Zhihe Qing

Activatable aptamer probe for contrast-enhanced in vivo cancer imaging based on cell membrane protein-triggered conformation alteration

Aptamers have emerged as promising molecular probes for in vivo cancer imaging, but the reported “always-on” aptamer probes remain problematic because of high background and limited contrast. To address this problem, we designed an activatable aptamer probe (AAP) targeting membrane proteins of living cancer cells and achieved contrast-enhanced cancer visualization inside mice. The AAP displayed a quenched fluorescence in its free state and underwent a conformational alteration upon binding to target cancer cells with an activated fluorescence. As proof of concept, in vitro analysis and in vivo imaging of CCRF-CEM cancer cells were performed by using the specific aptamer, sgc8, as a demonstration. It was confirmed that the AAP could be specifically activated by target cancer cells with a dramatic fluorescence enhancement and exhibit improved sensitivity for CCRF-CEM cell analysis with the cell number of 118 detected in 200 μl binding buffer. In vivo studies demonstrated that activated fluorescence signals were obviously achieved in the CCRF-CEM tumor sites in mice. Compared to always-on aptamer probes, the AAP could substantially minimize the background signal originating from nontarget tissues, thus resulting in significantly enhanced image contrast and shortened diagnosis time to 15 min. Furthermore, because of the specific affinity of sgc8 to target cancer cells, the AAP also showed desirable specificity in differentiating CCRF-CEM tumors from Ramos tumors and nontumor areas. The design concept can be widely adapted to other cancer cell-specific aptamer probes for in vivo molecular imaging of cancer.

Concatemeric dsDNA-templated copper nanoparticles strategy with improved sensitivity and stability based on rolling circle replication and its application in microRNA detection.

DNA-templated copper nanoparticles (CuNPs) have emerged as promising fluorescent probes for biochemical assays, but the reported monomeric CuNPs remain problematic because of weak fluorescence and poor stability. To solve this problem, a novel concatemeric dsDNA-templated CuNPs (dsDNA-CuNPs) strategy was proposed by introducing the rolling circle replication (RCR) technique into CuNPs synthesis. In this strategy, a short oligonucleotide primer could trigger RCR and be further converted to a long concatemeric dsDNA scaffold through hybridization. After the addition of copper ions and ascorbate, concatemeric dsDNA-CuNPs could effectively form and emit intense fluorescence in the range of 500-650 nm under a 340 nm excitation. In comparison with monomeric dsDNA-CuNPs, the sensitivity of concatemeric dsDNA-CuNPs was greatly improved with ~10,000 folds amplification. And their fluorescence signal was detected to reserve ~60% at 2.5 h after formation, revealing ~2 times enhanced stability. On the basis of these advantages, microRNA let-7d was selected as the model target to testify this strategy as a versatile assay platform. By directly using let-7d as the primer in RCR, the simple, low-cost, and selective microRNA detection was successfully achieved with a good linearity between 10 and 400 pM and a detection limit of 10 pM. The concatemeric dsDNA-CuNPs strategy might be widely adapted to various analytes that can directly or indirectly induce RCR.

Poly(Thymine)-Templated Fluorescent Copper Nanoparticles for Ultrasensitive Label-Free Nuclease Assay and Its Inhibitors Screening

Noble-metal fluorescent nanoparticles have attracted considerable interest on account of their excellent properties and potential applicable importance in many fields. Particularly, we recently found that poly(thymine) (poly T) could template the formation of fluorescent copper nanoparticles (CuNPs), offering admirable potential as novel functional biochemical probes. However, exploration of poly T-templated CuNPs for application is still at a very early stage. We report herein for the first example to develop a novel ultrasensitive label-free method for the nuclease (S1 nuclease as a model system) assay, and its inhibitors screening using the poly T-templated fluorescent CuNPs. In this assay, the signal reporter of poly T of 30 mer (T30) kept the original long state in the absence of nuclease, which could effectively template the formation of fluorescent CuNPs. In the presence of nuclease, poly T was digested to mono- or oligonucleotide fragments with decrease of fluorescence. The proposed method was low-cost and simple in its operation without requirement for complex labeling of probe DNA or sophisticated synthesis of the fluorescent compound. The assay process was very rapid with only 5 min for the formation of fluorescent CuNPs. The capabilities for target detection from complex fluids and screening of nuclease inhibitors were verified. A high sensitivity exhibited with a detectable minimum concentration of 5 × 10(-7) units μL(-1) S1 nuclease, which was about 1-4 orders of magnitude more sensitive than the developed approaches.

Natural Gelatin Capped Mesoporous Silica Nanoparticles for Intracellular Acid-Triggered Drug Delivery

This paper proposed a natural gelatin capped mesoporous silica nanoparticles (MSN@Gelatin) based pH-responsive delivery system for intracellular anticancer drug controlled release. In this system, the gelatin, a proteinaceous biopolymer derived from the processing of animal collagen, was grafted onto the MSN to form a capping layer via temperature-induced gelation and subsequent glutaraldehyde mediated cross-linking, resulting in gelatin coated MSN. At neutral pH, the gelatin capping layer could effectively prohibit the release of loaded drug molecules. However, the slightly acidic environment would lead to enhanced electrostatic repulsion between the gelatin and MSN, giving rise to uncapping and the subsequent controlled release of the entrapped drug. As a proof-of-concept, doxorubicin (DOX) was selected as the model anticancer drug. The loading and pH-responsive release experiments demonstrated that the system had excellent loading efficiency (47.3 mmol g(-1) SiO2), and almost no DOX was leaked at neutral. After being in the slightly acidic condition, the DOX release from the DOX-loaded MSN@Gelatin (DOX/MSN@Gelatin) occurred immediately. The cellular uptake and release studies using Hep-G2 hepatoma cells indicated that the DOX/MSN@Gelatin could be endocytosed and accumulated within lysosomes. Triggered by acidic endosomal pH, the intracellular release of the loaded DOX was obviously eventuated. Further cell viability results demonstrated that DOX/MSN@Gelatin exhibited dose-dependent toxicity and high killing efficacy (IC50 = 17.27 ± 0.63 μg mL(-1)), whereas the MSN@Gelatin showed negligible cytotoxicity (IC50 > 100 μg mL(-1)). This biocompatible and effective delivery system will provide great potential for developing delivery of cancer therapeutic agents.

Poly(thymine)-Templated Copper Nanoparticles as a Fluorescent Indicator for Hydrogen Peroxide and Oxidase-Based Biosensing

Biomineralized fluorescent metal nanoparticles have attracted considerable interest in many fields by virtue of their excellent properties in synthesis and application. Poly(thymine)-templated fluorescent copper nanoparticles (T-CuNPs) as a promising nanomaterial has been exploited by us recently and displays great potential for signal transducing in biochemical analysis. However, the application of T-CuNPs is rare and still at an early stage. Here, a new fluorescent analytical strategy has been developed for H2O2 and oxidase-based biosensing by exploiting T-CuNPs as an effective signal indicator. The mechanism is mainly based on the poly(thymine) length-dependent formation of T-CuNPs and the probes oxidative cleavage. In this assay, the probe T40 can effectively template the formation of T-CuNPs by a fast in situ manner in the absence of H2O2, with high fluorescent signal, while the probe is cleaved into short-oligonucleotide fragments by hydroxyl radical (·OH) which is formed from the Fenton reaction in the presence of H2O2, leading to the decline of fluorescence intensity. By taking advantage of H2O2 as a mediator, this strategy is further exploited for oxidase-based biosensing. As the proof-of-concept, glucose in human serum has been chosen as the model system and has been detected, and its practical applicability has been investigated by assay of real clinical blood samples. Results demonstrate that the proposed strategy has not only good detection capability but also eminent detection performance, such as simplicity and low-cost, holding great potential for constructing effective sensors for biochemical and clinical applications.

Target-Catalyzed Dynamic Assembly-Based Pyrene Excimer Switching for Enzyme-Free Nucleic Acid Amplified Detection

Because of the intrinsic importance of nucleic acid as biotargets, the simple and sensitive detection of nucleic acid is very essential for biological studies and medical diagnostics. Herein, a new strategy for enzyme-free nucleic acid amplified detection has been opened up by combining the signal-amplification capability of target-catalyzed dynamic assembly with the spatially sensitive fluorescent signal of the pyrene excimer. In this strategy, three metastable pyrene-labeled hairpin DNA probes were designed as assembly components, which were kinetically handicapped from cross-opening in the absence of the target DNA. However, in the presence of the target, the dynamic assembly of branched junctions was circularly catalyzed and accompanied by the switching of the pyrene excimer which emits at ~488 nm. Thus, the target DNA could be detected by this simple mix-and-detect amplification method, without expensive and perishable protein enzymes. A good detection capability exhibited with a detectable minimum target concentration of 10 pM, which was comparable to or even better than some reported enzyme-dependent amplification methods, and the potential for the target detection from complex fluids was verified. In addition, as a novel transformation of dynamic DNA assembly technology into enzyme-free signal-amplification analytical application, we infer that the proposed strategy will hold promising potential for application in a wider range of fields, including aptamer-based non-nucleic acid target sensing, biomedicine, and bioimaging.

Visual and portable strategy for copper(II) detection based on a striplike poly(thymine)-caged and microwell-printed hydrogel.

Due to its importance to develop strategies for copper(II) (Cu(2+)) detection, we here report a visual and portable strategy for Cu(2+) detection based on designing and using a strip-like hydrogel. The hydrogel is functionalized through caging poly(thymine) as probes, which can effectively template the formation of fluorescent copper nanoparticles (CuNPs) in the presence of the reductant (ascorbate) and Cu(2+). On the hydrogels surface, uniform wells of microliter volume (microwells) are printed for sample-injection. When the injected sample is stained by Cu(2+), fluorescent CuNPs will be in situ templated by poly T in the hydrogel. With ultraviolet (UV) irradiation, the red fluorescence of CuNPs can be observed by naked-eye and recorded by a common camera without complicated instruments. Thus, the strategy integrates sample-injection, reaction and indication with fast signal response, providing an add-and-read manner for visual and portable detection of Cu(2+), as well as a strip-like strategy. Detection ability with a detectable minimum concentration of 20 μM and practically applicable properties have been demonstrated, such as resistance to environmental interference and good constancy, indicating that the strategy holds great potential and significance for popular detection of Cu(2+), especially in remote regions. We believe that the strip-like hydrogel-based methodology is also applicable to other targets by virtue of altering probes.

Programmed packaging of mesoporous silica nanocarriers for matrix metalloprotease 2-triggered tumor targeting and release

The development of multifunctional nanocarrier with each unit functioning at the correct time and location is a challenge for clinical applications. With this in mind, a type of intelligent mesoporous silica nanocarrier (PGFMSN) is proposed for matrix metalloprotease 2 (MMP 2)-triggered tumor targeting and release by integrating programmed packing and MMP 2-degradable gelatin. Mesoporous silica nanoparticles (MSN) are first functionalized with folic acid (FA) as a target ligand to improve cell uptake. Then gelatin is introduced onto FA-MSN via temperature-induced gelation, where gelatin layer blocks drugs inside the mesopores and protects the targeting ligand. To prolong blood-circulation lifetime, PEG is further decorated to obtain PGFMSN. All units are programmatically incorporated in a simple way and coordinated in an optimal fashion. Cells, multicellular spheroids and in vivo results demonstrate that PGFMSN is shielded against nonspecific uptake. After circulating to tumor tissue, the up-regulated MMP-2 hydrolyzes gelatin layer to deshield PEG and switch on the function of FA, which facilitate the selective uptake by tumor cells through folate-receptor-mediated endocytosis. Meanwhile, the packaged drug is released due to the shedding of gelatin layer. It is shown that doxorubicin (DOX)-loaded exhibits superior tumor targeting, drug internalization, cytotoxicity, and antitumor efficacy over free DOX, non-PEGylated and non-targeted nanoparticles, which provides potential applications for targeted cancer therapy.

In situ formation of fluorescent copper nanoparticles for ultrafast zero-background Cu2+ detection and its toxicides screening

Copper pollution has become more and more serious in modern society as the increasing industrial emission and the acid mine drainage, and exposure to excess copper can result in damage to living organisms. Thus, the development of efficient strategy for copper ion (Cu(2+)) detection is very essential and significant. Here, a high-efficiency fluorescent method is proposed for Cu(2+) monitoring. The detection mechanism is based on the in situ formation of fluorescent copper nanoparticles (CuNPs). When the water sample is polluted by Cu(2+), fluorescence emission of CuNPs can be observed by a one-step manner, and the emission intensity is proportional to Cu(2+) concentration. Attractively, besides its advantages in operation and good detection capability, the generation of fluorescent signal is ultrafast, with a good signal response in 1 min; and there is no interference from background and other ions due to the in situ formation of signal unit. By virtue of its advantages, this strategy has been used to detect Cu(2+) from polluted tap and river water samples, good performances demonstrate that the proposed method can be practically applied for Cu(2+) monitoring in real drinking and environmental water. Simultaneously, great potential for Cu(2+) toxicides screening has been verified by direct analysis of the effects of different model molecules on Cu(2+), which will contribute to Cu(2+)-related sewage treatment and medical therapy.

Target-Activated Modulation of Dual-Color and Two-Photon Fluorescence of Graphene Quantum Dots for in Vivo Imaging of Hydrogen Peroxide

The development of nanoprobes suitable for two-photon microscopy techniques is highly desirable for mapping biological species in living systems. However, at the current stage, the nanoprobes are restricted to single-color fluorescence changes, making it unsuitable for quantitative detection. To circumvent this problem, we report here a rational design of a dual-emission and two-photon (TP) graphene quantum dot (GQD(420)) probe for imaging of hydrogen peroxide (H2O2). For specific recognition of H2O2 and lighting the fluorescence of TPGQD(420), a boronate ester-functionalized merocyanine (BMC) fluorophore was used as both target-activated trigger and the dual-emission fluorescence modulator. Upon two-photon excitation at 740 nm, TPGQD(420)-BMC displays a green-to-blue resolved emission band in response to H2O2 with an emission shift of 110 nm, and the H2O2 can be determined from 0.2 to 40 μM with a detection limit of 0.05 μM. Moreover, the fluorescence response of the TPGQD(420)-BMC toward H2O2 is rapid and extremely specific. The feasibility of the proposed method is demonstrated by two-photon ratiometrically mapping the production of endogenous H2O2 in living cells as well as in deep tissues of murine mode at 0-600 μm. To the best of our knowledge, this is the first paradigm to rationally design a dual-emission and two-photon nanoprobe via fluorescence modulation of GQDs with switchable molecules, which will extend new possibility to design powerful molecular tools for in vivo bioimaging applications.