Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Protein and Cell Detection and Quantification <s> An immunosensor using a long-period grating (LPG) was used for sensitive detection of antibody−antigen reactions. Goat anti-human IgG (antibody) was immobilized on the surface of the LPG, and detection of specific antibody−antigen binding was investigated. This sensor operates using total internal reflection where an evanescent field interacts with bound antibody immobilized over the grating region. The reaction between antibody and antigen altered the LPG transmission spectrum and was monitored in real time as a change in refractive index, thereby eliminating the need for labeling antigen molecules. Human IgG binding was observed to be concentration dependent over a range of 2−100 μg mL-1, and equilibrium bound antigen levels could be attained in ∼5 min using an initial rate determination. Binding specificity was confirmed using human interleukin-2 and bovine serum albumin as controls, and nonspecific adsorption of proteins did not significantly interfere with detection of binding. Antigen detection in a... <s> BIB001 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Protein and Cell Detection and Quantification <s> 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 /spl mu/m 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/spl times/10/sup -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. <s> BIB002
Since the first reports about the use of bare fiber gratings for biosensing BIB001 BIB002 , numerous experimental demonstrations, most often in complex media mimicking the final environment where the sensors should be used in practice, have confirmed that metal-coated fiber gratings can be successfully used for biochemical sensing. This section first summarizes prominent examples of biosensors based on metal-coated fiber gratings. Then, considering a practical study case where functionalized gratings are used for cancer diagnosis in tumors, Section 5.2 will outline the typical roadmap that needs to be followed to build such plasmonic optical fiber-grating immunosensors, ensuring their use for minimally-invasive diagnosis.