Light extinction and scattering from aggregates composed of submicron particles

Cremonesi L, Minnai C, Ferri F, Parola A, Paroli B, Sanvito T & Potenza MAC
Journal of Nanoparticle Research volume 22, Article number: 344 (2020)

ABSTRACT: The influence of the internal structure of inhomogeneous particles on their radiative properties is an open issue repeatedly questioned in many fields of science and technology. The importance of a refined description of the particle composition and structure, going beyond mean-field approximations, is generally recognized. Here, we focus on describing internal inhomogeneities from a statistical point of view. We introduce an analytical description based on the two-point density-density correlation function, or the corresponding static structure factor, to calculate the extinction cross sections. The model agrees with numerical predictions and is validated experimentally with colloidal aggregates in the 0.3–6 μm size range, which serve as an inhomogeneous model system that can be characterized enough to work without any free parameters. The model can be tightly compared to measurements with single particle extinction and scattering and spectrophotometry and suggests a simple behavior for 90° scattering from fractal aggregates as a function of extinction, which is also confirmed experimentally and numerically. We also discuss the case of absorbing particles and report the experimental results for water suspensions of black carbon for both the forward and 90° scattering properties. In this case, the total scattering and the extinction cross sections determine the single scattering albedo, which agrees with numerical simulations. The three parameters necessary to feed radiative transfer models, namely, extinction, asymmetry parameter, and single scattering albedo, can all be set by the analytical model, with explicit dependence on a few parameters. Results are applicable to radiative transfer problems in climate, paleoclimate, star and planetary formation, and nanoparticle optical characterization for science and industry, including the intercomparison of different optical methods such as those adopted by ISO standards.

Multiparametric optical characterization of airborne dust with Single Particle Extinction and Scattering

Cremonesi L, Passerini A, Tettamanti A, Paroli B, Delmonte B, Albani S, Cavaliere F, Viganò D, BettegaG , Sanvito T, Pullia A & Potenza MAC
Environment International, 123, 156-163 (2019)

ABSTRACT: We describe a robust, portable, deployable instrument for multiparametric optical characterization of single airborne particles. It is based on the Single Particle Extinction and Scattering method with additional sensors at 45° and 90° angles. Four independent optical parameters are associated to each particle. Basically, it provides a rigorous measurement of the extinction cross section and the complex amplitude of the forward scattered field. Moreover, thanks to the multiparametric single particle approach, it is possible to roughly classify the particles within a size range from a few hundreds of nanometers to some micrometers. By assigning a reasonable single scattering albedo for each population, our data are enough to fit the phase function with acceptable uncertainties. We report here the results of tests performed with water droplets, generating well controlled data without any free parameters. Data analysis is described in detail. We also report measurements performed on urban aerosol collected in the city of Milan by recovering the optical properties and feeding radiative transfer models. The findings reported here support the importance of an accurate measurement of the phase function, as already established by the Community.

Phytotoxicity of wear debris from traditional and innovative brake pads

Maiorana S, Teoldi F, Silvani S, Mancini A, Sanguineti A, Mariani F, Cella C, Lopez A, Potenza MAC, Lodi M, Dupin D, Sanvito T, Bonfanti A, Benfenati E, Baderna D
Environment International, 123, 156-163 (2019)

ABSTRACT: Traffic-related emissions include gas and particles that can alter air quality and affect human and environmental health. Limited studies have demonstrated that particulate debris thrown off from brakes are toxic to higher plants. The acute phytotoxicity of brake pad wear debris (BPWD) investigated using cress seeds grown in soil contaminated with increasing concentrations of debris. Two types of pads were used: a commercially available phenol based pad and an innovative cement-based pad developed within of the LIFE+ COBRA project. The results suggested that even through the BPWD generated by the two pads were similar in and morphology, debris from traditional pads were more phytotoxic than that from cementitious pads, causing significant alterations in terms of root elongation and loss of plasma membrane integrity.

Single Particle Extinction and Scattering allows novel optical characterization of aerosols

Mariani F, Bernardoni V, Riccobono F, Vecchi R, Valli G, Sanvito T, Paroli B, Pullia A, Potenza MAC
J Nanopart Res 19 (2017)

ABSTRACT: We apply to aerosols the optical method of Single Particle Extinction and Scattering recently proposed for characterizing liquid suspensions and specifically adapted to the aim. It provides simultaneous measurements of the real and imaginary parts of the field scattered in the forward direction by single airborne particles passing through a tightly focused laser beam. The intensity of transmitted light is collected in the forward direction, thus realizing a self-reference interferometric scheme relying on the fundamentals of the optical theorem. A high frequency (20 MS/s), extended dynamics (12 bits) sampling is performed by a cheap segmented photodiode, and a specific pulse shape analysis is exploited to validate the signals against a precise mathematical model. We show that accessing two independent physical quantities allows to exploit physical models to recover the aerosol size distribution from the measurement of the refractive index, either real or even complex. Laboratory measurements have been performed with polydisperse aerosols made of water droplets and NaCl in the submicron range, and the system has been accurately characterized. Examples of measurements of graphite nanoparticles and Pyrethrum smoke are shown. Limitations are discussed.

Shape and size constraints on dust optical properties from the Dome C ice core, Antarctica

Potenza MAC, Albani S, Delmonte B, Villa S, Sanvito T, Paroli B, Pullia A, Baccolo G, Mahowald N & Maggi V
Scientific Reports 6 (2016), Article

ABSTRACT: Mineral dust aerosol (dust) is widely recognized as a fundamental component of the climate system and is closely coupled with glacial-interglacial climate oscillations of the Quaternary period. However, the direct impact of dust on the energy balance of the Earth system remains poorly quantified, mainly because of uncertainties in dust radiative properties, which vary greatly over space and time. Here we provide the first direct measurements of the aerosol optical thickness of dust particles windblown to central East Antarctica (Dome C) during the last glacial maximum (LGM) and the Holocene. By applying the Single Particle Extinction and Scattering (SPES) technique and imposing preferential orientation to particles, we derive information on shape from samples of a few thousands of particles. These results highlight that clear shape variations occurring within a few years are hidden to routine measurement techniques. With this novel measurement method the optical properties of airborne dust can be directly measured from ice core samples, and can be used as input into climate model simulations. Based on simulations with an Earth System Model we suggest an effect of particle non-sphericity on dust aerosol optical depth (AOD) of about 30% compared to spheres, and differences in the order of ~10% when considering different combinations of particles shapes.

Optical characterization of particles for industries

Potenza MAC, Sanvito T, Fazio G
KONA Powder and Particle review (2015)

ABSTRACT: In this work we focus on the characterization of micro- and nano-powders typically adopted for chemical mechanical polishing, extensively used whenever the global and local planarization of surfaces is required as in nanoelectronic fabs. We present an innovative method for the accurate characterization of water suspensions of nanoparticles. It relies upon the combination of a new approach to extract light-scattering information from single particles and the recently developed diagnostic tool named Single Particle Extinction and Scattering. It can be used in line. Data interpretation becomes independent of any a-priori assumptions about the samples. The results of accurate measurements performed on ceria as well as aluminium oxide slurries are reported. We show the strong advantages of this method compared with traditional ones by explicitly reporting experimental results on calibrated spheres made of different materials. We discuss possible applications for in-line characterization of ultrapure water, chemicals, slurries for abrasive processes, for example, as well as the detection of any undesired particles – which could be the key for future improvements to advanced process control systems.

Particle shape accounts for instrumental discrepancy in ice core dust size distributions

Simonsen MF, Cremonesi L, Baccolo G, Bosch S, Delmonte B, Erhardt T, Kjær HA, Potenza M, Svensson A and Vallelonga P
Clim. Past, 14, 601-608 (2018)

ABSTRACT: light obscuration particle counter and coulter based particle counter are both used for measuring the size distribution of insoluble mineral dust particles in ice cores. While the coulter method measures particle volume accurately, the equivalent light obscuration method measurement deviates substantially from the coulter depending on the type of sample. We show that the difference between the light obscuration and the coulter method measurements is mainly caused by the irregular shape of dust particles in ice core samples. The irregular shape leads means that the calibration routine based on standard spheres must be adjusted. This new calibration routine gives an increased accuracy on light obscuration measurements, which may improve future ice core record intercomparisons. We derived an analytical model for extracting the aspect ratio of dust particles from the difference between light obscuration and coulter method data. For verification, we measured the aspect ratio of the same samples directly using a Single Particle Extinction and Scattering Instrument (SPES). The results demonstrate that the model is accurate enough to discern between samples of aspect ratio 0.3 and 0.4 using only the comparison of light obscuration and coulter method data.

In vitro assessment of silver nanoparticles immunotoxicity

Galbiati V, Cornaghi L, Gianazza E, Potenza MAC, Donetti E, Marinovich M, Corsini E
Food and Chemical Toxicology (2018), In press, Accepted Manuscript

ABSTRACT: This study aimed to characterize unwanted immune effects of nanoparticles (NP) using THP-1 cells, human whole blood and enriched peripheral blood monocytes. Commercially available silver NP (AgNP < 100 nm, also confirmed by Single Particle Extinction and Scattering) were used as prototypical NP. Cells were treated with AgNP alone or in combination with classical immune stimuli (i.e. LPS, PHA, PWM) and cytokine assessed; in addition, CD54 and CD86 expression was evaluated in THP-1 cells. AgNP alone induced dose-related IL-8 production in all models, with higher response observed in THP-1 cells, possibly connected to different protein corona formation in bovine versus human serum. AgNP potentiated LPS-induced IL-8 and TNF-α, but not LPS-induced IL-10. AgNP alone induced slight increase in IL-4, and no change in IFN-γ production. While responses to PHA in term of IL-4 and IFN-γ production were not affected, increased PWM-induced IL-4 and IFN-γ production were observed, suggesting potentiation of humoral response. Reduction in PHA-induced IL-10 was observed. Overall, results indicate immunostimulatory effects. THP-1 cells work as well as primary cells, representing a useful and practical alternative, with the awareness that from a physiological point of view the whole blood assay is the one that comes closest to reality.

Single-Particle Extinction and Scattering Method Allows for Detection and Characterization of Aggregates of Aeolian Dust Grains in Ice Cores

Potenza MAC, Cremonesi L, Delmonte B, Sanvito T, Paroli B, Pullia A, Baccolo G and Maggi V
ACS Earth Space Chem. (2017), Article

ABSTRACT: Mineral dust aerosol in ice cores is one of the most important proxies for paleoclimate research. Under certain conditions, in the deeper part of ice cores, the pristine paleoclimate signal can be altered by in situ formation of dust aggregates, following the relocation of the impurities. Thus, aggregate detection is a critical indication for post-depositional processes. Clues for the presence of aggregates have been provided by anomalously large dust size distributions, while small aggregates were basically invisible to conventional dust analysis techniques. In this paper, we propose an optical approach to this problem based on the single-particle extinction and scattering (SPES) method, which allows researchers to distinguish between compact and non-compact particles through the analysis of samples populated by isometric particles contained in the core samples. This method can potentially be used during continuous flow analyses of ice cores. It allows for the detection of even the tiniest aggregates, falling within the typical size interval of aeolian mineral aerosol. This approach will potentially provide key evidence for assessing the integrity of paleoclimate records.

Measuring shape and size of micrometric particles from the analysis of the forward scattered field

Villa S, Sanvito T, Paroli B, Pullia A, Delmonte B, Potenza MAC
J. Appl. Phys. 119 (2016)

ABSTRACT: Characterizing nano- and micro-particles in fluids still proves to be a significant challenge for both science and industry. Here we show how to determine shape and size distributions of polydisperse water suspensions of micron-sized particles by the analysis of the field scattered in the forward direction by single particles illuminated by a laser beam. We exploit the novel Single Particle Extinction and Scattering (SPES) method in connection with shear conditions which give preferred orientations to the particles passing through the scattering volume. Water suspensions of calibrated non-spherical particles, polydisperse standard monophasic mineral samples of quartz and kaolinite, and a mixture of quartz and illite are studied in details. Application and limitation of the method are discussed.

Single particle optical extinction and scattering allows real time quantitative characterization of drug payload and degradation of polymeric nanoparticles

Potenza MAC, Sanvito T, Argentiere S, Cella C, Paroli B, Lenardi C, Milani P
Scientific Reports 5 (2015)

ABSTRACT: The behavior of nanoparticles in biological systems is determined by their dimensions, size distribution, shape, surface chemistry, density, drug loading and stability; the characterization of these parameters in realistic conditions and the possibility to follow their evolution in vitro and in vivo are, in most of the cases, far from the capabilities of the standard characterization technologies. Optical techniques such as dynamic light scattering (DLS) are, in principle, well suited for in line characterization of nanoparticle, however their fail in characterizing the evolution of nanoparticle in solution where change in particle dimension and density is present. Here we present an in-line optical technique based on single particle extinction and scattering (SPES) overcoming the limitations typical of DLS and allowing for the efficient characterization of nanoparticle polydispersity, index of refraction and degradation dynamics in solution. Using SPES, we characterized the evolution of PLGA nanoparticles with different structures and drug payloads in solution and we compared the results with DLS. Our results suggest that SPES could be used as a process analytical technology for pharmaceutical nanoparticle production.

Single particle extinction and scattering optical method unveils in real time the influence of the blood components on polymeric nanoparticles

Sanvito T, Bigini P, Cavanna MV, Fiordaliso F, Violatto MB, Talamini L, Salmona M, Milani P, Potenza MAC
Nanomedicine (2017), Article

ABSTRACT: Here we report the quantitative in situ characterization of size distribution evolution of polymeric nanoparticles incubated in murine serum, filtered and unfiltered murine blood. We used an analytical optical approach, named Single Particle Extinction and Scattering (SPES), which relies on the measurements of two independent parameters of single particles. SPES is based on a robust self-reference interference optical scheme which allows a rejection of the spurious signals coming from the background caused by the medium. We employed polystyrene nanoparticles as reference system and polydisperse poly(lactic-co-glycolic acid) nanoparticles. Our results demonstrate that SPES can be used for carrying out ex vivo analysis of nanoparticles to evaluate the modifications that NPs undergo in vivo following different routes of entry. Conversely, Dynamic Light Scattering is not able to provide reliable results for these systems due to the presence of the biological components in solution.

Detecting the Shape of Anisotropic Gold Nanoparticles in Dispersion With Single Particle Extinction and Scattering

Potenza MAC, Krpetic Z, Sanvito T, Cai Q, Monopoli M, de Araújo JM, Cella C, Boselli L, Castagnola V, Milani M and Dawson KA
Nanoscale (2017), Advance Article

ABSTRACT: The shape and size of nanoparticles are important parameters affecting the biodistribution, bioactivity, and toxicity. The high-throughput characterisation of nanoparticle shape in the dispersion is a fundamental prerequisite for realistic in vitro and in vivo evaluation, however, with routinely available bench-top optical characterisation techniques, it remains a challenging task. Herein, we demonstrate the efficacy of Single Particle Extinction and Scattering (SPES) technique for the in situ detection of the shape of nanoparticles in dispersion, applied to a small library of anisotropic gold particles, with potential developments of in-line detection. The use of SPES paves the way to the routine quantitative analysis of nanoparticles dispersed in biologically relevant fluids, which is of importance for the nanosafety assessment and any in vitro and in vivo administration of nanomaterials.

Measuring the complex field scattered by single submicron particles

Potenza MAC, Sanvito T, Pullia A
AIP Advances 5 (2015)

ABSTRACT: We describe a method for simultaneous measurements of the real and imaginary parts of the field scattered by single nanoparticles illuminated by a laser beam, exploiting a self-reference interferometric scheme relying on the fundamentals of the Optical Theorem. Results obtained with calibrated spheres of different materials are compared to the expected values obtained through a simplified analytical model without any free parameters, and the method is applied to a highly polydisperse water suspension of Poly(D,L-lactide-co-glycolide) nanoparticles. Advantages with respect to existing methods and possible applications are discussed.

Accurate sizing of ceria oxide nanoparticles in slurries by the analysis of the optical forward-scattered field

Potenza MAC, Sanvito T, Pullia A
J Nanopart Res 17 (2014)

ABSTRACT: We characterize slurries composed of ceria nanoparticles in the range of 100–400 nm by exploiting a new approach which makes the data interpretation independent of any a priori assumption about the sample and provides very accurate and precise measurement of the particle size distribution, irrespectively of the huge polydispersity. The complex field scattered by single particles is determined by simultaneous measurements of the extinction cross section and the forward-scattered field amplitude. Moreover, we show how this approach overcomes typical issues encountered with this kind of suspensions such as the presence of aggregates, spurious components, and gas bubbles, at variance with any other method for measuring single particles. Applications are discussed.

Free nanoparticle characterization by optical scattering field analysis: opportunities and perspectives

Potenza MAC, Milani P
J Nanopart Res 16 (2014)

ABSTRACT: Methods for the facile and in-line characterization of size distribution and physical properties of unsupported nanoparticles are of paramount importance for fundamental research and industrial applications. The state-of-the-art free nanoparticle characterization methods do not provide accuracy, high throughput, and operation easiness to support widespread use for routine characterization. In this perspective paper, we describe and discuss the opportunities provided by approaches for nanoparticle characterization based on optical measurements of the field scattered by particles. In particular, we show how insightful is the measure of both the real and the imaginary parts of the field amplitude, a task that has been considered in the past but never had a widespread exploitation. A number of opportunities are generated by this approach, in view of assessing a more efficient characterization and a better understanding of the properties of nanoparticles. We focus our attention on the capability of characterizing nanoparticles of wide interest for applications, considering cases where traditional approaches are not currently effective. Possible exploitations are both in research and in industrial environments: to validate a synthetic process, for example, or for in-line monitoring of a production plant to generate advanced process control tools, as well as decision-making tools for acting in real time during the production.