Libo Nie

Planar distortion quantification to evaluate PDMS stamps affixed on glass support

This article describes a planar distortion quantification method for PDMS stamps used in soft lithography by introducing an angular parameter θ; the distortion θ is proportional to planar distortion in magnitude. We employ this method to evaluate PDMS stamps planar distortions supported on different treated glass with Micron XYZ Scope measurements. The average planar distortion of individual pattern (absolute distortion θ1) and their pattern-to-pattern distortion (relative distortion θ2) of PDMS stamps were determined by angular discrepancies (θ). The planar distortion quantification was evaluated among four different PDMS stamps affixation treatments, and the PDMS stamps supported on silane-modified glass showed strong binding and minimal planar distortion, its absolute angular distortion θ1 was 3.98x10-3 and relative angular distortion θ2 1.22x10-3. Such distortion quantification agreed with the results of linear and area shrinkages on the stamps surface patterns, the results showed high reliability and fidelity of PDMS stamps and similar elastomer micro-patterns supported on silane-modified glass by photo lithographic microfabrication method and their promising prospects for on-chip synthesis of DNA microarray and bio-devices fabrication in soft lithography. The distortion evaluations demonstrate a versatile method for quantifying and comparing planar distortions among patterns as well as screening elastomer stamps support in soft lithography.

Improvement of hybridization signals of colorimetric gene detection based on porous polypropylene membranes

Porous polypropylene (PP) membranes were modified by the plasma treatment in order to graft amino functional group (-NH2) onto the membrane surface. Oligonucleotides were in situ synthesized on the aminated polypropylene support. Gold nanoparticle labeled DNAs were bybridized to the synthesized oligonucleotide array. The membranes were exposed to the Silver Enhance Solution for singla amplification. The Hybridization signals of amino plasma-grafted polypropylene membranes were stronger than the commercial polyacrylamide modified polyproplylene membranes that load 0.07 μmol/cm2 free primary amino functions. Complementary and mismatched sequences were clearly distinguished. The diameter of nanogold particles and the concentration of thiol DNA modified gold nanoparticles were investigated to improve the hybridization signals. Bigger nanoparticle diameter, as well as higher concentration of thiol DNA modified gold nanoparticles lead to stronger hybridization signals.

In situ synthesis of oligonucleotides on plasma-modified PTFE for fabricating DNA chips

Oligonucleotide probe arrays were in-situ synthesized on the H2/N2 plasma modified poly(terafluoroethylene) (PTFE) surface via micro-fluidic channels connected with an automated synthesizer. A contact angle measurement of water droplets was used to ascertain the hydrophilicity of the surface. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of polar amino groups on the surface. Ultra-violet (UV) spectrum analysis indicated that the surface showed a coupling efficiency higher than 98% for in situ synthesis of oligonucleotides arrays. The probe array specificity was discriminated by hybridizing with fluorescent target sequencyes. Oligonucleotide probe arrays on modified PTFE surface showed high stability and durability after repetitive denaturing and hybridizing. The results implied the plasma modified PTFE surface was extremely stable, performed well in DNA hybridization assays and could service as a good substrate for high-density oligonucleotide array synthesis.