Optofluidic System Research Articles

A perfusion-based micro opto-fluidic system (PMOFS) for continuously in-situ immune sensing

This paper proposes a novel perfusion-based micro opto-fluidic system (PMOFS) as a reusable immunosensor for in-situ and continuous protein detection. The PMOFS includes a fiber optic interferometry (FOI) sensor housed in a micro-opto-fluidic chip covered with a microdialysis membrane. It features a surface regeneration mechanism for continuous detection. Gold nanoparticles (GNPs) labeled anti-rabbit IgG were used to enhance the immune conjugation signal by the elongated optical path from GNPs conjugation. Surface regeneration of the sensor was achieved through local pH level manipulation by means of a photoactive molecule, o-Nitrobenzaldehyde (o-NBA), which triggered the elution of immune complexes. Experimental results showed that the pH level of the o-NBA solution can be reduced from 7 to 3.5 within 20 seconds under UV irradiation, sufficient for an effective elution process. The o-NBA molecules, contained within poly(ethylene glycol) diacrylate (PEG) complexes, were trapped within the sensing compartment by the microdialysis membrane and would not leak into the outside environment. The pH variation was also limited in the neighborhood of the sensor surface, resulting in a self-contained sensing system. In-situ immune detection and surface regeneration of the sensing probe has been successfully carried out for two identical cycles by the same sensing probe, and the cycle time can be less than 8 minutes, which is so far the fastest method for continuous monitoring on protein/peptide molecules. In addition, the interference fringe shift of the sensor is linearly related to the concentration of anti-cytochrome C antibody solution and the detection limit approaches 10 ng/ml.

Additional amplifications of SERSvia an optofluidic CD-based platform

In this paper, signal amplifications of surface-enhanced Raman scattering (SERS) are realized by an optofluidic compact disc (CD)-based preconcentration method for effective label-free environmental and biomolecular detections. The preconcentration of target molecules is accomplished through the accumulation of adsorbed molecules on SERS-active sites by repeating a 'filling-drying' cycle of the assay solution in the optofluidic CD platform. After 30 cycles, the clear and high SERS signal of rhodamine 6G of 1 nM is readily detected. In addition to the preconcentration-based signal amplification by the optofluidic SERS system on the CD platform, we introduce a controlled precipitation of gold nanoparticles by CuSO4 for SERS substrates. This method provides high-throughput, high-sensitive and large-area uniform SERS substrates on the optofluidic CD platform. The uniform SERS signals from different positions in spots of 3 mm2 on the different CDs gives us confidence in the reliability and stability of our SERS substrates.

Three-dimensional fabrication of heterogeneous microstructures using soft membrane deformation and optofluidic maskless lithography

We propose a method for high-throughput generation of 3D microstructures using a membrane-mounted microfluidic channel. Utilizing an optofluidic maskless lithography system, photopolymerized 3D microstructures are fabricated in a layer-by-layer fashion with the thickness of each layer controlled by the deformation of the membrane. The combination of low numerical aperture optical systems for photopolymerization and a soft membrane for height control allows large area projection lithography with high vertical resolution, overcoming the trade-off between vertical resolution and the field-of-view. The material composition of each layer is varied using microfluidic control of photocurable resin and composite microstructures with heterogeneity in both lateral and vertical directions are generated. Using this technique, we demonstrate three-dimensional patterning of different types of cells in a hydrogel for a microfluidic platform to study co-culture and cell-to-cell interactions. The proposed technique is fast and simple, allowing parallel synthesis of complex heterogeneous 3D microstructures and in situ biomaterial patterning for microfluidic bioassays.

Design and Characterization of Optofluidic Photonic Crystal Structures for the Detection of Fluorescent-Labeled Biomolecules

The combination of optics and microfluidics into optofluidic systems has provided a means of creating portable integrated platforms for performing fluorescence emission analyses in fieldable systems. We present here the design of a photonic crystal transducer for highly sensitive and selective fluorescence-based biomolecule detection using a reduced-size lattice nanocavity tuned for resonance at emission wavelengths. This novel approach to biosensing is based upon photonic crystal defect structures that are engineered to act as waveguides, optical resonant cavities, and nanofluidic flow channels. This paper will discuss modeling, design, and nanofabrication of optofluidic photonic crystal (PhC) transducers in silicon and GaN materials. First-order results of PhC optical property characterization will be provided. Preliminary simulations indicate that fluorescence emission intensity inside of a PhC resonant defect nanocavity is enhanced to a level 26 times greater than emission outside of a defect due to resonant optical confinement and the Purcell effect.

Photonic crystal resonator integrated in a microfluidic system

We report on a novel optofluidic system consisting of a silica-based 1D photonic crystal, integrated planar waveguides, and electrically insulated fluidic channels. An array of pillars in a microfluidic channel designed for electrochromatography is used as a resonator for on-column label-free refractive index detection. The resonator was fabricated in a silicon oxynitride platform, to support electro-osmotic flow, and operated at lambda=1.55 microm. Different aqueous solutions of ethanol with refractive indices ranging from n=1.3330 to 1.3616 were pumped into the column/resonator, and the transmission spectra were recorded. Linear shifts of the resonant wavelengths yielded a maximum sensitivity of Deltalambda/Deltan=480 nm/RIU (refractive index unit), and a minimum difference of Deltan=0.007 RIU was measured.

An Integrated Optofluidic Platform for DNA Hybridization and Detection

There has been extensive research into micro total analysis systems (micro-TAS) and lab-on-a-chip research due to the benefits of increased sample throughput, reduced sample consumption, and rapid analysis times. The integration of low-cost fluidic and optical components offers the possibility of complex systems with increased functionality on a single detection platform. For the development of an integrated optofluidic system for DNA hybridization, the key areas are optical/fluidic integration and the efficiency of surface chemistry integration within the system. The impact of fluidic parameters such as flow rate, channel height, and time on hybridization performance is to optimize detection performance over conventional assay (microtiter plate formats). The use of a passive waveguide device means DNA binding events can be monitored using fluorescence excitation or refractive index measurement. The integration of the three areas is enhanced by the robustness of the waveguide material (oxide, nitride), enabling chemical functionalization by initial silanization followed by addition of a linker molecule 1,4 phenylene diisothiocyanate (PDITC) for covalent immobilization of DNA probes together with the possibility to define microfluidics on the waveguide substrate using standard SU8 photolithography. The fluidic design requires 240 nl of analyte to fill the integrated optofluidic system. Here, we report the novel integration and optimization of a covalent surface chemistry with microfluidic channels for fluidic delivery, and a standard resonant mirror (RM) waveguide detection platform. The optofluidic detection platform was tested using fluorescence and refractive index to monitor binding events between target and probe DNA. We describe the detection system, using simulations to explain the response to changes in refractive index and outline a method for covalent attachment of DNA probes surface chemistry protocol to immobilize probe DNA on the sensor surface and the optimization of fluidic design, achieving pM detection limit. We highlight the benefit of optimizing the fluidic component and its benefit in hybridization efficiency an approach often overlooked in sensor design and performance.

An integrated optofluidic platform for Raman-activated cell sorting

We report on integrated optofluidic Raman-activated cell sorting (RACS) platforms that combine multichannel microfluidic devices and laser tweezers Raman spectroscopy (LTRS) for delivery, identification, and simultaneous sorting of individual cells. The system allows label-free cell identification based on Raman spectroscopy and automated continuous cell sorting. Two optofluidic designs using hydrodynamic focusing and pinch-flow fractionation are evaluated based on their sorting design and flow velocity effect on the laser trapping efficiency at different laser power levels. A proof-of-principle demonstration of the integrated optofluidic LTRS system for the identification and sorting of two leukemia cell lines is presented. This functional prototype lays the foundation for the development of a label-free cell sorting platform based on intrinsic Raman markers for automated sampling and sorting of a large number of individual cells in solution.

Optofluidic maskless lithography system for real-time synthesis of photopolymerized microstructures in microfluidic channels

The authors propose an optofluidic maskless lithography technique that can dynamically synthesize free-floating polymeric microstructures inside microfluidic channels by selectively polymerizing photocurable resin with high-speed two-dimensional spatial light modulators. The combination of programable optical projection and microfluidic devices allows one to precisely control the timing and location of the photopolymerization process for microstructure fabrication. Real-time generation of microparticles with various shapes, sizes, ordering, and material contents are experimentally demonstrated. Long polymeric structures of which size is not limited by the exposure field of view can also be fabricated.

Characteristic of Opto-fluidic Control System

An opto-fluidic control system employing a laminar proportional amplifier was used to convert directly optical signal into fluidic signal by the thermal control of the supply jet's velocity distribution. It can work in hazardous environment because it doesn't use electric signals. A differential optical signal was introduced through opposing optical fibers into the light absorbing end sections of them constructing the opposing side-walls of the supply nozzle of the interface. The differential fl uidic output signal of the opto-fluidic interface was amplified by a three-stage laminar proportional amplifier gain block and turbulent proportional amplifiers.In this study, opto-fluidic conversion characteristics were clarified by numerical analysis and by the experiments using a experimental model having the size of four times that of the practical opto-fluidic interface. The appropriateness of the analytical model was proved by the experiment using the large-scale experimental model.

光音響効果を利用した光-流体変換器の特性

For realizing an opto-fluidic system without any mechanical moving part, opto-fluitlic controlling element using a photoacoustic cell as the control port of a laminar proportional amplifier was investigated. Carbon black was used as a light absorber of the photoacoustic cell.Effects of incident light intensity, light modulating frequency, light aqsorber thickness, and cell length on photoacoustic pressure amplitude are clarified. Conversion characteristics of the opto-fluidic converter employing the opto-fluidic controlling element, a laminar proportional amplifier gain block and a rectifier are also reported.

OPTO-FLUIDIC CONTROL DEVICE

For realizing an opto-fluidic system without any mechanical moving part, opto-fluidic converter employing a photoacoustic cell as the control port of a laminar proportional amplifier was investigated. Carbon black was used as a light absorber of the photoacoustic cell. Effects of the incident light intensity, the light modulating frequency, the absorber thickness, and the cell length on the photoacoustic pressure amplitude are clarified. Conversion characteristics of the opto-fluidic converter are also reported.