6 Bio-microelectromechanical Systems (BioMEMS) …
141
Corning display quality glass substrates were used to microfabricate the photodiodes arrays on them. Magnetron sputtering technique was used to deposit the
aluminum bottom contacts that were then patterned via photolithography and wet
etching technique to etch the contacts. Through PECVD, n-i-p a-Si:H photodiodes
were deposited. Doped p-type and n-type films were achieved through adding phosphine and diborane, respectively. Using RIE and a mixture of SF 6 and CHF 3 gases
the n-i-p stack was patterned and etched. Amorphous silicon nitride (a-SiN x ) was
deposited using PECVD for insulation of the sidewalls of the diodes, and by liftoff technique, has left an access on the top of the photodiodes for electrical contact.
Through sputtering method, a transparent top contact composed of ITO was deposited
on the device and patterned via lift-off. In order to protect the microfabricated structures, another a-SiN x passivation layer, was deposited via PECVD. RIE etching was
performed to allow access to pads. The photodiode chips were diced and wire-bonded
to a tailored designed PCBs which were positioned inside an aluminum box linked to
the circuit’s ground. The aluminum box consisted of two compartments: (i) a space
for the microcontroller and the amplifier PCB with a port for a USB connection, (ii)
and for the microfluidic devices combined with the photodiode PCB, with a lid to
protect it from the electromagnetic interference as well as the external light. Soft
lithography was used to fabricate the microfluidic devices and for the SU-8 mold
substrate the hard mask was used. This arrangement minimized the gap between the
SU-8 photoresist and the mask which led to a more accurate definition of the mold
structures.
A sequence of metal sputtering, photolithography and aluminum wet etch were
performed to fabricate an aluminum on glass hard mask. During the lithography, the
hard mask was cut before pouring the SU-8 50 over the top of the hard mask, which
was then spun, and baked. Afterwards, the SU-8 was subjected to UV and developed.
Additionally, a set of PMMA plates were first fabricated via laser ablation (CO 2 laser),
intended for definition of the PDMS device’s bulk shape and subsequently milled in
house to align the SU-8 molds with the PDMS bulk device. The SU-8 molds were
then placed onto the machined PMMA plates which produced the open microfluidic
inlets. The PDMS devices including the 3 inlets and the microfluidic structures and
were sealed. To increase the speed of capillary pumping, a piece of absorbent paper
was added to the end of the microfluidic circuit.
To demonstrate the performance of both the integrated detection system and
the autonomous capillary microfluidic device, a Model IgG/anti-IgG immunoassay
was employed. To perform the autonomous micro spot-based microfluidic ELISA,
luminol was used for CL generation as well as the anti-rabbit IgG labeled with HRP as
the target antibody (diluted in PBS). The autonomous capillary ELISA was launched
through placing the target antibody, PBS, and luminol solutions at 1st, 2nd and 3rd
inlets, respectively. To achieve the purpose of quantification and detection of the CL
signals, the microfluidic device was implanted in the integrated setup. In addition, to
align and hold the microfluidic device to the photodiode chip as an integrated LOC,
a set of machined PMMA parts, with the photodiode PCB connected were utilized.
The designed prototype conducted CL ELISA detection in approximately 15 min
with an antibody-antigen affinity constant of 2 10
7 M
−1 and with a LOD of 2 nM.
141
Corning display quality glass substrates were used to microfabricate the photodiodes arrays on them. Magnetron sputtering technique was used to deposit the
aluminum bottom contacts that were then patterned via photolithography and wet
etching technique to etch the contacts. Through PECVD, n-i-p a-Si:H photodiodes
were deposited. Doped p-type and n-type films were achieved through adding phosphine and diborane, respectively. Using RIE and a mixture of SF 6 and CHF 3 gases
the n-i-p stack was patterned and etched. Amorphous silicon nitride (a-SiN x ) was
deposited using PECVD for insulation of the sidewalls of the diodes, and by liftoff technique, has left an access on the top of the photodiodes for electrical contact.
Through sputtering method, a transparent top contact composed of ITO was deposited
on the device and patterned via lift-off. In order to protect the microfabricated structures, another a-SiN x passivation layer, was deposited via PECVD. RIE etching was
performed to allow access to pads. The photodiode chips were diced and wire-bonded
to a tailored designed PCBs which were positioned inside an aluminum box linked to
the circuit’s ground. The aluminum box consisted of two compartments: (i) a space
for the microcontroller and the amplifier PCB with a port for a USB connection, (ii)
and for the microfluidic devices combined with the photodiode PCB, with a lid to
protect it from the electromagnetic interference as well as the external light. Soft
lithography was used to fabricate the microfluidic devices and for the SU-8 mold
substrate the hard mask was used. This arrangement minimized the gap between the
SU-8 photoresist and the mask which led to a more accurate definition of the mold
structures.
A sequence of metal sputtering, photolithography and aluminum wet etch were
performed to fabricate an aluminum on glass hard mask. During the lithography, the
hard mask was cut before pouring the SU-8 50 over the top of the hard mask, which
was then spun, and baked. Afterwards, the SU-8 was subjected to UV and developed.
Additionally, a set of PMMA plates were first fabricated via laser ablation (CO 2 laser),
intended for definition of the PDMS device’s bulk shape and subsequently milled in
house to align the SU-8 molds with the PDMS bulk device. The SU-8 molds were
then placed onto the machined PMMA plates which produced the open microfluidic
inlets. The PDMS devices including the 3 inlets and the microfluidic structures and
were sealed. To increase the speed of capillary pumping, a piece of absorbent paper
was added to the end of the microfluidic circuit.
To demonstrate the performance of both the integrated detection system and
the autonomous capillary microfluidic device, a Model IgG/anti-IgG immunoassay
was employed. To perform the autonomous micro spot-based microfluidic ELISA,
luminol was used for CL generation as well as the anti-rabbit IgG labeled with HRP as
the target antibody (diluted in PBS). The autonomous capillary ELISA was launched
through placing the target antibody, PBS, and luminol solutions at 1st, 2nd and 3rd
inlets, respectively. To achieve the purpose of quantification and detection of the CL
signals, the microfluidic device was implanted in the integrated setup. In addition, to
align and hold the microfluidic device to the photodiode chip as an integrated LOC,
a set of machined PMMA parts, with the photodiode PCB connected were utilized.
The designed prototype conducted CL ELISA detection in approximately 15 min
with an antibody-antigen affinity constant of 2 10
7 M
−1 and with a LOD of 2 nM.