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The development of a simple and on-site assay for the detection of organophosphorus pesticed residues is very important for food safety and exosystem protection. This paper reports the surface coordination-originated fluorescence resonance energy transfer (FRET) of CdTe quantum dots (QDs) and a simple ligand-replacement turn-on mechanism for the highly sensitive and selective detection of organophosphorothioate pesticides. It has been demonstrated that coordination of dithizone at the surface of CdTe QDs in basic media can strongly quench the green emission of CdTe QDs by a FRET mechanism. Upon the addition of organophosphorothioate pesticides, the dithizone ligands at the CdTe QD surface are replaced by the hydrolyzate of the organophosphorothioate, and hence the fluorescence is turned on. The fluorescence turn on is immediate, and the limit of detection for chlorpyrifos is as low as ~0.1 nM. Two consecutive linear ranges allow a wide determination of chlorpyrifos concentrations from 0.1 nM to 10 [micro]M. Importantly, the fluorescence turn-on chemosensor can directly detect chlorpyrifos residues in apples at a limit of 5.5 ppb, which is under the maximum residue limit allowed by the U.S. Environmental Protection Agency. The very simple strategy reported here should facilitate the development of fluorescence turn-on chemesensors for chemo/biedetection. 10.1021/ac102531z

This paper reports a surface molecular self-assembly strategy for molecular imprinting in electropolymerized polyaminothiophenol (PATP) membranes at the surface of gold nanoparticles (AuNPs) modified glassy carbon (gc) electrode for the electrochemical detection of pesticide chlorpyrifos (CPF). Electropolmedzable p-aminothiophenol (ATP) was first assembled on the AuNPs at the gc electrode surface by the formation of Au--S bonds, and subsequently, the CPF template was further assembled onto the monolayer of ATP through the hydrogen-bonding interaction between amino group and CPF. A conductive hybrid membrane was fabricated at the assembled gc electrode by the electropolymerization in a mixing solution containing additional ATP and CPF templates, and meanwhile, the CPF was spontaneously imprinted into the PATP/AuNP film. The amount of imprinted sites at the PATP/AuNP film was significantly increased due to the additional replenishment of CPF templates. The cyclic voltammetric response of the imprinted PATP-AuNP-gc sensor to CPF is about 3.2-fold as compared with the imprinted PATP-Au sensor, and the detection limit for CPF is about 2 orders of magnitude lower than that by the imprinted PATP-Au sensor. An excellent electrochemical selectivity for CPF over other pesticides was also achieved. The combination of surface molecular self-ssembly with electropolymerized molecular imprinting on a larger surface area of a AuNP-medified electrode produces a high ratio of imprinted sites and, thus, provides an ultrasensitive electrochemical detection of organophosphate pesticide. 10.1021/ac901860t

This paper reports a resonance energy transfer-amplifying fluorescence quenching at the surface of silica nanoparticles for the ultrasensitive detection of 2,4,6-trinitrotoluene (TNT) in solution and vapor environments. Fluorescence dye and organic amine were covalently modified onto the surface of silica nanoparticles to form a hybrid monolayer of dye fluorophores and amine ligands. The fluorescent silica particles can specifically bind TNT species by the charge-transfer complexing interaction between electron-rich amine ligands and electron-deficient aromatic rings. The resultant TNT--amine complexes bound at the silica surface can strongly suppress the fluorescence emission of the chosen dye by the fluorescence resonance energy transfer (FRET) from dye donor to the irradiative TNT--amine acceptor through intermolecular polar--polar interactions at spatial proximity. The quenching efficiency of the hybrid nanoparticles with TNT is greatly amplified by at least 10-fold that of the corresponding pure dye. The nanoparticle-assembled arrays on silicon wafer can sensitively detect down to ~ 1 nM TNT with the use of only 10 [micro]L of solution (~2 pg TNT) and several ppb of TNT vapor in air. The simple FRET-based nanoparticle sensors reported here exhibit a high and stable fluorescence brightness, strong analyte affinity, and good assembly flexibility and can thus find many applications in the detection of ultratrace analytes.

[Mn.sup.2+]-doped ZnS nanocrystals with an amine-capping layer have been synthesized and used for the fluorescence detection of ultratrace 2,4,6-trinitrotoluene (TNT) by quenching the strong orange [Mn.sup.2+] photoluminescence. The organic amine-capped nanocrystals can bind TNT species from solution and atmosphere by the acid base pairing interaction between electron-rich amino ligands and electron-deficient aromatic rings. The resultant TNT anions bound onto the amino monolayer can efficiently quench the [Mn.sup.2+] photoluminescence through the electron transfer from the conductive band of ZnS to the lowest unoccupied molecular orbital (LUMO) of TNT anions. The amino ligands provide an amplified response to the binding events of nitroaromatic compounds by the 2- to ~5-fold increase in quenching constants. Moreover, a large difference in quenching efficiency was observed for different types of nitroaromatic analytes, dependent on the affinity of nitro analytes to the amino monolayer and their electron-acceptlng abilities. The amine-capped nanocrystals can sensitively detect down to 1 nM TNT in solution or several parts-per-billion of TNT vapor in atmosphere. The ion-doped nanocrystal sensors reported here show a remarkable air/solution stability, high quantum yield, and strong analyte affinity and, therefore, are well-suited for detecting the ultratrace TNT and distinguishing different nitro compounds.

This paper reports the molecular imprinting at the walls of highly uniform silica nanotubes for the recognition of 2,4,6-trinitrotoluene (TNT). It has been demonstrated that TNT templates were efficiently imprinted into the matrix of silica through the strong acid-base pairing interaction between TNT and 3-aminopropyltriethoxysilane (APTS). TNT-imprinted silica nanotubes were synthesized by the gelation reaction between APTS and tetraethylorthosilicate (TEOS), selectively occurring at the porous walls of APTS-modified alumina membranes. The removal of the original TNT templates leaves the imprinted cavities with covalently anchored amine groups at the cavity walls. A high density of recognition sites with molecular selectivity to the TNT analyte was created at the wall of silica nanotubes. Furthermore, most of these recognition sites are situated at the inside and outside surfaces of tubular walls and in the proximity of the two surfaces due to the ultrathin wall thickness of only 15 nm, providing a better site accessibility and lower mass-transfer resistance. Therefore, greater capacity and faster kinetics of uptaking target species were achieved. The silica nanotube reported herein is an ideal form of material for imprinting various organic or biological molecules toward applications in chemical/biological sensors and bioassay.

This paper reports the finding of an investigation of a surface molecular self-assembly strategy for molecular imprinting of polymer nanowires/nanotubes. It has been demonstrated that 2,4,6-trinitrotoluene (TNT) templates were spontaneously assembled onto aminopropyl group-modified alumina pore walls by a strong charge-transfer complexing interaction between amino groups and electron-deficient nitroaromatics, forming a novel basis of surface molecular imprinting. While an additional amount of TNT templates was further replenished into a precursor mixture, a stepwise progressive polymerization was designed toward the controllable preparation of TNT-imprinted polymer nanowire/nanotube arrays in an alumina membrane. The imprinted nanowires/nanotubes with a high density of surface-imprinted sites and regular interior sites exhibit the high capacity of binding TNT molecules, which is nearly 2.5-3.0-fold that of normal imprinted particles. Moreover, the imprinted nanotubes and nanowires have ~6- and 4-fold increase in the rate of binding TNT molecules, respectively. The combination of surface molecular assembly with nanostructures in the imprinting technique can create more effective recognition sites than the only use of porogens in traditional approaches. This novel, facile strategy reported herein can be further expected to fabricate various molecular recognition nanoarrays for sensing or analytic applications.

Inthis work, a general strategy was proposed for fine manipulatingintrinsic growth of water-soluble salts belonging to different crystalsystems. Various hollow microsphere hierarchical architectures assembledwith hopperlike single crystal blocks of cubic KBr, orthorhombic (NH4)2SO4, or hexagonal Na2SO3have been designed and prepared via microemulsions. Intrinsicgrowth manipulations of different water-soluble salts has been successfullyachieved by preventing growth of the outside surface of each singlecrystal block via a diffusion-limit effect of the interfaces betweenthe oil phase and aqueous droplets. As a result, hopperlike singlecrystals of water-soluble salts belonging to different crystal systemswere formed. Furthermore, octahedral NaCl hopperlike single crystal,rather than their typical cubic shape, has also been fabricated bymanipulating their growth rates along different lattice directionsin combination with urea as additives. The large amount of fine manipulationof intrinsic growth of water-soluble salts will provide us with adeep understanding of crystallography of inorganic salts, as wellas facilitate design and production of water-soluble salts architectureswith corresponding shapes, according to the different requirements. [ABSTRACT FROM AUTHOR]

This paper reports the finding of an investigation of a surface molecular self-assembly strategy for molecular imprinting of polymer nanowires/nanotubes. It has been demonstrated that 2,4,6-trinitrotoluene (TNT) templates were spontaneously assembled onto aminopropyl group-modified alumina pore walls by a strong charge-transfer complexing interaction between amino groups and electron-deficient nitroaromatics, forming a novel basis of surface molecular imprinting. While an additional amount of TNT templates was further replenished into a precursor mixture, a stepwise progressive polymerization was designed toward the controllable preparation of TNT-imprinted polymer nanowire/nanotube arrays in an alumina membrane. The imprinted nanowires/nanotubes with a high density of surface-imprinted sites and regular interior sites exhibit the high capacity of binding TNT molecules, which is nearly 2.5-3.0-fold that of normal imprinted particles. Moreover, the imprinted nanotubes and nanowires have ~6- and 4-fold increase in the rate of binding TNT molecules, respectively. The combination of surface molecular assembly with nanostructures in the imprinting technique can create more effective recognition sites than the only use of porogens in traditional approaches. This novel, facile strategy reported herein can be further expected to fabricate various molecular recognition nanoarrays for sensing or analytic applications. [ABSTRACT FROM AUTHOR]

In this paper, we report a simple polypeptide-directed strategy for fabricating large spherical assembly of CaCO3 nanoparticles. Stepwise growth and assembly of a large number of nanoparticles have been observed, from the formation of an amorphous liquidlike CaCO3-polypeptide precursor, to the crystallization and stabilization of polypeptide-capped nanoparticles, and eventually, the spherical assembly of nanoparticles. The "soft" poly(aspartate)-capping layer binding on a nanoparticle surface resulted in the unusual soft nature of nanoparticle assembly, providing a reservoir of primary nanoparticles with a moderate mobility, which is the basis of a new strategy for reconstructing nanoparticle assembly into complex nanoparticle architectures. Moreover, the findings of the secondary assembly of nanoparticle microspheres and the morphology transformation of nanoparticle assembly demonstrate a flexible and controllable pathway for manipulating the shapes and structures of nanoparticle assembly. In addition, the combination of the polypeptide with a double hydrophilic block copolymer (DHBC) allows it to possibly further control the shape and complexity of the nanoparticle assembly. A clear perspective is shown here that more complex nanoparticle materials could be created by using "soft" biological proteins or peptides as a mediating template at the organic−inorganic interface. [ABSTRACT FROM AUTHOR]