Multi-target pathogen detection using heterogeneous medical samples require continuous filtering, sorting, and trapping of debris, bioparticles, and immunocolloids within a diagnostic chip. We present an integrated AC dielectrophoretic ͑DEP͒ microfluidic platform based on planar electrodes that form three-dimensional ͑3D͒ DEP gates. This platform can continuously perform these tasks with a throughput of 3 L / min. Mixtures of latex particles, Escherichia coli Nissle, Lactobacillus, and Candida albicans are sorted and concentrated by these 3D DEP gates. Surface enhanced Raman scattering is used as an on-chip detection method on the concentrated bacteria. A processing rate of 500 bacteria was estimated when 100 l of a heterogeneous colony of 10 7 colony forming units /ml was processed in a single pass within 30 min.
We present a high throughput (maximum flow rate approximately 10 microl/min or linear velocity approximately 3 mm/s) continuous bio-particle sorter based on 3D traveling-wave dielectrophoresis (twDEP) at an optimum AC frequency of 500 kHz. The high throughput sorting is achieved with a sustained twDEP particle force normal to the continuous through-flow, which is applied over the entire chip by a single 3D electrode array. The design allows continuous fractionation of micron-sized particles into different downstream sub-channels based on differences in their twDEP mobility on both sides of the cross-over. Conventional DEP is integrated upstream to focus the particles into a single levitated queue to allow twDEP sorting by mobility difference and to minimize sedimentation and field-induced lysis. The 3D electrode array design minimizes the offsetting effect of nDEP (negative DEP with particle force towards regions with weak fields) on twDEP such that both forces increase monotonically with voltage to further increase the throughput. Effective focusing and separation of red blood cells from debris-filled heterogeneous samples are demonstrated, as well as size-based separation of poly-dispersed liposome suspensions into two distinct bands at 2.3 to 4.6 microm and 1.5 to 2.7 microm, at the highest throughput recorded in hand-held chips of 6 microl/min.
A total of 37 commercial samples of Ginseng Radix, the origins of which belonged to Panax ginseng C. A. Meyer, P. quinquefolia Linn. (American ginseng), and P. notoginseng Burkill (sanchi-ginseng), respectively, were collected from the Taiwan herbal markets. The contents of nine ginsenosides, Rb(1), Rb(2), Rc, Rd, Re, Rf, Rg(1), Rg(2), R(0), and three malonylginsenosides, mRb(1), mRb(2), mRc, in these samples were determined by high-performance liquid chromatography. It was found that the saponin contents in P. notoginseng and P. quinquefolia were generally higher than in P. ginseng. The ginsenosides that were of the highest contents in the white-ginseng, red-ginseng, and shihchu-ginseng samples of P. ginseng were Rb(1) and Rg(1); those in the root-hair of P. ginseng were Rb(1) and Re, those in P. notoginseng were Rb(1), Rg(1) and Rd, and those in P. quinquefolia were Rb(1), Re, and mRb(1). Among the samples, those of P. quinquefolia did not contain Rf and Rg(2), whilst those of shihehu-ginseng and red-ginseng of P. ginseng contained none or only traces of the malonylginsenosides. From the data of chemical analysis of a herb's constituents and its external appearance, we can postulate not only the quality but also the origin of the herb.
We present an analysis of the results of in situ surface-enhanced Raman scattering ͑SERS͒ of bacteria using a microfluidic chip capable of continuously sorting and concentrating bacteria via three-dimensional dielectrophoresis ͑DEP͒. Microchannels were made by sandwiching DEP microelectrodes between two glass slides. Avoiding the use of a metal nanoparticle suspension, a roughened metal surface is integrated into the DEP-based microfluidic chip for on-chip SERS detection of bacteria. On the upper surface of the slide, a roughened metal shelter was settled in front of the DEP concentrator to enhance Raman scattering. Similarly, an electrodepatterned bottom layer fabricated on a thin cover-slip was used to reduce fluorescence noise from the glass substrate. Gram positive ͑Staphylococcus aureus͒ and Gram negative ͑Pseudomonas aeruginosa͒ bacteria were effectively distinguished in the SERS spectral data. Staphylococcus aureus ͑concentration of 10 6 CFU/ ml͒ was continuously separated and concentrated via DEP out of a sample of blood cells. At a flow rate of 1 l / min, the bacteria were highly concentrated at the roughened surface and ready for on-chip SERS analysis within 3 min. The SERS data were successfully amplified by one order of magnitude and analyzed within a few minutes, resulting in the detection of signature peaks of the respective bacteria.
Molecular dielectrophoresis (DEP) is employed to rapidly (
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