Conjugated Polymer Film Fluorescence Enhances Images of Latent Fingerprints
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Conjugated Polymer Film Fluorescence Enhances Images of Latent Fingerprints Latent fingerprints—those left on surfaces without any ink—are often a critical clue for investigators at crime scenes. However, the high-sensitivity methods currently used in forensic science to detect latent fingerprints are cumbersome and difficult to employ. Now, in a recent issue of Chemical Communications (Issue 16, DOI: 10.1039/b902316j, p. 2112), G. Kwak, W.-E. Lee, W.-H. Kim, and H. Lee of Kyungpook University in Korea introduce a method of using a conjugated polymer thin film and florescent imaging for rapid, reusable latent fingerprint detection that may help overcome these issues. The highly fluorescent conjugated polymer poly[1-phenyl-2-(p-trimethylsilyl) phenylacetylene] (PTMSDPA) is known to have a large (0.26) fractional free volume as a film, which allows chemicals to easily diffuse into it. The research group
Percolation Model Developed to Describe Charge Transport in FETs Constructed from CNT Networks Films composed of random carbon nanotube (CNT) networks are increasingly being used for electronic applications. The low cost and flexibility of submonolayer CNT films have led to their use as sensors and as field effect transistors (FETs). Individual CNTs have been reported to have field effect mobilities of 10,000– 100,000 cm2/Vs. However, carbon nanotube network FETs (CNTN-FETs), which contain both metallic and semiconducting CNTs, display mobilities on the order of 10 cm2/Vs for unprocessed films and 80 cm2/Vs after the films are processed to break metallic network conduction. Because only the semiconducting CNTs can have their conductance modulated, it is critical to have semiconducting CNTs percolate the film, whereas a percolative metallic network would short out the device. Controlling tube density, tube-tube junction characteristics, and the fraction of tubes that are semiconducting may all lead to improved device performance. Recently, M.A. Topinka, M.W. Rowell, D. Goldhaber-Gordon, and M.D. McGehee of Stanford University and the SLAC National Accelerator Laboratory, Menlo Park, and D.S. Hecht and G. Gruner of the University of California, Los Angeles have investigated how current flows through CNTN-FETs, and have provided evidence for three possible types of CNTN-FETs with fundamentally different gating 396
previously determined that the intensity of fluorescence of PTMSDPA significantly increases when it absorbs certain chemicals, and speculated that this might also be the case for materials on human skin. To test this hypothesis, the group first exposed a free-standing, 30-μm-thick film of PTMSDPA to a sample of simulated human sebum (a 50:50 wt% mixture of a lipid standard and a fatty acid standard) and found that the fluorescent intensity of the film under UV illumination increased by more than an order of magnitude shortly after contact with the simulated sebum. Notably, no lateral diffusion of the fluorescence increase was observed until 30 minutes after the first exposure, suggesting that any spatial patt
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