Investigating a lock-in thermal imaging setup for the detection and characterization of magnetic nanoparticles

Magnetic hyperthermia treatments utilize the heat generated by magnetic nanoparticles stimulated by an alternating magnetic field. Therefore, analytical methods are required to precisely characterize the dissipated thermal energy and to evaluate potential amplifying or diminishing factors in order to ensure optimal treatment conditions. Here, we present a lock-in thermal imaging setup specifically designed to thermally measure magnetic nanoparticles and we investigate theoretically how the various experimental parameters may influence the measurement. We compare two detection methods and highlight how an affordable microbolometer can achieve identical sensitivity with respect to a thermal camera-based system by adapting the measurement time. Furthermore, a numerical model is used to demonstrate the optimal stimulation frequency, the degree of nanomaterial heating power, preferential sample holder dimensions and the extent of heat losses to the environment. Using this model, we also revisit some technical assumptions and experimental results that previous studies have stated and suggest an optimal experimental configuration

A new angle on dynamic depolarized light scattering: number-averaged size distribution of nanoparticles in focus

Size polydispersity is a common phenomenon that strongly influences the physicochemical properties of nanoparticles (NPs). We present an analytical approach that is universally applicable to characterizing optically anisotropic round NPs and determines directly the number-averaged size distribution and polydispersity via depolarized dynamic light scattering (DDLS). To demonstrate, we use aqueous suspensions of Au NPs of different sizes and surface functionalization

Avoiding drying-artifacts in transmission electron microscopy: Characterizing the size and colloidal state of nanoparticles

Standard transmission electron microscopy nanoparticle sample preparation generally requires the complete removal of the suspending liquid. Drying often introduces artifacts, which can obscure the state of the dispersion prior to drying and preclude automated image analysis typically used to obtain number-weighted particle size distribution. Here we present a straightforward protocol for prevention of the onset of drying artifacts, thereby allowing the preservation of in-situ colloidal features of nanoparticles during TEM sample preparation. This is achieved by adding a suitable macromolecular agent to the suspension. Both research- and economically-relevant particles with high polydispersity and/or shape anisotropy are easily characterized following our approach (http://bsa.bionanomaterials.ch), which allows for rapid and quantitative classification in terms of dimensionality and size: features that are major targets of European Union recommendations and legislation

Using lock-in thermography to investigate stimuli-responsive nanoparticles in complex environments

​© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The use of nanoparticles (NP) has been dramatically rising in the recent years and NPs can nowadays be found in various products ranging from food to composite materials or cosmetics. Currently, the most frequently employed NP types are titania (TiO 2 ), as a typical color additive, silica (SiO 2 ), as anticoagulation agent, and silver (Ag) NPs, which are added to textiles, due to their antimicrobial properties. Because of their outstanding physical and mechanical properties, carbon-containing nanomaterials, such as graphene and carbon nanotubes, have also experienced a surge in industrially relevant applications. About 30% of the NPs are suspended in liquids, ranging from water to creams and lotions to car lubricants, followed by applications containing surface-bound (e.g., in textiles) NPs and finally nanocomposites (e.g., polymer-CNT composites). Together with biological and physiological fluids, these matrices render the detection and quantification of NPs fairly complex. The broad range of chemical and biological compositions of these environments, including pH and ionic strength, are often detrimental to the colloidal stability of NPs, potentially causing aggregation or even dissolution effects and therefore render NP analysis fairly challenging

Taylor dispersion of inorganic nanoparticles and comparison to dynamic light scattering and transmission electron microscopy

Taylor dispersion analysis (TDA) is an analytical method that has so far mainly been utilized to determine the diffusion coefficient of small molecules, and proteins. Due to increasing interest in nanoscience, some research has been done on the applicability of TDA towards characterizing nanoparticles. This work aims to expand this knowledge and give insight into the range for which TDA can be used for nanoparticle characterization, focusing on various materials and sizes. The TDA setup shown in this work was successful in characterizing all engineered metallic, non-metallic nanoparticles, and proteins tested in this work. Results were compared to dynamic light scattering and electron microscopy, and were in good agreement with both methods. Taking into consideration the wide range of nanoparticle sizes that can be characterized, the minimal sample preparation, and sample volume, required and the simplicity of the method, TDA can be considered as a valuable technique for nanoparticle characterization

Dynamic and biocompatible thermo-responsive magnetic hydrogels that respond to an alternating magnetic field

Magnetic thermo-responsive hydrogels are a new class of materials that have recently attracted interest in biomedicine due to their ability to change phase upon magnetic stimulation. They have been used for drug release, magnetic hyperthermia treatment, and can potentially be engineered as stimuli-responsive substrates for cell mechanobiology. In this regard, we propose a series of magnetic thermo-responsive nanocomposite substrates that undergo cyclical swelling and de-swelling phases when actuated by an alternating magnetic field in aqueous environment. The synthetized substrates are obtained with a facile and reproducible method from poly-N- isopropylacrylamide and superparamagnetic iron oxide nanoparticles. Their conformation and the temperature-related, magnetic, and biological behaviors were characterized via scanning electron microscopy, swelling ratio analysis, vibrating sample magnetometry, alternating magnetic field stimulation and indirect viability assays. The nanocomposites showed no cytotoxicity with fibroblast cells, and exhibited swelling/de-swelling behavior near physiological temperatures (around 34 °C). Therefore these magnetic thermo-responsive hydrogels are promising materials as stimuli-responsive substrates allowing the study of cell-behavior by changing the hydrogel properties in situ

Heating behavior of magnetic iron oxide nanoparticles at clinically relevant concentration

Magnetic hyperthermia for cancer treatment has gained significant attention in recent years, due to its biocompatibility of applied nanoparticles and the possibility for spatially localized heating in deep tissues. Clinical treatments use nanoparticle concentrations of 112 mg Fe/mL, while the concentrations experimental studies have addressed are considerably smaller, usually between 0.1 and 30 mg/mL. Therefore, it is not clear whether such experiments correspond to the magnetic properties found in clinical applications. In this regard, we studied the thermal behavior of superparamagnetic iron oxide nanoparticles (SPION) with the most common particle shapes used in the field, including spherical (core diameters 11 and 19 nm), cubic (15 nm) and ellipsoidal (23 nm with an aspect ratio of 1.45), at concentrations ranging from 5 to 80 mg Fe/mL. Their shape, size, crystallinity, magnetic, and thermal behavior were characterized via transmission electron microscopy, dynamic light scattering, Taylor dispersion analysis, X-ray diffraction, alternating gradient magnetometry, and lock-in thermography. Spherical and cubic nanoparticles displayed linear heating slopes, independent from size, shape and concentration, resulting in unchanged specific absorption rates (SAR). Ellipsoids showed the same behavior until 50 mg/mL, above which a decreasing heating slope trend was found, without evidence as to what causes this behavior. However, the presented results highlight the importance of colloidally stable SPIONs in magnetic hyperthermia to obtain maximum heating power by minimum particle dosage

Lock‐in thermography to analyze plasmonic nanoparticle dispersions

The physicochemical properties of nanoparticles (NPs) strongly rely on their colloidal stability, and any given dispersion can display remarkably different features, depending on whether it contains single particles or clusters. Thus, developing efficient experimental methods that are able to provide accurate and reproducible measures of the NP properties is a considerable challenge for both research and industrial development. By analyzing different NPs, through size and concentration, it is demonstrated that lock‐in thermography, based on light absorption and heat generation, is able to detect and differentiate the distinct aggregation and re‐ dispersion behavior of plasmonic NPs, e.g., gold and silver. Most importantly, the approach is nonintrusive and potentially highly cost‐effective compared to standard analytical techniques

Continuous presence of genetically diverse rustrela virus lineages in yellow-necked field mouse reservoir populations in northeastern Germany.

Rustrela virus (RusV; species Rubivirus strelense, family Matonaviridae) was discovered in different zoo animal species affected by fatal encephalitis. Simultaneous RusV RNA detection in multiple yellow-necked field mice (Apodemus flavicollis) suggested this rodent as a reservoir of RusV. Here, we investigated 1,264 yellow-necked field mice and sympatric other small mammals from different regions in Germany for RusV RNA using an optimized reverse transcription-quantitative polymerase chain reaction (RT-qPCR) protocol and high-throughput sequencing. The investigation resulted in the detection of RusV RNA exclusively in 50 of 396 (12.6 per cent) yellow-necked field mice but absence in other sympatric species. RT-qPCR-determined tissue distribution of RusV RNA revealed the highest viral loads in the central nervous system, with other tissues being only very rarely affected. The histopathological evaluation did not reveal any hints of encephalitis in the brains of infected animals despite the detection of viral RNA in neurons by in situ hybridization (ISH). The positive association between the body mass of yellow-necked field mice and RusV RNA detection suggests a persistent infection. Phylogenetic analysis of partial E1 and full-genome sequences showed a high diversification with at least four RusV lineages (1A-1D) in northeastern Germany. Moreover, phylogenetic and isolation-by-distance analyses indicated evolutionary processes of RusV mostly in local reservoir populations. A comparison of complete genome sequences from all detected RusV lineages demonstrated a high level of amino acid and nucleotide sequence variability within a part of the p150 peptide of the non-structural polyprotein and its coding sequence, respectively. The location of this region within the RusV genome and its genetic properties were comparable to the hypervariable region of the rubella virus. The broad range of detected RusV spillover hosts in combination with its geographical distribution in northeastern Germany requires the assessment of its zoonotic potential and further analysis of encephalitis cases in mammals. Future studies have to prove a putative co-evolution scenario for RusV in the yellow-necked field mouse reservoir

Preparation and characterization of functional silica hybrid magnetic nanoparticles

We report on the synthesis and characterization of functional silica hybrid magnetic nanoparticles (SHMNPs). The co-condensation of 3-aminopropyltriethoxysilane (APTES) and tetraethyl orthosilicate (TEOS) in presence of superparamagnetic iron oxide nanoparticles (SPIONs) leads to hybrid magnetic silica particles that are surface-functionalized with primary amino groups. In this work, a comprehensive synthetic study is carried out and completed by a detailed characterization of hybrid particles׳ size and morphology, surface properties, and magnetic responses using different techniques. Depending on the mass ratio of SPIONs and the two silanes (TEOS and APTES), we were able to adjust the number of surface amino groups and tune the magnetic properties of the superparamagnetic hybrid particles