL in vivo vascular imaging of mouse brain under 1550 nm fs laser excitation, and a fine three-dimensional (3D) reconstruction with a depth of 500 μm was achieved.

Nonlinear optical properties of Au/Ag alloyed nanoboxes and their applications in both in vitro and in vivo bioimaging under long-wavelength femtosecond laser excitation

We synthesize Au/Ag alloyed nanoboxes (ANBs) with different LSPR (localized surface plasmon resonance) peak wavelengths and observe their various nonlinear optical properties. Both in vitro and in vivo bioimaging results show that Au/Ag ANBs are very good candidates for high-contrast and deep-tissue nonlinear optical imaging with negligible photothermal toxicity.

Aggregation-Induced Emission Luminogen with Near-Infrared-II Excitation and Near-Infrared-I Emission for Ultradeep Intravital Two-Photon Microscopy

Currently, a serious problem obstructing the large-scale clinical applications of fluorescence technique is the shallow penetration depth. Two-photon fluorescence microscopic imaging with excitation in the longer-wavelength near-infrared (NIR) region (>1100 nm) and emission in the NIR-I region (650-950 nm) is a good choice to realize deep-tissue and high-resolution imaging. Here, we report ultradeep two-photon fluorescence bioimaging with 1300 nm NIR-II excitation and NIR-I emission (peak ∼810 nm) based on a NIR aggregation-induced emission luminogen (AIEgen). The crab-shaped AIEgen possesses a planar core structure and several twisting phenyl/naphthyl rotators, affording both high fluorescence quantum yield and efficient two-photon activity. The organic AIE dots show high stability, good biocompatibility, and a large two-photon absorption cross section of 1.22 × 103 GM. Under 1300 nm NIR-II excitation, in vivo two-photon fluorescence microscopic imaging helps to reconstruct the 3D vasculature with a high spatial resolution of sub-3.5 μm beyond the white matter (>840 μm) and even to the hippocampus (>960 μm) and visualize small vessels of ∼5 μm as deep as 1065 μm in mouse brain, which is among the largest penetration depths and best spatial resolution of in vivo two-photon imaging. Rational comparison with the AIE dots manifests that two-photon imaging outperforms the one-photon mode for high-resolution deep imaging. This work will inspire more sight and insight into the development of efficient NIR fluorophores for deep-tissue biomedical imaging.

A portable confocal hyperspectral microscope without any scan or tube lens and its application in fluorescence and Raman spectral imaging

In this paper we prove the existence of Hall’s ray for the quadratic Lagrange spectrums of all real quadratic numbers. For a large class of real quadratic numbers, we compute the Hurwitz constants of their quadratic Lagrange spectrums.

The role of beryllium in the band structure of MgZnO: Lifting the valence band maximum

We investigate the effect of Be on the valence band maximum (VBM) of MgZnO by measuring the band offsets of MgxZn1−xO/BexMgyZn1−x−yO heterojunctions using X-ray photoelectron spectroscopy measurements. MgxZn1−xO and BexMgyZn1−x−yO films have been grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The valence band offset ( ΔEV) of Mg0.15Zn0.85O ( Eg = 3.62 eV)/Be0.005Mg0.19Zn0.805O ( Eg = 3.73 eV) heterojunction is 0.01 eV and Be0.005Mg0.19Zn0.805O has a lower VBM. The increased Mg composition is the main factor for the reduction of VBM. The VBM of MgxZn1−xO is lower by 0.03 eV with the enlargement of Eg from 3.62 eV to 3.73 eV by increasing Mg composition. Considering the effect of increased Mg composition, it is concluded that the little amount of Be makes the VBM go up by 0.02 eV when the Eg of the alloy is 3.73 eV. The ΔEV of Mg0.11Zn0.89O ( Eg = 3.56 eV)/Be0.007Mg0.12Zn0.873O ( Eg = 3.56 eV) heterojunction is calculated to be 0.03 eV and Be0.007Mg0.12Zn0.873O has a higher ...

Single-Molecular Near-Infrared-II Theranostic Systems: Ultrastable Aggregation-Induced Emission Nanoparticles for Long-Term Tracing and Efficient Photothermal Therapy

Second near-infrared (NIR-II, 1000-1700 nm) fluorescence bioimaging has attracted tremendous scientific interest and already been used in many biomedical studies. However, reports on organic NIR-II fluorescent probes for in vivo photoinduced imaging and simultaneous therapy, as well as the long-term tracing of specific biological objects, are still very rare. Herein we designed a single-molecular and NIR-II-emissive theranostic system by encapsulating a kind of aggregation-induced emission luminogen (AIEgen, named BPN-BBTD) with amphiphilic polymer. The ultra-stable BPN-BBTD nanoparticles were employed for the NIR-II fluorescence imaging and photothermal therapy of bladder tumors in vivo. The 785 nm excitation triggered photothermal therapy could completely eradicate the subcutaneous tumor and inhibit the growth of orthotopic tumors. Furthermore, BPN-BBTD nanoparticles were capable of monitoring subcutaneous and orthotopic tumors for a long time (32 days). Single-molecular and NIR-II-emitted aggregation-induced emission nanoparticles hold potential for the diagnosis, precise treatment, and metastasis monitoring of tumors in the future.