Environmental Engineering Reference
In-Depth Information
nuclease is only sensitive against the ssDNA. In the presence of the
non-complementary/mismatched target, this nuclease will cleave the ssDNA, pro-
ducing deoxynucleotide monophosphates (dNMPs) that stabilized the AuNPs
against salt-induced aggregation of Na
+
.
11.5.3 Detection of Whole Cell Bacteria or Virus
AuNPs are often used with antibodies and aptamers for the detection of bacteria.
For example, the DNA probe complementary to the DNA or total RNA of the
microbe is immobilized on the surface of AuNP. The aggregation or separation of
the AuNPs which can result in different colours may indicate the presence or
absence of the target bacteria. In one study of using paper-based assay to detect
Mycobacterium tuberculosis
complex, primer complementary to a specific region
of the RNA polymerase beta subunit gene was conjugated to AuNP. The genomic
DNA and the AuNP probe were mixed together and added into the wells that were
printed on the surface of a paper which are filled with MgCl
2
. The binding of the
probe on the surface of the AuNPs with the genomic DNA will result in red colour
while the absence of the target protein will result in blue or purple colour [
65
]. In
another system, an antibody-based sensor using AuNPs was also developed for the
detection of
Francisella tularensis
[
66
].
11.5.4 Detection of Cancers
The presence of tumour cells is often used as a method to diagnose the occurrence
of cancer among patients. In one study, melanin, natural light absorber in melanoma
cells, was used to induce photoacoustic waves for the detection of tumour cells. To
induce optical contrast in the non-pigmented cancer cells, attachment of the AuNPs
to the prostate cancer cell line was carried out. This enables the detection of the
cells by photoacoustic flow meter [
67
]. In a different method of detection, after
performing the selective labelling of cancer cells in suspension, interaction between
the AuNP and the proteins expressed on the surface of the cell membrane was
carried out [
68
]. This system enables the detection of up to 4
10
3
cancer cells.
Imaging of cancer cells was also made possible by using anti-epidermal growth
factor receptor (anti-EGFR) antibodies immobilized on the surface of AuNPs that
form complex with the EGFR on the surface of the cancer cells [
69
].
