Analytical Chemistry Chemical Cytometry Quantitates Superoxide
Analytical Chemistry Chemical Cytometry Quantitates Superoxide
Analytical Chemistry Chemical Cytometry Quantitates Superoxide
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Figure 4. The value of Ex650 nm/Ex520 nm of a solution of 80 mM Na3PO4 containing (A) 0.24 nM Tween 20-AuNPs and 0.1 M NaCl and (B) 0.48<br />
nM Tween 20-AuNPs and 0.01 M EDTA upon the addition of (A) 1 µM Hg 2+ and 100 µM other metal ions and (B) 1 µM Ag + and 100 µM other<br />
metal ions. The incubation time is 5 min.<br />
ments. SI Figure S7 shows the concentration-dependent TEM<br />
images of the aggregated AuNPs after adding different concentrations<br />
(0, 0.1, 1, and 10 µM) of Hg 2+ or Ag + to a solution<br />
of Tween 20-AuNPs. Moreover, the hydrodynamic size of<br />
the aggregated AuNPs increased with an increase in the<br />
concentration of Hg 2+ or Ag + (SI Figure S8). These results<br />
provide clear evidence that the aggregation degree of Tween<br />
20-AuNPs is highly dependent on the concentration of Hg 2+<br />
or Ag + . We observed that the ratio Ex650 nm/Ex520 nm<br />
increased linearly with increasing Hg 2+ and Ag + concentration<br />
over the range of 200 to 800 nM (R 2 ) 0.9943) and 400<br />
to 1000 nM (R 2 ) 0.9935), respectively (Figure 5C and D).<br />
A difference in linearity between two metal ions could be due<br />
to that the sensing mechanism of Tween 20-AuNPs for Hg 2+<br />
is different from that for Ag + . This probe could detect Hg 2+<br />
and Ag + at concentrations as low as 100 and 100 nM,<br />
respectively. The result is useful for detecting Ag + in<br />
drinking water, because the maximum level of silver in<br />
drinking water permitted by the United States Environmental<br />
Protection Agency (EPA) is 50 µg/L (∼460 nM).<br />
To test the practicality of the present approach, a solution of<br />
0.24 nM Tween 20-AuNPs was used to analyze Hg 2+ in drinking<br />
water and seawater. As shown in SI Figures S9 and S10,<br />
Ex650 nm/Ex520 nm increased linearly upon increasing the spiked<br />
concentration of Hg 2+ in drinking water over the range of<br />
200-600 nM (R 2 ) 0.9944) and in seawater over the range of<br />
300-1000 nM (R 2 ) 0.9977). Evidence of the Hg 2+ -induced<br />
aggregation of Tween 20-AuNPs in seawater can be seen in<br />
the HRTEM images (SI Figure S11). The lowest detectable<br />
concentrations of Hg 2+ in drinking water and seawater were<br />
6836 <strong>Analytical</strong> <strong>Chemistry</strong>, Vol. 82, No. 16, August 15, 2010<br />
estimated to be 200 and 100 nM, respectively. Although the<br />
sensitivity of this probe is insufficient to detect the maximum<br />
level of mercury (2 ppb) in drinking water permitted by the<br />
U.S. EPA, we suggest that Tween 20-AuNPs can be used as<br />
probes for solid-phase preconcentration of mercury in complex<br />
matrices prior to ICP-MS analysis. 30<br />
We also evaluated the feasibility of this approach for sensing<br />
of Ag + and AgNPs in drinking water. We obtained a linear<br />
correlation (R 2 ) 0.9963) between the ratio Ex650 nm/Ex520 nm<br />
and the concentration of Ag + spiked into the drinking water<br />
over the range of 400-1000 nM (SI Figure S12), which includes<br />
the maximum permissible limit of silver in drinking water.<br />
Moreover, since hazardous AgNPs may pose threats to human<br />
health or the environment, 45 this approach was further used to<br />
monitor AgNPs in drinking water. Under acidic conditions (1.0<br />
µM H3PO4), AgNPs (10 ± 2 nm) are oxidized to Ag + ions with<br />
1.0 mM H2O2. 12 The oxidation of AgNPs to Ag + was complete<br />
after 10 min. The generated Ag + was directly detected by 0.48<br />
nM Tween 20-AuNPs. The degree of aggregation of Tween 20-<br />
AuNPs increased when the concentration of AgNPs was<br />
increased from 1 to 10 pM (SI Figure S13). The correlation<br />
coefficient (R 2 ) for the determination of AgNPs in the range<br />
1-6 pM was 0.9988. These results suggest that this probe will<br />
be suitable for routine assays of AgNPs in consumer products<br />
such as cosmetics and fabrics. 46 Table 1 shows the quantitative<br />
measurements of Hg 2+ ,Ag + , and AgNPs in different matrices<br />
based on the use of Tween 20-AuNPs.<br />
(45) Lubick, N. Environ. Sci. Technol. 2008, 42, 8617.<br />
(46) Benn, T. M.; Westerhoff, P. Environ. Sci. Technol. 2008, 42, 4133–4139.