# Recent Advances in Plasmonic Sensor-Based Fiber Optic Probes for Biological Applications
## 8 Applications
### Environmental Monitoring  
Sensitivity monitoring of environmental pollutants, namely, pesticides, biological pollutants, disruptive chemicals, explosives, and toxins, is needed to safeguard environmental quality and therefore human health. To surpass the conventional chromatographic and spectroscopic technologies, which quantify the contamination in an environment with sophisticated instruments, a recently developed biosensor can be used for its simple protocols and cost-effectiveness. The functional biorecognition is a key concept of biosensors. Antibodies such as enzymes, antigens, aptamers, and DNAzyme are recurrently used as biorecognition molecules in optical fiber sensor technologies. A highly sensitive optical biosensor for interaction among environmental molecules with the sensitivity of 100 pg/mL has been reported [110]. Recently, a whole cell-based optical biosensor for detecting organic waste with a sensitivity of 0.74 ug/L was reported [111]. The applications of cell-based optical biosensors for environmental analysis and medical diagnostics were reviewed [112]. The environmental investigation requires more attention to diverse environmental phenomena including the fate and transport of contaminants. The other applications of the SPR-based FOBS are tabulated in Table 1 as follows: \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensor Configuration and Its** & **Operating** & **Functional Materials** & **Performance with Sample Range** & **Ref.** \\
**Application** & **Wavelength (nm)** & **Functional Materials** & **Range** & **Ref.** \\ \hline \hline Eched optical fiber for detection of salinity concentration & 1400–1600 & SMF + MMF + SMF coated with ITO & 7000 nm/RIU for RI ranges from 1.333 to 1.338. & [113] \\ Symmetrically-etched POF sensor for RI sensing application & 350–1100 & Etched POF coated with Au & 1600 nm/RIU for RT ranges from 1.335 to 1.3453. & [114] \\  & & & 1.257 nm/RIU for & \\ Eched-optical fiber Bragg grating for sensing deionized water and saline & 400–1600 & Etched D-shaped fiber Bragg grating coated with TiO\({}_{2}\) & air-deionized water and 0.857 nm/RIU for air-saline for the corresponding RI 1 & [115] \\ Tilted fiber Bragg grating sensor for detecting urinary protein variations & 1440–1540 & Tilted fiber Bragg grating coated with Ag & 8000 dB/RIU for RI ranges from 1.3400 to 1.3408 & [116] \\ Tapered fiber SPR-based sensing & 450–1700 & Cr + Au + TiO\({}_{2}\) coated on fiber & 5000 nm/RIU at 1500 nm for 1.3382 to 1.338. & [117] \\ Tapered multimode fiber sensor for RI detection sensors & 400–1200 & Ag + Au coated on fiber & 10 times as compared to the symmetric fiber sensing probe for RI ranges from 1.333–1.353 & [118] \\ Adiabatic tapered optical fiber sensor for biochemical sensing & 400–2000 & Tapered optical fiber + TiO\({}_{2}\) & 7096 nm/RIU for RI ranges from 1.3373 to 1.3500 & \\ Side polished single mode-multimode-single mode fiber & 1450–1610 & SMF + MMF + SMF 30 mm, 35 mm, 40 mm, and 45 mm & 1.33 to 1.39, and of 1190 & [120] \\   for sensing characteristics & & & nm/RIU in RI range from 1.43 to 1.45. & \\ Side-polished plastic optical fiber for biochemical application & 400–1100 & Ag + silicon + Polyacrylamide Gel with & 10.50 nm/mM in the range & [121] \\ Side-polished single-mode fiber for the detection of Legionella & 400–1800 & Au + SAM + antigen LP coated on fiber & Legionella pneumophila & [122] \\ pneumophila & & & coated on fiber & LOD 10\({}^{1}\) CFU/ml \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of selected experimental performances for fiber optic plasmonic probes. However, there are still some limitations to such SPR-based FOPS. For example, for the measurement of some physical parameters, such as curvature and displacement, the applications of the fiber optic SPR sensor are still limited because it is difficult to control the propagation angle of the light beam in the fiber and the intensity of the evanescent wave [134].