Sensing of Biomolecules - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 67

Fig. 2.9 Gate exposed is of
AlGaN/GaN HEMT
transistor for DNA detection

S

D

gate exposed area

easily detected on current dependences taken on a timescale of tens to hundreds of
minutes (the hybridization is completed after 20 min).
Other biomolecules detected with the help of HEMT have proven the validity
of this biodetection method. In this respect, the PSA marker of prostate cancer, the
KIM-1 urinary antigen for acute injury, as well as pH and glucose were all detected
individually in the exhaled breath condensation with HEMT biosensors. Recently,
with the same HEMT configuration as in Fig. 2.8 , fast detection of protozoan
pathogen Perkinsus marinus was performed. This protozoan causes widespread
mortality of oysters in farms or in their natural environment ( Wang et al. 2009 ).
In the case of this protozoan detection, the exposed gate length was of 5mand
was functionalized with an antibody linked to the metallic gate via the thioglycolic
acid. The water infected with this dangerous protozoan was monitored during
400-1,000 s. The gate attachment of Perkinsus marinus leads to the reduction of
the drain current with about 50A, allowing fast detection (less than 5 s) of the
infested water. Other details can be obtained from the extensive review of ( Pearton
et al. 2010 ) regarding wide-bandgap devices and, especially HEMTs, applications
for biological and gas detection.
Another important category of biosensors incorporates FETs with semiconducting
nanowire (NW) channels. Presently, NWs are produced on a large scale with high
yield and reproducible properties ( Lu and Lieber 2006 ). The mobility of FETs based
on NWs is low compared to that of HEMTs, but the NW technology is advancing
fast and starts to compete with the well-established CMOS technology. In any case,
the mobility is not the determinant parameter for biosensors. NW-based FETs have
various geometries and implicate several semiconductors such as Si, SiGe, GaAs,
GaN, etc. The typical configuration of a NW FET is represented in Fig. 2.10 .The
NW connects the source S and drain D electrodes and is isolated from the gate
electrode by an oxide layer.
In principle, a NW FET can be obtained by manipulating a single NW and
locating it between the drain and the source. This is, however, a demanding
task, so that usually the NWs are extracted from a colloidal suspension and
dispersed in the area of the S and D contacts. The procedure is illustrated in
Fig. 2.11 .