Investigation On A Bio-Sensor: A Theoretical Study On Modied Photonic Crystal Fiber Using Plasmonic Nanomaterial

A modified (HC-800) Photonic Crystal Fiber (PCF) using Gold nanoparticle as an active plasmonic material was used as bio a sensor. The Finite Element Method is used to compute numerical interpretations of sensing performance employing various liquids such as (Liver Blood, Colon Blood, Human Blood Plasma, Water, and Pentanol). In the proposed biosensor the sample (analyte material) is placed into a core, cladding air holes, and outside of the HC fiber structure. The sensitivity was calculated before and after adding the gold layer. The maximum amplitude sensitivity was found to be 769.5749 RIU -1 for Human blood Plasma and the best electric field was found to be 400V/m. In the same liquid when used the deposited PCF with a gold layer the maximum amplitude sensitivity was found to be 975.5352 RIU -1 at a best electric field of 477 V/m. And when the proposed sensor is considered as a refractive index sensor, where is it used the analyte samples only (inside the core and air holes) of PCF. The maximum amplitude sensitivity was found to be 869.8453 RIU -1 at a best electric field of 434 V/m.


I. INTRODUCTION
The photonic crystal fiber is a new type of optical fiber. The Photonic Crystal Fiber is made of a single material, such as silica glass, with air holes running the length of the fiber around a solid or hollow core. These 'air holes' serve to keep electromagnetic waves confinement within the fiber's core while also allowing them to be customized in terms of transmission properties [1]. With the possibility of filling the air holes with different liquids to enhance the optical properties. A wide range of sensing applications of photonic crystal fiber. Such as the Photonic biosensors have advanced significantly in recent decades in a variety of applications, including medical diagnostics, biochemical detection, and organic chemical detection [2] [3].
Biosensors are used to transform a biological transition into a quantifiable signal that can be transmitted via a transducer and is widely used for biological agent detection and identification.
Optical biosensors are a class of biosensors that use light as the transduced signal, and are desirable for their highly sensitive, often non-destructive analytical analysis [1]. The (PCF)based SPR sensing technique is considered to be a possible route to miniaturization of sensors.
PCF has proven its advantages as a good replacement for prism, such as small size, easier light launch, single-mode propagation and capacity to monitor evanescent field penetration [3].
Photonic crystal fiber (PCF) is an updated innovation of optical fiber that uses Photonic precious stones [4]. One important component of this kind is the number of air holes arranged [5]. Two types of PCFs exist: Solid core (SC) and Hollow core (HC) [5] [6] . Each type makes use of distinctive components in light propagation [6]. There is a particular distinction between the ordinary fiber and PCF which is the required RI, since PCF uses lower RI in the layer of cladding. PCFs are used in so many applications, such as meteorology, bio-prescription, imagery, media transmission, modern equipment, etc [7]. Nanoparticles (Nps) of noble metals turned out to be extraordinarily interesting materials in many scientific areas as a result of their unique properties and important applications [12].
Metallic nanoparticles (NPs), generally gold and silver, have been created with great enthusiasm due to their SPR-related properties, which are thought to be valuable for their biological applications [13]. Control of the size, shape and surface functionality are important problems in Au NP combination [14].Gold nanoparticles (Au-NPs) were at the focus of consideration in nano medicine because of their compound safety and noticeable optical properties [15].
Distinctive basic and morphological characteristics of created NPs can be constrained by laser fluidity, spot size, wavelength, beat width and laser beat redundancy [16].
Nanotechnology is a science that deals with nanometer-scale particles in the range of 1-100 nm [48]. Gold nanoparticles (NPs) are widely used for their unique optical and physical properties, such as surface plasmon oscillations for labelling, imaging, and sensing, as preferred materials in many fields [49]. Gold is chemically stable even in aqueous environments as an alternate plasmonic material. In addition, it demonstrates the greater shift in wavelength at the resonant wavelength, which helps to accurately detect the unknown analysis for easy detection and increased accuracy [50]. Gold is used because it is unreactive and is not sensitive to air or light for nanoparticle applications [51]. The conventional methods to create these particles can be categorized into three types (chemical, electrical, and laser ablation methods). Evidence shows that the latter method is preferred to other methods. Different structural and morphological characters of produced NPs can be. Controlled by laser flounce, spot size, wavelength, pulse width, and repetition rate of a laser pulse [52]. Gold NPs are proved to be more effective as it has good efficacy against bacteria, viruses and other eukaryotic microorganisms.
While gold NPs can be exploited in medicine for burn treatment, dental materials, coating stainless steel materials, textile fabrics, water treatment, sunscreen lotions, etc., and possess low toxicity to human cells, high thermal stability, and low volatility. The energy density of an Au NP varies with the size and shape of the particles, resulting in a special Au NP absorption band known as the band of plasmon resonance (PR).
This absorption band results when the frequency of an incident light is resonant with the conduction electron collective in the Au NP and is referred to as particle plasmon resonance During the last few decades, the wide range of sensing applications and high sensitivity has gotten a lot of interest to the Surface Plasmon Resonance (SPR) phenomenon. In biosensing applications such as biomolecular analytes detection, medical diagnostics, antibody-antigen interaction, and so on, the SPR sensor has shown remarkable progress [4] [5]. This paper simulated a simple HC-800 PCF biosensor based on the surface plasmon resonance phenomenon (SPR). That is will be done by preparing the PCF by etching it and then have been deposited the gold layer on the etched area (outside of the photonic crystal fiber) to enhance the sensitivity of the fiber sensor. The Gold metal was used, Because gold is chemically stable in aqueous environments and has a high resonance peak shift, it is used as the plasmonic material [6]. The properties of the sensor were studied numerically using the finite element method (FEM) by using the COMSOL Multiphysics program, with a layer of the perfectly matched layer (PML), used to absorb the scattered light from the structure of sensors.

II. STRUCTURE DESIGN AND SIMULATION METHOD
In the present work, use photonic crystal fiber (HC-800) with core diameter is 7.5 ±1 μm, the region diameter of PCF is 45 ± 5 μm and pitch of 2.4 μm. As Presented in Figure (

Figure (1): Geometry of the (HC-800) PCF in COMSOL Multiphysics.
In the current work, to study the performance of the proposed sensor used the Finite element method. And which depends on its work on divided The cross-sections of the proposed PCF into homogeneous triangular many subdomains. So used Maxwell's equations to solve the neighboring subspaces of the modal analysis of the PCF structure was done in the x-y plane.
Wherefore From Maxwell's equation, the vectorial wave equation can be deduced as follows [7].
Where the −1 the inverse of the PML matrix of 3×3, n represents the domain's refractive index, E the electric field vector, 0 represents the wave number in free space express it by the following equation: Where λ represented the wave length.
Because the cladding part of PCF has a limited number of air holes. Lead to the leakage of the light out of the structure of the fiber. So it results in the Confinement Loss (CL) can be calculated by found the imaginary part, neff. Using the following equation as a guide [8].
When the five different liquids filled the fiber, have various refractive indices as in the table below: In figure (2) the refractive index is represented as a function of wavelength between (400-1200) nm. Can recognize the RI it was decreased when increasing the Wavelength. As presented below.  And figure (4.c) showed the effective mode index which has two parts (real and imaginary).    is the loss different between two loss spectra. The sensitivity of wavelength interrogation computed by the following formula [17].
Where, ∆ represented the difference between to wavelength peak shifts, and is the difference between tow refractive index (RI). Where a change in the analyte refractive index Where, ∆ represented the difference between the two refractive index, ∆ = 0.1 [19] (the a standard assuming value for the minimum spectral resolution), ∆ is the difference between two peaks of wavelength. So the resolution of the suggested sensor is (1.25 × 10 −6 , 8.5 × 10 −6 , 7.1 × 10 −5 , and3.98 × 10 −5 ).
The figure (7) illustrate the amplitude sensitivity of the HC-PCF, Without gold layer. We found that the maximum value of amplitude sensitivity is 769.5749 RIU -1 at 0.61µm for refractive index (RI) of (1.330) for Human blood Plasma.      When the proposed biosensor with a layer of gold, Was Immersed and infiltrated with various liquids (Liver Blood, Colon Blood, Human Blood Plasma, Water, and Pentanol).

Figure (12): Amplitude sensitivity for different refractive index (RI).
In figure (13) we note The fundamental mode of liquids as compared to their electric field.
So we found the best electrical field for Human Blood Plasma equal to 477 V/m. which leads to it have high sensitivity best than other liquids.   The confinement losses explain in figure (15) by using eq (3). When the proposed RI sensor infiltrated by different liquids (Liver Blood, Colon Blood, Human Blood Plasma, Water, and Pentanol).

Figure (15): The Confinement loss of proposed Refractive index sensor
In figure (16) was calculated the wavelength sensitivity from the equation (5)  liver, and pentanol) .also, was found the maximum amplitude sensitivity from equation (4)    And found the best electrical field also for Human Blood Plasma equal to 434 V/m which leads to high sensitivity than other liquids.

CONCLUSION
This article displays A practically simple HC-800 PCF as a biosensor and RI sensor. We performed three calculations of the confinement losses and the sensitivity of the proposed sensor. As it has been studied numerically using (FEM). In the first case, before the gold layer was deposited on the fiber, the fiber was immersed with the analytical material from the outside and (inside core and air holes), and we noticed when the refractive index of the sample (analyte) increased, the confinement losses decreased. And the maximum amplitude sensitivity for (human blood plasma) is 769.5749 RIU -1 and the best electric field was found to be 400 V/m.
And in the second case of the same type of fiber, a plasmonic sensor was proposed when depositing the gold layer on the fiber from the outside, and also immersed by the analytical material, outside and (inside core and air holes) so we noticed the highest increase in the sensitivity of the sensor for the same analytical substance (human blood plasma), where it was equal to 975.5352 RIU -1 at the best electric field was found to be 477 V/m. In the third case, the same type of fiber was used, and also the same layer of gold was deposited on it from the outside, but it was considered as a refractive index sensor because the analytical material was only placed inside the fiber (inside the core and air holes) and the maximum sensitivity of the proposed sensor was calculated and found to be equal to 869.8453 RIU -1 for (human blood plasma) at the electric field 434 V/m.

1-Funding
The research reported in this manuscript has been done at the University of Technology, Baghdad, Iraq. Fully funded of our own financial support.

2-Conflicts of interest/Competing interests
We wish to draw the attention of the Editor to the following facts, We confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.

3-Availability of data and material
All our data presented in the manuscript

5-Authors' contributions
Our manuscript creates a paradigm for future studies to encourage researchers to focus on this area and all Authors were aware of about the paper content and approved its submission.

6-Consent to participate
We confirm that if accepted, the article will not be published elsewhere in the same form, in any language, without the written consent of the publisher.

7-Consent for publication
We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us.

8-Ethics approval
I am the undersigned on behalf of the authors declare that this manuscript is original, has not been published before, and is not currently being considered for publication elsewhere and not submitted to more than one journal for simultaneous consideration.
We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we confirm that we have followed the regulations of our institutions concerning intellectual property. We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He is responsible for communicating with the other authors about progress, submissions of revisions, and final approval of proofs.
We confirm that if accepted, the article will not be published elsewhere in the same form, in any language, without the written consent of the publisher.
Thank you for your consideration Sincerely,