The familiar saying "every journey begins with a single step" has a special meaning in the human body: many large-scale changes are triggered by a few "early responder" cells. Examples include allergic reactions, wound healing, and cancerous transformations. Even when many "identical" cells are exposed to the same conditions in a laboratory, some respond faster; such differences are clues to understanding how an entire process unfolds, and perhaps how medicine can influence it. Unfortunately, most methods of measuring cellular responses have one of the following limitations: (a) they only calculate averages over many cells, (b) they measure each cell only once, or (c) they inject chemicals that alter the cells' function. In this project, a new microscope system will be built without these limitations. Using only low levels of light, many individual cells will be monitored for extended periods of time, producing chemical and structural "histories" of the cells as they respond to stimuli. This measurement technique will be useful for identifying early-responding cells and understanding how they lead to large-scale behavior in the human body. In a particular case of interest, a cellular transformation called "platelet degranulation" will be studied because it is associated with increased levels of neurological illness in HIV-positive individuals.
This project applies a new biophotonic measurement technique, holographic angular-domain elastic scattering (HADES), to studies of single cells responding to stimuli. Angular scattering is highly sensitive to the average size of organelles, and therefore to changes in cellular contents. Holography will enable first-principles analysis of single cells? angular scattering for the first time. The HADES technique will be combined in a microscope with Raman spectroscopy, a complementary technique that provides chemical specificity. This instrument will acquire morphological and chemical "histories" of single cells as they undergo changes, for example (a) endothelial cells receiving damage to their mitochondrial membranes, (b) immune cells being stimulated, and (b) platelet cells undergoing degranulation, a process of interest to research on HIV-associated neurocognitive disorder (HAND). Such reactions can vary greatly from one cell to the next, and these differences can be important parameters to study. Yet many analytical methods do not provide single-cell data, and many that do so require exogenous labels that alter the very process being studied. There is therefore a need for non-labeling, non-destructive methods that can obtain detailed information repeatedly from single cells, without affecting cellular function or viability. The HADES microscopy platform will provide rich information for characterizing cellular transformations and their variability on a cell-by-cell basis.
This award is being made jointly by two Programs- (1) Instrument Development for Biological Research, in the Division of Biological Infrastructure (Biological Sciences Directorate), and (2) Biophotonics, in the Division of Chemical, Bioengineering, Environmental and Transport Systems (Engineering Directorate).
