S5
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
0
50
100
150
200
250
300
Current (A)
E (V vs Ag/AgCl)
Bare GC electrode
SiO
2
particles
RuDSNs
TPA
RuDSNs+TPA
Figure S4. CV curves of bare GC electrode (black line), GC electrode immobilized by either silica nanoparticles (red line) or RuDSNs (blue
line) in PBS buffer, and bare GC electrode (green line) and GC electrode immobilized by RuDSNs (purple line) in PBS buffer containing 100
mM TPA coreactant. The potential was cyclically scanned from 0 to 1.4 V at a scan rate of 20 mV/s.
As the potential continues to scan beyond 0.87 V, the ECL intensity of the nanoparticles starts to decrease,
although the oxidation current increases and then reaches a peak at 1.05 V. The contravention between the ECL
emission intensity and the oxidation current is attributed to direct anodic oxidation of TPA
•
at the electrode interface.
[1,
3]
It is noteworthy that we observe a small ECL peak at 1.19 V. It derives from the direct oxidation of Ru(bpy)
3
2+
inside
the nanoparticle based on the electron tunnelling/hopping mechanism,
[4]
which is consistent with the oxidation
current of Ru(bpy)
3
2+
(Figure S5). This phenomenon is supported by the numerical simulated result reported by
Paolucci and co-workers.
[2a]
RuDSN@Ru(bpy)
3
2+
– e → RuDSN@Ru(bpy)
3
3+
(7)
TPA
•
+ RuDSN@Ru(bpy)
3
3+
→ P
1
+ RuDSN@Ru(bpy)
3
2+
* (8)
RuDSN@Ru(bpy)
3
3+
+ RuDSN@Ru(bpy)
3
+
→ RuDSN@Ru(bpy)
3
2+
* + RuDSN@Ru(bpy)
3
2+
(9)
This is the first time that the ECL emission by the electron tunnelling and hopping mechanism at single-
nanoparticle level is observed, although the “revisited” route is verified by imaging the ECL profile in single
microbeads as well as SECM-ECL experiments.
[2b, 2c]
It is noteworthy that the ECL-potential curve can accurately
reveal specific electrochemical reaction without the interference from the charge-discharge current, side reactions
and water decomposition reaction, which are inevitable in traditional CV measurements. In addition, as illustrated in
Figure 2m, the ECL-potential curve shows a zero background signal from the blank electrode substrate during the
entire ECL process, which demonstrates the high accuracy and sensitivity for imaging local electrochemical reactions
by our ECL microscopy.
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-50
0
50
100
150
200
Current (A)
E (V vs. Ag/AgCl)
Ru(bpy)
3
2+
in PBS buffer
1.12 V
Figure S5. CV curve of 400 µM Ru(bpy)
3
2+
in 100 mM PBS buffer. Work electrode: GC electrode. The potential is cyclically scanned from 0
to 1.4 V at a scan rate of 100 mV/s.
Relationship between ECL reaction kinetics and the nature of electrode surface: A crucial point in the efficiency
of the ECL generation is the chemical and physical state of the electrode surface where the ECL process is initiated.
