Azoreductase-Responsive Nanoprobe for Hypoxia-Induced Mitophagy Imaging.

Mitophagy, as a crucial metabolic process, plays an essential role in maintaining cellular and tissue homeostasis. Various stresses especially hypoxia could improve intracellular reactive oxygen species (ROS) level to induce mitophagy. However, high-specific fluorescence imaging of mitophagy in living cells under hypoxia is still a challenge. Based on this, we report an azoreductase-responsive nanoprobe (termed Micelle@Mito-rHP@TATp, MCM@TATp) by encapsulating cationic spiropyrane derivative (Mito-rHP) to realize specific imaging of mitophagy in living cells under hypoxia. An azoreductase-responsive amphiphilic polymer, 1,2-distearoyl- sn-glycero-3-phosphoethanolamine-azo- N-[maleimide(polyethylene glycol-2000) (Mal-PEG2000-Azo-DSPE), was first self-assembled into a micelle in aqueous solution. Meanwhile, the synthetic Mito-rHP encapsulated into this formed micelle to construct MCM. By modifying the surface of MCM with cell-penetrating peptide (TATp) to form MCM@TATp, the nanoprobe could avoid endolysosomal trapping. Under hypoxic conditions, the azobenzene moiety-contained MCM@TATp would be disrupted by the highly expressed azoreductase, then the encapsulated Mito-rHP would be released. Since Mito-rHP is a mitochondria-targeted and pH-sensitive probe, thus it could target into mitochondria and displayed a desirable "off-on" fluorescence response to mitophagy during which mitochondria were regarded to undergo acidification. The results indicated that the MCM@TATp in our design could image mitophagy under hypoxia in high-specificity. As further application, we have also demonstrated that this MCM@TATp can perform well to realize mitophagy imaging under the photodynamic therapy (PDT) which can induce hypoxia in treatment of cancer. We expect this new strategy would be a powerful tool for hypoxia-related fundamental and clinical research.

Azoreductase and Target Simultaneously Activated Fluorescent Monitoring for Cytochrome c Release under Hypoxia.

Hypoxia-induced cell apoptosis is closely related to degenerative diseases, autoimmune disorders, and tumor disease. In the process of apoptosis, the release of cytochrome c (Cyt c) is deemed to be a critical factor of the intrinsic pathway. Strategies for tracking Cyt c release in living cells based on the subcellular localization have been proposed recently. However, they are inherently lack of specificity for distinguishing the release of Cyt c in apoptotic process induced by hypoxia from other stimulus. In this paper, an azoreductase and target simultaneously activated fluorescent aptameric nanosensor integrating gold nanoparticles (AuNPs) and Cyt c-targeted aptamer-consisted double-stranded DNA hybridization complex (DSDHC) was proposed. It is worth noting that the employment of azobenzene moiety labeled on the DSDHC first ensured the aptameric nanosensor could be conjugated to the surface of AuNPs and then specifically reduced by hypoxia-related azoreductase. Upon Cyt c released from mitochondrion under hypoxia, the competitive displacement of Cyt c subsequently activated the fluorescence of the aptameric nanosensor and the fluorescence enhancement depended principally on the content of Cyt c release. Inspired by this, a new strategy for quantitative analysis and in situ imaging of Cyt c under hypoxic condition was proposed. The high spatial resolution monitoring of the dynamics of Cyt c release under hypoxia will offer a potentially rich opportunity to understand the apoptotic mechanism under hypoxic conditions, thus further facilitating risk assessment and risk reduction for hypoxic environments.

Quantitative detection of exosomal microRNA extracted from human blood based on surface-enhanced Raman scattering.

Since the nature of the exosomal lipid bilayer can allow miRNAs to be protected from degradation by cellular RNAses in body fluids, exosomal microRNA (miRNA) has become an ideal source of non-invasive biomarkers for the early diagnosis and prognosis. In this paper, a new surface-enhanced Raman scattering (SERS) analysis strategy combining stable SERS reporter element and duplex-specific nuclease (DSN)-assisted signal amplification for quantitative detection of exosomal miRNA extracted from human blood is proposed. Firstly, we prepared SERS signal reporter of Au@R6G@AgAu nanoparticles (R6G attachment on the gold nanoparticles, then encapsulated in AgAu alloy shell nanoparticles named as ARANPs) with an inter small nanogap to generate stable SERS signal. Then, ARANPs and separating substrate of silicon microbead (SiMB) were then covalently attached to the 3'- and 5'- end of capture probe (CP) targeting exosomal miRNA. Upon target miRNA binding, DNA in heteroduplexes could be specifically cleaved by DSN and resulted in the release of ARANPs from the surface of SiMB. Meanwhile, target miRNA remained intact and subsequently involved in the next round of target-recycling amplification. The combination of stable SERS intensity and signal amplification significantly improved the sensitivity of the sensing systems, resulting in detection limits of 5 fM. More importantly, this method also could be used for the detection of exosomal miRNAs extracted from the blood collected from patients of recurrence in non-small-cell lung cancer (NSCLC), with a detection of 5.0µL of sample volume, which has potential for point-of-care testing (POCT) in clinical analysis.

Noninvasive and Highly Selective Monitoring of Intracellular Glucose via a Two-Step Recognition-Based Nanokit.

Accurate determination of intracellular glucose is very important for exploring its chemical and biological functions in metabolism events of living cells. In this paper, we developed a new noninvasive and highly selective nanokit for intracellular glucose monitoring via two-step recognition. The liposome-based nanokit coencapsulated the aptamer-functionalized gold nanoparticles (AuNPs) and the Shinkai's receptor together. When the proposed nanokit was transfected into living cells, the Shinkai's receptor could recognize glucose first and then changed its conformation to endow aptamers with binding and sensing properties which were not readily accessible otherwise. Then, the binary complexes formed by the intracellular glucose and the Shinkai's receptor can in situ displace the complementary oligonucleotide of the aptamer on the surface of AuNPs. The fluorophore-labeled aptamer was away from the AuNPs, and the fluorescent state switched from "off" to "on". Through the secondary identification of aptamer, the selectivity of the Shinkai's receptor could be greatly improved while the intracellular glucose level was assessed by fluorescence signal recovery of aptamer. In the follow-up application, the approach exhibits excellent selectivity and is noninvasive for intracellular glucose monitoring under normoxia and hypoxia. To the best of our knowledge, this is the first time that the advantages of organic receptors and nucleic acids have been combined and highly selective monitoring of intracellular glucose has been realized via two-step recognition. We expect it to open up new possibilities to integrate devices for diagnosis of various metabolic diseases and insulin delivery.

Programmable DNA triple-helix molecular switch in biosensing applications: from in homogenous solutions to in living cells.

Herein, we demonstrated a new gold nanoparticles (AuNPs)-integrated programmable triple-helix molecular switch (THMS) to realize the biosensing of multiple targets from in homogenous solution to in living cells. The results demonstrated that this proposed programmable THMS could be successfully used for imaging multiple messenger RNA (mRNA) in living cells and it significantly extends the scope of the THMS sensing platform.