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Device considerations for development of conductance-based biosensors
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Image of FIG. 1.
FIG. 1.

Schematic of FET biosensor. The device consists of source and drain regions and a channel region. The channel region is functionalized with receptor molecules and exposed to an analyte solution. The receptor molecule is designed to bind specifically to certain target species in the analyte solution which induces changes in the electrical properties of the channel region. The source and drain regions are isolated from the analyte by a passivation material.

Image of FIG. 2.
FIG. 2.

Nonideal modified semiconductor surface. For steric reasons, the receptor molecules cannot occupy every site on the semiconductor surface, leaving many surface atoms with termination such as hydrogen. Additional nonidealities include (a) nonspecific interaction of the receptor molecules with the surface, (b) dangling bonds or semiconductor surface radicals, [(c) and (f)] nonspecific interaction of the surface with analytes, (d) voids and defects in the receptor molecule film, (e) suboxide, and (g) surface oxide.

Image of FIG. 3.
FIG. 3.

An example of Si surface functionalization scheme for immobilization of thiolated receptor molecules. The component A can have an arbitrary chemical structure, which greatly affects the quality of molecular passivation and device characteristics.

Image of FIG. 4.
FIG. 4.

(a) GaAs JFET device structure. (b) Molecular structures of type-I and type-III SANDs with components Alk, Stb, and Cap.

Image of FIG. 5.
FIG. 5.

Transfer characteristics of GaAs JFETs functionalized with (a) type-I SAND and (b) type-III SAND. The direction of shifts is indicated by thick arrows. In addition, compared to hysteresis of as-fabricated devices, type-I SAND modification suppresses hysteresis while type-III SAND passivation results in a larger hysteresis. The sweep rate is 500 mV/s.

Image of FIG. 6.
FIG. 6.

Schematic illustrating charge sharing in a biosensor. The net charge of the adsorbed biomolecules on the sensor surface is shared between the sensor and the counterions present in the buffer . The independent parameter is the charge in the biomolecules and the potential of the molecular layer is determined by the relative values of the capacitances shown in the schematic.

Image of FIG. 7.
FIG. 7.

Operation modes of FET-based biosensors: (a) accumulation mode, (b) depletion mode, and (c) fully depleted mode.

Image of FIG. 8.
FIG. 8.

The potential distribution in a fully depleted semiconductor channel. The origin of -axis indicates the top semiconductor-insulator interface and is the effective back gate potential at the bottom semiconductor-insulator interface. The boundary conditions for the potential profile are indicated.

Image of FIG. 9.
FIG. 9.

(a) Schematic illustrating DNA conjugation on sensor surface. The separation of the target DNA from the sensor surface was varied by changing the length of the complimentary binding sequence (Ref. 91). (b) Comparison between experimental and numerical results [simulation of the nonlinear PB equation (Eq. (7))]. The simulation data have been normalized with respect to experimental results.


Generic image for table
Table I.

Changes in and of surface-modified GaAs JFETs and estimated and from 2D device simulation (MEDICI).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Device considerations for development of conductance-based biosensors