Low-Cost Microdevices for Point-of-Care Testing - Point-of-Care Diagnostics on a Chip - page 5

the range of analytes detected by low-cost microdevices at point-of-care and their
specific applications.

1.3 Classes of Analytes

Microdevices have been used in academic, government, nonprofit, and commercial
settings to detect a range of analytes using many types of biological fluids. These
studies have demonstrated assays with better performance than benchtop tests with
regards to speed, portability, sensitivity, and multiplexing. The classes of analytes
detected include proteins, nucleic acids, cells, and small molecules [ 5 ]. Each analyte
class will be described in the section on applications.

1.3.1 Proteins

Proteins in clinical specimens in whole blood, serum/plasma, saliva, urine, and other
sample matrices have been used for clinical diagnostics and monitoring disease
states [ 18 ]. Microdevice-based technologies at point-of-care for detecting proteins
have included both immunoassays and enzymatic assays. Currently available
clinical tests for microdevices at point-of-care include viral infections (anti-HIV
antibodies, antibodies against influenza A/B virus, rotavirus antigens), bacterial
infections (antibodies against Streptococcus AandB, Chlamydia trachomatis ,
Treponema pallidum ), parasitic infections (histidine-rich protein 2 for P. falciparum ,
trichomonas antigens), and noncommunicable diseases (PSA for prostate cancer,
C-reactive protein for inflammation, HbA1c for plasma glucose concentration)
[ 5 , 19 , 20 ]. For example, a saliva-based nano-biochip immunoassay has been
constructed to detect a panel of C-reactive protein, myoglobin, and myeloperoxidase
in acute myocardial infarction patients [ 21 ].

1.3.2 Cells

Cell-based POC testing is often needed for disease diagnosis and hematological
analysis. Full blood cell counts provide information in diagnosing and monitoring
conditions such as anemia and HIV/AIDS. For instance, CD4

C

lymphocyte
counting is used to monitor the progression of HIV/AIDS, and microdevices
have been developed to substitute the conventional method (bulky and expensive
instruments such as flow cytometry) for POC testing. Traditional methods also often
require trained personnel and ground electricity. On-chip cell sorting techniques
from heterogeneous cell suspensions (such as whole blood) can be classified
into two main categories: size- and density-based techniques and affinity-based