Here we present the design, fabrication and operation of a microfluidic device to trap droplets in a large array of droplet pairs in a controlled manner with the aim of studying the transport of small molecules across the resultant surfactant bilayers formed between the droplet pairs.

PDMS films of 10 μm thickness can be patterned within 30 min by combining dry etching to achieve substantially vertical sidewalls with wet etching to achieve high etch rates and to protect the underlying substrate from attack. Dry etching alone would have taken 5 h, and wet etching alone would produce severe undercutting. In addition, using either technique alone produces undesirable surface morphologies. The mask used during etching is critical to a successful patterning outcome. E-beam evaporated Al was found to work well, adhering strongly to oxygen-plasma-treated PDMS and holding up well during both dry and wet etching. To prevent wrinkling of the PDMS, a fast deposition rate should be used.

A microfluidic device capable of exploiting the permeability of small molecules through polydimethylsiloxane (PDMS) has been fabricated in order to control the contents of microdroplets stored in storage wells. We demonstrate that protein precipitation and crystallization can be triggered by delivery of ethanol from a reservoir channel, thus controlling the protein solubility in microdroplets. Likewise quorum sensing in bacteria was triggered by delivery of the auto-inducer N-(3-oxododecanoyl)-l-homoserine lactone (OdDHL) through the PDMS membrane of the device.

A variety of substituted aryl amines were transformed into aryl azides using t-BuONO and moist NaN 3 in t-BuOH in good to excellent yields. Smooth transformation was observed with anilines, having electron withdrawing and donating groups. Both acid-and base-sensitive groups survived the reaction conditions. Azides are versatile intermediates in organic synthesis. 1 A major application of this class of compounds is 1,3-dipolar cycloaddition with an unsaturated reactant to give a variety of five-membered heterocycles. 2 While numerous methods are available for the preparation of aliphatic azides, there is a limited choice for aryl azides. The most straightforward route for the preparation of aryl azides involves diazotization of amines with nitrous acid followed by addition of sodium azide at low temperature. 3 Alternatively, aryl amines have been transformed into aryl azides by treating the former with para-toluenesulfonyl azide in the presence of a Grignard reagent or strong base. 4 Aryl azides have also been prepared from arylmagnesium halides or aryl lithium reagents, generated from aryl halides, and para-toluenesulfonyl azide. 5 The above conversion has also been accomplished under mild condition using a combination of triflyl azide, CuSO 4, and triethylamine. 6 Very recently, the coupling of aromatic and vinyl halides with sodium azide under catalysis with CuI-L-proline was reported to produce aryl/vinyl azides in good to excellent yields. 7 However, all these transformations require either acidic or basic conditions, which are not compatible with many functional groups present in a substrate. This has prompted us to report our results for the same transformation.During the course of our ongoing investigations, we needed a process for the preparation of aryl azides from aryl amines, having acid-and base-sensitive groups. This led us to investigate neutral conditions for the preparation of aryl azides. Here we describe our successful efforts towards this endeavor. Scheme 2Deamination of aryl amines with alkyl nitrite is being carried out in our laboratories as a routine work (Scheme 1). We reasoned that in the presence of a strong nucleophile such as azide, a deamination reaction could be diverted to azide formation (Scheme 2), since aryl amines do undergo diazotization with alkyl nitrite. 8 Scheme 3We chose compound 1 as a model substrate to optimize the reaction conditions for the transformation to azide 2 (Scheme 3). Initially, the reaction was carried out in DMF in the presence of excess t-BuONO 9 (10 equiv) and NaN 3 (5 equiv) at 80°C leading to decomposition of the amine. Although azide formation was observed at room temperature, the reaction was not complete even after 24 hours. Subsequently, reactions were carried out in other solvents such as toluene, chloroform and t-BuOH. Reactions in toluene and chloroform were found to be very slow because of the poor solubility of NaN 3 in these solvents. Addition of a phase transfer catalyst, benzyltriethylammonium bromide, produced a mixture of products. On the...

In this paper, we investigated the intra-species bacterial quorum sensing at the single cell level using a double droplet trapping system. Escherichia coli transformed to express the quorum sensing receptor protein, LasR, were encapsulated in microdroplets that were positioned adjacent to microdroplets containing the autoinducer, N-(3-oxododecanoyl)- l-homoserine lactone (OdDHL). Functional activation of the LasR protein by diffusion of the OdDHL across the droplet interface was measured by monitoring the expression of green fluorescent protein (GFP) from a LasR-dependent promoter. A threshold concentration of OdDHL was found to induce production of quorum-sensing associated GFP by E. coli. Additionally, we demonstrated that LasR-dependent activation of GFP expression was also initiated when the adjacent droplets contained single E. coli transformed with the OdDHL synthase gene, LasI, representing a simple quorum sensing circuit between two droplets.