Parts per trillion detection of heavy metals in as-is tap water using carbon nanotube microelectrodes.

Heavy metal contamination of drinking water is a major global issue. Research reports across the globe show contamination of heavy metals higher than the set standards of the World Health Organization (WHO) and US Environmental Protection Agency (EPA). To our knowledge, no electrochemical sensor for heavy metals with parts per trillion (PPT) limits of detection (LOD) in as-is tap water has been reported or developed. Here, we report a microelectrode that consists of six highly densified carbon nanotube fiber (HD-CNTf) cross sections called rods (diameter ∼69 µm and length ∼40 µm) in a single platform for the ultra-sensitive detection of heavy metals in tap water and simulated drinking water. The HD-CNTf rods microelectrode was evaluated for the individual and simultaneous determination of trace level of heavy metal ions i.e. Cu2+, Pb2+ and Cd2+ in Cincinnati tap water (without supporting electrolyte) and simulated drinking water using square wave stripping voltammetry (SWSV). The microsensor exhibited a broad linear detection range with an excellent limit of detection for individual Cu2+, Pb2+ and Cd2+ of 6.0 nM, (376 ppt), 0.45 nM (92 ppt) and 0.24 nM (27 ppt) in tap water and 0.32 nM (20 ppt), 0.26 nM (55 ppt) and 0.25 nM (28 ppt) in simulated drinking water, respectively. The microelectrode was shown to detect Pb2+ ions well below the WHO and EPA limits in a broad range of water quality conditions reported for temperature and conductivity in the range of 5 °C-45 °C and 55 to 600 µS/cm, respectively.

The effect of the physicochemical properties of bioactive electroconductive hydrogels on the growth and proliferation of attachment dependent cells.

The physicochemical properties of soft electrode materials for the abio-bio interface of advanced biosensors and next generation bionic devices in the form of electroconductive hydrogels (ECH) of interpenetrating networks of polypyrrole formed within poly(hydroxyethylmethacrylate)-based hydrogels were examined. The 1.5 mol% UV-crosslinked tetraethyleneglycol diacrylate (TEGDA) (step 1) poly(HEMA) and the electropolymerized (step 2) polypyrrole co-networks were covalently joined by the inclusion of a bifunctional monomer (1.5 mol%), 2-methacryloyloxyethyl-4(3-pyrrolyl)butanate (MPB) that served to covalently link the two networks. The optical absorbance, degree of hydration, the frequency dependent electrical impedance and the elastic modulus were examined as a function of electropolymerization charge density (step 2) (1-900 mC/cm(2)) used to prepare the linked, interpenetrating co-networks. The absorption at 430 nm showed a monotonic increase with electropolymerization charge density and correlated with the increase in elastic modulus [56 (± 32)-499 (± 293) kPa], the decrease in % hydration (68-0%) and the decrease in membrane electrical resistance. Polypyrrole (PPy) grows initially from the gel-electrode interface to fill voids within the hydrogel and ultimately onto the surface of the hydrogel. Growth of attachment dependent Rhabdomyosarcoma (RMS13) and pheochromocytoma (PC 12) cells reflects this evolution, showing an increase to a maximal value and then to decrease again at high electropolymerization charge density.

Hydrodynamic focusing--a versatile tool.

The control of hydrodynamic focusing in a microchannel has inspired new approaches for microfluidic mixing, separations, sensors, cell analysis, and microfabrication. Achieving a flat interface between the focusing and focused fluids is dependent on Reynolds number and device geometry, and many hydrodynamic focusing systems can benefit from this understanding. For applications where a specific cross-sectional shape is desired for the focused flow, advection generated by grooved structures in the channel walls can be used to define the shape of the focused flow. Relative flow rates of the focused flow and focusing streams can be manipulated to control the cross-sectional area of the focused flows. This paper discusses the principles for defining the shape of the interface between the focused and focusing fluids and provides examples from our lab that use hydrodynamic focusing for impedance-based sensors, flow cytometry, and microfabrication to illustrate the breadth of opportunities for introducing new capabilities into microfluidic systems. We evaluate each example for the advantages and limitations integral to utilization of hydrodynamic focusing for that particular application.

On-demand controlled release of anti-inflammatory and analgesic drugs from conducting polymer films to aid in wound healing.

An electronically-controlled drug delivery system (eDDS) for the on-demand release of anti-inflammatory, anti-microbial and analgesic agents to aid in wound healing is currently under development. The loading of several drugs into conductive polymer films and their subsequent on-demand, controlled release upon application of an electrical potential to the polymer film has been demonstrated. The loading and release (active and passive) of Ibuprofen sodium salt - a negatively charged analgesic and anti-inflammatory agent - from polypyrrole films is described. Major challenges identified include precise control over drug loading and passive release from the conducting polymers in the absence of an applied potential.

A metabolic biofuel cell: conversion of human leukocyte metabolic activity to electrical currents.

An investigation of the electrochemical activity of human white blood cells (WBC) for biofuel cell (BFC) applications is described. WBCs isolated from whole human blood were suspended in PBS and introduced into the anode compartment of a proton exchange membrane (PEM) fuel cell. The cathode compartment contained a 50 mM potassium ferricyanide solution. Average current densities between 0.9 and 1.6 µA cm-2 and open circuit potentials (Voc) between 83 and 102 mV were obtained, which were both higher than control values. Cyclic voltammetry was used to investigate the electrochemical activity of the activated WBCs in an attempt to elucidate the mechanism of electron transfer between the cells and electrode. Voltammograms were obtained for the WBCs, including peripheral blood mononuclear cells (PBMCs - a lymphocyte-monocyte mixture isolated on a Ficoll gradient), a B lymphoblastoid cell line (BLCL), and two leukemia cell lines, namely K562 and Jurkat. An oxidation peak at about 363 mV vs. SCE for the PMA (phorbol ester) activated primary cells, with a notable absence of a reduction peak was observed. Oxidation peaks were not observed for the BLCL, K562 or Jurkat cell lines. HPLC confirmed the release of serotonin (5-HT) from the PMA activated primary cells. It is believed that serotonin, among other biochemical species released by the activated cells, contributes to the observed BFC currents.

Hydrodynamic and electrical considerations in the design of a four-electrode impedance-based microfluidic device.

A four-electrode impedance-based microfluidic device has been designed with tunable sensitivity for future applications to the detection of pathogens and functionalized microparticles specifically bound to molecular recognition molecules on the surface of a microfluidic channel. In order to achieve tunable sensitivity, hydrodynamic focusing was employed to confine the electric current by simultaneous introduction of two fluids (high- and low-conductivity solutions) into a microchannel at variable flow-rate ratios. By increasing the volumetric flow rate of the low-conductivity solution (sheath fluid) relative to the high-conductivity solution (sample fluid), increased focusing of the high-conductivity solution over four coplanar electrodes was achieved, thereby confining the current during impedance interrogation. The hydrodynamic and electrical properties of the device were analyzed for optimization and to resolve issues that would impact sensitivity and reproducibility in subsequent biosensor applications. These include variability in the relative flow rates of the sheath and sample fluids, changes in microchannel dimensions, and ionic concentration of the sample fluid. A comparative analysis of impedance measurements using four-electrode versus two-electrode configurations for impedance measurements also highlighted the advantages of using four electrodes for portable sensor applications.

Characterization of electroconductive blends of poly(HEMA-co-PEGMA-co-HMMA-co-SPMA) and poly(Py-co-PyBA).

Electroconductive hydrogels (ECH) prepared as blends of UV-cross-linked poly(hydroxyethylmethacrylate) [p(HEMA)]-based hydrogels and electropolymerized polypyrrole (PPy) were synthesized as coatings on microlithographically fabricated interdigitated microsensor electrodes (IMEs) and microdisc electrode arrays (MDEAs). Hydrogels were synthesized from tetraethyleneglycol diacrylate (TEGDA), hydroxyethylmethacrylate (HEMA), polyethyleneglycol monomethacrylate (PEGMA), N-[tris(hydroxymethyl)methyl]-acrylamide (HMMA), and 3-sulfopropyl methacrylate potassium salt (SPMA) to produce p(HEMA-co-PEGMA-co-HMMA-co-SPMA) hydrogels. The conductive polymer was synthesized from pyrrole and 4-(3'-pyrrolyl)butyric acid by electropolymerization within the electrode-supported hydrogel. ECH films produced with different electropolymerization charge densities were investigated using cyclic voltammetry, electrical impedance spectroscopy, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Polymer morphology was studied by SEM. The ECH demonstrated the desired characteristics of high electrical conductivity (low impedance), as well as high thermal stability compared to pure hydrogel. Signal enhancement was achieved by modifying the surface of an MDEA biotransducer with the ECH, with a 10-fold increase in the voltammetric current response associated with the ferrocene monocarboxylic acid (FcCO(2)H) redox reaction.

Towards an implantable biochip for glucose and lactate monitoring using microdisc electrode arrays (MDEAs).

A complete electrochemical cell-on-a-chip that uses the MicroDisc Electrode Array (MDEA) working electrode (WE) design was evaluated for eventual intramuscular implantation for the continuous amperometric monitoring of glucose and lactate in an animal trauma model. The microfabricated ECC MDEA5037 comprises two discrete electrochemical cells-on-a-chip (ECCs), each with a reference, counter, and MDEA working electrode. Each MDEA comprises 37 microdiscs (diameter = 50 microm) arranged in a Hexagonal Closed Packed (HCP) arrangement with a center to center distance (d) of 100 microm. Cyclic Voltammetry (CV) and Electrical Impendence Spectroscopy (EIS) reveals that this device scales in its interfacial properties with a corresponding MDEA 050 device that comprises 5,184 microdiscs. Parallel development of miniaturized mixed-signal integrated electronics for wireless reprogramming, data acquisition and communication addresses the key issues involved in developing measurement electronics, AD/DA processing, power management and telemetry for implantable amperometric biosensors. A generalized electronics platform based on the Texas Instruments TI NC01101 chip has been developed that may be readily applied to many types of biotransducers with minor modifications.

Biomimetic hydrogels for biosensor implant biocompatibility: electrochemical characterization using micro-disc electrode arrays (MDEAs).

Our interest is in the development of engineered microdevices for continuous remote monitoring of intramuscular lactate, glucose, pH and temperature during post-traumatic hemorrhaging. Two important design considerations in the development of such devices for in vivo diagnostics are discussed; the utility of micro-disc electrode arrays (MDEAs) for electrochemical biosensing and the application of biomimetic, bioactive poly(HEMA)-based hydrogel composites for implant biocompatibility. A poly(HEMA)-based hydrogel membrane containing polyethylene glycol (PEG) was UV cross-linked with tetraethyleneglycol diacrylate following application to MDEAs (50 mum discs) and to 250 mum diameter gold electrodes within 8-well culture ware. Cyclic voltammetry (CV) of the MDEAs revealed a reduction in the apparent diffusion coefficient of ferrocenemonocarboxylic acid (FcCO(2)H), from 6.68 x 10(-5) to 6.74 x 10(-6) cm(2)/s for the uncoated and 6 mum thick hydrogel coated devices, respectively. Single frequency (4 kHz) temporal impedance measurements of the hydrogels in the 8-well culture ware showed a reversible 5% change in the absolute impedance of the hydrogels when exposed to a pH change between 6.1 to 7.2 and a 20% drop between pH 6.1 and 8.8.

A 128-electrode three dimensional electrical impedance tomography system.

Electrical impedance tomography (EIT) is a new functional imaging technique. This paper presents the development of a new electrical impedance tomography system with 128 electrodes for impedance change detection and 3D imaging of the human thorax. The system consists of several modules, including multi-frequency current source, driving, measuring, data acquisition, and controlling and signal processing modules. A high speed digital signal processor (DSP) is used as the controller. The 64 driving electrodes and 64 measuring electrodes are positioned uniformly in four planes around the surface of a cylindrical phantom filled with a saline solution and objects of varying conductivities. The performance has been tested, and these preliminary experiments demonstrate the feasibility this system.

Platform technologies to support brain-computer interfaces.

There is a lack of adequate and cost-effective treatment options for many neurodegenerative diseases. The number of affected patients is in the millions, and this number will only increase as the population ages. The developing areas of neuromimetics and stimulative implants provide hope for treatment, as evidenced by the currently available, but limited, implants. New technologies are emerging that are leading to the development of highly intelligent, implantable sensors, activators, and mobile robots that will provide in vivo diagnosis, therapeutic interventions, and functional replacement. Two key platform technologies that are required to facilitate the development of these neuromimetic and stimulative implants are data communication channels and the devices' power supplies. In the research reported in this paper, investigators have examined the use of novel concepts that address these two needs. These concepts are based on ionic volume conduction (VC) to provide a natural communication channel to support the functioning of these devices, and on biofuel cells to provide a continuously rechargeable power supply that obtains electrons from the natural metabolic pathways. The fundamental principles of the VC communication channels, including novel antenna design, are demonstrated. These principles include the basic mechanisms, device sensitivity, bidirectionality of communication, and signal recovery. The demonstrations are conducted using mathematical and finite element analysis, physical experiments, and animal experiments. The fundamental concepts of the biofuel cells are presented, and three versions of the cells that have been studied are discussed, including bacteria-based cells and two white cell-based experiments. In this paper the authors summarize the proof or principal experiments for both a biomimetic data channel communication method and a biofuel cell approach, which promise to provide innovative platform technologies to support complex devices that will be ready for implantation in the human nervous system in the next decade.

Serotonin (5-HT) released by activated white blood cells in a biological fuel cell provide a potential energy source for electricity generation.

Previous studies by our group have demonstrated the ability of white blood cells to generate small electrical currents, on the order of 1-3 microA/cm(2), when placed at the anode compartment of a proton exchange membrane (PEM) biological fuel cell. In this research study, an electrochemical technique is used to further investigate the electron transfer ability of activated white blood cells at interfacing electrodes in an attempt to elucidate the mechanism of electron transfer in the original biological fuel cell experiments. Cyclic voltammograms were obtained for human white blood cells using a three-electrode system. The working and counter electrodes were made from carbon felt and platinum, respectively, while the reference was a saturated calomel electrode (SCE). Oxidation peaks were observed at an average potential of 363 mV vs. SCE for the PMA/ionomycin activated white blood cells in glucose solution. However a corresponding reduction peak was not observed, suggesting irreversibility of the redox reaction. The cyclic voltammograms recorded for the white blood cells bear very close similarities to those of the neurotransmitter serotonin (5-HT). Serotonin released by white blood cells into the extracellular environment may be irreversibly oxidized at the working electrode in the cyclic voltammetry experiments and at the PEM biological fuel cell anode in our earlier electrochemical cell studies.

Synthesizing multi-view video frames for coding patient monitoring video.

This paper presents a method to synthesize multi-view video frames to facilitate coding and transmission of patient monitoring video. The synthesis is carried out in the DCT domain by means of interlacing. The synthesized video provides a higher video coding efficiency, better synchronization of the video streams from multiple cameras, as well as the improved data loss resilience and protection of the video content. The viability of the presented method was demonstrated by experimental results on patient monitoring video.

Biofuel cells: a possible power source for implantable electronic devices.

Biofuel cells were designed to investigate electricity production from Escherichia coli and human white blood cells as a preliminary investigation into the possible future use of such fuel cells as power sources for implantable electronic devices. The biofuel cell's function is based on the coupling of glucose oxidation to the reduction of oxygen to water. It might, therefore, be possible to utilize the cellular processes involved in oxidative metabolism to generate electrical energy for numerous medical applications. In the bacteria experiment, we were able to generate small electrical currents, which gradually decreased over a (2) hour measurement period. In the human white blood cell experiment, our biofuel cell attained current outputs, which were smaller in magnitude than values recorded from the microbial biofuel cell.