Application of Silicon Nanowire in
Biosensor
Student: HongPhan
ID: 9735582
Professor: Cheng-Hsien Liu
Outline
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Introduction
The SiNW detector for protein
The SiNW detector for DNA
The SiNW detector for single molecule.
Conclusions
Introduction
• One dimensional silicon nanostructures (SiNW) have
attracted remarkable attentions due to their unique
electronic, optoelectronic and thermal properties.
• Recently, SiNWs became the promising architecture in
the present miniaturization of silicon-based devices,
enabling many potential applications for the new
generation nano-scale device including field-effect
transistors (FET), optoelectronics, solar cell and
especially biosensor
• Using SiNW to detect protein, DNA and single
molecules.
The SiNW detector for Protein
*The nanowires are modified with different (1, green;2, red) antibody receptors.
A cancer maker protein that binds to its receptor (on nanowire-1) will product
change characteristic of the surface charge on nanowire-1.
*Device 1,2,3 fabricated from similar nanowires. Using them to detect three
different cancer maker protein.
Nat.Biotechnol.2008, 23, 1294
The SiNW detector for DNA
Nanoletters, 8, 1066-1070 (2009)
Establishment of SiNW with PNA capture
probes
• Fabricated SiNWs by LPCVD.
• The PNA (peptide nucleic acid) capture probes with
amine groups at their N ends are covalently immobilized
on the SiNW surface by means of photochemical
hydrosilation.
PNA
Advantage of PNA instead of DNA
capture probes
• PNA_ neutral and to increase
the hybridization efficiency.
• Hybridization target DNAs to
take place at low ionic
strength.
• Minimized the build-up of a
strong electrical field at the
SiNW surface.
• Producing a high signal/noise
ratio
Experiment (1)
• Using seven 22-nucleotide (nt) target DNAs to hybridize
PNA of SiNW sensor.
Anal.Chem. 2007, 79, 3291
Experiment (2)
• The varied distance of the hybridization sites of DNAs to
PNA capture probes while maintaining the total number
of charges unchanged.
Results (1)
• Complementary target DNAs were completely
hybridized to immobilized PNA. Therefore, the PNA
capture probes are highly selective. (epi-fluorescence
microscopy)
Cy 3-labeled fully cDNA Cy 3-labeled seven-base cDNA Noncomplementary DNA
Result (2)
• The resistance changes decreases with the hybridization
sites moving away from the SiNW surface.
Conclusions
• Demonstrated the significance of charge layer distance
to ensure SiNW biosensing sensitivity
• Understanding the response of the SiNWs biosensors to
the location of charge layer.
The SiNW detector for single
molecules
Chem.Mater.2009
Introduction
• A facile method is demonstrated to metallize a SiNW array
just by dipping it into a deposition solution (such as AgNO3
& HF).
• The deposited AgNPs uniformly self-assembled along the
SiNW and developed into a metal covering with the NW as
its core.
• The metallized NW with a uniform distribution of AgNPs
tested as a SERS substrate and a high enhancement is
observed even from a single metallized NW alone.
Experiment
• Fabricated the SiNW chip ( NW and conductive circuit)
• The whole of SiNW chip will be dipped into the aqueous
deposition solution ( metal ion and HF) for several minutes
• Not only could Ag + be reduced and deposited onto the SiNW
surface, but Cu2+, Pd2+, Co2+, Au3+ and Pt4+ were also employed
to metallize the SiNW
The metallization process
• The metallization process includes
nucleation and growth process.
– The nucleation process is a redox
reaction, which includes:
• The reduction of metal ions to be
deposited as NPs.
• The oxidation of Si to provide the needed
electrons.
– SiO2 is momentarily formed but
quickly removed again by HF
– There are two growth processes:
coarsening and aggregation.
• The growth of the NPs was faster
along some particular
crystallographic directions than
along the rest. This is reason for the
appearance of nanostick.
• The dendrite structures originate
from the nanostick stem when the
growth time has been prolonged.
Results
• The highest intensity of Raman signal
was collected from the Ag NP substrate
with a deposition time of ~ 5 min.
• Other Ag NP arrays with longer or
shorter deposition time led to a
decreased intensity.
• A limit of detection of ~ 1nM R6G was
reached when incubation in the same
solution was employed to load the
Raman scattered.
• The signal was significantly enhanced
when the laser was focused on the
AgNPs assembled along the SiNWs.
• The blue background indicates that there
is little or no Raman response from the
gap area.
• The Raman signal collected along the
NW is much stronger than that from the
gap area, from green to yellow spots, the
intensity of which is uniform because of
the close intensity of Raman signal.
Conclusions
A strong SERS signal could be collected
from only one metallized NW. This approach
holds promise for trace-level and perhaps single
molecule detection.