# Surface Plasmon Resonance-Based Fiber Optic Sensors Utilizing Molecular Imprinting
## 6 Fiber Optic SPR Sensor Based on MITs
### Developments on FO-SPR-MIP-Based Sensors
#### 6.3.4 L-Nicotine  
Demands for drug detection methods have been increasing day by day due to their usage in medicines, ready-made foodstuffs and as waste elements in water bodies which affect the human body toxically. One drug, L-nicotine, is an important alkaloid that exists naturally as an organic nitrogen-containing base which affect the body physiologically. Nicotine is reported to affect the nervous system which can result in paralysis and respiratory block. It is actually an addictive, and behaves as a stimulant, which compels the user to use it again. L-Nicotine is a basic material used for medicines in a controlled way and also behaves as a pesticide in a large amount [161]. Hence the analysis of its quantity in medicines and even in tobacco-containing products is important. A fiber optic L-nicotine sensor using SPR and MIP on tapered plastic fiber has been reported [161]. The method was reported to have advantages over the already existing methods for the analysis of nicotine such as chromatography, GC-MS, etc. The ability to fabricate an inexpensive, simple and highly selective sensor using SPR and MIP outperformed all the existing methods and analyses.  
Figure 12: SPR curve recorded for the characterization of vitamin B\({}_{3}\) sensor using MIP for the concentration range of 0–10 mg/mL. Reprinted with permission from [159]. Copyright 2013 Elsevier.  
The work on nicotine sensing reported by [PERSON] et al. used polymeric fibers to exploit their advantages such as flexibility and manipulation possibilities, huge diameter and NA in addition to easy bending of the fibers. Moreover, the plastic material supports smaller bending radii than glass material and is of low cost. To increase the sensitivity, a tapered configuration was applied on the probe. The probe was fabricated on the fiber with core made of PMMA and fluorinated cladding. A sensing region of 10 mm length and taper ratio 1.8 was chosen. Gold film of 60 nm thickness was coated to establish SPR. Over the gold film, a pre-polymerized mix made of MAA as monomer, DVB as cross linker and AIBN as initiator with template-L-nicotine was coated. The molar ratio of template: MAA:DVB was set as 1:4:24 with the mixture properly sonicated and bubbled with nitrogen to remove oxygen. Polymerization was performed at a temperature of 70 \({}^{\circ}\)C for 16 h to achieve a thickness of 150 nm. To remove the template molecules, ethanol was used to wash the probe which produced the imprints. The sensor probe was characterized at 25 \({}^{\circ}\)C with a halogen lamp and spectrum analyzer having a resolution of 1.5 nm. The characterization was performed by electrochemical method indicating the adsorption of analyte on MIP layer. A right shift in the SPR spectrum was observed with the increase in L-nicotine concentration from 0-10\({}^{-2}\) M with a linear range up to 10\({}^{-3}\) M. A sensitivity of 1.3 \(\times\) 10\({}^{4}\) nm/M was obtained for probe with taper ratio of 1.8. In addition, the sensor possesses response time of 10 min and LOD of 1.86 \(\times\) 10\({}^{-4}\) M.