proteins and analyze them for the discovery of biomarkers using matrix-assisted laser

desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS), and liquid

chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) [9–11].

The common gynecological malignancy is endometrial cancer (ECa). It affects 6% of

women worldwide. The early-stage diagnosis of endometrial cancer is difficult. The non-

invasive and efficient diagnosis of ECa is through the detection of urinary proteins of ECa

patients. Urine is one of the important biofluids for screening protein biomarkers. The

kidney, prostate, and bladder cancers are also quantified by the urinary proteins. Urinary

proteins separated through 2DE can be analyzed by densitometry, mass spectrometry,

and database search. In a study conducted by Mu, Alan Kang-Wai, et al., urinary proteins

of ECa were analyzed by 2DE where Zn-α-2-glycoprotein, α-1-acid glycoprotein, and C59

were present in the urine of patients and the lower levels of nebulin proteins were

marked when compared with the control [12].

Huang, Hong‐Lei, et al. in their work analyzed the protein biomarkers of breast cancer

using 2DE. They identified a link between the proteins of breast cancer and tumor­

igenesis. They distinguished the normal cells from non-invasive and invasive cancerous

cells. They quantified the extracellular secreted proteins and the total cellular proteins

from normal and cancerous breast cancer cells. They identified 133 differentially ex­

pressed proteins and concluded that unreported proteins identified in their study have a

positive correlation with two-dimensional difference gel electrophoresis (2D-DIGE)

data. The novel proteins in their study can be used as diagnostic and therapeutic markers

for cancer [13].

8.3 Enzyme-Linked Immunosorbent Assay (ELISA)

ELISA is a diagnostic tool in clinical investigations. It provides selective, sensitive,

quantitative, and reproducible results in analyzing the analytes. It is a kind of gold

standard technique for detecting biomarkers. It detects antibodies, antigens, proteins,

glycoproteins, and hormones. It is used to test human immunodeficiency virus (HIV)

infections, pregnancy, and blood typing. ELISA is unable to detect the disease at an early

stage as biomarkers concentration is lower than the limit of detection of ELISA.

Oligonucleotide-based immunosorbent assay is being used nowadays for achieving more

sensitive results [14–16].

ELISA identifies one kind of biomarker at a time. In clinical diagnosis, a single bio­

marker hardly meets the clinical demand. The identification of multiple biomarkers

may enhance the accuracy of the diagnosis of various diseases. Semiconductor quantum

dots-based fluorescent immunosorbent assay is more sensitive, simultaneous, and

multiplexed in identifying the multiple biomarkers. Inflammatory biomarkers are the

indicators of many diseases. Low levels of C-reactive protein (CRP) indicate the pa­

thogenesis of cardiovascular disease while serum amyloid A (SAA) marks bacterial in­

fections. A dual quantum dot-based fluorescence-linked immunosorbent assay (FLISA)

was performed for detecting CRP and SAA. The as-fabricated assay has a broad linear

range and lower limits of detection for both proteins. The assay results showed good

specificity and efficiency and can thus be utilized for the simultaneous identification and

quantification of other disease biomarkers in in-vitro diagnostics and are described in

Figure 8.1 [17].

Biomarker Detection

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