Inhomogeneous nanoparticle layers are often modeled as effective homogeneous layers in order to simplify optical device design. MaxwellÀGarnett (MG) theory is often used to find the effective medium properties of localized surface plasmon resonance (LSPR) sensing layers. However, MG theory is only applicable for small spherical particles with low filling fractions, thus limiting its applicability. In this paper, an extraction method is used to determine the effective medium properties of an LSPR sensing layer consisting of metal nanoparticles of arbitrary shape. Complex reflection and transmission coefficients (S parameters) are found using CST Microwave Studio (CST MWS), a commercial software package. Effective index of refraction (n eff ) and impedance (z eff ) are calculated from the simulated S parameters. This method is extended to account for substrate effects on the effective medium properties. Thus, this method allows for more accurate homogenization of LSPR sensor layers made of any nanoparticle shape, enabling improved LSPR device design.

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The proposed Magnetotactic Bacteria (MTB) based bio-carrier has the potential to greatly improve pathogenic bacteria detection time, specificity, and sensitivity. Microbeads are attached to the MTB and are modified with a coating of an antibody or phage that is specific to the target pathogenic bacteria. Using magnetic fields, the modified MTB are swept through a solution and the target bacteria present become attached to the microbeads (due to the coating). Then, the MTB are brought to the detection region and the number of pathogenic bacteria is determined. The high swimming speed and controllability of the MTB make this method ideal for the fast detection of small concentrations of specific bacteria. This paper focuses on an impedimetric detection system that will be used to identify if a target bacterium is attached to the microbead. The proposed detection system measures changes in electrical impedance as objects (MTB, microbeads, and pathogenic bacteria) pass through a set of microelectrodes embedded in a microfluidic device. FEM simulation is used to acquire the optimized parameters for the design of such a system. Specifically, factors such as electrode/detection channel geometry, object size and position, which have direct effects on the detection sensitivity for a single bacterium or microparticle, are investigated. Polymer microbeads and the MTB system with an E. coli bacterium are considered to investigate their impedance variations. Furthermore, preliminary experimental data using a microfabricated microfluidic device connected to an impedance analyzer are presented.

The localized surface plasmon resonance (LSPR) phenomenon that is characteristic of gold and silver nanoparticles has applications in areas such as portable and remote chemical and biological sensing. However, fabrication of metal nanoparticle arrays with high uniformity and repeatability, at a reasonable cost, is difficult. Nanosphere lithography (NSL) has been used to produce inexpensive nanoparticle arrays, through the use of monolayers of self-assembled microspheres as a deposition mask. However, lack of control over the location and size of the arrays, as well as poor uniformity over large areas, limits its use to research purposes. Here, we present large-area fabrication of nanoparticle arrays through both convective self-assembly NSL (CSANSL) and our new method, geometrically confined NSL (GCNSL). In GCNSL, microsphere assembly is confined to geometric patterns defined in photoresist. We show that 400nm polystyrene microspheres can be assembled inside of large arrays of photoresist trenches from 4-20µm in width and 500µm in length, with high uniformity, repeatability, and quality. Compared to CSANSL, GCNSL allows precise patterning of nanoparticle arrays for use in practical LSPR sensing devices, while still remaining inexpensive.

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