(535b) Detection of Single Molecule H2O2 Signaling From Epidermal Growth Factor Receptor (EGFR) On A431 Cells Using Fluorescent Single Walled Carbon Nanotubes

An array of fluorescent, semiconducting single walled carbon nanotubes can image the incident flux of single hydrogen peroxide (H2O2) molecules that stochastically absorb and quench the emission, even from the surface of living A431 cells. When embedded in a type I collagen matrix, the array detects reversible absorption and is highly selective towards H2O2 over nitric oxide (NO), protons (H+), (NO2-), and (NO3-). Such arrays can distinguish between molecules originating near an interface, and those with no memory of origination (background). The arrays are used to measure the activity of human epidermal growth factor receptor (EGFR) on living human skin cancer cells. EGFR is known to produce a trace H2O2 flux in response to substrate binding. The SWNT arrays can measure, for the first time, the receptor generation of H2O2 after EGF stimulation and we report the dynamic response over a period of 30 min after exposure to EGF. Inhibition experiments suggest a mechanism whereby water oxidizes singlet oxygen at a catalytic site on the receptor itself, generating H2O2 in response to receptor binding.