Nanoparticle-based biosensors and bioassays - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 442

14.3 NANOPARTICLE-BASED OPTICAL BIOSENSORS AND
BIOASSAY

The driving force behind the use of nanoparticle labels in optical biosensors (or bio-
assays) has been to address the signifi cant chemical and spectra limitations of organic
fl uorophores. Early work by Mirkin and coworkers demonstrated that the aggregation of
gold nanoparticles, induced by DNA hybridization, leads to materials with remarkable
optical properties [10, 11]. For example, the distance-dependent optical properties of
aggregated gold nanoparticles were exploited for developing a simple and fast colorimet-
ric protocol for detecting polynucleotides [11]. Such hybridization-induced aggregation
of nanoparticle-modifi ed DNA led to a rapid change of the solution color from red to
blue. The resulting gold-nanoparticle-DNA bioassemblies displayed remarkably sharp
DNA melting curves that allowed convenient differentiation of oligonucleotides with
single-base imperfections [10, 12]. Taton et al. described a highly sensitive scanomet-
ric DNA array detection based on the use of oligonucleotide targets, labeled with gold
nanoparticles, for recognizing DNA segments on a chip (Fig. 14.1) [13]. A nanoparticle-
promoted reduction of silver(1) led to a dramatic (105-fold) signal amplifi cation and to

S' GGA TTA TTG TTA - AAT ATT GAT AAG GAT 3
CCT AXT AAC AAT TTA TAA CTA TTC CTA

Au

X = A (complementary),
G,C,T (mismatched)

( target DNA )

1.

Au

2.

Au

Ag

Ag
hydroquinone
(pH 3.8)

Au

Ag(s)
quinone

FIGURE 14.1 Scanometric DNA array detection with enlarged nanoparticle probes. Use of oligonucle-
otide targets, labeled with gold nanoparticles, for recognizing DNA segments on a chip (reproduced from
[13] with permission).