Development of Label-Free Optical Immunoassay Platform Integrating a Nanofluidic Preconcentrator with a Periodic Metallic Nanograting Surface Plasmon Resonance Sensor
Date Issued
2016
Date
2016
Author(s)
Lee, Wei-Hang
Abstract
In the field of bio microelectromechanical systems (bio MEMS), detection of the low-abundance analytes without labelling is challenging because of difficulties of integration of preconcentration and label free sensing. Previously, an electrokinetic trapping (EKT)-based nanofluidic preconcentrator had been reported for providing a million-fold concentration factors that enable the validation of concentration process and the detection of trace and fluorescence-labelled analytes. However, the use of fluorescence-labelled analytes has suffered several disadvantages, e.g., additional sample preparation in an experimental workflow, high cost of labeling reagents, and difficulty in analyzing trace analytes. To monitor the concentration process without labelling, our group has presented a real-time dual loop electric current measurement system for label-free EKT-based nanofluidic preconcentrator. In this work, we further demonstrated a label-free biosensing platform by integrating a label-free nanofluidic preconcentrator with label-free surface plasma resonance(SPR) sensors. Bio molecular sample preconcentration was realized by a preconcentrator consisted of two microchannels, a concentration channel and a buffer channel, cast in Polydimethylsiloxane (PDMS) and a porous membrane (Nafion). The nanograting SPR sensor was fabricated by e-beam lithography, e-gun evaporation followed by the lift-off process. After glass-based SPR sensors and PDMS microchannels were fabricated, we patterned Nafion membrane at a specific position adjacent to the SPR sensor by using a microflow patterning method. Finally, PDMS-based microchannels were bonded to a glass patterned with Nafion and two square SPR sensors via bonding technique with oxygen plasma treatment. Recently, a 20 ng/ml Bovine serum albumin (BSA) in PBS was pumped into the platform, and was detected by SPR sensor with a red-shifted value of 0.42 nm. After ten minutes of preconcentration, 20 ng/ml BSA in PBS was detected with a red-shifted value of 5.33 nm. Comparing the references of the red-shifted values at different concentrations of BSA established in advance, the red-shifted value (5 nm) of 20 ng/ml BSA in PBS after preconcentration is the same as the red-shifted value of 200 μg/ml BSA in PBS. Hence, the preconcentration factor in this label-free platform was then determined to be approximately 10000 fold. In summary, a label-free immunoassay platform combining a preconcentrator which can improve the sensitivity limit by about 10000 fold with highly sensitive SPR sensors is realized. With a simple electrical and optical, low abundance analytes can be preconcentrated and sensed by this label-free platform.
Subjects
Electrokinetic-based Nanofluidic Preconcentration
Periodic Metallic Nanograting Surface Plasma Resonance (SPR)
Biosensor
Label-free Immunoassay
Lab on a Chip
Type
thesis
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