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Light-induced actuating nanotransducers

  1. Jeremy J. Baumberga,1
  1. aNanoPhotonics Centre, Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, United Kingdom;
  2. bDepartment of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB3 0FS, United Kingdom;
  3. cDepartment of Physics, University of Bath, Bath, BA2 7AY, United Kingdom;
  4. dDepartment of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom

  1. Edited by Vinothan N. Manoharan, Harvard University, Cambridge, MA, and accepted by the Editorial Board March 30, 2016 (received for review December 9, 2015)

Significance

Scientists have dreamt of nanomachines that can navigate in water, sense their environment, communicate, and respond. Various power sources and propulsion systems have been proposed but they lack speed, strength, and control. We introduce here a previously undefined paradigm for nanoactuation which is incredibly simple, but solves many problems. It is optically powered (although other modes are also possible), and potentially offers unusually large force/mass. This looks to be widely generalizable, because the actuating nanotransducers can be selectively bound to designated active sites. The concept can underpin a plethora of future designs and already we produce a dramatic optical response over large areas at high speed.

Abstract

Nanoactuators and nanomachines have long been sought after, but key bottlenecks remain. Forces at submicrometer scales are weak and slow, control is hard to achieve, and power cannot be reliably supplied. Despite the increasing complexity of nanodevices such as DNA origami and molecular machines, rapid mechanical operations are not yet possible. Here, we bind temperature-responsive polymers to charged Au nanoparticles, storing elastic energy that can be rapidly released under light control for repeatable isotropic nanoactuation. Optically heating above a critical temperature <mml:math><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:mrow></mml:math>Tc = 32 °C using plasmonic absorption of an incident laser causes the coatings to expel water and collapse within a microsecond to the nanoscale, millions of times faster than the base polymer. This triggers a controllable number of nanoparticles to tightly bind in clusters. Surprisingly, by cooling below <mml:math><mml:mrow><mml:msub><mml:mi>T</mml:mi><mml:mi>c</mml:mi></mml:msub></mml:mrow></mml:math>Tc their strong van der Waals attraction is overcome as the polymer expands, exerting nanoscale forces of several nN. This large force depends on van der Waals attractions between Au cores being very large in the collapsed polymer state, setting up a tightly compressed polymer spring which can be triggered into the inflated state. Our insights lead toward rational design of diverse colloidal nanomachines.

Footnotes

  • ↵1To whom correspondence may be addressed. Email: dt413{at}cam.ac.uk or jjb12{at}cam.ac.uk.

  • Author contributions: T.D., V.K.V., and J.J.B. designed research; T.D., V.K.V., and A.R.S. performed research; A.R.S., C.J.F., S.K.S., and O.A.S. contributed new reagents/analytic tools; T.D., V.K.V., D.F., and J.J.B. analyzed data; and T.D., V.K.V., O.A.S., D.F., and J.J.B. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission. V.N.M. is a guest editor invited by the Editorial Board.

  • Data deposition: The raw data of the figures in this paper can be found at https://www.repository.cam.ac.uk/handle/1810/254762.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1524209113/-/DCSupplemental.

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