A Localized Surface Plasmon Resonance Imaging Instrument for Multiplexed Biosensing

Localized surface plasmon resonance (LSPR) spectroscopy has been widely used for label-free, highly sensitive measurements of interactions at a surface. LSPR imaging (LSPRi) has the full advantages of LSPR but enables high-throughput, multiplexed measurements by simultaneously probing multiple individually addressable sensors on a single sample surface. Each spatially distinct sensor can be tailored to provide data regarding different surface functionalities or reaction environments. Previously, LSPRi has focused on single-particle sensing where the size scale is very small. Here, we create defined macroscale arrays of nanoparticles that are compatible with common patterning methods such as dip-pen nanolithography and multichannel microfluidic delivery devices. With this new LSPR sensing format, we report the first demonstration of multiplexed LSPR imaging and show that the increased throughput of our instrument enables the collection of a complete Langmuir binding curve on a single sensor surface. In addition, the multiplexed LSPR sensor is highly selective, as demonstrated by the hybridization of single-stranded DNA to complementary sequences immobilized on the sensor surface. The LSPR arrays described in this work exhibit uniform sensitivity and tailorable optical properties, making them an ideal platform for high-throughput, label-free analysis of a variety of molecular binding interactions

Single Plasmonic Nanoparticle Tracking Studies of Solid Supported Bilayers with Ganglioside Lipids

Single-particle tracking experiments were carried out with gold nanoparticle-labeled solid supported lipid bilayers (SLBs) containing increasing concentrations of ganglioside (GM₁). The negatively charged nanoparticles electrostatically associate with a small percentage of positively charged lipids (ethyl phosphatidylcholine) in the bilayers. The samples containing no GM₁ show random diffusion in 92% of the particles examined with a diffusion constant of 4.3(±4.5) × 10^–9 cm²/s. In contrast, samples containing 14% GM₁ showed a mixture of particles displaying both random and confined diffusion, with the majority of particles, 62%, showing confined diffusion. Control experiments support the notion that the nanoparticles are not associating with the GM₁ moieties but instead most likely confined to regions in between the GM₁ clusters. Analysis of the root-mean-squared displacement plots for all of the data reveals decreasing trends in the confined diffusion constant and diameter of the confining region versus increasing GM₁ concentration. In addition, a linearly decreasing trend is observed for the percentage of randomly diffusing particles versus GM₁ concentration, which offers a simple, direct way to measure the percolation threshold for this system, which has not previously been measured. The percolation threshold is found to be 22% GM₁ and the confining diameter at the percolation threshold only ∼50 nm