Photonic crystal fiber as a biosensor
Creators: name: Khetani, Altaf
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2008
Subjects: subject: Engineering, Electronics and Electrical.

description: With the era of technological change at its all time high, advancements in the field of photonics offer us a wide range of innovative potential applications. Over the years photonics has played an important role in modern industries such as telecommunication, sensors and medical imaging. One of the fields which has received a lot of attention is Photonic Crystal Fibers (PCF) for biosensor application. Photonic crystal fiber is a unique type of optical fiber in which continuous channels of (typically) air run their entire length. These 'holes' serve to both confine electromagnetic waves within the core of the fiber and to tailor its transmission properties. The classification of photonic crystal fiber can be solid core PCF where the light is guided by total internal reflection, and Hollow core photonic bandgap fibers (PBF) in which light is guided through the photonic bandgap effect. Simulation of PCF has been done through commercial software known as COMSOL which follows the finite element approach. The focus of this thesis is on the application of PCF for different sensing applications. Traditionally, solid core PCF has been used for sensing purposes as the cladding channels can be filled with gas or liquid, thus serving as an efficient type of evanescent wave sensing. Hollow core PBF offers huge improvements as the interaction between light and matter is increased by the presence of sample in the core where most of the light is confined. Conventionally, HC-PBF is used for sensor purposes by selectively filling the core. Here we have used a non-selective filling technique wherein all the channels of PCF are being filled with samples. When the fiber is empty it guides a particular band, and upon filling with other samples, the bandgap is shifted, and depending on this shift one can determine the refractive index of the sample. This type of sensor has been able to detect as low as 10 -5 change in refractive index just by taking a few centimeters of HC-PBF. Laser Flash Photolysis is one of the leading methods used in photochemistry to determine the transient species such as radicals, excited states or ions, in chemical and biological systems. By using HC-PBF we have replaced the conventional technique of LFP where in a test-tube is used to hold the sample. The sample is excited through a laser and a monitoring beam is used to observe the amount of absorption. The sample required here is on the order of a milliliter which can be scaled down to pico liter by the use of PCF. The LFP results using PCF showed signal enhancement of at least an order of magnitude for samples like xanthone in toluene, xanthone in acetonitryl and water soluble benzoin in methyl viologen. Raman Spectroscopy is yet another area which had a surge of growth for label free detection of samples. One of the reasons for its popularity is that it provides a unique optical fingerprint of chemicals and biomolecules. In this thesis we have focused on developing HC-PBF for enhancing the Raman signal from the sample. We have obtained an enhancement of over 40 times when using a HC-PBF with a length of 9.5cm. We have also used HC-PBF to study the enhancement of Raman signal from colloidal nanoparticles in an aqueous solution. Supercontinuum generation is yet another area which has seen tremendous growth through the use of solid core PCF. Here we have covered the excitation of cladding and core mode in an endlessly single mode PCF which has the potential to be used as an effective type of biosensor as the penetration of light in the cladding channels is very strong compared to an evanescent wave field.