We report a MEMS (Micro-Electro-Mechanical Systems)-based microbial fuel cell (MFC) that produces a high power density. The MFC features 4.5-μL anode/cathode chambers defined by 20-μm-thick photo-definable polydimethylsiloxane (PDMS) films. The MFC uses a Geobacter-enriched mixed bacterial culture, anode-respiring bacteria (ARB) that produces a conductive biofilm matrix. The MEMS MFC generated a maximum current density of 16,000 μA cm(-3) (33 μA cm(-2)) and power density of 2300 μW cm(-3) (4.7 μW cm(-2)), both of which are substantially greater than achieved by previous MEMS MFCs. The coulombic efficiency of the MEMS MFC was at least 31%, by far the highest value among reported MEMS MFCs. The performance improvements came from using highly efficient ARB, minimizing the impact of oxygen intrusion to the anode chamber, having a large specific surface area that led to low internal resistance.

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Atrial fibrillation (AF) is characterized by multiple rapid and irregular atrial depolarization leading to rapid ventricular responses exceeding 100 beats per minute (bpm). We hypothesized that rapid and irregular pacing reduced intravascular shear stress (ISS) with implication to modulating endothelial responses. To simulate AF, we paced the left atrial appendage of New Zealand White (NZW) rabbits (n=4) at rapid and irregular intervals. Surface electrical cardiograms (ECG) were recorded for atrial and ventricular rhythm, and intravascular convective heat transfer was measured by micro thermal sensors, from which ISS was inferred. Rapid and irregular pacing decreased arterial systolic and diastolic pressures (baseline: 99/75 mmHg; rapid regular pacing: 92/73; rapid irregular pacing: 90/68; P < 0.001, n=4), temporal gradients (∂τ/∂t from 1275 ± 80 to 1056 ± 180 dyne/cm2·s), and reduced ISS (from baseline at 32.0 ± 2.4 to 22.7 ± 3.5 dyne/cm2). Computational fluid dynamics (CFD) code demonstrated that experimentally inferred ISS provided a close approximation to the computed wall shear stress (WSS) at a given catheter to vessel diameter ratio, shear stress range, and catheter position. In an in vitro flow system in which time-averaged shear stress was maintained at τavg=23 ±4 dyn·cm−2·s−1, we further demonstrated that rapid pulse rates at 150 bpm down-regulated endothelial nitric oxide (NO), promoted superoxide (O2·−) production, and increased monocyte binding to endothelial cells. These findings suggest that rapid pacing reduces ISS and ∂τ/∂t, and rapid pulse rates modulate endothelial responses.

We report a lab-on-a-chip (LOC) that can separate and detect Escherichia coli (E. coli) in simulated urine samples for urinary tract infection (UTI) applications. The LOC consists of two (concentration and sensing) chambers connected in series and an integrated impedance detector. The two-chamber approach is designed to reduce the nonspecific absorption of a protein, e.g., albumin, that potentially coexists with E. coli in urine. We directly separate E. coli K-12 from cocktail urine in a concentration chamber containing microsized magnetic beads conjugated with anti-E. coli antibody. The immobilized E. coli is transferred to a sensing chamber for the impedance measurement. The measurement at the concentration chamber suffers from nonspecific absorption of albumin on the gold electrode, which may lead to false-positive response. By contrast, the measured impedance at the sensing chamber shows a ∼60-kΩ impedance change. This is a clear distinction between 6.4 × 10 4 and 6.4 × 10 5 CFU/mL, covering the threshold of UTI (10 5 CFU/mL). The sensitivity of the LOC in detecting E. coli is characterized to be at least 3.4 × 10 4 CFU/mL. We also characterized the LOC for different age groups and white blood cell spiked samples. These preliminary data show promising potential for application in portable LOC devices for UTI detection.[ 2010-0263]Index Terms-Escherichia coli (E. coli), lab-on-a-chip (LOC), point-of-care testing, urinary tract infection (UTI).

We report a prototype protein separator that successfully miniaturizes existing technology for potential use in biocompatible health monitoring implants. The prototype is a liquid chromatography (LC) column (LC mini-column) fabricated on an inexpensive, flexible, biocompatible polydimethylsiloxane (PDMS) enclosure. The LC mini-column separates a mixture of proteins using size exclusion chromatography (SEC) with polydivinylbenzene beads (5-20 μm in diameter with 10 nm pore size). The LC mini-column is smaller than any commercially available LC column by a factor of ∼11 000 and successfully separates denatured and native protein mixtures at ∼71 psi of the applied fluidic pressure. Separated proteins are analyzed using NuPAGE-gel electrophoresis, high-performance liquid chromatography (HPLC) and an automated electrophoresis system. Quantitative HPLC results demonstrate successful separation based on intensity change: within 12 min, the intensity between large and small protein peaks changed by a factor of ∼20. In further evaluation using the automated electrophoresis system, the plate height of the LC mini-column is between 36 μm and 100 μm. The prototype LC mini-column shows the potential for real-time health monitoring in applications that require inexpensive, flexible implant technology that can function effectively under non-laboratory conditions.