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Femtomolar Detection of Silver Nanoparticles by Flow-EnhancedDirect-Impact Voltammetry at a Microelectrode Array

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ABSTRACT

20142014: Wereport the femtomolar detection of silver (Ag) nanoparticlesby direct-impact voltammetry. This is achieved through the use ofa random array of microelectrodes (RAM) integrated into a purpose-builtflow cell, allowing combined diffusion and convection to the electrodesurface. A coupled RAM-flow cell system is implemented and is shownto give reproducible wall-jet type flow characteristics, using potassiumferrocyanide as a molecular redox species. The calibrated flow systemis then used to detect and quantitatively size Ag nanoparticles atfemtomolar concentrations. Under flow conditions, it is found thenanoparticle impact frequency increases linearly with the volumetricflow rate. The resulting limit of detection is more than 2 ordersof magnitude smaller than the previous detection limit for direct-impact voltammetry (900 fM) [J. Ellison et al. Sens. Actuators, B, 200, 47], and is more than 30 times smaller than the previous detectionlimit for mediated-impact voltammetry (83 fM) [T.M. Alligrant et al. Langmuir, 30, 13462].

No MeSH data available.


Example current–time transients recorded at varying flowrates showing nanoimpact spikes. Current–time transients wereconducted at +0.60 V vs Ag/AgCl at a Ag NP concentration of 6.2 fMin 40 mM KCl. Inset shows an enlarged image of a current spike at10 mL min–1 (circled region in top portion of thefigure). The background consists mainly of capacitively coupled mainsinterference (50 Hz in the United Kingdom).
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fig4: Example current–time transients recorded at varying flowrates showing nanoimpact spikes. Current–time transients wereconducted at +0.60 V vs Ag/AgCl at a Ag NP concentration of 6.2 fMin 40 mM KCl. Inset shows an enlarged image of a current spike at10 mL min–1 (circled region in top portion of thefigure). The background consists mainly of capacitively coupled mainsinterference (50 Hz in the United Kingdom).

Mentions: Next, the flow dependence of Ag NP impacts was conductedusingthe RAM–flow cell. Figure 4 shows current–time transients, 20 s in duration,at +0.60 V vs Ag/AgCl at a NP concentration of 6.2 fM in 40 mM KClacross the experimental flow range of 0–50 mL min–1. This potential was chosen because it is suitable for the completeoxidation of Ag NPs up to 100 nm in diameter.12 No impacts were observed under stationary flow, because of the lowconcentration. When the NP suspension was flowed at 10 mL min–1, current spikes were detected, indicative of Ag NPoxidation. The frequency of spikes was observed to increase with increasingvolumetric flow rate. The noise of the system was not significantlyaffected by flow rate and remained <100 pA, even at the highestflow rate of 50 mL min–1, allowing clear, unambiguousdetection of the current spikes. The background current is likelydue to surface oxidation of the RAM electrodes and/or residual citrateused for capping the particles. In order to validate that the currentspikes observed were due to direct-impact voltammetryof the Ag NPs, these were analyzed using eq 3 to obtain the size distribution. This isshown in Figure SI 4 in the SupportingInformation, along with DLS characterization of the particles. Thesize of the particles determined by voltammetry and DLS was determinedto be 57.0 ± 1.5 nm and 58 nm, respectively, confirming quantitativesizing of the particles alongside detection at a Ag NP concentrationof 6.2 fM.


Femtomolar Detection of Silver Nanoparticles by Flow-EnhancedDirect-Impact Voltammetry at a Microelectrode Array
Example current–time transients recorded at varying flowrates showing nanoimpact spikes. Current–time transients wereconducted at +0.60 V vs Ag/AgCl at a Ag NP concentration of 6.2 fMin 40 mM KCl. Inset shows an enlarged image of a current spike at10 mL min–1 (circled region in top portion of thefigure). The background consists mainly of capacitively coupled mainsinterference (50 Hz in the United Kingdom).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5015217&req=5

fig4: Example current–time transients recorded at varying flowrates showing nanoimpact spikes. Current–time transients wereconducted at +0.60 V vs Ag/AgCl at a Ag NP concentration of 6.2 fMin 40 mM KCl. Inset shows an enlarged image of a current spike at10 mL min–1 (circled region in top portion of thefigure). The background consists mainly of capacitively coupled mainsinterference (50 Hz in the United Kingdom).
Mentions: Next, the flow dependence of Ag NP impacts was conductedusingthe RAM–flow cell. Figure 4 shows current–time transients, 20 s in duration,at +0.60 V vs Ag/AgCl at a NP concentration of 6.2 fM in 40 mM KClacross the experimental flow range of 0–50 mL min–1. This potential was chosen because it is suitable for the completeoxidation of Ag NPs up to 100 nm in diameter.12 No impacts were observed under stationary flow, because of the lowconcentration. When the NP suspension was flowed at 10 mL min–1, current spikes were detected, indicative of Ag NPoxidation. The frequency of spikes was observed to increase with increasingvolumetric flow rate. The noise of the system was not significantlyaffected by flow rate and remained <100 pA, even at the highestflow rate of 50 mL min–1, allowing clear, unambiguousdetection of the current spikes. The background current is likelydue to surface oxidation of the RAM electrodes and/or residual citrateused for capping the particles. In order to validate that the currentspikes observed were due to direct-impact voltammetryof the Ag NPs, these were analyzed using eq 3 to obtain the size distribution. This isshown in Figure SI 4 in the SupportingInformation, along with DLS characterization of the particles. Thesize of the particles determined by voltammetry and DLS was determinedto be 57.0 ± 1.5 nm and 58 nm, respectively, confirming quantitativesizing of the particles alongside detection at a Ag NP concentrationof 6.2 fM.

View Article: PubMed Central - PubMed

ABSTRACT

20142014: Wereport the femtomolar detection of silver (Ag) nanoparticlesby direct-impact voltammetry. This is achieved through the use ofa random array of microelectrodes (RAM) integrated into a purpose-builtflow cell, allowing combined diffusion and convection to the electrodesurface. A coupled RAM-flow cell system is implemented and is shownto give reproducible wall-jet type flow characteristics, using potassiumferrocyanide as a molecular redox species. The calibrated flow systemis then used to detect and quantitatively size Ag nanoparticles atfemtomolar concentrations. Under flow conditions, it is found thenanoparticle impact frequency increases linearly with the volumetricflow rate. The resulting limit of detection is more than 2 ordersof magnitude smaller than the previous detection limit for direct-impact voltammetry (900 fM) [J. Ellison et al. Sens. Actuators, B, 200, 47], and is more than 30 times smaller than the previous detectionlimit for mediated-impact voltammetry (83 fM) [T.M. Alligrant et al. Langmuir, 30, 13462].

No MeSH data available.