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RESEARCH NEWS

APRIL 2009 | VOLUME 12 | NUMBER 4 9

Feynman’s famous 1959 proclamation “There’splenty of room at the bottom” largely referredto the untapped storage ability for informationat the nanoscale. However, recently publishedresults by Banerjee and co-workers [Banerjee,et al., Nat. Nanotechnol. (2009), doi:10.1038/nnano.2009.37] show that this credoapplies to energy storage as well. The teamhas created arrays of nano-scale capacitorswith an unprecedented 100 μF/cm2 capacitance,more than 40 times larger than the equivalentcapacitance for a planar configuration.The devices were made by the successiveapplication by atomic layer deposition ofmetal (TiN) and insulator (Al2O3), onto ananoporous template of anodic aluminumoxide to create a densely packed array of

these capacitors. This nanoscale design allowsfor the desired combination of the typicallyhigh power density provided by capacitors(106 W/kg) along with the high energy densityavailable by tapping available surface area andvolume at the nanoscale (0.7 W*h/kg). In fact,these devices provide 10 times the energystorage density of commercially availabledevices. According to Rubloff, one of theauthors, “While electrostatic capacitors, whichhold energy simply as electrical charge on thesurface of opposing sheets of metal, are wellknown to provide high power, their energydensity has been low, and accordingly theyhave not been considered as part of the storagesolutions requiring significant energy. Nowwe have shown the potential of electrostatic

nanocapacitors to compete with conventionalelectrochemical capacitors, bringing a newplayer onto the field of storage solutions.”These new nanocapacitor devices may soonbe coming to the market. The technology isbeing developed for mass production as apanel similar in shape to solar panels. Thesepanels could be then integrated with energygeneration technologies such as solar cells orwind, to capture and store the time-varying,unpredictable energy generated. The uniquecombination of high energy, high power, andquick recharge times, coupled with the lowcost manufacturability, shows great promisefor this technology in next-generation energystorage.David Hecht

Atomic force microscopy (AFM) candetect osteoarthritis several monthsbefore conventional morphology-based diagnostic techniques,say researchers from Germany,Switzerland, and Italy [Stolz,et al.,

Nat. Nanotechnol. (2009), doi:10.1038/nnano.2008.410].Osteoarthritis is a degenerativedisease that starts at the molecularscale and progresses to themacroscale in cartilage, a load-bearing tissue located in bone joints.There is currently no cure for thedisease and early detection andthe ability to monitor the disease’sprogression would be a major stepforwards.

Cartilage tissue is made up of a network of moleculescalled collagen and proteoglycans. “In aging andosteoarthritis the soft sugar molecules, which arethe proteoglycans, change their structure, but thehard collagen fibrils are apparently not affectedat the early stages ”, explains Michael Stolz of theUniversity of Basel in Switzerland. “Therefore, inorder to detect early changes of osteoarthritis, thediagnostic tool needs to be sensitive to the changesin the proteoglycan moiety. Such analysis can be

done by biochemical and/or histological analysis,but such methods require biopsies and, therefore,are destructive. Even a very small biopsy taken fromthe hip- or knee joint would be a seeding point forosteoarthritis.”Another way of detecting cartilage deteriorationis by measuring the tissue’s stiffness. However,current techniques only work at the micron scale,by which time the disease has already progressedby around five months. In this new work, the team

uses an indentation-type atomic forcemicroscope (IT-AFM) to measurestiffness on the nanoscale and hencedetect the disease at a much earlierstage. Here, an AFM tip is pressed intothe material and the response is directlymeasured.When the researchers studied micewith the phenotype for osteoarthritis,they detected differences in stiffnessof cartilage tissue as early as onemonth into the mouse’s lifetimewhen compared with that of normalmice. Tests on humans undergoing hipreplacements also indicated a markedchange in nanoscale stiffness, even inthe early stages of osteoarthritis.

The next step is to develop a user-friendly in situ

indentation type-AFM for clinics. In the future theteam also hopes to study tumors, but there aresome major questions to be answered first. “It is notso clear how a change in the mechanical propertiesof breast tissue in a tumor relates to its functionalrole in the body. This leads to the difficulty of howto interpret measured changes. Moreover, canceroustissue is much more complex compared to cartilage”says Stolz.Katerina Busuttil

Nanoindentation on human cartilage

How stiff are your joints?NANOTECHNOLOGY

Nanoscale capacitors pack in the powerENERGY