Xiaoxiao Hu

A Smart Photosensitizer–Manganese Dioxide Nanosystem for Enhanced Photodynamic Therapy by Reducing Glutathione Levels in Cancer Cells

Photodynamic therapy (PDT) has been applied in cancer treatment by utilizing reactive oxygen species to kill cancer cells. However, a high concentration of glutathione (GSH) is present in cancer cells and can consume reactive oxygen species. To address this problem, we report the development of a photosensitizer-MnO2 nanosystem for highly efficient PDT. In our design, MnO2 nanosheets adsorb photosensitizer chlorin e6 (Ce6), protect it from self-destruction upon light irradiation, and efficiently deliver it into cells. The nanosystem also inhibits extracellular singlet oxygen generation by Ce6, leading to fewer side effects. Once endocytosed, the MnO2 nanosheets are reduced by intracellular GSH. As a result, the nanosystem is disintegrated, simultaneously releasing Ce6 and decreasing the level of GSH for highly efficient PDT. Moreover, fluorescence recovery, accompanied by the dissolution of MnO2 nanosheets, can provide a fluorescence signal for monitoring the efficacy of delivery.

Efficient Two-Photon Fluorescent Probe with Red Emission for Imaging of Thiophenols in Living Cells and Tissues

Thiophenols, a class of highly toxic and pollutant compounds, are widely used in industrial production. Some aliphatic thiols play important roles in living organisms. Therefore, the development of efficient methods to discriminate thiophenols from aliphatic thiols is of great importance. Although several one-photon fluorescent probes have been reported for thiophenols, two-photon fluorescent probes are more favorable for biological imaging due to its low background fluorescence, deep penetration depth, and so on. In this work, a two-photon fluorescent probe for thiophenols, termed NpRb1, has been developed for the first time by employing 2,4-dinitrobenzene-sulfonate (DNBS) as a recognition unit (also a fluorescence quencher) and a naphthalene-BODIPY-based through-bond energy transfer (TBET) cassette as a fluorescent reporter. The TBET system consists of a D-π-A structured two-photon naphthalene fluorophore and a red-emitting BODIPY. It displayed highly energy transfer efficiency (93.5%), large pseudo-Stokes shifts upon one-photon excitation, and red fluorescence emission (λem = 586 nm), which is highly desirable for bioimaging applications. The probe exhibited a 163-fold thiophenol-triggered two-photon excited fluorescence enhancement at 586 nm. It showed a high selectivity and excellent sensitivity to thiophenols, with a detection limit of 4.9 nM. Moreover, it was successfully applied for practical detection of thiophenol in water samples with a good recovery, two-photon imaging of thiophenol in living cells, and tissues with tissue-imaging depths of 90-220 μm, demonstrating its practical application in environmental samples and biological systems.

Efficient Two-Photon Fluorescent Probe for Nitroreductase Detection and Hypoxia Imaging in Tumor Cells and Tissues.

Hypoxia plays an important role in tumor progression, and the development of efficient methods for monitoring hypoxic degree in living systems is of great biomedical importance. In the solid tumors, the nitroreductase level is directly corresponded with the hypoxic status. Many one-photon excited fluorescent probes have been developed for hypoxia imaging in tumor cells via the detection of nitroreductase level. However, two-photon excited probes are more suitable for bioimaging. In this work, a two-photon probe 1 for nitroreductase detection and hypoxic status monitoring in living tumor cells and tissues was reported for the first time. The detection is based on the fact that the nitro-group of probe 1 could be selectively reduced to an amino-group by nitroreductase in the presence of reduced NADH, following by a 1,6-rearrangement-elimination to release the fluorophore, resulting in the enhancement of fluorescence. The probe exhibited both one-photon and two-photon excited remarkable fluorescence enhancement (∼70-fold) for nitroreductase, which afforded a high sensitivity for nitroreductase, with a detection limit of 20 ng/mL observed. Moreover, the applications of the probe for fluorescent bioimaging of hypoxia in living cells and two-photon bioimaging in tissues were carried out, with tissue-imaging depths of 70-160 μm observed, which demonstrates its practical application in complex biosystems.

A Cyanine Dye to Probe Mitophagy: Simultaneous Detection of Mitochondria and Autolysosomes in Live Cells

Mitophagy is a process in which cells remove dysfunctional mitochondria and recycle their constituents in a lysosome-dependent manner. To probe this process, two different fluorescent dyes specific for mitochondria and lysosomes, respectively, are often used in combination. However, current fluorescent dyes for lysosomes cannot distinguish mitochondria-containing autolysosomes from other lysosomes. Therefore, we herein report a cyanine dye, HQO, which can simultaneously probe mitochondria and autolysosomes in live cells by exhibiting different fluorescence properties. HQO selectively accumulates in mitochondria but then transforms to the protonated HQOH(+) form with the decrease of pH when dysfunctional mitochondria evolve into autolysosomes. Since HQO and HQOH(+) exhibit different absorption and emission with Ex/Em at 530/650 and 710/750 nm, respectively, in a low polarity environment, such as that found in micelles, they are uniquely suited to monitor mitophagy with the ability to distinguish autolysosomes from other lysosomes.

DNA Aptamer Selected against Pancreatic Ductal Adenocarcinoma for in vivo Imaging and Clinical Tissue Recognition

In this work, we have developed a truncated DNA aptamer, termed XQ-2d, with high affinity and specificity for pancreatic ductal adenocarcinoma (PDAC). Aptamer XQ-2d selectively binds to PL45 cells with a dissociation constant in the nanomolar range, as determined by its recognition of PL45 tumor cells in mice. Moreover, XQ-2d shows better recognition ratio for 40 tissue sections of clinical PDAC samples (82.5%) compared to the initial cell-SELEX selection library (5%). Therefore, XQ-2d can be considered a promising candidate as a tool for PDAC diagnosis and treatment.

An efficient two-photon fluorescent probe for monitoring mitochondrial singlet oxygen in tissues during photodynamic therapy

A promising two-photon fluorescent probe MNAH for detecting 1O2 during the PDT process in mitochondria was proposed for the first time. MNAH was successfully applied for two-photon imaging of 1O2 in living cells and tissues during the PDT process with deep-tissue imaging depth. MNAH can be a powerful molecular tool for studying 1O2 generation in mitochondria during the PDT process.

Dye-Doped Fluorescent Silica Nanoparticles for Live Cell and In Vivo Bioimaging

The need for novel design strategies for fluorescent nanomaterials to improve our understanding of biological activities at the molecular level is increasing rapidly. Dye-doped fluorescent silica nanoparticles (SiNPs) emerge with great potential for developing fluorescence imaging techniques as a novel and ideal platform for the monitoring of living cells and the whole body. Organic dye-containing fluorescent SiNPs exhibit many advantages: they have excellent biocompatibility, are non-toxic, highly hydrophilic, optically transparent, size-tunable and easily modified with various biomolecules. The outer silica shell matrix protects fluorophores from outside chemical reaction factors and provides a hydrophilic shell for the insoluble nanoparticles, which enhances the photo-stability and biocompatibility of the organic fluorescent dyes. Here, we give a summary of the synthesis, characteristics and applications of fluorescent SiNPs for non-invasive fluorescence bioimaging in live cells and in vivo. Additionally, the challenges and perspectives of SiNPs are also discussed. We prospect that the further development of these nanoparticles will lead to an exciting breakthrough in the understanding of biological processes.

Autofluorescence-Free Targeted Tumor Imaging Based on Luminous Nanoparticles with Composition-Dependent Size and Persistent Luminescence

Optical bioimaging is an indispensable tool in modern biology and medicine, but the technique is susceptible to autofluorescence interference. Persistent nanophosphors provide an easy-to-perform and highly efficient means to eliminate tissue autofluorescence. However, direct synthesis of persistent nanophosphors with tunable properties to meet different bioimaging requirements remains largely unexplored. In this work, zinc gallogermanate (Zn1+xGa2-2xGexO4:Cr, 0 ≤ x ≤ 0.5, ZGGO:Cr) persistent luminescence nanoparticles with composition-dependent size and persistent luminescence are reported. The size of the ZGGO:Cr nanoparticles gradually increases with the increase of x in the chemical formula. Moreover, the intensity and decay time of persistent luminescence in ZGGO:Cr nanoparticles can also be fine-tuned by simply changing x in the formula. In vivo bioimaging tests demonstrate that ZGGO:Cr nanoparticles can efficiently eliminate tissue autofluorescence, and the nanoparticles also show good promise in long-term bioimaging as they can be easily reactivated in vivo. Furthermore, an aptamer-guided ZGGO:Cr bioprobe is constructed, and it displays excellent tumor-specific accumulation. The ZGGO:Cr nanoparticles are ideal for autofluorescence-free targeted bioimaging, indicating their great potential in monitoring cellular networks and construction of guiding systems for surgery.

Visualization of Endoplasmic Reticulum Aminopeptidase 1 under Different Redox Conditions with a Two-Photon Fluorescent Probe

Endoplasmic reticulum aminopeptidase 1 (ERAP1), a metallopeptidase belonging to the M1 peptidase family, plays an important role in antigen processing in vivo. Additionally, many diseases are caused by ERAP1 perturbation. Thus, an efficient method for monitoring its content is extremely important for disease diagnosis and treatment. However, few fluorescent probes have been reported for efficiently monitoring ERAP1 in living cells and tissues. In this work, a two-photon fluorescent probe (SNCL) containing 1,8-naphthalimide (two-photon fluorophore), l-leucine (trigger moiety), and a methyl sulfonamide moiety (endoplasmic reticulum-targeting group) for imaging ERAP1 activity in living cells is reported for the first time. The optimized probe exhibited high sensitivity toward ERAP1, with about a 95-fold fluorescence enhancement at 550 nm. Herein, we monitored ERAP1 with SNCL by introducing interferon-γ to induce ERAP1 activity in living cells. The content of ERAP1 was dependent on the redox state of the endoplasmic reticulum, which was demonstrated by using SNCL to monitor the enzymatic activity of ERAP1 under different redox conditions. Excitingly, SNCL was also successfully applied for monitoring ERAP1 in tumor tissue with an imaging depth of 50-120 μm. In conclusion, SNCL not only can be used for the sensitive detection of endogenous ERAP1 in living cells and tumor tissues but also can serve as a potentially useful tool to reveal ERAP1-related diseases.

Selection and characterization of DNA aptamer for metastatic prostate cancer recognition and tissue imaging

Prostate cancer (PCa) is the second leading cause of death and most prevalent cancer in men. The absence of curative options for castration-resistant metastatic prostate cancer and biomarkers able to discriminate between indolent and aggressive tumors contribute to these statistics. In this study, a DNA aptamer termed DML-7 was successfully selected against human PCa cell line DU145 by using the cell-based systematic evolution of ligands by exponential enrichment (SELEX) method. The selected aptamer DML-7 was found to internalize into target cells in a temperature-dependent manner and exhibit high binding affinity for target cells with dissociation constants in the nanomolar range. Binding analysis further revealed that DML-7 only binds to DU145 and PC-3 cells with metastatic potential, but not to LNCaP or 22Rv1 cells with low or nonmetastatic potential, demonstrating that DML-7 has excellent selectivity for the recognition of the metastatic PCa cells. Clinical tissue imaging further confirmed these results. Therefore, both high binding affinity and specificity to metastatic PCa cells and tissues afford DML-7 with the potential for development into a novel tool for diagnosis and targeted drug delivery against metastatic prostate cancer.