Monday, September 1, 2008

Cell-Transistor-Hybrid

Biological cells are able to receive, process, and transmit information.
Connecting these cells to micro-electronic circuits opens up exciting new perspectives in bioelectronics, information technology, medical engineering and in sensor development. Living cells possess receptors of unmatched sensitivity that detect external signals of chemical nature (nutrients, hormones, neurotransmitters, changes in proton- or ion-concentration, etc.) or physical stimuli as a change in temperature, light, mechanical force, or even electromagnetic fields. These input parameters are processed by the cells. The internal “machinery” of the cell
includes signal amplification cascades and logic connections of high non-linearity, but the details remain to be unveiled. The resulting output signal may generate many physiological reactions inside the cell, as the synthesis of specific olecules, a change in gene expression or the storage of certain substances.
The output signals also allow the cell to communicate with its environment and with other cells. In order to provide selective long-term cell-transducer interfaces in vitro, microtechnology is used for the development of planar arrays with large numbers of field-effect transistors or metal electrodes in the size of the individual cells. These arrays usually consist of a culture chamber with embedded chip. For metalelectrode arrays (MEAs), insulated conductor paths are patterned lithographically. Their opened metallic ends form the sensing electrodes. In addition, field-effect transistor (FET) arrays have been developed to record the electrical signals from cells. Modifications of standard FET fabrication processes lead to devices with metal-free gate electrodes. A variation of these devices is the so-called ion-sensitive field-effect transistor (ISFET). Its gate dielectric is modified to yield higher sensitivity for certain ions. Sufficient electrical coupling between the cell and the electrode for extracellular signal recording is achieved only if a cell or a part of a cell is located directly on top of the electrode.
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Bioelectronic DNA detection involves forming an electronic circuit mediated by nucleic acid hybridization and it serves as the basis for a DNA detection system called eSensor™ [1-4]. This system uses low-density DNA chips containing electrodes coated with DNA capture probes. Target DNA present in the sample hybridizes specifically both to capture probes and ferrocene labeled signal probes in solution thereby generating an electric current. Currente Sensor DNA chips contain as many as 36 electrodes for simultaneous detection of multiple pathogens from a single sample.

Many pathogens cause both acute and chronic disease at relatively low copy number and may be difficult or impossible to propagate in culture. Thus, most pathogen detection systems rely on nucleic acid amplification by using polymerase chain reaction (PCR). One highly effective amplification strategy targets conserved sequences among the family of organisms of interest. Such broad-range PCR strategies have been used to identify and characterize several known and previously uncharacterized bacteria [5,6] and viruses [7,8]. In order to maximize the utility of these effective pathogen nucleic acid amplification systems, amplification needs to be coupled with rapid, sensitive, and specific detection. Bioelectronic DNA detection by use of the eSensor chip might fulfill this need.

Human papillomaviruses (HPV) serve as an ideal model system for determining the efficiency and feasibility of eSensor DNA detection technology since there are at least 30 distinct genital HPV types that can be effectively amplified with broad-range consensus PCR primers. We designed two eSensor chips, each containing 14 probes specific for the conserved L1 region of the HPV genome. We evaluated clinical cervical cytology samples known to contain one or more HPV types. The eSensor DNA detection platform successfully detected the correct HPV type in most of these clinical samples, demonstrating that the system provides a rapid, sensitive, specific, and economical approach for multiple-pathogen detection and identification from a single sample.Background We used human papillomaviruses (HPV) as a model system to evaluate the utility of a nucleic acid, hybridization-based bioelectronic DNA detection platform (eSensor) in identifying multiple pathogens.