Recent Developments in Human Odor Detection Technologies

Human odor detection technologies have drawn attention due to the wide possibility of potential applications they open up in areas such as biometrics, criminal investigation and forensics, search for survivors under rubble, and security checkpoint screening. Gas chromatography/mass spectrometry (GC/MS) has been the most successful and powerful analytical approach developed to date for human odor analysis, and hundreds of human odorants have been identified using this tool. GC/MS has already enabled a good understanding to be obtained regarding human odor composition. Over the past two decades, research and development of E-nose technologies has accelerated at a fast pace, and in time may provide a complementary technology to those based on GC/MS. During the past several years, proof of concept has been demonstrated on the application of E-noses for real-time human odor detection and classification. In this review, the current state of technologies will be given on human odor analysis, detection, and classification, along with a discussion of each technology with a specific focus on recent developments. Technologies covered in this article include: various E-nose technologies; as well as gas chromatography integrated with mass spectrometry, ion mobility spectrometry, or other gas detectors. Other technologies will also be described such as optical sensors that have recently emerged for human odor detection, and the possibilities of exploiting absorbance spectroscopy and hyperspectral imaging.

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Electronic-nose Applications in Forensic Science and for Analysis of Volatile Biomarkers in the Human Breath

The application of electronic-nose (E-nose) technologies in forensic science is a recent new development following a long history of progress in the development of diverse applications in the related biomedical and pharmaceutical fields. Data from forensic analyses must satisfy the needs and requirements of both the scientific and legal communities. The type of data collected from electronic-nose devices provides a means of identifying specific types of information about the chemical nature of evidentiary objects and samples under investigation using aroma signature profiles of complex gaseous mixtures containing volatile organic compounds (VOCs) released from manufactured products and parts of the human body. E-nose analyses also provide useful qualitative information about the physicochemical characteristics and metabolic conditions of human subjects without the need for time-consuming analyses to identify all chemical components in human-derived volatile mixtures. E-nose devices are capable of providing information for a wide range of forensic applications, useful for answering many types of questions relating to past events and details of circumstances and conditions that led to criminal activities involving human subjects and the perpetrators involved. E-nose devices have been used to help locate live subjects, buried in the rubble of collapsed buildings following natural disasters, as well as hidden bodies and the human remains of victims of accidents and crimes of aggression. The noninvasive analysis of gaseous mixtures in the human breath and lungs of living and deceased individuals provides a means for identifying the existence of diseases or adverse physiological conditions of human subjects (both before death and postmortem) potentially useful in determining the cause of death, time of death, and pertinent factors contributing to lethal events such as homicides and other violent crimes.

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Analysis of Sweat Simulant Mixtures using Multiplexed Arrays of DNA-Carbon Nanotube Vapor Sensors

Carbon nanotube (NT) based electronic vapor sensors were tested against synthetic sweat solutions, consisting of 13 volatile organic compounds (VOCs) in saline, in order to probe the device ability to analyze and differentiate vapors derived from complex biological samples. Arrays of up to 56 NT devices each were fabricated and functionalized with single stranded DNA to increase sensitivity and selectivity. DNA/NT devices were able to differentiate changes as small as 50% in a compound with estimated concentration in the vapor at part-per-billion levels, in a complex vapor background that contained the thirteen VOCs. This sensor class has vapor response times on the order of ten seconds, and is reusable and self-refreshing. The fabrication process is scalable, and sensor arrays are compact compared to traditional analysis equipment such as gas chromatography/mass spectrometry (GC/MS). The detectable differences among the simulated sweat mixtures were on the same scale as person-to-person variations in VOCs reported by others previously, demonstrating that DNA/NT vapor sensors show great promise for odor-based chemical biometric applications.

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Characteristic Human Scent Compounds Trapped on Natural and Synthetic Fabrics as analyzed by SPME-GC/MS

The collection of human odor volatiles is of interest to forensic applications as a path to investigate canine scent discriminations in legal investigations. A study using a selected array of previously identified human odor compounds has been conducted to determine the retention and release capabilities of five (5) natural and synthetic fabric types, cotton (mercerized fabric and gauze matrix), polyester, rayon and wool. A direct spike approach as well the use of a dynamic airflow device were the two approaches used for the collection of the selected volatile organic mix. The direct spike experiment showed how natural, cellulosic fibers such as viscose rayon showed an enhanced ability to release a reproducible volatile odor profile. Rayon demonstrated to be the fabric type with the highest recovered scent mass amounts, followed by wool and polyester. As was expected cotton showed the lowest recovered amounts, possibly due to its complex fiber morphology which enhances the possibility of chemicals to be retained in higher rates within the structure of the cotton fiber. Samples collected on the same fabric substrate showed a reproducible odor profile as measured via hierarchical clustering which corroborates previous live human odor studies and which can be pivotal in forensic biometric measurements. The introduction of an airflow variable to volatile collection decreased the amounts recovered for all fiber types. The reproducibility for each fabric type between replicate sampling was also reduced and a statistical significant difference (P<0.001) was observed in the interaction between airflow speed and fabric type. The cotton fabric was the material which showed enhance collection at the low airflow speed as observed by the recovered mass amount. In conclusion, these findings do indicate that chemical retention is strongly affected by fiber type and outside environmental variables such as airflow, which can alter the odor profile of a collected scent sample.

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Two basic reactions occur during the anodizing of aluminum: 1) the aluminum is consumed and 2) an oxide grows. By accepting this statement as true, the anodizing process can be viewed as a corrosion process, and anodizing can be modeled using the Tafel Equation. Anodizing process parameters of electrolyte chemistry and concentration, temperature, aluminum substrate resistance and current density are presented as they relate to the Tafel Equation and how they impact the anodic aluminum oxide structure and properties. Understanding this relationship is consequent in making anodizing an engineering process, one that enables tuning the structure such that it yields distinct characteristics to fulfill design and application requirements.

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The anodization of aluminum foils having micrometer thickness is a common process and results in hexagonally self-ordered alumina membranes. However, anodic aluminum oxide (AAO) membranes fabricated from nanometer-thin films present new challenges to the anodization process, since aluminum films adheres poorly on supporting substrates and the smoothness of the film is highly related to the kind of substrate. In the current work we studied the effect of the aluminum thickness and roughness, using films ranging from 100 to 800 nm in thickness and from 2 to 15 nm in root means square roughness (on a scan area of 100 μm2), on the final alumina morphology. We deposited Al thin films by sputtering method on transparent conductive glass substrates. A strong dependence between the Al film roughness and the final alumina pore organization was observed. It was also determined that by reducing the Al film thickness, smaller Al grains were generated, leading to a homogenous pore formation. It was found that, for thicknesses below 300 nm, the electrolyte used to perform anodization becomes a critical parameter due to the competitive effect of aluminum delamination with respect to the anodization reaction. Phosphoric acid showed less delamination problems than oxalic acid. Keywords:Anodic aluminum oxides; Thin films anodization; Hexagonal symmetry; Delamination; Nanometer thickness.

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Anodic Oxidation of Titanium in Sulphuric Acid and Phosphoric Acid Electrolytes

Anodisation of pure titanium has been carried out in sulphuric and in phosphoric acid solutions at potentials ranging from 50 to 150V. The SEM and AFM morphological analysis indicates that, within this potential range, oxidation in sulphuric acid solution produces better developed mesoporous oxide layers. XPS analysis of the Ti2p core level region and Raman spectroscopy measurements show that oxide layers grown in sulphuric acid are characterised by a better defined oxidation state of titanium and by a higher content in anatase crystalline phase. XPS measurements indicate that oxidation in phosphoric acid solution produces oxide layers with two components of stoichiometric oxide and with the presence of phosphate inclusions which can be interesting in view of biomedical applications.

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Fabrication of Ordered Arrays of Anodic Aluminum Oxide Pores with Interpore Distance Smaller than the Pitch of Nano-pits formed by Ion Beam Etching

We investigated a method for preparation of ordered nanopore arrays with the interpore distance of 60 nm by guided self-organization of anodic aluminum oxide with a prepatterned array of pits in the starting Al film. An ordered triangular array of 100 nm-pitch pits was formed on Al film by ion beam etching through an electron beam lithography fabricated mask, and then it was used as a guide for formation of anodic aluminum oxide pores. We found it was possible to reduce the interpore distance to 1/√3 of the pitch of the pits by the appropriate choice of the parameters of ion beam etching and anodization voltage.

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Preparation of Large Area Anodic Alumina Membranes and their Application to Thin Film Fuel Cell

The design of an electrochemical reactor for the preparation of self-supported comparatively thin (up to 10 μm) and large area (up to 50 cm2) anodic alumina membranes is described allowing growth of porous alumina at high applied potential (up to 150 V) without burning. Residual Al and barrier oxide beneath the porous film are dissolved through a vessel equipped with a gaskets system, which allows to expose to the dissolving solution an Al area lower than the anodised surface on the front leading to self-supported alumina membranes. According to scanning electron microscopy inspection and Hg-porosity measurements, the anodizing cell and conditions lead to the production of 25 and 50 cm2 Al2O3 porous layers with structural and morphological features very similar to those shown by commercial membranes (pore diameters 200 nm and pore densities 1012 pores/m2). The application of such large area membranes as support of inorganic proton conductors in thin film fuel cell proves their performance scalability.

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Fabrication of Vertical Cu2ZnSnS4 Nanowire Arrays by Two-Step Electroplating Method into Anodic Aluminum Oxide Template

Vertical Cu2ZnSnS4 (CZTS) nanowire arrays have been synthesized via two-step electroplating method into anodized aluminum oxide template. For deposition of CZTS nanowires, anodized aluminum oxide (AAO) was used as the growth mask for the growth of the nanowires. AAO templates with hole sizes of 70 nm in diameter were used in the experiments. After electroplating of CuZu/CuSn, vertical CuZu/CuSn nanowires were obtained on Mo-coated Si substrates and the typical size of nanowire and AAO of the same size.
And the elemental compositions of unannealed CuZu/CuSn nanowires about 2:1:1. Sulfurization was performed at 600 0C for 10 min in CS2 +Ar atmosphere. X-ray diffraction patterns indicate that the annealed CZTS have a kesterite structure including secondary metal and metal sulfide phases. It is found that the conditions of sulfurization treatment affect the quality of CZTS absorber layer.

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Anodic aluminum oxide doped with vanadyl citrate chelate complex anions was formed by a two-step self-organized anodization in 2 wt. % sulfuric acid containing 0.04 M V2O5 and 0.08 M citric acid at voltage range 13-23 V, and at 0 and 15 oC. The combination of two temperatures and at least four voltages (depending on the applied temperature) was applied as the operating conditions of anodization. It was found that formed nanoporous alumina was doped with vanadium (up to 0.08 at. %). The analysis of the photoluminescence of the grown oxide exhibits separate bands for the incorporated vanadyl citrate chelate anions (emission maxima at λ = 270 nm) and F – centers (emission maxima at λ = 455 nm). Moreover, due to the complex electronic structure of the incorporated anions, relatively long fluorescence decays were achieved (up to 44.6 ns). Despite incorporation of relatively large anions, pore diameter and interpore
distance were still linear functions of the voltage. Conducted research allowed to understand the fundamental aspects of the anions incorporation in the anodic alumina and allowed to form a new type of luminescent material.


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Synthesis of BaTiO3 Nanowires via Anodic Aluminum Oxide Template Method Assisted by Vacuum-and-Drop Loading

In recent years, miniaturization of sensors, actuators, capacitors and micro-electro-mechanical systems makes rapid progress. In order to realize the further miniaturization, nanostructured piezoelectric ceramics have been intensively studied. By controlling their nanostructures, one can make them to exhibit phase transition behavior and dielectric constants different from those of the bulk, partially due to the particle size effect [1-4]. To date, besides equiaxed nanoparticles and nanoceramics, one-dimensional (1-D) ferroelectric and piezoelectric nanomaterials are of great concern.


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