Enhancement of Aggregation-Induced Emission in Dye-Encapsulating Polymeric Micelles for Bioimaging

Wu, Wen-Chung,Chen, Ching-Yi,Tian, Yanqing,Jang, Sei-Hum,Hong, Yuning,Liu, Yang,Hu, Rongrong,Tang, Ben Zhong,Lee, Yi-Ting,Chen, Chin-Ti,Chen, Wen-Chang,Jen, Alex K.-Y. WILEY-VCH Verlag 2010 Advanced Functional Materials Vol.20 No.9

<P>Three amphiphilic block copolymers are employed to form polymeric micelles and function as nanocarriers to disperse hydrophobic aggregation-induced emission (AIE) dyes, 1,1,2,3,4,5-hexaphenylsilole (HPS) and/or bis(4-(N-(1-naphthyl) phenylamino)-phenyl)fumaronitrile (NPAFN), into aqueous solution for biological studies. Compared to their virtually non-emissive properties in organic solutions, the fluorescence intensity of these AIE dyes has increased significantly due to the spatial confinement that restricts intramolecular rotation of these dyes and their better compatibility in the hydrophobic core of polymeric micelles. The effect of the chemical structure of micelle cores on the photophysical properties of AIE dyes are investigated, and the fluorescence resonance energy transfer (FRET) from the green-emitting donor (HPS) to the red-emitting acceptor (NPAFN) is explored by co-encapsulating this FRET pair in the same micelle core. The highest fluorescence quantum yield (∼62%) could be achieved by encapsulating HPS aggregates in the micelles. Efficient energy transfer (>99%) and high amplification of emission (as high as 8 times) from the NPAFN acceptor could also be achieved by spatially confining the HPS/NPAFN FRET pair in the hydrophobic core of polymeric micelles. These micelles could be successfully internalized into the RAW 264.7 cells to demonstrate high-quality fluorescent images and cell viability due to improved quantum yield and reduced cytotoxicity.</P> <B>Graphic Abstract</B> <P>Highly efficient fluorescence probes are achieved through the encapsulation of aggregation-induced emission molecules, 1,1,2,3,4,5-hexaphenylsilole (HPS) and/or bis(4-(N-(1-naphthyl) phenylamino)-phenyl)fumaronitrile (NPAFN) in the core of polymeric micelles. Bright fluorescence cell images are shown with tunable colors of green directly from HPS aggregates and red through efficient fluorescence resonance energy transfer (FRET) from HPS aggregates to NPAFN aggregates. <img src='wiley_img_2010/1616301X-2010-20-9-ADFM200902043-content.gif' alt='wiley_img_2010/1616301X-2010-20-9-ADFM200902043-content'> </P>

Redox Regulation of Apoptosis before and after Cytochrome C Release

Chen, Quan,Crosby, Meredith,Almasan, Alex The Korean Society for Integrative Biology 2003 Korean journal of biological sciences Vol.7 No.1

Programmed cell death, or apoptosis, is one of the most studied areas of modern biology. Apoptosis is a genetically regulated process, which plays an essential role in the development and homeostasis of higher organisms. Mitochondria, known to play a central role in regulating cellular metabolism, was found to be critical for regulating apoptosis induced under both physiological and pathological conditions. Mitochondria are a major source of reactive oxygen species (ROS) but they can also serve as its target during the apoptosis process. Release of apoptogenic factors from mitochondria, the best known of which is cytochrome c, leads to assembly of a large apoptosis-inducing complex called the apoptosome. Cysteine pretenses (called caspases) are recruited to this complex and, following their activation by proteolytic cleavage, activate other caspases, which in turn target for specific cleavage a large number of cellular proteins. The redox regulation of apoptosis during and after cytochrome c release is an area of intense investigation. This review summarizes what is known about the biological role of ROS and its targets in apoptosis with an emphasis on its intricate connections to mitochondria and the basic components of cell death.

Contact Angle and Adhesion Dynamics and Hysteresis on Molecularly Smooth Chemically Homogeneous Surfaces

Chen, Szu-Ying,Kaufman, Yair,Schrader, Alex M.,Seo, Dongjin,Lee, Dong Woog,Page, Steven H.,Koenig, Peter H.,Isaacs, Sandra,Gizaw, Yonas,Israelachvili, Jacob N. American Chemical Society 2017 Langmuir Vol.33 No.38

<P>Measuring truly equilibrium adhesion energies or contact angles to obtain the thermodynamic values is experimentally difficult because it requires loading/unloading or advancing/receding boundaries to be measured at rates that can be slower than 1 nm/s. We have measured advancing-receding contact angles and loading-unloading adhesion energies for various systems and geometries involving molecularly smooth and chemically homogeneous surfaces moving at different but steady velocities in both directions, ±<I>V</I>, focusing on the thermodynamic limit of ±<I>V</I> → 0. We have used the Bell Theory (1978) to derive expressions for the dynamic (velocity-dependent) adhesion energies and contact angles suitable for both (i) dynamic adhesion measurements using the classic Johnson-Kendall-Roberts (JKR, 1971) theory of “contact mechanics” and (ii) dynamic contact angle hysteresis measurements of both rolling droplets and syringe-controlled (sessile) droplets on various surfaces. We present our results for systems that exhibited both steady and varying velocities from <I>V</I> ≈ 10 mm/s to 1 nm/s, where in all cases but one, the advancing (<I>V</I> > 0) and receding (<I>V</I> < 0) adhesion energies and/or contact angles converged toward the same theoretical (thermodynamic) values as <I>V</I> → 0. Our equations for the dynamic contact angles are similar to the classic equations of Blake & Haynes (1969) and fitted the experimental adhesion data equally well over the range of velocities studied, although with somewhat different fitting parameters for the characteristic molecular <I>length/dimension</I> or <I>area</I> and characteristic bond formation/rupture <I>lifetime</I> or <I>velocity</I>. Our theoretical and experimental methods and results unify previous kinetic theories of adhesion and contact angle hysteresis and offer new experimental methods for testing kinetic models in the thermodynamic, <I>quasi-static</I>, limit. Our analyses are limited to kinetic effects only, and we conclude that hydrodynamic, i.e., viscous, and inertial effects do not play a role at the interfacial velocities of our experiments, i.e., <I>V</I> < (1-10) mm/s (for water and hexadecane, but for viscous polymers it may be different), consistent with previously reported studies.</P> [FIG OMISSION]</BR>

Atomic Level Distributed Strain within Graphene Divacancies from Bond Rotations

Chen, Qu,Robertson, Alex W.,He, Kuang,Gong, Chuncheng,Yoon, Euijoon,Lee, Gun-Do,Warner, Jamie H. American Chemical Society 2015 ACS NANO Vol.9 No.8

<P>Vacancy defects play an important role in influencing the properties of graphene, and understanding their detailed atomic structure is crucial for developing accurate models to predict their impact. Divacancies (DVs) are one of the most common defects in graphene and can take three different structural forms through various sequences of bond rotations to minimize the energy. Using aberration-corrected transmission electron microscopy with monochromation of the electron source, we resolve the position of C atoms in graphene and measure the C–C bond lengths within the three DVs, enabling a map of bond strain to be generated. We show that bond rotations reduce the maximum single bond strain reached within a DV and help distribute the strain over a larger number of bonds to minimize the peak magnitude.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-8/acsnano.5b03801/production/images/medium/nn-2015-038016_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b03801'>ACS Electronic Supporting Info</A></P>

Atomic Structure and Spectroscopy of Single Metal (Cr, V) Substitutional Dopants in Monolayer MoS₂

Robertson, Alex W.,Lin, Yung-Chang,Wang, Shanshan,Sawada, Hidetaka,Allen, Christopher S.,Chen, Qu,Lee, Sungwoo,Lee, Gun-Do,Lee, Joohee,Han, Seungwu,Yoon, Euijoon,Kirkland, Angus I.,Kim, Heeyeon,Suenag American Chemical Society 2016 ACS NANO Vol.10 No.11

<P>Dopants in two-dimensional dichalcogenides have a significant role in affecting electronic, mechanical, and interfacial properties. Controllable doping is desired for the intentional modification of such properties to enhance performance; however, unwanted defects and impurity dopants also have a detrimental impact, as often found for chemical vapor deposition (CVD) grown films. The reliable identification, and subsequent characterization, of dopants is therefore of significant importance. Here, we show that Cr and V impurity atoms are found in CVD grown MoS2 monolayer 2D crystals as single atom substitutional dopants in place of Mo. We attribute these impurities to trace elements present in the MoO3 CVD precursor. Simultaneous annular dark field scanning transmission electron microscopy (ADF-STEM) and electron energy loss spectroscopy (EELS) is used to map the location of metal atom substitutions of Cr and V in MoS2 monolayers with single atom precision. The Cr and V are stable under electron irradiation at 60 to 80 kV, when incorporated into line defects, and when heated to elevated temperatures. The combined ADF-STEM and EELS differentiates these Cr and V dopants from other similar contrast defect structures, such as 2S self-interstitials at the Mo site, preventing misidentification. Density functional theory calculations reveal that the presence of Cr or V causes changes to the density of states, indicating doping of the MoS2 material. These transferred impurities could help explain the presence of trapped charges in CVD prepared MoS2.</P>

Molecular profiling of human gliomas by cDNA expression array

Wei Zhang,Alex Chenchik,Stephen Chen,Paul Siebert,Chang Hun Rhee 대한의학유전학회 1997 대한의학유전학회지 Vol.1 No.1

Simple-to-Apply Wetting Model to Predict Thermodynamically Stable and Metastable Contact Angles on Textured/Rough/Patterned Surfaces

Kaufman, Yair,Chen, Szu-Ying,Mishra, Himanshu,Schrader, Alex M.,Lee, Dong Woog,Das, Saurabh,Donaldson Jr., Stephen H.,Israelachvili, Jacob N. American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.10

<P>Rough/patterned/textured surfaces with nano/microcavities that broaden below the surface known as 're-entrants'-can be omniphobic (macroscopic contact angle greater than 90 for both water and oils). The existing theoretical models that explain the effects of texture on wetting are complex and do not provide a simple procedure for predicting the thermodynamically stable and metastable states and their corresponding contact angles (for example, wetting states that involve partially filled cavities). Here, we develop a simple-to-apply wetting model that allows for (1) predicting a priori the wetting state (partially or fully filled) of the cavities both under and outside the liquid droplet and the corresponding macroscopic contact angles on any type of textured surface; (2) determining the conditions under which metastable states exist; and (3) engineering specific nano/microtextures that yield any desired macroscopic contact angle, theta(v) for a given intrinsic contact angle theta(0). Subsequently, we experimentally demonstrate how one can use the model to predict the metastable and the thermodynamically stable contact angles on nondeformable textured surfaces consisting of arrays of axisymmetric cavities/protrusions. In this model, we do not consider the effects of gravitational forces, Laplace pressure of the droplet, line tension, droplet impact velocity, and quantitative aspects of contact angle hysteresis. Nonetheless, the model is suitable for accurately predicting the contact angles of macroscopic droplets (droplet volume similar to 1 mu L and base diameters <2 mm), which is of immense relevance in engineering. In the experimental section we also discuss the suitability of the model to be extended in order to include the effects of contact angle hysteresis on the macroscopic apparent contact angle on textured surfaces. Controlling these macroscopic contact angles, whether higher or lower than the intrinsic angle, theta(0), is desirable for many applications including nonwetting, self-cleaning, and antifouling surfaces and for completely wetting/spreading applications, such as creams, cosmetics, and lubricant fluids.</P>

Molecular profiling of human gliomas by cDNA expression array

Zhang, Wei,Chenchik, Alex,Chen, Stephen,Siebert, Paul,Rhee, Chang-Hun Korean Society of Medical Genetics 1997 대한의학유전학회지 Vol.1 No.1

Rates of cavity filling by liquids

Seo, Dongjin,Schrader, Alex M.,Chen, Szu-Ying,Kaufman, Yair,Cristiani, Thomas R.,Page, Steven H.,Koenig, Peter H.,Gizaw, Yonas,Lee, Dong Woog,Israelachvili, Jacob N. National Academy of Sciences 2018 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.115 No.32

<P>Understanding the fundamental wetting behavior of liquids on surfaces with pores or cavities provides insights into the wetting phenomena associated with rough or patterned surfaces, such as skin and fabrics, as well as the development of everyday products such as ointments and paints, and industrial applications such as enhanced oil recovery and pitting during chemical mechanical polishing. We have studied, both experimentally and theoretically, the dynamics of the transitions from the unfilled/partially filled (Cassie-Baxter) wetting state to the fully filled (Wenzel) wetting state on intrinsically hydrophilic surfaces (intrinsic water contact angle <90 degrees, where the Wenzel state is always the thermodynamically favorable state, while a temporary metastable Cassie-Baxter state can also exist) to determine the variables that control the rates of such transitions. We prepared silicon wafers with cylindrical cavities of different geometries and immersed them in bulk water. With bright-field and confocal fluorescence microscopy, we observed the details of, and the rates associated with, water penetration into the cavities from the bulk. We find that unconnected, reentrant cavities (i.e., cavities that open up below the surface) have the slowest cavity-filling rates, while connected or non-reentrant cavities undergo very rapid transitions. Using these unconnected, reentrant cavities, we identified the variables that affect cavity-filling rates: (i) the intrinsic contact angle, (ii) the concentration of dissolved air in the bulk water phase (i.e., aeration), (iii) the liquid volatility that determines the rate of capillary condensation inside the cavities, and (iv) the presence of surfactants.</P>

Indacenodithiophene and Quinoxaline-Based Conjugated Polymers for Highly Efficient Polymer Solar Cells

Zhang, Yong,Zou, Jingyu,Yip, Hin-Lap,Chen, Kung-Shih,Zeigler, David F.,Sun, Ying,Jen, Alex K.-Y. American Chemical Society 2011 Chemistry of materials Vol.23 No.9

<P>Two new low-band-gap conjugated polymers based on the polymerization between indacenodithiophene and 2,3-diphenylquinoxaline or phenanthrenequinoxaline were synthesized. Due to the fused phenanthrenequinoxaline unit, the polymer (PIDT-phanQ) possesses better planarity than PIDT-diphQ, resulting in an improved hole mobility in organic field-effect transistors and power conversion efficiency in polymer solar cells.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2011/cmatex.2011.23.issue-9/cm200316s/production/images/medium/cm-2011-00316s_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm200316s'>ACS Electronic Supporting Info</A></P>