Mehmet Ozdogan

This work represents a step toward the elucidation of the biological mechanisms underpinning live cell physiology with nanometer resolution. Using low-energy (30 keV), low-fluence, probe-corrected, integrated differential phase-contrast scanning transmission electron microscopy, in conjunction with a liquid flow cell, genetically engineered Mycoplasma strains, M. mobile and M. pneumoniae, which are among the smallest self-replicating cells, were scrutinized with nanometer resolution without compromising viability. Following exposure to a 30 keV electron beam, viability was scored at a lethal fluence to 50% (LF50) of the population at LF50 > 4,700 e–/nm2 by expression of an inducible fluorescent reporter, which is in stark contrast with the LF50 < 57 e–/nm2 observed at a beam energy of 300 keV. The higher LF50 at the lower beam energy of 30 keV afforded a wide window for high-resolution imaging of cell physiology. In this window, the mechanisms for “gliding” motility in Mycoplasma, which are supposed to be essential to infection and mediate attachment to a host, were visualized with nanometer resolution.

Nicotinamide Adenine Dinucleotide Phosphate (NADPH) is a redox cofactor that plays an important role in maintaining cellular redox homeostasis, driving biosynthetic pathways, and regulating antioxidant defense mechanisms. Accurate detection of NADPH is essential for investigating metabolic regulation and oxidative stress-related diseases. In this study, we leveraged the potential of nanomaterials to develop a nanozyme that would detect and quantify NADPH. Nanozymes are synthetic nanomaterials with enzyme-like catalytic activity and have attracted significant attention due to their structural tunability, stability, suitable catalytic activity, and low production cost. Among these nanozymes, graphene quantum dots (GQDs)-based nanozymes are particularly promising for biosensing applications because of their distinctive optical and electronic properties. We designed and developed iron and nitrogen co-doped graphene quantum dots (FeN4-GQDs) with catalytic activity specific toward NADPH. The FeN4-GQDs were synthesized through a hydrothermal approach using polyethylenimine (PEI) and hemin as precursors. Comprehensive structural characterization confirmed the successful incorporation of iron and nitrogen. The synthesized nanozyme exhibited strong fluorescence signals with a quantum yield of 61%, surpassing the quinine sulfate control. The nanozyme displayed uniform morphology with an average hydrodynamic diameter of 7.1 ± 1.1 nm. Notably, this work introduces an enzyme-free platform that combines strong intrinsic fluorescence with highly sensitive and selective NADPH detection. The nanozyme demonstrated a concentration-dependent and specific fluorescence quenching response toward NADPH, attributed to efficient electron transfer between NADPH and the doped graphene domains, with a limit of detection of 17.1 nM. Biocompatibility studies in mouse brain-derived microvascular endothelial cells (BMVECs) confirmed the suitability of nanozymes for use in both normal and metabolically distressed conditions, demonstrating their potential for applications in metabolic disease research.

Lyme disease, caused by the bacterium Borrelia burgdorferi (B. burgdorferi), is a significant public health concern in North America, with approximately 500 000 cases reported annually in the United States. The dissemination of B. burgdorferi from the initial tick bite site to various tissues is facilitated by surface adhesins that bind to extracellular matrix proteins such as fibronectin (Fn). This study investigates the binding dynamics of B. burgdorferi surface proteins RevA, BBK32, BmpA, OspA, FlaB, and OspC to Fn using atomic force microscopy-based single-molecule force spectroscopy. Our results demonstrate that RevA and BBK32 form strong, stable bonds with Fn, highlighting their roles as key mediators of host-cell attachment. By quantifying the rupture forces and kinetic parameters of these interactions, we provide a deeper understanding of B. burgdorferi adhesion mechanics and offer insights into potential therapeutic strategies targeting early bacterial attachment.

We investigated the thermal resistance of SnSe nanoflakes using scanning thermal microscopy (SThM), an extension of atomic force microscopy that allows for nanoscale thermal mapping. The nanoflakes studied ranged in thickness from 5 to 40 nm, enabling us to observe the thermal properties across a wide range of dimensions. Our findings reveal a clear trend of increasing thermal resistance with SnSe nanoflake thickness, suggesting that heat transport in SnSe is governed by diffusive mechanisms that limit the effectiveness of nanostructuring in further reducing thermal conductivity. This investigation showcases the capabilities of SThM for nanoscale thermal analysis, providing critical insights into the intrinsic thermal transport properties of SnSe.

We present nanoscale friction measurements performed on sputter-deposited high entropy alloy (HEA) sulfide thin films [(VNbTaMoW)S2] via atomic force microscopy. The results reveal (i) the influence of deposition time on the film morphology and (ii) the presence of isolated areas of low friction on film surfaces. We compare the friction results on HEA sulfide thin films with those on a prototypical solid lubricant, sputter-deposited molybdenum disulfide (MoS2), and find that they are superior in terms of lubricative performance. Variable temperature x-ray diffraction, performed up to 973 K, reveals that HEA sulfide thin films exhibit improved oxidation resistance when compared with MoS2 films. Combined, our results show that HEA sulfide thin films have considerable potential as oxidation-resistant solid lubricant coatings.