Biomedical Engineering Reference
In-Depth Information
(a) PSi /
DNA
(b) PSi /
DNA / cDNA
(c) Differential Signal
600
650
700 750
Wavelength (nm)
800
850
900
Fig. 7.15.
Photoluminescence spectra of a mesoporous silicon microcavity with a
thick defect layer supporting six clearly resolved reflectance dips (PL peaks). (
a
)
After functionalization of the pore surface with probe DNA segments; (
b
) after
capture of complementary DNA segments; (
c
) differential spectrum
a core sugar, and lipid A. As lipid A is common to all LPS subtypes, it
is a natural target. An organic receptor, tetratryptophan
ter-
cyclo pentane
(TWTCP) was designed and synthesized as the probe molecule. TWTCP
specifically binds to diphosphoryl lipid A in water with a dissociation constant
of 592 nM [59].
After the microcavity sensor was exposed to 3-glycidoxypropyltrimethoxy
silane, a mixture of TWTCP and glycine methyl ester was applied to the sen-
sor. Glycine methyl ester was used as a blocker molecule to avoid the reaction
of the four amino groups of the tetratryptophan receptor with the epoxide-
terminated PSi surface. As shown in Fig. 7.16, upon exposure of lysed Gram(-)
cells (
Escherichia coli)
to the immobilized TWTCP sensor, a 4 nm red shift of
the photoluminescence spectrum of the microcavity was detected [21]. How-
ever, when the sensor was exposed to a solution of lysed Gram(+) cells (
Bacil-
lus subtilis
), no shift of the spectrum was observed. These results were con-
firmed with all Gram(-) and Gram(+) bacteria tested.
7.3.3 Protein Detection
A protein biosensor based on macroporous silicon microcavity was demon-
strated with the streptavidin-biotin couple [8]. Biotin is a small molecule, while
streptavidin is relatively large (67 kDa), making its infiltration di
cult into
