Papers by Keyword: Label-Free Detection

Abstract: Optical resonator biosensors have emerged as one of the most sensitive and practical microsystem biodetection technology. Here, we have developed a model for an optical microring resonator to be used as an ultrasensitive biosensor. A linear correlation between increasing the radius of the microring and the red shift in the resonance wavelengths has been observed. In fact, resonance shifts for very small changes in microring radius, as low as 10 nm, have been detected. Furthermore, sensing capability of the resonator has been simulated by introducing TiDO₂ nanoparticles and protein molecules to the resonator surface by varying both thickness and effective refractive index of the attached layer such that the layer size has been changed from 10 nm to 100 nm with an increment of 10 nm. We have observed readily detectable unique resonance shifts for both TiDO₂ nanoparticles and protein molecules. Moreover, effective medium approach has been implemented in order to account for refractive index fluctuations in sensing medium. As a consequence, combination of optical resonators with microfluidics could produce a simple-to-operate, portable and robust diagnostic tool enabling new insights into biomolecular function and recognition.

Abstract: Genetic engineering has been used extensively for improving cold resistance in plants. In this paper, an optical immunoassay was developed by the optic reflectance spectroscopy of the porous silicon biosensor to monitor the success of transgenic frost-resistant cotton. Transgenic cotton extract samples and anti- antifreeze protein (AFP) antibodies were employed as the target and probe, respectively. Porous silicon is functionalized by using oxidation and silanization, then anti- AFP antibodies were immobilized to the porous silicon pore used a crosslink method. The changes of reflectance spectrum before and after antigen-antibody react ion are observed. The results show that transgenic frost-resistant cotton extract samples caused obvious red shift in reflectance spectrum of porous silicon while common cotton was not. Control experiment with negative antibodies shows high specifcity and conventional ELASA and Western experiment were also carried for comparison. Compare to conventional ELASA and Western, porous silicon biosensor is quick and accurate determination for the detection of transgenic cotton of antifeezing protein.

Abstract: A novel immunosensor based on porous silicon (PSi) for antigen detection was reported in this paper. The antigen (SpaA) and the specificity of the antibodies are employed as the target and the probe in our laboratory, respectively. The immunosensor structure was prepared using bioconjungation. After the antigen-antibody reaction, the red shift of the reflection spectrum of the immunosensor increases in proportion to the concentration of SpaA. The sensitivity of this immunosensor is 41nm/ µg•ml-1 and the detection limit is 2.44×102pg•ml-1, they are better compared with our previous work by using this method. Controlled experiments were also presented with non-immune antibody and the results show that this immunosensor possesses high specificity.

Abstract: Photonic crystals have wide applications not only in optoelectronic fields but also in bioassays. In this review, we summarized our work on colloidal photonic crystals as novel biomolecular supports in multiplex bioassays. Except for enhancing the fluorescence signal and encoding the biomolecular carriers in fluorphore labeled bioassays, photonic crystal can also encode suspended arrays. From the point view of practicality, the synthesis and self-assembly of monodispersed colloidal spheres for colloidal crystals is involved.