Carmichael’s Concise Review Coming Events


Inter/Micro July 11–15, 2011 Chicago, IL www.mcri.org/home/section/101/inter-micro


Denver X-ray Conference August 1–5, 2011 Colorado Springs, CO www.dxcicdd.com


2011 Microscopy & Microanalysis 2011 August 7–11, 2011 Nashville, TN


Microscopy Conference MC 2011 August 28–September 11, 2011 Kiel, Germany www.mc2011.de


Multinational Congress on Microscopy September 4–9, 2011 Urbino, Italy www.mcm2011urbino.it


ICXOM21 September 5–8, 2011 Campinas, Brazil icxom21.lnls.br


EMAG 2011 September 6–9, 2011 Birmingham, UK www.emag-iop.org


National Society for Histotechnology September 16–21, 2011 Cincinnati, OH www.nsh.org


FEMMS 2011 September 18–23, 2011 Sonoma County, CA www.femms2011.llnl.gov


CIASEM 2011 September 25–30, 2011 Mérida, Mexico www.ciasem.com


Neuroscience 2011 November 12–16, 2011 Washington, DC www.sfn.org


2012 Microscopy & Microanalysis 2012 July 29–August 2, 2012 Phoenix, AZ


2013 Microscopy & Microanalysis 2013 August 4–8, 2013 Indianapolis, IN


2014 Microscopy & Microanalysis 2014 August 3–7, 2014 Hartford, CT


More Meetings and Courses Check the complete calendar near the back of this magazine and in the MSA journal Microscopy and Microanalysis.


8


Wrapped for Accurate Imaging Stephen W. Carmichael1* and Philip Oshel2 1Mayo Clinic, Rochester, MN 55905 2Central Michigan University, Mt. Pleasant, MI 48859


* carmichael.stephen@mayo.edu Since transmission electron microscopy (TEM) was developed about 80 years ago,


numerous strategies have been attempted to visualize living cells at high resolution. T e harsh environment within the TEM (mostly the vacuum and damage from a fi xed beam of electrons) presents challenges. Some approaches have been to fabricate chambers within the TEM that provide a more “friendly” environment for living cells (that is, less stringent vacuum), but they have limitations. Impressive images have been generated with various cryogenic techniques, but frozen cells are not alive or in their native state in the traditional sense. Nihar Mohanty, Monica Fahrenholtz, Ashvin Nagaraja, Daniel Boyle, and Vikas Berry have developed an ingenious solution to the problem by “wrapping” cells with modifi ed graphene [1]. Graphene is an allotrope of carbon composed of single sheets of graphite


(the carbon form found in pencil lead). T e Nobel Prize in Physics last year went to Andre Geim and Konstantin Novoselov for what the Nobel Committee termed “groundbreaking experiments regarding the two-dimensional material graphene.” T e point here is that graphene is a material that has a lot of potential uses, and Berry’s group has discovered a novel one. Sheets of modifi ed graphene can be used to confi ne bacterial cells within an


easy-to-apply impermeable and electron-transparent encasement that retains the cellular water, while enabling imaging by TEM. T e layer is just a few atoms thick of an element of low atomic number. T e outer shells of electrons (the π electrons) of the carbon atoms are so close that even small atoms cannot pass through the graphenic sheets, yet it is strong enough to contain an internal pressure when the wrapped cell is in a vacuum. T e modifi ed graphene is fl exible, allowing wrapping to conform to the cell surface. Finally, the graphenic sheets have a high electrical conductivity (again, due to the π electrons) to signifi cantly reduce electrostatic charge buildup and a high thermal conductance to dissipate heat while in the electron beam. Specifi cally, Mohanty et al. demonstrated


that protein-functionalized graphene (PFG) can wrap bacteria in such a way as to enable wet-phase TEM imaging. In a proof-of-concept study, they used an unstained Gram-positive bacteria (Bacillus subtilis), which is about 70 percent water (by volume) with a wall thickness of 16 to 30 nm. An aqueous suspension of graphene oxide (GO) sheets was covalently bonded to Concanavalin-A, which has a specifi c affi nity for the polyteichoic moieties on the bacterial cell wall. When this was mixed with a purifi ed bacterial suspension, the mixture clouded, and this is attributed to the encasement of the bacteria by the PFGs. T is interpretation is supported by control experiments in which GO not functionalized with Concanavalin-A did not yield wrapped bacteria. Cross sections of wrapped bacteria cut


at 90 nm were examined in the TEM, and about 90 percent were fully wrapped, with the


doi:10.1017/S1551929511000423


Figure 1: Wrapped bacterium. (a) Repre- sentative TEM images of wrapped bacterium exhibits no shrinkage from the original size after 20 minutes inside the TEM chamber at ~10–5 Torr. (b) Representative unwrapped bacteria (UWB) exhibit ~76% shrinkage after 20 minutes under TEM vacuum. Note that in (a) under the same conditions, the cell wall of the wrapped bacteria is clearly discernible. Courtesy of Dr. Vikas Berry and the American Chemical Society.


www.microscopy-today.com • 2011 July


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