ECE PhD Prospectus Defense: Panagis Samolis

Title: Label Free Vibrational Infrared Photothermal Amplitude and Phase Signals (VIPPS) Microscopy for Chemical Imaging and Thermal Diffusion Characterization

Time: Apr 19, 2021 10:00 AM Eastern Time (US and Canada)

Location: Join Zoom Meeting

Meeting ID: 810 9378 1433

Passcode: P2mZ0k

Advisor: Michelle Sander (ECE, BME, MSE)

Chair: Roberto Paiella (ECE, MSE)

Committee: Jerome Mertz (BME, ECE, Physics)


The molecular fingerprint region in the mid-infrared has attracted significant interest due to the presence of characteristic vibrational resonances of many chemical compounds including proteins, lipids and nucleic acids. Mid-infrared photothermal microscopy has demonstrated unique capabilities for its ability to target characteristic absorption bands of biological interest with sub-diffraction limited resolution as well as high sensitivity and specificity. However, standard amplitude photothermal imaging can have limiting contrast from different chemical features that have overlapping absorption bands. In this work, we are developing VIPPS (Vibrational Infrared Photothermal and Phase Signals) imaging to overcome this limitation. The above technique is based on the simultaneous acquisition of both the amplitude and lock-in phase signals, which allows imaging of the sample based on both the absorption as well as thermal diffusion properties respectively. This enables high contrast from detected changes in the induced spatio-temporal temperature gradients and in the rate of heat transport even from features with overlapping absorption profiles. For proof of concept, we performed a study at which individual absorbing melamine beads were embedded in an also absorbing medium. Combining higher harmonic detection with lock-in phase analysis, beads with dimensions 8 times smaller than the diffraction limited mid-infrared spot size were identified. For a biological application, we performed VIPPS imaging on fibroblast cells grown in a collagen extracellular matrix. Due to similar absorption properties, mid-infrared imaging of protein distribution in cells at the subcellular level has previously been mostly performed on cells grown directly on the imaging windows and not in a protein rich extracellular matrix. With VIPPS we observed high contrast based on changes in the rate of heat transport near the cell plasma and nuclear membrane. To the best of our knowledge, this is the first demonstration of imaging sub-cellular features (i.e. cell nucleus) with mid-infrared photothermal microscopy of cells grown in a protein rich extracellular matrix. Overall VIPPS provides an additional contrast mechanism in label free microscopy methods and paves the way for high contrast imaging of weakly absorbing features in a strongly absorbing medium, mapping intracellular heat dynamics and high resolution imaging of biological interfaces.

When 10:00 am to 12:00 pm on Monday, April 19, 2021
Location Zoom