Cucurbituril and Azide Cofunctionalized Graphene Oxide for Ultrasensitive Electro-Click Biosensing

To achieve high selectivity and sensitivity simultaneously in an electrochemical biosensing platform, cucurbituril and azide cofunctionalized graphene oxide, a new functional nanomaterial that acts as a go-between to connect the recognition element with amplified signal architecture, is developed in this work. The cucurbituril and azide cofunctionalized graphene oxide features a high specific surface area with abundant levels of the two types of functional groups. Specifically, it emerges as a powerful tool to link recognition elements with simplicity, high yield, rapidity, and highly selective reactivity through azide-alkynyl click chemistry. Moreover, it possesses many host molecules to interact with guest molecules (also signal molecules)-grafted branched ethylene imine polymer, through which the detection sensitivity can be greatly improved. Together with electro-click technology, a highly controllable, selective, and sensitive biosensing platform can be easily created. For VEGF₁₆₅ protein detection, the electro-click assay has high selectivity and sensitivity; a dynamic detection range from 10 fg mL^–1 to 1 ng mL^–1 with a detection limit of 8 fg mL^–1 was achieved. The electro-click biosensing strategy based on cucurbituril and azide cofunctionalized graphene oxide would have great promise for other target analytes with a broad range of applications

An Improved Ultrasensitive Enzyme-Linked Immunosorbent Assay Using Hydrangea-Like Antibody–Enzyme–Inorganic Three-in-One Nanocomposites

Protein–inorganic nanoflowers, composed of protein and copper­(II) phosphate (Cu₃(PO₄)₂), have recently grabbed people’s attention. Because the synthetic method requires no organic solvent and because of the distinct hierarchical nanostructure, protein–inorganic nanoflowers display enhanced catalytic activity and stability and would be a promising tool in biocatalytical processes and biological and biomedical fields. In this work, we first coimmobilized the enzyme, antibody, and Cu₃(PO₄)₂ into a three-in-one hybrid protein–inorganic nanoflower to enable it to possess dual functions: (1) the antibody portion retains the ability to specifically capture the corresponding antigen; (2) the nanoflower has enhanced enzymatic activity and stability to produce an amplified signal. The prepared antibody–enzyme–inorganic nanoflower was first applied in an enzyme-linked immunosorbent assay to serve as a novel enzyme-labeled antibody for <i>Escherichia coli</i> O157:H7 (<i>E. coli</i> O157:H7) determination. The detection limit is 60 CFU L^–1, which is far superior to commercial ELISA systems. The three-in-one antibody (anti-<i>E. coli</i> O157:H7 antibody)–enzyme (horseradish peroxidase)–inorganic (Cu₃(PO₄)₂) nanoflower has some advantages over commercial enzyme–antibody conjugates. First, it is much easier to prepare and does not need any complex covalent modification. Second, it has fairly high capture capability and catalytic activity because it is presented as aggregates of abundant antibodies and enzymes. Third, it has enhanced enzymatic stability compared to the free form of enzyme due to the unique hierarchical nanostructure

Fe-Porphyrin-Based Covalent Organic Framework As a Novel Peroxidase Mimic for a One-Pot Glucose Colorimetric Assay

Covalent organic frameworks (COFs) have recently emerged as very fascinating porous polymers due to their attractive design synthesis and various applications. However, the catalytic application of COF materials as enzymatic mimics remains largely unexplored. In this work, the Fe-porphyrin-based covalent organic framework (Fe-COF) has been successfully synthesized through a facile postsynthetic strategy for the first time. In the presence of hydrogen peroxide (H₂O₂), the Fe-COF can catalyze a chromogenic substrate (3,3′,5,5′-tetramethylbenzidine (TMB)) to produce color, and this just goes to show that it has an inner peroxidase-like activity. Moreover, the kinetic studies indicate that the Fe-COF nanomaterial has a higher affinity toward both the substrate H₂O₂ and TMB than the natural enzyme, horseradish peroxidase (HRP). Under the optimized conditions, the Fe-COF nanomaterial was applied in a colorimetric sensor for the sensitive detection of H₂O₂. The detection range was from 7 to 500 μM, and the detection limit was 1.1 μM. Furthermore, the combination of the Fe-COF with glucose oxidase (GOx) can be implemented to measure glucose by a one-pot method, and the obtained detection range was from 5 to 350 μM; the detection limit was 1.0 μM. It was proved that the sensor can be successfully used to detect the concentration of glucose in human serum samples. As a peroxidase mimic, the Fe-COF exhibits the advantages of easy preparation, good stability, and ultrahigh catalytic efficiency. We believed that the proposed method in this work would facilitate the applications of COF-based composites as enzymatic mimics in biomedical fields

Aggregation of Individual Sensing Units for Signal Accumulation: Conversion of Liquid-Phase Colorimetric Assay into Enhanced Surface-Tethered Electrochemical Analysis

A novel concept is proposed for converting liquid-phase colorimetric assay into enhanced surface-tethered electrochemical analysis, which is based on the analyte-induced formation of a network architecture of metal nanoparticles (MNs). In a proof-of-concept trial, thymine-functionalized silver nanoparticle (Ag-T) is designed as the sensing unit for Hg²⁺ determination. Through a specific T-Hg²⁺-T coordination, the validation system based on functionalized sensing units not only can perform well in a colorimetric Hg²⁺ assay, but also can be developed into a more sensitive and stable electrochemical Hg²⁺ sensor. In electrochemical analysis, the simple principle of analyte-induced aggregation of MNs can be used as a dual signal amplification strategy for significantly improving the detection sensitivity. More importantly, those numerous and diverse colorimetric assays that rely on the target-induced aggregation of MNs can be augmented to satisfy the ambitious demands of sensitive analysis by converting them into electrochemical assays via this approach