A microfluidic optical platform for real-time monitoring of pH and oxygen in microfluidic bioreactors and organ-on-chip devices.
ABSTRACT: There is a growing interest to develop microfluidic bioreactors and organ-on-chip platforms with integrated sensors to monitor their physicochemical properties and to maintain a well-controlled microenvironment for cultured organoids. Conventional sensing devices cannot be easily integrated with microfluidic organ-on-chip systems with low-volume bioreactors for continual monitoring. This paper reports on the development of a multi-analyte optical sensing module for dynamic measurements of pH and dissolved oxygen levels in the culture medium. The sensing system was constructed using low-cost electro-optics including light-emitting diodes and silicon photodiodes. The sensing module includes an optically transparent window for measuring light intensity, and the module could be connected directly to a perfusion bioreactor without any specific modifications to the microfluidic device design. A compact, user-friendly, and low-cost electronic interface was developed to control the optical transducer and signal acquisition from photodiodes. The platform enabled convenient integration of the optical sensing module with a microfluidic bioreactor. Human dermal fibroblasts were cultivated in the bioreactor, and the values of pH and dissolved oxygen levels in the flowing culture medium were measured continuously for up to 3 days. Our integrated microfluidic system provides a new analytical platform with ease of fabrication and operation, which can be adapted for applications in various microfluidic cell culture and organ-on-chip devices.
Project description:There is an increasing interest in developing microfluidic bioreactors and organs-on-a-chip platforms combined with sensing capabilities for continual monitoring of cell-secreted biomarkers. Conventional approaches such as ELISA and mass spectroscopy cannot satisfy the needs of continual monitoring as they are labor-intensive and not easily integrable with low-volume bioreactors. This paper reports on the development of an automated microfluidic bead-based electrochemical immunosensor for in-line measurement of cell-secreted biomarkers. For the operation of the multi-use immunosensor, disposable magnetic microbeads were used to immobilize biomarker-recognition molecules. Microvalves were further integrated in the microfluidic immunosensor chip to achieve programmable operations of the immunoassay including bead loading and unloading, binding, washing, and electrochemical sensing. The platform allowed convenient integration of the immunosensor with liver-on-chips to carry out continual quantification of biomarkers secreted from hepatocytes. Transferrin and albumin productions were monitored during a 5-day hepatotoxicity assessment in which human primary hepatocytes cultured in the bioreactor were treated with acetaminophen. Taken together, our unique microfluidic immunosensor provides a new platform for in-line detection of biomarkers in low volumes and long-term in vitro assessments of cellular functions in microfluidic bioreactors and organs-on-chips.
Project description:Continual monitoring of secreted biomarkers from organ-on-a-chip models is desired to understand their responses to drug exposure in a noninvasive manner. To achieve this goal, analytical methods capable of monitoring trace amounts of secreted biomarkers are of particular interest. However, a majority of existing biosensing techniques suffer from limited sensitivity, selectivity, stability, and require large working volumes, especially when cell culture medium is involved, which usually contains a plethora of nonspecific binding proteins and interfering compounds. Hence, novel analytical platforms are needed to provide noninvasive, accurate information on the status of organoids at low working volumes. Here, we report a novel microfluidic aptamer-based electrochemical biosensing platform for monitoring damage to cardiac organoids. The system is scalable, low-cost, and compatible with microfluidic platforms easing its integration with microfluidic bioreactors. To create the creatine kinase (CK)-MB biosensor, the microelectrode was functionalized with aptamers that are specific to CK-MB biomarker secreted from a damaged cardiac tissue. Compared to antibody-based sensors, the proposed aptamer-based system was highly sensitive, selective, and stable. The performance of the sensors was assessed using a heart-on-a-chip system constructed from human embryonic stem cell-derived cardiomyocytes following exposure to a cardiotoxic drug, doxorubicin. The aptamer-based biosensor was capable of measuring trace amounts of CK-MB secreted by the cardiac organoids upon drug treatments in a dose-dependent manner, which was in agreement with the beating behavior and cell viability analyses. We believe that, our microfluidic electrochemical biosensor using aptamer-based capture mechanism will find widespread applications in integration with organ-on-a-chip platforms for in situ detection of biomarkers at low abundance and high sensitivity.
Project description:Microfluidic sensing platforms facilitate parallel, low sample volume detection using various optical signal transduction mechanisms. Herein, we introduce a simple mixing microfluidic device, enabling serial dilution of introduced analyte solution that terminates in five discrete sensing elements. We demonstrate the utility of this device with on-chip fluorescence and surface-enhanced Raman scattering (SERS) detection of analytes, and we demonstrate device use both when combined with a traditional inflexible SERS substrate and with SERS-active nanoparticles that are directly incorporated into microfluidic channels to create a flexible SERS platform. The results indicate, with varying sensitivities, that either flexible or inflexible devices can be easily used to create a calibration curve and perform a limit of detection study with a single experiment.
Project description:A sensitive DNA isothermal amplification method for the detection of DNA at fM to aM concentrations for pathogen identification was developed using a non-stick-coated metal microfluidic bioreactor. A portable confocal optical detector was utilized to monitor the DNA amplification in micro- to nanoliter reaction assays in real-time, with fluorescence collection near the optical diffraction limit. The non-stick-coated metal microfluidic bioreactor, with a surface contact angle of 103°, was largely inert to bio-molecules, and DNA amplification could be performed in a minimum reaction volume of 40 nL. The isothermal nucleic acid amplification for Mycoplasma pneumoniae identification in the non-stick-coated microfluidic bioreactor could be performed at a minimum DNA template concentration of 1.3 aM, and a detection limit of three copies of genomic DNA was obtained. This microfluidic bioreactor offers a promising clinically relevant pathogen molecular diagnostic method via the amplification of targets from only a few copies of genomic DNA from a single bacterium.
Project description:Cholangiocarcinoma (CCA), a biliary tract malignancy, accounts for 20% of all liver cancers. There are several existing methods for diagnosis of CCA, though they are generally expensive, laborious, and suffer from low detection rates. Herein we first developed a means of partially purifying human bile for consequent injection into a microfluidic chip. Then, the novel microfluidic system, which featured 1) a cell capture module, 2) an immunofluorescence (IF) staining module featuring two CCA-specific biomarkers, and 3) an optical detection module for visualization of antibody probes bound to these CCA marker proteins, was used to detect bile duct cancer cells within partially purified bile samples. As a proof of concept, CCA cells were successfully captured and identified from CCA cell cultures, blood samples inoculated with CCA cells, and clinical bile specimens. In 7.5?ml of bile, this system could detect >2, 0, and 1 positive cells in advanced stage patients, healthy patients, and chemotherapy-treated patients, respectively. In conclusion, our microfluidic system could be a promising tool for detection of cancer cells in bile, even at the earliest stages of CCA when cancer cells are at low densities relative to the total population of epithelial cells.
Project description:Optofluidics, which integrates microfluidics and micro-optical components, is crucial for optical sensing, fluorescence analysis, and cell detection. However, the realization of an integrated system from optofluidic manipulation and a microfluidic channel is often hampered by the lack of a universal substrate for achieving monolithic integration. In this study, we report on an integrated optofluidic-microfluidic twin channels chip fabricated by one-time exposure photolithography, in which the twin microchannels on both surfaces of the substrate were exactly aligned in the vertical direction. The twin microchannels can be controlled independently, meaning that fluids could flow through both microchannels simultaneously without interfering with each other. As representative examples, a tunable hydrogel microlens was integrated into the optofluidic channel by femtosecond laser direct writing, which responds to the salt solution concentration and could be used to detect the microstructure at different depths. The integration of such optofluidic and microfluidic channels provides an opportunity to apply optofluidic detection practically and may lead to great promise for the integration and miniaturization of Lab-on-a-Chip systems.
Project description:We present a novel image-based method to measure the on-chip microfluidic pressure and flow rate simultaneously by using the integrated optofluidic membrane interferometers (OMIs). The device was constructed with two layers of structured polydimethylsiloxane (PDMS) on a glass substrate by multilayer soft lithography. The OMI consists of a flexible air-gap optical cavity which upon illumination by monochromatic light generates interference patterns that depends on the pressure. These interference patterns were captured with a microscope and analyzed by computer based on a pattern recognition algorithm. Compared with the previous techniques for pressure sensing, this method offers several advantages including low cost, simple fabrication, large dynamic range, and high sensitivity. For pressure sensing, we demonstrate a dynamic range of 0-10 psi with an accuracy of ±2% of full scale. Since multiple OMIs can be integrated into a single chip for detecting pressures at multiple locations simultaneously, we also demonstrated a microfluidic flow sensing by measuring the differential pressure along a channel. Thanks to the simple fabrication that is compatible with normal microfluidics, such OMIs can be easily integrated into other microfluidic systems for in situ fluid monitoring.
Project description:This study reports an integrated microfluidic system which utilizes virus-bound magnetic bead complexes for rapid serological analysis of antibodies associated with an infection by the dengue virus. This new microfluidic system integrates one-way micropumps, a four-membrane-type micromixer, two-way micropumps and an on-chip microcoil array in order to simultaneously perform the rapid detection of immunoglobulin G (IgG) and immunoglobulin M (IgM). An IgM/IgG titer in serum is used to confirm the presence of dengue virus infection. By utilizing microfluidic technologies and virus-bound magnetic beads, IgG and IgM in the serum samples are captured. This is followed by purification and isolation of these beads utilizing a magnetic field generated from the on-chip array of microcoils. Any interfering substances in the biological fluids are washed away automatically by the flow generated by the integrated pneumatic pumps. The fluorescence-labelled secondary antibodies are bound to the surface of the IgG/IgM complex attached onto the magnetic beads. Finally, the entire magnetic complex sandwich is transported automatically into a sample detection chamber. The optical signals are then measured and analyzed by a real-time optical detection module. The entire process is performed automatically on a single chip within 30min, which is only 1/8th of the time required for a traditional method. More importantly, the detection limit has been improved to 21pg, which is about 38 times better when compared to traditional methods. This integrated system may provide a powerful platform for the rapid diagnosis of dengue virus infection and other types of infectious diseases.
Project description:Coculturing multiple cell types together in 3-dimensional (3D) cultures better mimics the in vivo microphysiological environment, and has become widely adopted in recent years with the development of organ-on-chip systems. However, a bottleneck in set-up of these devices arises as a result of the delivery of the gel into the microfluidic chip being sensitive to pressure fluctuations, making gel confinement at a specific region challenging, especially when manual operation is performed. In this paper, we present a novel design of an on-chip regulator module with pressure-releasing safety microvalves that can facilitate stable gel delivery into designated microchannel regions while maintaining well-controlled, non-bursting gel interfaces. This pressure regulator design can be integrated into different microfluidic chip designs and is compatible with a wide variety of gel injection apparatuses operated automatically or manually at different flow rates. The sensitivity and working range of this pressure regulator can be adjusted by changing the width of its pressure releasing safety microvalve design. The effectiveness of the design is validated by its incorporation into a microfluidic platform we have developed for generating 3D vascularized micro-organs (VMOs). Reproducible gel loading is demonstrated for both an automatic syringe pump and a manually-operated micropipettor. This design allows for rapid and reproducible loading of hydrogels into microfluidic devices without the risk of bursting gel-air interfaces.
Project description:Optical read-out of motion is widely used in sensing applications. Recent developments in micro- and nano-optomechanical systems have given rise to on-chip mechanical sensing platforms, potentially leading to compact and integrated optical motion sensors. However, these systems typically exploit narrow spectral resonances and therefore require tuneable lasers with narrow linewidth and low spectral noise, which makes the integration of the read-out extremely challenging. Here, we report a step towards the practical application of nanomechanical sensors, by presenting a sensor with ultrawide (?80?nm) optical bandwidth. It is based on a nanomechanical, three-dimensional directional coupler with integrated dual-channel waveguide photodiodes, and displays small displacement imprecision of only 45?fm/Hz1/2 as well as large dynamic range (>30?nm). The broad optical bandwidth releases the need for a tuneable laser and the on-chip photocurrent read-out replaces the external detector, opening the way to fully-integrated nanomechanical sensors.