Figure 3. (A) HRTEM image of 80 μM
C8-TPE-C4TAB. (B) CL signals of the
luminol-Co2+-H2O2system upon adding CTAB and
C8-TPE-C4TAB. (C) CL signals of the
luminol-Co2+-H2O2system upon adding CTAB with the different concentrations. (D) CL
signals of the
luminol-Co2+-H2O2system upon adding conventional cationic surfactants.
Mechanism of
C8-TPE-C4TAB-mediated intensive and
long-lasting CL emissions. As indicated above, the addition of
C8-TPE-C4TAB endowed more effective CL
reaction than conventional cationic surfactants. It is reported that
cationic micelle can adsorb anionic reactants and benefit the CL
reaction.39 At pH 7.4, the
C8-TPE-C4TAB micelle was positively
charged (+11.0 mV) because of the outside ternary ammonium cation
(Figure S5), while luminol was negatively charged (–4.8 mV). The
electrostatic attraction between positively charged
C8-TPE-C4TAB micelle and negatively
charged luminol dianion/peroxide anion easily leads to surface
adsorption and enrichment of reactants.40-42 Such an
electrostatic attraction-assisted CL emission was also provided by SDS
(sodium dodecyl sulfonate, a kind of typical anionic surfactant). As
shown in Figure S6, the CL intensity of
luminol-Co2+-H2O2system distinctly decreased upon adding SDS. This is because the outside
sulfonic acid groups make SDS micelle negatively charged, which
possesses strong electrostatic repulsion toward luminol dianion and
peroxide anion.20
To further understand the mechanism of
C8-TPE-C4TAB-enhanced CL intensity and
long-lasting emission, a few characterizations were performed. The
generation of reactive oxygen species (ROS) is important to the CL
signals. We tested the CL inhibition with the addition of different ROS
scavengers. As displayed in Figure S7, p -benzoquinone (HQ) and
thiourea caused visible CL suppression, while NaN3induced slight CL decrease, suggesting the primary ROS were superoxide
radical (O2•−) and hydroxyl raidical
(•OH).43,44 The electron
paramagnetic resonance results also demonstrated the continuous
generation of O2•− and•OH during the CL reaction (Figure 4). It is reported
that many ROS possess longer lifetime in hydrophobic
environment.45 When inserting TPE into the backbone of
surfactant in this work, the hydrophobicity of alkyl chain increased,
this might benefit the stabilization of ROS and promote the CL reaction.