Robust microfabricated field-effect sensor for monitoring molecular adsorption in liquids

Cooper, E. B.; Fritz, Jürgen; Wiegand, Gerald; Wagner, P.; Manalis, Scott R.

doi:10.1063/1.1423776

Cited by 17 publications

(17 citation statements)

References 18 publications

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“…The field-effect sensors used in this work are EIS capacitors microfabricated at the termini of silicon cantilevers according to a process described in detail elsewhere (ref. 23; Fig. 1c).…”

Section: Methodsmentioning

confidence: 99%

“…The high-impedance EIS structure prevents faradaic processes on the sensor surface that could deteriorate the sensors or analytes. Sensors are operated at a bias voltage where their response is linear and most sensitive to surface potential changes, i.e., at the inflection point of their capacitance-versus-voltage curves (23). The resulting periodic charging current on the sensors is amplified and measured by using a lock-in amplifier with a 100-ms time constant.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Electronic detection of DNA by its intrinsic molecular charge

Fritz

Cooper

Gaudet

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

428

320

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We report the selective and real-time detection of label-free DNA using an electronic readout. Microfabricated silicon field-effect sensors were used to directly monitor the increase in surface charge when DNA hybridizes on the sensor surface. The electrostatic immobilization of probe DNA on a positively charged poly-L-lysine layer allows hybridization at low ionic strength where field-effect sensing is most sensitive. Nanomolar DNA concentrations can be detected within minutes, and a single base mismatch within 12-mer oligonucleotides can be distinguished by using a differential detection technique with two sensors in parallel. The sensors were fabricated by standard silicon microtechnology and show promise for future electronic DNA arrays and rapid characterization of nucleic acid samples. This approach demonstrates the most direct and simple translation of genetic information to microelectronics. Awide range of techniques for detecting nucleic acids is based on their hybridization to DNA probes on a solid surface (ref. 1, entire issue, and ref. 2). In the methods used most routinely, the physical nature of the readout requires the attachment of reporter molecules such as fluorescent, chemiluminescent, redox, or radioactive labels (1, 3, 4). Although labeldependent methods achieve the highest sensitivities (5-7), eliminating the labeling steps has the advantage of simplifying the readout and increasing the speed and ease of nucleic acid assays, which is especially desirable for characterizing infectious agents, scoring sequence polymorphisms and genotypes, and measuring mRNA levels during expression profiling. The development of label-independent methods that can monitor hybridization in real time and that are simple and scalable is still in its infancy (8-11). Here we describe a label-free method for electronically detecting DNA by its intrinsic molecular charge using microfabricated field-effect sensors.The field-effect sensor is based on an electrolyte-insulator-silicon (EIS) structure. Variations in the insulator-electrolyte surface potential, which arise from the binding of charged molecules (e.g., nucleic acids) to the insulator surface ( Fig. 1 a and b), modify the charge distribution in the silicon below the electrolyte. Surface charge and surface potential at this interface are related according to the Grahame equation (12). The surface potential can be measured by changes in conductivity (13) or capacitance (14) in the silicon part of the EIS structure. We have chosen to measure the capacitance, because it requires only one electrical connection to the silicon. The measured capacitance between the silicon and counter electrode in the electrolyte solution is dominated by the insulator capacitance and the capacitance of the charge-depleted region in the silicon. These two capacitances appear in series, and only the silicon depletion capacitance is modulated by the insulator surface potential. The capacitance-versus-voltage dependence of EIS structures (15) is similar to that of metal-oxide-semiconducto...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Electronic detection of DNA by its intrinsic molecular charge

Fritz

Cooper

Gaudet

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

428

320

View full text Add to dashboard Cite

show abstract

“…The p-type field-sensitive region was biased into partial depletion to maximize sensitivity to changes in surface potential. The n-type substrate was biased to 1 V. Capacitance-voltage curves of the EIS structure were acquired to determine the optimal p-type bias point (51). The surface potential resolution was Ϸ10 V in a 1-Hz bandwidth and the linear range was Ϸ100 mV.…”

Section: Methodsmentioning

confidence: 99%

“…EIS structures enable a simple and highly sensitive measurement of surface potential at the electrolyte insulator interface, (37,38), and they have been previously used to measure pH and the adsorption of highly charged molecules such as DNA (39,40). To address the need for LMWH monitoring, we demonstrate that a protamine-functionalized EIS can measure the concentration of enoxaparin and that an AT-IIIfunctionalized EIS can selectively detect the physiologically active pentasaccharide domain in unfractionated heparin and fondaparinux.…”

mentioning

confidence: 99%

Monitoring of heparin and its low-molecular-weight analogs by silicon field effect

Milović

Behr

Godin

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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Heparin is a highly sulfated glycosaminoglycan that is used as an important clinical anticoagulant. Monitoring and control of the heparin level in a patient's blood during and after surgery is essential, but current clinical methods are limited to indirect and off-line assays. We have developed a silicon field-effect sensor for direct detection of heparin by its intrinsic negative charge. The sensor consists of a simple microfabricated electrolyte-insulatorsilicon structure encapsulated within microfluidic channels. As heparin-specific surface probes the clinical heparin antagonist protamine or the physiological partner antithrombin III were used. The dose-response curves in 10% PBS revealed a detection limit of 0.001 units͞ml, which is orders of magnitude lower than clinically relevant concentrations. We also detected heparin-based drugs such as the low-molecular-weight heparin enoxaparin (Lovenox) and the synthetic pentasaccharide heparin analog fondaparinux (Arixtra), which cannot be monitored by the existing near-patient clinical methods. We demonstrated the specificity of the antithrombin III functionalized sensor for the physiologically active pentasaccharide sequence. As a validation, we showed correlation of our measurements to those from a colorimetric assay for heparin-mediated anti-Xa activity. These results demonstrate that silicon field-effect sensors could be used in the clinic for routine monitoring and maintenance of therapeutic levels of heparin and heparin-based drugs and in the laboratory for quantitation of total amount and specific epitopes of heparin and other glycosaminoglycans.heparin sensors ͉ label-free sensing ͉ medical devices ͉ enoxaparin ͉ fondaparinux

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“…6,7 However, in order to detect DNA molecules, it is required to immobilize single-stranded probes on the surface of the ion-sensitive devices for the hybridization of single-stranded complementary target molecules in the electrolyte solution [8][9][10] or to deposit a positively charged layer such as poly-L-lysine on the sensing electrodes to attract the negatively charged nucleic acid molecules. 11,12 These additional processes increase reaction time and the complexity in detection protocols. Furthermore, it is difficult to incorporate the continuous monitoring for repetitive assays ͑e.g., real-time quantitative PCR͒ for these protocols because the regeneration of the sensing surface requires a complicated rinsing sequence.…”

mentioning

confidence: 99%

Real-time label-free quantitative monitoring of biomolecules without surface binding by floating-gate complementary metal-oxide semiconductor sensor array integrated with readout circuitry

Kim

Yoo

Shim

et al. 2007

Applied Physics Letters

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We report a label-free field-effect sensing array integrated with complementary metal-oxide semiconductor (CMOS) readout circuitry to detect the surface potential determined by the negative charge in DNA molecules. For real-time DNA quantification, we have demonstrated the measurements of DNA molecules without immobilizing them on the sensing surface which is composed of an array of floating-gate CMOS transistors. This nonimmobilizing technique allows the continuous monitoring of the amount of charged molecules by injecting DNA solutions sequentially. We have carried out the real-time quantitative measurement of 19bp oligonucleotides and analyzed its sensitivity as a function of pH in buffer solutions.

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Robust microfabricated field-effect sensor for monitoring molecular adsorption in liquids

Cited by 17 publications

References 18 publications

Electronic detection of DNA by its intrinsic molecular charge

Electronic detection of DNA by its intrinsic molecular charge

Monitoring of heparin and its low-molecular-weight analogs by silicon field effect

Real-time label-free quantitative monitoring of biomolecules without surface binding by floating-gate complementary metal-oxide semiconductor sensor array integrated with readout circuitry

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