Single Molecule Detection of Nitric Oxide Enabled by d(AT)15 DNA Adsorbed to Near Infrared Fluorescent Single-Walled Carbon Nanotubes

We report the selective detection of single nitric oxide (NO) mols. using a specific DNA sequence of d(AT)15 oligonucleotides, adsorbed to an array of near-IR fluorescent semiconducting single-walled carbon nanotubes (AT15-SWNT). While SWNT suspended with eight other variant DNA sequences show fluorescence quenching or enhancement from analytes such as dopamine, NADH, L-ascorbic acid, and riboflavin, d(AT)15 imparts SWNT with a distinct selectivity toward NO. In contrast, the electrostatically neutral polyvinyl alc. enables no response to nitric oxide, but exhibits fluorescent enhancement to other mols. in the tested library. For AT15-SWNT, a stepwise fluorescence decrease is obsd. when the nanotubes are exposed to NO, reporting the dynamics of single-mol. NO adsorption via SWNT exciton quenching. We describe these quenching traces using a birth-and-death Markov model, and the max. likelihood estimator of adsorption and desorption rates of NO is derived. Applying the method to simulated traces indicates that the resulting error in the estd. rate consts. is less than 5% under our exptl. conditions, allowing for calibration using a series of NO concns. As expected, the adsorption rate is found to be linearly proportional to NO concn., and the intrinsic single-site NO adsorption rate const. is 0.001 s-1 μM NO-1. The ability to detect nitric oxide quant. at the single-mol. level may find applications in new cellular assays for the study of nitric oxide carcinogenesis and chem. signaling, as well as medical diagnostics for inflammation. [on SciFinder(R)]