Real-time detection of DNA interactions with long-period fiber-grating-based biosensor

Abstract

Using an optical biosensor based on a dual-peak long-period fiber grating, we have demonstrated the detection of interactions between biomolecules in real time. Silanization of the grating surface was successfully realized for the covalent immobilization of probe DNA, which was subsequently hybridized with the complementary target DNA sequence. It is interesting to note that the DNA biosensor was reusable after being stripped off the hybridized target DNA from the grating surface, demonstrating a function of multiple usability. © However, some of these demonstrated optical biosensors have limitations for real-time hybridization studies and monitoring hybridization kinetics. Here we implement an optical biosensor based on a dualpeak long-period fiber grating (LPFG) for detecting biomolecular interactions at a silica-liquid interface with the advantages of high sensitivity, real-time monitoring, and reusability. To achieve high-sensitivity detection of the designed biomolecular interaction, the most sensitive LPFG structures should be used. It has been reported that the coupling condition of LPFGs with relatively short periods are close to the dispersion turning points, resulting in conjugate dual-peak cladding modes that are extremely sensitive to external perturbations [9,10]. Several dual-peak LPFGs with a relatively small period ͑ϳ160 m͒ were UV inscribed in H 2 -loaded SMF-28 fibers employing the point-by-point method and a frequency-doubled Ar laser. All the gratings were annealed at 80°C for 48 h to stabilize their optical properties. Figure 1 shows the spectral evolution of a 30 mm long LPFG with a period of 161 m during the UV inscription process. It is clear that with increasing UV exposure the conjugate dual peaks were increasing in strength and moving close to each other as the coupling condition approached the dispersion turning point.The ability of LPFGs to couple light from the fiber core mode to cladding modes allows optically detecting the change in refractive index at the grating surface. This thus provides an optical detection method to monitor biochemical and biomolecular interactions. Figure 2 shows the basic scheme of the functionalization of a LPFG as a DNA-array biosensor. Silanization is a process for modification of the glass surface to adsorb biomolecules. The LPFG surface is first silanized, followed by the activation of cross linkers to facilitate the immobilization of probe DNA and then to be used to monitor in situ the hybridization of targeted DNA. The DNA hybridization process modifies the refractive index of the LPFG surface, thus resulting in its spectral shift. By demodulating the spectral shift, the designed DNA hybridization can be monitored with high sensitivity.All the biochemical experiments were performed in a fume cupboard. To minimize the bend cross sensitivity, the dual-peak LPFG with a 161 m period was placed straight in a V-groove container on a Teflon plate, and all the chemicals and solvents were added and withdrawn from the container by carefully pipetting.Prior ...

EDC-Mediated Oligonucleotide Immobilization on a Long Period Grating Optical Biosensor

“…Glass fiber surface pre-treatment and silanization: The successful amino functionalization of LPG's with (3-aminopropyl)triethoxysilane (APTES) has been well-documented for use in protein immobilization [8,11,29], as determined by fluorescent microscopy of the subsequentlyimmobilized protein [8,11]. We therefore employed this method of amino functionalization in the current study.…”

“…The most important advantages of this biosensor platform are that it is able to provide biosensing with unique features of label-free, real-time, multiplex, and in-line determination. Various fiber optic biosensors have been presented by employing long period gratings (LPGs) [7,8], tilted fiber gratings (TFGs) [9][10][11] micro fiber Bragg gratings (mFBGs) [12] LPGs in photonic crystal fibers [13] and surface plasmon resonance (SPR) [14].…”

“…The evanescent field decays away from the surface of an optical fiber in a distance of a few micrometers [14], which is sufficient to penetrate into surrounding medium and sense its optical properties. Hence, LPGs can be used to detect changes when a target bioanalyte interacts with a recognition element on the LPG sensor [8,18].…”

“…plays a crucial role in the development of the biosensor. To date, various fiber optic biosensors have been developed for the detection of antibody-antigen interactions [26] DNA hybridization [8,27], biotinstreptavidin [28], cellular behavior [14], enzyme-glucose binding [11,29], and specific detection of bacteria using bacteriophages [25]. DNA biosensor technology is becoming an important area of high throughput research in basic biological and disease pathways.…”

Novel glucose sensor based on enzyme-immobilized 81° tilted fiber grating

“…With their surface functionalized by molecular recognition elements (i.e., antibodies, enzyme, etc. ), the biosensors mentioned above have been reported for the detection of antigen [8,12], DNA [10,13,14], escherichia coli bacteria [15], and medically relevant parameters [16].…”