While various effects of physicochemical parameters (e.g., size, facet, composition, and internal structure) on the catalytic efficiency of nanozymes (i.e., nanoscale enzyme mimics) have been studied, the strain effect has never been reported and understood before. Herein, we demonstrate the strain effect in nanozymes by using Pd octahedra and icosahedra with peroxidase-like activities as a model system. Strained Pd icosahedra were found to display 2-fold higher peroxidase-like catalytic efficiency than unstrained Pd octahedra. Theoretical analysis suggests that tensile strain is more beneficial to OH radical (a key intermediate for the catalysis) generation than compressive strain. Pd icosahedra are more active than Pd octahedra because icosahedra amplify the surface strain field. As a proof-of-concept demonstration, the strained Pd icosahedra were applied to an immunoassay of biomarkers, outperforming both unstrained Pd octahedra and natural peroxidases. The findings in this research may serve as a strong foundation to guide the design of high-performance nanozymes.

Strain Effect in Palladium Nanostructures as Nanozymes

In recent decade, palladium-based (Pd-based) nanomaterials have shown significant potential for biomedical applications because of their unique optical properties, excellent biocompatibility and high stability in physiological environment. Compared with other intensively studied noble nanomaterials, such as gold (Au) and silver (Ag) nanomaterials, research on Pd-based nanomaterials started late, but the distinctive features, such as high photothermal conversion efficiency and high photothermal stability, have made them getting great attention in the field of nanomedicine. The goal of this review is to provide a comprehensive and critical perspective on the recent progress of Pd-based nanomaterials as imaging contrast agents and therapeutic agents. The imaging section focuses on applications in photoacoustic (PA) imaging, single-photon emission computed tomography (SPECT) imaging, computed tomography (CT) imaging and magnetic resonance (MR) imaging. For treatment of cancer, single photothermal therapy (PTT) and PTT combined with other therapeutic modalities will be discussed. Finally, the safety concerns, forthcoming challenges and perspective of Pd-based nanomaterials on biomedical applications will be presented.

Palladium-based nanomaterials for cancer imaging and therapy.

Hard/soft ferrite nanocomposites (NCs) (SrHF)/xMCD (1.0 ≤ x ≤ 3.0) consisting of SrFe12O19 HF (SrHF) and Mg0.5Cd0.5Dy0.03Fe1.97O4 (MCD) were obtained via one-pot sol-gel auto-combustion approach. The measurements of impedance spectroscopy are presented for new fractional (SrHF)/xMCD (1.0 ≤ x ≤ 3.0) hard/soft ferrite NCs, including reference soft and hard ferrites. The electrical conductivity and activation energies of fractional composite ferrites are observed to be regulated depending on the fractional ratios. It has been established that the temperature dependence of the DC conductivity obeys the Arrhenius law, especially for the fractional composite ferrites. To control the conduction mechanism, the conductivity and its frequency power exponent are evaluated based on a small polaron tunnelling model. Magnetic properties were verified by applying a DC magnetic field up to ±70 kOe at 300 and 10 K. Magnetization data significantly decreased with increasing fraction of MCD in NCs. These results showed that exchange-coupling was not achieved in these NCs by one-pot approach. Additionally, anticandidal activity of the synthesized nanomaterials was studied by evaluating the colony forming unit (CFU). The obtained results are significant for potential applications in the field of biomedicine.

Developing the magnetic, dielectric and anticandidal characteristics of SrFe12O19/(Mg0.5Cd0.5Dy0.03Fe1.97O4)x hard/soft ferrite nanocomposites

Comprehensive studies on the size effect in nanozyme (i. e., nanomaterials with enzyme-like activities)-based catalysis have rarely been reported. In this work, we systematically investigated the size effect in nanozymes by using Pd-Ir core-shell nanoparticles with peroxidase-like activities as a model system. Pd-Ir nanoparticles with four different sizes (3.3, 5.9, 9.8 and 13.0 nm), but identical shapes and surface structures, were designed and synthesized. We found that the catalytic activity for individual nanozymes increased with particle size. The area-specific catalytic activity was similar for nanoparticles of 3.3-9.8 nm, but decreased slightly when particle size reached 13.0 nm. By using an enzyme-linked immunosorbent assay (ELISA) as a model platform, the size effect of Pd-Ir nanoparticles in biosensing applications was investigated; smaller nanoparticles were found to offer lower detection limits. This work not only demonstrates the size effect, but also provides an effective strategy to enhance the performance of nanozymes in certain applications.

Size Effect in Pd-Ir Core-Shell Nanoparticles as Nanozymes.

A method for the aqueous synthesis of stable and biocompatible citrate-coated palladium nanoparticles (PdNPs) in the size range comparable to natural enzymes (4-8 nm) has been developed. The toxicological profile of PdNPs was assessed by different assays on several cell lines demonstrating their safety in vitro also at high particle concentrations. To elucidate their cellular fate upon uptake, the localization of PdNPs was analyzed by Transmission Electron Microscopy (TEM). Moreover, crucial information about their intracellular stability and oxidation state was obtained by Sputtering-Enabled Intracellular X-ray Photoelectron Spectroscopy (SEI-XPS). TEM/XPS results showed significant stability of PdNPs in the cellular environment, an important feature for their biocompatibility and potential for biomedical applications. On the catalytic side, these PdNPs exhibited strong and broad antioxidant activities, being able to mimic the three main antioxidant cellular enzymes, i.e., peroxidase, catalase, and superoxide dismutase. Remarkably, using an experimental model of a human oxidative stress-related disease, we demonstrated the effectiveness of PdNPs as antioxidant nanozymes within the cellular environment, showing that they are able to completely re-establish the physiological Reactive Oxygen Species (ROS) levels in highly compromised intracellular redox conditions.

https://www.mdpi.com/2079-4991/10/1/99/pdf

Intracellular Antioxidant Activity of Biocompatible Citrate-Capped Palladium Nanozymes.

Palladium (Pd) nanoparticles are of particular interest to various fundamental studies and emerging areas of technology. The properties of Pd nanoparticles have a strong dependence on particle size...

One-Pot Synthesis of Single-Crystal Palladium Nanoparticles with Controllable Sizes for Applications in Catalysis and Biomedicine

Rapid testing, generally refers to the paper-based diagnostic platform known as “lateral flow assay” (LFA), has emerged as a critical asset to the containment of coronavirus disease 2019 (COVID-19) around the world. LFA technology stands out amongst peer platforms due to its cost-effective design, user-friendly interface, and low sample-to-readout times. This article aims to introduce its design, use, and practicality for the purpose of diagnosing SARS-CoV-2 infection. A connection is made from the normal COVID-19 immune response to the design and efficacy of rapid testing. Interference in test results is a challenge shared by most diagnostic platforms and can be rooted in various underlying issues. The current knowledge and situation about interference in rapid COVID-19 tests due to variant strains as well as vaccination are discussed. The cost and societal impact are reviewed as they play important roles in determining how to properly implement public testing practices. Perspectives on improving the performance, especially detection sensitivity, of LFA for COVID-19 are provided.

/pdf/rapid-testing-for-coronavirus-disease-2019-covid-19-3ogs6ctq.pdf

Rapid testing for coronavirus disease 2019 (COVID-19)

Rapid testing, generally refers to the paper-based diagnostic platform known as “lateral flow assay” (LFA), has emerged as a critical asset to the containment of coronavirus disease 2019 (COVID-19) around the world. LFA technology stands out amongst peer platforms due to its cost-effective design, user-friendly interface, and low sample-to-readout times. This article aims to introduce its design, use, and practicality for the purpose of diagnosing SARS-CoV-2 infection. A connection is made from the normal COVID-19 immune response to the design and efficacy of rapid testing. Interference in test results is a challenge shared by most diagnostic platforms and can be rooted in various underlying issues. The current knowledge and situation about interference in rapid COVID-19 tests due to variant strains as well as vaccination are discussed. The cost and societal impact are reviewed as they play important roles in determining how to properly implement public testing practices. Perspectives on improving the performance, especially detection sensitivity, of LFA for COVID-19 are provided. Graphical abstract

/pdf/rapid-testing-for-coronavirus-disease-2019-covid-19-23gq1gv0.pdf

Cary 60 UV-vis spectrophotometer. Transmission electron microscopy (TEM) images were taken using a JEOL 1011 microscope operated at 200 kV. High-angle annular dark-field scanning TEM (HAADF-STEM) images were taken using a FEI 200 kV Titan Themis scanning transmission electron microscope. The amount of Ir nanoparticles (NPs), WO 2.72 nanorods (NRs), and the Ir/W atomic ratios of Ir/WO 2.72 nanocomposites (NCs) were obtained from inductively coupled plasma mass spectroscopy (ICP-MS) analyses using a Thermo Scientific iCAP RQ, where Ir and W were converted to ionic species through the digestion of aqua regia. X-ray Diffraction (XRD) patterns were recorded using a PANalytical Empyrean diffractometer (1.8 KW Copper X-ray Tube). X-ray photoelectron spectroscopy (XPS) was performed on a Physical Electronics 5400 ESCA spectrometer system. The fourier transform infrared (FT-IR) spectroscopy was recorded from the machine of Jasco 6600 MIR and FIR FT-IR with ATR. Microtiter plates were shaken using a Corning LSE digital microplate shaker. The absorbance of samples in microtiter plates was read

Ultrasmall Iridium Nanoparticles as Efficient Peroxidase Mimics for Colorimetric Bioassays

Over the past few decades, peroxidase mimics made of platinum-group metal nanoparticles (PGM NPs) have been actively developed and applied to various biosensing platforms. Nevertheless, there is a lack of a comprehensive study that compares the peroxidase-like activities of PGM NPs and their performance in biosensing. Here, we report a systematic study of PGM NPs as peroxidase mimics, including Pd, Pt, Rh, and Ir NPs. NPs of these elements were uniformly synthesized and their nanoscale features were probed to ensure a consistent size, shape, and chemical ligand on the surface. Our measurements indicate that the Ir NP is the most active one with a catalytic constant as high as 6.27 × 105 s–1, followed by Pt, Rh, and Pd NPs. The binding affinities of NPs to peroxidase substrates during catalysis were also quantitively analyzed and compared. Using enzyme-linked immunosorbent assay as a model biosensing platform, the performance of PGM NPs in detecting carcinoembryonic antigen (a cancer biomarker) was evaluated. The results showed that the detection sensitivity was correlated to the catalytic activity of PGM NPs, where Ir NPs achieved the highest sensitivity with a limit of detection at the level of low picogram per milliliter. 

Alexander Biby

Papers

One-Pot Synthesis of Single-Crystal Palladium Nanoparticles with Controllable Sizes for Applications in Catalysis and Biomedicine

Rapid testing for coronavirus disease 2019 (COVID-19)

Rapid testing for coronavirus disease 2019 (COVID-19)

Ultrasmall Iridium Nanoparticles as Efficient Peroxidase Mimics for Colorimetric Bioassays

Platinum-Group Metal Nanoparticles as Peroxidase Mimics: Implications for Biosensing