3.1 Molecular Diagnostics
Numerous MF systems have been used for the analysis of various molecules
including DNA, RNA and other chemicals for general purpose as well as for disease
detection. A large number of devices used for diagnosis of disease including
pathogen detection have reported MF as the general theme of fabrication
[ 73 ]. Most of the currently designed devices focus on single molecule or single
disease identification but the future lies in the fabrication of multiplexed MF
devices that can screen hundreds of diseases simultaneously. For detection of
bacteria, and virus two methods are commonly used i.e. immunosensing (discussed
in next subsection) and nucleic acid based detection. The later detection method
employed four fundamental steps (1) designing of a MF platform, (2) lysis of the
target bacterial or viral cells, (3) target DNA and RNA purification and amplifica-
tion, and (4) detection of the target analyte using various transducers. Malhotra
et al. has fabricated impedimetric microfluidic–based nucleic acid sensor for
quantification of DNA sequences specific to cancer. The MF chip was prepared
by patterning an indium–tin–oxide coated glass substrate followed by sealing with
PDMS microchannel (Fig.8.9)[ 74 ]. An integrated MF device used by Dimov
et al. for tmRNA purification and nucleic acid sequence-based amplification
[ 75 ]. The device consists of two separate chambers one for RNA purification and
other for nucleic acid amplification. The device efficacy was demonstrated by
integrating on-chip purification, amplification, and real-time detection of
100 Escherichia coli (E. coli)bacteria in 100 mL of crude lysate. The device
took less than 30 min for on-chip purification, amplification, and real-time detection
of 100E. colibacteria in 100 mL of crude lysate, thereby, demonstrating the device
efficacy. Recently, Chang et al. detected live bacteria from the human joint using an
MF platform based on ethidium monoazide (EMA) [ 76 ]. The detection process was
based on utilization of labeled gold nanoparticles. The limit of detection was 10^2 –
104 CFU for typing bacteria by an on-chip PCR. The system overcomes the
problem of human contamination by use of an integrated MF system replacing
the usage of RNA sample by EMA to distinguish live and dead bacteria. Lee
et al. reported 3D-printed MF device for rapid and facile detection ofE. coliin
milk [ 77 ]. They used stereo-lithography to fabricate a vertically designed helical
micro-channel around a cylindrical chamber. UV–Vis spectroscopy was used as the
detection method and the sensitivity achieved was 100 CFU mL^1. Boehm
et al. developed a simple and rapid biosensor with immobilized monoclonal anti-
bodies for the identification and detection of bacteria using an MF LoC [ 78 ]. The
MF chip utilizes impedance-based measurement and showed that the sensor could
detect 9 105 CFU mL^1 E. coliin the solution. The sensitivity of the chip with
immobilized bacteria is governed by the height of the sensing chamber. The
selectivity of the sensor to different bacterial strains was demonstrated by the
identification ofE. coliin a suspension ofE. coliandM. catarrhalis. Specific
extraction of DNA of Hepatitis B virus has been done and several other reports are
there for MF based detection of different viruses and bacteria [ 79 ].
8 Biological Applications of Microfluidics System 211