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Covalent organic frameworks (COFs), as one of the most significant members of the porous organic frameworks, have been well used in the photocatalysis owing to their outspread π-conjugated framework, high crystallinity and regular pore structure. Herein, after reducing the labile imine-linked COF-300 to the more stable amine-linked COF-300-AR, we for the first time demonstrated that COF-300-AR was the light-responsive oxidase mimic. COF-300-AR exhibited excellent oxidase-mimicking activity under purple light stimulation (λ = 400 nm), which can catalyze the oxidation of classical substrates such as 3,3',5,5'-tetramethylbenzydine (TMB) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) by the formation of •OH and O2•- free radicals in the presence of dissolved oxygen. The COF-300-AR oxidase mimic has outstanding advantages of easy light control, high stability, good reusability, and highly catalytic oxidation capacity and has been applied to detect glutathione (GSH) levels in HL60 cells with good selectivity and high sensitivity. This study will broaden the sensing applications of COFs and offer a promising build block for the construction of artificial enzymes.

An ingenious and viable method for preparing heterogeneous Co3O4 dodecahedrons that contain carbon and encapsulated Au nanoparticles (Au@C-Co3O4) was proposed via pyrolysis of Au nanoparticle-encapsulated zeolitic imidazolate framework-67 (Au@ZIF-67). The obtained Au@C-Co3O4 possessed hierarchically porous structure, abundant active sites, excellent conductivity, and durability, all of which can significantly improve the analysis performance of the biosensor. Meanwhile, the fabricated electrode based on the porous Au@C-Co3O4 showed remarkable electrocatalytic performance towards H2O2 with a limit of detection of 19 nM and ultra-high sensitivity of 7553 μA mM−1 cm−2, even when the Au content in the composite was as low as 0.85 wt%. This novel biosensor was successfully used to monitor H2O2 concentration released from living cells, and the results can be used to identify cancer cells, thus advancing the use of transition metal oxides in the field of biosensing.

β-Secretase (BACE1) is an important drug target in the treatment of Alzheimer's disease (AD). Therefore, sensitive detection of BACE1 is essential for AD treatment and drug discovery. In this work, a facile and sensitive fluorescence biosensing platform was developed for BACE1 detection. This sensing platform was constituted based on the interaction between a WS2 nanosheet and a peptide sequence. In the absence of BACE1, a FAM-labeled peptide substrate could be adsorbed on the surface of the WS2 nanosheet, thereby quenching its fluorescence. However, in the presence of BACE1, the hydrolysis of the peptide substrate by BACE1 triggers could occur with the subsequent release of short FAM-linked peptide fragments which could not be adsorbed on the surface of the WS2 nanosheet. This resulted in weak fluorescence quenching, thus restoring the fluorescence signal. By measuring the change in the fluorescence of the FAM-labeled peptide substrate, the fluorescence sensing platform based on the WS2 nanosheet could monitor BACE1. The proposed WS2 nanosheet-based platform exhibited excellent specificity and high sensitivity with a detection limit of 66 pM for BACE1. Importantly, we also demonstrated that this platform was suitable for the screening of BACE1 inhibitors. The proposed sensing platform not only provides a novel strategy for the BACE1 assay but also offers a potential tool for screening drugs.

In this work, we report a durable and sensitive H2O2 biosensor based on boronic acid functionalized metal-organic frameworks (denoted as MIL-100(Cr)-B) as an efficient immobilization matrix of horseradish peroxidase (HRP). MIL-100(Cr)-B features a hierarchical porous structure, extremely high surface area, and sufficient recognition sites, which can significantly increase HRP loading and prevent them from leakage and deactivation. The H2O2 biosensor can be easily achieved without any complex processing. Meanwhile, the immobilized HRP exhibited enhanced stability and remarkable catalytic activity towards H2O2 reduction. Under optimal conditions, the biosensor showed a fast response time (less than 4s) to H2O2 in a wide linear range of 0.5-3000μM with a low detection limit of 0.1μM, as well as good anti-interference ability and long-term storage stability. These excellent performances substantially enable the proposed biosensor to be used for the real-time detection of H2O2 released from living cells with satisfactory results, thus showing the potential application in the study of H2O2-involved dynamic pathological and physiological process.

Au nanoparticles (AuNPs) were electrodeposited onto glassy carbon electrode (GCE) and used as the scaffold to combine with l -cysteine (L-Cys) through Au S bonding, and polypyrrole (PPy) films templated with L-Cys were obtained by in situ polymerization of pyrrole (Py) on the L-Cys self-assembled monolayers. The L-Cys templates were removed via two successive steps: (a) electrooxidation of L-Cys templates to l -cysteic acid; (b) removal of l -cysteic acid through electrostatic repulsion between l -cysteic acid and overoxidized PPy (OPPy). The molecularly imprinted OPPy-AuNPs were applied for chiral electrochemical recognition of Cys enantiomers for the first time, and the recognition efficiency was superior to that at the molecularly imprinted OPPy. The enhanced recognition efficiency was attributed to the existence of AuNPs, which could adsorb L-Cys templates effectively and increase the number of recognition sites. Various important experimental factors influencing the performance of the molecularly imprinted OPPy-AuNPs were also investigated in the present work.

Mercaptosuccinic acid (MSA) molecules were inserted into potato starch, leading to the breaking of intrinsic H-bonds within macromolecular chains of starch and the formation of intermolecular H-bonds between MSA and starch, which could be verified by Fourier transform infrared spectroscopy (FT-TR). MSA modified porous starch xerogels (PSX/MSA) were obtained after freeze-drying the MSA modified starch, and they were characterized by field emission scanning electron microscopy (FESEM), exhibiting the intriguing porous structure due to the separation of starch chains by MSA molecules. The PSX/MSA were then used as the adsorbents to remove gardenia yellow (GY), a natural colorant with genotoxicity. Due to the porous structure of PSX and the introduced carboxyl groups from MSA, the adsorption capacity of the PSX/MSA was much higher than that of the starch xerogels alone (SX). The adsorption behaviors of GY by the PSX/MSA fitted both the Freundlich isotherm model and the pseudo-second-order kinetic model, and the efficient adsorption of GY suggested that the PSX/MSA might be potential adsorbents for the removal of dyes from contaminated aquatic systems.

Strong circular dichroism (CD) effect has gained great interest in nano-optical sensing and detection due to its desirable applications. In this work, we theoretically demonstrate that CD effects can be extremely enhanced in hybrid graphene–metal metamaterials at the near-infrared region. Benefiting from the strong coupling between graphene sheets and chiral metal nanocrystals, the maximum peak value of CD responses can be reached at 9.2% and the other peak value is more than twice as much as the without-graphene systems. When there is one more graphene layer covered on the chiral nanocrystals, the CD responses increase further. For single-layer graphene nanoribbons covered on the spacer, the CD response increases with the increasing filling ratio. The simulation results show that the CD response decreases rapidly with the increase of the distance between the chiral nanocrystals and the graphene sheet. Besides, with the increase of the thickness of the spacer, two CD resonance peaks, one increases faster and the other goes from decreasing to increasing compared with the without-graphene systems. Overall, we can greatly enhance CD effects in the near-infrared region by adding graphene layers, which can provide potential applications in the fields of biosensing and optoelectronic devices.

Plasmonic chirality has attracted a lot of interests because it could result in dramatically increased chiroptical interactions and offer many potential applications in chiral molecules analysis, catalysis, and other nanotechnology. In particular, one-handed chiral field is required in many applications for the reason that molecules are generally distributed randomly in some region of structures. In this work, benefiting from the coupling effect and energy focusing effect, we propose a heterodimer-film nanostructure to achieve one-handed chiral fields under linearly polarized light illumination. The results indicate that there are just opposite one-handed chiral fields in different gaps of the heterodimer-film nanostructure. The volume averaged optical chirality in the gaps can reach 102 and the optical chirality of hot spots can reach 103, which has potential applications in chiral sensing and Raman optical activity.