Blood
testing allows for diagnosis and monitoring of numerous conditions
and illnesses; it forms an essential pillar of the health industry
that continues to grow in market value. Due to the complex physical
and biological nature of blood, samples must be carefully collected
and prepared to obtain accurate and reliable analysis results with
minimal background signal. Examples of common sample preparation steps
include dilutions, plasma separation, cell lysis, and nucleic acid
extraction and isolation, which are time-consuming and can introduce
risks of sample cross-contamination or pathogen exposure to laboratory
staff. Moreover, the reagents and equipment needed can be costly and
difficult to obtain in point-of-care or resource-limited settings.
Microfluidic devices can perform sample preparation steps in a simpler,
faster, and more affordable manner. Devices can be carried to areas
that are difficult to access or that do not have the resources necessary.
Although many microfluidic devices have been developed in the last
5 years, few were designed for the use of undiluted whole blood as
a starting point, which eliminates the need for blood dilution and
minimizes blood sample preparation. This review will first provide
a short summary on blood properties and blood samples typically used
for analysis, before delving into innovative advances in microfluidic
devices over the last 5 years that address the hurdles of blood sample
preparation. The devices will be categorized by application and the
type of blood sample used. The final section focuses on devices for
the detection of intracellular nucleic acids, because these require
more extensive sample preparation steps, and the challenges involved
in adapting this technology and potential improvements are discussed.