Stochastic Analysis of Stepwise Fluorescence Quenching Reactions on Single-Walled Carbon Nanotubes: Single Molecule Sensors

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Year: 2008
Type of Publication: Article
  • Hong Jin, Jong-Ho Kim Daniel A. Heller
Journal: Nano Letters Volume: 8
Number: 12 Pages: 4299-4304
Month: DEC 2008
PT: J; TC: 30; UT: WOS:000261630700038
The ID quantum confinement of photogenerated excitons in single-walled carbon nanotubes (SWNT) can amplify the detection of molecular adsorption to where single-molecule discrimination is realizable, even from within living cells and tissues. Toward this aim, we present a type I collagen film, similar to those used as 3D cell scaffolds for tissue engineering, containing embedded SWNT capable of reporting single-molecule adsorption of quenching molecules. We utilize hidden Markov modeling to link single-molecule adsorption events to rate constants for H(2)O(2), H(+), and Fe(CN)(6)(3-). Among the three kinds of reactant molecules studied, H(2)O(2) has the highest quenching equilibrium constant of 1.59 at 20 mu M, whereas H(+) is so insensitive that a similar equilibrium constant is achieved only with a concentration of 0.1 M (pH 1). The results were self-consistent because reverse (unquenching) rate constants (600 mu s(-1) for H(2)O(2), 1130 mu s(-1) for H(+) and 4000 mu s(-1) for Fe(CN)63-) were observed to be concentration-independent and the forward (quenching) rate constants varied monotonically with concentration. The quenching rate constants also increased with an increase in the redox potential of the quencher, indicating that electron transfer increases the adsorption equilibrium constant on the nanotube surface and, hence, the dwell time of the quencher. These developments provide the material, analytical, and mechanistic groundwork for SWNT to function as single-molecule stochastic biosensors.