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mouse immunoglobulin G (GaM-IgG), was conjugated (Fig. 9.13). Proteins,
such as polyclonal mouse IgG or human serum albumin (HSA), were detected
by Raman scattering upon the binding of GaM-IgG-conjugated SWCNTs
(GaM-IgG-SWCNTs). Surprisingly, the detection limit of the SWCNT Raman
assay was three orders of magnitude superior than standard luorescence
assays. Moreover, the authors suggested that, although this work focused on
antibody-antigen interactions, it could be applied for probing protein-protein
interactions and nucleic acid hybridisation as well. That is why in a further
experiment, 72 the researchers labelled cancer cells bearing speciic receptors
with three differently “coloured” SWCNTs conjugated with various targeting
ligands; they included Herceptin (anti-Her2), Erbitux (anti-Her1) and RGD
peptide. This allowed multicolour Raman imaging of cells in a multiplexed
manner ( Fig. 9.14) .
Alternatively, semiconducting SWCNTs were proposed as NIR luorescent
tags for selective probing of cell surface receptors and cell imaging; this was
demonstrated by the conjugation of SWCNT-PEG with antibodies such as
Rituxan, which was able to selectively recognise CD20 receptors present on
the cell surface of B cells, with minimal non-speciic binding. 73
GaM-IgG- SWNT
aHSA
HSA
Au/6arm -PEG -COOH
Figure 9.13 Sandwich assay scheme. Immobilised proteins in a surface spot were
used to capture an analyte (antibody) from a serum sample. Detection of the analyte
by Raman scattering measurement was carried out after incubation of SWCNTs
conjugated to goat anti-mouse antibody (GaM-IgG-SWCNTs), speciic to the captured
analyte. Figure redrawn from Chen et al . 71 See also Colour Insert.
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