Osteoarthritis (OA) is one of the most common human diseases, and the occurrence of OA is likely to increase with the increase of population ages. The diagnosis of OA is based on patientrelevant measures, structural measures, and measurement of biomarkers that are released through joint metabolism. Traditionally, radiography or magnetic resonance imaging (MRI) is used to diagnose OA and predict its course. However, diagnostic imaging in OA provides only indirect information on pathology and treatment response. A sensing of OA based on the detection of biomarkers insignificantly improves the accuracy and sensitivity of diagnosis and reduces the cost compared with that of radiography or MRI. In our former study, we proposed microfluidic platform to detect biomarker of OA. But the platform can detect only one biomarker because it has one microfluidic channel. In this report, we proposes microfluidic platform that can detect several biomarkers. The proposed platform has three layers. The bottom layer has gold patterns on a Si substrate for optical sensing. The middle layer and top layer were fabricated by polydimethysiloxane (PDMS) using soft-lithography. The middle layer has four channels connecting top layer to bottom layer. The top layer consists of one sample injection inlet, and four antibody injection inlets. To this end, we designed a flow-balanced microfluidic network using analogy between electric and hydraulic systems. Also, the designed microfluidic network was confirmed by finite element model (FEM) analysis using COMSOL FEMLAB. To verify the efficiency of fabricated platform, the optical sensing test was performed to detect biomarker of OA using fluorescence microscope. We used cartilage oligomeric matrix protein (COMP) as biomarker because it reflects specific changes in joint tissues. The platform successfully detected various concentration of COMP (0, 100, 500, 1000 ng/ml) at each chamber. The effectiveness of the microfluidic platform was verified computationally and experimentally.
This paper presents a simple and reliable multi-immunosensing lab-on-a-chip detecting antibodies as multi-disease markers using electrochemical method suitable for a portable point-of-care system. Since multi-immunosensing LOCs are to be disposable and cheap, the complications associated with the liquid control need to be removed. The main complication arises from the active microfluidic part driven by the external electric power. In this paper, a multi-stacked PDMS LOC including PDMS passive valves is proposed. The sequential liquid driving by capillary attraction and the action of check valve provide a reliable immunosensing tool simply triggered by an air bladder push without an electrical power. The immunosensing-LOC with the size of "25mm × 20mm × 6 mm" is fabricated with PDMS using the replica molding and oxygen plasma bonding. The LOC consists of a PDMS valve, channel, and a glass substrate. The fluidic tests were performed using DI water. The liquids are controlled by two kinds of passive valve, one is capillary stop valve and the other is membrane type check valve. The capillary stop valve stops liquids using pressure barrier of expanded channel. The check valve stops the liquid triggered by an air bladder from flowing backward. The assembly of these two valves assures the well controlled liquid driving for the immunosensing. The model experiments were performed with anti-DNP antibody and anti-biotin antibody as target analytes. The antibodies conjugated with GOX are used as a signaling molecule for cyclic voltammetry. The different amplified signals show different target analyte affinities and make sure the multi-immunosensing.
Multichannel images of 11-Mercaptoundecanoic acid and 11-Mercapto-1-undecanol self-assembled monolayers (SAMs) together with a biospecific interferon-gamma (IFN-gamma)/anti-IFN-gamma antibody immunoreaction were observed by two-dimensional surface plasmon resonance (2D-SPR) imaging system. Patterning process for SAM was simplified by exploiting direct photooxidation of thiol bonding (photolysis) instead of conventional photolithography. Sharper images were resolved by using a white light source in combination with a narrow bandpass filter, minimizing the diffraction patterns on the images. The line profile calibration of the image contrast caused by different resonance conditions at each points on the sensor surface enabled us to discriminate the monolayer thickness in a sub-nanometer scale. For protein patterning, a precipitation scheme induced by biocatalytic reaction was implied for the signal amplification. Specific binding of IFN-gamma antigen with surface-immobilized antibody was found detectable down to the concentration of 1 ng/mL.