The Chemical Measurement and Imaging program (CMI) of the Division of Chemistry supports Professor Richard P. Van Duyne and his group at Northwestern University to develop new instrumentation and concepts for fast, parallel biosensing. The long-term aim is to enable many new experiments such as (1) real-time 3D nanoparticle tracking in low viscosity media to study nanoparticle growth dynamics; (2) extending the biosensor sensitivity to the single molecule limit; (3) developing multiplexed biosensors utilizing single nanoparticles; (4) measuring the internal fluctuational dynamics of nanoparticle assemblies constructed with molecular linkers; and (5) intracellular biosensing. The instrumentation developed will lead to fundamentally new understanding of the chemistry of single molecules (or small clusters) adsorbed onto single nanoparticles.
This research has potential for broad impact on: (1) nanoscale science & technology in general and plasmonics in particular; (2) the education of graduate students, postdoctoral scholars, undergraduates, and secondary school teachers; (3) the training of women and minority scientists for careers in industry and academia; and (4) the dissemination of information about nanoscale science & technology to broad audiences. Substantial scientific and societal impact will derive from applications such as new plasmonic sensors for in vivo glucose monitoring, clinical diagnostics for Alzheimer?s disease, chemical/biological warfare agent detection, and art conservation studies. Students and postdocs working on this project will receive extensive training in mechanical and electronics construction as well as instrument control programming. As a consequence they will have the tool set needed to become independent and innovative research leaders in chemical measurement science.
Single nanoparticle tracking has emerged as an important tool in studying fundamental cellular behavior, disease diagnostics, and understanding protein binding. However, these systems often contain a narrow field of view with few particles and operate on a limiting time scale. A previously developed wide-field imaging setup successfully tracked nanoparticles and their localized surface plasmon resonance spectrum (LSPR), however at slower tracking speeds and required a highly viscous media. In order to overcome these limitations, a newly developed super resolution microscope setup equipped with an electron multiplying CCD camera and an acousto-optic tunable filter (AOTF) demonstrated 33 millisecond time resolution, 6.7 nm spatial resolution, and 1 nm spectral resolution. Through the funding of this project from NSF, an improved wide-field imaging apparatus was constructed for tracking plasmonic nanoparticles, and provided new insight on cell membrane dynamics in real time. A second-generation wide-field imaging setup was used to track gold nanoparticles moving in a cell membrane mimetic, supported lipid bilayers, in water. Within the bilayers, a small concentration of positively charged lipids attracted the negatively charged nanoparticles, and a ganglioside lipid (GM1) corralled the particles between cluster domains on the surface. As the GM1 concentration increased, from 0% to 20%, the particles exhibited increasingly confined diffusion, and a percolation threshold was determined. At this point, a protein, as represented by the particle, becomes compartmentalized from the rest of the membrane, and this disrupts cellular function and signaling. Future applications for the wide-field setup include moving toward live cells and tracking particle diffusion in healthy and cancerous cells, and unlike fluorescent dyes or quantum dots, nanoparticles do not blink or photobleach. Additionally, the unique properties of nanoparticles enable detection of different analytes in complex media, such as blood or serum, and create a real time, multiplexed detection assay. This can be accomplished using two spectrally distinct nanoparticles, such as a prism and sphere, where the antigen-antibody pair would decrease the particle diffusion and the change in the environment from the binding pair shifts the LSPR spectrum. The large size of antibodies, in comparison to the nanoparticles, sterically hinders multiple binding sites between the two particles, and only a single antibody would bind to one antigen. The tracking of different particles shapes and sizes to their specific antigens becomes readily achievable in this binding scheme. Recent studies suggest detecting a panel of markers in blood, such as in Alzheimer’s disease, provides greater insight in disease progression and treatment effectiveness than just one. In addition, the wide-field can act as a antibody screening assay, with multiple antibodies in a single sample for one antigen to identify the best binding pair.
