Abstract
We present the development and simplification of label-free fiber optic biosensors based on immobilization of oligonucleotides on dual-peak long period gratings (dLPGs). This improvement is the result of a simplification of biofunctionalization methodology. A one-step 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-mediated reaction has been developed for the straightforward immobilization of unmodified oligonucleotides on the glass fiber surface along the grating region, leading to covalent attachment of a 5´-phosphorylated probe oligonucleotide to the amino-derivatized fiber grating surface. Immobilization is achieved via a 5´phosphate-specific linkage, leaving the remainder of the oligonucleotide accessible for binding reactions. The dLPG has been tested in different external media to demonstrate its inherent ultrahigh sensitivity to the surrounding-medium refractive index (RI) achieving 50- fold improvement in RI sensitivity over the previously-published LPG sensor in media with RI’s relevant to biological assays. After functionalization, the dLPG biosensor was used to monitor the hybridization of complementary oligonucleotides showing a detectable oligonucleotide concentration of 4 nM. The proposed one-step EDC reaction approach can be further extended to develop fiber optic biosensors for disease analysis and medical diagnosis with the advances of label-free, real-time, multiplex, high sensitivity and specificity.
Highlights
Biosensors have been developed to play a significant analytical role in medicine, diagnosis, life science, food, security and defense, environmental and industrial monitoring [1]
An long period gratings (LPGs) in a single mode fiber couples the light from the core mode to co-propagating cladding modes resulting in the transmission spectrum containing a series of attenuation bands
LPGs with such dual-peak features are defined as dual-peak LPGs
Summary
Biosensors have been developed to play a significant analytical role in medicine, diagnosis, life science, food, security and defense, environmental and industrial monitoring [1]. The traditional methods based on culture collection and colony counting were complicated, hazardous, expensive, time consuming and may require signal amplification or labeling. To overcome these drawbacks, the development of a portable, easy-to-use and highly sensitive biosensor for label-free and real-time detection is essential [2]. Besides the inherent advantages exhibited by fiber technology, such as compact size, light weight, and electromagnetic interference immunity, fiber sensing platforms can provide higher sensitivity and selectivity than the traditional sensors. 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]
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