Nanobiosensors - Nanomaterials for Medical Applications - page 132

Fujiwara et al. recently found that duplex DNA in phosphoric acid form (or
in acidic solution) was successfully adsorbed into mesoporous silicas even in
low-salt aqueous solution. The adsorption behaviors of DNA in diluted NaCl
solutions into mesoporous silicas were influenced by the pore diameter between
2.80- and 3.82-nm peak pore diameters. They predicted that the adsorption
resulted from the formation of the hydrogen bond between P(O)OH groups in
DNA and adsorbed water, SiOH groups, or both on silica surfaces were the
main factors for the adsorption.
4.3.2 Direct Adsorption Protocol
Direct adsorption of biomolecules on NMs may be done following conventional
adsorption techniques. 51 The adsorption method results from hydrophobic inter-
action or electrostatic interaction between the biomolecules and the NP surface.
A sample adsorption method used by Wang et al. is described below.
4.3.2.1 Chemicals
(1) 136 µL of 10-µM dye-labeled ssDNA.
(2) 400 µL of 5-nm AuNP hydrosol or to 200 µL of 10-nm AuNP hydrosol.
(3) 10 mM phosphate buffer, pH 7.0.
(4) TE (20 mM Tris-HCl and 20 mM EDTA, pH 7.5) with 0.1 M NaCl.
4.3.2.2 Protocol
(1) ssDNA was adsorbed on AuNPs by adding 136 µL of 10-µM dye-labeled
ssDNA solution to 400 µL of 5-nm AuNP hydrosol or to 200 µL of 10-nm
AuNP hydrosol.
(2) To this was added 10 mM phosphate buffer (pH 7.0) to make the final con-
centration of ssDNA 1.36 µM for 5-nm AuNPs or 2.72 µM for 10-nm AuNPs.
(3) The mixture was incubated for 24 h inside the refrigerator.
(4) NaCl solution was added to a final concentration of 0.1 M.
(5) The solution was incubated further for 40 h.
(6) The DNA +AuNP was purified through centrifugation for the removal of
excess DNA.
(7) The red oily precipitate was washed with 0.1 M PBS and then redispersed
in TE with 0.1 M NaCl.
(8) The absorption signal was measured using a spectrophotometer.
This protocol was used as described. 51 The parameters must be optimized in
every situation to suit the needs of the experiment.
Detection of specific ONT sequences has important applications in medi-
cal research and diagnosis. 13,20,21,33,40,61-64 In most cases, specific sequence are
identified through hybridization of an immobilized probe that is complementary
to the target analyte after the latter has been modified with a covalently linked
label such as a fluorescent or enzyme tag. 13,33,37,40,61,65 ONT detection schemes