Yuan-Tai Tseng

Fluid filling into micro-fabricated reservoirs

Abstract This study reports that the success of reservoir-filling strongly depends on the designs of the hydrophilic wall surface and the well shape/size of the flow network. The idea is illustrated both by experiments and numerical simulations: micro-particle-image-velocimetry (μ-PIV) system is setup to monitor the process of a liquid slug moving in and out of the micro-reservoir and numerical computations are performed by solving first principle equations to provide the details of the flow process. The cross-check between measurements and computations validate the computations. Numerical computations solve conservation equations similar to homogenous flow model used in two phase flow calculation in co-operation with volume-of-fluid (VOF) interface tracking methodology and continuum surface force (CSF) model. The simulations show that wall surface property as hydrophilic/hydrophobic is a dominating factor in filling processes of reservoirs of various shapes. A flow system consisting of micro-channels and micro-wells is fabricated using MEMS technology to demonstrate the filling process and validate numerical simulation. The agreement between measurement and computation helps to fully understand the process.

A novel in vitro and in situ immunoassay biosensor based on fiber optic Fabry-Perot interferometry

This paper proposes a novel fiber optic immunoassay biosensor based on the Fabry-Perot (F-P) interferometry. The PDMS dip coating and self-assembly monolayers coating are employed to prepare the fiber probes in the formation of F-P cavity and modification of the tip surface respectively. As the fiber probe inserting into the target solution, the immunoreaction will be introduced on the fiber tip. The covalent binding of the Rabbit IgG and Anti Rabbit IgG-Cy3 molecules on the fiber tip will contribute to the variation of the refractive index of interface as well as the reflectance. The interference spectrum will be shifted due to the reflectance variation. The time response is also implemented by taking the in-situ measurement of spectrum valley shift and the signal will reach the steady state within 15 minutes. Finally, the sensitivity of this immunoassay biosensor has also been demonstrated that the lowest detectable concentration of the target sample Anti Rabbit IgG-Cy3 is 10-12 g/ml, which is lower than the detection limit of ELISA of 5*10-11 g/ml. This fiber optic immunoassay biosensor will be applied in the brain resarch for in-vivo and in-situ monitoring the biochemical reactions of the neurocytes.

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.

Dual fiber-optic Fabry-Perot interferometer temperature sensor with low-cost light-emitting diode light source

A dual fiber-optic Fabry–Perot interferometer (FFPI) sensor system with a low-coherence communication-system light-emitting diode (LED) as a light source is investigated to detect temperature variation signals. In this system, there are two FFPIs: the sensing and reference FFPIs. When the perturbation of interest, such as that of temperature, disturbs the sensing FFPI to produce a phase shift, the light reflected from the sensor is demodulated by the reference FFPI to extract the measurand. A low-power (sub-nW) optical signal is converted into an electrical signal and processed by a designed optical receiver. This setup is availably applied in biosensors to compensate the temperature variation in a sensing environment or sense the temperature effect in a certain measurement on an interior local site.

Nanostructure-Enhanced Fiber-Optic Interferometry for Label-Free Immune Sensing

This paper proposes a nanostructure-enhanced fiber-optic interferometry (NSFOI) biosensor, combining the abilities of high sensitivity, real-time monitoring and in-situ measurement for label-free immunological detection, by employing high-aspect-ratio pillar-like nanostructures on the tip of sensor surface. The nanostructure layer, fabricated by a simple etching process on resonant cavity without mask patterning, was employed not only for the improvement of the detection limit to reach 1ng/ml for rabbit-IgG (~6.7pM) due to the increase of the biomolecular binding surface, but also for the enhancement of the optical path length to enlarge the maximum magnitude of fringe shift which was approximated to 1.4nm by both experimental and theoretical results.

gold-nanoparticle-enhanced IGG immunological detection by in-situ fabry-perot sensor

This paper proposes a needle-type biosensor for immunological application, which combines the abilities of real-time monitoring, in-situ measurement and high sensitivity, by adopting gold-nanoparticles (GNPs) coated with antibody to enhance the signal of Fabry-Perot (F-P) interferometry in an optic fiber sensing system. Strong reflection induced by larger index mismatch and longer optical path from GNPs-protein conjugation are suggested to attribute most to the signal enhancement in F-P interference shift. The experiments carry out the monitoring of immuno-sensing in real-time by the employment of rabbit IgG conjugate to GNPs-anti-rabbit IgG And the detection limit was demonstrated to approach 0.17 nM (-25.5 ng/ml), which was three orders of magnitude better than those of the traditional fiber-based F-P biosensors. Besides, the reproducibility of the sensor has been tested through at least three cycles of detection/surface-regeneration process and demonstrated a reasonable consistency. The relationship between the concentrations of GNPs-antibody and F-P spectrum shift has also been characterized. The time-constant of this sensor to complete one cycle of biomolecule-detection and surface-regeneration can be as low as 4 minutes.

Gold-nanoparticle enhanced fiber sensor based on Fabry-Perot interferometry

This paper proposes a novel method by employing gold-nanoparticle to enhance optic fiber Fabry-Perot (F-P) interferometry signal for bio-molecule detection. PDMS dip coating and self-assembly monolayers were employed to prepare the fiber probes in the formation of F-P cavity and modification of the tip surface, respectively. Cysteine molecules were immobilized on the sensor surface to allow gold-nanoparticles attachment in the experiment. Experiment result shows that the signal amplitude has more than 40% enhancement and the spectrum shift can be improved by one order of magnitude when employing 40 nm nanoparticles compare to the traditional detection ways by Fabry-Perot interferometry. This result provides a minimum detectable gold-nanoparticles concentration of 1 /spl times/ 10/sup 7/ particles//spl mu/l for 40 nm particle diameter enhanced optic fiber Fabry-Perot interferometry.

Experimental and numerical studies on micro-droplet movement driven by Marangoni effect

This work is a fundamental study on the movement of various sized micro-liter droplets on a surface subjected to temperature gradients by high speed CCD camera and numerical predictions based on first principle equations. The study indicates that the differences and the change of dynamic receding/advancing contact angles and temperature gradients across the droplets are the key parameters determining the moving behavior.

Size Effect on Micro-Droplet Movement Due to Marangoni Effect

Fundamental physics are studied on the movement of droplets for sizes ranging from 0.1 μl to 1.0 μl on a solid surface subjected to temperature gradients using numerical computations and the comparison with experiments. The receding/advancing contact angles relating to the droplet size and shape are the key parameters of droplet moving and the differences subjected to the temperature gradients induce unbalanced recirculation zones inside the moving droplet, thus induces driving force to drag the droplet. It is found that droplet of smaller size moves faster with smoothly changing speed and the droplet of larger size moves with fluctuating speed and the average moving speed is roughly the same magnitude as that with two-dimensional heating.Copyright

Shape Effect on Fluid Filling for Microfabricated Reservoir

This study demonstrates the shape effect on filling process of protein solution/water into micro-wells for microfabricated microchips. Two approaches are employed (1) high speed camera system is set up to record the liquid slug moving in and out of the micro-well and (2) numerical simulations by solving first principle equations provide the details of the flow process.