Highly sensitive electrochemical detection of trace liquid peroxide explosives at a Prussian-blue 'artificial-peroxidase' modified electrode

A highly sensitive electrochemical assay of the peroxide-based explosives triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) at a Prussian-blue (PB) modified electrode is reported. The method involves photochemical degradation of the peroxide explosives and a low potential (0.0 V) electrocatalytic amperometric sensing of the generated hydrogen peroxide at the PB transducer and offers nanomolar detection limits following a short (15 s) irradiation times. The electrochemical sensing protocol should facilitate rapid field screening of peroxide explosives.     

A colorimetric sensor array for detection of triacetone triperoxide vapor

Triacetone triperoxide (TATP), one of the most dangerous primary explosives, has emerged as an explosive of choice for terrorists in recent years. Owing to the lack of UV absorbance, fluorescence, or facile ionization, TATP is extremely difficult to detect directly. Techniques that are able to detect generally require expensive instrumentation, need extensive sample preparation, or cannot detect TATP in the gas phase. Here we report a simple and highly sensitive colorimetric sensor for the detection of TATP vapor with semiquantitative analysis from 50 ppb to 10 ppm. By using a solid acid catalyst to pretreat a gas stream, we have discovered that a colorimetric sensor array of redox sensitive dyes can detect even very low levels of TATP vapor from its acid decomposition products (e.g., H(2)O(2)) with limits of detection (LOD) below 2 ppb (i.e., <0.02% of its saturation vapor pressure). Common potential interferences (e.g., humidity, personal hygiene products, perfume, laundry supplies, volatile organic compounds, etc.) do not generate an array response, and the array can also differentiate TATP from other chemical oxidants (e.g., hydrogen peroxide, bleach, tert-butylhydroperoxide, peracetic acid).     

Turn-on fluorescence detection of H2O2 and TATP

Peroxide-based explosives, like triacetone triperoxide (TATP), are important targets for detection because of their broad use in improvised explosives but pose challenges. We report a highly sensitive turn-on fluorescence detection for H2O2 and organic peroxides, including TATP. The detection strategy relies on oxidative deboronation to unmask H2Salen, which subsequently binds Zn(2+) to form fluorescent Zn(Salen). Sensitivity is excellent, with detection limits below 10 nM for H2O2, TATP, and benzoyl peroxide. In addition, acid treatment is necessary to sense TATP, suggesting the potential to discriminate between H2O2 and TATP based upon minimal sample pretreatment.     

Enhanced stability of a Prussian blue/sol-gel composite for electrochemical determination of hydrogen peroxide

We have prepared a sol–gel that incorporates Prussian Blue (PB) as a redox mediator. It is shown that the PB in the pores of the sol–gel retains its electrochemical activity and is protected from degradation at acidic and neutral pH values. TEM and EDX studies revealed the PB nanoparticles to possess a cubic crystal structure and to be well entrapped and uniformly dispersed in the pores of the matrix. The electrocatalytic activity of the materials toward hydrogen peroxide (H₂O₂) was studied by cyclic voltammetry and amperometry. The modified electrode displays good sensitivity for the electrocatalytic reduction of H₂O₂ both in acidic (pH 1.4) and neutral media. The sensor has a dynamic range from 3 to 210 μM of H₂O₂, and the detection limit is 0.6 μM (at an SNR of 3).

A field test for the detection of peroxide-based explosives

A rapid and simple field test for the detection of triacetone-triperoxide (TATP) and hexamethylenetriperoxidediamine (HMTD), two explosives which find significant illegal use, has been developed. Unknown samples are first treated with a catalase solution to remove hydrogen peroxide traces, in order to provide selectivity towards peroxide-based bleaching agents which are contained in commercial laundry detergents. Subsequently, the peroxide-based explosives are decomposed via UV irradiation, thus yielding hydrogen peroxide, which is determined by the horseradish peroxidase (POD) catalysed formation of the green radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS). The limits of detection for this method are 8 x 10(-6) mol dm(-3) for TATP and 8 x 10(-7) mol dm(-3) for HMTD, respectively. As an option, p-hydroxyphenylacetic acid (pHPAA) may be used as peroxidase substrate, resulting in lower limits of detection (8 x 10(-7) mol dm(-3) for TATP and HMTD). The complete method uses a mobile setup to be applied under field conditions.     

TATP的质子转移反应的质谱研究

利用密度泛函理论(DFT), 在B3LYP/cc-pVDZ水平上, 对三过氧化三丙酮(Triacetone triperoxide, TATP)及其质子化离子[TATP+H]+进行了构型优化和质子亲和势(Proton Affinity, PA)计算, 研究结果表明, PA(TATP)=866.73 kJ/mol大于PA(H2O)=691.0 kJ/mol, TATP与H3O+可发生质子转移反应. 在自行研制的质子转移反应质谱(Proton transfer reaction mass spectrometry, PTR-MS) 装置上, 研究了TATP与H3O+反应生成的特征离子. 当漂移管中E/N=1.4×10-15 V·cm2时, 在荷质比m/z=91, 75, 74, 59, 43等处观察到了产物离子. 降低E/N至0.5×10-15 V·cm2后, 在m/z=223处观察到了质子化产物离子([TATP+H]+), 验证了计算结果; 结合[TATP+H]+的构型, 分析了TATP质子转移反应产物离子可能的归属及其形成过程. 结合PTR-MS漂移管内E/N的改变引起m/z=223, 91, 43等离子的变化特征, 可实现TATP的准确识别和快速定量检测, 检测下限达到5.0×10-10 mol/L(±50%).     

3,3,6,6,9,9‐Hexaethyl‐1,2,4,5,7,8‐hexaoxacyclononane at 296 K

The title molecule (diethyl ketone triperoxide, DEKTP), C₁₅H₃₀O₆, is a cyclic triperoxide closely related to triacetone triperoxide (TATP), one of the most unstable explosives known. However, the stability of DEKTP is ca 20–50 times greater than that of TATP. DEKTP crystallizes with two molecules in the asymmetric unit, with virtually identical geometry. The cyclononane core is stabilized in a twisted boat–chair conformation (approximate D₃ symmetry), very close to that previously described for TATP. The explanation for the safe thermal behaviour of DEKTP compared with TATP should thus not be sought in the molecular dimensions, but rather in the thermal decomposition kinetics.     

Photochemical synthesis of Prussian blue film from an acidic ferricyanide solution and application

We describe a novel photochemical method to synthesize compacted Prussian blue (PB) film from an acidic ferricyanide solution. The key step is the photochemical reduction of ferricyanide ion to ferrocyanide ion that subsequently coordinates with the free ferric ion dissociated from the ferricyanide in acidic medium to form Prussian blue on the illuminated electrode surface. The prepared PB film electrode shows high electrocatalytic activity towards the reduction of hydrogen peroxide and the amperometric responses show a linear dependence on the concentration of hydrogen peroxide in a range of 1.0 × 10⁻⁶ to 1.2 × 10⁻³ M with a detection limit down to 4 × 10⁻⁷ M. The present photochemical method provides a simple and promising route for the local fabrication of patterned molecular magnets, ion-selective sensors, and electro- or photochromic devices.     

Electrochemical detection of triacetone triperoxide employing the electrocatalytic reaction of iron(II/III)-ethylenediaminetetraacetate and hydrogen peroxide

An electrochemical method for the detection of triacetone triperoxide (TATP) is proposed and examined. In this method, TATP solutions were treated with 1.08 M HCl for 10 min releasing H₂O₂ and/or hydroperoxides. Subsequently, these peroxides undergo an electrocatalytic reduction through the Fe^II/IIIethylenediaminetetraacetate (EDTA) complex at a glassy carbon electrode. Cyclic voltammetric results indicate that no redox reaction was observed between Fe^IIEDTA and TATP. Acid treated TATP yielded voltammograms indicative of electrocatalysis of ROOH/HOOH reduction via Fe^II/IIIEDTA redox cycling. Chronoamperometric results yielded a detection limit of 0.89 μM for TATP and a sensitivity of 0.025 mA mM⁻¹. The influence of pH and O₂ interference on the analytical signal is briefly discussed.     

New Nanocomposite Based on Prussian Blue Nanoparticles/Carbon Nanotubes/Chitosan and Its Application for Assembling of Amperometric Glucose Biosensor

Abstract

A new nanocomposite was developed by combination of prussian blue (PB) nanoparticles and multiwalled carbon nanotubes (MWNTs) in the matrix of biopolymer chitosan (CHIT). The PB and MWNTs had a synergistic electrocatalytic effect toward the reduction of hydrogen peroxide. The CHIT/MWNTs/PB nanocomposite‐modified glassy carbon (GC) electrode could amplify the reduction current of hydrogen peroxide by ～35 times compared with that of CHIT/MWNTs/GC electrode and reduce the response time from ～60 s for CHIT/PB/GC to 3 s. Besides, the CHIT/MWNTs/PB nanocomposite‐modified GC electrode could reduce hydrogen peroxide at a much lower applied potential and inhibit the responses of interferents such as ascorbic acid (AA) uric acid (UA) and acetaminophen (AC). With glucose oxidase (GOx) as an enzyme model, a new glucose biosensor was fabricated. The biosensor exhibited excellent sensitivity (the detection limit is down to 2.5 µM), fast response time (less than 5 s), wide linear range (from 4 µM to 2 mM), and good selection.     

Gas chromatography/mass spectrometry analysis of triacetone triperoxide (TATP) degradation products

Interest in the analysis and detection of triacetone triperoxide (TATP) and other organic peroxides has increased in recent years. Also of interest is the degradation and decomposition of the peroxides, not only to gain more detailed chemical information from organic peroxide samples, but also to investigate possible new procedures or mechanisms for chemical neutralisation. This report investigates the chemical degradation products of TATP after it has been treated with different acids within a sealed system over a period of 14 days. The samples were collected and analysed by solid-phase microextraction (SPME) and direct liquid injection gas chromatography/mass spectrometry (GC/MS). The results of the experiments indicate that the rate of chemical degradation of TATP and the products formed are dependent on the type of acid. The observed differences enables the type of acid used in the degradation process to be determined, provide complementary information to identify the presence of TATP, and possibly indicate new pathways that may be used to chemically neutralise TATP.     

3-Glycidoxypropyltrimethoxysilane mediated in situ synthesis of noble metal nanoparticles: application to hydrogen peroxide sensing

The in situ synthesis is reported of noble metal nanoparticles via 3-glycidoxypropyltrimethoxysilane mediated reduction of 3-aminopropyltrimethoxysilane treated metal salts during sol-gel processing. The method described involves the synthesis of uniform spherical nanoparticles of gold, silver and palladium with controlled size that can be directly utilized for thin film preparation. A detailed study of the synthesis and application of gold nanoparticles to the electrochemical detection of hydrogen peroxide was carried out and reveals that the amplification of hydrogen peroxide sensing is size-dependent. In addition, these nanoparticles exhibit excellent compatibility towards composite preparation. As an example, a nanocomposite with Prussian Blue (PB) is synthesized and found to be useful for the fabrication of chemically modified electrodes (CME). The resulting CME shows dramatic improvement in the electrochemistry of PB with gradual enhancement in electrocatalytic efficiency towards hydrogen peroxide sensing. The nanocomposite is used to study the direct and horseradish peroxidase (HRP)-catalyzed reduction of hydrogen peroxide. The results recorded for hydrogen peroxide analysis show an improvement in sensitivity and limit of detection on decreasing the size of gold nanoparticles in all cases.     

Neutral desorption using a sealed enclosure to sample explosives on human skin for rapid detection by EESI-MS

A novel air-tight neutral desorption enclosure has been fabricated to noninvasively sample low picograms of explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX), triacetone triperoxide (TATP), and nitroglycerin (NG) from human skin using a neutral nitrogen gas beam. Without further sample pretreatment, the explosive mixtures collected from the skin surface were directly transported by a nitrogen carrier gas over a 4-m distance for sensitive detection and rapid identification by extractive electrospray ionization tandem mass spectrometry.     

Chronocoulometric study of the electrochemistry of Prussian blue

During the electrochemical oxidation of Prussian blue (PB) to Prussian yellow (PY), an electrocatalytic oxygen production proceeds at the electrode when aqueous electrolyte solutions are used. The formed oxygen is scavenged by the PY, probably by absorption, and it is consumed during the electrochemical reduction of PY to PB by a heterogeneous chemical reaction of PB with oxygen to PY and hydrogen peroxide. Because of this catalytic regeneration of PY, it is impossible to determine the amount of low-spin iron by chronocoulometry using a potential program in which PB is first oxidized to PY and then the charge is measured to reduce PY to PB. The latter charge is biased by the electrocatalytic PY regeneration.     

Amperometric sensing of hydrogen peroxide vapor for security screening

Rapid detection of the hydrogen peroxide precursor of peroxide explosives is required in numerous security screening applications. We describe a highly sensitive and selective amperometric detection of hydrogen peroxide vapor at an agarose-coated Prussian-blue (PB) modified thick-film carbon transducer. The sensor responds rapidly and reversibly to dynamic changes in the level of the peroxide vapor, with no apparent carry over and with a detection limit of 6 ppbv. The remarkable selectivity of the PB-based screen-printed electrode towards hydrogen peroxide leads to effective discrimination against common beverage samples. For example, blind tests have demonstrated the ability to selectively and non-invasively identify concealed hydrogen peroxide in drinking cups and bottles. The attractive performance of the new microfabricated PB-based amperometric peroxide vapor sensor indicates great potential for addressing a wide range of security screening and surveillance applications. Figure Experimental setup (left) with three electrode electrochemical Hydrogen Peroxide sensor hanging above container of “unknown” liquid. Schematic (right) demonstrating fundamental principles of operation of the sensor.     

High-throughput walkthrough detection portal for counter terrorism: detection of triacetone triperoxide (TATP) vapor by atmospheric-pressure chemical ionization ion trap mass spectrometry

With the aim of improving security, a high‐throughput portal system for detecting triacetone triperoxide (TATP) vapor emitted from passengers and luggage was developed. The portal system consists of a push‐pull air sampler, an atmospheric‐pressure chemical ionization (APCI) ion source, and an explosives detector based on mass spectrometry. To improve the sensitivity of the explosives detector, a novel linear ion trap mass spectrometer with wire electrodes (wire‐LIT) is installed in the portal system. TATP signals were clearly obtained 2 s after the subject under detection passed through the portal system. Preliminary results on sensitivity and throughput show that the portal system is a useful tool for preventing the use of TATP‐based improvised explosive devices by screening persons in places where many people are coming and going. Copyright © 2011 John Wiley & Sons, Ltd.     

A quantitative chemiluminescent assay for analysis of peroxide-based explosives

A quantitative chemiluminescent method, enabling indirect identification of the peroxide-based explosives TATP (triacetone triperoxide) and HMTD (hexamethylene triperoxide diamine) has been developed. Treatment of these compounds with acidic solutions produced peroxides, which were transformed into radical derivatives by horseradish peroxidase (HRP) and then quantified by measuring the light emitted during their oxidation of luminol. The method was first developed in the microplate format and later optimized for a portable luminometer, to enable rapid application of the assay directly on site. When the portable luminometer was used each analysis took only 5–10 min. The method had good selectivity, sensitivity, and reproducibility; in the microplate format the limits of detection (LOD) and quantification (LOQ) were 40 and 50 ng mL⁻¹, respectively, for both TATP and HMTD. When the portable luminometer was used the LOD and LOQ were 50 and 100 ng mL⁻¹, respectively, for both compounds. Introduction of light emission-enhancing compounds did not improve the analytical performance of the assay. Imprecision (CV values) was always below 10%. Recovery varied rapidly with time, with an average value of 78% after 5 min. No false-positive result was detected on measurement of a variety of samples; this is an important feature for analysis on site. The method was applied both to contaminated materials and to fortified soil samples, simulating operational conditions.     

Prussian Blue Dispersed Sphere Catalytic Labels for Amplified Electronic Detection of DNA

A highly sensitive electrochemical DNA hybridization assay using Prussian blue (PB)-modified polymeric spheres as the oligonculeotide labeling tag is described. The sandwich assay relies on a secondary nucleic-acid probe functionalized with polystyrene beads loaded with numerous Prussian blue nanoparticles. The very strong catalytic activity of the captured PB 'artificial peroxidase' tag towards the reduction of hydrogen peroxide, along with the encapsulation of numerous catalytic particles onto polymeric beads, allows amperometric detection of the DNA target down to the 50 fM level (2.5 amol). Imaging and spectroscopic measurements are used to characterize the PB-tagged polystyrene beads. Such coupling of PB catalytic labels with polymeric carrier beads offers great promise for amplified transduction of different biomolecular interactions.     

Fluorescent signaling based on sulfoxide profluorophores: application to the visual detection of the explosive TATP

The first visual fluorescence-based assay for the peroxide explosive triacetone triperoxide (TATP) is described. The assay is based on a conceptually new fluorescence signaling mechanism, in which nonemissive pyrenyl sulfoxide profluorophores are oxidized to visibly emissive pyrenyl sulfones. Although not without limitations, these first-generation fluorescent probes can provide a visual response to ca. 100 nmol of TATP. In addition, the success of this assay suggests the potential for broader application of aryl sulfoxides in fluorescent chemosensing.     

Analysis of triacetone triperoxide by gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry by electron and chemical ionization

The explosive triacetone triperoxide (TATP) has been analyzed by gas chromatography/mass spectrometry (GC/MS) and sub-nanogram detection limits are reported by ammonia positive ion chemical ionization (PICI), electron ionization (EI) and methane negative ion chemical ionization (NICI). Analysis by methane PICI and ammonia NICI gave detection limits in the low nanogram range. Analyses were carried out on (linear) quadrupole and ion trap instruments. Analysis of TATP by PICI using ammonia reagent gas is the preferred analytical method, producing low limits of detection as well as an abundant (greater than 60% of base peak) diagnostic adduct ion at m/z 240 corresponding to [TATP + NH4]+. Isolation of the [TATP + NH4]+ ion with subsequent collision-induced dissociation (CID) produces extremely low abundance product ions at m/z values greater than 60, and the m/z 223 ion corresponding to [TATP + H]+ was not observed. Density functional theory (DFT) calculations at the B88LYP/DVZP level indicate that dissociation of the complex to form NH4+ and TATP occurs at energies lower than peroxide bond dissociation, while protonation of TATP leads to cleavage of the ring structure. These results provide a method for pico-gram detection levels of TATP using commercial instrumentation commonly available in forensic laboratories. As a point of comparison, a detection limit of 15 ng was obtained by flame ionization detection.