Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Biochemical functionalization <s> A novel fiber optical refractive index sensor based on gold nanoshells immobilized on the surface of an etched single-mode fiber including a Bragg grating is demonstrated. The nanoparticle coating induces refractive index dependent waveguide losses, because of the variation of the evanescently guided part of the light. Hence the amplitude of the Bragg reflection is highly sensitive to refractive index changes of the surrounding medium. The nanoshell functionalized fiber optical refractive index sensor works in reflectance mode, is suitable for chemical and biochemical sensing, and shows an intensity dependency of 4400% per refractive index unit in the refractive index range between 1.333 and 1.346. Furthermore, the physical length of the sensor is smaller than 3 mm with a diameter of 6 μm, and therefore offers the possibility of a localized refractive index measurement. <s> BIB001 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Biochemical functionalization <s> This study reports on the development of a surface plasmon resonance (SPR) optical fiber biosensor based on tilted fiber Bragg grating technology for direct detection of small biomarkers of interest for lung cancer diagnosis. Since SPR principle relies on the refractive index modifications to sensitively detect mass changes at the gold coated surface, we have proposed here a comparative study in relation to the target size. Two cytokeratin 7 (CK7) samples with a molecular weight ranging from 78 kDa to 2.6 kDa, respectively CK7 full protein and CK7 peptide, have been used for label-free monitoring. This work has first consisted in the elaboration and the characterization of a robust and reproducible bioreceptor, based on antibody/antigen cross-linking. Immobilized antibodies were then utilized as binding agents to investigate the sensitivity of the biosensor towards the two CK7 antigens. Results have highlighted a very good sensitivity of the biosensor response for both samples diluted in phosphate buffer with a higher limit of detection for the larger CK7 full protein. The most groundbreaking nature of this study relies on the detection of small biomolecule CK7 peptides in buffer and in the presence of complex media such as serum, achieving a limit of detection of 0.4 nM. <s> BIB002 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Biochemical functionalization <s> This work presents the development of an innovative plasmonic optical fiber (OF) immunosensor for the detection of cytokeratin 17 (CK17), a biomarker of interest for lung cancer diagnosis. The development of this sensing platform is such that it can be assessed in non-liquid environments, demonstrating that a surface plasmon resonance (SPR) can be excited in this case. For this purpose, detections have been first carried out on CK17 encapsulated in gel matrix in the aim of mimicking tissue samples. Gold-coated OF immunosensors were embedded in a specifically designed packaging providing enough stiffness to penetrate into soft matters. Resulting reflected spectra have revealed, for the first time, the presence of a stable SPR signal recorded in soft matters. Experiments conducted to detect CK17 trapped in a porous polyacrylamide gel matrix have highlighted the specific and selective biosensor response towards the target protein. Finally, the packaged OF immunosensor has been validated by a preliminary test on human lung biopsy, which has confirmed the ex-vivo CK17 detection. Consequently, this work represents an important milestone towards the detection of biomarkers in tissues, which is still a clinical challenge for minimally-invasive in vivo medical diagnosis. <s> BIB003
-Metal surface cleaning, usually with absolute ethanol. -Covalent immobilization of bioreceptors. This step strongly depends on the targets, as described in Section 3.2. -Deposition of blocking agents (most often bovine serum albumin (BSA) or milk caseins) to avoid unspecific interactions. -Rinsing to remove all non-linked molecules. -Surface cleaning with absolute ethanol. -SAM of S 2 PEG 6 COOH alkanethiols on the gold surface. -Surface activation using NHS/EDC process. -Anchoring of anti-CK17 antibodies by immersion in a pH-controlled solution. -Deposition of BSA (5 % w/v in phosphate-buffered saline (PBS)). -Rinsing with PBS. 4. Interrogation and data-processing -Splicing of the grating to fiber pigtails. -Connection to a measurement set-up including polarization control to record the reflected/transmitted amplitude spectrum (remote computer control for real-time operation). -Data-processing based on the tracking of the SPR mode as a function of time. -Use of a MicronOptics FBG interrogator and a polarization controller, allowing to record spectral measurements at 10 Hz rate with 1 pm wavelength resolution). -Insertion of the sensors in various complex media (PBS + serum, gel matrices and fresh biopsied lung tissues). -Record of the amplitude spectrum and computation of the wavelength shift and amplitude variation of the most sensitive cladding mode resonance in the P-polarized spectrum. Depending on the applications, these steps can be complemented with: (1) Mirror deposition on the fiber cross-section to operate in reflection mode. Optical fibers containing gratings are cleaved beyond the grating location to use them in reflection, through the use of a silver mirror deposited on the cleaved fiber end face. This can be as simple as using a silver glue. (2) Grating insertion into a specially-designed protective packaging allowing it to be used in various media. In BIB003 , a packaging was made of a hollow cylindrical needle manufactured in polyoxymethylene C2521 Hostaform. As depicted in Figure 12 , this packaging provides a window to expose the sensor location to the surrounding medium. It has been tailored for possible insertion in the operating channel of an endoscope. The study conducted in BIB002 BIB001 has demonstrated that these immunosensors reach a limit of detection of 1 pM in phosphate buffered saline (PBS) media supplemented with 10 % of serum. Then, the detection of cytokeratins trapped in the crosslinked polymer network of a porous gel matrix was reported, despite the non-liquid nature of the hosting medium. These results have allowed the sensors to be inserted in fresh tissues obtained from a biopsy. Such measurements have been conducted at the hospital and have demonstrated a positive biosensor response in tumoral tissues. These first results constitute an important milestone towards the possible demonstration of in vivo diagnosis using plasmonic fiber-grating biosensors. To this end, numerous developments and validation tests remain to be done, both in terms of extensive testing of the devices in different kinds of tumors and to fully demonstrate the biocompatibility and compatibility with standard practices in the sterilization of the probes.