The main goal of this research is the synthesis of water soluble core-shell CdSe/ZnS quantum dots

(QDs) and their suitability in biosensing using an electrochemiluminescence-based detection method.

Water soluble QDs have been synthesized using the ligand exchange method. We synthesized

dimethylaminoethanethiol (DAET)-capped CdSe/ZnS QDs from CdSe/ZnS Lumidots® in toluene.

DAET/CdSe/Zns QDs showed an emission peak (see Fig. 1) maximum at 670 nm which corresponds

to a particle size of 6.3 nm (dark red emission). DAET ligand is used as a surfactant which renders the

CdSe/ZnS QDs water soluble. The ligand on the surface of a quantum dot prevents aggregation of

individual particles. A ligand exchange phase transfer method allowed changing the original

hydrophobic ligand (TOPO) with the hydrophilic ligand on the surface of the quantum dots. Because

DAET QDs are positively charged, they have been incorporated within negatively charged Nafion

polymer. A major drawback of ligand exchange reactions is that they are commonly accompanied by

a significant decrease in quantum yield. The quantum yield typically drops down in a range between

1%-25%, depending on the quantum yield before the ligand exchange. The quantum yield for the

DAET-QD emission is determined to be less than 5% (Rhodamine 6G as reference).

640nm Quantum Dots with DAET in Water Absorption/Emission Spectrum

0.00

0.10

0.20

0.30

0.40

0.50

350 400 450 500 550 600 650 700 750 800

Wavelength (nm)

Abso

rptio

n

-2.8

97.2

197.2

297.2

397.2

497.2

597.2

0 100 200 300 400 500 600 700 800 900

Emis

sion

Absorption

Emission

Fig.1. Absorption and emission spectrum of DAET-protected QDs.

We investigated the ECL behaviour of QDs deposited directly on glassy carbon electrodes or on a

pre-formed Nafion layer. DAET-CdSe/ZnS QDs (positively charged) were incorporated into Nafion

(negatively charged) by electrostatic interactions. Hydrogen peroxide was used as co-reactant for the

generation of the ECL signal. Also, we developed a novel strategy in order to be able to produce both

cathodic (via QDs) and anodic (via [Ru(bpy)3]2+) ECL by incorporating into Nafion both QDs and

[Ru(bpy)3]2+ (Fig.2, left).

The ECL from [Ru(bpy)3]2+ is not at the moment fully understood, since hydrogen peroxide is not a

co-reactant for the ruthenium complex. The ECL may be ascribed to the generation of oxygen radicals

which react with [Ru(bpy)3]3+ obtained during the anodic scan (right). Recent reports seems to

confirm that oxygen can act as enhancer when [Ru(bpy)3]2+ is incorporated in thin films of Nafion.

The ECL signal scales with hydrogen peroxide concentration (Fig.2, right). Therefore CdSe/ZnS QDs

can potentially be used for the detection of H2O2. Strong ECL was also observed (Figure not shown)

when peroxidisulphate was used a a co-reactant. We are currently drafting a manuscript regarding

ECL of QDs incorporated within Nafion films. In another work (see publication in Langmuir 2010)

we have synthesized dimethyalaminopyridine (DMAP)-Au NPs incorporated in a ruthenium

metallopolymer.

Fig.1. ECL of DAET-CdSe/ZnS incorporated into Nafion film in the presence of H2O2 as a coreactant

(right) and Nafion/QDs/Nafion/Ru(bpy)32+ (left).

Another part of the scientific activity involved the preparation of gold nanocavities for SERS

applications. Polystyrene microspheres (8µm diameter) were deposited on gold substrates. Then, Au

was electrodeposited and the polystyrene spheres removed. Typical SEM pictures of the cavities are

reported in Figure 3.

Fig.3. SERM images of Au Nanocavities deposited on Au substrates

Currently, work is in progress to deposit platelets on Au nanocavities for investigation using SERS.

Published words:

Nr. 2 invited reviews on ECL: Annu. Rev. Anal. Chem. (2009) and Biosens. Bioelectron (2009)

Nr 1 paper on ECL of DMAP-Au/NPs- Ru metallopolymer

We expect to publish a paper with the results regarding the ECL of QDs into Nafion.

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8saline PBS pH 7, 0.03 M H2O2

0.1V s-1

ECL

/ a.u

.

E / V vs Ag/AgCl

Nafion/CdSe-DAET/Nafion/Ru(bpy)32+

-2.0 -1.5 -1.0 -0.5 0.0

0.00

0.25

0.50

0.75

1.00

ECL

/ a.u

.E/V vs Ag/AgCl

6x10-3 mol dm-3 H2O

2

1.2x10-2 mol dm-3 H2O

2

6x10-2 mol dm-3 H2O

2