The Comparisons of Physical Functional Performances between Older Adults with and without Regular Physical Activity in Two Different Living Settings.

We compared the physical function performances of community-dwelling and day care center older adults with and without regular physical activity (PA). A total of 163 Taiwanese older adults living in rural communities participated. PA habits and physical functional performances were assessed. The participants were divided into community-dwelling (CD) and senior day care (DC) center groups that were further classified into regular physical activity (RPA) and non-physical activity (NPA) subgroups. Comparison took place between subgroups. In the CD group, only the grip strength, pinch strength, and box and blocks test scored significantly better for the participants with regular PA. Muscle strength, flexibility, and three items of functional ability of participants with regular PA were significantly better in the DC group. An active lifestyle contributes to a good old-age life. The effective amount of PA and the reduction of sedentary time should be advocated to prevent frailty and disability in older adults.

A bead-based immunofluorescence-assay on a microfluidic dielectrophoresis platform for rapid dengue virus detection.

The proof of concept of utilizing a microfluidic dielectrophoresis (DEP) chip was conducted to rapidly detect a dengue virus (DENV) in vitro based on the fluorescence immunosensing. The mechanism of detection was that the DEP force was employed to capture the modified beads (mouse anti-flavivirus monoclonal antibody-coated beads) in the microfluidic chip and the DENV modified with fluorescence label, as the detection target, can be then captured on the modified beads by immunoreaction. The fluorescent signal was then obtained through fluorescence microscopy, and then quantified by ImageJ freeware. The platform can accelerate an immuno-reaction time, in which the on-chip detection time was 5min, and demonstrating an ability for DENV detection as low as 104 PFU/mL. Furthermore, the required volume of DENV samples dramatically reduced, from the commonly used ~50µL to ~15µL, and the chip was reusable (>50x). Overall, this platform provides a rapid detection (5min) of the DENV with a low sample volume, compared to conventional methods. This proof of concept with regard to a microfluidic dielectrophoresis chip thus shows the potential of immunofluorescence based-assay applications to meet diagnostic needs.

Increasing local density and purity of molecules/bacteria on a sensing surface from diluted blood using 3D hybrid electrokinetics.

We present a long-range and selective nanocolloid/molecular/bacteria concentrator based on 3D hybrid AC electrokinetics (ACEK) that includes AC dielectrophoresis (DEP) and biased AC electroosmosis (ACEO). Through a convergency comb-shaped electrode design, this long-range ACEO allows the effective transport of a high number of targets into the centre of the detection zone. In the proposed 3D hybrid electrokinetics model, 3D ACEO provides long-range transportation, and the 3D DEP provides an effective separation mechanism. Thus, detection targets ranging from nanoscale to micrometers could be selectively concentrated long-range from diluted blood. The proposed design was used for selectively concentrating nanocolloids and bacteria in the diluted blood sample, respectively. Compared to a 3D short-range dipolar electrode configuration, the detection limit of long-range 3D convergency tripolar electrode configuration is one order of magnitude higher. The result also shows that the 3D hybrid ACEK demonstrated a higher purity of any plane above the electrode, which compared positively to the same design of a 2D hybrid ACEK. The concentration factor of the proposed 3D hybrid electrokinetics device increased by several orders of local density and raised the local purity at least 6 orders (from 0.05% to greater than 99.9%). The chip is capable of making a DNA/protein/bacterial aggregate characterized by high local density and purity for further molecular and bacteria detection/analysis.

Antibody-free isolation of rare cancer cells from blood based on 3D lateral dielectrophoresis.

We present an antibody-free approach for the high-purity and high-throughput dielectrophoretic (DEP) isolation of circulating tumour cells (CTCs) from blood in a microfluidic chip. A hydrodynamic sheath flow is designed upstream in the chip to direct the suspension samples to the channel side walls, thus providing a queue to allow DEP-induced lateral displacements. High-throughput continuous cancer cell sorting (maximum flow rate: ~2.4 mL h(-1), linear velocity: ~4 mm s(-1)) is achieved with a sustained 3D lateral DEP (LDEP) particle force normal to the continuous through-flow. This design allows the continuous fractionation of micro/nanosized particles into different downstream subchannels based on the differences in their different critical negative DEP strengths/mobilities. The main advantage of this separation strategy is that increasing the channel length can effectively increase the throughput proportionally. The effective separation of rare cancer cells (<0.001%) from diluted human blood in a handheld chip is demonstrated. An enrichment factor of 10(5) and a recovery rate of ~85% from a 0.001% cancer cell sample are achieved at an optimal flow rate of 20 µL min(-1) passing through a 6 cm long LDEP channel with an appropriate voltage at a frequency of 10 kHz. A higher throughput of 2.4 mL h(-1) is also achieved with a 13 cm long metal-based microchannel.

Rapid identification of bacteria utilizing amplified dielectrophoretic force-assisted nanoparticle-induced surface-enhanced Raman spectroscopy.

Dielectrophoresis (DEP) has been widely used to manipulate, separate, and concentrate microscale particles. Unfortunately, DEP force is difficult to be used in regard to the manipulation of nanoscale molecules/particles. For manipulation of 50- to 100-nm particles, the electrical field strength must be higher than 3 × 10(6) V/m, and with a low applied voltage of 10 Vp-p, the electrode gap needs to be reduced to submicrons. Our research consists of a novel and simple approach, using a several tens micrometers scale electrode (low cost and easy to fabricate) to generate a dielectrophoretic microparticle assembly to form nanogaps with a locally amplified alternating current (AC) electric field gradient, which is used to rapidly trap nanocolloids. The results show that the amplified DEP force could effectively trap 20-nm colloids in the nanogaps between the 5-µm particle aggregates. The concentration factor at the local detection region was shown to be approximately 5 orders of magnitude higher than the bulk solution. This approach was also successfully used in bead-based surface-enhanced Raman spectroscopy (SERS) for the rapid identification of bacteria from diluted blood.

Ripple structure-generated hybrid electrokinetics for on-chip mixing and separating of functionalized beads.

We present an electrokinetics-based microfluidic platform that is capable of on-chip manipulating, mixing, and separating microparticles through adjusting the interrelated magnitudes of dielectrophoresis and AC electroosmosis. Hybrid electrokinetic phenomenon is generated from an electric field-induced micro-ripple structure made of ultraviolet-curable glue. Size-dependent particle separation and selective removal over the ripple structure is demonstrated successfully. Varying the waveform from sine-wave to square-wave allows generating a fluid convection at specific positions to mix the antibody-functionalized beads and antigen. Potential application in the bead-based immunoassay was also demonstrated for immuno-reaction and subsequently separating the bead-bead aggregate and non-binding beads on-chip.

A rapid electrochemical biosensor based on an AC electrokinetics enhanced immuno-reaction.

Fluorescent labelling and chromogenic reactions that are commonly used in conventional immunoassays typically utilize diffusion dominated transport of analytes, which is limited by slow reaction rates and long detection times. By integrating alternating current (AC) electrokinetics and electrochemical impedance spectroscopy (EIS), we construct an immunochip for rapid, sensitive, and label-free detection. AC electroosmosis (ACEO) and positive dielectrophoresis (DEP), induced by a biased AC electric field, can rapidly convect and trap the analyte onto an EIS working electrode within a few minutes. This allows the change of electron-transfer resistance (ΔRet) caused by the antibody-antigen (IgG-protein A) binding to be measured and quantified in real time. The measured impedance change achieves a plateau after electrokinetic concentration for only 90 s, and the detection limit is able to reach 200 pg ml⁻¹. Compared to the conventional incubation method, the electrokinetics-enhanced method is approximately 100 times faster in its reaction time, and the detection limit is reduced by 30 times. The ΔRet of the positive response is two orders of magnitude higher than the negative control, demonstrating excellent specificity for practical applications.

Screening of antibiotic susceptibility to ß-lactam-induced elongation of Gram-negative bacteria based on dielectrophoresis.

We demonstrate a rapid antibiotic susceptibility test (AST) based on the changes in dielectrophoretic (DEP) behaviors related to the ß-lactam-induced elongation of Gram-negative bacteria (GNB) on a quadruple electrode array (QEA). The minimum inhibitory concentration (MIC) can be determined within 2 h by observing the changes in the positive-DEP frequency (pdf) and cell length of GNB under the cefazolin (CEZ) treatment. Escherichia coli and Klebsiella pneumoniae and the CEZ are used as the sample bacteria and antibiotic respectively. The bacteria became filamentous due to the inhibition of cell wall synthesis and cell division and cell lysis occurred for the higher antibiotic dose. According to the results, the pdfs of wild type bacteria decrease to hundreds of kHz and the cell length is more than 10 µm when the bacterial growth is inhibited by the CEZ treatment. In addition, the growth of wild type bacteria and drug resistant bacteria differ significantly. There is an obvious decrease in the number of wild type bacteria but not in the number of drug resistant bacteria. Thus, the drug resistance of GNB to ß-lactam antibiotics can be rapidly assessed. Furthermore, the MIC determined using dielectrophoresis-based AST (d-AST) was consistent with the results of the broth dilution method. Utilizing this approach could reduce the time needed for bacteria growth from days to hours, help physicians to administer appropriate antibiotic dosages, and reduce the possibility of the occurrence of multidrug resistant (MDR) bacteria.

Dielectrophoresis and shear-enhanced sensitivity and selectivity of DNA hybridization for the rapid discrimination of Candida species.

We present a dielectrophoresis (DEP)-based microfluidic chip that is capable of enhancing the sensitivity and selectivity of DNA hybridization using an AC electric field and hydrodynamic shear in a continuous through-flow. Molecular DEP was employed to rapidly trap ssDNA molecules in a flowing solution to a cusp-shaped nanocolloid assembly on a microfluidic chip with a locally amplified AC electric field gradient. The detection time can be accelerated to sub-minute periods, and the sensitivity can reach the pico-molar level due to the AC DEP-enhanced molecule concentration (at an optimal AC frequency of 900 kHz) in a small region (∼100 µm(2)) instead of the broad area used in a tank reactor (∼10(6) µm(2)). Continuous flow in a microchannel provides a constant and high shear rate that can shear off most non-specific target-probe binding to promote the discriminating selectivity. On-chip multi-target discrimination of Candida species can be achieved within a few minutes under optimal conditions.

Antibiotic susceptibility test based on the dielectrophoretic behavior of elongated Escherichia coli with cephalexin treatment.

This study reports the use of dielectrophoresis (DEP), which determined the crossover frequency (cof) of antibiotic-induced elongation of Escherichia coli (E. coli) with regard to the rapid antibiotic susceptibility test (AST). Different dielectric properties and elongation rates of E. coli are caused by various concentrations of cephalexin treatment. According to the authors' results, significant changes in the cof of bacteria treated with 32 µg∕ml antibiotic for 60 min can be found by using a quadruple electrode array, and the results of DEP-based AST correspond with that of agar dilution method. Utilizing this approach could greatly reduce the period of bacteria growth, and obtain the minimum inhibition concentration of E. coli to cephalexin.

A dielectrophoretic chip with a roughened metal surface for on-chip surface-enhanced Raman scattering analysis of bacteria.

We present an analysis of the results of in situ surface-enhanced Raman scattering (SERS) of bacteria using a microfluidic chip capable of continuously sorting and concentrating bacteria via three-dimensional dielectrophoresis (DEP). 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 electrode-patterned bottom layer fabricated on a thin cover-slip was used to reduce fluorescence noise from the glass substrate. Gram positive (Staphylococcus aureus) and Gram negative (Pseudomonas aeruginosa) bacteria were effectively distinguished in the SERS spectral data. Staphylococcus aureus (concentration of 10(6) CFUml) was continuously separated and concentrated via DEP out of a sample of blood cells. At a flow rate of 1 mulmin, 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.

A rapid field-use assay for mismatch number and location of hybridized DNAs.

Molecular dielectrophoresis (DEP) is employed to rapidly (

A continuous high-throughput bioparticle sorter based on 3D traveling-wave dielectrophoresis.

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.

An integrated dielectrophoretic chip for continuous bioparticle filtering, focusing, sorting, trapping, and detecting.

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 (DEP) microfluidic platform based on planar electrodes that form three-dimensional (3D) DEP gates. This platform can continuously perform these tasks with a throughput of 3 muLmin. 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 mul of a heterogeneous colony of 10(7) colony forming units ml was processed in a single pass within 30 min.