A SnO2 Solution-Gated Transistor Biosensor With High Sensitivity and Low Operating Voltage: Application to Detect Hg2+

Owing to inherent signal amplification, solution-gated transistor biosensor (SGTB) features high sensitivity. Herein, an SGTB based on polycrystalline SnO2 thin film (PSTF) was fabricated, which was obtained by thermal oxidizing of Sn layer. In order to realize high sensitivity and low operating voltage of SGTB, the field-effect mobility (
$\mu _{\text {FE}}$
) and electrical conductivity of PSTF can be tuned by changing the oxidation temperature and related grain size. Without doping, a high
$\mu _{\text {FE}}$
(418.8 cm2/
$\text{V}\cdot \text{s}$
) and a moderate conductivity (
$\sim $
3.5 S/cm) of PSTF were realized with an optimum grain size of
$\sim $
23 nm. The L-cysteine (L-Cys) modified SGTB was applied to detect Hg
$^{{2}+}$
in water with a low detection limit (4 nM), a wide linear range (4 nM–
$7.4 \mu \text{M}$
), a high sensitivity (0.46 lg
$\mu \text{A}$
/lg
$\mu \text{M}$
), as well as a low operating voltage (0.5 V). The detection limit can meet the requirement of WHO for drinking water (5 nM).