Search

Background: In recent years, electrochemical sensors are widely preferred because of their high sensitivity, rapid response, low cost and easy miniaturization. Covalent organic frameworks (COFs), a porous crystalline polymer formed by organic units connected by covalent bonds, have been widely used in gas adsorption and separation, drug transportation, energy storage, photoelectric catalysis, electrochemistry and other aspects due to their large specific surface, excellent stability, high inherent porosity, good crystallinity as well as structural and functional controllability. The topological structure of COFs can be designed in advance, the structural units and linkage are diversified, and the structure is easy to be functionalized, which are all beneficial to their application in electrochemical sensors. Methods: The types, synthesis methods, properties of covalent organic frameworks and some examples of using covalent organic frameworks in electrochemical sensors are reviewed. Results: Due to their characteristics of a large specific surface, high porosity, orderly channel and periodically arranged π electron cloud, COFs are often used to immobilize metal nanoparticles, aptamers or other materials to achieve the purpose of building electrochemical sensors with high sensitivity and good stability. Since the structure of COFs can be predicted, different organic units can build COFs with different structures and properties. Therefore, organic units with certain functional groups can be selected to build COFs with certain properties and used directly for electrochemical sensors. Conclusion: COFs have a good application prospect in electrochemical sensors.

Herein, PPy@MnO2 nanocomposites were first harvested by anchoring MnO2 nanosheets on polypyrrole (PPy) nanoparticles via an in situ redox reaction, then polyethylene glycol (PEG) modifier and methylene blue (MB) photosensitizer were linked through electrostatic interactions to obtain PPy@MnO2-PEG-MB nanoarchitectures. PPy nanoparticles ensure photothermal therapy (PTT) ability and MnO2 nanosheets ameliorate tumor hypoxia for enhanced photodynamic therapy (PDT). Therefore, a multifunctional nanotherapeutic system was constructed for the combined PTT/PDT of tumors. For extracellular photothermal properties, the optimal temperature elevation was 52.6 °C with 54.4% photothermal conversion efficiency. The extracellular PDT ability was measured by detecting 1O2 generation; more 1O2 was produced under acidic conditions in the presence of H2O2 (a simulated tumor microenvironment). The effective cellular uptake of the nanotherapeutic system in HeLa cells was observed by confocal laser scanning microscopy (CLSM). CLSM also indicated that more 1O2 was generated by the nanotherapeutic system as compared to free MB in HeLa cells, confirming the amelioration of tumor hypoxia by MnO2 nanosheets. MTT assays demonstrated that the nanotherapeutic system possessed superior biocompatibility without laser irradiation, and the lowest cell viabilities for single PTT and PDT groups were 13.78%, 38.82% respectively, while there was only 1.29% cell viability in the combined PTT and PDT group. These results suggest that the strategy of assembling PPy with MnO2 for a multifunctional PTT and enhanced PDT nanoplatform was realized, and opens up an unimpeded approach for integrating photothermal reduction materials with MnO2 for use in synergistic PTT and PDT.

β-Cyclodextrin modified graphene oxide–magnetic (MGC) nanocomposite as an innovative drug carrier was the first to be developed via an effective layer-by-layer-assembly method. Doxorubicin hydrochloride (DOX) and epirubicin hydrochloride (EPI) as model drugs were loaded onto the MGC via π–π stacking, hydrogen bonding and hydrophobic interactions. The MGC exhibits remarkably higher loading capacity for DOX (909.09 mg g−1) and EPI (781.25 mg g−1) than magnetic graphene oxide (MG). The release profiles of the drugs are pH-sensitive which would control the release in the acidic cytoplasm of cancer cells. Furthermore, cellular uptake using fluorescein isothiocyanate (FITC) labeled MGC proves successful internalization of MGC into the cytoplasm of MCF-7 cells. The fluorescence images demonstrate that MGC/DOX, to a certain extent, displays a more excellent delivery and superior release than MGC/EPI, due to the chiral selective function of β-cyclodextrin (β-CD). The pure MGC shows no obvious cytotoxicity while drug loaded MGC reveals significantly high potency for killing MCF-7 breast cancer cells, suggesting that multi-functionalized MGC is an efficient nanoplatform for targeted delivery and controlled release of stereoisomeric anticancer drugs for biomedical applications.