3 Aptamer-Based Point of Care Testing Schemes
67
signature was detected around 830 GHz, fitted to a Lorentz oscillator. This signature
was thought to arise from the bending of hydrogen bonds formed between adjacent
hydrated DNA bases surrounded by water molecules [76].
The aptamer-based microfulidic chips have attracted attention due to their advantages of miniaturization, sensitivity and high specifity. Microbial detection is very
important in the field of clinical diagnosis. It is highly desirable to develop a sensitive
and rapid method for microbial detection. Zhang et al. developed a novel aptamerbased microfluidic chip NOA81 (Norland Optical Adhesive) for rapid and specific
recognition of Lactobacillus acidophilus. The microfluidic chip has four microchannels consisting four spots in which aptamers were immobilized on the glass surface
in order to capture the microorganism specifically [77].
Bhardwaj and Sandeep fabricated a PMMA microfluidic chip and combined the
chip with a simple fluorescence detection setup using optical fiber, filter, detector
and a commercial spectroscopy software. In their approach, they used two different
strategies to use aptamers as probes. In the first strategy, detection of any nucleic acid
could be doneusing simple DNA hybridization with aptamer probe. Such strategy
can be used in pathogenanalysis. They proved that using the known sequence of
ssDNA aptamer probe immobilized on the detection zone on microchip and its
FAM-labeled complementary strand could be passed over it for pathogen detection. In other method, they attempted detection of thrombin protein using sandwich
fluorimetric technique with primary and labeled secondary aptamer immobilized on
sensing region [78].
Luo et al. developed a microchip electrophoretic method for sensing E.coli
O157:H7 by using E. coli O157:H7 aptamer (apt-E) for specific bacteria recognition together with catalyzed hairpin assembly (CHA) for improving the sensitivity
of bacteria detection. Three nucleic acid strands (apt-E, hairpin H1, and H2) were
used in the CHA amplification. Since different quantities of H1/H2 complexes were
formed due to the circle amplification with different amounts of apt-E, the correlation
between the concentrations of apt-E and E. coli O157:H7, E. coli O157:H7 thus could
be quantified by the detection of H1/H2 complexes with microchip electrophoresis
(MCE) [79].
3.3.7 Microbeads and Nanomaterial-Based Aptasensors
Aptamers are flexible molecules that can be modified with chemical functional groups
compatible with microbeads or nanoparticles. Using a microbeads-based approach,
a glucose meter was used to detect a nonglucose target as a way to generate a
POC device. In this study, using streptavidin MagneSphere
® paramagnetic particles (PMPs) with average diameters of 1.0 ± 0.5 μm, anti-PDGF-BB aptamer was
used as the capturing probe. Then, aptamer-attached invertase was used for the detection. This combination was successful, and the conversion of sucrose by invertase was
observed by measuring the glucose molecules (Fig. 3.8). Using this setup, researchers
67
signature was detected around 830 GHz, fitted to a Lorentz oscillator. This signature
was thought to arise from the bending of hydrogen bonds formed between adjacent
hydrated DNA bases surrounded by water molecules [76].
The aptamer-based microfulidic chips have attracted attention due to their advantages of miniaturization, sensitivity and high specifity. Microbial detection is very
important in the field of clinical diagnosis. It is highly desirable to develop a sensitive
and rapid method for microbial detection. Zhang et al. developed a novel aptamerbased microfluidic chip NOA81 (Norland Optical Adhesive) for rapid and specific
recognition of Lactobacillus acidophilus. The microfluidic chip has four microchannels consisting four spots in which aptamers were immobilized on the glass surface
in order to capture the microorganism specifically [77].
Bhardwaj and Sandeep fabricated a PMMA microfluidic chip and combined the
chip with a simple fluorescence detection setup using optical fiber, filter, detector
and a commercial spectroscopy software. In their approach, they used two different
strategies to use aptamers as probes. In the first strategy, detection of any nucleic acid
could be doneusing simple DNA hybridization with aptamer probe. Such strategy
can be used in pathogenanalysis. They proved that using the known sequence of
ssDNA aptamer probe immobilized on the detection zone on microchip and its
FAM-labeled complementary strand could be passed over it for pathogen detection. In other method, they attempted detection of thrombin protein using sandwich
fluorimetric technique with primary and labeled secondary aptamer immobilized on
sensing region [78].
Luo et al. developed a microchip electrophoretic method for sensing E.coli
O157:H7 by using E. coli O157:H7 aptamer (apt-E) for specific bacteria recognition together with catalyzed hairpin assembly (CHA) for improving the sensitivity
of bacteria detection. Three nucleic acid strands (apt-E, hairpin H1, and H2) were
used in the CHA amplification. Since different quantities of H1/H2 complexes were
formed due to the circle amplification with different amounts of apt-E, the correlation
between the concentrations of apt-E and E. coli O157:H7, E. coli O157:H7 thus could
be quantified by the detection of H1/H2 complexes with microchip electrophoresis
(MCE) [79].
3.3.7 Microbeads and Nanomaterial-Based Aptasensors
Aptamers are flexible molecules that can be modified with chemical functional groups
compatible with microbeads or nanoparticles. Using a microbeads-based approach,
a glucose meter was used to detect a nonglucose target as a way to generate a
POC device. In this study, using streptavidin MagneSphere
® paramagnetic particles (PMPs) with average diameters of 1.0 ± 0.5 μm, anti-PDGF-BB aptamer was
used as the capturing probe. Then, aptamer-attached invertase was used for the detection. This combination was successful, and the conversion of sucrose by invertase was
observed by measuring the glucose molecules (Fig. 3.8). Using this setup, researchers