Nuri Oncel

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.

Lyme disease, caused by the bacterium Borrelia 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 (ECM) proteins such as fibronectin (Fn). This study investigates the binding dynamics of B. burgdorferi surface proteins RevA, BBK32, BmpA, OspA, and OspC to Fn using atomic force microscopy-based single-molecule force spectroscopy (AFM-SMFS). 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.

In this study, a three-dimensional (3D) structured nanomaterial has been developed to enhance the electrochemical properties of supercapacitors. The nanomaterial's structure was engineered by incorporating divalent metal ions (M²⁺: Ni²⁺ and Co²⁺) into reduced graphene oxide (rGO) layers supported on nickel foam (3D NC-rGO@Ni-foam), forming a binder-free hybrid electrode. This was accomplished through a combination of in situ wet-chemistry and hydrothermal techniques. This binder-free electrode material has stacked layers of rGO, which improve conductivity, while the M²⁺ ions intercalated between these layers function as redox couples, thereby significantly improving the specific capacitance. Furthermore, the Ni-foam substrate offers a porous configuration and works as the current collector. In contrast to traditional slurry coating methods, the in situ growth of nanostructures on Ni-foam is expected to enhance strong adhesion, high conductivity, and effective ion transport. The structural morphology, chemical composition, and electrochemical behavior of the 3D NC-rGO@Ni-foam electrode were comprehensively investigated using techniques such as scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and other analytical methods. This binder-free 3D hybrid electrode material demonstrated a specific capacitance (C _s) of 2612 F/g at 1 A/g. The symmetric device fabricated also demonstrated a substantial energy density (E) of 55 W·h/kg and a power density (P) of 155 W/kg across a wide potential window of 2.5 V. The electrochemical characteristics and mechanical stability of 3D NC-rGO@Ni-foam indicate its potential as a high-performance electrode material for scalable energy storage systems.

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.

In this study, we employed lateral force microscopy, a specialized technique within atomic force microscopy, to explore the nanoscale frictional properties of 2D SnSe and SnSe$_2$ layers, and we compared these findings with graphene, a commonly used solid lubricant. Our results revealed that SnSe and SnSe2 layers exhibited superior lubricative performance compared to graphene with similar thickness, with SnSe$_2$ demonstrating friction levels up to three times lower. This lower friction observed in SnSe$_2$, as compared to SnSe, was further substantiated by extensive Density Functional Theory (DFT) calculations, confirming the intrinsic material properties contributing to their enhanced lubricative behavior.

We investigated the thermal resistance of SnSe nanoflakes using scanning thermal microscopy, an extension of atomic force microscopy that allows for nanoscale thermal mapping. The nanoflakes studied ranged in thickness from 5 nm to 40 nm, enabling us to observe the thermal properties across a wide range of dimensions. Our results show a clear trend: as the thickness of the nanoflakes increases, the thermal resistance also increases. This suggests that diffusive mechanisms govern heat transport in SnSe nanoflakes and follow Fourier's law of heat conduction. The observed behavior can be attributed to the inherently short phonon mean free path in SnSe which is on the order of 5 nm at room temperature.

X-ray Photoelectron Spectroscopy (XPS) is generally used for chemical analysis of surfaces and interfaces. This method involves the analysis of changes in binding energies and peak shapes of elements under consideration. It is also possible to use XPS to study the effect of X-ray radiation on the electrical properties of thin films. We measured the Si 2p peak using X-ray powers of 300 W and 150 W on approximately 135 nm silicon dioxide (SiO2) thin films grown on both n- and p-type substrates while applying DC or AC external biases. Using the shifts in the binding energy of the Si 2p peak, we calculated the resistances and the capacitances of the SiO2 thin film. The way that the binding energies of the Si 2p peak and the capacitance of the thin film change as a function of the type of Si substrate and the power of the X-ray are explained using band bending.