Silica-Based Nanoparticles: Design and Properties - Advanced Fluorescence Reporters in Chemistry and Biology - page 237

nanoparticles were applied to multiplexed immunoassays and the simultaneous
detection of multiple samples. Further, the dual-DDSNs were extended to triple-
DDSNs [ 12 ]. With the assistance of F¨ster resonance energy transfer (FRET)
various distinct colors from green to dark red were obtained (Fig. 3 ).
Often, rather than emission of multiple wavelengths, the purpose of doping more
than one type of dye molecules is to use one dye as an internal standard [ 6 , 62 ], such
as a real-time ratiometric oxygen nanosensor employing probes encapsulated by
biologically localized embedding (PEBBELs) [ 63 ]. In this nanosensor, an oxygen-
sensitive dye, Ru(II)-tris (4,7-diphenyl-1,10-phenanthroline) chloride (Ru(dpp) 3 2+ ),
was doped as the oxygen probe. Meanwhile, an oxygen-inert dye, Oregon Green
488-dextran, was doped as a reference. In the presence of oxygen, the fluorescence
of Ru(dpp) 3 2+ was quenched, while the fluorescence signal of the reference
remained relatively stable. The results showed that the fluorescence intensity ratio
of these two dyes was inversely proportional to the concentration of oxygen. Thus
the oxygen could be quantitatively detected using the PEBBELs. The reference dye
as an internal standard ensured the accuracy of the measurement.
2.3.2 Core-Shell Configurations
Recently, the design of multiple-layer DDSNs becomes popular [ 61 ]. These multi-
ple-layer configurations can be categorized as a core-shell structure. Frequently,
this core-shell structure involves metal enhancement. The dye-doped silica exists
either as a fluorescent core coated with a silica shell or as a fluorescent shell on a
metal core. These new designs have provided DDSNs with advanced fluorescence
Fig. 3 (a) Normalized excitation and emission spectra of 5-(and-6)-carboxy-fluorescein, succini-
midyl ester, rhodamine 6G (R6G), and 6-carboxy-X-rhodamine dyes in pH 7.4 phosphate buffer.
(b) Confocal fluorescence image of a mixture of five types of microsphere-DDSN complexes
under 488-nm Argon-ion laser excitation. Reproduced with permission from Ref. [ 12 ]