Nanosensors - Nanotechnologies for Water Environment Applications - page 425

abilities but may also have built-in coding systems for rapid and multiplex target
identification. Nanoparticle labeling is expected to be more sensitive, more flexible in
target selection (e.g., adding new genes or single-nucleotide mutations), more diversified
in bar coding, faster in binding kinetics due to the pseudo-homogeneous reaction, less
expensive to produce and less physically interferential in the biological recognition
events due to the nanoscale-size particles (Han et al., 2001).

Fluorescent
emi ssion

Laser

Laser

Fluorescent
emission

si lica

si lica

RuB py-dye
Surface antigen
antibody

Target DNA

RuBpy-dye
Biotin
Avidin

Capture
probe

Target cell

biochip

Figure 13.5 (a) RuBpy-doped silica nanoparticle based DNA labeling scheme using in
(Lian et al., 2004), (b) RuBpy-doped silica nanoparticle labeling based immunological
scheme used in (Zhao et al., 2004).

Figure 13.6 (a) Scanning electron microscopy (SEM) image of E. coli O157:H7 cell
incubated with dye doped NPs (b) SEM image of E. coli DH5 cells incubated with dye
doped NPs (negative control) (c) fluorescence image of a single E. coli O157:H7 cell.
Copyright PNAS 2004. Reproduced with permission.

It should be noted, however, that the gain in signal enhancement (hence the
improvement in detection limit) by using nanoparticle-based labeling approaches may
vary by several orders of magnitude at the cell and the DNA level. This is illustrated in
Figure 13.5 and Table 13.3, which compares the enhancement in detection limit from
two studies using similar dye-doped nanoparticle labeling; one uses the label at the cell