Recently, the development of nanozymes with high catalytic performance is gaining more and more attention due to the ever-growing demands for their practical applications. The elaborate design of its morphology has demonstrated to be an effective approach to improve the performance of these nanozymes. Herein, a hybrid of iron disulfide nanoparticles (FeS2 NPs) encapsulated by two-dimensional (2D) carbon nanosheets (NSs), denoted as FeS2@C NSs, demonstrates both superior peroxidase-like activity and excellent stability. The incorporation of 2D carbon sheets endows the proposed FeS2@C nanozymes with high specific surface area, providing abundant active sites to facilitate the contact with substrates. Moreover, the embedded FeS2 NPs are kept from aggregation due to the encapsulation and confinement of 2D carbon sheets, avoiding the conventional failure of single-component nanozymes. Based on glucose oxidase (GOx) and the elaborately designed FeS2@C nanozymes, a colorimetric method for glucose detection is then developed with excellent simplicity and sensitivity. The detection limit of the sensing platform is as low as 0.19 μM for a glucose assay. More notably, this method can be successfully employed for the glucose assay in some real samples, indicating the great potential of this FeS2@C NS-based nanozymes in the fields of biotechnology and clinical diagnostics.

In the past few years, the development of novel nanozymes with excellent performance has attracted increasing attention in biosensing. However, most of those nanozymes were found to possess peroxidase activity with the prerequisite of the presence of H2O2. In contrast, oxidase mimics can catalyze the oxidation of substrates without H2O2, delivering a higher signal-to-noise ratio than that of peroxidase mimics in practical applications. Herein, for the first time, two-dimensional (2D) nanosheets composed of iron phosphide embedded in a carbon matrix (FeP@C nanosheets) were found to demonstrate a robust oxidase-like property, different from those previously reported peroxidase mimics based on transition metal phosphides (TMPs). Based on this intriguing observation, the fluorescent substrate Amplex Red (AR) of peroxidase can be effectively oxidized by FeP@C nanosheets in the absence of H2O2. Benefiting from the oxidase-like enzymatic activity of the FeP@C nanosheets, a novel fluorescence sensing platform was developed for the detection of cysteine (Cys) and Cu2+. The outstanding performance of the 2D FeP@C nanosheets endows the proposed platform with superior sensitivity and selectivity compared to many previously reported approaches. Besides, the inherent features of simplicity, being label free, and low cost also allow this methodology to stand out among many other strategies, revealing its huge potential in practical analysis and detection applications.

In this study, the effect of single-stranded DNA (ssDNA) on the intrinsic peroxidase-like activity of MIL-53(Fe) was investigated.

In the last decades, enzyme mimics have been regarded as strong substitutes to natural enzymes. The construction of biosensors based on these enzyme mimics with competitive catalytic activity and substrate specificity has attracted a lot of research interest. Herein, for the first time, we investigated the capability of nanoscale FeS2 to serve as enzyme mimics. Then, a facile and effective biosensor is fabricated based on its intrinsic peroxidase-like catalytic activity. In the presence of H2O2, FeS2 nanoparticles (NPs) possess high peroxidase-like activity to 3,3',5,5'-tetramethylbenzidine (TMB) oxidation, which can be ascribed to the generation of hydroxyl radicals (·OH) from the H2O2 decomposition catalyzed by FeS2 NPs. As for TMB, the resulting Michaelis-Menten constant (Km) value of FeS2 NPs is found to be about 12 times lower than that of natural horseradish peroxidase (HRP), highlighting the superiority of FeS2 NPs. Based on these intriguing observations, a reliable colorimetric method is then developed for detection of H2O2 and glutathione (GSH) by a simple mix-and-detect strategy. The detection limits of H2O2 and GSH are as low as 0.91 μM and 0.15 μM (3σ/slope), respectively. Moreover, FeS2 NPs can also catalyse the photoluminescence (PL) substrate terephthalic acid (TA) under the assistance of H2O2. This work remarkably extends the utilization of FeS2 NPs in the construction of colorimetric and PL biosensors in the fields of biosensing, environmental monitoring, and medical diagnosis.

Numerous nanomaterials have been utilized for novel biosensors with sensitivity and selectivity in the last decades due to their intrinsic unique properties. Herein, a facile fluorescence method for nucleic acid detection was developed by employing TiO2 nanowires (NWs) as the sensing platform. The quenching effect of TiO2 NWs to fluorophore-labelled single-stranded DNA (ssDNA) was found to be more significant than that to fluorophore-labelled double-stranded DNA (dsDNA) or triplex DNA probes. More importantly, the whole quenching process was also fast since it just took about ten minutes to reach the equilibrium. Based on the different affinities of TiO2 NWs to ssDNA, dsDNA and triplex DNA probes, the sequence-specific nucleic acids were detected with sensitivity and specificity. Further investigation has demonstrated that the quenching efficiency of TiO2 NWs to long ssDNA was apparently superior than that to short ssDNA. Moreover, the fluorescence from various ssDNA probes labelled with a wide spectrum of fluorescent dyes could also be quenched by TiO2 NWs. These inspiring results reveal that TiO2 NWs could be an excellent universal nanoquencher used in the next-generation biosensors.

Nitrogen-doped graphene quantum dots (N-GQDs), with superior biocompatibility, strong resistance to photobleaching and convenient surface grafting, have sparked a surge of related-bio applications. In this study, combined with chromium picolinate (CrPic), N-GQDs synthesized by a facile hydrothermal approach are used to construct an environmentally-friendly sensor for the detection of cholesterol by exploiting the fluorescence enhancement of N-GQDs/CrPic. Herein, CrPic is grafted on N-GQDs via the linker of cysteamine (Cys), and the fluorescence of the N-GQDs is quenched by photoinduced electron transfer (PET), wherein CrPic functions as an electron donating group and the N-GQDs serves as an electron accepting group. Besides, cholesterol is stimulated to form a favourable complex with N-GQDs/CrPic because CrPic also acts as a potential receptor for cholesterol by strong affinity and π-π interaction, and the fluorescence of N-GQDs/CrPic is enhanced indicating that cholesterol could impede electron transfer from CrPic to the N-GQDs. This N-GQDs/CrPic-based sensor has been successfully applied to selectively determine the concentration of cholesterol with a linear range of 0-520 μM and a limit of detection (LOD) of 0.4 μM. Meanwhile, this present sensing strategy in human serum has acceptable practicability, reproducibility and precision.