Superior Catalytic Activity of Electrochemically Reduced Graphene Oxide Supported Iron Phthalocyanines toward Oxygen Reduction Reaction

Structure and surface properties of supporting materials are of great importance for the catalytic performance of the catalysts. Herein, we prepared the iron phthalocyanine (FePc) functionalized electrochemically reduced graphene oxide (ERGO) by the electrochemical reduction of FePc/GO. The resultant FePc/ERGO exhibits higher catalytic activity toward ORR than that of FePc/graphene. More importantly, the onset potential for ORR at FePc/ERGO positively shifts by 45 mV compared with commercial Pt/C in alkaline media. Besides, FePc/ERGO displays enhanced durability and selectivity toward ORR. The superior catalytic performance of FePc/ERGO for ORR are ascribed to the self-supported structure of ERGO, uniformly morphology and size of FePc nanoparticles

Selective and Sensitive Detection of Methylcytosine by Aerolysin Nanopore under Serum Condition

Detection of DNA methylation in real human serum is of great importance to push the development of clinical research and early diagnosis of human diseases. Herein, taking advantage of stable pore structure of aerolysin in a harsh environment, we distinguish methylated cytosine from cytosine using aerolysin nanopore in human serum. Since wild-type (WT) aerolysin enables high sensitivity detection of DNA, the subtle difference between methylated cytosine and cytosine could be measured directly without any specific designs. Methylated cytosine induced a population of <i>I</i>/<i>I</i>₀ = 0.53 while cytosine was focused on <i>I</i>/<i>I</i>₀ = 0.56. The dwell time of methylated cytosine (5.3 ± 0.1 ms) was much longer than that of cytosine (3.9 ± 0.1 ms), which improves the accuracy for the discrimination of the two oligomers. Moreover, the pore-membrane system could remain stable for more than 2 h and achieve the detection of methylated cytosine with zero-background signal in the presence of serum. Additionally, event frequency of methylated cytosine is in correspondence with the relative concentration and facilitate the quantification of methylation

Alcohol Dehydrogenase-Catalyzed Gold Nanoparticle Seed-Mediated Growth Allows Reliable Detection of Disease Biomarkers with the Naked Eye

Here, we reported a strategy-based plasmonic enzyme-linked immunosorbent assay (ELISA) using alcohol dehydrogenase-catalyzed gold nanoparticle seed-mediated growth to serve as a colorimetric signal generation method for detecting disease biomarkers with the naked eye. This system possesses the advantages of outstanding robustness, sensitivity, and universality. By using this strategy, we investigated the hepatitis B surface antigen (HBsAg) and α-fetoprotein (AFP) with the lowest concentration of naked-eye detection down to 1.0 × 10^–12 g mL^–1. Experiments with real serum samples from HBsAg-infected patients are presented, demonstrating the potential for clinical analysis. Our method eliminates the need for sophisticated instruments and high detection expenses, making it possible to be a reliable alternative in resource-constrained regions

Investigation of Silver Nanoparticle Induced Lipids Changes on a Single Cell Surface by Time-of-Flight Secondary Ion Mass Spectrometry

Lipids are the main component of the cell membrane. They not only provide structural support of cells but also directly participate in complex cellular metabolic processes. Lipid signaling is an important part of cell signaling. Evidence showed that abnormal cellular metabolism may induce lipids changes. Besides, owing to single cell heterogeneity, it is necessary to distinguish different behaviors of individual cells. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a sensitive surface analysis technique with high spatial resolution, which is useful in single cell surface analysis. Herein, we used ToF-SIMS to investigate silver nanoparticle induced lipids changes on the surface of single macrophage cells. Delayed extraction mode of ToF-SIMS was used to simultaneously obtain high mass resolution of mass spectra and high spatial resolution of single cell chemical imaging. Principle component analysis (PCA) results showed good agreement with the cytotoxicity assay results. Clear distinctions were observed between the cell groups treated with high or low dose of silver nanoparticles. The loadings plots revealed that the separation was mainly due to changes of cholesterol and diacylglycerol (DAG) as well as monoacylglycerol (MAG). Meanwhile, the chemical mapping of single cell components showed that cholesterol and DAG tend to migrate to the surrounding of the cells after high dose silver nanoparticles (Ag NPs) treatment. Our results demonstrated the feasibility of ToF-SIMS for characterizing the changes of the lipids on a single cell surface, providing a better understanding of the mechanism of cell–nanoparticle interactions at the molecular level

Binary System for MicroRNA-Targeted Imaging in Single Cells and Photothermal Cancer Therapy

Abnormal expression of microRNAs (miRNAs) is often associated with tumorigenesis, metastasis, and progression. Among them, miRNA-21 is found to be overexpressed in most of the cancer cells. Here, a binary system is designed for miRNA-21 targeted imaging and photothermal treatment in single cells. The binary system is composed by a pair of probes (probe-1 and probe-2), which are encapsulated in liposomes for cell delivery. Both of the two probes adopt gold nanoparticles (AuNPs) as the core material, and the AuNPs are functionalized with Cy5-marked molecular beacon (MB-1/MB-2 for probe-1/probe-2, respectively). The loop part of MBs are designed to be complementary with miRNA-21. Therefore, after the binary system enters into the cytoplasm, MBs can be opened upon miRNA-21 triggered hybridization, which turns “on” the fluorescence of Cy5 for the localization of miRNA-21. At the same time, a cross-linking between the probes occurs since the far ends of MB-1 and MB-2 are designed to be complementary with each other. The miRNA-induced aggregation shifts the absorption of AuNPs to near-infrared, which can be observed under dark-field microscopy (DFM) and used for the following photothermal therapy. Under near-infrared (NIR) irradiation, MCF-7 breast cancer cells are successfully killed. The proposed system can be further applied in tumor-bearing mice and shows significant therapeutic effect. This work provides a new tool for intracellular miRNA analysis and targeted treatment against cancer

Monitoring Dopamine Quinone-Induced Dopaminergic Neurotoxicity Using Dopamine Functionalized Quantum Dots

Dopamine (DA) quinone-induced dopaminergic neurotoxicity is known to occur due to the interaction between DA quinone and cysteine (Cys) residue, and it may play an important a role in pathological processes associated with neurodegeneration. In this study, we monitored the interaction process of DA to form DA quinone and the subsequent Cys residue using dopamine functionalized quantum dots (QDs). The fluorescence (FL) of the QD bioconjugates changes as a function of the structure transformation during the interaction process, providing a potential FL tool for monitoring dopaminergic neurotoxicity

Redox-Mediated Indirect Fluorescence Immunoassay for the Detection of Disease Biomarkers Using Dopamine-Functionalized Quantum Dots

Here, we report a redox-mediated indirect fluorescence immunoassay (RMFIA) for the detection of the disease biomarker α-fetoprotein (AFP) using dopamine (DA)-functionalized CdSe/ZnS quantum dots (QDs). In this immunoassay, tyrosinase was conjugated with the detection antibody and acted as a bridge connecting the fluorescence signals of the QDs with the concentration of the disease biomarkers. The tyrosinase label used for RMFIA catalyzed the enzymatic oxidation of DAs on the surface of functionalized QDs and caused fluorescence quenching in the presence of the analyte. Using this technique, we obtained a limit of detection as low as 10 pM for AFP. This assay’s potential for clinical analysis was demonstrated by detecting the real sera of patients with hepatocellular carcinoma (HCC). This study makes the first use of RMFIA for the rapid detection of AFP, opening up a new pathway for the detection of disease biomarkers

Enhanced Resolution of Low Molecular Weight Poly(Ethylene Glycol) in Nanopore Analysis

A design with conjugation of DNA hairpin structure to the poly­(ethylene glycol) molecule was presented to enhance the temporal resolution of low molecular weight poly­(ethylene glycol) in nanopore studies. By the virtue of this design, detection of an individual PEG with molecular weight as low as 140 Da was achieved at the single-molecule level in solution, which provides a novel strategy for characterization of an individual small molecule within a nanopore. Furthermore, we found that the current duration time of poly­(ethylene glycol) was scaled with the relative molecular weight, which has a potential application in single-molecule detection

Accurate Data Process for Nanopore Analysis

Data analysis for nanopore experiments remains a fundamental and technological challenge because of the large data volume, the presence of unavoidable noise, and the filtering effect. Here, we present an accurate and robust data process that recognizes the current blockades and enables evaluation of the dwell time and current amplitude through a novel second-order-differential-based calibration method and an integration method, respectively. We applied the developed data process to analyze both generated blockages and experimental data. Compared to the results obtained using the conventional method, those obtained using the new method provided a significant increase in the accuracy of nanopore measurements

Single Ag Nanoparticle Electro-oxidation: Potential-Dependent Current Traces and Potential-Independent Electron Transfer Kinetic

Potential-dependent current traces were first observed for the same sized nanoparticles (NPs) during the dynamic electro-oxidation process of single AgNPs. In this work, we demonstrated that the motion trajectories of NPs, coupled with electrochemical kinetics parameters, qualitatively predicted from the series of the experimentally observed current traces obtained single AgNPs collision behaviors. Based on the Poisson–Boltzmann equation for a general electrochemical reaction, a rate constant of Ag oxidation could be further estimated to be 1 × 10^–6 mol·cm^–2·s^–1 for electron transfer between AgNPs and the Au electrode by comparing the experimental results. Our method provided a meaningful attempt to test electron transfer kinetics and motion behaviors of single NPs using the high-resolution electrochemical signal