Feeling the Light

Phototransduction in Drosophila microvillar photoreceptor cells is mediated by a G protein–activated phospholipase C (PLC). PLC hydrolyzes the minor membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP₂), leading by an unknown mechanism to activation of the prototypical transient receptor potential (TRP) and TRP-like (TRPL) channels. We found that light exposure evoked rapid PLC-mediated contractions of the photoreceptor cells and modulated the activity of mechanosensitive channels introduced into photoreceptor cells. Furthermore, photoreceptor light responses were facilitated by membrane stretch and were inhibited by amphipaths, which alter lipid bilayer properties. These results indicate that, by cleaving PIP₂, PLC generates rapid physical changes in the lipid bilayer that lead to contractions of the microvilli, and suggest that the resultant mechanical forces contribute to gating the light-sensitive channels.

 Science 12 October 2012:
Vol. 338 no. 6104 pp. 260-263
DOI: 10.1126/science.1222376
 

Functionalized multiwalled carbon nanotubes as ultrasound contrast agents

1.  Published online before print September 24, 2012, doi: 10.1073/pnas.1208312109 PNAS October 9, 2012 vol. 109 no. 41 16612-16617  
2. Ultrasonography is a fundamental diagnostic imaging tool in everyday clinical practice. Here, we are unique in describing the use of functionalized multiwalled carbon nanotubes (MWCNTs) as hyperechogenic material, suggesting their potential application as ultrasound contrast agents. Initially, we carried out a thorough investigation to assess the echogenic property of the nanotubes in vitro. We demonstrated their long-lasting ultrasound contrast properties. We also showed that ultrasound signal of functionalized MWCNTs is higher than graphene oxide, pristine MWCNTs, and functionalized single-walled CNTs. Qualitatively, the ultrasound signal of CNTs was equal to that of sulfur hexafluoride (SonoVue), a commercially available contrast agent. Then, we found that MWCNTs were highly echogenic in liver and heart through ex vivo experiments using pig as an animal model. In contrast to the majority of ultrasound contrast agents, we observed in a phantom bladder that the tubes can be visualized within a wide variety of frequencies (i.e., 5.5–10 MHz) and 12.5 MHz using tissue harmonic imaging modality. Finally, we demonstrated in vivo in the pig bladder that MWCNTs can be observed at low frequencies, which are appropriate for abdominal organs. Importantly, we did not report any toxicity of CNTs after 7 d from the injection by animal autopsy, organ histology and immunostaining, blood count, and chemical profile. Our results reveal the enormous potential of CNTs as ultrasound contrast agents, giving support for their future applications as theranostic nanoparticles, combining diagnostic and therapeutic modalities.

Reading Disc-Based Bioassays with Standard Computer Drives

Hua-Zhong Yu *†, Yunchao Li *†‡, and Lily M.-L. Ou †

^† Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada

^‡ Department of Chemistry, Beijing Normal University, Beijing 100875, People's Republic of China

Acc. Chem. Res., Article ASAP

DOI: 10.1021/ar300104b

Publication Date (Web): October 1, 2012

Copyright © 2012 American Chemical Society

Traditional methods of disease diagnosis are both time-consuming and labor-intensive, and many tests require expensive instrumentation and trained professionals, which restricts their use to biomedical laboratories. Because patients can wait several days (even weeks) for the results, the consequences of delayed treatment could be disastrous. Therefore, affordable and simple point-of-care (POC) biosensor devices could fill a diagnostic niche in the clinic or even at home, as personal glucose meters do for diabetics. These devices would allow patients to check their own health conditions and enable physicians to make prompt treatment decisions, which could improve the chances for rapid recovery and cure.

Compact discs (CDs) provide inexpensive substrate materials for the preparation of microarray biochips, and conventional computer drives/disc players can be adapted as precise optical reading devices for signal processing. Researchers can employ the polycarbonate (PC) base of a CD as an alternative substrate to glass slides or silicon wafers for the preparation of microanalytical devices. Using the characteristic optical phenomena occurring on the metal layer of a CD, researchers can develop biosensors based on advanced spectroscopic readout (interferometry or surface plasmon resonance). If researchers integrate microfluidic functions with CD mechanics, they can control fluid transfer through the spinning motion of the disc, leading to “lab-on-a-CD” devices.

Over the last decade, our laboratory has focused on the construction of POC biosensor devices from off-the-shelf CDs or DVDs and standard computer drives. Besides the initial studies of the suitability of CDs for surface and materials chemistry research (fabrication of self-assembled monolayers and oxide nanostructures), we have demonstrated that an ordinary optical drive, without modification of either the hardware or the software driver, can function as the signal transducing element for reading disc-based bioassays quantitatively.

In this Account, we first provide a brief introduction to CD-related materials chemistry and microfluidics research. Then we describe the mild chemistry developed in our laboratory for the preparation of computer-readable biomolecular screening assays: photochemical activation of the polycarbonate (PC) disc surface and immobilization and delivery of probe and target biomolecules. We thoroughly discuss the analysis of the molecular recognition events: researchers can “read” these devices quantitatively with an unmodified optical drive of any personal computer. Finally, and critically, we illustrate our digitized molecular diagnosis approach with three trial systems: DNA hybridization, antibody–antigen binding, and ultrasensitive lead detection with a DNAzyme assay. These examples demonstrate the broad potential of this new analytical/diagnostic tool for medical screening, on-site food/water safety testing, and remote environmental monitoring.

Roll up nanowire battery from silicon chips

1. Alexandru Vlad^a,^b,¹, 
2. Arava Leela Mohana Reddy^a,¹, 
3. Anakha Ajayan^a,
4. Neelam Singh^a, 
5. Jean-François Gohy^c, 
6. Sorin Melinte^b, and
7. Pulickel M. Ajayan^a,²

1. 1. Published online before print September 4, 2012, doi:10.1073/pnas.1208638109PNAS September 18, 2012vol. 109 no. 38 15168-15173
   

   Here we report an approach to roll out Li-ion battery components from silicon chips by a continuous and repeatable etch-infiltrate-peel cycle. Vertically aligned silicon nanowires etched from recycled silicon wafers are captured in a polymer matrix that operates as Li⁺ gel-electrolyte and electrode separator and peeled off to make multiple battery devices out of a single wafer. Porous, electrically interconnected copper nanoshells are conformally deposited around the silicon nanowires to stabilize the electrodes over extended cycles and provide efficient current collection. Using the above developed process we demonstrate an operational full cell 3.4 V lithium-polymer silicon nanowire (LIPOSIL) battery which is mechanically flexible and scalable to large dimensions

Mechanical Drawing of Gas Sensors on Paper

1. Dr. Katherine A. Mirica, 
2. Jonathan G. Weis,
3. Dr. Jan M. Schnorr, 
4. Dr. Birgit Esser, 
5. Prof. Dr. Timothy M. Swager^*

Article first published online: 4 OCT 2012

DOI: 10.1002/anie.201206069

Pencil it in: Mechanical abrasion of compressed single-walled carbon nanotubes (SWCNTs) on the surface of paper produces sensors capable of detecting NH₃ gas at sub-ppm concentrations. This method of fabrication is simple, inexpensive, and entirely solvent-free, and avoids difficulties arising from the inherent instability of many SWCNT dispersions.

Nanocomposite Nanostructures: CdS–Polymer Nanocomposites and Light-Emitting Fibers by In Situ Electron-Beam Synthesis and Lithography

1. Luana Persano^1,2,*, 
2. Andrea Camposeo^1,2,
3. Francesca Di Benedetto¹, 
4. Ripalta Stabile¹,
5. Anna M. Laera⁴, 
6. Emanuela Piscopiello⁴,
7. Leander Tapfer⁴, 
8. Dario Pisignano^1,2,3

Article first published online: 2 OCT 2012

DOI: 10.1002/adma.201290237

Electron-beam scanning is used to realize spatially-controlled in situ synthesis of nanocrystals, as reported by Luana Persano and co-workers on page 5320. A smart combination of complementary nanofabrication approaches including nanoimprinting, electrospinning, and electron-beam decomposition of nanocrystal precursors, and subsequent nucleation of nanoparticles in a polymer matrix, allows the exploitation the most favorable flow conditions of organics to produce various nanocomposite nanostructures.

Direct Imaging of Complex Nano- to Microscale Interfaces Involving Solid, Liquid, and Gas Phases

Konrad Rykaczewski †‡*, Trevan Landin §, Marlon L. Walker ‡, John Henry J. Scott ‡, and Kripa K. Varanasi †*

^† Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States

^‡ Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States

^§ FEI Company, Hillsboro, Oregon 97124, United States

ACS Nano, Article ASAP

DOI: 10.1021/nn304250e

Publication Date (Web): September 28, 2012

Copyright © 2012 American Chemical Society

Surfaces with special wetting properties not only can efficiently repel or attract liquids such as water and oils but also can prevent formation of biofilms, ice, and clathrate hydrates. Predicting the wetting properties of these special surfaces requires detailed knowledge of the composition and geometry of the interfacial region between the droplet and the underlying substrate. In this work we introduce a 3D quantitative method for direct nanoscale visualization of such interfaces. Specifically, we demonstrate direct nano- to microscale imaging of complex fluidic interfaces using cryostabilization in combination with cryogenic focused ion beam milling and SEM imaging. We show that application of this method yields quantitative information about the interfacial geometry of water condensate on superhydrophilic, superhydrophobic, and lubricant-impregnated surfaces with previously unattainable nanoscale resolution. This type of information is crucial to a fundamental understanding as well as the design of surfaces with special wetting properties.