Silver Nanoparticles as an Electrochemical Bio-Label
Paul K. Wilson1, Mateusz Szymanski2, Robert A. Porter1*
1.
Argento Diagnostics Ltd., Knowledge & Innovation Centre, National Physical Laboratory, Teddington, Middlesex, TW11 0LW
2.
Analytical Science Team, National Physical Laboratory, Teddington, Middlesex, TW11 0LW
Introduction
Electrochemical behaviour of AgNPs
Immunoassays with electrochemical detection of metal marker
generally follows the same procedure. That is the dissolution of metal
nanoparticle (NP) and the consecutive quantification of solubilized metal
ions by anodic striping voltammetry (ASV) at carbon electrode.
This work presents a new strategy for using silver
nanoparticles (AgNPs) as a metal marker with the dissolution step that
does not require a chemical oxidant and thus offering advantages for
application in terms of fast response, reduced cost of analysis and
procedural simplicity.
Silver Nanoparticles Aggregation
1. Silver sol dissolution and formation of electroactive
chelate: amonium thiocyanatosilver(I) at +0.6 V for 15 s.
Ag
Ag
0
l Ag
m ( NH
4
) m ( SCN
) n ] m n 1
ASV scans of silver colloid (4-80%) in 1M NH4SCN
2.500x10
-1
0.201x10-4
0.151x10-4
i/A
0
3
0.176x10-4
0.101x10-4
Silver Sol in 1M NH4SCN
2.5
2
1
y = 0.0305x - 0.028
2
R = 0.9993
0.5
0
0
0.076x10-4
-2.500x10
-1
-5.000x10
-1
-7.500x10
-1
-10.000x10
-1
-12.500x10
-1
-15.000x10
-1
-17.500x10
-1
1.5
20
40
60
80
Silver Sol [% ]
0.051x10-4
SCN-
SCN-
4
-4
0.026x10
E/V
SCN-
) o [ Ag ( NH
The analytical signal of different concentration of Silver colloid.
SCNSCN-
[ Ag ( NH 4 ) m ( SCN ) n ] m n o [ Ag ( NH 4 ) m ( SCN ) n ] m n 1 e SCN-
SCN-
) n ( SCN
3. Stripping step of ASV (oxidation) -1.2V Æ +0.1V
0.126x10-4
NH4SCN
e
[ Ag ( NH 4 ) m ( SCN ) n ] m n 1 e o [ Ag ( NH 4 ) m ( SCN ) n ] m n
AgNPs in the presence of thiocyanate forms aggregates
surrounded with the SCN- ion layer.
SCN-
2. Accumulation step of ASV (reduction) at ––1.2V
Microcoulombs [µC]
The dissolution step is very important as it ensures the high
sensitivity due to release of huge number of metal ions from one single
NP. However, it requires the use of harmful reagents (such as HBr/Br2
mixture for gold or HNO3 for silver).
Electrochemical reactions at the working electrode.
0.001x10-4
SCNSCN-
-0.024x10-4
-0.049x10-4
61.533
61.783
62.033
62.283
62.533
62.783
t/s
Ø = 40 nm
Zeta Potential = -50 mV
Ø = 400 nm
Zeta Potential = -10 mV
Mechanism of AgNPs dissolution.
Both UV-Vis and Dynamic Light Scattering confirm the aggregation
process.
-
Carbon Screen Printed Electrodes
The measurement takes place in 50-µL droplet on the surface of a
carbon screen printed electrode.
Counter Electrode
The influence of dissolution step parameters on ASV signal.
Working Electrode
NH4SCN molarity
Duration
Potential value
10
Reference Electrode
10
9
8
8
10
2.5 ppm Ag+
M ic ro c o u lo m b s [µC ]
80% Silver Sol
6
6
4
1
2
0.5
1
[NH4SCN] [mol/L]
1.5
2
3
-1.6
-1.1
-0.6
-0.1
0.4
0.9
potential [V]
1.4
0
0
10
time [s]
20
30
Conclusion
AgNPs dissolution
+0.6 V
Stripping (oxidation)
plating (reduction)
-1.2 V
-1.6 V
nucleation
2
4
0
V
4
5
0
Steps of Anodic Stripping Voltammetry:
8
7
6
Time
[s]
We have demonstrated and explained the mechanism of
AgNPs dissolution on the surface of carbon electrode without the need
of any oxidant. This process can be applied for development of
electrochemical metalloimmunoassays. Removing the need for using
harsh oxidant is very advantageous especially in terms of building new
point of care tests.
This project was funding by the UK Government’’s Chemistry and Biology
National Measurement System Programme under the Bioanalysis theme.
* Contact: [email protected]
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