Tuning the architectural integrity of high-performance magneto-fluorescent core-shell nanoassemblies in cancer cells

Electrostatic Linear Ion Trap Optimization Strategy for High Resolution Charge Detection Mass Spectrometry

Single ion mass measurements allow mass distributions to be recorded for heterogeneous samples that cannot be analyzed by conventional mass spectrometry. In charge detection mass spectrometry (CD-MS), ions are detected using a conducting cylinder coupled to a charge sensitive amplifier. For optimum performance, the detection cylinder is embedded in an electrostatic linear ion trap (ELIT) where trapped ions oscillate between end-caps that act as opposing ion mirrors. The oscillating ions generate a periodic signal that is analyzed by fast Fourier transforms. The frequency yields the m/z, and the magnitude provides the charge. With a charge precision of 0.2 elementary charges, ions can be assigned to their correct charge states with a low error rate, and the m/z resolving power determines the mass resolving power. Previously, the best mass resolving power achieved with CD-MS was 300. We have recently increased the mass resolving power to 700, through the better optimization of the end-cap potentials. To make a more dramatic improvement in the m/z resolving power, it is necessary to find an ELIT geometry and end-cap potentials that can simultaneously make the ion oscillation frequency independent of both the ion energy and ion trajectory (angular divergence and radial offset) of the entering ion. We describe an optimization strategy that allows these conditions to be met while also adjusting the signal duty cycle to 50% to maximize the signal-to-noise ratio for the charge measurement. The optimized ELIT provides an m/z resolving power of over 300 000 in simulations. Coupled with the high precision charge determination available with CD-MS, this will yield a mass resolving power of 300 000. Such a high mass resolving power will be transformative for the analysis of heterogeneous samples.

Applications of Charge Detection Mass Spectrometry in Molecular Biology and Biotechnology

Charge detection mass spectrometry (CDMS) is a single-particle technique where the masses of individual ions are determined from simultaneous measurement of their mass-to-charge ratio (m/z) and charge. Masses are determined for thousands of individual ions, and then the results are binned to give a mass spectrum. Using this approach, accurate mass distributions can be measured for heterogeneous and high-molecular-weight samples that are usually not amenable to analysis by conventional mass spectrometry. Recent applications include heavily glycosylated proteins, protein complexes, protein aggregates such as amyloid fibers, infectious viruses, gene therapies, vaccines, and vesicles such as exosomes.

Impact of RAFT chain transfer agents on the polymeric shell density of magneto-fluorescent nanoparticles and their cellular uptake

The impact of nanoparticle surface chemistry on cell interactions and especially cell uptake has become evident over the last few years in nanomedicine. Since PEG polymers have proved to be ideal tools for attaining stealthiness and favor escape from the in vivo mononuclear phagocytotic system, the accurate control of their geometry is of primary importance and can be achieved through reversible addition-fragmentation transfer (RAFT) polymerization. In this study, we demonstrate that the residual groups of the chain transfer agents (CTAs) introduced in the main chain exert a significant impact on the cellular internalization of functionalized nanoparticles. High-resolution magic angle spinning ¹H NMR spectroscopy and fluorescence spectroscopy permitted by the magneto-fluorescence properties of nanoassemblies (NAs) revealed the compaction of the PEG comb-like shell incorporating CTAs with a long alkyl chain, without changing the overall surface potential. As a consequence of the capability of alkyl units to self-assemble at the NA surface while hardly contributing more than 0.5% to the total polyelectrolyte weight, denser PEGylated NAs showed notably less internalization in all cells of the tumor microenvironment (tumor cells, macrophages and healthy cells). Interestingly, such differentiated uptake is also observed between pro-inflammatory M1-like and immunosuppressive M2-like macrophages, with the latter more efficiently phagocytizing NAs coated with a less compact PEGylated shell. In contrast, the NA diffusion inside multicellular spheroids, used to mimic solid tumors, appeared to be independent of the NA coating. These results provide a novel effort-saving approach where the sole variation of the chemical nature of CTAs in RAFT PEGylated polymers strikingly modulate the cell uptake of nanoparticles upon the organization of their surface coating and open the pathway toward selectively addressing macrophage populations for cancer immunotherapy.

Recent Advances in Multimodal Molecular Imaging of Cancer Mediated by Hybrid Magnetic Nanoparticles

Cancer is the second leading cause of death in the world, which is why it is so important to make an early and very precise diagnosis to obtain a good prognosis. Thanks to the combination of several imaging modalities in the form of the multimodal molecular imaging (MI) strategy, a great advance has been made in early diagnosis, in more targeted and personalized therapy, and in the prediction of the results that will be obtained once the anticancer treatment is applied. In this context, magnetic nanoparticles have been positioned as strong candidates for diagnostic agents as they provide very good imaging performance. Furthermore, thanks to their high versatility, when combined with other molecular agents (for example, fluorescent molecules or radioisotopes), they highlight the advantages of several imaging techniques at the same time. These hybrid nanosystems can be also used as multifunctional and/or theranostic systems as they can provide images of the tumor area while they administer drugs and act as therapeutic agents. Therefore, in this review, we selected and identified more than 160 recent articles and reviews and offer a broad overview of the most important concepts that support the synthesis and application of multifunctional magnetic nanoparticles as molecular agents in advanced cancer detection based on the multimodal molecular imaging approach.

Mass spectrometry for multi-dimensional characterization of natural and synthetic materials at the nanoscale

Characterization of materials at the nanoscale plays a crucial role in in-depth understanding the nature and processes of the substances. Mass spectrometry (MS) has characterization capabilities for nanomaterials (NMs) and nanostructures by offering reliable multi-dimensional information consisting of accurate mass, isotopic, and molecular structural information. In the last decade, MS has emerged as a powerful nano-characterization technique. This review comprehensively summarizes the capabilities of MS in various aspects of nano-characterization that greatly enrich the toolbox of nano research. Compared with other characterization techniques, MS has unique capabilities for real-time monitoring and tracking reaction intermediates and by-products. Moreover, MS has shown application potential in some novel aspects, such as MS imaging of the biodistribution and fate of NMs in animals and humans, stable isotopic tracing of NMs, and risk assessment of NMs, which deserve update and integration into the current knowledge framework of nano-characterization.

Weighing synthetic polymers of ultra-high molar mass and polymeric nanomaterials: What can we learn from charge detection mass spectrometry?

Advances in soft ionization techniques for mass spectrometry (MS) of polymeric materials make it possible to determine the masses of intact molecular ions exceeding megadaltons. Interfacing MS with separation and fragmentation methods has additionally led to impressive advances in the ability to structurally characterize polymers. Even if the gap to the megadalton range has been bridged by MS for polymers standards, the MS-based analysis for more complex polymeric materials is still challenging. Charge detection mass spectrometry (CDMS) is a single-molecule method where the mass and the charge of each ion are directly determined from individual measurements. The entire molecular mass distribution of a polymer sample can be thus accurately measured. Described in this perspective paper is how molecular weight distribution as well as charge distribution can provide new insights into the structural and compositional studies of synthetic polymers and polymeric nanomaterials in the megadalton to gigadalton range of molecular weight. The recent multidimensional CDMS studies involving couplings with separation and dissociation techniques will be presented. And, finally, an outlook for the future avenues of the CDMS technique in the field of synthetic polymers of ultra-high molar mass and polymeric nanomaterials will be provided.

Luminophore and Magnetic Multicore Nanoassemblies for Dual-Mode MRI and Fluorescence Imaging

Nanoassemblies encompass a large variety of systems (organic, crystalline, amorphous and porous). The nanometric size enables these systems to interact with biological entities and cellular organelles of similar dimensions (proteins, cells, …). Over the past 20 years, the exploitation of their singular properties as contrast agents has led to the improvement of medical imaging. The use of nanoprobes also allows the combination of several active units within the same nanostructure, paving the way to multi-imaging. Thus, the nano-object provides various additional information which helps simplify the number of clinical procedures required. In this review, we are interested in the combination between fluorescent units and magnetic nanoparticles to perform dual-mode magnetic resonance imaging (MRI) and fluorescent imaging. The effect of magnetic interaction in multicore iron oxide nanoparticles on the MRI contrast agent properties is highlighted.

Organic Fluorescent Dye-based Nanomaterials: Advances in the Rational Design for Imaging and Sensing Applications

Self-assembled fluorescent nanomaterials based on small-molecule organic dyes are gaining increasing popularity in imaging and sensing applications over the past decade. This is primarily due to their ability to combine spectral properties tunability and biocompatibility of small molecule organic fluorophores with brightness, chemical and colloidal stability of inorganic materials. Such a unique combination of features comes with rich versatility of dye-based nanomaterials: from aggregates of small molecules to sophisticated core-shell nanoarchitectures involving hyperbranched polymers. Along with the ongoing discovery of new materials and better ways of their synthesis, it is very important to continue systematic studies of fundamental factors that regulate the key properties of fluorescent nanomaterials: their size, polydispersity, colloidal stability, chemical stability, absorption and emission maxima, biocompatibility, and interactions with biological interfaces. In this review, we focus on the systematic description of various types of organic fluorescent nanomaterials, approaches to their synthesis, and ways to optimize and control their characteristics. The discussion is built on examples from reports on recent advances in the design and applications of such materials. Conclusions made from this analysis allow a perspective on future development of fluorescent nanomaterials design for biomedical and related applications.

Small Molecule-Based Fluorescent Organic Nanoassemblies with Strong Hydrogen Bonding Networks for Fine Tuning and Monitoring Drug Delivery in Cancer Cells

Bright supramolecular fluorescent organic nanoassemblies (FONs), based on strongly polar red-emissive benzothiadiazole fluorophores containing acidic units, are fabricated to serve as theranostic tools with large colloidal stability in the absence of a polymer or surfactant. High architectural cohesion is ensured by the multiple hydrogen-bonding networks, reinforced by the dipolar and hydrophobic interactions developed between the dyes. Such interactions are harnessed to ensure high payload encapsulation and efficient trapping of hydrophobic and hydrogen-bonding drugs like doxorubicin, as shown by steady state and time-resolved measurements. Fine tuning of the drug release in cancer cells is achieved by adjusting the structure and combination of the fluorophore acidic units. Notably delayed drug delivery is observed by confocal microscopy compared to the entrance of hydrosoluble doxorubicin, demonstrating the absence of undesirable burst release outside the cells by using FONs. Since FON-constituting fluorophores exhibit a large emission shift from red to green when dissociating in contact with the lipid cellular content, drug delivery could advantageously be followed by dual-color spectral detection, independently of the drug staining potentiality.

Bioconjugated fluorescent organic nanoparticles targeting EGFR-overexpressing cancer cells

The field of optical bioimaging has considerably flourished with the advent of sophisticated microscopy techniques and ultra-bright fluorescent tools. Fluorescent organic nanoparticles (FONs) have thus recently appeared as very attractive labels for their high payload, absence of cytotoxicity and eventual biodegradation. Nevertheless, their bioconjugation to target specific receptors with high imaging contrast is scarcely performed. Moreover, assessing the reality of bioconjugation represents high challenges given the sub-nanomolar concentrations resulting from the commonly adopted nanoprecipitation fabrication process. Here, we describe how the combination of a magnetic shell allows us to easily generate red-emitting FONs conjugated with the epidermal growth factor ligand (EGF), a small protein promoting cancer cell proliferation by activating the EGF receptor (EGFR) pathway. Dual color fluorescence correlation spectroscopy combined with immunofluorescence is originally harnessed in its time trace mode to unambiguously demonstrate covalent attachment between the FON and EGF at sub-nanomolar concentrations. Strong asymmetric clustering of EGF-conjugated FONs is observed at the membrane of MDA-MB-468 human breast cancer cells overexpressing EGF receptors using super-resolution fluorescence microscopy. Such high recruitment of EGF-conjugated FONs is attributed to their EGF multivalency (4.7 EGF per FON) which enables efficient EGFR activation and subsequent phosphorylation. The large hydrodynamic diameter (D_H ∼ 301 nm) of EGF-conjugated FONs prevents immediate engulfment of the sequestered receptors, which provides very bright and localized spots in less than 30 minutes. The reported bioconjugated nanoassemblies could thus serve as ultra-bright probes of breast cancer cells with EGFR-overexpression that is often associated with poor prognosis.

PEGylated Anionic Magnetofluorescent Nanoassemblies: Impact of Their Interface Structure on Magnetic Resonance Imaging Contrast and Cellular Uptake

Controlling the interactions of functional nanostructures with water and biological media represents high challenges in the field of bioimaging applications. Large contrast at low doses, high colloidal stability in physiological conditions, the absence of cell cytotoxicity, and efficient cell internalization represent strong additional needs. To achieve such requirements, we report on high-payload magnetofluorescent architectures made of a shell of superparamagnetic iron oxide nanoparticles tightly anchored around fluorescent organic nanoparticles. Their external coating is simply modulated using anionic polyelectrolytes in a final step to provide efficient magnetic resonance imaging (MRI) and fluorescence imaging of live cells. Various structures of PEGylated polyelectrolytes have been synthesized and investigated, differing from their iron oxide complexing units (carboxylic vs phosphonic acid), their structure (block- or comblike), their hydrophobicity, and their fabrication process [conventional or reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization] while keeping the central magnetofluorescent platforms the same. Combined photophysical, magnetic, NMRD, and structural investigations proved the superiority of RAFT polymer coatings containing carboxylate units and a hydrophobic tail to impart the magnetic nanoassemblies (NAs) with enhanced-MRI negative contrast, characterized by a high r₂/r₁ ratio and a transverse relaxation r₂ equal to 21 and 125 s^-1 mmol^-1 L, respectively, at 60 MHz clinical frequency (∼1.5 T). Thanks to their dual modality, cell internalization of the NAs in mesothelioma cancer cells could be evidenced by both confocal fluorescence microscopy and magnetophoresis. A 72 h follow-up showed efficient uptake after 24 h with no notable cell mortality. These studies again pointed out the distinct behavior of RAFT polyelectrolyte-coated bimodal NAs that internalize at a slower rate with no adverse cytotoxicity. Extension to multicellular tumor cell spheroids that mimic solid tumors revealed the successful internalization of the NAs in the periphery cells, which provides efficient deep-imaging labels thanks to their induced T₂* contrast, large emission Stokes shift, and bright dotlike signal, popping out of the strong spheroid autofluorescence.