Cesium ion-guided detection of trichloroethylene in air.

Whereas the close associations of cesium ion with organochlorine compounds have been previously documented, the present report is the first attempt to exploit these interactions to create a trichloroethylene (TCE)-selective sensor. Gold monolayer-protected clusters peripherally functionalized with Cs+ ions were used to prepare a chemiresistance film on MEMS-fabricated interdigitated electrodes. Vapor sensing properties of the cesium-rich chemiresistor were determined using a panel of chlorinated hydrocarbons including TCE as well as polar and non-polar VOCs for comparison. The sensor was selective and highly sensitive toward VOCs containing a 1,2-dichloro group at concentrations as low as 0.1 ppm. The results suggest the key interaction contributing to sensor response is a bidentate, metallocycle-like coordination of the 1,2-dichloro group to the cesium cations at the sensor surface.

Harnessing the cation-π interactions of metalated gold monolayer-protected clusters to detect aromatic volatile organic compounds.

The strong, non-covalent interactions between π-systems and cations have been the focus of numerous studies on biomolecule structure and catalysis. These interactions, however, have yet to be explored as a sensing mechanism for detecting trace levels of volatile organic compounds (VOCs). In this article, we provide evidence that cation-π interactions can be used to elicit sensitive and selective chemiresistor responses to aromatic VOCs. The chemiresistors are fitted with carboxylate-linked alkali metals bound to the surface of gold monolayer-protected clusters formulated on microfabricated interdigitated electrodes. Sensor responses to aromatic and non-aromatic VOCs are consistent with a model for cation-π interactions arising from association of electron-rich aromatic π-systems to metal ions with the relative strength of attraction following the order K+ > Na+ > Li+. The results point toward cation-π interactions as a promising research avenue to explore for developing aromatic VOC-selective sensors.

Effect of Thiol Molecular Structure on the Sensitivity of Gold Nanoparticle-Based Chemiresistors toward Carbonyl Compounds.

Increasing both the sensitivity and selectivity of thiol-functionalized gold nanoparticle chemiresistors remains a challenging issue in the quest to develop real-time gas sensors. The effects of thiol molecular structure on such sensor properties are not well understood. This study investigates the effects of steric as well as electronic effects in a panel of substituted thiol-urea compounds on the sensing properties of thiolate monolayer-protected gold nanoparticle chemiresistors. Three series of urea-substituted thiols with different peripheral end groups were synthesized for the study and used to prepare gold nanoparticle-based chemiresistors. The responses of the prepared sensors to trace volatile analytes were significantly affected by the urea functional motifs. The largest response for sensing acetone among the three series was observed for the thiol-urea sensor featuring a tert-butyl end group. Furthermore, the ligands fitted with N, N'-dialkyl urea moieties exhibit a much larger response to carbonyl analytes than the more acidic urea series containing N-alkoxy-N'-alkyl urea and N, N'-dialkoxy urea groups with the same peripheral end groups. The results show that the peripheral molecular structure of thiolate-coated gold nanoparticles plays a critical role in sensing target analytes.

Tunable Aminooxy-Functionalized Monolayer-Protected Gold Clusters for Non-Polar or Aqueous Oximation Reactions.

Aminooxy (-ONH2) groups are well known for their chemoselective reactions with carbonyl compounds, specifically aldehydes and ketones. The versatility of aminooxy chemistry has proven to be an attractive feature that continues to stimulate new applications. This work describes application of aminooxy 'click chemistry' on the surface of gold nanoparticles. We present here a trifunctional amine-containing aminooxy alkane thiol ligand for use in the functionalization of gold monolayer protected clusters (Au MPCs). Diethanolamine is readily transformed into an organic-soluble aminooxy thiol (AOT) ligand using a short synthetic path. The synthesized AOT ligand was coated on ≤ 2 nm diameter hexanethiolate (C6S)-capped Au MPCs using a ligand exchange protocol to afford organic-soluble AOT/C6S (1:1 ratio) Au mixed monolayer protected clusters (MMPCs). This work describes the synthesis of Au(C6S)(AOT) MMPCs and representative oximation reactions with various types of aldehyde-containing molecules, highlighting the ease and versatility of the chemistry and how amine protonation can be used to switch solubility characteristics.