A METHOD OF PREPARING SUBSTRATE WITH TUNABLE OPTICAL RESONANCE

Abstract

The present subject matter relates to a method of preparing substrate with tunable optical resonance. The method comprises synthesizing anisotropic nanoparticles. Coating the prepared anisotropic nanoparticles on a glass substrate by dipping the glass substrate in the synthesized anisotropic nanoparticle for a predefined time. Heating the coated glass substrate at a predefined rate till predefined temperature to tune the optical resonance. The predefined temperature depends on the needed optical resonance. Figure 1

Specification

Description:"A METHOD OF PREPARING SUBSTRATE WITH TUNABLE OPTICAL RESONANCE"

TECHNICAL FIELD
[0001] The present disclosure, in general, relates to a substrate with tunable optical resonance. The present disclosure, particularly, relates to a method of preparing substrate with tunable optical resonance.

BACKGROUND
[0002] Plasmonic nanoparticles are a special grade of metallic nanoparticles that shows enhanced electric field resonances. Metals like Gold, sliver and copper shows resonances in the visible range of the optical spectrum. When an electromagnetic wave interacts with the nanoparticle the free electrons are shifted to one end of the nanoparticle forming a dipole. This electron cloud then oscillates about its core with change in the electric field of the electromagnetic wave. The frequency of this oscillation resonates with that of a wavelength of the spectrum. This resonance is called the localized surface plasmon resonance (LSPR). This resonance is affected by the particle's shape, as the electron dipole displacement from its core is higher for anisotropic nanoparticles. The electric field density is higher, mainly at the sharp tips of the particles, compared to the smooth surface. At these particular LSPRs the electromagnetic field of these plasmonic particles is enhanced, resulting in a higher signal-to-noise ratio.
[0003] Existing methods for fabricating substrates with a specific resonance wavelength typically involve synthesizing nanoparticles of a desired size and shape, which are then applied to functionalized glass surfaces for further use. Achieving precise control over nanoparticle shape and size during synthesis via wet chemical methods, however, is challenging and lacks consistency. A significant limitation of this approach is the variability in particle size produced in each synthesis batch. Even with standardized synthesis techniques, nanoparticles tend to exhibit a size range rather than a uniform, exact size. This inconsistency affects the final resonance wavelength, requiring multiple synthesis attempts to achieve nanoparticles with the desired size and resonance properties.
[0004] The problems with the existing method include:
• The current synthesis processes for most anisotropic nanoparticles with high throughput are still unoptimized and lack precise size control.
• Substrates coated with spherical nanoparticles or thin film-based models do not support simultaneous dual-mode activation on the same substrate.
• Most nanoparticle models lack the sharp tips characteristic of bipyramid structures. These sharp edges are essential for achieving high electric field density at the tips, resulting in more localized surface plasmon resonances. This, in turn, leads to greater signal enhancement and an improved signal-to-noise ratio for SERS analysis compared to other platforms.
[0005] To address the issue of nanoparticles lacking sharp tips and dual-mode activation, gold nanobipyramid particles are utilized, as their sharp pyramid tips provide significant signal enhancement. However, the challenge of synthesizing nanoparticles with the desired size and shape to precisely control optical resonance persists. Tuning the resonance of plasmonic particles is difficult with the wet synthesis method, and preparing a substrate with the desired resonance remains problematic, as achieving uniform particle size in synthesis is nearly impossible. As a result, the resonance often deviates from the target, requiring repeated attempts.
[0006] Accordingly, there is a need for a method of preparing substrate with tunable optical resonance so that optical resonance can be tuned to desired value.


OBJECTS OF THE INVENTION
[0001] The objectives are provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. These objectives are not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
[0002] It is one of the primary objectives of the present invention to develop a method of preparing substrate with tuneable optical resonance.
[0003] It is another objective of the present invention to develop a method of preparing substrate with tuneable optical resonance which is cost-effective.
[0004] It is another objective of the present invention to develop a method of preparing substrate with tuneable optical resonance with repeatable tuning property.
[0005] It is another objective of the present invention to develop a method of preparing substrate with tunable optical resonance which can be used as SERS substrate.
[0006] It is another objective of the present invention to develop a method of preparing substrate with tunable optical resonance which support simultaneous dual-mode activation.
[0007] It is another objective of the present invention to develop a method of preparing substrate with tunable optical resonance through which size and shape of the nanoparticles can be controlled accurately.
SUMMARY
[0007] This summary is provided to introduce concepts related to a method of preparing substrate with tunable optical resonance. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0008] The present subject matter relates to a method of preparing substrate with tunable optical resonance. The method comprises synthesizing anisotropic nanoparticles having size in the range of - 40 to 60 nm in length having optical resonance at a wavelength in the range of 530 nm to near IR range; coating the prepared anisotropic nanoparticles on a glass substrate by dipping the glass substrate in the synthesized anisotropic nanoparticle for a predefined time, wherein the glass substrate is functionalized before coating the prepared anisotropic nanoparticles; heating, by a heating arrangement, the coated glass substrate at a predefined rate till predefined temperature to tune the optical resonance, wherein the predefined temperature depends on the needed optical resonance.
[0009] In an aspect, the anisotropic nanoparticle is gold nano bipyramids particle.
[0010] In an aspect, the substrate is able to withstand the temperature up to 800°C.
[0011] In an aspect, the method to functionalize the substrate comprises coating the glass substrate with five alternative coatings of Poly(allylamine hydrochloride), PAH, and Poly(styrene sulfonate), PSS, to achieve a top layer of Poly(styrene sulfonate), PSS.
[0012] In an aspect, the predefined time to dip the glass substrate in the synthesized anisotropic nanoparticle is in the range of 10 hrs to 12 hrs.
[0013] In an aspect, the heating arrangement has a very sensitive heating controller to change the temperature in very small incremental steps to bring change in the shape of the anisotropic nanoparticles on the glass substrate.
[0014] In an aspect, after heating the coated glass substrate to the predefined temperature, the spectrum of the substrate is measured by a spectrometer to determine the optical resonance.
[0015] To further understand the characteristics and technical contents of the present subject matter, a description relating to the context will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit the scope of the present subject matter.
[0016] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
BRIEF DESCRIPTION OF FIGURES
[0017] The illustrated embodiments of the present disclosure will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:
[0018] FIG. 1 illustrates a flow chart of exemplary method that can be utilized to implement one or more exemplary embodiment of the present subject matter;
[0019] FIG. 2 illustrates a block diagram of substrate preparation in accordance with one of the embodiments of present subject matter;
[0020] FIG. 3 illustrates a block diagram showing the changes on heating the substrate in accordance with one of the embodiments of present subject matter;
[0021] FIG. 4 illustrates a spectral graph showing reflection vs wavelength peak shift with change in shape on heating; and
[0022] FIGs. 5a,-5d illustrates the results of heating the coated substrate.
[0023] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION
[0024] A few aspects of the present disclosure are explained in detail below with reference to the various figures. Example implementations are described to illustrate the disclosed subject matter, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a number of equivalent variations of the various features provided in the description that follows.
Definitions
[0025] In the disclosure hereinafter, one or more terms are used to describe various aspects of the present disclosure. For a better understanding of the present disclosure, a few definitions are provided herein for better understating of the present disclosure.
[0026] "Glass Substrate" may be defined, in the context of the invention, as a foundational glass layer used as a base material onto which nanoscale metallic structures are deposited. These metallic structures create localized surface plasmon resonances when illuminated with laser light, enhancing the Raman scattering of molecules near the surface of the substrate.
[0027] "Gold Nanobipyramids" may be defined, in the context of the invention, as nanoscale particles shaped like elongated bipyramids, typically synthesized from gold. They consist of two pyramidal structures joined at their bases, creating a central axis with two pointed ends. This unique shape gives them distinct optical properties, especially in plasmonic applications, where they are valued for their strong and tunable localized surface plasmon resonance (LSPR) across visible and near-infrared wavelengths.

EXEMPLARY IMPLEMENTATIONS
[0028] While the present disclosure may be embodied in various forms, there are shown in the drawings, and will hereinafter be described, some exemplary and non-limiting embodiments, with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated. Not all of the depicted components described in this disclosure may be required, however, and some implementations may include additional, different, or fewer components from those expressly described in this disclosure. Variations in the arrangement and type of the components may be made without departing from the scope of the claims as set forth herein.
[0029] The present disclosure provides a method of preparing substrate with tunable optical resonance.
[0030] The proposed method is developed to create SERS substrates with a targeted optical resonance within the optical range. Gold nanobipyramids can exhibit an optical resonance with wavelength in the range 530 nm to near IR range, depending on their size. By synthesizing larger gold nanoparticles and coating them onto the substrate, then heating to achieve precise size adjustments at specific temperatures, this method provides a simple and cost-effective way to produce substrates with tunable optical resonance. Unlike in the liquid phase, where anisotropic nanoparticles may change shape and size, coating them onto the substrate preserves their form. Heating the coated substrate allows for fine control over the shape and size, directly influencing the optical resonance of the substrate. This capability enables tuning of the optical response across the entire substrate or within localized areas, making it useful for various advanced applications.
[0031] The substrates prepared by the method can be easily tuned to the desired wavelength employing heating. When heated to different temperatures, the sharp edges of the particles gradually round off, transforming into a more spherical shape. By heating gold nanobipyramid-coated substrates to around 400°C, this shape modification can be achieved, allowing for precise control over the substrate's optical resonance. In applications like Surface-Enhanced Raman Spectroscopy (SERS), matching the wavelength of the laser to that of the nanoparticles is essential to enhance the signal-to-noise ratio, resulting in a clear, strong Raman signal from the sample with minimal background noise. Obtaining lasers of specific wavelengths can be challenging and costly, and each requires separate filters. Thus, creating substrates with the desired resonance wavelength offers a more economical alternative.
[0032] FIG. 1 illustrates a flow chart of exemplary method that can be utilized to implement one or more exemplary embodiment of the present subject matter.
[0033] At step 102, the anisotropic nanoparticle is synthesized using existing techniques including wet chemical method. The anisotropic nanoparticles synthesized in this step are kept bigger in size. It is important to keep the particle size bigger In an aspect of the invention, the synthesized anisotropic nanoparticles are gold nanobipyramid particle. In another aspect of the invention, the synthesized anisotropic gold nanobipyramid particles have size in the range of 40 to 60 nm, having wavelength in the range 530 nm to near IR range. The goal is to synthesize larger anisotropic nanoparticles. If the initial wavelength is too low, the tunability range is reduced. Since this is an irreversible, one-way process, if the anisotropic nanoparticles lack resonance at a higher wavelength than the target, the substrate will not be able to adjust it down to a desired higher wavelength.
[0034] Due to their anisotropic shape, gold nanobipyramids have an aspect ratio (length to width) greater than 1. This characteristic results in two distinct resonance wavelengths: one from transverse resonance and another from longitudinal resonance. An advantage of using gold nanobipyramids in substrates is their dual resonance mode, enabling simultaneous excitation at two different resonance wavelengths.
[0035] At step 104, the prepared anisotropic nanoparticles are coated on a glass substrate. The coating operation on the glass substrate is performed by dipping the glass substrate in the synthesized anisotropic nanoparticle for a predefined time. In an aspect of the invention, the predefined time to dip the glass substrate in the synthesized anisotropic nanoparticle is in the range of 10hrs to 12 hrs. Before coating the anisotropic nanoparticle over the glass substrate, the glass substrate is functionalized for better results. Further, the glass substrate used is able to with stand higher temperatures up to 800oC.
[0036] At step 106, the optical resonance of the prepared substrate is tuned by heating the coated glass substrate. The heating of the coated glass substrate is performed by a heating arrangement at a predefined rate till the predefined temperature. The predefined temperature depends on the needed optical resonance and the predefined temperature upto which the coated glass substrate is heated changes as the needed optical resonance changes. Accordingly, the optical resonance of the coated glass substrate is tuned by heating the coated glass substrate at an optimal rate till the optimal temperature.
[0037] FIG. 2 illustrates a block diagram of substrate preparation in accordance with one of the embodiments of present subject matter. The glass substrate is functionalized before coating process so that the anisotropic nanobipyramids particles can attached to the surface. The glass substrate is coated with poly electrolyte coating. In an aspect of the invention, the poly electrolyte coating comprises of two polymers namely Poly(allylamine hydrochloride) (PAH) and Poly(styrene sulfonate) (PSS).
[0038] PAH carries a positive charge, while PSS carries a negative charge. The gold nanobipyramids, stabilized with CTAB, have a net positive charge on their surfaces. We coat the glass with five alternating layers of PAH and PSS, ensuring that the final layer is PSS. This layering enables the nanobipyramids to adhere to the substrate surface through positive-negative charge interactions.
[0039] After functionalization of the glass substrate, the anisotropic nanoparticles (gold nano bipyramid particles) are coated over the functionalized glass substrate. The coating is performed by dipping the functionalized glass substrate in synthesized anisotropic nanoparticles for a predefined time. In an aspect of the invention, the functionalized glass substrate is dipped into the synthesized anisotropic nanoparticles for 10 hrs to 12 hrs. As can be seen in the figure, the anisotropic nanoparticles (gold nano bipyramid particles) get attached over the functionalized surface of the glass substrate.
[0040] FIG. 3 illustrates a schematic showing the changes on heating the substrate in accordance with one of the embodiments of present subject matter. On heating the prepared anisotropic nanoparticle coated glass substrate, the shape and size of the coating changes from bipyramidal shape to spherical shape. As the shape of the coating particles changes, the resonance wavelength also changes. Accordingly, the optical resonance of the prepared substrate is tuned by controlled heating of the substrate.
[0041] The shape of the anisotropic nanoparticle (gold nano bipyramid particles) changes as the temperature of the surface changes on heating. The heating is performed with precise temperature control and a spectrometer to measure the spectrum of the substrate before and after heating. On reaching the desirable spectrum the heating is stopped.
[0042] FIG. 4 illustrates a spectral graph showing reflection vs wavelength. It is clearly depicted in the graph how wavelength of the substrate changes as the shape changes. The longitudinal LSPR peak at a higher wavelength disappears as the bipyramid nanoparticles lose their length and become spherical.
[0043] FIGs. 5a-5d illustrates the results of heating the coated substrate. FIG. 5a shows the different temperature range that is heated. FIG. 5b shows different reflection resonance peak at different heating temperature. FIG. 5c shows image of glass substrate heated at different temperatures. FIG. 5d shows electron microscopy image of nanoparticles on the substrate heated to different temperatures. The Figures 5a-5d depicts:
• On heating the coated substrate shape and size of nano particles change leading to change in resonance wavelength.
• At different temperature we get different shape and size of particles, thus different color.
• There is no visible change till 100°C. There is no shape change from 100°C from electron microscopy image. The shape change and color change happens above 100°C to 400°C.
• The figure 5a shows that heating the substrate at 100°C, 200°C, 300°C and 400°C and hold at that temperature for 10 minutes.
• Thus, the resonance wavelength can be tuned by heating the substrate.
ADVANTAGES
[0044] The proposed method for preparing substrate with tunable optical resonance is reliable method for shape and size modification of nanoparticles. The proposed method can be used to produce substrates in bulk with small number of nanoparticles in liquid state and multiple sample heating on the heating stage. Further, the method can be used to make substrates with optical resonance tunability in localized areas. Accordingly, the resultant coated substance is able to produce multiple resonance frequencies on the same surface.
[0045] The above description does not provide specific details of the manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[0046] Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure.
, Claims:We Claim:
1. A method of preparing substrate with tunable optical resonance, the method comprises:
synthesizing anisotropic nanoparticles having size in the range of 40 to 80 nm having optical resonance at a wavelength in the range of 530 nm to near IR range;
coating the prepared anisotropic nanoparticles on a glass substrate by dipping the glass substrate in the synthesized anisotropic nanoparticle for a predefined time, wherein the glass substrate is functionalized before coating the prepared anisotropic nanoparticles;
heating, by a heating arrangement, the coated glass substrate at a predefined rate till predefined temperature to tune the optical resonance, wherein the predefined temperature depends on the needed optical resonance.
2. The method as claimed in claim 1, wherein the anisotropic nanoparticle is gold nano bipyramids particle.
3. The method as claimed in claim 1, wherein the substrate is able to withstand the temperature upto 800°C.
4. The method as claimed in claim 1, wherein the method to functionalize the substrate comprises coating the glass substrate with five alternative coatings of Poly(allylamine hydrochloride), PAH, and Poly(styrene sulfonate), PSS, to achieve a top layer of Poly(styrene sulfonate), PSS.
5. The method as claimed in claim 1, wherein the predefined time to dip the glass substrate in the synthesized anisotropic nanoparticle is in the range of 10 hrs to 12 hrs.
6. The method as claimed in claim 1, wherein the heating arrangement has a very sensitive heating controller to change the temperature in very small incremental steps to bring change in the shape of the anisotropic nanoparticles on the glass substrate.
7. The method as claimed in claim 1, wherein after heating the coated glass substrate to the predefined temperature, the spectrum of the substrate is measured by a spectrometer to determine the optical resonance.

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