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Bioelectronic DNA Chips for the Clinical Laboratory

¹ Clinical Diagnostics, Motorola Life Sciences, 757 South Raymond Ave., Pasadena, CA 91105, Fax 626-584-1471

^aE-mail dan.farkas{at}motorola.com

To the Editor:

I read with interest the fine review by Dr. Ronald McGlennen of miniaturization technologies (1). My colleagues and I applaud Dr. McGlennen’s focus on technology that may allow the hurdles of reimbursement, regulation, education, and utility to be addressed so that the fruits of the Human Genome Project can be realized as improved therapeutics and diagnostics.

For the sake of accuracy, I want to update the readership on the most current information about the technology we have developed; some of this information may not have been available to Dr. McGlennen during the research for his review. Clinical Micro Sensors, Inc. (CMS; Pasadena, CA) was acquired by Motorola in June 2000 and is now part of Motorola Life Sciences. Dr. McGlennen’s paragraph on CMS (Motorola) focused on our ultimate vision of a point-of-care instrument for molecular diagnostics. Our vision is to integrate nucleic acid amplification and, ultimately, specimen preparation and to provide wireless communication of results to a laboratory information system, pharmacy, or physician along with transaction support and other features. For the near term, we have developed enabling technology for the clinical molecular diagnostics laboratory that exploits postamplification bioelectronic detection of nucleic acids (DNA or RNA targets) via hybridization to oligonucleotide capture probes on gold electrode arrays affixed to printed circuit boards or chips (Fig. 1 ).

View larger version (56K): [in this window] [in a new window]   Figure 1. Photograph of Motorola Life Sciences eSensor Chip. The green printed circuit board is encased in a hybridization chamber that holds 100 µL of reagents (target, signaling probe, and hybridization buffer). Inside the hybridization chamber are 16 gold electrodes (small dots; 36 electrode chips are also available). Below and to the right of the array of 16 electrodes is one larger electrode (auxiliary electrode) and above the array, sequestered in the filling channel, is the reference electrode. The chip is capped with a handle that allows insertion into the eSensor 4800, the electronic reader device (not shown). The electrical connection between the chip and the reader is made through the connectors seen at the bottom of the chip.

Bioelectronic detection technology rests on the specific generation of electrical current through the reversible oxidation and reduction of metal complex labels on nucleic acid targets. The eSensor^TM chips have electronically active gold electrodes as well as reference and auxiliary electrodes. Each electrode is coated with a specific DNA capture probe. The capture probes (25 bases in length) are deposited on the gold electrode surfaces as a mixed monolayer of the capture probes and alkylthiol molecules. The modified electrode surface inhibits nonspecific binding and blocks electrochemical signals from both unbound label and extraneous redox compounds. Bioelectronic detection proceeds via a sandwich assay where a nucleic acid target of interest is bound simultaneously by capture probes on the electrode surface and a second probe in the system referred to as a signaling probe. Signaling probes are single-stranded oligonucleotide probes complementary to a portion of the target different from, but adjacent to, the region bound by capture probe. Signaling probes serve to label the target on hybridization.

Covalently bound to signaling probes is the organometallic, electroactive label, ferrocene. Hybridization between target and signaling probe couples the now ferrocene-labeled target to the underlying electrode. When the regions of the target complementary to the capture probe and the signaling probe hybridize, the ferrocene labels are brought into sufficient proximity to the electrode surface for detection. Application of an alternating current voltage to the electrode produces reversible reduction and oxidation of ferrocenes. Electrons are transferred between the label and the electrode surface only when the target is present and hybridized by both signaling probe and capture probe. The current generated by this system is detectable with the electronic detection system called the eSensor 4800 system, which can analyze 48 chips at a time. A molecular representation of the chemical structures on the electrode surface has been published (2).

The system has been described in more detail elsewhere (2)(3), and eSensor chips for clinical applications as well as detection of pharmacogenomic targets, infectious disease agents, genetic mutations, and industrial targets (transgenic crops, veterinary pathogens, and food safety) are in development. Chip density will range from 16 to 36 electrodes, providing a clinically relevant panel size.

References

1. McGlennen RC. Miniaturization technologies for molecular diagnostics. Clin Chem 2001;47:392-402.
2. Umek RM, Lin SW, Vielmetter J, Terbrueggen RH, Yu CJ, Kayyem JF, et al. Electronic detection of nucleic acids: a versatile platform for molecular diagnostics. J Mol Diagn 2001;3:74-84.[Abstract/Free Full Text]
3. Umek RM, Lin SW, Chen Y-P, Irvine B, Paulluconi G, Chan V, et al. Bioelectronic detection of point mutations using discrimination of the H63D polymorphism of the Hfe gene as a model. Mol Diagn 2000;5:321-328.[Medline] [Order article via Infotrieve]

This Article Extract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (12) Citing Articles via Google Scholar Google Scholar Articles by Farkas, D. H. Search for Related Content PubMed PubMed Citation Articles by Farkas, D. H. Related Collections Molecular Diagnostics and Genetics