Quantification of nanoparticles' concentration inside polymer films using lock-in thermography.

Thin nanocomposite polymer films embedding various types of nanoparticles have been the target of abundant research to use them as sensors, smart coatings, or artificial skin. Their characterization is challenging and requires novel methods that can provide qualitative as well as quantitative information about their composition and the spatial distribution of nanoparticles. In this work, we show how lock-in thermography (LIT) can be used to quantify the concentration of gold nanoparticles embedded in polyvinyl alcohol (PVA) films. LIT is an emerging and non-destructive technique that measures the thermal signature produced by an absorbing sample illuminated by modulated light with a defined frequency. Films with various concentrations of gold nanoparticles of two different sizes have been prepared by evaporation from homogeneous aqueous PVA gold nanoparticle suspensions. When the thin films were illuminated with monochromatic light at a wavelength close to the plasmonic resonance signature of the nanoparticles, the amplitude of the thermal signature emitted by the nanoparticles was recorded. The measurements have been repeated for multiple modulation frequencies of the incident radiation. We have developed a mathematical method to quantitatively relate the concentration of nanoparticles to the measured amplitude. A discussion about the conditions under which the sample thickness can be determined is provided. Furthermore, our results show how LIT measurements can easily detect the presence of concentration gradients in samples and how the model allows the measured signal to be related to the respective concentrations. This work demonstrates the successful use of LIT as a reliable and non-destructive method to quantify nanoparticle concentrations.

A Near-Infrared Mechanically Switchable Elastomeric Film as a Dynamic Cell Culture Substrate.

Commercial static cell culture substrates can usually not change their physical properties over time, resulting in a limited representation of the variation in biomechanical cues in vivo. To overcome this limitation, approaches incorporating gold nanoparticles to act as transducers to external stimuli have been employed. In this work, gold nanorods were embedded in an elastomeric matrix and used as photothermal transducers to fabricate biocompatible light-responsive substrates. The nanocomposite films analysed by lock-in thermography and nanoindentation show a homogeneous heat distribution and a greater stiffness when irradiated with NIR light. After irradiation, the initial stiffness values were recovered. In vitro experiments performed during NIR irradiation with NIH-3T3 fibroblasts demonstrated that these films were biocompatible and cells remained viable. Cells cultured on the light stiffened nanocomposite exhibited a greater proliferation rate and stronger focal adhesion clustering, indicating increased cell-surface binding strength.

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.

Rapid and sensitive quantification of cell-associated multi-walled carbon nanotubes.

Evaluating nanomaterial uptake and association by cells is relevant for in vitro studies related to safe-by-design approaches, nanomedicine or applications in photothermal therapy. However, standard analytical techniques are time-consuming, involve complex sample preparation or include labelling of the investigated sample system with e.g. fluorescent dyes. Here, we explore lock-in thermography to analyse and compare the association trends of epithelial cells, mesothelial cells, and macrophages exposed to gold nanoparticles and multi-walled carbon nanotubes over 24 h. The presence of nanomaterials in the cells was confirmed by dark field and transmission electron microscopy. The results obtained by lock-in thermography for gold nanoparticles were validated with inductively coupled plasma optical emission spectrometry; with data collected showing a good agreement between both techniques. Furthermore, we demonstrate the detection and quantification of carbon nanotube-cell association in a straightforward, non-destructive, and non-intrusive manner without the need to label the carbon nanotubes. Our results display the first approach in utilizing thermography to assess the carbon nanotube amount in cellular environments.

A comparative study of silver nanoparticle dissolution under physiological conditions.

Upon dissolution of silver nanoparticles, silver ions are released into the environment, which are known to induce adverse effects. However, since dissolution studies are predominantly performed in water and/or at room temperature, the effects of biological media and physiologically relevant temperature on the dissolution rate are not considered. Here, we investigate silver nanoparticle dissolution trends based on their plasmonic properties under biologically relevant conditions, i.e. in biological media at 37 °C over a period of 24 h. The studied nanoparticles, surface-functionalized with polyvinylpyrrolidone, beta-cyclodextrin/polyvinylpyrrolidone, and starch/polyvinylpyrrolidone, were analysed by UV-Vis spectroscopy, lock-in thermography and depolarized dynamic light scattering to evaluate the influence of these coatings on silver nanoparticle dissolution. Transmission electron microscopy was employed to visualize the reduction of the nanoparticle core diameters. Consequently, the advantages and limitations of these analytical techniques are discussed. To assess the effects of temperature on the degree of dissolution, the results of experiments performed at biological temperature were compared to those obtained at room temperature. Dissolution is often enhanced at elevated temperatures, but has to be determined individually for every specific condition. Furthermore, we evaluated potential nanoparticle aggregation. Our results highlight that additional surface coatings do not necessarily hinder the dissolution or aggregation of silver nanoparticles.

Combined exposure of diesel exhaust particles and respirable Soufrière Hills volcanic ash causes a (pro-)inflammatory response in an in vitro multicellular epithelial tissue barrier model.

BACKGROUND: There are justifiable health concerns regarding the potential adverse effects associated with human exposure to volcanic ash (VA) particles, especially when considering communities living in urban areas already exposed to heightened air pollution. The aim of this study was, therefore, to gain an imperative, first understanding of the biological impacts of respirable VA when exposed concomitantly with diesel particles. METHODS: A sophisticated in vitro 3D triple cell co-culture model of the human alveolar epithelial tissue barrier was exposed to either a single or repeated dose of dry respirable VA (deposited dose of 0.26 ± 0.09 or 0.89 ± 0.29 µg/cm2, respectively) from Soufrière Hills volcano, Montserrat for a period of 24 h at the air-liquid interface (ALI). Subsequently, co-cultures were exposed to co-exposures of single or repeated VA and diesel exhaust particles (DEP; NIST SRM 2975; 0.02 mg/mL), a model urban pollutant, at the pseudo-ALI. The biological impact of each individual particle type was also analysed under these precise scenarios. The cytotoxic (LDH release), oxidative stress (depletion of intracellular GSH) and (pro-)inflammatory (TNF-α, IL-8 and IL-1ß) responses were assessed after the particulate exposures. The impact of VA exposure upon cell morphology, as well as its interaction with the multicellular model, was visualised via confocal laser scanning microscopy (LSM) and scanning electron microscopy (SEM), respectively. RESULTS: The combination of respirable VA and DEP, in all scenarios, incited an heightened release of TNF-α and IL-8 as well as significant increases in IL-1ß, when applied at sub-lethal doses to the co-culture compared to VA exposure alone. Notably, the augmented (pro-)inflammatory responses observed were not mediated by oxidative stress. LSM supported the quantitative assessment of cytotoxicity, with no changes in cell morphology within the barrier model evident. A direct interaction of the VA with all three cell types of the multicellular system was observed by SEM. CONCLUSIONS: Combined exposure of respirable Soufrière Hills VA with DEP causes a (pro-)inflammatory effect in an advanced in vitro multicellular model of the epithelial airway barrier. This finding suggests that the combined exposure to volcanic and urban particulate matter should be further investigated in order to deduce the potential human health hazard, especially how it may influence the respiratory function of susceptible individuals (i.e. with pre-existing lung diseases) in the population.

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.