Monitoring plasmon coupling and SERS enhancement through in situ nanoparticle spacing modulation.

Self-assembled nanoparticle (NP) arrays at liquid interfaces provide a unique optical response which has opened the door to new tuneable metamaterials for sensing and optical applications. NPs can spontaneously assemble at a liquid-liquid interface, forming an ordered, self-healing, low-defect 2D film. The close proximity of the NPs at the interface results in collective plasmonic modes with a spectral response dependent on the distance between the NPs and induces large field enhancements within the gaps. In this study, we assembled spherical and rod-shaped gold NPs with the aim of improving our understanding of NP assembly processes at liquid interfaces, working towards finely controlling their structure and producing tailored optical and enhanced Raman signals. We systematically tuned the assembly and spacing between NPs through increasing or decreasing the degree of electrostatic screening with the addition of electrolyte or pH adjustment. The in situ modulation of the nanoparticle position on the same sample allowed us to monitor plasmon coupling and the resulting SERS enhancement processes in real time, with sub-nm precision.

A microfluidic approach for high-throughput droplet interface bilayer (DIB) formation.

We present a simple, automated method for high-throughput formation of droplet interface bilayers (DIBs) in a microfluidic device. We can form complex DIB networks that are able to fill predefined three dimensional architectures. Moreover, we demonstrate the flexibility of the system by using a variety of lipids including 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC).

Droplet-based compartmentalization of chemically separated components in two-dimensional separations.

We demonstrate that nanolitre-sized droplets are an effective tool in coupling two-dimensional separations in both time and space. Using a microfluidic droplet connector, chemically separated components can be segmented into nanolitre droplets. After oil filtering and droplet merging, these droplets are loaded into a second dimension for comprehensive separations.

Quantitative detection of protein expression in single cells using droplet microfluidics.

We demonstrate that single cells can be controllably compartmentalized within aqueous microdroplets; using such an approach we perform high-throughput screening by detecting the expression of a fluorescent protein in individual cells with simultaneous measurement of droplet size and cell occupancy.

Velocity measurement of particulate flow in microfluidic channels using single point confocal fluorescence detection.

This article presents a non-invasive, optical technique for measuring particulate flow within microfluidic channels. Confocal fluorescence detection is used to probe single fluorescently labeled microspheres (0.93 microm diameter) passing through a focused laser beam at a variety of flow rates (50 nL min(-1)-8 microL min(-1)). Simple statistical methods are subsequently used to investigate the resulting fluorescence bursts and generate velocity data for the flowing particles. Fluid manipulation is achieved by hydrodynamically pumping fluid through microchannels (150 microm wide and 50 microm deep) structured in a polydimethylsiloxane (PDMS) substrate. The mean fluorescence burst frequency is shown to be directly proportional to flow speed. Furthermore, the Poisson recurrence time and width of recovered autocorrelation curves is demonstrated to be inversely proportional to flow speed. The component-based confocal fluorescence detection system is simple and can be applied to a diversity of planar chip systems. In addition, velocity measurement only involves interrogation of the fluidic system at a single point along the flow stream, as opposed to more normal multiple-point measurements.