Biomedical Engineering Reference
In-Depth Information
ELISA, and whole-blood sample results were compared to those of both ELISA
and HerpeSelect HSV-1 and HSV-2 immunoblotting. The HSV-2 LFIA had a sen-
sitivity of 100% compared with HerpeSelect ELISA. Although the specificity was
97.3% there was cross-reactivity with HSV-1 IgG-positive serum samples, 2.9% for
rubella virus, and 6.2% for Epstein-Barr virus. There was concordance of results
between capillary whole blood, Ethylenediamine tetraacetic acid-treated (EDTA-
treated) venous whole blood, heparin-treated venous whole blood, and serum.
Hepatitis virus B was detected in LFIAs using antibodies that were covalently
conjugated onto europium chelate-loaded silica NPs with dextran as a linker.
154
The resulting NP conjugates were used as labels in LFIA for the quantitative detec-
tion of hepatitis B surface antigen (HBsAg) with a digital camera and Adobe Photo-
shop software. This assay was used to detect as low as 0.03 µg/L HBsAg which was
100 times lower than the colloidal gold-based LFIAs and lower than ELISA. The
assay gave a linear range at 0.05-3.13 µg/L. It was used to detect hepatitis B in 286
clinical samples the resulted in complete agreement with AuNP-LFIA and ELISA.
Tanaka et al.
155
used secondary antibodies labeled with AuNPs to enhance
the signal in an immunochromatographic assay for the detection of human
chorionic gonadotropin and total prostate-specific antigen in serum. The col-
orimetric assay resulted in lower detection limits of 1 pg/mL and 0.2 ng/mL,
respectively, in less than 15 min. This research showed that AuNPs can be used
for whole-blood analysis using their near-infrared emission.
Aside from excellent sensitivity and specificity, low cost, and rapid assays,
LFIA using NPs allow easy diagnosis of various diseases. There are over the
counter LFIA colloidal AuNPs for detection of pregnancy, ovulation, and HIV
infection. These AuNPs based LFIA are commonly used worldwide resulting in
a huge market for nanotechnology-based medical devices. It has been predicted
that the market size for nanotechnologies will increase by 10-30% annually.
156
4.8 APPLICATIONS
Today, there are already in vitro diagnostic products on the market, based on
NPs with estimated $780 million in sales for 2004.
157
For in vitro diagnostics,
NMs are used for the development of novel sensors and in vitro tests that offer
several advantages: improve the sensitivity of existing tests; allow for point-of-
care applications, or to develop new diagnostic test platforms. Nanotechnology
applications can be broadly divided into two main approaches: (1) the use of
NPs as markers for biomolecules and (2) novel sensor platforms that use NMs,
such as carbon nanotubes, lateral nanostructures, or nanothin surface layers.
A few examples of these NM-based in vitro diagnostic sensors are given below.
4.8.1 DNA Nanobiosensors
DNA nanobiosensors provide powerful tools for the rapid and sensitive determi-
nation of pathogens, diseases, genetic disorders, drug screening, and other in vitro
