Biomedical subjects

Miodrag Micic

Publications and source records attributed to Miodrag Micic.

4 recordsLinked to original sources

PubMed2004

Intermittent single-molecule interfacial electron transfer dynamics.

We report on single-molecule studies of photosensitized interfacial electron transfer (ET) processes in Coumarin 343 (C343)-TiO(2) nanoparticles (NP) and Cresyl Violet (CV(+))-TiO(2) NP systems, using time-correlated single-photon counting coupled with scanning confocal fluorescence microscopy. Fluorescence intensity trajectories of individual dye molecules adsorbed on a semiconductor NP surface showed fluorescence fluctuations and blinking, with time constants distributed from milliseconds to seconds. The fluorescence fluctuation dynamics were found to be inhomogeneous from molecule to molecule and from time to time, showing significant static and dynamic disorders in the interfacial ET reaction dynamics. We attribute fluorescence fluctuations to the interfacial ET reaction rate fluctuations, associating redox reactivity intermittency with the fluctuations of molecule-TiO(2) electronic and Franck-Condon coupling. Intermittent interfacial ET dynamics of individual molecules could be characteristic of a surface chemical reaction strongly involved with and regulated by molecule-surface interactions. The intermittent interfacial reaction dynamics that likely occur among single molecules in other interfacial and surface chemical processes can typically be observed by single-molecule studies but not by conventional ensemble-averaged experiments.

Journal Article↗

PubMed2004

Correlated atomic force microscopy and fluorescence lifetime imaging of live bacterial cells.

We report on imaging living bacterial cells by using a correlated tapping-mode atomic force microscopy (AFM) and confocal fluorescence lifetime imaging microscopy (FLIM). For optimal imaging of Gram-negative Shewanella oneidensis MR-1 cells, we explored different methods of bacterial sample preparation, such as spreading the cells on poly-L-lysine coated surfaces or agarose gel coated surfaces. We have found that the agarose gel containing 99% ammonium acetate buffer can provide sufficient local aqueous environment for single bacterial cells. Furthermore, the cell surface topography can be characterized by tapping-mode in-air AFM imaging for the single bacterial cells that are partially embedded. Using in-air rather than under-water AFM imaging of the living cells significantly enhanced the contrast and signal-to-noise ratio of the AFM images. Near-field AFM-tip-enhanced fluorescence lifetime imaging (AFM-FLIM) holds high promise on obtaining fluorescence images beyond optical diffraction limited spatial resolution. We have previously demonstrated near-field AFM-FLIM imaging of polymer beads beyond diffraction limited spatial resolution. Here, as the first step of applying AFM-FLIM on imaging bacterial living cells, we demonstrated a correlated and consecutive AFM topographic imaging, fluorescence intensity imaging, and FLIM imaging of living bacterial cells to characterize cell polarity.

Bacteria↗

PubMed2004

Study of the lignin model compound supramolecular structure by combination of near-field scanning optical microscopy and atomic force microscopy.

In this paper, we present a nanoscale study of the supramolecular structure of the dehydrogenate polymer (ZL-DHP) lignin model compound. The combination of near-field scanning optical microscopy (NSOM or SNOM) and atomic force microscopy (AFM) has been utilized to explore physicochemical properties of the lignin model compound on a scale ranging from individual macromolecules to globular supramolecular assemblies. By utilizing NSOM in transmission mode, the optical inhomogeneity in the lignin supramolecular structure has been observed for the first time. In particular, the transmission-mode NSOM images reveal a combination of hollow and layered supramolecular globular structure in the lignin model compound. Through the paired use of TappingMode and pulsed-mode AFM, we have also confirmed the existence of regions with different rheological properties on the single lignin model compound supramolecular assembly.

Alcohols↗

PubMed2002

ZL-DHP lignin model compound at the air-water interface.

In this paper we present our surface chemistry studies of enzymatically polymerized, poly-coniferyl alcohol lignin model compound (dehydrogenate polymer a.k.a. ZL-DHP) at the air-water interface. Using the CHCl(3)/MeOH (5:1 v/v) spreading solvent, we found an average molecular area of ZL-DHP of approximately 1200 A(2). The monolayer expresses a high compressibility with a collapsed area of 500 A(2) and collapsed surface pressure of 28 mN m(-1). In the range of applied surface pressures, ZL-DHP polymer have no phase changes, as shown by the very high linearity (R=0.994) of absorbance vs. surface pressure cure. There was no symmetry transitions observed as shown by absence of shifts of absorption peak maximums.

Air↗