Figure 3: Fluorescence spectroscopy of the SWCNT–fibrinogen interaction.
(a) Relative fluorescent response of DPPE-PEG(5000)-SWCNT (1 mg l−1) sensor to fibrinogen fragments (20 μg ml−1). (b) Fluorescent emission spectra of DPPE-PEG(5000)-SWCNT with 0, 10−4, 2 × 10−4, 4 × 10−4, 8 × 10−4, 1.2 × 10−3, 1.6 × 10−3, 2 × 10−3, 4 × 10−3, 8 × 10−3, 1.2 × 10−2, 1.6 × 10−2, 2 × 10−2, 4 × 10−2, 8 × 10−2 and 0.2 mg ml−1 fibrinogen show substantial decrease in emission intensity with increasing protein concentration. Inset: absorption spectra of DPPE-PEG(5000)-SWCNT suspension before (solid black curve) and after (dashed red curve) the addition of 0.02 mg ml−1 fibrinogen. (c) Excitation–emission profile of the DPPE-PEG(5000)-SWCNT solution before and (d) after the addition of 0.02 mg ml−1 fibrinogen. (e) The normalized fluorescent response of the various chiralities in the DPPE-PEG(5000)-SWCNT suspension to the addition of different concentrations of fibrinogen (dots). The fit according to the model described in the text is plotted as solid lines. (f) The parameters of the model used for data fitting in d and their 95% confidence intervals. Dashed lines are guides to the eye. Top panel: the proportional parameter β used to fit the normalized fluorescent response model. Bottom panel: the parameters Kd1, and (Kd23)1/2 used to fit the normalized fluorescent response model (blue squares and red circles, respectively). (g) Wavelength redshift of the (6,5) fluorescent emission peak of the DPPE-PEG(5000)-SWCNT suspension to the addition of different concentrations of fibrinogen (dots). The fit according to the model described in the text is plotted as a solid line. (h) Sensor performance in a complex environment: relative fluorescent response of DPPE-PEG(5000)-SWCNT suspension following a two-step analyte addition. First, either albumin (columns 1–3), fibrinogen (columns 4–6), or an equal mixture of both (columns 7–9) was added to the solution to a final concentration of 20 μg ml−1 and incubated for an hour. Then either PBS (columns 1, 4 and 7), albumin (columns 2, 5 and 8), or fibrinogen (columns 3, 6 and 9) was added to a final protein concentration of 40 μg ml−1. The fluorescent response was measured after an additional 1 h incubation. (i) Relative fluorescent response of DPPE-PEG(5000)-SWCNT (5 mg l−1) sensor to fibrinogen (0.05, 0.5 and 5 mg ml−1) in serum. Error bars represent the s.d. between three replicate experiments.
