Analytical Chemistry Chemical Cytometry Quantitates Superoxide

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Figure 2. (A, B) Effect of the concentration of (A) Hg 2+ and (B) Ag + on the composition ratio of (A) Au to Ag and (B) Au to Hg of the precipitates. A series of concentration of (A) 0-1000 nM Hg 2+ and (B) 0-1000 nM Ag + was added to 1.0 mL of 0.48 nM Tween 20-AuNPs. The precipitates were obtained by five cycles of centrifugation of the resulting solutions. (C, D) EDX spectra of the precipitates obtained after the addition of (a) 0.1, (b) 1, and (c) 10 µM (C) Hg 2+ and (D) Ag + to a solution of 0.48 nM Tween 20-AuNPs. Tween 20-AuNPs are prepared in 20 mM phosphate at pH 12.0. The incubation time is 5 min. extinction values of the solution at 650 and 520 nm corresponded to the quantities of dispersed and aggregated AuNPs, respectively. Thus, the molar ratio of dispersed to aggregated AuNPs can be expressed by the ratio of the extinction value Ex at 650 nm to that at 520 nm (Ex650 nm/Ex520 nm). As shown in Figure 3A, the addition of both Hg2+ and Ag + to a solution of Tween 20-AuNPs resulted in a high value of Ex650 nm/Ex520 nm. However, when we replaced Tween 20 with Tween 40, the value of Ex650 nm/ Ex520 nm became small. This suggests a relatively small amount of Hg-Au alloys or Ag on the surface of Tween 40-modified AuNPs, resulting in a small degree of NP aggregation. Similar phenomena were observed in the case of Tween 60- and Tween 80-modifed AuNPs. To further confirm our hypothesis, ICP- MS was used to determine the composition of the NPs. After adding 1 µM Hg2+ to different kinds of AuNPs, the concentrations of Hg in Tween 20-, 40-, 60-, and 80-modified AuNPs were 148, 64, 58, and 51 ppb, respectively. Similarly, upon the addition of 1 µM Ag + , the concentrations of Ag in Tween 20-, 40-, 60-, and 80-modified AuNPs were 65, 19, 24, and 25 ppb, respectively. On the basis of these results, Tween 20 was selected for the following studies. Previous studies have shown that the sensitivity of a AuNPbased sensor is highly dependent on the concentration of 6834 Analytical Chemistry, Vol. 82, No. 16, August 15, 2010 AuNPs. 44 At relatively high concentrations of Tween 20-AuNPs, the deposition of Hg2+ or Ag + on the surface of a single particle decreased, reducing the degree of NP aggregation. Moreover, the aggregation rate of NPs increased with increasing NP concentration. It can be seen that the optimum concentrations of Tween 20-AuNPs for sensing Hg2+ and Ag + were 0.24 and 0.48 nM, respectively, when the incubation time was fixed at 5 min (Figure 3B). Moreover, we investigated the effect of Na3PO4 concentration on the colorimetric sensitivity of Tween 20- AuNPs to Hg2+ and Ag + .SI Figure S5 shows that the zeta potential of Tween 20-AuNPs reduced with increasing Na3PO4 concentration, implying that electrostatic repulsion between Tween 20-AuNPs decreased with increasing ionic strength of the solution. Thus, under conditions of high ionic strength, the slight electrostatic repulsion between Tween 20-AuNPs provided a low barrier for metal-ion-induced NP aggregation. As expected, the difference in Ex650 nm/Ex520 nm for the cases with and without 1.0 µM Hg2+ gradually increased with increasing Na3PO4 concentration and reached a plateau at 80 mM Na3PO4 (Figure 3C). A similar effect was found in the analysis of Ag + (Figure 3D). Consequently, 80 mM Na3PO4 was chosen for the following studies. (44) Huang, C.-C.; Tseng, W.-L. Anal. Chem. 2008, 80, 6345–6350.
Figure 3. (A) The value of Ex650 nm/Ex520 nm of Tween 20- 40-, 60-, and 80-modified AuNPs (0.48 nM) after the addition of (a) 1 µM Hg 2+ and (b) 1 µM Ag + . (B) Effect of the concentration of Tween 20-AuNPs on the ratio Ex650 nm/Ex520 nm in the presence of (a) 1 µM Hg 2+ and (b) 1 µM Ag + . (C) Effect of phosphate concentration on the ratio Ex650 nm/Ex520 nm of 0.24 nM Tween 20-AuNPs in the (a) absence and (b) presence of 1 µM Hg 2+ . (D) Effect of phosphate concentration on the ratio Ex650 nm/Ex520 nm of 0.48 nM Tween 20-AuNPs in the (a) absence and (b) presence of 1 µM Ag + . (A, B) Tween 20-AuNPs are prepared in 20 mM phosphate at pH 12.0. (A-D) The incubation time is 5 min. Selectivity, Sensitivity, and Application. To realize the selectivity of 0.24 and 0.48 nM Tween 20-AuNPs toward Hg 2+ and Ag + , respectively, other metal ionssincluding Li + ,Na + ,K + , Mg 2+ ,Ca 2+ ,Sr 2+ ,Ba 2+ ,Cr 3+ ,Mn 2+ ,Fe 2+ ,Fe 3+ ,Co 2+ ,Ni 2+ ,Cu 2+ , Zn 2+ ,Cd 2+ ,Al 3+ ,Pb 2+ ,Hg 2+ , and Ag + swere examined under identical conditions. Only Hg 2+ and Ag + caused the aggregation of both 0.24 and 0.48 nM Tween 20-AuNPs (SI Figure S6), revealing that this probe is selective for Hg 2+ and Ag + . To circumvent this problem, we tested the effect of masking agents, including NaCl and EDTA. It is well-known that the solubility product of AgCl is 1.8 × 10 -10 , whereas HgCl2 is soluble in water (70 g/L). Accordingly, we tested the ability of NaCl to mask the interfering metal ions in our sensing system. In the presence of 0.1 M NaCl, the addition of 1 µM Hg 2+ to a solution of 0.24 nM Tween 20-AuNPs resulted in an apparent change in Ex650 nm/Ex520 nm, whereas the remaining metal ions (100 µM) had negligible effects on the same system (Figure 4A). The selectivity of this probe is more than 100-fold for Hg 2+ over all other tested metal ions. Additionally, to improve the selectivity of 0.48 nM Tween 20-AuNPs for Ag + , we chose EDTA as a masking agent, since it forms a more stable complex with Hg 2+ than with Ag + . As expected, the presence of 0.01 M EDTA masked Tween 20-AuNPs toward Hg 2+ (Figure 4B). As a result, Tween 20-AuNPs provided high selectivity (>100-fold) toward Ag + over all other tested metal ions. Under optimum conditions (for sensing Hg 2+ : 0.24 nM Tween 20-AuNPs, 80 mM Na3PO4, and 0.1 M NaCl; for sensing Ag + : 0.48 nM Tween 20-AuNPs, 80 mM Na3PO4, and 0.01 M EDTA), we evaluated the sensitivity of this probe toward Hg 2+ and Ag + . When the concentrations of Hg 2+ varied from 0 to 1000 nM, the extinction spectra of 0.24 nM Tween 20-AuNPs showed a gradual increase in extinction at 650 nm and their color gradually changed from red to purple (Figure 5A). A solution of 0.48 nM Tween 20-AuNPs showed a similar response to Ag + (Figure 5B). These spectra showed clear isosbestic points at 556 and 549 nm upon the addition of Hg 2+ and Ag + , respectively. This observation reveals that the aggregation of Tween 20-AuNPs is directly related to the concentration of Hg 2+ or Ag + . This result was further confirmed by HRTEM images and DLS measure- Analytical Chemistry, Vol. 82, No. 16, August 15, 2010 6835
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Anal. Chem. 2010, 82, 6745-6750 Let
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purchased from Invitrogen-Molecular
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Figure 3. Electropherograms of TPP-
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Anal. Chem. 2010, 82, 6751-6755 Res
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(pH 8.0) with cysteine and cystamin
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Figure 4. Ion mobility mass spectra
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GOx glucose + O298 gluconic acid +
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coater at 2000 rpm for 20 s, and th
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Figure 5. Comparison of cyclic volt
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in channels with either no grooves
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indicators of atmospheric processin
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Figure 1. GC/MS total ion chromatog
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Table 2. Concentrations and Stable
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on a substrate are preferred. 20-24
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Figure 4. SERS analysis of NAADP co
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Anal. Chem. 2010, 82, 6775-6781 Hig
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tion, 2 µL of proprionaldehyde wer
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Figure 4. Analysis of 2a by HPLC-MS
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eaction of 1a with PBH can be condu
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Table 1. Intraday Precision and Acc
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Anal. Chem. 2010, 82, 6887-6894 Fer
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Figure 1. Infrared spectra of (A) u
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Figure 3. Cyclic voltammograms obta
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Figure 6. Calculated charge from ch
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Anal. Chem. 2010, 82, 6895-6903 Ele
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Table 1. Chemical Structure, pKa Va
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pH with a tilted baseline (Figure 1
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Table 2. Linearity and Detection Li
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ascorbic acid (AA), uric acid (UA),
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the multielement capabilities, the
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RESULTS AND DISCUSSION Sulfur Detec
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Table 2. Molecular Properties and C
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Anal. Chem. 2010, 82, 6911-6918 Dir
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dilution and hybridization buffer.
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solution under appropriate incubati
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Figure 4. Standardization curve for
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Anal. Chem. 2010, 82, 6919-6925 Ele
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the ×10 objective, to have a large
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Figure 2. With a suitable removal o
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the NB signal in a much better foot
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Scheme 1. Reactions of Selenium Rea
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Figure 2. (a) ESI-MS spectrum showi
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Figure 4. (a) ESI-MS spectrum showi
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Anal. Chem. 2010, 82, 6933-6939 Dif
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trode 28 by a finite element using
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Figure 4. Comparison between simula
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Figure 6. Comparison between simula
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educed in the vicinity of double bo
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Figure 2. Normalized product ion ab
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Figure 4. EID (a) and IRMPD (b) of
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Anal. Chem. 2010, 82, 6947-6957 Ide
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Figure 1. Schematic flowchart showi
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difference, ppm compound Table 1. I
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isoforms, its successful use, in th
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Figure 5. Extracted ion current ESI
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m/z 1172.935 was observed for Ser14
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linked products via affinity tags.
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Scheme 2. Fragmentation Mechanism o
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Figure 1. (A) ESI-LTQ-CID-MS 2 prod
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Figure 3. (A) ESI-LTQ-CID-MS 2 prod
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Figure 5. (A) MALDI-TOF/TOF product
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Anal. Chem. 2010, 82, 6969-6975 Ana
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Figure 3. Equilibrium response as a
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Figure 6. The average measured resp
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for the fill time, and we find that
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nucleotide tails. 3-5 Thus, the amo
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allow the use of higher aptamer con
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quent ligation of the aptamers afte
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Anal. Chem. 2010, 82, 6983-6990 Imp
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Figure 2. Configuration editor wind
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Figure 4. Dependencies between volu
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Since the time for liquid expulsion
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Anal. Chem. 2010, 82, 6991-6999 Int
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Figure 1. Representation of the Car
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Table 2. Capillary Electrophoresis
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Figure 4. (A) Typical raw electroph
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field. DNA profiles were delivered
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Another approach to handle this lim
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(principal components, PCs) in whic
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Figure 5. Relevant score plots and
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CONCLUSIONS In this paper we have i
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electroactive-species loaded liposo
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Figure 2. Qdot-based FLFTS response
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Figure 6. Fluorescence imaging of Q
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Anal. Chem. 2010, 82, 7015-7020 Sel
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Table 1. Effect of 1 D-LC Condition
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Figure 3. Peak-production rate vers
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Anal. Chem. 2010, 82, 7021-7026 Cel
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luciferase (T7 control vector) was
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Figure 3. Inhibitory effects of luc
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Anal. Chem. 2010, 82, 7027-7034 Pat
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Electrochemistry. Electrochemical m
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Figure 2. SEM images of Au substrat
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Table 3. Film Thickness Measurement
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Anal. Chem. 2010, 82, 7035-7043 Qua
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Figure 1. (A) FL spectra of BSPOTPE
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Figure 4. (A) Variation in the FL i
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Figure 6. (A) FL spectra of BSPOTPE
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Scheme 1. Proposed Mechanism for Fl
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one or more drawbacks including poo
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Figure 2. Free fluorophores do not
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Anal. Chem. 2010, 82, 7049-7052 Dev
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Figure 2. Comparative analysis of d
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