Popular science articles

Printable Optical Sensors Based on H-Bonded Supramolecular Cholesteric Liquid Crystal Networks

Nicole Herzer†, Hilal Guneysu†, Dylan J. D. Davies†, Derya Yildirim†, Antonio R. Vaccaro†, Dirk J. Broer†, Cees W. M. Bastiaansen†‡, and Albertus P. H. J. Schenning*†

^† Functional Organic Materials & Devices, Eindhoven University of Technology, PO Box 513, Eindhoven, The Netherlands

^‡ Department of Materials, Queen Mary University of London, Mile End Road, London E1 4NS, U.K.

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja301845n

Publication Date (Web): April 23, 2012

A printable H-bonded cholesteric liquid crystal (CLC) polymer film has been fabricated that, after conversion to a hygroscopic polymer salt film, responds to temperature and humidity by changing its reflection color. Fast-responding humidity sensors have been made in which the reflection color changes between green and yellow depending on the relative humidity. The change in reflection band is a result of a change in helix pitch in the film due to absorption and desorption of water, resulting in swelling/deswelling of the film material. When the polymer salt was saturated with water, a red-reflecting film was obtained that can potentially act as a time/temperature integrator. Finally, the films were printed on a foil, showing the potential application of supramolecular CLC materials as low-cost, printable, battery-free optical sensors.

Three Distinct Water Structures at a Zwitterionic Lipid/Water Interface Revealed by Heterodyne-Detected Vibrational Sum Frequency Generation

Jahur A. Mondal, Satoshi Nihonyanagi, Shoichi Yamaguchi, and Tahei Tahara*

Molecular Spectroscopy Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja300658h

Publication Date (Web): April 26, 2012

Lipid/water interfaces and associated interfacial water are vital for various biochemical reactions, but the molecular-level understanding of their property is very limited. We investigated the water structure at a zwitterionic lipid, phosphatidylcholine, monolayer/water interface using heterodyne-detected vibrational sum frequency generation spectroscopy. Isotopically diluted water was utilized in the experiments to minimize the effect of intra/intermolecular couplings. It was found that the OH stretch band in the Imχ⁽²⁾spectrum of the phosphatidylcholine/water interface exhibits a characteristic double-peaked feature. To interpret this peculiar spectrum of the zwitterionic lipid/water interface, Imχ⁽²⁾spectra of a zwitterionic surfactant/water interface and mixed lipid/water interfaces were measured. The Imχ⁽²⁾ spectrum of the zwitterionic surfactant/water interface clearly shows both positive and negative bands in the OH stretch region, revealing that multiple water structures exist at the interface. At the mixed lipid/water interfaces, while gradually varying the fraction of the anionic and cationic lipids, we observed a drastic change in the Imχ⁽²⁾spectra in which spectral features similar to those of the anionic, zwitterionic, and cationic lipid/water interfaces appeared successively. These observations demonstrate that, when the positive and negative charges coexist at the interface, the H-down-oriented water structure and H-up-oriented water structure appear in the vicinity of the respective charged sites. In addition, it was found that a positive Imχ⁽²⁾ appears around 3600 cm^–1 for all the monolayer interfaces examined, indicating weakly interacting water species existing in the hydrophobic region of the monolayer at the interface. On the basis of these results, we concluded that the characteristic Imχ⁽²⁾ spectrum of the zwitterionic lipid/water interface arises from three different types of water existing at the interface: (1) the water associated with the negatively charged phosphate, which is strongly H-bonded and has a net H-up orientation, (2) the water around the positively charged choline, which forms weaker H-bonds and has a net H-down orientation, and (3) the water weakly interacting with the hydrophobic region of the lipid, which has a net H-up orientation.

A Semisynthetic Fluorescent Sensor Protein for Glutamate

Matthias A. Brun, Kui-Thong Tan, Rudolf Griss, Anna Kielkowska, Luc Reymond, and Kai Johnsson*

Institute of Chemical Sciences and Engineering, Institute of Bioengineering, National Centre of Competence in Research Chemical Biology, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja3002277

Publication Date (Web): April 23, 2012

We report the semisynthesis of a fluorescent glutamate sensor protein on cell surfaces. Sensor excitation at 547 nm yields a glutamate-dependent emission spectrum between 550 and 700 nm that can be exploited for ratiometric sensing. On cells, the sensor displays a ratiometric change of 1.56. The high sensitivity toward glutamate concentration changes of the sensor and its exclusive extracellular localization make it an attractive tool for glutamate sensing in neurobiology.

What Really Drives Chemical Reactions on Contact Charged Surfaces?

Bilge Baytekin, H. Tarik Baytekin, and Bartosz A. Grzybowski*

Department of Chemistry and Department of Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja300925h

Publication Date (Web): April 11, 2012

Although it is known that contact-electrified polymers can drive chemical reactions, the origin of this phenomenon remains poorly understood. To date, it has been accepted that this effect is due to excess electrons developed on negatively charged surfaces and to the subsequent transfer of these electrons to the reactants in solution. The present study demonstrates that this view is incorrect and, in reality, the reactions are driven by mechanoradicals created during polymer–polymer contact.

Rapid, Sensitive, and Quantitative Detection of Pathogenic DNA at the Point of Care through Microfluidic Electrochemical Quantitative Loop-Mediated Isothermal Amplification†

Kuangwen Hsieh^2,‡,
Adriana S. Patterson^3,‡,
Dr. B. Scott Ferguson²,
Prof. Kevin W. Plaxco³,
Prof. H. Tom Soh^1,2,

^{Article first published online: 4 APR 2012
DOI: 10.1002/anie.201109115
Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ingle-step DNA detection: A microfluidic electrochemical loop-mediated isothermal amplification platform is reported for rapid, sensitive, and quantitative detection of pathogen genomic DNA at the point of care (see picture). DNA amplification was electrochemically monitored in real time within a monolithic microfluidic device, enabling the detection of as few as 16 copies of Salmonella genomic DNA through a single-step process in less than an hour.}

Magnetic Click Colloidal Assembly

Stefano Sacanna*†, Laura Rossi‡, and David J. Pine†

^† Center for Soft Matter Research, Department of Physics, New York University, 4-6 Washington Place, New York, New York 10003, United States

^‡ Van’t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nano-materials Science,Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands

J. Am. Chem. Soc., 2012, 134 (14), pp 6112–6115

DOI: 10.1021/ja301344n

Publication Date (Web): March 27, 2012

We introduce a new class of spherical colloids that reversibly self-assemble into well-defined nonlinear structures by virtue of “magnetic patches”. This assembly is driven by tunable magnetostatic binding forces that originate from microscopic permanent magnets embedded underneath the surface of the particles. The resulting clusters form spontaneously in the absence of external magnetizing fields, and their geometry is determined by an interplay between magnetic, steric, and electrostatic interactions. Imposing an external magnetic field enables the clusters to unbind or change their geometry allowing, in principle, the creation of materials with a reconfigurable structural arrangement.