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ABSTRACT: The rapid mixing of fluids passing through a microfluidic channel is very important for various applications of microfluidic
systems. It has been a great challenge to achieve highly efficient mixing in a microfluidic system because it is very difficult
to generate turbulence in a submillimeter-size channel at low Reynolds numbers (Re). In this paper, we fabricated a pillar obstruction microfluidic mixer and evaluated its mixing efficiency at various flow
rates. The mixing behavior of confluent streams was estimated using a fluorescence microscope. Three different sets of miscible
solutions (phosphate-buffered solution, gold nanocolloids and 20% glycerol), with Rhodamine 6G aqueous solution, were used
as sample laminar flows. According to our experimental results, the pillar obstruction microfluidic mixer shows an excellent
mixing performance in the low Re range. Here, the mixing performance was strongly dependent on the characteristic viscosity changes of different sets of miscible
solutions. The pillar obstruction microfluidic mixer designed here is expected to benefit a wide range of lab-on-a-chip applications
because fabrication is very simple and the mixing efficiency is excellent at low Re.
Microfluidics and Nanofluidics 04/2012; 7(2):267-273. · 3.37 Impact Factor
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ABSTRACT: The development of ultrafast Raman-based detection is one of the most interesting challenges underpinning the application of droplet-based microfluidics. Herein, we describe the use of surface-enhanced resonance Raman spectroscopy (SERRS) with submillisecond time resolution as a powerful detection tool in microdroplet reactors. Individual droplets containing silver nanoparticle aggregates functionalized with Raman reporters are interrogated and characterized by full spectra acquisitions with high spatial resolution in real time. Whereas previous works coupling SERRS with droplet-based microfluidics acquire a single spectrum over single or multiple droplets, we build upon these results by increasing our temporal resolution by 2 orders of magnitude. This allows us to interrogate multiple points within one individual droplet. The SERRS signals emitted from the aggregates are utilized to access the influence of flow rate on droplet size and throughput. Accordingly, our approach allows for high-throughput analysis that facilitates the study of other biological assays or molecular interactions.
Analytical Chemistry 03/2011; 83(8):3076-81. · 5.86 Impact Factor
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ABSTRACT: A surface-enhanced Raman scattering (SERS)-based gradient optofluidic sensor has been developed for a fast and sensitive immunoassay. In this work, a novel microfluidic sensor with functional internal structures has been designed and fabricated. This sensor is composed of three compartments consisting of the gradient channel that serially dilutes the target marker, the injection and mixing area of antibody-conjugated hollow gold nanospheres and magnetic beads, and the trapping area of sandwich immunocomplexes using multiple solenoids. Quantitative analysis of a specific target marker is performed by analyzing its characteristic SERS signals. This SERS-based gradient optofluidic sensor can replace the set of microwells or microtubes used in manual serial dilutions that have been traditionally used in enzyme-linked immunosorbent assay (ELISA)-type assays. The limit of detection for rabbit immunoglobin (IgG) is estimated to be 1-10 ng/mL. This novel SERS-based optofluidic immunoassay system is expected to be a powerful clinical tool for the fast and sensitive medical diagnosis of a disease.
Analytical Chemistry 06/2010; 82(12):5290-5. · 5.86 Impact Factor
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ABSTRACT: We report recent progress in the development of surface-enhanced Raman scattering (SERS)-based optofluidic platforms for the fast and sensitive detection of chemical and biological analytes. In the current context, a SERS-based optofluidic platform is defined as an integrated analytical device composed of a microfluidic element and a sensitive Raman spectrometer. Optofluidic devices for SERS detection normally involve nanocolloid-based microfluidic systems or metal nanostructure-embedded microfluidic systems. In the current review, recent advances in both approaches are surveyed and assessed. Additionally, integrated real-time sensing systems that combine portable Raman spectrometers with microfluidic devices are also reviewed. Such real-time sensing systems have significant utility in environmental monitoring, forensic science and homeland defense applications.
The Analyst 05/2010; 135(5):837-44. · 4.23 Impact Factor
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ABSTRACT: We report a new method for the trace analysis of mercury (II) ions in water. The approach involves the use of droplet-based microfluidics combined with surface-enhanced Raman scattering (SERS) detection. This novel combination provides both fast and sensitive detection of mercury (II) ions in water. Specifically, mercury (II) ion detection is performed by using the strong affinity between gold nanoparticles and mercury (II) ions. This interaction causes a change in the SERS signal of the reporter molecule rhodamine B that is a function of mercury (II) ion concentration. To allow both reproducible and quantitative analysis, aqueous samples are encapsulated within nanoliter-sized droplets. Manipulation of such droplets through winding microchannels affords rapid and efficient mixing of the contents. Additionally, memory effects, caused by the precipitation of nanoparticle aggregates on channel walls, are removed since the aqueous droplets are completely isolated by a continuous oil phase. Quantitative analysis of mercury (II) ions was performed by calculating spectral peak area of rhodamine B at 1,647 cm(-1). Using this approach, the calculated concentration limit of detection was estimated to be between 100 and 500 ppt. Compared with fluorescence-based methods for the trace analysis of mercury (II) ions, the detection sensitivities were enhanced by approximately one order of magnitude. The proposed analytical method offers a rapid and reproducible trace detection capability for mercury (II) ions in water.
Analytical and Bioanalytical Chemistry 06/2009; 394(7):1827-32. · 3.78 Impact Factor
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ABSTRACT: An integrated real-time sensing system that uses a portable Raman spectrometer and a micropillar array chip has been developed for field analysis. The problem of poor detection sensitivity, caused by miniaturization in the portable Raman spectrometer, was overcome by using the surface-enhanced Raman scattering (SERS) technique. The problem of poor reproducibility in the SERS detection, caused by different particle sizes and inhomogeneous degrees of aggregation, was also overcome by using continuous flow and homogeneous mixing between the analytes and nanocolloidal silver in a micropillar array microfluidic chip. Two hazardous materials, dipicolinic acid and malachite green, were quantitatively analysed using our integrated portable Raman sensor system. The observed limit of detection was estimated to be 200 ppb and 500 ppb, respectively. Our proposed analytical method, using a micropillar array PDMS chip and a portable SERS system, offers a rapid and reproducible trace detection capability for hazardous materials in the field.
Lab on a Chip 01/2009; 8(12):2214-9. · 5.67 Impact Factor
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ABSTRACT: A conceptually new technique for fast DNA detection has been developed. Here, we report a fast and sensitive online fluorescence resonance energy transfer (FRET) detection technique for label-free target DNA. This method is based on changes in the FRET signal resulting from the sequence-specific hybridization between two fluorescently labelled nucleic acid probes and target DNA in a PDMS microfluidic channel. Confocal laser-induced microscopy has been used for the detection of fluorescence signal changes. In the present study, DNA hybridizations could be detected without PCR amplification because the sensitivity of confocal laser-induced fluorescence detection is very high. Two probe DNA oligomers (5'-CTGAT TAGAG AGAGAA-TAMRA-3' and 5'-TET-ATGTC TGAGC TGCAGG-3') and target DNA (3'-GACTA ATCTC TCTCT TACAG GCACT ACAGA CTCGA CGTCC-5') were introduced into the channel by a microsyringe pump, and they were efficiently mixed by passing through the alligator teeth-shaped PDMS microfluidic channel. Here, the nucleic acid probes were terminally labelled with the fluorescent dyes, tetrafluororescein (TET) and tetramethyl-6-carboxyrhodamine (TAMRA), respectively. According to our confocal fluorescence measurements, the limit of detection of the target DNA is estimated to be 1.0 x 10(-6) to 1.0 x 10(-7)M. Our result demonstrates that this analytical technique is a promising diagnostic tool that can be applied to the real-time analysis of DNA targets in the solution phase.
Biosensors and Bioelectronics 08/2008; 23(12):1878-82. · 5.60 Impact Factor
