Yongmo Yang

A μL-scale micromachined microbial fuel cell having high power density

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.

Surface plasmon resonance protein sensor using Vroman effect

We report a new surface plasmon resonance (SPR) protein sensor using the Vroman effect for real-time, sensitive and selective detection of protein. The sensor relies on the competitive nature of protein adsorption onto the surface, directly depending upon proteins molecular weight. The sensor uses SPR for highly sensitive biomolecular interactions detection and the Vroman effect for highly selective detection. By using the Vroman effect we bypass having to rely on bio-receptors and their attachment to transducers, a process known to be complex and time-consuming. The protein sensor is microfabricated to perform real-time protein detection using four different proteins including aprotinin (0.65kDa), lysozyme (14.7kDa), streptavidine (53kDa), and isolectin (114kDa) on three different surfaces, namely a bare-gold surface and two others modified by OH- and COOH-terminated self-assembled monolayer (SAM). The real-time adsorption and displacement of the proteins are observed by SPR and evaluated using an atomic force microscope (AFM). The sensor can distinguish proteins of at least 14.05kDa in molecular weight and demonstrate a very low false positive rate. The protein detector can be integrated with microfluidic systems to provide extremely sensitive and selective analytical capability.

Miniaturized protein separation using a liquid chromatography column on a flexible substrate

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.

Separating and Detecting Escherichia Coli in a Microfluidic Channel for Urinary Tract Infection Applications

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 × 104 and 6.4 × 105 CFU/mL, covering the threshold of UTI (105 CFU/mL). The sensitivity of the LOC in detecting E. coli is characterized to be at least 3.4 × 104 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.

Separation of beta-human chorionic gonadotropin and immunoglobulin G by a miniaturized size exclusion chromatography column

This report describes a miniaturized size exclusion chromatography column that effectively preseparates raw samples for medical point-of-care testing (POCT) devices. The minicolumn is constructed of polydimethylsiloxane fabricated on a glass slide. The minicolumn separates 300 ng/ml of beta-human chorionic gonadotropin (β-hCG) from an immunoglobulin G (IgG)-rich solution (100 μg/ml) in 7.7 min, with 2.23 resolution and 0.018 mm plate height. The complete analyte discrimination shows potential for the sample preparation stage of POCT devices for cancer screening, prognosis, and monitoring.

Miniaturized HPLC column with nano-pore beads for protein separation on flexible medical implants

This paper reports a miniaturized HPLC (high performance liquid chromatography) column packed with nano-pore beads for flexible medical implants applications. The all-flexible-polymer column capable of integrating with micro/nano-devices on a chip separates biological entities to relax stringent requirements on subsequent detectors and to enable parallel detection in a detector array. The fabricated device has successfully separated a protein mixture using nano-pore beads in a miniaturized column. According to HPLC analysis, the intensity ratio of large to small protein varies significantly, more than a factor of 300, over sample collecting time, ~12mins, suggesting very high separation performance.

Separation of α-Fetoprotein and IgG by a Miniaturized Size Exclusion Chromatography (SEC) Column

Abstract We report a miniature separator for medical microdevices. The separator uses a size-exclusion chromatography (SEC) mini-column in liquid chromatography (LC). The mini-column is fabricated on a glass slide with polydimethylsiloxane (PDMS) for structure. Polydivinlybenzene nanobeads (5–20 µm in diameter, 100-nm pore size) were used. The SEC mini-column successfully separates α-fetoprotein (AFP) and immunoglobulin G (IgG) at 5 and 9 min, respectively, with 0.86 resolution and 0.06-mm plate height. The mini-column shows potential for use in onboard sample preparation in a total analysis system (µTAS) for a point-of-care testing (POCT) device that could be used effectively in cancer screening, diagnosis, and prognosis.

A Compact Separation Column For Hazardous Chemicals

This paper reports a miniaturized reverse-phase high performance liquid chromatography (HPLC) column for chemically hazardous molecules. The mini-column is designed to generate a phase delay for mixed sample molecules by the reverse-phase separation mechanism. The reverse-phase separation is performed by silica-based nano-pore beads (C-18) as stationary phase and a mixture of methanol and DI water as mobile phase. The C-18 beads are packed inside the compact chamber enclosed by a custom built PDMS (polydimethylsiloxane) housing, equipped with microfluidic channels, inlet/outlet ports, and connectors. The mobile phase and target analytes are controlled by a syringe pump capable of manipulating two different flow rates using LabVIEW interface. The mini-column successfully separates two sample chemical molecules: acetaminophen and aspirin. The intensity ratio of two molecules decreases 35% from two different samples collecting at 3 and 8 min.

Two-phase mini-separator to separate alpha-fetoProtein from fibrinogen and Immunoglobulin

This paper reports a two-phase mini-column separator that depletes Immunoglobulin G (IgG) and separates α-fetoProtein (AFP) and fibrinogen. A mixture of IgG, fibrinogen, and AFP goes through the two-phase separator, where IgG is depleted by an affinity mini-column using Protein A/G agarose beads in the first phase. In the second phase, AFP is separated from fibrinogen by Size Exclusion Chromatography (SEC). The IgG depletion and SEC separation results are confirmed by evaluating fluorescent intensity of the eluents. Red (IgG), green (AFP), and blue (fibrinogen) intensities show that over 99.5% of IgG is depleted and, in 10 min, the second phase SEC mini-column separates AFP (1 µg/mL) from fibrinogen-rich solution (10 µg/mL) with 2.78 resolution and 0.0056 mm plate height.