Removal of electrostatic artifacts in magnetic force microscopy by controlled magnetization of the tip: application to superparamagnetic nanoparticles

Magnetic force microscopy (MFM) has been demonstrated as valuable technique for the characterization of magnetic nanomaterials. To be analyzed by MFM techniques, nanomaterials are generally deposited on flat substrates, resulting in an additional contrast in MFM images due to unavoidable heterogeneous electrostatic tip-sample interactions, which cannot be easily distinguished from the magnetic one. In order to correctly interpret MFM data, a method to remove the electrostatic contributions from MFM images is needed. In this work, we propose a new MFM technique, called controlled magnetization MFM (CM-MFM), based on the in situ control of the probe magnetization state, which allows the evaluation and the elimination of electrostatic contribution in MFM images. The effectiveness of the technique is demonstrated through a challenging case study, i.e., the analysis of superparamagnetic nanoparticles in absence of applied external magnetic field. Our CM-MFM technique allowed us to acquire magnetic images depurated of the electrostatic contributions, which revealed that the magnetic field generated by the tip is sufficient to completely orient the superparamagnetic nanoparticles and that the magnetic tip-sample interaction is describable through simple models once the electrostatic artifacts are removed

Development of new AFM based methodologies for the quantitative magnetic characterization of nanoparticles for biomedical applications

L'objectif du projet de doctorat est le développement d'une procédure innovante de mesure et post-traitement des données pour obtenir des informations quantitatives sur les paramètres magnétiques de nanoparticules magnétiques individuelles par l'utilisation de la Microscopie à Force Magnétique (MFM). Les nanoparticules magnétiques (MNP), grâce à leurs propriétés magnétiques particulières (monodomaine, superparamagnétisme, etc.) et leur taille nanométrique, conviennent à plusieurs applications biomédicales, telles que les systèmes d'administration de médicaments, les traitements de hyperthermie magnétique, l'étiquetage cellulaire, les agents de contraste pour l'imagerie a résonance magnétique (IRM). La conception de ces techniques requiert une connaissance détaillée des propriétés magnétiques des nanomatériaux utilisès, comme l'aimantation de saturation Ms, le champ magnétique de saturation Hs, la coercivité Hc. Les techniques standard, comme les dispositifs supraconducteurs à interférence quantique (SQUID) ou la magnétomètrie à échantillon vibrant (VSM), permettent la détection des propriétés magnétiques globales des populations de nanoparticules. Mais la détection des propriétés magnétiques des particules isolées n'est pas possible et l'évaluation de ces propriétés en fonction de la taille des particules n'est pas explicite. Grâce à sa résolution latérale nanométrique et sa capacité à détecter des champs magnétiques faibles, MFM est un outil puissant pour la caractérisation de dimensions de nanoparticules isolées, ainsi que leurs propriétés magnétiques. Cependant, une méthodologie pour obtenir des informations quantitatives sur les caractéristiques magnétiques de nanoparticules isolées par MFM n'a pas été individualisée, principalement en raison de i) la complexité des interactions pointe-échantillon qui affectent les mesures MFM et qui produisent également des phénomènes non magnétiques (par exemple, des interactions électrostatiques), et ii) l’absence d'un modèle théorique décrivant les interactions magnétiques entre la pointe et une nanoparticule de manière cohérente avec les données expérimentales détectées. Pour exploiter toutes le potentialités de la technique MFM en tant qu'instrument de nanométrologie magnétique, la stratégie proposée et suivie dans ce projet est organisée en 4 phases:1) a vérification théorique et expérimentale et la rationalisation des problemes ouvertes limitant l'applicabilité de la MFM à la caractérisation magnétique quantitative des NP individuels; Dans cette phase, la présence d'artefacts électrostatiques a été individualisée comme principale limite responsable de l'incohérence entre les données expérimentales et les modèles théoriques décrivant les interactions tip-NP. 2) le développement d'un appareil instrumental et d'une procédure de mesure pour évaluer et éliminer les contributions non magnétiques (électrostatiques) affectant quantitativement les données MFM; 3) l'individuation d'un modèle théorique décrivant l'interaction magnétique pointe-NP, cohérente avec les données expérimentales, et capable d'établir une relation précise entre les données mesurées et les paramètres physiques à déterminer (magnétisation dans le cas spécifique); 4) le développement d'une procédure pour mesurer quantitativement les propriétés magnétiques, et eventuellement d'autres paramètres, de nanoparticules isolées par MFM. Les résultats obtenus avec les procédures et les méthodologies présentées dans cette thèse ont démontré la possibilité de réaliser des mesures magnétiques quantitatives sur des NP magnétiques individuelles par la plateforme technologique MFM.The objective of the PhD project is the development of a innovative measurement procedure and a data post-processing method to obtain quantitative information about the magnetic parameters of single magnetic nanoparticles through the use of the Magnetic Force Microscopy (MFM) technique. Magnetic nanoparticles (MNPs), thanks to their particular magnetic properties (single domains, superparamagnetism, etc.) and their nanometric size, are thought to be suitable for several biomedical applications, such as drug delivery systems, magnetic hyperthermia treatments, cell labelling, contrast agents for Magnetic Resonance Imaging (MRI). The design of these techniques requires a detailed knowledge on the magnetic properties of the adopted nanomaterials, like the saturation magnetization Ms, the saturation magnetic field Hs, the coercivity Hc. Standard techniques, like Superconducting Quantum Interference Devices (SQUID) or Vibrating Sample Magnetometer (VSM), to allow the detection of global magnetic properties of nanoparticles populations. Nevertheless, the detection of magnetic properties of single particles is not possible and the evaluation of the particle size dependence is not explicit. Thanks to its nanometric lateral resolution and its capability to detect weak magnetic fields, MFM is a potential powerful tool for the characterization of single nanoparticles dimensions, together with their magnetic properties. However, a methodology to extract quantitative information about the magnetic characteristics of single nanoparticles through MFM has not been individuated, mainly because of the complexity of tip-sample interactions affecting MFM measurements, which produces also non magnetic phenomena (e.g. electrostatic interactions), and the lack of a theoretical model describing the magnetic tip-NP interactions consistently with the detected experimental data. In order to exploit all the potential capabilities of MFM as a magnetic nanometrology tool, the strategy proposed and followed in this project is organized in the following four phases: 1) the theoretical and experimental verification and rationalization of the open issues and the problems limiting the applicability of MFM to the quantitative magnetic characterization of single NPs; in this phase the presence of electrostatic artifacts has been individuated as the main limitation responsible for the inconsistency between experimental data and theoretical models describing the tip-NP interactions. 2) the development of an instrumental apparatus and a measurement procedure to evaluate and eliminate the non-magnetic (electrostatic) contributions quantitatively affecting the MFM data; 3) the individuation of a theoretical model describing the magnetic tip-NP magnetic interaction, coherent with the experimental data, and able to establish a precise relationship between the measured data and the physical parameters desired to be determined (magnetization in the specific case); 4) the development of a procedure to quantitatively measure the magnetic properties, and eventually other parameters, of single nanoparticles by MFM. The results obtained with the procedures and methodologies presented in this thesis demonstrated the possibility of performing quantitative magnetic measurements on single magnetic NPs by MFM technology platform.L'obiettivo del progetto di dottorato è lo sviluppo di una procedura di misura innovativa e di un metodo di elaborazione dei dati al fine di ottenere informazioni quantitative sui parametri magnetici di singole nanoparticelle magnetiche attraverso l'uso della Microscopia a Forza Magnetica MFM. Le nanoparticelle magnetiche (MNPS), grazie alle loro particolari proprietà magnetiche (singolo dominio, superparamagnetismo, etc.) e le loro dimensioni nanometriche, stanno recentemente trovando grande applicazione in diverse tecniche in campo biomedico, come i sistemi di somministrazione mirata di farmaci, trattamenti di tumori tramite ipertermia magnetica, l'etichettatura cellulare, gli agenti di contrasto per la risonanza magnetica nucleare (MRI). Il design e l’ottimizzazione di queste tecniche richiede una conoscenza dettagliata delle proprietà magnetiche dei nanomateriali adottati, come la magnetizzazione di saturazione Ms, il campo magnetico di saturazione Hs, la coercitività Hc. Le tecniche standard, come i Superconducting Quantum Interference Devices (SQUID) o i magnetometro a vibrazione del campione (VSM), consentono il rilevamento delle proprietà magnetiche globali di numerose popolazioni di nanoparticelle. Ma il rilevamento delle proprietà magnetiche di singole particelle non è possibile e la valutazione di queste proprietà in dipendenza della dimensione delle particelle non è esplicito. Grazie alla risoluzione laterale nanometrica e la sua capacità di rilevare i campi magnetici deboli, la tecnica MFM rappresenta uno strumento ad elevato potenziale per la caratterizzazione delle proprietà magnetiche di singole nanoparticelle, insieme alle loro dimensioni. Tuttavia, un metodo per estrarre informazioni quantitative sulle caratteristiche magnetiche di singole nanoparticelle attraverso la tecnica MFM non è stato individuato, soprattutto a causa della complessità delle interazioni punta-campione che interessano le misurazioni e che possono dare luogo anche a contributi non magnetici (ad esempio interazioni elettrostatiche), e alla mancanza di un modello teorico in grado di descrivere le interazioni magnetiche punta-NP in modo coerente con i dati sperimentali rilevati. Al fine di individuare e superare i limiti della tecnica MFM che ne limitano l’utilizzo come strumento nanometrologico magnetico, la strategia proposta e seguita in questo progetto di dottorato è organizzata nelle seguenti 4 fasi: 1) la verifica teorica e sperimentale e la razionalizzazione delle problematiche che limitano l'applicabilità della tecnica MFM alla caratterizzazione magnetica quantitativa di singole NP; in questa fase la presenza di artefatti elettrostatici è stato individuata come il principale limite responsabile per la riscontrata l'inconsistenza tra i dati sperimentali e modelli teorici che descrivono le interazioni tip-NP. 2) lo sviluppo di un apparato strumentale e una procedura miosura per la valutazione ed eliminazione dei contributi elettrostaticie non magnetici che influiscono quantitativamente sui dati MFM; 3) l'individuazione di un modello teorico che descrive l'interazione magnetica punta-NP coerentemente con i dati sperimentali, e in grado di stabilire una relazione precisa tra i dati misurati e i parametri fisici che si desiderano misurare (magnetizzazione nel caso specifico); 4) lo sviluppo di un procedimento per misurare quantitativamente le proprietà magnetiche, ed eventualmente altri parametri, di singole nanoparticelle tramite MFM. I risultati ottenuti con le procedure e le metodologie presentate in questa tesi hanno dimostrato la possibilità di effettuare misure magnetiche quantitative su singole NP magnetiche facendo uso della piattaforma tecnologica MFM

Magnetic force microscopy characterization of cobalt nanoparticles: a preliminary study

In order to characterize magnetic properties of cobalt-based nanoparticles synthesized through electrodeposition on metal substrates, methods must be employed which enable the imaging of sample surface, the selection of a specific nanoparticle, and the accurate evaluation of local magnetic parameters, such as magnetic moment or saturation magnetization. Due to the combination of imaging capability and quantitative probing of ultra-low magnetic field through the use of a nanometer sized tip with a magnetic coating, magnetic force microscopy (MFM) is a promising tool to characterize Co-based nanoparticles directly on substrates. In this work, the report the preliminary results of the use of MFM to analyze Co nanoparticles electrodeposited on an Al substrate. The aim wa to assess the effective capability of this technique to investigate this kind of nanomaterials, foresee offered possibilities, and highlight current limitations to overcome

Chitosan Glutamate-Coated Niosomes: a proposal for Nose-to-Brain delivery

The aim of this in vitro study is to prepare and characterize drug free and pentamidine loaded chitosan glutamate coated niosomes for intranasal drug delivery to reach the brain through intranasal delivery. Mucoadhesive properties and stability testing in various environments were evaluated to examine the potential of these formulations to be effective drug delivery vehicles for intranasal delivery to the brain. Samples were prepared using thin film hydration method. Changes in size and ζ-potential of coated and uncoated niosomes with and without loading of pentamidine in various conditions were assessed by dynamic light scattering (DLS), while size and morphology were also studied by atomic force microscopy (AFM). Bilayer properties and mucoadhesive behavior were investigated by fluorescence studies and DLS analyses, respectively. Changes in vesicle size and ζ-potential values were shown after addition of chitosan glutamate to niosomes, and when in contact with mucin solution. In particular, interactions with mucin were observed in both drug free and pentamidine loaded niosomes regardless of the presence of the coating. The characteristics of the proposed systems, such as pentamidine entrapment and mucin interaction, show promising results to deliver pentamidine or other possible drugs to the brain via nasal administration

Detection of stiff nanoparticles within cellular structures by contact resonance atomic force microscopy subsurface nanomechanical imaging

Detecting stiff nanoparticles buried in soft biological matrices by atomic force microscopy (AFM) based techniques represents a new frontier in the field of scanning probe microscopies, originally developed as surface characterization methods. Here we report the detection of stiff (magnetic) nanoparticles (NPs) internalized in cells by using contact resonance AFM (CR-AFM) employed as a potentially non-destructive subsurface characterization tool. Magnetite (Fe3O4) NPs were internalized in microglial cells from cerebral cortices of mouse embryos of 18 days by phagocytosis. Nanomechanical imaging of cells was performed by detecting the contact resonance frequencies (CRFs) of an AFM cantilever held in contact with the sample. Agglomerates of NPs internalized in cells were visualized on the basis of the local increase in the contact stiffness with respect to the surrounding biological matrix. A second AFM-based technique for nanomechanical imaging, i.e., HarmoniX™, as well as magnetic force microscopy and light microscopy were used to confirm the CR-AFM results. Thus, CR-AFM was emonstrated as a promising technique for subsurface imaging of nanomaterials in biological samples

Magnetic Force Microscopy

Magnetic force microscopy (MFM) refers to a family of scanning probe techniques based on atomic force microscopy (AFM), which allow one to image the magnetic properties of the sample surface at the nanoscale, simultaneously to its topography. Here, we review the most widespread MFM techniques, mainly dynamic MFM although static MFM is also briefly described for the sake of completeness. We illustrate the working principles, the experimental setups, and the analytical models describing the MFM response, which are fundamental for understanding and quantitatively interpreting the contrast in MFM images. An overview is given of the application fields of MFM, which cover almost all the magnetic materials, from recording media to ferromagnetic materials, nanomaterials and nanoparticles, alone and in organic or biological systems. Finally, some advances, hot topics, new applications, and open issues are presented, including the effect of external magnetic fields, nonmagnetic interactions, MFM tips calibration and advanced probes, and magnetic imaging with variable temperature

Identification of nanoparticles and nanosystems in biological matrices with scanning probe microscopy

Identification of nanoparticles and nanosystems into cells and biological matrices is a hot research topic in nanobiotechnologies. Because of their capability to map physical properties (mechanical, electric, magnetic, chemical, or optical), several scanning probe microscopy based techniques have been proposed for the subsurface detection of nanomaterials in biological systems. In particular, atomic force microscopy (AFM) can be used to reveal stiff nanoparticles in cells and other soft biomaterials by probing the sample mechanical properties through the acquisition of local indentation curves or through the combination of ultrasound-based methods, like contact resonance AFM (CR-AFM) or scanning near field ultrasound holography. Magnetic force microscopy can detect magnetic nanoparticles and other magnetic (bio)materials in nonmagnetic biological samples, while electric force microscopy, conductive AFM, and Kelvin probe force microscopy can reveal buried nanomaterials on the basis of the differences between their electric properties and those of the surrounding matrices. Finally, scanning near field optical microscopy and tip-enhanced Raman spectroscopy can visualize buried nanostructures on the basis of their optical and chemical properties. Despite at a still early stage, these methods are promising for detection of nanomaterials in biological systems as they could be truly noninvasive, would not require destructive and time-consuming specific sample preparation, could be performed in vitro, on alive samples and in water or physiological environment, and by continuously imaging the same sample could be used to dynamically monitor the diffusion paths and interaction mechanisms of nanomaterials into cells and biological systems. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology

Mechanical characterization of methanol plasma treated fluorocarbon ultrathin films through atomic force microscopy

Methanol plasma has been proposed as an effective way to improve the performances of fluorocarbon (CFx) ultrathin films as stent coatings as it can successfully modulate fluorine content and wettability of the films. Nevertheless, plasma treatment may affect mechanical properties of the films, which therefore need comprehensively characterizing to verify the suitability of treated films for application as stent coating materials. In this work we investigate mechanical properties of methanol plasma treated CFx ultrathin films on stainless steel. In particular, cohesion of the films and their adhesion to the substrate is investigated using small punch test combined with atomic force microscopy (AFM) imaging. Also, elastic and viscoelastic properties are investigated at the nanometer scale using two different AFM based advanced technique for nanomechanical characterization, i.e., HarmoniX extsuperscript{TM} and contact resonance AFM (CR-AFM). Overall, methanol plasma treated CFx films have been demonstrated to be suitable for application as stent coating also on the basis of their nanomechanical properties

Surface treatments of ss316l substrates for plasma-based diamond like carbon coatings: Study of the surface properties

[No abstract available

Analisi microtomografica del tessuto osseo trabecolare: influenza della soglia di binarizzazione sul calcolo dei parametri istomorfometrici

Nel presente studio sono state esaminate le immagini provenienti dalla scansione con microtomografia tridimensionale computerizzata di quattro campioni di tessuto osseo spugnoso. È stata analizzata l’influenza del valore di soglia assegnato per la binarizzazione delle immagini sui risultanti valori dei parametri istomorfometrici. Da tale analisi è stata riscontrata un’elevata dipendenza dei parametri istomorfometrici rispetto alla scelta del valore di soglia. Sono stati elaborati e analizzati gli istogrammi dei livelli di grigio estraibili dalle matrici numeriche delle porzioni significative delle immagini e sono state individuate alcune loro significative caratteristiche. Viene presentata una modellizzazione matematica dell’andamento degli istogrammi dell’area dei campioni di tessuto osseo spugnoso. Sulla base di tale modellizzazione sono stati delineati tre criteri per la determinazione dei valori di soglia basandosi sugli elementi quantitativi estraibili dall’andamento degli istogrammi stessi. Sono stati calcolati i relativi valori per i quattro campioni esaminati