This critical review is focused on examples reported from 1947 to 2010 related to the design of chromo-fluorogenic chemosensors and reagents for explosives (141 references).

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Optical chemosensors and reagents to detect explosives

Combining nanomaterials and biomolecule recognition units is promising in developing novel clinic diagnostic and protein analysis techniques. In this work, a highly sensitive and specific fluorescence resonance energy transfer (FRET) aptasensor for thrombin detection is developed based on the dye labeled aptamer assembled graphene. Due to the noncovalent assembly between aptamer and graphene, fluorescence quenching of the dye takes place because of FRET. The addition of thrombin leads to the fluorescence recovery due to the formation of quadruplex−thrombin complexes which have weak affinity to graphene and keep the dyes away from graphene surface. Because of the high fluorescence quenching efficiency, unique structure, and electronic properties of graphene, the graphene aptasensor exhibits extraordinarily high sensitivity and excellent specificity in both buffer and blood serum. A detection limit as low as 31.3 pM is obtained based on the graphene FRET aptasensor, which is two orders magnitude lower than ...

Graphene Fluorescence Resonance Energy Transfer Aptasensor for the Thrombin Detection

Ionic liquids in analytical chemistry.

TNT is one of the most commonly used nitro aromatic explosives used for landmine and military purpose. Due to the significant detrimental effects, contamination of soil and groundwater with TNT is the major concern. Driven by the need to detect trace amounts of TNT from environmental samples, this article demonstrates for the first time a highly selective and ultra sensitive, cysteine modified gold nanoparticle based label-free surface enhanced Raman spectroscopy (SERS) probe, for TNT recognition in 2 pico molar (pM) level in aqueous solution. Due to the formation of Meisenheimer complex between TNT and cysteine, gold nanoparticles undergo aggregation in the presence of TNT via electrostatic interaction between Meisenheimer complex bound gold nanoparticle and cysteine modified gold nanoparticle. As a result, it formed several hot spots and provided a significant enhancement of the Raman signal intensity by 9 orders of magnitude through electromagnetic field enhancements. A detailed mechanism for termendous SERS intensity change has been discussed. Our experimental results show that TNT can be detected quickly and accurately without any dye tagging in lower pM level with excellent discrimination against other nitro compounds and heavy metals.

Gold nanoparticle based label-free SERS probe for ultrasensitive and selective detection of trinitrotoluene.

To detect trace trinitrotoluene (TNT) explosives deposited on various surfaces instantly and on-site still remains a challenge for homeland security needs against terrorism. This work demonstrates a new concept and its utility for visual detection of TNT particulates on various package materials. The concept takes advantages of the superior fluorescent properties of quantum dots (QDs) for visual signal output via ratiometric fluorescence, the feasibility of surface grafting of QDs for chemical recognition of TNT, and the ease of operation of the fingerprint lifting technique. Two differently sized CdTe QDs emitting red and green fluorescences, respectively, have been hybridized by embedding the red-emitting one in silica nanoparticles and covalently linking the green-emitting one to the silica surface, respectively, to form a dual-emissive fluorescent hybrid nanoparticle. The fluorescence of red QDs in the silica nanoparticles stays constant, whereas the green QDs functionalized with polyamine can selectively bind TNT by the formation of Meisenheimer complex, leading to the green fluorescence quenching due to resonance energy transfer. The variations of the two fluorescence intensity ratios display continuous color changes from yellow-green to red upon exposure to different amounts of TNT. By immobilization of the probes on a piece of filter paper, a fingerprint lifting technique has been innovated to visualize trace TNT particulates on various surfaces by the appearance of a different color against a yellow-green background under a UV lamp. This method shows high selectivity and sensitivity with a detection limit as low as 5 ng/mm(2) on a manila envelope and the attribute of being seen with the naked eye.

http://www.dstuns.iitm.ac.in/grouppresentations/2011/Instant%20Visual.pdf

Instant Visual Detection of Trinitrotoluene Particulates on Various Surfaces by Ratiometric Fluorescence of Dual-Emission Quantum Dots Hybrid

A highly selective, sensitive, and low-cost hybrid sensing platform is developed based on extraordinary properties of explosives in an ionic liquid and an integrated electrochemical and colorimetric approach.

A hybrid electrochemical-colorimetric sensing platform for detection of explosives.

Real-time detection of trace chemicals, such as explosives, in a complex environment containing various interferents has been a difficult challenge. We describe here a hybrid nanosensor based on the electrochemical reduction of TNT and the interaction of the reduction products with conducting polymer nanojunctions in an ionic liquid. The sensor simultaneously measures the electrochemical current from the reduction of TNT and the conductance change of the polymer nanojunction caused from the reduction product. The hybrid detection mechanism, together with the unique selective preconcentration capability of the ionic liquid, provides a selective, fast, and sensitive detection of TNT. The sensor, in its current form, is capable of detecting parts-per-trillion level TNT in the presence of various interferents within a few minutes.

A Hybrid Nanosensor for TNT Vapor Detection

We present an ammonia sensor for human breath analysis based on electrically conducting polymer nanojunctions. Each nanojunction is formed by bridging a pair of gold nanoelectrodes on a silicon chip separated by a small gap (<60 nm) with electrodeposited polyaniline. The signal transduction mechanism of the sensor is the change in the nanojunction conductance as a result of polymer dedoping by ammonia. The sensor response to human breath is validated by comparison with a reference method for detection of ammonium ion combined with an optimized breath ammonia trapping system. The nanojunction sensor is capable of in situ detection of parts per billion (ppb) levels of ammonia in human breath.

A Breath Ammonia Sensor Based on Conducting Polymer Nanojunctions

We demonstrate a heavy metal-ion sensor for drinking water analysis using a conducting polymer nanojunction array. Each nanojunction is formed by bridging a pair of nanoelectrodes separated with a small gap (<60nm) with electrodeposited peptide-modified polyanilines. The signal transduction mechanism of the sensor is based on the change in the nanojunction conductance as a result of polymer conformational changes induced by the metal-ion chelating peptide. The nanojunction sensor allows real-time detection of Cu2+ and Ni2+ at ppt range.

Chemical sensors using peptide-functionalized conducting polymer nanojunction arrays

An integrated sensor is capable of detecting analytes using electrochemical (EC), electrical (E), and optical (O) signals or EC and O signals. The sensor introduces synergetic new capabilities and enhances the sensitivity and selectivity for real-time detection of an analyte in complex matrices, including the presence of high concentration of interferences in liquids and in gas phases.

Alvaro Diaz Aguilar

Papers

A hybrid electrochemical-colorimetric sensing platform for detection of explosives.

A Hybrid Nanosensor for TNT Vapor Detection

A Breath Ammonia Sensor Based on Conducting Polymer Nanojunctions

Chemical sensors using peptide-functionalized conducting polymer nanojunction arrays

Systems and methods for integrated detection