Emulsion-Based Technique To Measure Protein Crystal Nucleation Rates of Lysozyme

We measured the nucleation rates of lysozyme protein crystals using microfluidically produced emulsion drops containing supersaturated protein solution. The technique involves quenching several thousand independent nanoliter drops by rapidly lowering the temperature and then counting the number of drops that have not nucleated as a function of time at constant temperature. We fit the number distribution to a theoretical model developed by Pound and La Mer (J. Am. Chem. Soc. 1952, 74, 2323–2332) for heterogeneous nucleation and extract two nucleation rates and the number of nucleation sites per drop. We describe the technique in detail and present our analysis of the measured nucleation rates within the context of Classical Nucleation Theory, which adequately describes our observations. Of the two nucleation rates, one is a slow rate that varies with temperature and one is a fast rate independent of temperature. The nucleation barrier and kinetic prefactors are obtained for each rate. Notably, there is no detectable barrier for the fast rate. Both rates are inconsistent with the process of homogeneous nucleation and are consistent with heterogeneous nucleation

Emulsion-Based Technique To Measure Protein Crystal Nucleation Rates of Lysozyme

We measured the nucleation rates of lysozyme protein crystals using microfluidically produced emulsion drops containing supersaturated protein solution. The technique involves quenching several thousand independent nanoliter drops by rapidly lowering the temperature and then counting the number of drops that have not nucleated as a function of time at constant temperature. We fit the number distribution to a theoretical model developed by Pound and La Mer (<i>J. Am. Chem. Soc.</i> <b>1952</b>, <i>74</i>, 2323–2332) for heterogeneous nucleation and extract two nucleation rates and the number of nucleation sites per drop. We describe the technique in detail and present our analysis of the measured nucleation rates within the context of Classical Nucleation Theory, which adequately describes our observations. Of the two nucleation rates, one is a slow rate that varies with temperature and one is a fast rate independent of temperature. The nucleation barrier and kinetic prefactors are obtained for each rate. Notably, there is no detectable barrier for the fast rate. Both rates are inconsistent with the process of homogeneous nucleation and are consistent with heterogeneous nucleation

Synchronization of Chemical Micro-oscillators

Many phenomena of biological, physical, and chemical importance involve synchronization of oscillatory elements. We explore here, in several geometries, the behavior of diffusively coupled, nanoliter volume, aqueous drops separated by oil gaps and containing the reactants of the oscillatory Belousov−Zhabotinsky (BZ) reaction. A variety of synchronous regimes are found, including in- and antiphase oscillations, stationary Turing patterns, and more complex combinations of stationary and oscillatory BZ drops, including three-phase patterns. A model consisting of ordinary differential equations based on a simplified description of the BZ chemistry and diffusion of messenger (primarily inhibitory) species qualitatively reproduces most of the experimental results

Numerical analysis of the propagation modes of photo-switching PDMS-arylazopyrazole optical waveguide and thin-film spectroscopic characterization

A new light responsive arylazopyrazole (AAP) containing polymer matrix thin film is fabricated by spin-coating of different concentrations of the AAP azo dye into the polydimethylsiloxane (PDMS) polymer at 150C. The new AAP molecular switch was also used to fabricate a solid-state PDMS-AAP waveguide by contact lithography and soft replica modeling methods in the micrometer scale. The refractive index of the spin-coated photoswitchable material can be modulated via the reversible trans-to-cis photoisomerization behavior of the AAP unit using different concentrations. When 0.01 M solution of the AAP unit was used, the refractive of the composite was 2.32 in the trans state and dropped to 1.85 in the cis state in the operating wavelength of 340 nm. At higher concentrations of 0.020 and 0.03 M, a wide refractive index tuning is achieved under the same wavelength. In 0.030 M the refractive index was 2.65 for the trans state and 2.0 for the cis state. The results suggest that the increase in refractive index tuning is related to the concentration of the AAP unit of the composite film. Theoretically, the spectral properties of the composite film are also simulated with two methods: 1) the Maxwell Equations; and 2) the frequency dependent finite element, showing excellent agreement for the different propagation modes of the proposed waveguide for regulated signals of 365/525 nm wavelengths. Furthermore, the photoisomerization of the PDMS-AAP thin film is analyzed with UV-vis spectroscopy to demonstrate the isomerization responses of the AAP moiety in the solid state. Additionally, preliminary photomechanical actuation properties of the composite film have been investigated. The PDMS-AAP waveguide described in this study provides a new approach for optically tunable photonics applications in the Visible-IR region

Control and Measurement of the Phase Behavior of Aqueous Solutions Using Microfluidics

A microfluidic device denoted the Phase Chip has been designed to measure and manipulate the phase diagram of multicomponent fluid mixtures. The Phase Chip exploits the permeation of water through poly(dimethylsiloxane) (PDMS) in order to controllably vary the concentration of solutes in aqueous nanoliter volume microdrops stored in wells. The permeation of water in the Phase Chip is modeled using the diffusion equation, and good agreement between experiment and theory is obtained. The Phase Chip operates by first creating drops of the water/solute mixture whose composition varies sequentially. Next, drops are transported down channels and guided into storage wells using surface tension forces. Finally, the solute concentration of each stored drop is simultaneously varied and measured. Two applications of the Phase Chip are presented. First, the phase diagram of a polymer/salt mixture is measured on-chip and validated off-chip, and second, protein crystallization rates are enhanced through the manipulation of the kinetics of nucleation and growth

Control and Measurement of the Phase Behavior of Aqueous Solutions Using Microfluidics

A microfluidic device denoted the Phase Chip has been designed to measure and manipulate the phase diagram of multicomponent fluid mixtures. The Phase Chip exploits the permeation of water through poly(dimethylsiloxane) (PDMS) in order to controllably vary the concentration of solutes in aqueous nanoliter volume microdrops stored in wells. The permeation of water in the Phase Chip is modeled using the diffusion equation, and good agreement between experiment and theory is obtained. The Phase Chip operates by first creating drops of the water/solute mixture whose composition varies sequentially. Next, drops are transported down channels and guided into storage wells using surface tension forces. Finally, the solute concentration of each stored drop is simultaneously varied and measured. Two applications of the Phase Chip are presented. First, the phase diagram of a polymer/salt mixture is measured on-chip and validated off-chip, and second, protein crystallization rates are enhanced through the manipulation of the kinetics of nucleation and growth

Unnatural Peptide Assemblies Rapidly Deplete Cholesterol and Potently Inhibit Cancer Cells

Cholesterol-rich membranes play a pivotal role in cancer initiation and progression, necessitating innovative approaches to target these membranes for cancer inhibition. Here we report the first case of unnatural peptide (1) assemblies capable of depleting cholesterol and inhibiting cancer cells. Peptide 1 self-assembles into micelles and is rapidly taken up by cancer cells, especially when combined with an acute cholesterol-depleting agent (MβCD). Click chemistry has confirmed that 1 depletes cell membrane cholesterol. It localizes in membrane-rich organelles, including the endoplasmic reticulum, Golgi apparatus, and lysosomes. Furthermore, 1 potently inhibits malignant cancer cells, working synergistically with cholesterol-lowering agents. Control experiments have confirmed that C-terminal capping and unnatural amino acid residues (i.e., BiP) are essential for both cholesterol depletion and potent cancer cell inhibition. This work highlights unnatural peptide assemblies as a promising platform for targeting the cell membrane in controlling cell fates

Unnatural Peptide Assemblies Rapidly Deplete Cholesterol and Potently Inhibit Cancer Cells

Cholesterol-rich membranes play a pivotal role in cancer initiation and progression, necessitating innovative approaches to target these membranes for cancer inhibition. Here we report the first case of unnatural peptide (1) assemblies capable of depleting cholesterol and inhibiting cancer cells. Peptide 1 self-assembles into micelles and is rapidly taken up by cancer cells, especially when combined with an acute cholesterol-depleting agent (MβCD). Click chemistry has confirmed that 1 depletes cell membrane cholesterol. It localizes in membrane-rich organelles, including the endoplasmic reticulum, Golgi apparatus, and lysosomes. Furthermore, 1 potently inhibits malignant cancer cells, working synergistically with cholesterol-lowering agents. Control experiments have confirmed that C-terminal capping and unnatural amino acid residues (i.e., BiP) are essential for both cholesterol depletion and potent cancer cell inhibition. This work highlights unnatural peptide assemblies as a promising platform for targeting the cell membrane in controlling cell fates

Control and Measurement of the Phase Behavior of Aqueous Solutions Using Microfluidics

A microfluidic device denoted the Phase Chip has been designed to measure and manipulate the phase diagram of multicomponent fluid mixtures. The Phase Chip exploits the permeation of water through poly(dimethylsiloxane) (PDMS) in order to controllably vary the concentration of solutes in aqueous nanoliter volume microdrops stored in wells. The permeation of water in the Phase Chip is modeled using the diffusion equation, and good agreement between experiment and theory is obtained. The Phase Chip operates by first creating drops of the water/solute mixture whose composition varies sequentially. Next, drops are transported down channels and guided into storage wells using surface tension forces. Finally, the solute concentration of each stored drop is simultaneously varied and measured. Two applications of the Phase Chip are presented. First, the phase diagram of a polymer/salt mixture is measured on-chip and validated off-chip, and second, protein crystallization rates are enhanced through the manipulation of the kinetics of nucleation and growth

Control and Measurement of the Phase Behavior of Aqueous Solutions Using Microfluidics

A microfluidic device denoted the Phase Chip has been designed to measure and manipulate the phase diagram of multicomponent fluid mixtures. The Phase Chip exploits the permeation of water through poly(dimethylsiloxane) (PDMS) in order to controllably vary the concentration of solutes in aqueous nanoliter volume microdrops stored in wells. The permeation of water in the Phase Chip is modeled using the diffusion equation, and good agreement between experiment and theory is obtained. The Phase Chip operates by first creating drops of the water/solute mixture whose composition varies sequentially. Next, drops are transported down channels and guided into storage wells using surface tension forces. Finally, the solute concentration of each stored drop is simultaneously varied and measured. Two applications of the Phase Chip are presented. First, the phase diagram of a polymer/salt mixture is measured on-chip and validated off-chip, and second, protein crystallization rates are enhanced through the manipulation of the kinetics of nucleation and growth