SECM imaging of MMD-enhanced latent fingermarks

Abstract

Scanning electrochemical microscopy (SECM) has been used to image latent fingermarks enhanced by adsorption of gold nanoparticles onto which silver is chemically deposited, a process known as ''multi-metal-deposition'' (MMD).When a finger touches a surface, secretions are deposited leaving an impression of the finger's ridge pattern, referred to as a latent fingermark, which requires physical or chemical treatments to enable visualization. Fingermarks are still most widely used for personal identification. 1 They provide valuable physical evidence of contact between a finger and a surface. For years, forensic scientists have been seeking new methods or trying to improve existing methods for the visualization of latent fingermarks. The structured combination of optical methods (diffused reflection, luminescence, UV absorption and reflection), physical methods (powdering, small particle reagent, vacuum metal deposition), physico-chemical methods (physical developer, multi-metal-deposition (MMD), iodine, cyanoacrylate) and chemical methods (ninhydrin and its analogues, DFO, etc.) permits a rational and highly efficient processing of the secretions deposited by the fingers on a great variety of substrates. 2 To visualize these developed fingermarks, alternative light sources (such as Crimescope or Polilight) or laser-based detection methods are commonly used. However, these optical methods do not work in all possible cases, and certain types of latent fingermarks or object surfaces may be problematic. The major challenges in fingermark detection with laser techniques stem from both low emission levels from the fingermark secretions and interferences from the background signal, for example the background fluorescence when imaging a fingermark on bank notes. Up to now, no electrochemical imaging method has been reported to detect the latent fingermarks.Scanning electrochemical microscopy (SECM), a scanning probe technique, has been developed into a powerful technique for the kinetic measurements of localized processes at solid-liquid or liquid-liquid interfaces, for high-resolution imaging of the chemical activity and/or topography of various interfaces on a localized scale, and for microfabrication. 3 In SECM experiments, the probe is a noble metal microelectrode brought to the vicinity of the substrate surface, where the amperometric response (either for an oxidation or a reduction process) that depends on the electrochemical reactivity of the substrate is recorded as a function of the lateral probe position (x, y) for imaging. SECM is able to resolve differences on the micron or sub-micron length scale, an advantage which is clear in many reported applications. 4 We have previously shown that SECM could be used in the feedback mode to image silver or copper stained proteins, by generating at the microelectrode an oxidizer to oxidize these metals. 5 These reports proved the feasibility of using SECM for imaging protein spots on a membrane surface. Very recently, we have shown that SECM combined with silver stainin...

Soft Stylus Probes for Scanning Electrochemical Microscopy

“…[47][48][49][50][51] Despite these efforts, challenges remain both for achieving higher lateral resolution and for inspection of larger sample regions. This paper addresses the latter issue encountered, for example when imaging silver-stained proteins after gel electrophoresis, 52 human fingerprints, 53,54 and negative photographic films. 55 Here, we propose a new type of amperometric probe for SECM produced by sealing with a polymer film a carbon track microfabricated on a polyethylene terephthalate sheet.…”

Adsorbed protein detection by scanning electrochemical microscopy

“…liquid/solid, liquid/liquid and gas/solid interfaces) [25][26][27][28][29][30][31]. As a result, SECM has been applied in various fields such as biology to study the respiratory chain of Escherichia coli [32] or in forensic sciences to image human fingerprints [33,34].…”

SECM photography

“…These reports demonstrated the feasibility of using SECM to detect metallic nanoparticles on a porous membrane surface. Then, we applied this technique as a highly sensitive tool for imaging proteinmodified latent fingermarks on a poly(vinylidene difluoride) (PVDF) membrane and fingermarks on glass enhanced by a multi-metal-deposition (MMD) approach [35,36]. This methodology takes advantage of the high sensitivity of SECM toward the small variation of electrochemical properties at the substrate surface.…”