We describe the design and use of a microfluidic fluorescence cell for nanoparticle spectroscopy. The cell allows for microfluidic control of solvent and surfactant environments to study interfacial processes of nanoscale systems. We present a spectroscopic investigation on the effect of surfactant type and concentrations on the first subband exciton transition of (6,5) single-wall carbon nanotubes (SWNTs). SWNT fluorescence here serves as a surface-sensitive probe of changes at the surfactant−nanotube interface. The experiments show that a displacement of H 2 O or of adsorbed DNA by sodium cholate from solution leads to a pronounced blue-shift of exciton emission features and a roughly 5-fold increase of photoluminescence (PL) intensities. This is due to a combination of physical and chemical interactions. The major contribution to changes in PL quantum yield and exciton peak position can be attributed to changes in dielectric screening and its effect on exciton oscillator strengths.

The interaction of sodium cholate (NaC) with (6,5) single-wall carbon nanotubes (SWNTs) is investigated using photoluminescence spectroscopy. Dilution of SWNT-NaC suspensions is accompanied by changes in the exciton PL quantum yield and peak emission energy. An abrupt change of the exciton emission peak energy at NaC concentrations between 10 and 14 mM indicates strongly cooperative formation of a micellar phase on (6,5) SWNT surfaces with a Hill coefficient of nH = 65 ± 6. This is in contrast to the formation of free NaC micelles with aggregation numbers of only about 4 and suggests that the cooperativity of NaC micelle formation on nanotube surfaces is strongly substrate-enhanced. The temperature dependence of this previously unobserved transition is used for a determination of ΔmicG(⊖)/(1 + β) = -(11.4 ± 0.2) kJ·mol(-1) which, for typical Na(+) counterion binding with β ≈ 0.2, yields a free SWNT-NaC micellization enthalpy ΔmicG(⊖) of -13.7 kJ·mol(-1).