Aidin Lak

Molecular nanorulers are essential tools for mapping intramolecular distances and studying nucleic acid and protein interactions. Here, we present MARs ( MA gnetic molecular nano R ulers), a fundamentally new class of nanorulers based on measuring the magnetization dynamics of rationally engineered and ultra-responsive colloidal magnetic nanoparticles with magnetic particle spectrometry (MPS). By tuning the grafting density of DNA receptors on MARs, we reveal surface molecular crowding as a simple, yet programmable parameter to tune the response of MARs over a broad range of target DNA concentrations. We show that MARs can distinguish target binding positions along receptor strands by regulating how much the binding effect is translated into the response. Combining their switchable binding-to-response and DNA hairpins, we show that MARs can resolve the full combinatorial space of four short DNA targets (2 ⁴ -1) in a one-design-for-all fashion, with blind assays achieving 80% best-prediction accuracy. By modelling MPS response of MARs using the Fokker-Planck equation, we demonstrate that their response is well predictable. Using biotinylated DNA constructs and calibrating their lengths for different numbers of base pair, we reveal that MARs can determine the distance between bound monostreptavidin and their surface with a dynamic distance range of up to 13 nm and a resolution of 1.3 ± 0.2 nm. Our study establishes a new class of molecular nanorulers for resolving conformational changes in nucleic acids and measuring distances at the molecular level in free solution via an adaptable, simple, and rapid workflow, making MARs highly promising for high throughput screening assays.

Magnetic nanoparticles (MNPs) enable unique capabilities for biosensing and actuation via coupling to DNA origami, yet how DNA grafting density affects their dynamics and accessibility remains poorly understood. Here, we demonstrate functionalization of MNPs with single-stranded DNA (ssDNA) via click chemistry conjugation with tunable grafting density. Several complementary methods show that particle translational and rotational dynamics exhibit a sigmoidal dependence on ssDNA grafting density. At low densities ssDNA strands are coiled and cause small changes to particle dynamics, while at high densities they form polymer brushes that cooperatively change particle dynamics. Intermediate ssDNA densities show the highest magnetic biosensing sensitivity for detection of target nucleic acids. Finally, we demonstrate that MNPs with high grafting densities are required to efficiently couple them to DNA origami. These results together establish ssDNA grafting density as a critical parameter for functionalization of MNPs for use in a broad range of applications.

Immunoassays exploiting magnetization dynamics of magnetic nanoparticles are highly promising for mix-and-measure, quantitative, and point-of-care diagnostics. However, how single-core magnetic nanoparticles can be employed to reduce particle concentration and concomitantly maximize assay sensitivity is not fully understood. Here, we design monodisperse Néel and Brownian relaxing magnetic nanocubes (MNCs) of different sizes and compositions. We provide insights into how to decouple physical properties of these MNCs to achieve an ultrahigh sensitivity. We find that a tri-component-based Zn0.06Co0.80Fe2.14O4 particles, with out-of-phase to initial magnetic susceptibility χ^''/χ_0 ratio of 0.47 out of nominal ratio of 0.50 for thoroughly magnetically blocked particles, show the ultrahigh magnetic sensitivity by providing rich magnetic particle spectroscopy harmonics spectrum despite bearing a lower saturation magnetization value than di-component Zn0.1Fe2.9O4 with a high value of saturation magnetization. The Zn0.06Co0.80Fe2.14O4 MNCs, coated with polyethylene glycol-based ligands, show three orders of magnitude better sensitivity than commercially available particles of comparable size.

Iron oxide nanoparticles have tremendous scientific and technological potential in a broad range of technologies, from energy applications to biomedicine. To improve their performance, single‐crystalline and defect‐free nanoparticles have thus far been aspired. However, in several recent studies, defect‐rich nanoparticles outperform their defect‐free counterparts in magnetic hyperthermia and magnetic particle imaging (MPI). Here, an overview on the state‐of‐the‐art of design and characterization of defects and resulting spin disorder in magnetic nanoparticles is presented with a focus on iron oxide nanoparticles. The beneficial impact of defects and disorder on intracellular magnetic hyperthermia performance of magnetic nanoparticles for drug delivery and cancer therapy is emphasized. Defect‐engineering in iron oxide nanoparticles emerges to become an alternative approach to tailor their magnetic properties for biomedicine, as it is already common practice in established systems such as semiconductors and emerging fields including perovskite solar cells. Finally, perspectives and thoughts are given on how to deliberately induce defects in iron oxide nanoparticles and their potential implications for magnetic tracers to monitor cell therapy and immunotherapy by MPI.

Multifunctional imaging nanoprobes continue to garner strong interest for their great potential in the detection and monitoring of cancer. In this study, we investigate a series of spatially arranged iron oxide nanocube-based clusters (i.e., chain-like dimer/trimer, centrosymmetric clusters, and enzymatically cleavable two-dimensional clusters) as magnetic particle imaging and magnetic resonance imaging probes. Our findings demonstrate that the short nanocube chain assemblies exhibit remarkable magnetic particle imaging signal enhancement with respect to the individually dispersed or the centrosymmetric cluster analogues. This result can be attributed to the beneficial uniaxial magnetic dipolar coupling occurring in the chain-like nanocube assembly. Moreover, we could effectively synthesize enzymatically cleavable two-dimensional nanocube clusters, which upon exposure to a lytic enzyme, exhibit a progressive increase in magnetic particle imaging signal at well-defined incubation time points. The increase in magnetic particle imaging signal can be used to trace the disassembly of the large planar clusters into smaller nanocube chains by enzymatic polymer degradation. These studies demonstrate that chain-like assemblies of iron oxide nanocubes offer the best spatial arrangement to improve magnetic particle imaging signals. In addition, the nanocube clusters synthesized in this study also show remarkable transverse magnetic resonance imaging relaxation signals. These nanoprobes, previously showcased for their outstanding heat performance in magnetic hyperthermia applications, have great potential as dual imaging probes and could be employed to improve the tumor thermo-therapeutic efficacy, while offering a readable magnetic signal for image mapping of material disassemblies at tumor sites.

Iron oxide nanoparticles have tremendous scientific and technological potential in a broad range of technologies, from energy applications to biomedicine. To improve their performance, single-crystalline and defect-free nanoparticles have thus far been aspired. However, in several recent studies defect-rich nanoparticles outperform their defect-free counterparts in magnetic hyperthermia and magnetic particle imaging. Here, an overview on the state-of-the-art of design and characterization of defects and resulting spin disorder in magnetic nanoparticles is presented with a focus on iron oxide nanoparticles. The beneficial impact of defects and disorder on intracellular magnetic hyperthermia performance of magnetic nanoparticles for drug delivery and cancer therapy is emphasized. Defect-engineering in iron oxide nanoparticles emerges to become an alternative approach to tailor their magnetic properties for biomedicine, as it is already common practice in established systems such as semiconductors and emerging fields including perovskite solar cells. Finally, perspectives and thoughts are given on how to deliberately induce defects in iron oxide nanoparticles and their potential implications for magnetic tracers to monitor cell therapy and immunotherapy by magnetic particle imaging.

Multi-dentate ligands enabling a quick and high yield water transfer of inorganic nanocrystals (NCs) via a ligand exchange process is of great interest to promote the applications of NCs in the biomedical field. Here, we describe a facile two-step protocol for the synthesis of polymeric multi-dentate ligands that are suitable for the water transfer of hydrophobic colloidal inorganic nanocrystals (NCs). This protocol first exploits the photo-induced atom transfer radical (photo-ATRP) copolymerization of ester-activated N-succinimidyl methacrylate and oligoethylene glycol methyl ether methacrylate. A high monomer conversion rate along with a fair control over the polymerization is confirmed by size exclusion chromatography and nuclear magnetic resonance spectroscopy. In the second step, the activated carboxyl moieties of the copolymers are reacted with nucleophilic agents such as 2-aminoethylphosphonic acid or histamine dihydrochloride via a post-polymerization reaction to generate phosphonic- or amino-based multi-dentate ligands, respectively. As shown here, polymers comprising poly-phosphonic acid moieties are suitable as multi-dentate ligands for water transfer of multiple varieties of NCs with distinct compositions including iron oxide nanoparticles, CdSe@CdS quantum dots (QDs) and up-converting nanoparticles (UCNPs). Meanwhile the polymers containing histamine groups are also able to strongly coordinate to the surface of semiconductor QDs, thus enabling their water transfer. Notably, the NCs exhibit long-term stability in physiological media (saline) upon water transfer, while their size, shape, magnetic properties, and optical properties were also maintained. The UCNPs could be imaged when excited under an infrared laser while the QDs show a bright fluorescence signal under UV irradiation. QDs coated with a poly-phosphonic acid-based ligand resulted in a more homogeneous coating as demonstrated by the narrow band on gel electrophoresis, along with a higher quantum yield (QY ∼48%) in comparison with the polyimidazole-based ones (QY ∼31%). The aqueous IONPs instead were proven to provide a transversal relaxation making them useful as contrast agents in magnetic resonance imaging. The water transfer procedure is straightforward thanks to the full solubility of the amphiphilic polymer in the NC chloroform solution. This enables the right interaction between the anchoring moieties on the polymer chains and the surface of NCs, thus replacing the surfactant molecules. The gram scale production of the polymer together with the very simple steps of the water transfer protocol enables a quick translation of the protocol for large scale production of aqueous stabilized nanoparticles.

Magnetic nanoparticles are critical to a broad range of applications, from medical diagnostics and therapeutics to biotechnological processes and single molecule manipulation. To advance these applications, facile and robust routes to synthesize highly magnetic nanoparticles over a wide size range are needed. Here, we demonstrate that changing the degassing temperature of thermal decomposition of metal acetylacetonate precursors from 90 to 25°C tunes the size of ferrimagnetic Zn_xFe_3-xO₄ nanocubes from 25 to 100 nm, respectively. We show that degassing at 90°C nearly entirely removes acetylacetone ligands from the reaction, which results in an early formation of monomers and a reaction-controlled growth following LaMer's model towards small nanocubes. In contrast, degassing at 25°C only partially dissociates acetylacetone ligands from the metal center and triggers a delayed formation of monomers, which leads to intermediate assembled structures made of tiny irregular crystallites and an eventual formation of large nanocubes via a diffusion-controlled growth mechanism. Using complementary techniques, we determine the substitution fraction x of Zn²⁺ to be in the range of 0.35-0.37. Our method reduces the complexity of the thermal decomposition method by narrowing the synthesis parameter space to a single physical parameter and enables fabrication of highly magnetic and uniform zinc ferrite nanocubes over a broad size range. The resulting particles are promising for a range of applications, from magnetic fluid hyperthermia to actuation of macromolecules.

Magnetic nanoparticles are critical to a broad range of applications, from medical diagnostics and therapeutics to biotechnological processes and single molecule manipulation. To advance these applications, facile and robust routes to synthesize highly magnetic nanoparticles over a wide size range are needed. Here, we demonstrate that changing the degassing temperature of thermal decomposition of metal acetylacetonate precursors from 90 to 25°C tunes the size of ferrimagnetic ZnxFe3-xO4 nanocubes from 25 to 100 nm, respectively. We show that degassing at 90°C nearly entirely removes acetylacetone ligands from the reaction, which results in an early formation of monomers and a reaction-controlled growth following LaMer's model towards small nanocubes. In contrast, degassing at 25°C only partially dissociates acetylacetone ligands from the metal center and triggers a delayed formation of monomers, which leads to intermediate assembled structures made of tiny irregular crystallites and an eventual formation of large nanocubes via a diffusion-controlled growth mechanism. Using complementary techniques, we determine the substitution fraction x of Zn2+ to be in the range of 0.35-0.37. Our method reduces the complexity of the thermal decomposition method by narrowing the synthesis parameter space to a single physical parameter and enables fabrication of highly magnetic and uniform zinc ferrite nanocubes over a broad size range. The resulting particles are promising for a range of applications, from magnetic fluid hyperthermia to actuation of macromolecules.

Herein, by studying a stepwise phase transformation of 23 nm FeO–Fe₃O₄ core–shell nanocubes into Fe₃O₄, we identify a composition at which the magnetic heating performance of the nanocubes is not affected by the medium viscosity and aggregation. Structural and magnetic characterizations reveal the transformation of the FeO–Fe₃O₄ nanocubes from having stoichiometric phase compositions into Fe²⁺-deficient Fe₃O₄ phases. The resultant nanocubes contain tiny compressed and randomly distributed FeO subdomains as well as structural defects. This phase transformation causes a 10-fold increase in the magnetic losses of the nanocubes, which remain exceptionally insensitive to the medium viscosity as well as aggregation unlike similarly sized single-phase magnetite nanocubes. We observe that the dominant relaxation mechanism switches from Néel in fresh core–shell nanocubes to Brownian in partially oxidized nanocubes and once again to Néel in completely treated nanocubes. The Fe²⁺ deficiencies and structural defects appear to reduce the magnetic energy barrier and anisotropy field, thereby driving the overall relaxation into Néel process. The magnetic losses of these nanoparticles remain unchanged through a progressive internalization/association to ovarian cancer cells. Moreover, the particles induce a significant cell death after being exposed to hyperthermia treatment. Here, we present the largest heating performance that has been reported to date for 23 nm iron oxide nanoparticles under intracellular conditions. Our findings clearly demonstrate the positive impacts of the Fe²⁺ deficiencies and structural defects in the Fe₃O₄ structure on the heating performance into intracellular environment.