Sensitive and long-term stable disposable biosensor for organophosphorus analysis.

Flow control-based paper devices have recently shown great potential for point-of-need analysis, since they allow for the easy operation of multi-step assays by minimizing user operation. In this work, a wax printing method was evaluated as a means to control liquid flow in 3D microfluidic paper-based analytical devices (μPADs). The resulting flow controlbased 3D μPADs were applied to determine paraoxon-ethyl as a typical organophosphate pesticide model system. The analytical procedure is as simple as applying a 200-μL sample solution, resulting in reproducible (relative standard deviation of colorimetric signals from 6 independently fabricated devices, 2.63%) colorimetric signals within 1 h of the assay time with the limit of detection (LOD) reaching 25.0 μg/L. Finally, results obtained for pesticide-spiked water samples analyzed by flow control-based 3D μPADs showed good agreement with those from a conventional HPLC analysis with UV detection.

The dimerization of alkanethiol mixtures (hexanethiol, octanethiol, and dodecanethiol) to form self‐assembled monolayers (SAMs) from headspace on nanoporous gold surfaces was studied for the first time using gas chromatography (GC/MS) and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). The nanoporous gold surfaces were obtained by an acidic etching of a 585‐gold alloy. Field emission scanning electron microscopy (FE‐SEM) was utilized to study the change of the surface geometry and porosity of the gold surfaces before and after etching. Alkanethiols were deposited from the vapor phase above the thiol solutions (headspace) on nanoporous gold plates and nanoporous gold solid‐phase vmicroextraction (SPME) fibers. The nanoporous gold substrates were analyzed by TOF‐SIMS and GC/MS, respectively. The TOF‐SIMS spectra exhibited various gold–sulfur ion clusters and specific peaks related to the adsorption of thiols such as deprotonated monomers, thiolate–Au, dimers (e.g., dialkyl sulfides–Au and dialkyl disulfides–Au). The GC/MS analysis of headspace extractions of alkanethiol mixtures by nanoporous gold SPME fibers showed a high extraction efficiency of alkanethiol, dialkyl sulfide, and dialkyl disulfide when compared with the commercial SPME fibers (DVB‐CAR‐PDMS and CAR‐PDMS). Different GC/MS optimization factors were studied including the extraction time and desorption temperature.