Structure and activity assay of nanozymes prepared by the coimmobilization of practically useful enzymes and hydrophilic block copolymers on gold nanoparticles

Surface Ligand Engineering Ruthenium Nanozyme Superior to Horseradish Peroxidase for Enhanced Immunoassay

Nanozymes have great potential to be used as an alternative to natural enzymes in a variety of fields. However, low catalytic activity compared with natural enzymes limits their practical use. It is still challenging to design nanozymes comparable to their natural counterparts in terms of the specific activity. In this study, a surface engineering strategy is employed to improve the specific activity of Ru nanozymes using charge-transferrable ligands such as polystyrene sulfonate (PSS). PSS-modified Ru nanozyme exhibits a peroxidase-like specific activity of up to 2820 U mg-1 , which is twice that of horseradish peroxidase (1305 U mg-1 ). Mechanism studies suggest that PSS readily accepts negative charge from Ru, thus reducing the affinity between Ru and ·OH. Importantly, the modified Ru-peroxidase nanozyme is successfully used to develop an immunoassay for human alpha-fetoprotein and achieves a 140-fold increase in detection sensitivity compared with traditional horseradish-peroxidase-based enzyme-linked immunosorbent assay. Therefore, this work provides a feasible route to design nanozymes with high specific activity that meets the practical use as an alternative to natural enzymes.

Enhanced and Prolonged Activity of Enzymes Adsorbed on TEMPO-Oxidized Cellulose Nanofibers

2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNs) have a width of about 4 nm and a very large specific surface area. TOCN is a negatively charged bionanomaterial having carboxy groups on the surface and promising physical properties. In particular, TOCN can be used as an adsorbent for biomolecules for biotechnological applications, but the adsorption behavior of biomolecules on the TOCN surface requires investigation. Thus, in this study, we investigated the adsorption behavior of pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) on TOCN and evaluated the activity, structure, and long-term stability of the adsorbed enzyme. Transmission electron microscopy observation revealed that the enzyme was aligned and adsorbed on the TOCNs, and circular dichroism measurements were used to determine the structure of the enzyme adsorbed on TOCN. Interestingly, the adsorbed enzyme showed higher activity after adsorption, resulting in long-term retention of enzyme activity, probably because the stability of PQQ-GDH was improved by adsorption. These results suggest that TOCN is an excellent biomolecule immobilization material. Our results can be used for the development of biomaterials using TOCN as a scaffold for the adsorption of enzymes with increased stability and activity.

Emerging Biomedical Applications of Enzyme-Like Catalytic Nanomaterials

Nanomaterials have been developed for many biomedical applications, including medical imaging, drug delivery, and antimicrobial coatings. Intriguingly, nanoparticles can display 'enzyme-like' activity and have been explored as alternatives to natural enzymes in several industrial and energy-related applications. Recently, these catalytic nanomaterials with enzyme-mimetic properties have found new biomedical applications, from biofilm disruption to protection against neurodegeneration and tumor prevention. In this review we focus on recent in vivo studies demonstrating potential therapeutic uses of catalytic nanomaterials. We also provide insights about the relationships between catalytic activity, therapeutic efficacy, and biocompatibility that are critical for clinical translatability. Finally, we discuss current challenges and future directions for the use of these nanomaterials as novel platforms for the development of sustainable, affordable, and safe therapeutics.

Implantable diagnostic device for cancer monitoring

Biopsies provide required information to diagnose cancer but, because of their invasiveness, they are difficult to use for managing cancer therapy. The ability to repeatedly sample the local environment for tumor biomarker, chemotherapeutic agent, and tumor metabolite concentrations could improve early detection of metastasis and personalized therapy. Here we describe an implantable diagnostic device that senses the local in vivo environment. This device, which could be left behind during biopsy, uses a semi-permeable membrane to contain nanoparticle magnetic relaxation switches. A cell line secreting a model cancer biomarker produced ectopic tumors in mice. The transverse relaxation time (T(2)) of devices in tumor-bearing mice was 20+/-10% lower than devices in control mice after 1 day by magnetic resonance imaging (p<0.01). Short term applications for this device are numerous, including verification of successful tumor resection. This may represent the first continuous monitoring device for soluble cancer biomarkers in vivo.

Design of poly(ethylene glycol)/streptavidin coimmobilized upconversion nanophosphors and their application to fluorescence biolabeling

Infrared-to-visible upconversion phosphors (i.e., rare earth ion-doped Y2O3 nanoparticles (UNPs)) were synthesized by the homogeneous precipitation method. Because the charge on the erbium (Er) ion-doped Y2O3 (Y2O3:Er) NP (UNP1) surface is positive under neutral conditions, the UNP1 surface was electrostatically PEGylated using negatively charged poly(ethylene glycol)- b-poly(acrylic acid) (PEG- b-PAAc). The adsorption of PEG- b-PAAc was confirmed by Fourier transform infrared (FT-IR) measurements and thermal gravimetric analysis (TGA). The surface charge of the PEGylated UNP1s (PEG-UNP1s) was effectively shielded by the PEGylation. The dispersion stability of the UNP1s was also significantly improved by the PEGylation. The PEG-UNP1s were dispersed over 1 week under physiological conditions as a result of the steric repulsion between the PEG chains on the UNP1 surface. The upconversion emission spectrum of PEG-UNP1s was observed under physiological conditions and was confirmed by near-infrared excited fluorescence microscope observation. Streptavidin (SA)-installed ytterbium (Yb) and Er ion-codoped Y2O3 (Y2O3:Yb,Er) NPs (UNP2s) were prepared by the coimmobilization of PEG- b-PAAc and streptavidin. The PEG/SA coimmobilized UNP2s (PEG/SA-UNP2s) specifically recognized biotinylated antibodies and emitted strong upconversion luminescence upon near-infrared excitation. The obtained PEG/streptavidin coimmobilized UNPs are promising as high-performance near-infrared biolabeling materials.