Label-free imaging of cells and their extracellular matrix by SPR imaging

Cellular remodeling of their neighboring environment, extracellular matrix (ECM), is an important biological process from development biology, to wound healing, to diseases and cancers – this is a challenging process to measure and quantify.

Surface plasmon resonance imaging (SPRI) has been developed as a quantitative, label-free microscopy to image real time observation of live cell engagement with the surface, and protein deposition and remodeling. The SPRI technique is an alternative to the commonly used fluorescence microscopy for examining cell-matrix interactions. This technique removes the requirement for modified biological molecules and transfected cells.

Researchers here have improved upon the spatial resolution of SPRI enabling the ability to visualize subcellular structures near the sensor surface.   Along with quantitative interpretation of the images, essentially refractive index measurements, dry mass values of subcellular components can now be measured.  For example, a smooth muscle cell has been measured to have focal adhesion dry mass of 980 ng/cm²  and can deposit up to 120 ng/cm² of protein around it’s periphery under normal growth condition.   

Focal adhesion mass measurement

 

Cell secreted material measurement

 

Accomplishments have been:

1. Measurement of ECM, protein deposition, and cell phenotype with SPRI.
   • Surface plasmon resonance imaging of cells and surface-associated fibronectin
2. Quantification of cell areas, dynamic changes in cell-substrate, and changes in surface protein density over time.
   • Using surface plasmon resonance imaging to probe dynamic interactions between cells and extracellular matrix
3. Improvement of spatial resolution to visualize subcellular components
   • High Resolution Surface Plasmon Resonance Imaging for Single Cells
4. Quantitative mass measurements of focal adhesions in single cells

   • Mass Measurements of Focal Adhesions in Single Cells Using High Resolution Surface Plasmon Resonance Microscopy

5. Calibration and correction strategy for quantitative analysis by optical modeling
   • Surface plasmon resonance microscopy: achieving a quantitative optical response

Research here is underway to develop SPRI as an imaging biosensor that can visualize dry mass changes down to a single bacterium that is part of a bacterial biofilm.  Measuring antibiotic drug response at an individual cell level in addition to the biofilm as a whole can provide insight and understanding of how biofilms contribute to antibiotic drug resistance. 

NIST has submitted a patent for this technology and is looking for collaborations with industry to commercialize this measurement technique.