Laccases are effective native biocatalysts for the oxidation of o-/p-diphenols, aminophenols, polyphenols and polyamines. To overcome the intrinsic limitations of native laccase involving pH, temperature and storage, highly dispersive Pt nanoparticles were synthesized by employing different oligonucleotides as stabilizing agents including A10, T10, C10 and G10, and their catalytic activities were assessed in the oxidation of laccase substrates under ambient air. This kind of Pt nanozyme displays high stability in the range of 20–90 °C and pH 3–9, beyond the range for native laccase. The laccase-like activities of Pt nanoparticles are greatly associated with the size distribution and the surface charge, which can be easily regulated by the sequence composition and the molar ratio of [precursor]/[template]. The most efficient C10-templated Pt nanozyme with 4.6 nm in size, exhibit three times higher affinity toward 2,4-dichlorophenol than that of native laccase. DNA-stabilized Pt nanoparticles display excellent catalytic performance in the oxidation of a wide range of substrates including dopamine, catechol, hydroquinone and p-phenylenediamine. This study paves a way to explore artificial nanoparticles to replace native laccase in the fields of biosensing and green synthesis.

Cytosine-rich oligonucleotides are effective templates to stabilize Pd-based enzymatic nanoparticles with a size distribution of 3.7–5.1 nm, with different surface charge conditions and peroxidase mimicking activities. The d(C10)-stabilized Pd nanozyme with an average diameter of 4.8 nm possesses a Km value of 0.033 mM toward TMB and 91.29 mM toward H2O2. On the basis of the thiol-induced shielding of peroxidase-like activity of d(C10)-Pd, a Pd-based nanozyme is employed for the first time in the sensitive detection of biothiols including cysteine and homocysteine, with a limit of detection of 3.7 nM for cysteine and 4.3 nM for homocysteine. This Pd-based peroxidase nanomimetic material exhibits promising applications in the quantitative detection of thiol-containing compounds in biological fluids.

•The peroxidase-like activity of Cu2+ is greatly enhanced by DNA templates.•G-rich DNA–Cu(II) possesses highly peroxidase-like activity.•G20–Cu(II) is employed to develop a colorimetric turn-on assay of ALP.•The LOD is 0.84 U/L with high selectivity against other proteins.•This colorimetric system is probably applicable in biological fluids.DNA-based peroxidase mimetics are facilely constructed through Cu(II)-coordination with different oligonucleotides involving G20, C20, A20 and T20, respectively, with high peroxidase mimicking activity as well as high stability against proteins. Peroxidase-like activities of DNA–Cu(II) complexes are greatly associated with the sequence composition of DNA templates, which decrease in the following order: G20>C20>A20>T20. G20–Cu(II) complex ([Cu2+]/[base]=0.05) possesses the Km value of 0.257 mM toward 3,3′,5,5′-tetramethylbenzidine and 102.3 mM toward hydrogen peroxide at 25 °C. G20–Cu(II) complexes are employed to develop a colorimetric turn-on assay of alkaline phosphatase with high sensitivity and selectivity, on the basis of pyrophosphate-induced inhibition of their intrinsic peroxidase-like activities. The limit of detection is achieved as 0.84 U/L with the linear response region of 20–200 U/L. Such colorimetric assay system is probably applicable for the quantitative determination of ALP in biological fluids.

Glutathione (GSH) is chosen as a nucleation template to synthesize Pt-based peroxidase nanomimetics ranging from 2.3 to 3.6 nm, of which the surface charge states are greatly associated with the molar ratio of [K2PtCl4]/[GSH]. GSH-Pt3.3 consisting of 67% Pt0 and 33% Pt2+ possesses the highest peroxidase-like activity, while GSH-Pt3.6 comprising 82% Pt0 and 18% Pt2+ exhibits the most efficient radical scavenging capability. Owing to the Hg2+-induced inhibition of peroxidase mimicking activities, a series of Pt-based nanozymes are employed to explore colorimetric assays of Hg2+ in aqueous samples with ultrahigh sensitivity. The limit of detection (LOD) can reach 0.25 nM by using GSH-Pt with an average diameter of 3.6 nm. GSH-Pt is a promising candidate for colorimetric assay of Hg2+ in both drinking water and biological fluid.

•BSA stabilizes Pt nanoparticles of 2 nm.•Pt nanoparticles possess intrinsic peroxidase-like activity.•Hg2+ ions down-regulate the enzymatic activity of Pt nanoparticles.•Pt nanozyme can sense Hg2+ ions in aqueous solution and drinking water.•The detection limit of 7.2 nM is achieved without significant interference.Bovine serum albumin (BSA) is chosen as the nucleation templates to synthesize Pt-based peroxidase nanomimetics with the average diameter of 2.0 nm. The efficient Pt nanozymes consist of 57% Pt0 and 43% Pt2+, which possess highly peroxidase-like activity with the Km values of 0.119 mM and 41.8 mM toward 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H2O2), respectively. Interestingly, Hg2+ is able to down-regulate the enzymatic activity of Pt nanoparticles, mainly through the interactions between Hg2+ and Pt0. It is the first report to explore a colorimetric Hg2+ sensing system on the basis of peroxidase mimicking activities of Pt nanoparticles. One of our most intriguing results is that BSA-stabilized Pt nanozymes demonstrate the ability to sense Hg2+ ions in aqueous solution without significant interference from other metal ions. The Hg2+ detection limit of 7.2 nM is achieved with a linear response range of 0–120 nM, and the developed sensing system is potentially applicable for quantitative determination of Hg2+ in drinking water.