Dieyan Chen

Afterpulsing and its correction in fluorescence correlation spectroscopy experiments

Afterpulsing arises from feedback in a photon detector. This means that each real signal pulse can be followed by an afterpulse at a later time. This effect is particularly troubling in photon correlation experiments. Few treatments of this effect have appeared in the literature, and few software programs to solve the problem have been written. We demonstrate the afterpulsing effect in fluorescence correlation spectroscopy by using different avalanche photodiodes. We prove theoretically that under simple and reasonable conditions afterpulsing in autocorrelation can be eliminated to the leading order; we have found it easy to program software for the correction. We compare our results with those from cross correlation. We also discuss some experimental parameters that may affect the afterpulsing.

Reconstruction of complementary images in second harmonic generation microscopy

Second harmonic generation microscopy(SHGM) has become widely used to image biological samples. Due to the complexity of biological samples, more and more effort has been put on polarization imaging in SHGM technology to uncover their structures. In this work, we put forward a novel stitching method based on careful mathematical calculation, and accomplish it by rotating laser polarization. We first show its validity in imaging a perfectly synthesized bio-origin polymer poly (3-hyroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx). Then, we test its power by getting a true image of fibrillar collagen structure of rat-tail tendon.

Voltammetric studies of the effect of Cisplatin-liposome on Hela cells

In this paper, the voltammetric method was used for the first time to study the effect of Cisplatin-liposome on Hela cells. The results showed the voltammetric behavior of Hela cells was irreversible and the peak current had linear relationship with the cell number. With both Cisplatin-liposome concentration and treating time increasing, the peak current decreased. The peak current decreasing was in accordance with the nuclear damage and loss of mitochondrial membrane potential revealed by two-photon laser scanning microscopy and confocal laser scanning microscopy. This voltammetric method may provide a simple way to study the electron-transfer mechanism in drug-treating cells.

Determination of Biodegradation Products from Benzene, Toluene, Ethylbenzene and Xylenes in Seawater by Purge and Trap Gas Chromatography

Abstract Benzene, toluene, ethylbenzene and xylenes (BTEX) are commonly found in crud oil and used as the direct indicating substance in the Geochemical Investigation for Oil and Gas. BTEX are easily volatile and can be degraded by microorganism, which affects the precise measurement seriously. A method for the determination of the biodegradation process of BTEX in seawater is described. The determination is performed by dynamic headspace (purge and trap) gas chromatography with a photoionization detector (PID). The features of the described method are: detection limits of 7.3–13.2 ng l−1, no sample preparation required, and recovery rate of 92.84%–100.92%. The results of the BTEX biodegradation process are of great significance in the collection, transportation, preservation, and measurement of samples in the Geochemical Investigation for Oil and Gas.

Label-free subcellular 3D live imaging of preimplantation mouse embryos with full-field optical coherence tomography

Early patterning and polarity is of fundamental interest in preimplantation embryonic development. Label-free subcellular 3D live imaging is very helpful to its related studies. We have developed a novel system of full-field optical coherence tomography (FF-OCT) for noninvasive 3D subcellular live imaging of preimplantation mouse embryos with no need of dye labeling. 3D digitized embryos can be obtained by image processing. Label-free 3D live imaging is demonstrated for the mouse embryos at various typical preimplantation stages with a spatial resolution of 0.7 [micro sign]m and imaging rate of 24 fps. Factors that relate to early patterning and polarity, such as pronuclei in zygote, shapes of zona pellucida, location of second polar body, cleavage planes, and the blastocyst axis, can be quantitatively measured. The angle between the two second cleavage planes is accurately measured to be 87 deg. It is shown that FF-OCT provides a potential breakthrough for early patterning, polarity formation, and many other preimplantation-related studies in mammalian developmental biology.

The study of autoionizing states of lutetium atoms by resonance ionization spectroscopy

The authors describe the investigation of the autoionizing states of lutetium atoms by exciting the states 2D3/2o, 2D5/2o, 4D3/2o and 4D5/2o with tunable dye lasers by means of a resonance ionization time-of-flight mass spectrometer. Twenty eight autoionizing transitions were measured and 12 autoionizing states were found. Their Shore-Fano profile parameters were determined by a nonlinear fitting program. The ionization probability for different schemes and some ionization cross sections were compared. On the basis of this, the authors have given the optimal schemes of lutetium atom photoionization through autoionizing states. In addition, the relation between ion signal and the laser pulse energy was discussed.

Understanding three-dimensional spatial relationship between the mouse second polar body and first cleavage plane with full-field optical coherence tomography

Abstract. The morphogenetic relationship between early patterning and polarity formation is of fundamental interest and remains a controversial issue in preimplantation embryonic development. We use a label-free three-dimensional (3-D) imaging technique of full-field optical coherence tomography (FF-OCT) successfully for the first time to study the dynamics of developmental processes in mouse preimplantation lives. Label-free 3-D subcellular time-lapse images are demonstrated to investigate 3-D spatial relationship between the second polar body (2PB) and the first cleavage plane. By using FF-OCT together with quantitative study, we show that only 25% of the predicted first cleavage planes, defined by the apposing plane of two pronuclei, pass through the 2PB. Also only 27% of the real cleavage planes pass through the 2PB. These results suggest that the 2PB is not a convincing spatial cue for the event of the first cleavage. Our studies demonstrate the feasibility of FF-OCT in providing new insights and potential breakthroughs to the controversial issues of early patterning and polarity in mammalian developmental biology.

Rydberg and autoionizing states of neutral ytterbium

In the study of Yb atomic Rydberg states, new members of 6sns 1S0 series for n=23, 24, 66-116 and 6snd 1D2 series for n=81-114 were observed. The data are in excellent agreement with the MQDT analysing results. The autoionizing Rydberg series 6p12 /ns ( 1/2 , 1/2 )10 were investigated by three-step laser excitation. The ICE model was used to explain the experimental spectrum, and it has been proved to be suitable for describing the excitation of the autoionizing Rydberg states with a weakly-excited core.

Capillary electrophoresis and circular dichroism study of trichosanthin and its mutants

The type-I ribosome-inactivating protein trichosanthin (TCS) has a broad spectrum of biological and pharmacological activities, including abortifacient, anti-tumor and anti-human-immunodeficiency-virus (anti-HIV). In this study, circular dichroism (CD) and capillary electrophoresis were used for the first time to study TCS and its two TCS mutants of Y55G TCS (tyrosine 55 converted to glycine) and FYY140-142GSA TCS (tripeptide phenylalanine-tyrosine-tyrosine 140-142 converted to glycine-serine-alanine). The results indicated that the substitution of amino acids changed the secondary structures and the hydrophobility of TCS. Moreover, both Y55G TCS and FYY140-142GSA TCS demonstrated attenuated cytotoxicity and reactive oxygen species (ROS) production in human choriocarcinoma cells (JAR cells) as compared to natural TCS and wild-type TCS. Our results demonstrated the cytotoxicity of TCS on JAR cells and TCS-induced production of ROS might be TCS-conformational related, suggesting that CD and capillary electrophoresis study might throw new insight into the anti-tumor and anti-HIV mechanism of TCS.

Noninvasive three-dimensional live imaging methodology for the spindles at meiosis and mitosis

Abstract. The spindle plays a crucial role in normal chromosome alignment and segregation during meiosis and mitosis. Studying spindles in living cells noninvasively is of great value in assisted reproduction technology (ART). Here, we present a novel spindle imaging methodology, full-field optical coherence tomography (FF-OCT). Without any dye labeling and fixation, we demonstrate the first successful application of FF-OCT to noninvasive three-dimensional (3-D) live imaging of the meiotic spindles within the mouse living oocytes at metaphase II as well as the mitotic spindles in the living zygotes at metaphase and telophase. By post-processing of the 3-D dataset obtained with FF-OCT, the important morphological and spatial parameters of the spindles, such as short and long axes, spatial localization, and the angle of meiotic spindle deviation from the first polar body in the oocyte were precisely measured with the spatial resolution of 0.7 μm. Our results reveal the potential of FF-OCT as an imaging tool capable of noninvasive 3-D live morphological analysis for spindles, which might be useful to ART related procedures and many other spindle related studies.