Dye-Doped Polymeric Particles for Sensing and Imaging - Advanced Fluorescence Reporters in Chemistry and Biology - page 194

5 Selected Examples of Dye-Doped Polymeric Bead Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
5.1 Water-Dispersible Nanosensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
5.2 Dye-Doped Beads as Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
5.3 Dye-Doped Beads in Composite Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
5.4 Sensor Arrays Based on Dye-Doped Beads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
5.5 Magnetic Dye-Doped Polymeric Beads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
5.6 Dye-Doped Beads for Other Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
6 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

1 Introduction

Optical chemical sensors mostly rely on advanced materials that reversibly respond
to a chemical parameter in altering their optical properties [ 1 ]. A polymer serves not
only as a host material for an indicator but also as a permeation-selective mem-
brane. The sensor material is usually coated onto the tip of an optical fiber, a planar
transparent support or any other surface of interest (such as a surface of an aircraft
in case of pressure-sensitive paints). Dye-doped micro- and nanobeads represent yet
another format of optical sensor materials that became widespread in the last
decade [ 2 - 4 ]. These smart materials are self-contained analytical tools which can
be either used on their own (“nanosensors”) to measure an analytical parameter in
solution (extra- or intracellularly) or in combination with other beads in arrays and
composite materials such as multianalyte sensors. Compared to planar optodes that
sometimes make use of absorption-based indicators, the dye-doped beads almost
exclusively rely on luminescent indicators. Although one can certainly distinguish
between microbeads ( Ø

Ø

> 1 m m), submicrobeads (100 nm < < 1 m m) and

nanobeads ( Ø 100 nm), the borders are still rather vague. Some dendrimeric

systems also perform very similarly to dyed polymeric beads. Moreover, the
methods established for manufacturing of dye-doped micro- and nanobeads often
are the same, and so are the sensing chemistries used. Often beads bear no indicator
(that responds to the analyte of interest) but an inert luminescent dye, and act as
labels or tracers in various assays. In the following sections, we will describe the
materials and methods used for preparation of dyed beads, interrogation schemes
and provide examples of the sensing materials.

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2 Materials Used for Preparation of the Dye-Doped Beads

2.1 Monomers and Polymers

A variety of monomers and polymers have been used for preparation of sensing
beads and many more may also be suitable. Many polymers are already commer-
cially available as a dispersion of nano- or microbeads (such as e.g., carboxylated