Biomedical Engineering Reference
In-Depth Information
4.6
Impedimetric Genosensors for Point-of-Care
Diagnosis
h e analysis of DNA for point-of-care medical diagnosis is focused on two
main issues: the identii cation of a specii c DNA sequence belonging to
some microorganisms or virus which are the vectors for the development
of a certain disease, and the identii cation of nucleotide polymorphisms on
specii c genes, the presence of which is related to the development of a spe-
cii c disease. A single nucleotide polymorphism (SNP) is a DNA sequence
variation occurring when a single nucleotide in the genome dif ers between
members of the same species. h e SNPs can occur in every 100-300 base
pairs and have been correlated to the development of dif erent inherited
diseases and genetic disorders.
In the application for the detection of a real sample, synthetic sequences are
immobilized on the electrode surface, which are complementary to the gene
of interest. h e kind of nitrogenous bases and their order in the specii c target
gene can be found in the several “gene banks” or public databases available on
the Web. At er that, for the detection of the target gene, the real sample (e.g.,
microorganism or virus culture, cell culture, blood cells or other human l u-
ids) needs to be pretreated in order to extract the nucleic acid (DNA or RNA),
purify it, and i nally amplify it by polymerase chain reaction (PCR).
For the i rst purpose, impedimetric genosensors employing nanoma-
terials have been applied for the identii cation of DNA sequences specii c
for human immunodei ciency virus (HIV) [144, 154, 155] or belonging to
H1N1 inl uenza A virus [93]. Also, impedimetric genosensors have been
used to detect the Hepatitis B virus [94]. In the detection of polymorphisms
on a specii c gene, impedance spectroscopy was successfully employed
for the identii cation of DNA sequences correlated to the development of
Alzheimer's disease [18, 119, 121], kidney syndrome [69], metabolic syn-
drome [156], and cystic i brosis [30, 31,137, 157, 158], the latter, one of the
most common genetically inherited diseases in Northern Europe. A sensi-
tive and specii c detection of genes from Staphylococcus aureus bacteria
with antibiotic resistance employing a label-free impedance protocol made
possible the therapy with the optimal antibacterial agent [159], in a lucid
example of theranostics, the use of proper diagnostics to tailor the therapy.
A further work from the same laboratory demonstrated the diagnostic of
type of human wound infection at point-of-care testing, at the fM concen-
tration level, without any PCR or labeling step. h is was possible through
use of a peptide nucleic acid (PNA) as probe and optimized electrode
platform with specii c self assembled monolayer over gold [160]. Also, in
