1. Elucidation of structure and dynamics of biological systems using nano-Raman and nano-IR

Amyloid oligomers and viruses are structurally heterogeneous species that are either cause or directly linked to numerous diseases such as Alzheimer’s and Parkinson’s disease, AIDS, rabies and influenza. Amyloid oligomers are intrinsically unstable protein species that exhibit high structural heterogeneity and present only at low sub-nanomolar concentrations. Similar structural heterogeneity has been observed for viruses. Self-assembly of these protein-nucleic acid systems often occurs with multiple miss-assembly steps resulting in the formation of aberrant structures. Alternatively, several structurally different forms of the same virus can be simultaneously formed. Such structurally different viral forms have different virulence. In our laboratory, we elucidate structure and dynamics of viruses and amyloid oligomers using two modern optical nanoscopy techniques: Atomic Force Microscope Infrared (AFM-IR) and Tip-Enhanced Raman Spectroscopy (TERS). Our goal is to reveal the relationship between structure and toxicity or virulence of these pathogenic species.

• Zhou, L., Kurouski, D. (2020) Structural Characterization of Individual α-Synuclein Oligomers Formed at Different Stages of Protein Aggregation by Atomic Force Microscope Infrared Spectroscopy. Anal. Chem., accepted.
  
• Rizevsky, S., Kurouski, D. (2019) Nanoscale Structural Organization of Insulin Fibril Polymorphs Revealed By Atomic Force Microscope Infrared Spectroscopy (AFM-IR). ChemBioChem, 20, 1-6.
  
• Farber, C., Wang, R., Chemelewski, R., Mullet, J., Kurouski, D. (2019) Nanoscale Structural Organization of Plant Epicuticular Wax Probed by Atomic Force Microscope Infrared Spectroscopy Anal. Chem., 91, 2472–2479.  

2. Digital farming: diagnostics of biotic and abiotic stresses on plants; non-invasive plant phenotyping

As the human population grows from its current size of 7 billion to the projected 9.7 billion in 2050, we will need to produce ~70% more food. These demands can be met by continuous improvement of crop productivity and minimization of losses associated with biotic and abiotic stresses. However, all currently available technologies for detection of plant disease, drought or nutrient deficiencies are either inefficient or too expensive for farmers and plant breeders. To overcome this problem, we propose to develop the use of Raman spectroscopy (RS) for confirmatory and non-invasive diagnostics of biotic and abiotic stresses on plants. Using RS, we aim to achieve rapid, label-free, non-invasive and quantitative diagnostics of viral, bacterial and fungal diseases on a large variety of plant species. We also develop RS for pre-symptomatic diagnostics of abiotic stresses, including drought and nutrient deficiencies caused by a lack of nitrogen (N), phosphorus (P) and potassium (K) elements. Lastly, we explore the potential of RS for non-invasive plant phenotyping. Our ultimate goal is to make this Raman-based diagnostic approach broadly available for farmers and plant breeders in the U.S and abroad.

• Farber, C., Mahnke, M., Sanchez, L., Kurouski, D. (2019) Advanced Spectroscopic Techniques for Plant Disease Diagnostics. A Review. Trends Analyt. Chem., 118, 43-49.
• Farber, C., Sanchez, L., Rizevsky, S., Ermolenkov, A., McCutchen, B., Cason, J., Simpson, C., Burow, M., Kurouski, D. (2020) Raman Spectroscopy Enables Non-Invasive Identification of Peanut Genotypes and Value-Added Traits. Nature Sci. Rep., 10, 7730.

3. Forensic Analysis of Artificial Hair Dyes

Hair is one of the most common types of physical evidence found at a crime scene. Forensic examination can suggest connections between a suspect and a crime scene or victim, or demonstrate an absence of such associations. Therefore, forensic analysis of hair evidence is invaluable to criminal investigations. Current hair forensic examinations are primarily based on a subjective microscopic comparison of hair found at the crime scene with a sample of suspect’s hair. Since this is often inconclusive, development of alternative and more accurate hair analysis techniques is critical. We develop surface-enhanced Raman spectroscopy (SERS) for confirmatory identification of dyes on hair. Using SERS, we can (1) identify whether hair was artificially dyed or not, (2) determine if permanent or semi-permanent colorants were used, and (3) distinguish the commercial brands that are utilized to dye hair. Expanding upon these results, we continue developing SERS-based dye diagnostics that can be used to solve many important problems in criminalistics and cosmetics.

• Esparza, I., Wang, R., Kurouski, D. (2019) Surface-Enhanced Raman Analysis of Underlaying Colorants On Re-Dyed Hair. Anal. Chem., 91, 7313-7318.

4. Plasmonic Catalysis at the Nanoscale

Plasmonic catalysis is a new emerging direction in organic synthesis. It is based on a unique property of noble metal nanostructures to harvest electromagnetic radiation converting it into hot carriers. These high energy species can catalyze chemical reactions in molecules located in the vicinity to surfaces of the plasmonic nanostructures. Traditional plasmonic metals such as gold (Au) and silver (Ag) are useful only for a limited number of chemical reactions. Common catalytic metals such as palladium (Pd) or platinum (Pt) provide a much broader spectrum of chemical transformations. However, these catalytic metals are not efficient in harvesting electromagnetic radiation. The new paradigm of solid-state catalysis is that coupling of plasmonic and catalytic metals can be used to achieve much higher catalytic efficiency relative to their counterparts. Also, chemical reactions on such bimetallic nanostructures are light-driven, which essentially enables ‘green catalysis’ in organic synthesis. Catalytic efficiency of bimetallic platforms directly depends on their nanoscale structure, which remains poorly understood. Using TERS, we investigate nanoscale catalytic properties of such bimetallic nanostructures. Our goal is to investigate the relationship between nanoscale structural organization of bimetallic nanostructures and their catalytic activity.

• Li, Z., Kurouski, D. (2020) Elucidation of Photo-Catalytic Properties of Goldplatinum Bimetallic Nanoplates Using Tip-Enhanced Raman. J. Phys. Chem C., accepted.  
  
• Wang, R., He, Z., Sokolov, A., Kurouski, D. (2020) Gap-Mode Tip-Enhanced Raman Scattering on Au Nanoplates of Varied Thickness. J. Phys. Chem. Lett., 11, 3815−3820 .  
  
• Wang, R. and Kurouski, D. (2019) Thermal Reshaping of Gold Microplates: Three Possible Routes and Their Transformation Mechanisms. ACS Materials & Interfaces, 11, 41813-41820.