Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L1/00—Measuring force or stress, in general
  • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
  • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
  • G01L1/246—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using integrated gratings, e.g. Bragg gratings
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
  • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
  • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
  • G01N21/774—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides the reagent being on a grating or periodic structure

Definitions

• the present invention relates to a highly sensitive optical biosensor for biological and chemical sensing applications. More specifically the present invention relates to dendrimer functionalized nano carbon materials coated on etched fiber Bragg grating (eFBG) and methods of fabrication thereof.
• eFBG etched fiber Bragg grating
• Fiber Bragg grating is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelength of light and transmits all others. This is achieved by adding periodic variations to refractive index of fiber core, which generates a wavelength specific dielectric mirror.
• Optical sensors based on fiber Bragg gratings have emerged as important sensing elements for measurements of temperature, pressure, chemical and biological agents. These sensors offer attractive characteristics such as small size, light weight, high sensitivity, and low losses, making them very suitable. They are also immune to electro-magnetic interference, are capable of performing remote sensing, and can provide multiplexed sensing and detection within a single device.
• FBGs fiber Bragg gratings
• Distributed Bragg reflector constructed in a short segment of optical fiber reflects particular wavelength of light and transmits all others when light is passed through it. This is achieved by grating inscripted in fiber which adds periodic variations to the refractive index of the fiber core, which generates a wavelength specific dielectric mirror.
• the grating typically has sinusoidal refractive index variation over a defined fiber core length.
• An interference pattern of maxima and minima is formed causing permanent periodic change to the refractive index of core. This results into a reflection of small amount of wavelength at each modified core segment with reflection of small amount of light at each index variation.
• the reflected wavelength ⁇ ⁇ is termed as the Bragg wavelength, which is defined by the relationship:
• ⁇ %s is the effective refractive index of the grating in the fiber core and &. is the grating period.
• f fi quantifies the velocity of propagating light as compared to its velocity in vacuum. s3 ⁇ 4e depends not only on the wavelength but also (for multimode waveguides) on the mode in which the light propagates. Therefore, change in Bragg wavelength can be used to study various parameters in biological and chemical fields.
• US Patent US 7,010, 182 discloses a coating of dendrimer on the long period gratings (LPGs) surface to detect the binding receptor of the substrate by forming a bond between them causing a change in the refractive index.
• LPGs long period gratings
• ⁇ 82 does not disclose dendrimer attached nano carbon materials coated on etched FBG.
• ⁇ 82 further does not disclose or teach measuring a shift in Bragg wavelength as an output measurand.
• 12544-12552 discloses single walled carbon nanotubes functionalized with PAMAM (Polyamidoamine) dendrimer through a tedious process of covalent attachment involving a lot of chemistry. Stephane does not discuss SWNTs - dendrimer complex coated on eFBG and the biosensing application thereof by measuring shift in Bragg wavelenth.
• PAMAM Polyamidoamine
• Lijun Li et al. discloses coating of carbon nanotubes on the surface of the FBG by drop casting the SWNT solution and drying it on the surface of the FBG. They have shown the increase in the reflectivity in SWNTs coated FBG over normal FBG caused by the anisotropic property of refractive index of SWNTs. Lijun does not discuss SWNTs - dendrimer complex coated on eFBG and the biosensing application thereof by measuring shift in Bragg wavelength.
• eFBG etched fiber Bragg grating
• Another object of the present invention is to provide a method of fabrication of an optical biosensor comprising of dendrimer functionalized nano carbon materials coated on eFBG.
• Yet another object of the present invention is to provide a simpler and easier method of coating nano carbon materials on surface of eFBG wherein surfaces of nano carbon materials and eFBG are made hydrophilic.
• the present invention relates to an optical biosensor comprising of an etched fiber Bragg grating (eFBG) having a plurality of coatings comprising of:
• nano carbon materials are attached with one or more dendrimer molecule(s) and coated onto surface of the FBG or eFBG.
• Optical biosensor of the present invention is highly sensitive and accurate for biochemical sensing applications, particularly for detecting carbohydrate-protein interactions as an example of antigen-antibody interactions.
• One or more dendrimer molecule(s) of the present invention can be attached with a carbohydrate or antibody to form a carbohydrate or antibody attached dendrimer coated nano carbon materials coated optical biosensor.
• nano carbon materials are selected from a group consisting of Single Walled Carbon Nanotubes (SWNTs), Graphene Oxide (GO).
• SWNTs Single Walled Carbon Nanotubes
• GO Graphene Oxide
• the one or more dendrimer molecule(s) are selected from the group consisting of: carboxylic acid terminated poly(propyl ether imine) dendrimers, hydroxyl terminated poly(propyl ether imine) dendrimers, amine terminated poly(propyl ether imine) dendrimers, cyano terminated poly(propyl ether imine) dendrimers, carboxylic acid terminated polyamdioamine dendrimers, amine terminated polyamidoamine dendrimers, amine terminated poly propylene imine dendrimer, and hydroxyl terminated polyamidoamine dendrimers.
• one or more dendrimer molecule(s) are selected from one or more of carboxylic acid terminated poly (propyl ether imine) dendrimers and amine terminated poly (propyl ether imine) dendrimers attached with various antibodies.
• optical biosensor of the present disclosure measures a shift in Bragg wavelength ( ⁇ ⁇ ) of eFBG that is coated with dendrimer functionalized nano carbon materials, as an output measurand or readout in detection of carbohydrate-protein or antigen- antibody interactions.
• the shift in Bragg wavelength is very significant and can measure very small changes in optical properties such as refractive index of the nano carbon materials coated due to antibody-antigen interactions or carbohydrate-protein interactions.
• optical biosensor of the present invention can measure about 1-2 pm (10 "12 meter) shift in Bragg wavelength.
• Such high sensitivity of 1 2 pm can allow measurement of very small changes that occur in refractive index of nano carbon materials due to antibody - antigen interaction, which makes the optical biosensor of the present invention disclosure highly sensitive and thus accurate.
• Another embodiment of the present invention allows sensitivity in readout to be increased 5 times in SWNTs coated eFBG and 10 times in GO coated eFBG when compared to the sensitivity without the coating of nano carbon materials.
• Dendrimer having multiple functionalities further provides a large number of active sites to increase the sensitivity.
• dendrimer can be attached to nano carbon materials non - covalently.
• the present invention further allows writing of multiple gratings of different Bragg wavelengths on a single fiber to detect many specific antibody - antigen interactions simultaneously.
• the present disclosure also relates to methods of fabrication of an optical biosensor comprising of a Fiber Bragg grating (FBG), preferably of an etched Fiber Bragg grating (eFBG), with a plurality of coatings comprising of: (a) nano carbon materials and (b) one or more dendrimer molecule(s), wherein dendrimer functionalized nano carbon materials are coated onto eFBG.
• FBG Fiber Bragg grating
• eFBG etched Fiber Bragg grating
• surfaces of the nano carbon materials and the eFBG are made hydrophilic to.
• One preferred embodiment of the present invention provides a method of fabrication of an optical biosensor comprising the steps of:
• the suitable reagent in step (ii) is a base comprising of NaOH.
• the nano carbon materials can be selected from a group comprising of Single Walled Carbon Nanotubes (SWNT), Graphene Oxide (GO).
• SWNT Single Walled Carbon Nanotubes
• GO Graphene Oxide
• the method of fabrication of the present invention further comprises the step of treating surface of the SWNT with a suitable reagent to make the surface of the SWNT hydrophilic.
• the SWNT is treated with a suitable reagent to make surface of the SWNT hydrophilic.
• the suitable reagent can be an acid comprising of H 2 S0 4 , HN0 3 or mixtures thereof.
• a method of fabrication of the present invention further comprises the step of functionalizing dendrimer with at least a suitable molecule to produce multiple active sites on surface of the dendrimer.
• the suitable molecule can be a carbohydrate.
• Figure 1 (a) illustrates a schematic representation of a preferred embodiment of the invention showing coatings of SWNT, GO and dendrimer on etched FBGs and how a binding receptor attaches to the active sites of the dendrimer coating.
• Figure 1 (b) depicts an SEM image of GO coated eFBG.
• Figure 2 illustrates a variation of ⁇ ⁇ / ⁇ ° ⁇ with respect to concentration of Con
• Figure 3 illustrates a variation of ⁇ ⁇ / ⁇ ° ⁇ of GO - Dendrimer (DM) coated eFBG after dipping it in different concentrations of lectins.
• Figure 4 illustrates a variation of ⁇ ⁇ / ⁇ ° ⁇ of the GO - DM coated FBG after dipping it in different concentrations of Con A.
• Figure 5 illustrates a change in a cladding refractive index (surrounding medium) as a function of concentration of Con A solution for both SWNTs (red color open circles) and GO (black color open squares) coated eFBGs.
• Figure 6 illustrates a block diagram of multiple gratings inscribed on eFBG which can be used as optical biosensor for many specific antibody - antigen interactions; (a) GO coated eFBGs with different antibodies (b) SWNTs coated eFBGs with different antibodies.
• SWNT single- walled nanotube
• FBG fiber bragg grating
• the present invention is directed towards optical biosensors which are highly sensitive and accurate for bio-chemical sensing applications particularly for detecting carbohydrate-protein interactions as an example of antigen-antibody interactions.
• the present invention relates to an optical biosensor comprising of etched Fiber Bragg grating (eFBG) having a plurality of coatings comprising of:
• the nano carbon materials are attached with one or more dendrimer molecule(s) and coated onto surface of the eFBG.
• active sites on the dendrimers are oriented away from the FBG or eFBG, enabling them to complex with specific target molecules having specific binding receptors.
• Specific target molecules can comprise, for example, carbohydrates and proteins.
• Specific active sites can exist on commercially available dendrimers on their own or can be created on dendrimers by functionalisation with specific molecules.
• dendrimer molecules can be reacted with specific carbohydrate molecules to create specific carbohydrate sites on the dendrimers in order to detect specific proteins or antibodies.
• dendrimer molecule(s) can be attached with a carbohydrate to form a carbohydrate coated dendrimer functionalised nano carbon materials coated optical biosensor, which can bind to a specific protein.
• Protein-carbohydrate interactions play an important role in biological functions such as but not limited to cell adhesion, signal transduction, host-pathogen recognition, and inflammation, among others. Carbohydrates are often specifically recognized by other biomolecules.
• Antibody binding site of an antigen is constituted by the combination of various amino acids and when the antibody is a kind of carbohydrate, the binding can be regard as antibody-antigen interaction or carbohydrate-protein interaction.
• Dendrimers and dendrimer polymers typically have a central core, an interior dendritic structure, and an exterior dendritic surface, wherein they are highly branched macromolecules with known functional end groups (or terminal groups) and are also sometimes classified as nanomaterials.
• Different families of dendrimers exist with hundreds of end group modifications, wherein the size of the dendrimer is generally controlled by growth cycle during the synthesis of the material and is referred to as the generation number. For instance, if a dendrimer is made by convergent synthesis and the branching reactions are performed onto the core molecule three times, the resulting dendrimer is considered a fourth generation dendrimer. Each successive generation results in a dendrimer that has roughly twice the molecular weight of the previous generation. Higher generation dendrimers also have more exposed functional groups on the surface.
• one or more dendrimer molecule(s) can be selected from one or more of carboxylic acid terminated poly(propyl ether imine) dendrimers, hydroxyl terminated poly (propyl ether imine) dendrimers, amine terminated poly(propyl ether imine) dendrimers, poly(propyl ether imine) dendrimers, cyano terminated poly(propyl ether imine) dendrimers, carboxylic acid terminated polyamdioamine dendrimers, amine terminated polyamidoamine dendrimers, amine terminated poly (propyl eneimine) dendrimer, and hydroxyl terminated polyamidoamine dendrimers.
• one or more dendrimer molecule(s) can be selected from one or more of poly (propyl ether imine) (PETIM) dendrimers, preferably carboxylic acid terminated PETIM dendrimers.
• PETIM poly (propyl ether imine)
• nano carbon materials can be selected from one or more of Single Walled Carbon Nanotubes (SWNT), Graphene Oxide (GO).
• SWNT Single Walled Carbon Nanotubes
• GO Graphene Oxide
• One aspect of the present invention relates to enhancing sensitivity of a biosensor by disposing on an etched Fiber Bragg Grating (eFBG), a coating comprising nano carbon materials attached with dendrimer molecules.
• sensitivity of biosensor can be greatly enhanced by a coating comprising SWNT or GO attached with multivalent specifically functionalized dendrimer molecules and disposing the coating on an etched fiber bragg grating.
• the present invention further enables measurement of a shift in Bragg wavelength as an output measurand instead of measuring reflectivity or intensity changes as found in the existing art.
• the shift in Bragg wavelength ⁇ ⁇ is found to be significant, making the optical sensor of the present invention highly sensitive.
• Figure 1 (a) illustrates a schematic representation of a preferred embodiment of the invention.
• surface of eFBG 104 or 106 can be coated with a coating comprising SWNT 112 or GO 110, wherein Fiber Bragg grating (FBG) 102 comprises uniform dimensions all over its surface, which is decladded by an etching process to produce the eFBG 104.
• FBG Fiber Bragg grating
• SWNTs are hydrophobic whereas GO, by preparation, is hydrophilic.
• One embodiment of the present invention makes surfaces of the SWNTs 112 and the eFBG 104 hydrophilic by virtue of which the two different natured nano carbon materials SWNT and GO can be coated onto the eFBG surface 106.
• One preferred embodiment of the present invention provides a method of fabrication of an optical biosensor comprising the steps of:
• step (ii) treating surface of the eFBG or FBG with a suitable reagent to make the surface of the FBG or eFBG hydrophilic; iii. coating nano carbon materials onto the surface of the hydrophilic eFBG or FBG made in step (ii); and
• the suitable reagent in step (ii) is a base comprising of NaOH.
• the nano carbon materials can be selected from a group comprising of Single Walled Carbon Nanotubes (SWNT), Graphene Oxide (GO).
• SWNT Single Walled Carbon Nanotubes
• GO Graphene Oxide
• the method of fabrication of the present invention further comprises the step of treating surface of the SWNT with a suitable reagent to make the surface of the SWNT hydrophilic.
• the SWNT is treated with a suitable reagent to make surface of the SWNT hydrophilic.
• the suitable reagent can be an acid comprising of H2SO4, HNO3 or mixtures thereof.
• a method of fabrication of the present invention further comprises the step of functionalizing dendrimer with at least a suitable molecule to produce multiple active sites on surface of the dendrimer.
• the suitable molecule can be a carbohydrate.
• eFBG 104 can be treated with NaOH and the like to produce hydroxyl functions 108 resulting onto eFBG 106.
• the treatment of the surface eFBG with NaOH and the like produces surface roughness and few hydroxyl functions making surface of the eFBG hydrophilic.
• surface of eFBG 104 surface is treated with 0.2 to 0.4 N NaOH solution at 30 °C - 50 °C, more preferably at 40 °C for a few hours, preferably 3-4 hours, more preferably 3.5 hours and subsequently kept in the NaOH solution for about 30 minutes at room temperature.
• the treated eFBG 106 is rinsed with deionised water for about 10 minutes.
• the surface treatment can lead to a decrease in the Bragg wavelength ( ⁇ ⁇ ) by 15-25 pm.
• SWNTs 112 have an average diameter in range of 0.7 nm -lnm, more preferably around 0.8nm, with chirality (6, 5), purchased from M/s South-West Nanotechnologies.
• Surface of SWNTs can be made hydrophilic by following a procedure known in the literature for example in Hussain, S., Jha, P. et al, 2011. Journal of Modern Physics, 2, 538-543, by treating with 3 : 1 cone. H 2 S0 4 :conc. HN0 3 for 3 hrs at 40 °C. The mixture is centrifuged and the residue is washed with water several times and dried at 100 °C.
• cladding of the FBG 102 can be removed by an etching process.
• the etching can be carried out by dipping only the grating region of the FBG 102 in a range of 200-300 ⁇ . of 40% Hydro Fluoric acid (HF) solution placed in a teflon block for few hours, more preferably approximately 2 hours.
• HF Hydro Fluoric acid
• This process can render the diameter of the etched FBG 106 to 6 ⁇ -12 ⁇ more preferably 8 ⁇ - ⁇ with a few nm downshift more preferably lnm downshift in ⁇ ⁇ .
• surface roughness and hydrophilicity of eFBG 106 leads to attachment of the acid treated SWNTs and ⁇ ⁇ is found to increase by about 10-14 pm after the attachment of SWNTs (with respect to the ⁇ ⁇ after NaOH treatment). This increase in ⁇ ⁇ is due to the increase in the effective refractive index due to the SWNTs coating.
• GO 110 suspensions (0.25mg/ml) can be prepared according to a method known in the literature (Vasu, K. S., Biswanath et al, 2010. Solid State Communications. 150, 1295-1298; Stankovich, S. et al, 2007. Carbon. 45, 1558-1565; Hummers et al, 1958. J. Am. Chem. Soc. 80, 1339).
• Figure 1 (b) illustrates a scanning electron microscopic image of GO coated eFBG captured using ULTRA 55, Field Emission Scanning Electron Microscope (M/s Karl Zeiss).
• one or more dendrimer molecule(s) can be reacted with specific molecules to create specific active sites on the dendrimer in order to detect specific proteins or antigens.
• the one or more dendrimer molecule(s) can be attached with a carbohydrate to form a carbohydrate coated dendrimer functionalized nano carbon materials coated optical biosensor, which can then bind to a specific protein.
• the carbohydrate is mannose.
• carbohydrate-protein interactions can be detected using mannose attached PETEVI dendrimer as a multivalent carbohydrate ligand.
• Mannose attached PETFM dendrimer (generation 4) solutions in water with a concentration of 0.5mM can be prepared by a method as described in Vasu, K. S. et al, 2012. Appl. Phys. Lett. 101, 053701.
• the nano carbon materials 110 or 112 coated eFBG 106 can be dipped in the Dendrimer solution to create carbohydrate (mannose) sites.
• SWNTs are p - type, DM molecules 114 form SWNT - DM complexes, through charge transfer interactions.
• SWNT 112 - DM 114 complexes can result in the decrease of ⁇ ⁇ by about 8- 12pm more preferably 10 pm with respect to the ⁇ ⁇ of eFBG 106 coated with SWNTs 112.
• the Bragg wavelength ( ⁇ ° ) of the eFBG 106, after the formation of the SWNT - DM complex is 1539.09 nm.
• Carbohydrate coated dendrimer functionalized nano carbon materials coated eFBG of the present invention can then bind to a specific protein such as Lectin for detecting carbohydrate-protein interactions or antigen-antibody interactions.
• Lectins are a group of proteins that bind specific carbohydrate structures including but not limited to for example mannose binding lectins such as Concanavalin A (ConA), Galactose binding lectins such as Peanut agglutinin, Jacalin and Wheat Germ Agglutinin, among others.
• Concanavalin A is a lectin originally extracted from the jack-bean, Canavalia ensiformis that interacts with diverse receptors containing mannose carbohydrates, notably rhodopsin, blood group markers, insulin-receptor the Immunoglobulins and the carcino-embryonary antigen (CEA). It also interacts with lipoproteins.
• Peanut agglutinin (PNA) is plant lectin protein derived from the fruits of Arachis hypogaea. Peanut agglutinin binds preferentially to T-antigen, a galactosyl ( ⁇ -1, 3) N-acetylgalactosamine structure.
• solutions of Con A specific to mannose and non-specific PNA can be prepared in water (pH ⁇ 6.5 to 6.7) in a concentration range of 100 pM to 5 ⁇ .
• the Bragg wavelength values can be monitored after treating the SWNT 112 - DM 114 coated eFBG 106 at different concentrations of aqueous solutions of Con A from InM to 5 ⁇ . It was found that with increase of Con A concentration, the difference ⁇ ⁇ ( ⁇ ⁇ - ⁇ ° ) significantly increases.
• Millipore water of 18 ⁇ resistance and pH varying from 6.5 to 6.7 can be used for making dendrimer mannose, Con A and PNA solutions, SWNTs and GO suspensions.
• Figure 2 shows variation in the ratio ⁇ ⁇ / ⁇ ° ⁇ with respect to concentration of Con A and PNA. As shown in Figure 2, even for InM of Con A, the shift ⁇ ⁇ is ⁇ 2pm and after an addition of 5 ⁇ Con A, the shift ⁇ ⁇ increases to ⁇ 75pm.
• Another exemplary embodiment of the present invention is configured to measure variation in the ratio ⁇ ⁇ / ⁇ ° ⁇ with respect to concentration of a non-specific lectin, PNA. It is observed that ⁇ ⁇ value after 5 ⁇ PNA treatment is only ⁇ 5pm. The ⁇ ⁇ for 5 ⁇ of PNA treatment is lesser than the ⁇ ⁇ for 2nM of Con A treatment, showing a very high specificity of the optical biosensor for the mannose - Con A interactions.
• Figure 3 depicts another embodiment of the present invention wherein a change in ⁇ ⁇ / ⁇ ° ⁇ of the GO - DM coated eFBG is shown after dipping in different concentrations of lectins.
• a change in ⁇ ⁇ / ⁇ ° ⁇ is measured for the GO-DM coated eFBG as a function of lectin concentration.
• the Bragg wavelength ( ⁇ ° ⁇ ) of the eFBG coated with the GO - DM complex is found to be approximately 1546.55nm.
• the change in ⁇ ⁇ after addition of ⁇ ⁇ Con A ⁇ ⁇ is found to be ⁇ 150pm as compared to a ⁇ ⁇ of ⁇ 20pm for ⁇ ⁇ PNA.
• the ⁇ ⁇ value for ⁇ ⁇ PNA detection is same as the ⁇ ⁇ value for 500pM of Con A.
• ⁇ ⁇ concentration of Con A treatment value of ⁇ ⁇ for the GO coated eFBG is twice as compared to the value of ⁇ ⁇ for SWNTs coated eFBG.
• the enhanced sensitivity of GO coated eFBG over SWNTs coated eFBG is due to the fact that the surface area of GO is more than SWNTs and also GO covers more area on the surface of eFBG, resulting in larger number of DM molecules to get attached to the GO coated eFBG.
• sensor readout or output measurand a relative change in the Bragg wavelength A B / ° B as a function of lectin concentration is shown to obey the Langmuir type isotherm, giving the affinity constant value of 4.2 x 10 7 M "1 for SWNTs coated eFBG and 3.4 x 10 8 M "1 for GO coated eFBG.
• Equation (1) can be applied to extract K A values of Con A -mannose interaction yielding 4.2 x 10 7 M “1 for SWNTs coated eFBG and 3.4 x 10 8 M "1 for GO coated eFBG.
• the observed K A value in SWNT coated eFBG optical sensor is 40 times more than the K A value in the SWNT FET sensor as measured in Vasu, K. S., Naresh, K., Bagul, R. S., Jayaraman, N., Sood, A. K., 2012. Appl. Phys. Lett. 101, 053701.
• Figure 4 depicts variation in ⁇ ⁇ / ⁇ ° ⁇ of the GO coated directly on cladding of the FBG with respect to different concentrations of Con A wherein sensitivity of carbohydrate - protein interactions are found to be negligible when the GO is directly coated on cladding of the FBG. Thus showing that etching of FBG enhances the sensitivity.
• Figure 5 depicts change in cladding refractive index (surrounding medium) as a function of concentration of Con A solution for both SWNTs (red color open circles) and GO (black color open squares) coated eFBGs.
• the change in the refractive index of the surrounding medium which acts as cladding to the etched FBG causes the change in the effective refractive index which in turn causes a change in ⁇ ⁇ .
• the change in the cladding refractive index (surrounding medium) was calculated using the equation given by Matthew, P. D., Zheng, Z., Mira, S., Saeed, P., Christopher, C. D., James, S. S., William,E. B., 2000. Anal. Chem. 72, 2895-2900.
• n c i ad , n cor are refractive indices of cladding and core of a FBG.
• core refractive index is taken as 1.471 and not accounted for periodic change in it to calculate the change in the cladding refractive index.
• the effective area of coating by SWNTs and GO is 50%-60% more preferably 55% and 60%-70% more preferably 65% respectively.
• Figure 6 illustrates another embodiment of the present invention showing a block diagram of multiple gratings inscribed on eFBG 106 which can be used as an optical biosensor for many specific antibody - antigen interactions.
• Figure 6(a) illustrates eFBG coated with graphene oxide (GO) 110 attached with different antibodies such as Antibody 1 602, Antibody 2 604, Antibody 3 606 and so on upto Antibody n 608.
• Figure 6(b) illustrates eFBG 106 coated with SWNTs 112 attached with different antibodies such as Antibody 1 602, Antibody 2 604, Antibody 3 606 and so on upto Antibody n 608.
• the antibodies can bind with specific antigens such as Antigen 1 601, Antigen 2 603, Antigen 3 605 and so on upto Antigen n 609.
• the biosensor of the present invention can be implied to detect a large number of specific antibody- antigen interactions.
• the biosensor of the present invention can be used in different biological and chemical sensing applications by attaching specific ligands to the nano carbon materials coated on etched Fiber Bragg Grating.
• the present invention provides to write multiple gratings of different bragg wavelengths on a single optical fiber to detect many specific antibody - antigen interactions simultaneously.
• the present invention provides an optical biosensor which is highly sensitive and accurate for biological and chemical sensing applications wherein a coating of nano carbon materials attached with dendrimer molecules is disposed on etched fiber Bragg grating (eFBG).
• eFBG etched fiber Bragg grating
• the present invention further provides an optical biosensor which is used in detection of carbohydrate-protein interactions as an example of antibody-antigen interactions.
• the present invention further provides an optical biosensor which measures a shift in Bragg wavelength as an output measurand wherein the shift in wavelength is very sensitive to small changes in optical properties such as refractive index of the nano carbon materials coated eFBG due to antibody-antigen interactions or carbohydrate-protein interactions.
• the present invention further provides an optical biosensor where multiple gratings of different Bragg wavelengths can be inscribed on a single optical fiber to detect many specific antibody - antigen interactions simultaneously.
• the present invention further provides an optical biosensor wherein a multivalent Dendrimer having multiple functionalities further provides a large number of active sites to increase the sensitivity in detection of antibody-antigen interactions or carbohydrate-protein interactions .
• the present invention further provides a method of fabrication of an optical biosensor comprising of dendrimer functionalized nano carbon materials coated on eFBG.
• the present invention further provides a simpler and easier method of coating of nano carbon materials on surface of eFBG wherein surfaces of nano carbon materials and eFBG are made hydrophilic.

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