Using novel interferometric quantitative phase microscopy methods, we demonstrate that the surface integral of the optical phase associated with live cells is invariant to cell water content. Thus, we provide an entirely noninvasive method to measure the nonaqueous content or "dry mass" of living cells. Given the extremely high stability of the interferometric microscope and the femtogram sensitivity of the method to changes in cellular dry mass, this new technique is not only ideal for quantifying cell growth but also reveals spatially resolved cellular and subcellular dynamics of living cells over many decades in a temporal scale. Specifically, we present quantitative histograms of individual cell mass characterizing the hypertrophic effect of high glucose in a mesangial cell model. In addition, we show that in an epithelial cell model observed for long periods of time, the mean squared displacement data reveal specific information about cellular and subcellular dynamics at various characteristic length and time scales. Overall, this study shows that interferometeric quantitative phase microscopy represents a noninvasive optical assay for monitoring cell growth, characterizing cellular motility, and investigating the subcellular motions of living cells. phase microscopy; interferometric microscopy; cell growth PHASE-CONTRAST (PC) and differential interference contrast (DIC) microscopy have been used extensively to study live cells without the need for exogenous contrast agents (32). The tremendous success of these methods is due to the fact that the optical phase shift through a given sample contains information about the refractive index (n) variations that directly result from structural features within the sample. Refractive index n can therefore be regarded as a powerful endogenous contrast agent for cellular structure (6). However, as the relationship between the irradiance and phase of the image field is generally nonlinear (30, 39), both PC and DIC are qualitative in nature and limited to morphological observations without specific structural data.Quantitative phase microscopy has received substantial interest in recent years, as quantifying optical phase shifts associated with cells provides structural and dynamical information at the nanometer scale without the need for any cell preparation or the use of exogenous contrast or labels. Existing methods for biological quantitative phase measurements can be divided into single-point and full-field techniques. Several point measurement techniques have been used for investigating the local structure and dynamics of live cells (1,7,10,14,29,36,37). In contrast, full-field phase measurement techniques provide simultaneous information from a large region of the sample, which offers the additional benefit of studying both the temporal and spatial behavior of the sample (2, 5, 9, 13, 18 -20, 40, 41).Over the past several years, our laboratory has developed new full-field phase imaging techniques that are suitable for spatially resolved investigation of live cell...

Red blood cells (RBCs) play a crucial role in health and disease, and structural and mechanical abnormalities of these cells have been associated with important disorders such as Sickle cell disease and hereditary cytoskeletal abnormalities. Although several experimental methods exist for analysis of RBC mechanical properties, optical methods stand out as they enable collecting mechanical and dynamic data from live cells without physical contact and without the need for exogenous contrast agents. In this report, we present quantitative phase microscopy techniques that enable imaging RBC membrane fluctuations with nanometer sensitivity at arbitrary time scales from milliseconds to hours. We further provide a theoretical framework for extraction of membrane mechanical and dynamical properties using time series of quantitative phase images. Finally, we present an experimental approach to extend quantitative phase imaging to 3-dimensional space using tomographic methods. By providing non-invasive methods for imaging mechanics of live cells, these novel techniques provide an opportunity for high-throughput analysis and study of RBC mechanical properties in health and disease.

We employ a novel optical technique, dynamic scattering microscopy (DSM), to extract the frequency dependence of the viscoelastic modulus associated with the red blood cell membrane. This approach applies the principle of dynamic light scattering to micro beads attached to the red blood cell membrane in thermal fluctuation. This allows for highthroughput characterization of a large number of cells simultaneously, which represents a significant advantage over current methods. The results in terms of the effective loss and storage moduli indicate the generic behavior of a viscoelastic material, characterized by power laws with exponents between 0 and 1.

Two novel type I catechol 1,2-dioxygenases inducible on aniline media were isolated from Acinetobacter lwoffii K24. Although the two purified enzymes, CD I 1 and CD I 2 , had similar intradiol cleavage activities, they showed different substrate specificities for catechol analogs, physicochemical properties, and amino acid sequences. Two catA genes, catA 1 and catA 2 , encoding by CD I 1 and CD I 2 , respectively, were isolated from the A. lwoffii K24 genomic library by using colony hybridization and PCR. Two DNA fragments containing the catA 1 and catA 2 genes were located on separate regions of the chromosome. They contained open reading frames encoding 33.4-and 30.4-kDa proteins. The amino acid sequences of the two proteins matched well with previously determined sequences. Interestingly, further analysis of the two DNA fragments revealed the locations of the catB and catC genes as well. Moreover, the DNA fragment containing catA 1 had a cluster of genes in the order catB 1 -catC 1 -catA 1 while the catB 2 -catA 2 -catC 2 arrangement was found in the catA 2 DNA fragment. These results may provide an explanation of the different substrate specificities and physicochemical properties of CD I 1 and CD I 2 .Catechol 1,2-dioxygenase is the initial enzyme of one branch of the ␤-ketoadipate pathway. This enzyme cleaves catechol intermediates into cis,cis-muconate (19,29). There are two types of catechol 1,2-dioxygenases, type I catechol 1,2-dioxygenase and type II catechol 1,2-dioxygenase (chlorocatechol 1,2-dioxygenase), which are distinguished by their substrate specificities. Type I catechol 1,2-dioxygenase has little or no cleavage activity against chlorocatechols, whereas type II catechol 1,2-dioxygenase can cleave these compounds and is found mainly in degradative pathways for chlorinated aromatic compounds (13). Catechol 1,2-dioxygenases (types I and II) have been purified, cloned, and characterized intensively in a number of different bacteria (7, 22-24, 27, 31). The organization and regulation mechanisms of cat genes (type I catechol 1,2-dioxygenase) have been reported in Acinetobacter calcoaceticus and Pseudomonas putida (1,2,15,26,30,34). In addition, several isozymes of catechol 1,2-dioxygenases were found in Pseudomonas arvilla C-1, Frateuria sp. strain ANA-18, Pseudomonas acidovorans CA28, and Pseudomonas sp. strain B13 (4,8,14,23). P. acidovorans CA28 (14) and Pseudomonas sp. strain B13 (8) were found to have both types of catechol 1,2-dioxygenases, which were separately induced when introduced into chloroaromatic compound and nonchloroaromatic compound media, indicating their involvement in different regulation and metabolism processes. But P. arvilla C-1 (23) and Frateuria sp. strain ANA-18 (4) induced three and two isozymes of type I catechol 1,2-dioxygenases in media containing nonchloroaromatic compounds such as benzoate and aniline, respectively. It has been proposed that two isozymes of Frateuria sp. strain ANA-18 should be complementary to each other in the cell because of their different chem...

This study aimed to investigate the wear performance of laser direct energy deposited Fe-8Cr3V-2Mo-2W alloy under various wear environments, in terms of different heat treatment conditions. Ball on disk tribology tests were performed using high-carbon steel and zirconia balls as counter materials. The wear rates of the alloy depended significantly on both the wear sliding speed and the wear load. Microstructural observations of the worn surface and the wear debris indicated intensive tribo-oxidative wear that was presumably responsible for the strong dependency of the wear rate on the wear sliding speed. Regardless of the type of counter materials, the alloy in the as-built state had better wear performance than the alloy with heat treatments. Therefore, the use of the alloy without post heat treatment would be favorable to obtain long-term durability of the alloy in severe wear environments. The wear tests with two different counter materials of high-carbon steel and zirconia showed the high-carbon steel counter material had a higher wear rate than the zirconia. This was thought to be due to that strong third-body abrasive actions of the high-carbon steel counter material, evidenced by the severe abrasive wear of the counter material.