Optics and Imaging

Faculty currently associated with this research theme.

Optics and Imaging in the University of Michigan Chemistry department spans traditional sub-disciplines, featuring research in Physical Chemistry, Analytical Chemistry, and Biochemistry. A few examples of our work in Optics and Imaging include:

Walter Lab +

Super-Resolution Imaging Detects Chemical Reactions on Single DNA Nano-Pegboards.

Impact: Folding DNA as an origami into any desired shape has laid the foundation for a multitude of nanoscale devices that permit control over dynamic chemical or optoelectronic processes. Many of these devices are chemically heterogeneous and labile, with components that are often too closely spaced, small, flexible, or fragile to be monitored by techniques such as atomic force microscopy (AFM). Fluorescence super-resolution microscopy (“nanoscopy”) combines high spatial resolution and tunable chemical specificity with relatively low invasiveness, and therefore holds promise for the spatiotemporal imaging and quality control of a wide variety of functional nanomaterials such as DNA pegboards.

Objective: To perform quality control on individual soft nanodevices that interact with and position reagents in solution.

Approach: We employ two-color PAINT (points accumulation for imaging in nanoscale topography) to follow enzyme-catalyzed chemical reactions on individual origami, and to show that single nano-pegboards exhibit stable, spatially heterogeneous probe-binding patterns, or “fingerprints”.

 

Biteen Lab +

New Methods for Single-Molecule Imaging in Nano-Environments and Live Cells.

The Biteen Group is developing new techniques for imaging single fluorescent molecules with nanometer-scale resolution with applications ranging from biomolecules in live bacteria cells to the nanofluidic devices. Figure A – Single-Molecule Micelle-Assisted Blink (MAB) Microscopy allows super-resolution imaging in constrained geometries inaccessible by conventional super-resolution microscopy. The method, based on micelles and thiol-related photoswitching, is used to measure reversibly size-adjustable PDMS nanochannels in situ. A constant delivery of thiol is required to restore emission in reversibly non-fluorescent dye molecules, and transport of such reagents in the nanofluidic channels is permitted by SDS micelles. We use MAB microscopy to probe with better than 40-nm accuracy the nano-environment and reveal biologically relevant information about the sizes of the nanochannels. Figure B - The diffusion of individual Nile red molecules in three different crystalline microporous coordination polymers (MCPs) is visualized with single-molecule fluorescence microscopy. By localizing molecules with high spatial resolution, the trajectories of the diffusing dyes are reconstructed with nanometer-scale precision. A detailed analysis of these tracks reveals different dynamics and guest−host interactions in each crystal as well as distinct motion types within the same system, suggesting the presence of structural heterogeneities in local environments.

Link to Biteen Lab

Zellers Lab +

Enhanced Optical Detection of Volatile Organic Compounds.

Optical detection of volatile organic compounds (VOC) can be greatly enhanced through the use of high quality whispering-gallery-mode (WGM) resonators. Sensors made from optical resonators, as a class, operate by probing sorptive interfacial films for changes in the effective refractive index caused by reversible vapor interaction. This project concerns the fabrication and testing of the first microfabricated optofluidic ring resonator (µOFRR), which integrates microfluidic and sensing functions in a single structure for on-chip detection of VOCs. The device is a cylindrical SiO­­x tube grown, and subsequently released, from a Si frame, with a spherical expansion section to provide lateral confinement of optical modes. Devices with 50-200 µm diameters and ~2 µm wall thicknesses have been fabricated and characterized as optical resonators. In experiments, light from a coherent source was coupled into the walls of the structure evanescently; monitoring output intensity while varying wavelength produced a series of characteristic “peaks” with quality factors exceeding 104. Recently we have fabricated 250 µm diameter µOFRRs with on-chip fluidics and capillary interconnects, and structures for permanent anchoring of aligned fiber optic waveguides. This new design will facilitate use of these resonators as vapor sensors for micro gas chromatographic analysis systems, and will allow for several devices to be integrated into arrays for multi-vapor discrimination. Multi-wavelength probing of µOFRRs with plasmonic nanoparticle interface materials is also being explored as a means of enhancing the selectivity of responses among different VOCs.

Link to Zellers Lab