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Electrochemical Nanoparticle Sizing Via Nano-Impacts: How Large a Nanoparticle Can be Measured?

Bartlett TR, Sokolov SV, Compton RG - ChemistryOpen (2015)

Bottom Line: The 'nano-impacts' technique is an excellent and qualitative in situ method for nanoparticle characterization.Two complementary studies on silver and silver bromide nanoparticles (NPs) were used to assess the large radius limit of the nano-impact method for NP sizing.Noting that by definition a NP cannot be larger than 100 nm in diameter, we have shown that the method quantitatively sizes at the largest limit, the lower limit having been previously reported as ∼6 nm.1.

View Article: PubMed Central - PubMed

Affiliation: Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford South Parks Road, Oxford, OX1 3QZ, UK.

ABSTRACT
The field of nanoparticle (NP) sizing encompasses a wide array of techniques, with electron microscopy and dynamic light scattering (DLS) having become the established methods for NP quantification; however, these techniques are not always applicable. A new and rapidly developing method that addresses the limitations of these techniques is the electrochemical detection of NPs in solution. The 'nano-impacts' technique is an excellent and qualitative in situ method for nanoparticle characterization. Two complementary studies on silver and silver bromide nanoparticles (NPs) were used to assess the large radius limit of the nano-impact method for NP sizing. Noting that by definition a NP cannot be larger than 100 nm in diameter, we have shown that the method quantitatively sizes at the largest limit, the lower limit having been previously reported as ∼6 nm.1.

No MeSH data available.


Chronoamperometry at +0.60 V vs. SCE. Red: 20 mm KCl. Black: 20 mm KCl and Ag NPs (total [Ag]=2.8 μgml−1). Lines offset by 1 nA for clarity. Inset shows zoomed-in region from 13.50–13.70 s.
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fig08: Chronoamperometry at +0.60 V vs. SCE. Red: 20 mm KCl. Black: 20 mm KCl and Ag NPs (total [Ag]=2.8 μgml−1). Lines offset by 1 nA for clarity. Inset shows zoomed-in region from 13.50–13.70 s.

Mentions: Figure 8 shows the obtained current-time transient in the presence (black line) and the absence (red line) of the NPs, whereby the spikes are only observed in the presence of the Ag NPs. The spikes correspond to direct electrolytic impacts and are due to the oxidation of the colliding silver nanoparticles. The resultant spikes were analysed, and the resultant size distribution was calculated using Equation 1. Figure 9 shows the calculated electrochemical size distribution in comparison to the SEM data. The mean spherical diameter was determined from nano-impacts to be 85 nm. From the SEM images, the mean spherical diameter was 100 nm. For further confirmation, nanoparticle tracking analysis (NTA) of the silver NPs was performed using a NanoSight LM10 (NanoSight, Amesbury, UK), equipped with a sample chamber with a 638 nm laser. The sample was measured for 60 s with automatic settings at 30 frames per second. The software used for capturing and data analysis was the Nanosight NTA 2.3. The size distribution shown in Figure 10 has the mean diameter of 106 nm and standard deviation of 33 nm. The data is in good agreement with the SEM image analysis which shows a similar mean diameter; however, a significantly larger standard deviation is observed (33 nm from the NTA vs. 4 nm from the SEM), which may be caused by an artificial broadening.4 The size distributions obtained from the three techniques are in close agreement, but the nano-impact sizing distribution for the 20 mm potassium chloride concentration is smaller. This discrepancy is attributed to the reduced electrolyte concentration. The apparent smaller diameter might likely be caused by incomplete dissolution of the silver nanoparticles. By contrast, according to the literature, excellent agreement with the SEM data was obtained for 0.10 m potassium chloride.19 This suggests that in order for a particle to undergo complete oxidation, potential drop across the interface must be minimized, which is only achieved for the higher concentration of the supporting electrolyte as observed for molecular electrochemistry.23


Electrochemical Nanoparticle Sizing Via Nano-Impacts: How Large a Nanoparticle Can be Measured?

Bartlett TR, Sokolov SV, Compton RG - ChemistryOpen (2015)

Chronoamperometry at +0.60 V vs. SCE. Red: 20 mm KCl. Black: 20 mm KCl and Ag NPs (total [Ag]=2.8 μgml−1). Lines offset by 1 nA for clarity. Inset shows zoomed-in region from 13.50–13.70 s.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608527&req=5

fig08: Chronoamperometry at +0.60 V vs. SCE. Red: 20 mm KCl. Black: 20 mm KCl and Ag NPs (total [Ag]=2.8 μgml−1). Lines offset by 1 nA for clarity. Inset shows zoomed-in region from 13.50–13.70 s.
Mentions: Figure 8 shows the obtained current-time transient in the presence (black line) and the absence (red line) of the NPs, whereby the spikes are only observed in the presence of the Ag NPs. The spikes correspond to direct electrolytic impacts and are due to the oxidation of the colliding silver nanoparticles. The resultant spikes were analysed, and the resultant size distribution was calculated using Equation 1. Figure 9 shows the calculated electrochemical size distribution in comparison to the SEM data. The mean spherical diameter was determined from nano-impacts to be 85 nm. From the SEM images, the mean spherical diameter was 100 nm. For further confirmation, nanoparticle tracking analysis (NTA) of the silver NPs was performed using a NanoSight LM10 (NanoSight, Amesbury, UK), equipped with a sample chamber with a 638 nm laser. The sample was measured for 60 s with automatic settings at 30 frames per second. The software used for capturing and data analysis was the Nanosight NTA 2.3. The size distribution shown in Figure 10 has the mean diameter of 106 nm and standard deviation of 33 nm. The data is in good agreement with the SEM image analysis which shows a similar mean diameter; however, a significantly larger standard deviation is observed (33 nm from the NTA vs. 4 nm from the SEM), which may be caused by an artificial broadening.4 The size distributions obtained from the three techniques are in close agreement, but the nano-impact sizing distribution for the 20 mm potassium chloride concentration is smaller. This discrepancy is attributed to the reduced electrolyte concentration. The apparent smaller diameter might likely be caused by incomplete dissolution of the silver nanoparticles. By contrast, according to the literature, excellent agreement with the SEM data was obtained for 0.10 m potassium chloride.19 This suggests that in order for a particle to undergo complete oxidation, potential drop across the interface must be minimized, which is only achieved for the higher concentration of the supporting electrolyte as observed for molecular electrochemistry.23

Bottom Line: The 'nano-impacts' technique is an excellent and qualitative in situ method for nanoparticle characterization.Two complementary studies on silver and silver bromide nanoparticles (NPs) were used to assess the large radius limit of the nano-impact method for NP sizing.Noting that by definition a NP cannot be larger than 100 nm in diameter, we have shown that the method quantitatively sizes at the largest limit, the lower limit having been previously reported as ∼6 nm.1.

View Article: PubMed Central - PubMed

Affiliation: Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford South Parks Road, Oxford, OX1 3QZ, UK.

ABSTRACT
The field of nanoparticle (NP) sizing encompasses a wide array of techniques, with electron microscopy and dynamic light scattering (DLS) having become the established methods for NP quantification; however, these techniques are not always applicable. A new and rapidly developing method that addresses the limitations of these techniques is the electrochemical detection of NPs in solution. The 'nano-impacts' technique is an excellent and qualitative in situ method for nanoparticle characterization. Two complementary studies on silver and silver bromide nanoparticles (NPs) were used to assess the large radius limit of the nano-impact method for NP sizing. Noting that by definition a NP cannot be larger than 100 nm in diameter, we have shown that the method quantitatively sizes at the largest limit, the lower limit having been previously reported as ∼6 nm.1.

No MeSH data available.