Essay: Localized Surface Plasmon Resonance project

Abstract

Localized Surface Plasmon Resonance (LSPR) is an optical phenomenon of the interaction of free electron with electromagnetic field of light at the metal nanoparticles surface. The LSPR is very sensitive to the dielectric surrounding medium, hence its widely used for sensing application. The development of plasmonic sensor has been developed for toxic detection in solution form. This system consists of a light source that is connected to a fiber optic duplex system with two arms. The first arm transmits light from the light source beam to the sample and the second arm sent the reflected light from the sample to the spectrometer. The sensing process was done in the sensor chamber made from PLA (polylactic acid) material with a sliding drawer is used to place the sample or known as sensing material. OceanView software was used to analyze the recorded spectrum from      the spectrometer. In this study, the testing of the plasmonic sensor was carried out using targeted analyte namely chlorpyrifos with deionized water that is set as a reference medium. Gold nanoparticles which are nanosphere were used as sensing materials. The sensing parameters are based on changing of their resonance peak position and its wavelength. This plasmonic sensor was compare with UV-VIS spectrometer data to make sure it standardize and function correctly. Besides, the sensing process toward different concentration of target analyte have been done. As conclusion, the plasmonic sensor was successful developed for toxic detection in solution form.

Chapter 1

Introduction

1.1 Introduction

Localized Surface Plasmon Resonance (LSPR) have become powerful bio-sensing techniques. This technique applications are used in medical diagnostics, environmental monitoring and food safety. The implementation of LSPR is very broad in sensor application because of its sensitivity to refractive index of surrounding medium and dielectric[1].

LSPR had been used for the detection of formilin liquid using gold nanospherical as its sensing material. In addition, the plasmonic sensor has been used to detect the biological for disease and cancer cell in medical field. Plasmonic sensor also use air as a medium to detect a toxic gaseous namely carbon monoxide (CO) and sulfur hexafluoride (SF6)[2].

The plasmonic sensor is an optical sensing which will develop to detect toxic materials in solution form. This system consists of a light source that is connected to a duplex fiber optic which has two arms. The first arm transmits light from the light source beam to the sample and the second arm sent the reflected light from the sample to the spectrometer. The sensing process was done in the sensor chamber with metal nanoparticle used as sensing material. The testing of the plasmonic sensor will carried out using targeted analyte namely chlorpyrifos with deionized water that is set as a reference medium. The sensing parameters are based on changing of their wavelength and its resonance peak position.

1.2 Problem Statement

Human exposure to toxic can occur through food, inhalation of breath or even just a touch of skin on your land that has been contaminated. There are many sensor used to detect toxic such as ultrasensitive aptasensor and immunosensor[3]. Those sensor has many procedure with difference method to sensing the toxic material. Besides that, they may not be as sensitive for some compounds as conventional method. In this study, plasmonic sensor is chosen because it is direct toxic detection in solution which not changing the chemical properties.

1.3 Objectives

The objectives of this project are:

1. To design a sensor chamber as a platform to place the sensing material.

2. To develop the plasmonic sensor for detection of chlorpyrifos in solution form.

3. To analyze the sensitivity and repeatability of the plasmonic sensor towards chlorpyrifos.

1.4 Scope of Project

In order to fulfill the objectives, the scope of this project will divided into three phases. The detail explanation as follows:

i. To design a sensor chamber as a platform to place the gold nanoparticle for sensing material.

a. The sensor chamber will be design using SolidWork software. Then it will be printed using 3D printer with PLA (polylactic acid) material. The range of the chamber size is 40cm x 50cm x 60cm. The chamber has two hole on top which to place the fiber optic and toxic solution. Besides, the chamber is anti-vibration and stable.

ii. To develop the plasmonic sensor to detection of chlorpyrifos in solution form. Consists of five components.

a) The light source that provides electromagnetic radiation visible light to excite the resonance properties of metal nanoparticles. It used from tungsten halogen lamp which it can emit visible light and near infrared radiation.

b) The duplex fiber optic acts as a medium for transmit the light source to the sample inside the sensor chamber and subsequently sent the reflected light by the sample to spectrometer.

c) The sensor chamber as a platform to place the gold nanoparticle for sensing material and the ferrule of duplex fiber optic.

d) The spectrometer will be used to record the reflected light spectrum by the sample that passed through the fiber optic.

e) The computer act as the data collection from the spectrometer to analyze the sample spectrum by using OceanView software.

iii. To analyze the sensitivity and repeatability of the plasmonic sensor towards chlorpyrifos.

a) Provide the concentration range of targeted analyte namely chlorpyrifos. Besides, get resonance peaks position and wavelength in the spectrum as sensing parameter.

Chapter 2

LITERATURE REVIEW

2.1 Definition of Localized Surface Plasmon Resonance (LSPR)

Localized surface plasmon resonance (LSPR) is a resonance phenomenon of free electron waves in a metal nanostructure such as gold, silver and lead which has smaller sizes than light wavelength. It has a unique characteristics that gain interest among scientist and researchers in various field such as catalytic, solar cell, Surface-Enhanced Raman Spectroscopy (SERS) and sensor. The LSPR in based sensor also known as plasmonic sensor that has been operated based on the changing of optical characteristics of metal nanostructures in analyte either liquid or gaseous form. Its use deionized (DI) water as a reference medium for LSPR in based liquid while inert gaseous such as nitrogen for LSPR in based gaseous[2]. LSPR has emerged as a leader among label-free bio-sensing techniques in that it offers sensitive, robust, and facile detection. Traditional LSPR in based bio-sensing utilizes the sensitivity of the plasmon frequency to changes in local index of refraction at the nanoparticle surface. Although surface plasmon resonance technologies are now widely used to measure biomolecular interactions, several challenges remain[4].

2.2 Surface Plasmon Resonance (SPR) and Localized Surface Plasmon Resonance (LSPR)

Surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) are both powerful tools for label-free bio-sensing in biochemistry due to their high sensitivity to the refractive index change caused by their interactions with molecules such as DNA or proteins. SPR is known as a phenomenon excited when the frequency of evanescent electromagnetic wave propagating at the metal-dielectric interface is resonant with the oscillation of the surface conduction electrons in metal. LSPR often refers to metallic nanoparticles as it occurs when the frequency of incident photon is resonant with the collective oscillation of conduction electrons in metallic nanoparticles. Traditional SPR sensors are fabricated based on the Kretschmann configuration where a thin noble metal film is coated on a prism. LSPR sensors, on the other hand, are normally fabricated on a chip that noble metal nanoparticles are coated on a substrate such as glass slide[5]. The sensing principle for SPR and LSPR system was show in Figure 2.1.

Figure 2.1: Schematics of the sensing principle for the SPR (left) and LSPR (right) systems[5].

The advantages of SPR:

1.Label-free which less expensive and easier to perform.

2.Small sample volumes in range of 100-200uL.

3.High sensitivity that can be used for small molecules to large proteins.

4.Real-time which giving deeper insight into the binding kinetics compared to yes/no binding or affinity techniques.

5.Quantitative

The advantages of LSPR:

1. The optical hardware needed is much less complex since no prism is needed to couple the light, so the instrument can be made smaller and more affordable.
2. Since the angle is not important, the instrument is much more robust against vibration and mechanical noise.
3. Not as sensitive to bulk refractive index changes, which causes errors in experimental data, because it has a much shorter electromagnetic field decay length.
4. No strict temperature control is needed, simplifying the instrument.
5. The sensor chips can be manufactured at a much more affordable price.
6. Easier to use and maintain.

Although SPR sensors have a much higher refractive index sensitivity than LSPR sensors but their sensitivity towards bio-molecular binding events is similar. This because of the much shorter electromagnetic decay length of nanoparticles compared to gold films, which confines the response to a smaller sensing volume. This smaller sensing volume means that LSPR is more sensitive to molecular binding and less sensitive to bulk effects. The smaller decay length and sensitivity associated with LSPR reduces artifacts caused by external variables such as buffer refractive index changes[6].

2.3 General Principles of Localized Surface Plasmon Resonance

LSPR is the interaction of light with noble metal nanoparticles produces a collective oscillation of conduction band electrons. Only materials with a negative real and small positive imaginary dielectric constant such as gold and silver are capable of supporting surface plasmons. The resonance condition is met when the incident electromagnetic field matches that of the oscillating electrons on the surface of the nanoparticle, see Figure 2.2[4].

Figure 2.2: Schematic diagram illustrating the LSPR on a nanoparticle surface[4].

This resonant oscillation produces large wavelength-selective increases in absorption, scattering, and electromagnetic field at the nanoparticle surface. The increasing of absorption and scattering have been utilized towards LSPR bio-sensing. While the increasing of electromagnetic fields have also proven very useful in surface enhanced Raman spectroscopic (SERS) detection of biological analytes. This review will only cover LSPR biosensing and not SERS-based platforms. When a biological analyte binds to the surface of the nanoparticle, a change in refractive index at the nanoparticle surface is induced, which in turn shifts the LSPR peak frequency. This shift of LPSR frequency is also affected by the makeup and different shape of the nanoparticle. Gold having the largest negative real dielectric constant of all the plasmonic materials which is the most sensitive to changes in local refractive index. Since refractive index sensitivity is key for detecting a biological molecule of interest, many endeavors in recent years have attempted to make nanoparticle substrates that exhibit high sensitivity to changes in refractive index[4].

2.4 Gold Nanoparticle

For this project, gold nanoparticles have been chosen as a sensing material. Gold have their unique optical properties that been extensively used for applications both in biology and technology. These properties are conferred by the interaction of light with electrons on the gold nanoparticles surface. At a specific wavelength or frequency of light, collective oscillation of electrons on the gold nanoparticles surface cause a phenomenon resulting in strong extinction of light which is absorption and scattering. The particular wavelength or frequency of light where this occurs is strongly dependent on the gold nanoparticles size, shape and surface[7].

The range of applications for gold nanoparticles is growing rapidly and includes [9]:

1. Electronics – Gold nanoparticles are designed for use as conductors from printable inks to electronic chips. As the world of electronics become smaller, nanoparticles are important components in chip design. Nanoscale gold nanoparticles are being used to connect resistors, conductors, and other elements of an electronic chip.
2. Photodynamic Therapy – Near-IR absorbing gold nanoparticles (including gold nanoshells and nanorods) produce heat when excited by light at wavelengths from 700 to 800 nm. This enables these nanoparticles to eradicate targeted tumors. Â When light is applied to a tumor containing gold nanoparticles, the particles rapidly heat up, killing tumor cells in a treatment also known as hyperthermia therapy
3. Therapeutic Agent Delivery – Therapeutic agents can also be coated onto the surface of gold nanoparticles. The large surface area-to-volume ratio of gold nanoparticles enables their surface to be coated with hundreds of molecules (including therapeutics, targeting agents, and anti-fouling polymers).
4. Sensors – Gold nanoparticles are used in a variety of sensors. For example, a colorimetric sensor based on gold nanoparticles can identify if foods are suitable for consumption. Other methods, such as surface enhanced Raman spectroscopy, exploit gold nanoparticles as substrates to enable the measurement of vibrational energies of chemical bonds. This strategy could also be used for the detection of proteins, pollutants, and other molecules label-free.
5. Probes – Gold nanoparticles also scatter light and can produce an array of interesting colors under dark-field microscopy. The scattered colors of gold nanoparticles are currently used for biological imaging applications. Also, gold nanoparticles are relatively dense, making them useful as probes for transmission electron microscopy.
6. Diagnostics- Gold nanoparticles are also used to detect biomarkers in the diagnosis of heart diseases, cancers, and infectious agents. They are also common in lateral flow immunoassays, a common household example being the home pregnancy test.
7. Catalysis – Gold nanoparticles are used as catalysts in a number of chemical reactions. Â The surface of a gold nanoparticle can be used for selective oxidation or in certain cases the surface can reduce a reaction (nitrogen oxides). Gold nanoparticles are being developed for fuel cell applications. These technologies would be useful in the automotive and display industry.

2.5 Chlorpyrifos Toxic

Chlorpyrifos is an organophosphate insecticide. Pure chlorpyrifos is made up of white or colorless crystals. It has a slightly skunky odor like rotten eggs or garlic. Chlorpyrifos is used to control many different kinds of pests including termites, mosquitoes, and roundworms. Products with chlorpyrifos in them are used in agriculture for feed and food crops and in cattle ear tags. They may be used on golf courses and to control fire ants and mosquitoes for public health purposes. Products containing chlorpyrifos are also used to treat wood fences and utility poles.

Chlorpyrifos can be harmful if it is touched, inhaled, or eaten. Chlorpyrifos works by blocking an enzyme which controls messages that travel between nerve cells. When the enzyme is blocked, the nervous system can’t send normal signals.  Chlorpyrifos affects the nervous system of people, pets, and other animals the same way it affects the target pest. Chloropyrifos can inhibit the nervous system enzyme acetyl cholinesterase in humans, leading to overstimulation of the nervous system causing nausea, dizziness, and confusion. At very high exposures (from spills or accidents), respiratory arrest and death can occurs. Chlorpyrifos does pose acute and reproductive risks to many non-target aquatic and terrestrial animals. In general, estuarine species are more at risk than freshwater species. Birds appear to be more at risk than most mammals[10].

Chapter 3

Methodology

3.1 Introduction

In order to complete and achieve the aim of this project, a good methodology has to be planned so that the project development runs smoothly. Methodology is the method and way the project developed including how the development process carried out, how testing is done and what other steps from beginning until the end of the project. This project consist of two major part that is software and hardware development, thus the steps and procedures must be planned carefully and systematically. The description and detail about the steps and procedures during the project development will be explained in chapter.

3.2 Software for Project Development

There are three software’s was used during the project development which has their own function. The software’s are SolidWorks, UV Probe and OceanView. This software’s will help to complete the project system and act as the data collection medium.

3.2.1 SolidWorks

SolidWorks software was used in this project for design the sensor chamber. SolidWorks is a solid modeling computer-aided design (CAD) and computer-aided engineering (CAE) computer program that runs on Microsoft Windows. SolidWorks is a solid modeler, and utilizes a parametric feature-based approach to create models and assemblies.

Figure 3.1: Start screen of SolidWorks

Figure 3.2: Design screen of SolidWorks

The basic things in SolidWorks software was about the parameter, design, features, building and part assembly. To determine the shape or geometry of the model value, its refer to the parameter. Parameter can be either numeric parameters, such as line lengths or circle diameters, or geometric parameters.

Design refer on how the creator of the part wants it to respond, changes and updates. For example, designer want the hole to stay at the top surface, regardless of the height or size of the can. SolidWorks allows to specify that the hole is a feature on the top surface, and will then honor the design intent no matter what height they later assign to the can.

Next, build the blocks of the part was refer to features. They are the shapes and operations that construct the part. This shape feature begin with 2D or 3D sketch and then will extruded or cut to add or remove material from the part. For building a model designer can start with 2D or 3D sketches. During sketching, designer can use dimensions to define or change the size and location of the geometry.

Lastly, assembly which the analog to sketch relations are mates. rawings can be created either from parts or assemblies. Views are automatically generated from the solid model, and notes, dimensions and tolerances can then be easily added to the drawing as needed[8].

3.2.2 UVProbe

UVProbe is a software that use for getting data from UV-VIS spectrometer. It is multifunctional and easy to use software supplied as standard with UV-VIS spectrometers. This software is free-format report creation which can be created with a free layout of graphs and tables. The thickness and color of graph lines can be changed, and text and diagrams pasted. Finished layouts can be conveniently saved as templates. Measurement modules with diverse data-processing and calculation functions. Comprehensive data-processing functions are provided for each mode.

Figure 3.3: Start screen of UVProbe

Figure 3.4: UVProbe user interface

This software also have security functions. When the security functions are enabled, an identification code and password are required when logging in. Advanced settings are available for the password. The functions assigned to each user can be restricted as well. Other function of this software is audit trail functions which all data is stored in a file inside a directory structure. After calculations and other data processing based on original acquired data, the results are saved by creating new data inside the same file separate from the original data. The history log of user, date and operations is also maintained inside this file.

3.2.3 OceanView

OceanView is a software that use for getting data from the spectrometer. This software allows to perform the three basic spectroscopic experiments which is absorbance, reflectance and emission, as well as absolute irradiance and Raman. Signal-processing functions such as electrical dark-signal correction, boxcar pixel smoothing and signal averaging are also included. Scope mode, the spectrometer operating mode in which raw data or signal is acquired by the detector, allows you to establish these signal-conditioning parameters. The basic concept for the software is that real time display of data allows users to evaluate the effectiveness of their experimental setups and data processing selections, make changes to these parameters, instantly see the effects and save the data.

Figure 3.5: Start screen of OceanView

Figure 3.6: OceanView user interface

OceanView gives the complete control of setting the parameters for all system functions such as acquiring data, designing the graph display, and using spectra overlays. OceanView has the benefit of providing various software-controlled triggering options for external events such as laser firing or light source pulsing. Other advanced features give several data-collection options. User  can independently store and retrieve dark, reference, sample and processed spectra. All data can be saved to disk using autoincremented filenames. One feature prints the spectra and another copies spectral data into other software such as Excel and Word.

3.3 The Hardware Development

There are five components to develop this sensor which are the light source, duplex fiber optic, sensor chamber, spectrometer and computer.

3.3.1 Light Source

This project was use the light source from Avantes AvaLight-HAL-Mini model.  It’s a compact and stabilized halogen light source with adjustable focusing of the fiber connection, maximizing output power at the desired wavelength. The light source also has adjustable output power to provide extra power or longer bulb life.  The adjustable focus helps to get the most out of your light source which makes sure all possible power is transmitted through your optical fiber. Bulb replacement is easy and can be done in a matter of minutes.

Figure 3.7: The light source from Avantes

Figure 3.8: Front view of the light source

Figure 3.9: Back view of the light source

The principle for light emission is the same as that for a standard incandescent bulb. Electric current is supplied to a filament and its becomes hot then the light is emitted. The bulb in a halogen lamp is filled with inert gas and a small amount of a halogen. While the tungsten used as the filament evaporates due to the high temperature, the halide causes the tungsten to return to the filament. This helps create a bright light source with a long service life.

3.3.2 Duplex Fiber Optic

Duplex fiber optic from Ocean Optics has been use for this project. This duplex has 600 μm core probes can even be used to excite and sense fluorescence from solid samples. The fiber optic is 6-around-1 fiber bundle design which the 6 fiber leg connects to light source and the single fiber leg connects to spectrometer for best performance. While the 600 μm probes come with a 3.175 mm diameter ferrule for fluorescence measurements.

Figure 3.10: The duplex fiber optic

Figure 3.11: The fiber optic ferrule

Figure 3.12: The fiber optic probes

3.3.3 Spectrometer

This project also has used the spectrometer USB2000 model from Ocean Optics. The spectrometer function is to take in light and break it into its spectral components. Then its digitize the signal as a function of wavelength and read it out and display it through a computer. The first step in this process is to direct light through a fiber optic cable into the spectrometer through a narrow aperture known as an entrance slit. The slit vignettes the light as it enters the spectrometer. In most spectrometers, the divergent light is then collimated by a concave mirror and directed onto a grating. The grating then disperses the spectral components of the light at slightly varying angles, which is then focused by a second concave mirror and imaged onto the detector. Alternatively, a concave holographic grating can be used to perform all three of these functions simultaneously.

Figure 3.13: The spectrometer from Ocean Optics

Figure 3.14: Front view of the spectrometer

Figure 3.15: Side view of the spectrometer

Once the light is imaged onto the detector the photons are then converted into electrons which are digitized and read out through a USB or serial port to a computer. The software then interpolates the signal based on the number of pixels in the detector and the linear dispersion of the diffraction grating to create a calibration that enables the data to be plotted as a function of wavelength over the given spectral range. This data can then be used and manipulated for countless spectroscopic applications, some of which will be discussed here later on.

3.3.4 The 3D Printer

3D printer has been used to print the sensor chamber. 3D printing is an additive manufacturing process that builds a three-dimensional object from a digital file. An object is formed by adding material in layers based on the digital design in a computer controlled process. In other words, 3D printing refers to any computer controlled process that builds an object by adding material in layers following instructions from a digital file. Cubicon software has been used as the user interface that connect to the 3D printer. All the design need to setup in this software before it printed.

Figure 3.16: Start screen of Cubicon software

Figure 3.17: Cubicon software user interface

Figure 3.18: The printed process in progress

Figure 3.19: 3D printer multi function display

Figure 3.20: The parts had been printed

In 3D printing there are three main steps. The first step is the preparation a 3D file of the object want to print. This 3D file can be created using CAD software such SolidWorks. After user have checked, then the 3D file is ready to be printed. After that can proceed to the second step.

The second step is the printing process. User need to choose which best material that required for their object. In 3D printing the variety of materials used is very broad. The material includes plastics, ceramics, resins, metals, sand, textiles, bio-materials and glass. Most of these materials also allow for plenty of finishing options that enable to achieve the precise design result and some others that are not easily accessible yet.

The last step is the finishing process. This step requires specific skills and materials. When the object was finish printed, often it cannot be directly used or delivered until it has been sanded, lacquered or painted to complete it as intended.

3.4 The Configuration of the Sensor System

Figure 3.21 shows the schematic diagram of a sensor system set up to evaluate the sensor performance. From the diagram, light from a light source is connected to the duplex fiber optic probe. The sensor probe is dipped into a solution with a known refractive index and the reflected signal is captured by a spectrometer which is connected to the other side of the coupler. The signal produced could be displayed and monitored by a computer connected to the spectrometer. Figure 3.22 shows the sensor system setup.

Figure 3.21: Schematic diagram of a sensor

Figure 3.22: The sensor setup diagram

To test the response of gold nanoparticles to the presence of chlorpyrifos, the gold nanoparticles substrate was firstly immersed into a water media and laid flat at the bottom of the water container. A duplex fiber probe was positioned normal to the substrate surface. The responses were studied by transmitting the light from the source into one of the fiber arms as shown in the Figure 3.22, reaching the gold nanoparticles sample at the other probe end. Some light was scattered back to the probe and the rest was transmitted through the substrate. Then the light will reaching the rough liquid container base and then reflected back to the probe[9].

The scattered light was collected by a probe and transmitted to the spectrometer using another arm of the fiber. The scattered light that comes from the bottom of the liquid container as well as the contribution of medium refractive change to the absorption spectrum profile were discarded by recording the reference spectrum of the light using a blank quartz substrate. Therefore, the recorded light spectrum by the spectrometer solely came from the scattered light by the gold nanoparticles. The plasmonic sensitivity property of the gold nanoparticles to this chemical were studied by obtaining the optical absorption of the gold nanoparticles in the presence of chlorpyrifos with several concentrations[9].

Chapter 4

RESULTS AND ANALYSIS

4.1 Introduction

In this chapter, the result and analysis of the project will be discussed. The result and analysis is done to see the effectiveness of the system in term of functionality.  Several test have been done carried out to see how the system perform and works. The first tests are conducted to the test of gold nanopartical with air and DI water using UV-VIS spectrometer and plasmonic sensor which to identify whether the sensor work well or not. Second test is the detection of chlorpyrifos toxic with different concentration using plasmonic sensor. The wavelength and peak position of spectrum have been take as sensing parameter.

4.2  The Design of Sensor Chamber

The sensor chamber have been design by using SolidWorks software. It has divide by two parts which is the drawer and housing. All design was in unit millimeter (mm).

4.2.1  The Drawer

Figure 4.1, Figure 4.2 and Figure 4.3 show the view of the drawer design. The function of the drawer is to place the sensing material and the targeted analyte.

Figure 4.1: Front view of the drawer

There are two holes (A) and (B) refer to the Figure 4.2. The hole (A) is for placing the target analyte while hole (B) for placing the sensing material.

Figure 4.2: Top view of the drawer

Figure 4.3: Side view of the drawer

4.2.2  The Housing

Figure 4.4, Figure 4.5 and Figure 4.6 show the view of the housing design. The function of the housing is to place the drawer and the fiber optic probe.

The hole (C) is for placing the drawer refer to Figure 4.4.

Figure 4.4: Front view of the housing

The hole (D) is for placing the fiber optic probe refer to Figure 4.5.

Figure 4.5: Top view of the housing

The hole (E) is the place for make sure the fiber optic probe and target analyte is insert properly. After that, the hole (E) will be cover by black plane before the sensing activity carried out. Refer to Figure 4.6.

Figure 4.6: Side view of the housing

4.2.3  The Full View of Sensor Chamber

Figure 4.7, Figure 4.8 and Figure 4.9 show the view of the sensor chamber design that is a combination of the housing and drawer. The drawer can be sliding in the housing.

Figure 4.7: Front view of the chamber

Figure 4.8: Top view of the chamber

Figure 4.9: Side view of the chamber

4.2.4  The Printed Sensor Chamber

Figure 4.10 and Figure 4.11 shows the sensor chamber that has print by 3D printer. The chamber has been printed with white PLA material. It takes about three hours to print the sensor chamber. The weight of the sensor chamber is among sixty gram. At the base of sensor chamber was add with perspex plate to make the chamber become heavier and stable.

Figure 4.10: The sensor chamber

Figure 4.11: The drawer of sensor chamber

4.3  The Development of Plasmonic Sensor

The plasmonic sensor was include with light source, fiber optic, sensor chamber, spectrometer and computer. Figure 4.12 show the plasmonic sensor setup. The fiber optic ferrule was place above the sensor chamber as shown at Figure 4.13. The ferrule is perpendicular to the drawer. A mirror have been place in the drawer to make better reflection of light on the sensing material.

Figure 4.12: The sensor setup

Figure 4.13: The position of fiber optic ferrule at the sensor chamber

Figure 4.14: The drawer with mirror

4.4  Analysis Data

Analysis data for this project are to analyse the graph produce from the UV-VIS spectrometer and plasmonic sensor. Both was use same gold nanoparticals which is nanosphere as the sensing material to sense with air and DI water. After that, the plasmonic sensor was used to detect the targeted analyte namely chlorpyrifos. The chlorpyrifos will dilute with DI water to get the different concentration.

4.4.1  UV-VIS Spectrometer Test Toward Air and DI Water

Figure 4.15 and Figure 4.16 shows the spectrum for the gold nanoparticals sample with air and DI water using UV-VIS spectrometer. While the Table 4.1 and Table 4.2 shows the value of wavelength and peak position of the spectrum for air and DI water detection from UV-VIS spectrometer.

Figure 4.15: Spectrum of sample with air

Figure 4.16: Spectrum of sample with DI water

Figure 4.17: The different of both spectrum

From the Table 4.1, it shows the test of gold nanoparticles sample with air have obtained 528.18nm wavelength and peak position of absorbance at 0.268 a.u. While the test of gold nanaparticles sample with DI water  have obtained 548.93nm wavelength and peak position of absorbance at 0.356 a.u which higher than the test with air. This result will be use as a reference to the test of plasmonic sensor.

Table 4.1: Sample with air result using UV-VIS

Parameter UV-VIS

Wavelength (nm) 528.18

Peak position (absorbance) 0.268 a.u

Table 4.2: Sample with DI water result using UV-VIS

Parameter UV-VIS

Wavelength (nm) 548.93

Peak position (absorbance) 0.356 a.u

4.4.2  The Plamonic Sensor Test Toward Air and DI Water

This plasmonic sensor was use same gold nanoparticles sample and test with air and also DI water. The OceanView software has been used to produce data from the spectrometer. Figure 4.18 and Figure 4.19 shows the spectrum produce for the sample test with air and DI water. While the Table 4.3 and Table 4.4 shows the value of wavelength and peak position of the spectrum for air and DI water detection from the sensor.

Figure 4.18: Spectrum of sample with air

Figure 4.19: Spectrum of sample with DI water

From the Table 4.3 below, it shows the test of gold nanoparticles sample with air have obtained 607.50nm wavelength and peak position of intensity at 1775.53 a.u. While the test of gold nanaparticles sample with DI water  have obtained 610.66nm wavelength and peak position of intensity at 2333.15 a.u which higher that the test with air.

Table 4.3: Sample with air result using sensor

Parameter Sensor

Wavelength (nm) 607.50

Peak position (intensity) 1775.53 a.u

Table 4.4: Sample with DI water result using sensor

Parameter Sensor

Wavelength (nm) 610.66

Peak position (intensity) 2333.15 a.u

From the test result using UV-VIS spectrometer and plasmonic sensor, there are similar for both test which the wavelength and peak position of DI water is higher than air. This show that the sensor was function correctly.

4.4.3  The Plamonic Sensor Test Toward Chlorpyrifos

The plasmonic sensor was test to detect the targeted analyte namely chlorpyrifos and the DI water as a reference. For this test, the chlopyrifos was dilute with DI water in different quantity to produce different concentration. The wavelength and peak position as the sensing parameter will be analyze. Figure 4.20, 4.21, 4.22 and 4.23 shows the spectrum for the detection of targeted analyte.

Figure 4.20:  Spectrum of sample with targeted analyte

(0.5ml chlorpyrifos dilute with 50ml DI water)

Figure 4.21: Spectrum of sample with targeted analyte

(0.5ml chlorpyrifos dilute with 100ml DI water)

Figure 4.22: Spectrum of sample with targeted analyte

(0.5ml of chlorpyrifos dilute with 150ml DI water)

Figure 4.23: Spectrum of sample with targeted analyte

(0.5ml of chlorpyrifos dilute with 200ml DI water)

By comparing Table 4.4 with Table 4.5, it shows that the sensor was detect the presence of chlorphrifos toxic in DI water. This can be evidenced by the changes of wavelength and the peak position of the spectrum. Besides, the wavelength and peak position was increase when the quantity of DI water dilute with chlorpyrifos increase.

Table 4.5: Sample toward targeted analyte result

Chlorpyfiros (ml) DI Water (ml) Wavelength (nm) Peak position (intensity)

0.5 50 660.64 112.76 a.u

100 667.84 137.31 a.u

150 670.23 304.44 a.u

200 670.57 403.88 a.u

Chapter 5

Conclusion

5.1  Conclusion

As a conclusion, the LSPR is a leading technique for bio-sensing. Although the potential for LSPR technologies to greatly impact bio-sensing is high, clear challenges and limitations exist. LSPR technology use the optical hardware which is much less complex and the instrument can be made smaller and more affordable. In addition, with the use of gold nanoparticles, sensor chips can be manufactured at a much more affordable price.

Overall, the plasmonic sensor was successful developed for to detect toxic in solution form. The sensor chamber have been design and printed well using 3D printer. Besides, the sensor system which consist of light source, duplex fiber optic, sensor chamber and spectrometer had been setup properly and works fine. The sensor with gold nanoparticals as their sensing material are sensitive toward the presence of targeted analyte. The sensing parameters are based on changing of their wavelength and resonance peak position. One key challenge is to increase the sensitivity of the sensor and improve the limit of detection of desired analyte. Indirectly, this project was achieve the whole objectives.

5.2 Recommendation

Even though this project has been successful developed, there are still need to do an improvement to make it more better and quality. Following are a few recommendations that can be implement to improve the system in this project:

1. Design and build the sensor chamber with suitable size and more stable.

2. Use suitable distance between fiber optic ferrule and gold nanoparticals substrate because it affects the level of light absorption.

3. Use different shape of gold nanoparticles such as nanorod which make the sensor become more sensitive.

References

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[7] C. L. Nehl and J. H. Hafner, “Shape-dependent plasmon resonances of gold nanoparticles,” J. Mater. Chem., vol. 18, no. 21, pp. 2415, 2008.

[8] Dassault, “Introducing SolidWorks,” 2009.

[9] S. Nengsih, A. A. Umar, M. M. Salleh, and M. Oyama, “Detection of formaldehyde in water: A shape-effect on the plasmonic sensing properties of the gold nanoparticles,” Sensors (Switzerland), vol. 12, no. 8, pp. 10309–10325, 2012.

[10] Reregistration Eligibility Decision (RED) for Chlorpyrifos; U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, U.S. Government Printing Office: Washington, DC: 2006.

Previously published on 15.10.2019