32
K. Sinha et al.
2.3 Preparation of Serotonin Solution
Serotonin hydrochloride (1 mg/ml) has been utilized as the target molecule purchased
from Sigma-Aldrich, USA. For the purpose of electrical measurements, several serial
dilutions of serotonin hydrochloride have been performed with phosphate buffer
saline (PBS) (pH 7.2) and 20 mM ionic strength to produce concentration ranging
from 1 fM to 1 μM. Thereafter, to carry out further measurements in physiological
sample, serotonin hydrochloride has been spiked in human blood serum. The blood
samples were kept at room temperature to separate the serum following the standard
protocol. The selectivity of the fabricated FET biosensor has been examined with
dopamine and uric acid molecules by separately spiking each of the samples.
2.4 Electrical Measurement
Each sensor chip has been used to interface with the PC through a sensor holder
setup. In the setup, the bond pads of the sensors have been set just below the probes
of the sensor holder. The probes of the sensor holder are connected with drain and
source electrodes and are spring loaded and the adjustment screws are provided to
align with the bond pads. The gate electrode has been inserted by a small gap in the
setup and soldered to a metal connector. The gate electrode has been fixed to a DC
power supply (Keysight technologies). A high-frequency signal of 20 mV amplitude
in the frequency range of 200–1000 kHz has been applied through a signal generator
(Agilent 33521A) at the drain electrode. The high-frequency signal with a reference
signal of 1.43kHz has been modulated using a lock-in amplifier (Stanford Research,
SR 830) and provided to the ZnO FET at the source terminal.
2.5 Characterization Techniques
To characterize the surface morphology of the ZnO nanorods, growth was recorded
with field emission scanning electron microscopy (FESEM) (ZEISS SUPRA-40).
The X-ray diffraction (XRD) was employed using RIGAKU diffractometer to
confirm the crystal structure of ZnO nanorod.
2.6 Real Sample Analysis
Human blood samples were collected from Nashipur Block Primary Health Centre,
West Bengal and were used for the experiment. They were kept in sterilized containers
and were centrifuged for 10 min at approximately 3000 rpm. The obtained serum was
K. Sinha et al.
2.3 Preparation of Serotonin Solution
Serotonin hydrochloride (1 mg/ml) has been utilized as the target molecule purchased
from Sigma-Aldrich, USA. For the purpose of electrical measurements, several serial
dilutions of serotonin hydrochloride have been performed with phosphate buffer
saline (PBS) (pH 7.2) and 20 mM ionic strength to produce concentration ranging
from 1 fM to 1 μM. Thereafter, to carry out further measurements in physiological
sample, serotonin hydrochloride has been spiked in human blood serum. The blood
samples were kept at room temperature to separate the serum following the standard
protocol. The selectivity of the fabricated FET biosensor has been examined with
dopamine and uric acid molecules by separately spiking each of the samples.
2.4 Electrical Measurement
Each sensor chip has been used to interface with the PC through a sensor holder
setup. In the setup, the bond pads of the sensors have been set just below the probes
of the sensor holder. The probes of the sensor holder are connected with drain and
source electrodes and are spring loaded and the adjustment screws are provided to
align with the bond pads. The gate electrode has been inserted by a small gap in the
setup and soldered to a metal connector. The gate electrode has been fixed to a DC
power supply (Keysight technologies). A high-frequency signal of 20 mV amplitude
in the frequency range of 200–1000 kHz has been applied through a signal generator
(Agilent 33521A) at the drain electrode. The high-frequency signal with a reference
signal of 1.43kHz has been modulated using a lock-in amplifier (Stanford Research,
SR 830) and provided to the ZnO FET at the source terminal.
2.5 Characterization Techniques
To characterize the surface morphology of the ZnO nanorods, growth was recorded
with field emission scanning electron microscopy (FESEM) (ZEISS SUPRA-40).
The X-ray diffraction (XRD) was employed using RIGAKU diffractometer to
confirm the crystal structure of ZnO nanorod.
2.6 Real Sample Analysis
Human blood samples were collected from Nashipur Block Primary Health Centre,
West Bengal and were used for the experiment. They were kept in sterilized containers
and were centrifuged for 10 min at approximately 3000 rpm. The obtained serum was