Detecting hybridization of DNA by highly sensitive evanescent field etched core fiber Bragg grating sensors

Highly sensitive fiber Bragg grating sensors were developed by etching away the cladding and part of the core of the fiber and detecting the change of Bragg wavelength due to the change of index of the surrounding medium. A sensitivity of 1394 nm/riu was achieved when the diameter of the grating core was 3.4 μm and the index of the surrounding medium was close to the index of the core of the fiber. Assuming a detectable spectral resolution of 0.01 nm realized in the experiment, the sensor achieves a minimum detectable index resolution of 7.2×10^-6. Higher sensitivity at lower surrounding index was achieved by using higher order modes excited in the Bragg grating region. The use of the fiber Bragg grating sensor was further investigated to detect hybridization of DNA. Single stranded DNA oligonucleotide probes of 20 bases were immobilized on the surface of the fiber grating using relatively common glutarahyldehyde chemistry. Hybridization of complimentary target single strand DNA oligonucleotide was monitored in situ and successfully detected. The demonstrated fiber Bragg grating sensors provide an elegant method to monitor biological changes in an in situ manner, and provide temporal information in a single experiment.