DNA-Programmed Tuning of the Growth and Enzyme-Like Activity of a Bimetallic Nanozyme and Its Biosensing Applications.

Nanozymes, which combine the merits of both nanomaterials and natural enzymes, have aroused tremendous attention as new representatives of artificial enzyme mimics. However, it still remains to be a great challenge to rationally engineer the morphologies and surface properties of nanostructures that lead to the desired enzyme-like activities. Here, we report a DNA-programming seed-growth strategy to mediate the growth of platinum nanoparticles (PtNPs) on gold bipyramids (AuBPs) for the synthesis of a bimetallic nanozyme. We find that the preparation of a bimetallic nanozyme is in a sequence-dependent manner, and the encoding of a polyT sequence allows the successful formation of bimetallic nanohybrids with greatly enhanced peroxidase-like activity. We further observe that the morphologies and optical properties of T15-mediated Au/Pt nanostructures (Au/T15/Pt) change over the reaction time, and the nanozymatic activity can be tuned by controlling the experimental conditions. As a concept application, Au/T15/Pt nanozymes are used to establish a simple, sensitive, and selective colorimetric assay for the determination of ascorbic acid (AA), alkaline phosphatase (ALP), and the inhibitor sodium vanadate (Na3VO4), demonstrating excellent analytical performance. This work provides a new avenue for the rational design of bimetallic nanozymes for biosensing applications.

"Three-in-one" nanocomposites as multifunctional nanozymes for ultrasensitive ratiometric fluorescence detection of alkaline phosphatase.

Nanozymes, as a unique class of nanomaterials with enzyme-like properties, have attracted significant interest due to their potential applications in many significant fields. Great endeavours have been made to improve the catalytic activities of nanozymes; however, it is still a challenging issue to develop nanozymes that can functionally mimic multiplex enzymes with broader application prospects. Here, we develop a simple hydrothermal method to construct "three-in-one" nanocomposites as multifunctional nanozymes for the ultrasensitive ratiometric fluorescence detection of alkaline phosphatase (ALP). The prepared flower-like Fe3O4 nanocomposites (Fef NCs) are composed of ternary components, in which hierarchical MnO2 nanosheets (NSs) are assembled on Fe3O4 nanoparticles (NPs), followed by the decoration of CeO2 NPs. Fef NCs present tetra-enzyme-like activities, i.e., oxidase-, peroxidase-, catalase-, and superoxide dismutase-like activity. More importantly, Fef NCs can effectively catalyze the oxidation of phenolic compounds (i.e., 3,5-DTBC and dopamine) to produce the corresponding o-quinones, demonstrating specific catechol oxidase-like activity. Based on the excellent catalytic oxidation and fluorescence quenching abilities of Fef NCs, we established a ratiometric fluorescence strategy using two fluorogenic substrates for label-free, ultrasensitive, and selective detection of ALP. The fluorescence bioassay exhibits a linear relationship between the fluorescence ratio and the ALP concentration ranging from 0.2 to 1.0 mU mL-1, with a detection limit down to be 0.19 mU mL-1. Furthermore, this bioassay can detect ALP in mixture and human serum samples, presenting good selectivity as well as real-world applicability. This work not only provides a novel approach for the preparation of a multiple-enzyme-like nanozyme but also offers an advanced ratiometric fluorescence sensing platform for ultrasensitive bioanalysis.

Construction of Bio-Nano Interfaces on Nanozymes for Bioanalysis.

Nanomaterials with enzyme-like activity (nanozymes) have been of great interest in broad applications ranging from biosensing to biomedical applications. Despite that much effort has been devoted to the development of the synthesis and applications of nanozymes, it is essential to understand the interactions between nanozymes and most commonly used biomolecules, i.e., avidin, streptavidin (SA), bovine serum albumin (BSA), immunoglobulin G (IgG), and glutathione (GSH), yet they have been rarely explored. Here, a series of bio-nano interfaces were constructed through direct immobilization of proteins on a variety of iron oxide and carbon-based nanozymes with different dimensions, including Fe3O4 nanoparticles (NPs, 0D), Fe3O4@C NPs (0D), Fe3O4@C nanowires (NWs, 1D), and graphene oxide nanosheets (GO NSs, 2D). Such interfaces enabled the modulation of the catalytic activities of the nanozymes with varying degrees, which allowed a good identification of multiplex proteins with high accuracy. Given the maximum inhibition on Fe3O4@C NP by BSA, we established molecular switches based on aptamer and toehold DNA, as well as Boolean logic gates (AND and NOR) in response to both DNA and proteins. Also importantly, we developed an on-particle reaction strategy for colorimetric detection of GSH with ultrahigh sensitivity and good specificity. The proposed sensor achieved a broad dynamic range spanning 7 orders of magnitude with a detection limit down to 200 pg mL-1, which was better than that of an in-solution reaction-based biosensor by 2 orders of magnitude. Furthermore, we explored the mechanisms of the interactions at bio-nano interfaces by studying the interfacial factors, including surface coverage, salt concentration, and the curvature of the nanozyme. This study offered new opportunities in the elaborate design and better utilization of nanozymes for bioanalysis in clinical diagnosis and in vivo detection.