Biosensors & Bioelectronics 16 (2001) 187–194
A laminated, flex structure for electronic transport and
hybridization of DNA
Anita H. Forster *, Michael Krihak, Paul D. Swanson, Trevor C. Young,
Donald E. Ackley
1
Department of Ad6anced Technology, Nanogen, Inc.,
10398
Pacific Center Court, San Diego, CA
92121
, USA
Received 21 July 2000; received in revised form 4 September 2000; accepted 14 February 2001
Abstract
We have developed the first prototypes of a three-dimensional, electrophoretically driven microlaboratory for the analysis of
proteins and DNA. By selecting the appropriate spacing and geometrical configuration, oligonucleotides were transported, in a
controlled, rapid fashion, by electrophoresis in free-space. Transport efficiencies over 2 mm distances exceeded 70%. Electrodes of
similar design were combined with an electronically addressed DNA hybridization chip to form a fully electrophoretic
microlaboratory. In this instance, gold-plated copper electrodes were patterned ona2milthick polyimide substrate. This
polyimide layer was stiffened with 20 mil of polyimide to provide support for flip-chip bonding of our standard 100-site
Nanochip™. This composite structure illustrated three-dimensional transport of target oligonucleotides, through a via in the
polyimide, along a series of electrodes and onto the diagnostic chip. Upon reaching the diagnostic chip, electronic hybridization
was performed for a competitive reverse dot blot assay. The electronic assay showed a specific to nonspecific ratio in excess of
20:1. These results suggested that this type of structure might be of practical consequence with the development of a
microlaboratory for biowarfare applications. © 2001 Elsevier Science B.V. All rights reserved.
Keywords
:
Electronic DNA hybridization; Flip-chip; Flexible electronics
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1. Introduction
Over the past decade, there has been considerable
interest in developing DNA (deoxyribonucleic acid)
diagnostic arrays on miniaturized substrates or ‘‘chips’’.
Several groups have employed DNA chips in a variety
of applications such as the analysis of microorganisms
for infectious diseases, mutations in the human genome,
drug discovery, genetic identification and gene expres-
sion. Unlike these DNA array technologies, Nanogen
chips are fabricated by semiconductor technology and
provide electronically driven assays.
In greater detail, the Nanochip™ combines the ad-
vantages of DNA microarrays with rapid, electronically
multiplexed assay reactions. Each reaction site is
defined by an electrode that is supplied with a con-
trolled electrical current. Application of an electronic
bias generates an electric field at each site that concen-
trates or repels charged molecules in solution depending
upon the voltage polarity (Heller et al., 2000). There-
fore, the electrophoretic transport of DNA towards the
electrode, under a positive bias, accelerates hybridiza-
tion reaction kinetics by increasing the target concen-
tration in the electrode vicinity and by the localized pH
change (Edman et al., 1997). Conversely, a negative
bias on the electrode repels DNA and blocks reactions
near the electrode. In addition, the application of a
negative bias after the hybridization step provides elec-
tronic stringency, thus removing target DNA as selec-
tive as a single base pair mismatch (Sosnowski et al.,
1997). Since there is an array of sites, a plurality of
electrodes may be activated to perform a multitude of
reactions simultaneously (Heller et al., 1999).
As technology pushes towards miniaturization, sev-
eral researchers have launched efforts for the integra-
tion of multiple laboratory procedures into a compact,
* Corresponding author. Tel.: +1-858-410-4658; fax: + 1-858-410-
4848.
E-mail address
:
aforster@nanogen.com (A.H. Forster).
1
Present address: Redon, Inc., 124 Mt. Auburn Street, Cambridge,
MA, USA
0956-5663/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0956-5663(01)00121-X