(a)
(b)
(a)
(b)
C[ClO ]/10–5 molL–1
−
1.0
0.8
0.6
0.4
0.2
0.0
0
10 20 30 40 50
C[ClO ]/10–5 molL–1
−
Figure 2. (a) Fluorescence emission spectra of FHSNs
(0.2 g L¹1) in the presence of different concentrations of
Figure 4. (a) FT-IR spectra of FHSNs and RN-40. (b) UV-vis
spectra of FHSNs in the presence of different concentrations of
hypochlorite anion (0-4.5 © 10¹4 mol L¹1) and HSN-CHO.
¹1
¹1
hypochlorite anion (0-4.5 © 10¹4 mol L
) in 0.01 mol L
Tris-HCl buffer solution, pH 7.2. (b) The normalized fluorescent
¹
intensity at 457 nm evolution with ClO concentrations.
¹
The FHSNs, after reaction with ClO (concentration:
40 © 10¹5 mol L¹1), were collected by centrifugation, washing,
and vacuum drying (denoted as RN-40). RN-40 was studied by
FT-IR analysis (Figure 4a). The peak shape and position of
RN-40 remained almost the same as that of FHSNs. The
0.8
0.6
¹1
absorption peaks at about 1640 and 2900-3000 cm confirmed
that the -C=N bond and -CH2 group also existed in the RH-40.
However, in the RN-40 spectrum, a new absorption peak
appeared at 1725 cm¹1, which belonged to the -C=O stretching
vibration in the -CHO group. UV-vis spectral analysis of
FHSNs was also carried out upon adding different volumes of
0.4
Φ
0.2
0.0
¹
ClO to FHSN in Tris-HCl buffer solution (Figure 4b). The
0
10 20 30 40 50
C[ClO ]/10–5 molL–1
−
original FHSNs have a wide absorption at about 351 nm. When
¹
only a small amount of ClO (5-10 © 10¹5 mol L¹1) was added,
Figure 3. Quantum yields (Φ) of FHSNs (0.2 g L¹1) in the
presence of different concentrations of hypochlorite anion (0-
the shape and position of the absorption peaks remained almost
the same. However, when the concentration reached 15 ©
10¹5 mol L¹1, a new absorption peak appeared at 403 nm; further
4.5 © 10¹4 mol L¹1) in 0.01 mol L Tris-HCl buffer solution,
¹1
¹
increasing the ClO concentration to 20 © 10¹5 mol L¹1, the
pH 7.2. Inset at (a): photographs of solutions of FHSNs in the
presence of different concentrations of hypochlorite from low
(left) to high (right), taken under UV illumination (365 nm).
new peak became prominent and intensity of the new peak
¹
increased with further increase in ClO concentration (25-
45 © 10¹5 mol L¹1). This may suggest that one new species was
formed during the titration process.
¹
blue-shifts were observed with increasing ClO concentrations
(Figure 2a). Fluorescent intensity decreased dramatically with
To further confirm the structure of the new species, imitating
the procedure of preparing FHSNs, we introduced 4,4¤-difor-
myltriphenylamine on the surface of HSNs, giving aldehyde-
containing HSNs (denoted as HSN-CHO). The UV-vis spectral
analysis of HSNs-CHO was performed under the same con-
ditions as that of FHSNs (Figure 4b). Interestingly, the new peak
position was identical to that of the HSN-CHO. Both the FT-IR
and UV-vis spectra demonstrated the -CH=N-OH ¼ -CHO
mechanism. Furthermore, fluorescent effect experiment of HSN-
CHO showed that the emission of HSN-CHO was hardly
detectable.
The fluorescence properties of the corresponding free probe
were also investigated (Figure S3). The photophysical data of
FHSNs and the corresponding free probe are summarized in
Table 1. Compared to the free probe, the UV absorbance was
red-shifted by 67 nm. Meanwhile, it can be found that Φ of
FHSNs was 3 times larger than that of the free probe. The
LOD of the FHSNs (1.77 © 10¹8 mol L¹1) is much lower than
that of the free probe (2.3 © 10¹6 mol L¹1) (see Supporting
Information). All of these data implied that FHSNs were more
suitable for medical and biological use.
¹
the addition of ClO up to
a concentration of 2.5 ©
10¹4 mol L¹1, then leveled off (Figure 2b). To check the
reproducibility of the FHSNs, the above experiments were
repeated thrice. The error bars were small and the reproducibility
was relatively good. The limit of detection (LOD) was estimated
to be 1.77 © 10¹8 mol L¹1. (see detailed calculation of LOD in
Supporting Information).
To quantitatively determine the fluorescent intensity of
¹
FHSNs as a function of ClO concentration, quantum yields
(Φ, see Supporting Information) in the presence of different
¹
concentrations of ClO were calculated (Figure 3). As demon-
strated in Figure 3, quantum yields decreased with increasing
¹
ClO concentration, then leveled off when the concentration was
over 2.5 © 10¹4 mol L¹1, in accordance with the progressively
weaker emissions, as shown in the photos of the solutions taken
in dark upon excitation by a UV lamp at the wavelength of
365 nm.
¹
The mechanism for detecting the ClO of FHSNs was also
¹
investigated, which was the -CH=N-OH reacted with ClO and
formed the new -CHO group in the detection process.
© 2015 The Chemical Society of Japan