1. DNA conjugation and reversibility on chitosan surfaces
Rubloff Research Group Accomplishments

2. DNA conjugation and reversibility on chitosan surfaces
Accomplishment
Single string DNA (ssDNA, probe) was conjugated to chitosan surface via glutaraldehyde activation
Target ssDNA was hybridized to matching probe ssDNA via self-assembly
Reversible DNA hybridization was achieved under urea denaturation and hybridization
Significance
The chitosan-based DNA hybridization is simple to achieve spatially selective assembly
The probe is sensitive and is applied to sandwich assay of total RNA sample
The probe is robust and provides reproducible measurements with a high signal-to-noise ratioseven after repeated hybridization and denaturation cycles
People involved
Hyunmin Yi, Greg Payne, Bill Bentley, Gary Rubloff
Collaborations with Li-Qun Wu, Reza Ghodssi,,
Links
Hyunmin Yi et al, Anal. Chem. 76 (2), (2004)

3. Chitosan Electrodeposition
Unusual polysaccharide
Low pH, soluble
High pH, insoluble O H N 3 + * n 2 2n
Chitosan electrodeposition
High pH region at negative electrode due to hydrogen evolution
Chitosan molecules deprotonated, immobilized at electrode surface
Cathode -
pH gradient
NH3+
pH>6.3
2H+ + 2e-  H2 H2
Chitosan biopolymer is emerging candidate for our application due to its intrinsic properties.
This material has pH dependant solubility since the the primary amine group is protonated at low pH and deprotonated in high pH.
(Nitrogen in amine group has a lone electron pair available which can accept a H+ ion.)
(Polarity of amine of chitosan molecule contribute to the solubility due to hydrogen bonding between water molecules )
This property enables electrodeposition of chitosan film on the negative electrode.
When we applied potential, Proton consumption occurs at the cathode and instantly water molecules dissociate to compensate proton and OH accumulate.
Therefore pH gradient is generated near the surface of negative electrode.
Chitosan molecule which is electrostatically transported to the cathode and in the high pH region near cathode, are deprotonated and immobilized.
(Or it could be reduction of O2 and the reduction (addition of electron, hydrogen removal of oxygen) of H2O,

4. DNA Hybridization on Chitosan
Probe
ssDNA
Target
ssDNA
Activated
Surface

5. Reversible DNA Hybridization on Chitosan

6. Reversible DNA Hybridization
Yi et al, Anal. Chem. 76 (2), (2004)

7. Analysis of Purified Total RNA from Escherichia coli culture by Sandwich Assay
Yi et al, Anal. Chem. 76 (2), (2004)
Hybridization
ssDNA (sandwich probe)
mRNA (analyte)
Hybridization
Electrode  Chitosan  Glutaraldehyde  ssDNA (probe)

8. Virus Assembly on Chitosan
300 nm
Yi et al, Nano Lett 5 (10) (2005)