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Flat-field fluorescence microscopy

Toward quantitative fluorescence imaging with homogeneous illumination (epi/HILO/TIRF)

Khaw & Croop et al., Opt. Express (2018)

HIST microscopy

A thinner illumination with larger FOV allows 3D single-molecule imaging with high contrast.

Tang & Han, Optica, in press (2018)

Multifunctional fiber-based high-resolution imaging

Collaboration with Rodrigo Amezcua Correa (coming soon).

High-speed and minimally photo-damaging STED microscopy using nanolaser arrays.

The nanolaser array may bring several desirable features to STED microscopy: (i) small individual laser size, (ii) addressability to each laser with high speed, (iii) controllable power, (iv) co-aligned excitation and donut-shaped STED beams, (v) extremely compact lighting system, and (vi) very low cost.

Single-molecule pull-down assay on endogenous proteins

Traditional biochemical assays usually require large amount of samples. However, SiMPull enables to (i) directly count immunoprecipitated proteins from crude cell lysates with single-molecule sensitivity, and (ii) determine an stoichiometry of macromolecular complexes using photobleaching analysis. We are studying important biomarkers of neurodegenerative diseases using human brain samples from Parkinson's and Altzheimer's diseases patients.

Je & Croop et al., Anal. Chem. 89, 13044-13048 (2017)

Two-photon excitation microscopy using semiconductor laser.

Collaboration with Peter Delfyett (coming soon).

Prior to CREOL

Fluorescence Nanoscopy   
[See also Nobel Prize in Chemistry 2014]

With a conventional objective lens and visible light, the maximum resolution of optical microscopy is fundamentally limited by diffraction, about 200 nm. Stimulated emission depletion (STED) microscopy is one of the most powerful approaches that overcome the diffraction barrier. In STED microscopy, an excitation beam is overlapped with a doughnut-shaped depletion beam where the STED light turns off fluorescence of molecules in the periphery region via stimulated emission depletion; as a result, it produces sub-diffraction sized focal spot. As the intensity of STED light increases, the effective spot size can shrink down below 10 nm. To overcome current fluorescence nanoscopy, we aim to develop 1) high-speed 3D nanoscope with low photo-damage, and 2) wide field-of view nanoscope with high throughput imaging for biomedical applications.

Nature Photonics 3,144-147 (2009); Nano Lett. 9, 3323-3329 (2009)

Nano Lett. 10, 3199-3203 (2010); Nature Methods 8, 571-573 (2011)

Opt. Lett. 40, 2653-2656 (2015); Sci. Reports 5, 17804 (2015)

Fluorescent Probes

Nitrogen-vacancy (NV) center: NV center is a defect made of nitrogen and adjacent vacancy in diamond. It has several unique optical properties: 1) its ground state is triplet; 2) it neither shows photo-blinking nor photo-bleaching; 3) it is possible to readout spin state using fluorescence intensity. These advantages have allowed NV center to be used in quantum computation, nanoscale magnetometry and bioimaging.

Spinach RNA mimic of green fluorescent protein (GFP): RNA plays essential roles in biology; it transmits genetic information from DNA to proteins and also controls gene expression in various ways. Particularly, its location and copy number strongly affect the development of organisms. However, visualizing RNA in living cells has been challenging due to the lack of genetically modifiable fluorophores like GFP. We use RNA aptamer system (called Spinach) that can specifically bind to a small (non-fluorescent) molecule, eliciting bright fluorescence, in order to study gene expression of mRNA and non-coding RNA in bacteria and mammalian cells.

J. Am. Chem. Soc. 135, 19033-19038 (2013); Sci. Reports 5, 17295 (2015)

Nucleic Acids Res. 45, 4081-4093 (2017)

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