EDITORIAL pubs.acs.org/JPCL
Nanosensing: The Art of Seeing Things Invisible
O
ne reason that nanotechnology has generated so much attention beyond the realm of science and engineering is that it involves materials and processes that are too small to see, leaving much to the imagination. As Jonathan Swift said, “vision is the art of seeing things invisible.” To those who see the glass as half full, the vision is that nanotechnology holds great promise for improving our lives. To those who see the glass as half empty, the vision is that nanotechnology is fraught with poorly understood dangers. The general public may well become more comfortable with nanotechnology as more consumer and medical devices are introduced that derive clear and unique benefits from nanoscale phenomena. Nanosensing is one area of nanotechnology with enormous potential in this regard. A nanosensor acts as a transducer that provides information about nanoscale objects or processes in a manner that is useful to a macroscale system. Nature solved this problem long ago, as evidenced by the fact that you are reading this page by detecting individual photons. As is clear from two Perspectives in this issue of JPC Letters, scientists and engineers are beginning to make substantial progress on catching up to Nature in this area. The power of nanotechnology lies in its operation in a size regime in which chemical and physical properties can differ vastly both from those of the corresponding bulk materials and from those of their constituent atoms or molecules. Many of these properties can be harnessed for the optical transduction of nanoscale information. For instance, nanotechnology can be used to make optical elements and detectors that outperform their conventional counterparts.1 3 The Perspective by Suslick and co-workers4 discusses other types of nanosensors that take advantage of nanostructured materials to enable sensitive and selective optical detection. Advances in the preparation of nanomaterials, both by synthesis and fabrication, have enabled the development of a wide range of new optical nanosensor technologies. For instance, nanostructured metal substrates have facilitated the development of a new generation of sensors that take advantage of localized surface plasmon resonances. Other classes of optical nanosensors, such as porous silicon photonic crystals and ormosil-based colorimetric sensors, take advantage of the extremely high surface-tovolume ratio of nanomaterials. The porosity and surface area of these materials allows for rapid response times when exposed to an analyte, and the materials are amenable to the creation of highly multiplexed sensor systems. Another attractive route to the transduction of signals from nanoscale sensors is through electrical means. A prominent example of electrical nanosensors is field effect transistors based on nanowires and nanotubes.5 The Perspective by Strano and coworkers6 discusses the intriguing new field of electrical detection of molecules as they pass through the inside of single-walled carbon nanotubes (SWCNTs) with small diameters. In this method, a SWNT acts as a conduit between two wells that contain aqueous solutions. A voltage is applied across the wells, and the current through the SWCNT is measured. When a solute enters the SWCNT, there is a dip in current until the solute has r 2011 American Chemical Society
emerged from the other side. By monitoring these switches between so-called Coulter states, it is possible to count particles passing through the SWCNT. One area in which this technology is of great interest is in DNA separation and sequencing, and preliminary results suggest that single DNA molecules can pass through SWCNTs.7 Strano and co-workers caution, however, that the nominally impermeable barriers between the wells can have nanoscale cracks in them, allowing molecules to pass along the outside of the nanotubes or even directly through the barrier. Improved barrier materials should alleviate these problems. Nanosensing is still a field that is in its relative infancy, but as these Perspectives demonstrate that it holds tremendous potential not only for applications but also to teach us interesting new chemistry and physics. John T. Fourkas Senior Editor University of Maryland, College Park, Maryland, United States
’ REFERENCES (1) Konstantatos, G.; Sargent, E. H. Nanostructured Materials for Photon Detection. Nat. Nanotechnol. 2010, 5, 391–400. (2) Schwartz, J. J.; Stavrakis, S.; Quake, S. R. Colloidal Lenses Allow High-Temperature Single-Molecule Imaging and Improve Fluorophore Photostability. Nat. Nanotechnol. 2010, 5, 127–132. (3) Zhu, J.; Ozdemir, S. K.; Xiao, Y.-F.; Li, L.; He, L.; Chen, D.-R.; Yang, L. On-Chip Single Nanoparticle Detection and Sizing by Mode Splitting in an Ultrahigh-Q Microresonator. Nat. Photon. 2010, 4, 46–49. (4) Kemling, J. W.; Qavi, A. J.; Bailey, R. C.; Suslick, K. S. Nanostructured Substrates for Optical Sensing. J. Phys. Chem. Lett. 2011, 2, 2934–2944. (5) Ramgir, N. S.; Yang, Y.; Zacharias, M. Nanowire-Based Sensors. Small 2010, 6, 1705–1722. (6) Ulissi, Z.; Shimizu, S.; Lee, C. Y.; Strano, M. Carbon Nanotubes as Molecular Conduits: Advances and Challenges for Transport through Isolated Sub-2 nm Pores. J. Phys. Chem. Lett. 2011, 2, 2892–2896. (7) Liu, H.; He, J.; Tang, J.; Liu, H.; Pang, P.; Cao, D.; Krstic, P.; Joseph, S.; Lindsay, S.; Nuckolls, C. Translocation of Single-Stranded DNA through Single-Walled Carbon Nanotubes. Science 2010, 327, 64–67.
Published: November 17, 2011 2945
dx.doi.org/10.1021/jz201284e | J. Phys. Chem. Lett. 2011, 2, 2945–2945
