Sang Myung Lee

Detection of Hepatitis B Virus (HBV) DNA at femtomolar concentrations using a silica nanoparticle-enhanced microcantilever sensor.

We report Hepatitis B Virus (HBV) DNA detection using a silica nanoparticle-enhanced dynamic microcantilever biosensor. A 243-mer nucleotide of HBV DNA precore/core region was used as the target DNA. For this assay, the capture probe on the microcantilever surface and the detection probe conjugated with silica nanoparticles were designed specifically for the target DNA. For efficient detection of the HBV target DNA using silica nanoparticle-enhanced DNA assay, the size of silica nanoparticles and the dimension of microcantilever were optimized by directly binding the silica nanoparticles through DNA hybridization. In addition, the correlation between the applied nanoparticle concentrations and the resonant frequency shifts of the microcantilever was discussed clearly to validate the quantitative relationship between mass loading and resonant frequency shift. HBV target DNAs of 23.1 fM to 2.31 nM which were obtained from the PCR product were detected using a silica nanoparticle-enhanced microcantilever. The HBV target DNA of 243-mer was detected up to the picomolar (pM) level without nanoparticle enhancement and up to the femtomolar (fM) level using a nanoparticle-based signal amplification process. In the above two cases, the resonant frequency shifts were found to be linearly correlated with the concentrations of HBV target DNAs. We believe that this linearity originated mainly from an increase in mass that resulted from binding between the probe DNA and HBV PCR product, and between HBV PCR product and silica nanoparticles for the signal enhancement, even though there is another potential factor such as the spring constant change that may have influenced on the resonant frequency of the microcantilever.

Optimization of silicon oxynitrides by plasma-enhanced chemical vapor deposition for an interferometric biosensor

In this paper, silicon oxynitride layers deposited with different plasma-enhanced chemical vapor deposition (PECVD) conditions were fabricated and optimized, in order to make an interferometric sensor for detecting biochemical reactions. For the optimization of PECVD silicon oxynitride layers, the influence of the N2O/SiH4 gas flow ratio was investigated. RF power in the PEVCD process was also adjusted under the optimized N2O/SiH4 gas flow ratio. The optimized silicon oxynitride layer was deposited with 15 W in chamber under 25/150 sccm of N2O/SiH4 gas flow rates. The clad layer was deposited with 20 W in chamber under 400/150 sccm of N2O/SiH4 gas flow condition. An integrated Mach–Zehnder interferometric biosensor based on optical waveguide technology was fabricated under the optimized PECVD conditions. The adsorption reaction between bovine serum albumin (BSA) and the silicon oxynitride surface was performed and verified with this device.

Simple and sensitive method of microcantilever-based DNA detection using nanoparticles conjugates

As the real sample diagnosis using resonance-based microcantilevers, a simple method is strongly suggested that capture probe immobilized on the cantilever directly hybridize with nanoparticles conjugated detection probe. Two different dimensions of microfabricated piezoelectric cantilevers and two different sizes of nanoparticles were used in this experiment. As a result, the most suitable conditions, the 30times90 mum2 (width times length) of the cantilever and the 140 nm of the nanoparticles, were chosen for this method. And quantitative analysis was carried out in different concentrations of nanoparticles conjugated detection probe which are 1 mug/mL, 10 mug/mL and 100 mug/mL. In addition, the sensitivity of this method was demonstrated through the SNP (single nucleotide polymorphism) detection by comparing with quantitative data of hybridization in full matched sequence at same concentration.

Interaction Between Carbonaceous Structure and Functionalized Single-Walled Carbon Nanotubes

The properties of functionalized single-walled carbon nanotube (f-SWCNT) supernatant samples obtained through steps of acid oxidation-centrifugation-decantation were characterized by spectroscopic tools. Fourier transform IR spectroscopy provided evidence for the chemical and structural variations generated on the f-SWCNTs within each supernatant sample. The results from UV-visible near-IR spectroscopy revealed that the density difference of the carbonaceous impurity with functional groups on the f-SWCNTs contributed to the attenuation of electrical conductivity. In the Raman results, the shift of frequency in the radial breathing mode (RBM) was associated with an increase in diameter of the f-SWCNTs and a decrease in RBM intensity was attributed to the depletion of valence band electrons. The redshift of the tangential mode indicates the reduction in the bandgaps of the f-SWCNTs by the decrease in carbonaceous impurity.

Enhancement method of limit of frequency resolution using magnetic bead on the microcantilever

The sensitivity of immunoassays strongly depends on the binding affinity of the antibodies, which is also limited by a variety of other factors that are specific to the assay configuration, the type of label and instrument system used for detection. Magnetic beads are used in order to increase sensitivity in diagnosis system using the piezoelectric microcantilever. Use of magnetic beads is seemingly viable to insure the high sensitivity as well as the stable immunoassay. The ultra-sensitive magneto-mechanic detection of protein is accomplished by monitoring resonant frequency change of a cantilever functionalized with magnetic beads. The resonant frequency is surely shifted by mass and magnetic field effect. As a result, we practiced sandwich assay using CRP secondary antibody-coated magnetic bead on cantilever. Resonant frequency of the cantilever is changed by mass effect. When CRP secondary antibody-coated magnetic beads are attached to a CRP antigen, the changes in normalized resonant frequency shift deltaf/f1 were found to definitely increase about 30 times.