Abstract
Spatially selective electrodeposition of poly-3,4-ethylenedioxythiophene (PEDOT) thin films on metallic surfaces is shown to be an effective means of visualizing latent fingerprints. The technique exploits the fingerprint deposit as an insulating mask, such that electrochemical processes (here, polymer deposition) may only take place on deposit-free areas of the surface between the ridges of the fingerprint deposit; the end result is a negative image of the fingermark. Use of a surfactant (sodium dodecylsulphate, SDS) to solubilise the EDOT monomer allows the use of an aqueous electrolyte. Electrochemical (coulometric) data provide a total assay of deposited material, yielding spatially averaged film thicknesses, which are commensurate with substantive filling of the trenches between fingerprint deposit ridges, but not overfilling to the extent that the ridge detail is covered. This is confirmed by optical microscopy and AFM images, which show continuous polymer deposition within the trenches and good definition at the ridge edges. Stainless steel substrates treated in this manner and transferred to background electrolyte (aqueous sulphuric acid) showed enhanced fingerprints when the contrast between the polymer background and fingerprint deposit was optimised using the electrochromic properties of the PEDOT films. The facility of the method to reveal fingerprints of various ages and subjected to plausible environmental histories was demonstrated. Comparison of this enhancement methodology with commonly used fingerprint enhancement methods (dusting with powder, application of wet powder suspensions and cyanoacrylate fuming) showed promising performance in selected scenarios of practical interest.
Highlights
Fingerprints have been used as a means of biometric identification since the mid 1800s and, despite the rise of other methods such as those based on DNA, remain a cornerstone of the identification of individuals for forensic and other purposes
We focus here on PEDOT films deposited potentiostatically from such solutions; comments on the outcomes for less effective protocols are provided in the Supporting Information.w
We do not explore the details of coupled electron/ion transfer, which have been discussed previously for diverse electrolytes,[38] save to note the practically critical feature that voltammetric currents were linear with potential scan rate and that injected/recovered charge was independent of scan rate in the range 1 o v/mV sÀ1 o 250
Summary
Fingerprints have been used as a means of biometric identification since the mid 1800s and, despite the rise of other methods such as those based on DNA, remain a cornerstone of the identification of individuals for forensic and other purposes. The approach is complementary to most visualization methods, in that it involves interaction not with the fingerprint but with the uncovered regions of the substrate This first stage of the concept (illustrated in Scheme 1) was described by Bersellini et al.,[23] who deposited polypyrrole electrochemically on fingerprinted metal surfaces such as Pt, Au, Ag and Ergal (Al alloy).[23] The fundamental extension pursued here is subsequent potential control of the deposited polymer to vary its optical properties, Scheme 1 Schematic representation of strategy for visualizing latent fingerprints by deposition of electrochromic polymer. Focuses on fundamental aspects of these objectives, extending the polyaniline-based proof-of-concept;[25] complementary performance aspects are the subject of a parallel report.[34] As we shall show, PEDOT deposition from aqueous media provides a powerful means of latent fingerprint enhancement on metals, with access to second and third level detail via the added visual dimension of electrochromism. Images (100 mm  100 mm) were acquired in tapping mode (resonant frequency 200 kHz) at a scan rate of 0.6 Hz, i.e. 120 mm sÀ1
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
