Title: Opticaldetection of single biomoleculesusing photonic-crystal membranes
Authors: Jon Olav Grepstad1, Peter Kaspar2, Ib-Rune Johansen3, Johannes Skaar1,6, Aasmund S. Sudbø5,6, Olav Solgaard7
1 NTNU, Trondheim, Norway
2 ETH Zürich, Electronics Laboratory, Gloriastrasse 35, CH-8092 Zürich, Switzerland
3SINTEF IKT, Microsystems and Nanotechnology, Gaustadalléen 23 C, 0373 Oslo, Norway
4SINTEF IKT, Instrumentation, Forskningsveien 1, 0373 Oslo, Norway
5 UiO,Department of Physics, Oslo, Norway
6University Graduate Center, Kjeller, UNIK - University Graduate Center P.O. Box 70, N-2007 KJELLER, Norway
7 E.L. Ginzton Laboratory, Stanford, CA 94305-4088, USA
In a recent publication [1], we present the design and fabrication of a2D photonic crystal (PC) membrane with submicronthickness and through holes.Its optical properties has been characterized by a custom built imagingsystem, using an optical microscope and a 2D CCD camera, measuring transmittance of monochromatic normal incident light.Figure 1(A),shows how a nano-particle insidea hole in the PC membraneappears as a bright spot in the microscope.Considering nano-particles in the form of DNA, proteins and viruses, we see a potential use of the sensor in biosensing if chemical methods are incorporated that allow capture of specific molecules in the holes.
Figure 1 - (A) Nano-particle trapped in the PC membrane, compared to (B) a single latex sphere on a glass substrate, both imaged with an optical microscope. (C) Normalized pixels values, along a horizontal line crossing the particle locations, give an impression of the difference in contrast [2].
The nano-particle, used as a model for a biomolecule in [1], is in reality a defect left after fabrication. A comparison of the PC membrane before and after particle capture can hence not be done. Consequently, ameasure the detection limit in particle size is not provided in [1].
In order to produce an approximate measure of sensitivity, we havecompared the appearance of the nano-particle trapped in the PC membrane, with particles, corresponding in size, placed on glass slides. The appearance of a 100 nm latex sphere on a glass substrate is shown in Figure 1(B). A comparison to the ~50 nm particle trapped in the PC membrane is provided in Figure 1(C). Results indicate that the contrast is improved to allow detection of particle sizes down to 20 nm in radius with the currently produced PC membranes.
[1] J. O. Grepstad et.al, Optics Express, p. 7954, 20 (2012)
[2] J. O. Grepstad et.al, Oral presentation,Imaging and Applied Optics Congress (2012)