256
J. Xu et al.
facilitated cell detection to give a sharp, constant, and unambiguous signal because
healthy RBCs are able to squeeze through narrow microchannels with diameters as
small as 2 µm. Schaap et al. reported the rapid screening, real-time monitoring, and
initial classification of algae using a WG-integrated optofluidic device [76]. Rapid
identification of algae species is useful for assessing water quality and monitoring
adverse events in response to an increase in nutrients such as nitrates or phosphates.
The device consisted of a square channel with a cross-section of 100 µm × 100 µm
and a 90° curved WG whose end facet was situated perpendicular to the surface of
the square channel (Fig. 8.3b). The curvature of the WG prevented uncoupled light
from interacting with the photodiode. The radius of curvature was 18 mm, as determined based on laser-induced refractive index change, so as to avoid bending losses.
Initially, the sample-containing water was introduced into the channel, after which
a laser source delivered by an optical fiber was coupled into the WG to illuminate
the entire cross-section of the channel. Finally, the light passing through the channel
was analyzed with a four-quadrant photodetector. The movement of a cell or particle
through the channel cast a shadow on the photodetector, and the four quadrants of
the photodetector generated two specific signals depending on the size and shape of
the samples, allowing identification of the species. Using this device, nine different
species of algae flowing in the channel could be identified, with an accuracy of 85%.
Bragheri et al. performed successive single-cell fluorescence detection and sorting
in WG-integrated optofluidic devices based on fused silica [25]. The device design,
shown in Fig. 8.3c, was based on an X-shaped channel. Two input channels were
merged into a single, center straight channel in which fluorescence detection and
sorting were performed in sequence, followed by separation into two output channels. The liquid sample containing cells or particles is introduced from input IN1,
while a buffer solution was obtained from input IN2. By appropriately controlling the
flow rates of both solutions, a laminar flow was produced such that the entire liquid
sample introduced from input IN1 was expelled through output OUT1 along with
cells or particles, while the entire buffer solution from the IN2 was sent to OUT2.
As a result, the target cells or particles in the sample liquid could be detected by
fluorescence measurements using a laser beam delivered via a fluorescence waveguide (FWG). When a specific fluorescence signal from a target cell or particle was
detected, the optical force laser beam was switched on to guide the signal to the
channel via the sorting waveguide (SWG) with a moderate delay time. As a result,
the optical force laser beam pushed the target cell or particle into the buffer solution
to eventually sort it into OUT2.
Integration of various other microoptic components, such as microlenses, is
possible by FLAE of glass substrates [77, 78]. Wang et al. employed an optofluidic device together with WGs and microlenses for absorption and fluorescence
spectroscopic analysis of liquid samples. The device is illustrated in Fig. 8.3d, which
shows the long WG connected to a microreservoir formed in Foturan glass [77].
This WG was used to transfer either the fluorescence excitation light from a laser
or a broadband beam from a white lamp for absorbance measurements. To avoid
divergence of optical signals, two microlenses were also integrated into the device
by FLAE, both beside and behind the microreservoir. In this case, the microreservoir
J. Xu et al.
facilitated cell detection to give a sharp, constant, and unambiguous signal because
healthy RBCs are able to squeeze through narrow microchannels with diameters as
small as 2 µm. Schaap et al. reported the rapid screening, real-time monitoring, and
initial classification of algae using a WG-integrated optofluidic device [76]. Rapid
identification of algae species is useful for assessing water quality and monitoring
adverse events in response to an increase in nutrients such as nitrates or phosphates.
The device consisted of a square channel with a cross-section of 100 µm × 100 µm
and a 90° curved WG whose end facet was situated perpendicular to the surface of
the square channel (Fig. 8.3b). The curvature of the WG prevented uncoupled light
from interacting with the photodiode. The radius of curvature was 18 mm, as determined based on laser-induced refractive index change, so as to avoid bending losses.
Initially, the sample-containing water was introduced into the channel, after which
a laser source delivered by an optical fiber was coupled into the WG to illuminate
the entire cross-section of the channel. Finally, the light passing through the channel
was analyzed with a four-quadrant photodetector. The movement of a cell or particle
through the channel cast a shadow on the photodetector, and the four quadrants of
the photodetector generated two specific signals depending on the size and shape of
the samples, allowing identification of the species. Using this device, nine different
species of algae flowing in the channel could be identified, with an accuracy of 85%.
Bragheri et al. performed successive single-cell fluorescence detection and sorting
in WG-integrated optofluidic devices based on fused silica [25]. The device design,
shown in Fig. 8.3c, was based on an X-shaped channel. Two input channels were
merged into a single, center straight channel in which fluorescence detection and
sorting were performed in sequence, followed by separation into two output channels. The liquid sample containing cells or particles is introduced from input IN1,
while a buffer solution was obtained from input IN2. By appropriately controlling the
flow rates of both solutions, a laminar flow was produced such that the entire liquid
sample introduced from input IN1 was expelled through output OUT1 along with
cells or particles, while the entire buffer solution from the IN2 was sent to OUT2.
As a result, the target cells or particles in the sample liquid could be detected by
fluorescence measurements using a laser beam delivered via a fluorescence waveguide (FWG). When a specific fluorescence signal from a target cell or particle was
detected, the optical force laser beam was switched on to guide the signal to the
channel via the sorting waveguide (SWG) with a moderate delay time. As a result,
the optical force laser beam pushed the target cell or particle into the buffer solution
to eventually sort it into OUT2.
Integration of various other microoptic components, such as microlenses, is
possible by FLAE of glass substrates [77, 78]. Wang et al. employed an optofluidic device together with WGs and microlenses for absorption and fluorescence
spectroscopic analysis of liquid samples. The device is illustrated in Fig. 8.3d, which
shows the long WG connected to a microreservoir formed in Foturan glass [77].
This WG was used to transfer either the fluorescence excitation light from a laser
or a broadband beam from a white lamp for absorbance measurements. To avoid
divergence of optical signals, two microlenses were also integrated into the device
by FLAE, both beside and behind the microreservoir. In this case, the microreservoir