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British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
Quantum Dot Sensors: Technology and
Commercial Applications
Copyright © 2013 Pan Stanford Publishing Pte. Ltd.
All rights reserved. This book, or parts thereof, may not be reproduced in any
form or by any means, electronic or mechanical, including photocopying,
recording or any information storage and retrieval system now known or
to be invented, without written permission from the publisher.
For photocopying of material in this volume, please pay a copying fee
through the Copyright Clearance Center, Inc., 222 Rosewood Drive,
Danvers, MA 01923, USA. In this case permission to photocopy is not
required from the publisher.
ISBN 978-981-4316-00-2 (Hardcover)
ISBN 978-981-4364-61-4 (eBook)
Printed in the USA

Contents
Preface
ix
1. Quantum Dot Synthesis Methods 1
Yurii K. Gun’ko and Stephen Byrne
1.1 Introduction 1
1.2 High-Temperature Synthesis in Organic Solvents 2
1.2.1 Organometallic Synthesis 2
1.2.2 QD Synthesis from Non-Organometallic
Precursors 7
1.2.3 Microwave Synthesis 10
1.2.4 Transfer of QDs from Organic to
Aqueous Phase 11
1.3 Direct Aqueous Syntheses of QDs 14
1.4 Micellar Synthetic Approaches 17
1.5 Solvothermal Approaches 18
1.6 QD Luminescence Improvement 20
1.6.1 Surface Passivation and Core–Shell
Structure Formation 20
1.6.2 Photoetching of QDs 24
1.6.3 Role of Capping Ligands 27
1.7 Further Functionalisation and Bioconjugation of QDs 30
1.8 Concluding Remarks and Future Outlook 33
2. Biocompatible CdSe–ZnS Core–Shell Quantum Dots 43
Ibrahim Yildiz and Françisco M. Raymo
2.1 Semiconductor Quantum Dots 43
2.2 CdSe–ZnS Core–Shell Quantum Dots 44
2.3 Ligand Exchange 46
2.4 Ligand Interdigitation 51
2.5 Bioconjugation 52

vi
Contents
2.6 Cytotoxicity 56
2.7 Conclusions 56
3. Electrochemical Properties of Semiconductor
Quantum Dots 63
Matteo Amelia, Alberto Credi, and Serena Silvi
3.1 Introduction 63
3.2 Basic Electronic Properties of QDs 64
3.3 Overview of Electrochemical Techniques Employed
for the Investigations on QDs 67
3.3.1 Voltammetry 68
3.3.2 Electrochemiluminescence 70
3.3.3 Spectroelectrochemistry 71
3.4 CdSe Nanocrystals 72
3.4.1 Voltammetry 72
3.4.2 Electrochemiluminescence 78
3.4.3 Spectroelectrochemical Measurements 82
3.5 CdTe Nanocrystals 85
3.5.1 Voltammetric Measurements 85
3.5.2 Electrochemiluminescence 87
3.5.3 Spectroelectrochemical Measurements 89
3.6 Nanocrystals Functionalized with Electroactive
Molecules 89
3.7 Applications of Electroactive Quantum Dots 92
3.7.1 Electrochemical QD Sensors 92
3.7.2 Electrochemiluminescent QD Sensors 95
3.7.3 QD-Based Electrochemical Signal Transducers 99
3.7.4 Other Systems 101
3.8 Conclusions 104
4. Electron Transfer Quenching for Biosensing with
Quantum Dots 111
David E. Benson, Stacey R. De Haan, Chase E. Hulderman,
and Marla D. Swain
4.1 Electron Transfer Quenching 113
4.2 Initial Receptor-Based Biosensors 119

Contents
vii
4.3 Protease-Based Biosensors Show Multiplexing Ability 121
4.4 Recent Distance-Dependent Biosensors
Demonstrate Analyte Modularity 122
4.5 Toward Biological Imaging of Analyte Concentrations 125
5. Quantum Dot Probes Based on Energy
Transfer Mechanisms 135
John F. Callan, Bridgeen McCaughan, Colin Fowley, Narinder Singh,
Navneet Kaur, and Suban Sahoo
5.1 Introduction 135
5.2 pH, Ion and Small Molecule FRET Sensors 138
5.3 QD-Peptide/Oligonucleotide FRET Sensors 148
5.4 QD–Antibody Conjugates 152
5.5 QD FRET Probes for Enzyme Activity 154
5.6 Conclusions 158
6. Quantum Dot Reactive Oxygen Species Generation
and Toxicity in Bacteria: Mechanisms and
Experimental Pitfalls 163
Jay Nadeau
6.1 Overview 163
6.2 Quantum Dots Cores, Shells, and Caps 164
6.3 Band Edge Energies and Possible Reactions
in Solution 168
6.4 Measuring Reactive Oxygen Species in the
Presence of QDs 171
6.5 Pitfalls: Dyes to Use with Caution 176
6.6 Deliberate Toxicity: Photosensitized QDs 177
6.7 Toxicity to Bacteria: Introduction 181
6.8 CdSe Core QDs 184
6.9 CdSe/ZnS and Photosensitization 193
6.10 Discussion 196
Index 205

Preface
The past two decades have witnessed the emergence of semiconductor
quantum dots (QDs) as versatile nanoparticles with a
wide range of applications from energy-efficient lighting and displays
to biomolecular sensors. This book focuses on the incorporation of
QDs into optical- and electrochemical-based sensing systems for
chemical and biologically relevant target analytes. This arena
has traditionally been dominated by organic-dye-based sensors.
However, the realisation of the impressive optical properties of
QDs has seen them emerge as serious rivals to their all-organic
counterparts. QDs are now commercially available from many
different vendors with a wide range of surface chemistries suitable
for derivatisation.
In this book, we chart the progress in the development of QDs
over the past two decades with a particular focus on the use of
CdS-, CdSe- and CdTe-based QDs in sensing systems. Chapter
1 details the range of synthetic methods used to prepare QDs,
including solvothermal, aqueous-based, microwave-assisted and
micellar approaches with the benefits and potential drawbacks
of each approach outlined. The preparation of biocompatible QDs
is discussed in Chapter 2, which details how native hydrophobic
QDs can be transferred into aqueous solution using methods such
as ligand exchange and amphiphilic polymer encapsulation. Again,
the advantages and disadvantages of the different approaches for
the preparation of biocompatible QDs are outlined.
Modifying the surface of QDs with organic ligands or biomolecules
is central to the development of QD-based sensors. This surface
derivatisation can have a dramatic effect on the electrochemical
properties of the semiconductor nanoparticle and affect its optical
performance. Chapter 3 discusses the electrochemical properties
of core and core–shell QDs and how these properties can change
depending on the nature and thickness of the shell and the type
of ligands attached to its surface. This chapter also details how
the electroactivity of QDs can be exploited in the development of
electrochemical-based sensing systems.

Preface
Although examples of electrochemical-based QD sensing
are emerging, optical-based sensing methods still dominate the
literature. The modulation of the QD optical signal in the analyte-free
and bound states can be controlled by electron transfer or energy
transfer mechanisms. Chapter 4 discusses how electron transfer
between the QD and attached ligands or between the QD and the
analyte itself (if the analyte is redox active) can be utilised to develop
QD-based sensors. Chapter 5 details how QDs can be utilised as
energy donors and integrated with a wide range of energy acceptors
in energy transfer (FRET)-based sensors. Sensors for a wide range
of analytes are discussed, ranging from simple protons to complex
biomolecules. Finally, Chapter 6 discusses how differences in the
core–shell composition of QDs and physical/chemical factors such
as the size and nature of attached ligands can influence their toxicity
in prokaryotic cells.
The aim of this book is to give the reader a detailed overview of
how QDs can be prepared and incorporated as the signalling unit
in electrochemical/optical-based sensors. The editors are indebted
to the chapter authors for their contributions, the Pan Stanford
publishing group and the Universities of Ulster and Miami for their
assistance and support. We hope this book will be a useful reference
text and will help in promoting QDs as viable alternatives in the
design of optical sensors.
John F. Callan
Françisco M. Raymo
Winter 2012