ION-IMPRINTING IN CARBON DOTS FOR THE DETECTION OF CADMIUM (II) IONS

Abstract

TITLE OF INVENTION Sheet l ION-IMPRINTING IN CARBON DOTS FOR THE DETECTION OF CADMIUM (II) IONS ABSTRACT This invention focuses on modifying the Carbon Dots (CDs) based on ion-imprinting strategy utilizing Poly (styrene sulphonate) [PSS] as precursors. The proposed ion imprinting strategy for the detection of Cd (II) involves three step modifications of CDs, monitoring the fluorescence response of each of those steps. The Cd (II) ions tethered CDs (PSS-Cd-CDs) were synthesized through hydrothermal treatment of PSS in the corresponding metal ion solution in aqueous medium. The Cd (II) ions bound to the CDs surface were removed using the appropriate eluting solvent. This removal results in vacancies on the CDs surface previously occupied.by these Cd (II) ions, thereby altering the fluorescence properties. The fluorescence response of the rebinding of the Cd (II) ions on the vacancies created on the surface of the CDs upon the addition of Cd (II) ions as analyte constitute the utility of this technique. We demonstrate the effectiveness of proposed ion imprinting approach by analysing the selective and sensitive fluorescence response for cadmium ions with limit of detection (LOD) of 118 nM. The cadmium ions are presumed to form coordinate bonds with oxygen-containing groups on CDs, resulting in the development of a novel, cost-effective sensor. This study on the Cd (II) detection employing ion imprinting strategy of CDs represents pioneering effort in the field.

Specification

FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
and
THE PATENTS RULES, 2003
PROYISIONAL/COMPLETE SPECIFICATION
(See section 10 and rule 13)
710082667
TITLE OF THE INVENTION:
ION-IMPRINTING IN CARBON DOTS FOR THE DETECTION OF CADMIUM (II) IONS
2. APPLICANT(S)______
Name
CHRIST UNIVERSITY
Nationality
INDIAN
Address

Hosur Road,
Bangalore - 560029,
Karnataka,
India
3. PREAMBLE TO THE DESCRIPTION
COMPLETE (>/)
The following specification particularly describes the
invention and the manner in which it is to be performed
4. DESCRIPTION (Description shall start from next page.)
ATTACHED
5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble- "1/ We claim" on
separate page)
ATTACHED

6. DATE AND SIGNATURE (to be given at the end of last page of specification)

Date: 16th October 2024
(1) AISHWARYA JOJI MATHEW
(2) VINOD T. P.
7. ABSTRACT OF THE INVENTION (to be given along with complete specification on separate page)
ATTACHED

TITLE OF INVENTION
ION-IMPRINTING IN CARBON DOTS FOR THE DETECTION OF CADMIUM (II) IONS

DESCRIPTION

FIELD OF INVENTION
[0001 ] This invention focuses on modifying the Carbon Dots (CDs) based on ion-imprinting strategy utilizing Poly (styrene sulphonate) [PSS] as precursors. A novel, efficient, time saving and cost effective sensor was developed by ion-imprinting on the surface of the CDs for the detection of Cd (II) ions.

BACKGROUND OF INVENTION
[0002] The development of sensitive and selective sensors for heavy metal detection has become increasingly vital due to the environmental and health risks associated with metal ion contamination. Among various sensing platforms, carbon dots (CDs) have emerged as promising candidates owing to their unique photoluminiscence properties, biocompatibility, and ease of functionalization. Herein we present a novel approach of ion-imprinting on the surface of CDs.1 We propose a unique ion-imprinting strategy on the surface of CDs which could selectively bind Cd (II) ions. This method not only enhances the sensitivity and selectivity of the sensors but also offers cost-effective and environmentally friendly advantages.

[0003] Carbon dots (CDs) are zero-dimensional, carbon-based nanomaterials typically smaller than 10 nanometers in size. They are renowned for their exceptional optical properties, including strong photoluminescence and tunable fluorescence emission across the visible and near-infrared spectra. CDs are synthesized from carbon sources such as organic molecules, polymers, or carbon precursors through simple and cost-effective methods like hydrothermal treatment and microwave irradiation. These nanomaterials possess a high surface area and can be easily functionalized or modified with various functional groups, making them versatile in sensing, biomedical, imaging, and optoelectronic applications.

[0004] Ion-imprinting is a technique used to create specific binding sites for target ions or molecules within a polymer matrix or on the surface of nanoparticles. It involves the template-induced formation of recognition sites that are complementary in shape, size, and functionality to the target species. After removing the template molecules, the resulting imprinted materials exhibit selective recognition and binding affinity towards the target ions or molecules. This approach is widely employed in various applications including sensing, separation, catalysis, and drug delivery, offering advantages such as high selectivity, stability, and reusability compared to traditional methods. Ion-imprinting continues to be an active area of research, driving innovations in molecular recognition and materials design.

[0005] The present invention focuses on modifying CDs through ion-imprinting strategy utilizing Poly (styrene sulphonate) [PSS] as precursors. The proposed method for the detection of Cd (II) ions involves three-step modification of CDs monitoring the fluorescence response at each stage. Initially, Cd (II) ions tethered CDs (PSS-Cd-CDs) are synthesized by hydrothermally treating PSS in the respective metal solution in the aqueous medium. Subsequently, Cd (II) ions bound to the CDs surface are removed using suitable eluting solvent. This process creates vacancies of Cd (II) ions on the CDs surface previously occupied by these metal ions, thereby altering their fluorescence properties. The fluorescence response upon reintroducing Cd (II) ions as analyte to these vacancies on the CDs surface constitute the utility of this technique.

[0006] The PSS-Cd-CDs appeared quasi spherical, with the average size of ~5.56 nm throughout the imprinting process according to TEM analysis without any change in the morphology. The rebinding of the Cd (II) ions into the vacancies created on the surface of the CDs were also confirmed using XPS and AAS analysis. These PSS-Cd-CDs exhibited excitation dependent fluorescence emissions and was found to be highly sensitive and selective to cadmium ions as compared to other heavy metals with LOD of 118 nM.

[0007] Accordingly, the objective of the present invention is to develop a novel, cost effective and efficient sensor for the detection of Cd (II) utilizing the ion-imprinting strategy on the CDs.

[0008] CN106902654B describes the synthesis of lithium ion imprinted poly ether sulphone composite utilizing monomer and cross linking agent for modification and was capable of showing high adsorption and separation capacity for lithium ions. CN10262661 IB reports preparation of amino functionalized metal ion imprinted adsorbent widely applied for the rapid detection of metal ions in different water bodies. CN109370565B presents a method for preparation of biological functionalized materials, in particular to a double-emission fluorescent molecularly imprinted polymer nano particle. According to this invention, carbon quantum dots were coated in silica nanospheres served as an inner core of a ratiometric fluorescent probe, for selective detection of dopamine.

BRIEF DESCRIPTION OF THE INVENTION
[0009] In accordance with one embodiment of the present invention, the proposed ionimprinting strategy spans three steps of recording the fluorescence responses of CDs. The central part of the strategy is synthesising the Cd (II) ions tethered CDs (PSS-Cd-CDs) through hydrothermal treatment of Poly (styrene sulphonate) [PSSJ. The synthesis of PSS- Cd-CDs Involved weighing 0.09g of PSS and U.009g of Cd (11) ions dispersed in 20 ml of water and probe sonicated for 5 min. Then the above solution was transferred to teflon lined autoclave and was subjected to hydrothermal reaction at 160° for 14 hours. Once cooled, the resulting solution was filtered using 0.22 pm nylon membrane, dialyzed and was stored at 4 c for further analysis.

[0010] In accordance with another embodiment of the disclosure, the imprinting strategy described in the study involves a three-step process applied to Cd (II) tethered CDs, focusing on their fluorescence response. Initially, Cd (II) ions are tethered to the CD surface, forming coordinate bonds with oxygen-containing functional groups to create Cd (II) ion tethered CDs. In the second step, these Cd (II) ions are removed by precipitation method using an appropriate eluting solvent, resulting in vacancies of Cd (II) ions on the CD surface. In the third step, the Cd (II) ion tethered CDs lacking Cd (II) ions are exposed to an analyte solution containing metal ions, where they are anticipated to exhibit a specific and selective fluorescence response. This specificity and selectivity are based on the ability of the metal ions in the analyte solution to form coordinate bonds, influenced by factors such as ionic radius, coordination number, and charge.

[00111 The present invention is described in detail below, including a comprehensive explanation and detailed illustrations that provide further clarification. These figures represent a typical embodiment of the current invention, but they can be studied further to explore potential extensions and applications. The appended description and illustrations aim
to provide a complete understanding of the invention's features and functions, including any variations or modifications that may be possible.

|0012) We claim,
1. The Cd (II) ions tethered CDs (PSS-Cd-CDs) were synthesized through hydrothermal treatment of Poly (styrene sulphonate) [PSS] in the corresponding metal ion solution (stage I)

2. The PSS-Cd-CDs, as claimed in claim 1, were treated with a suitable eluting solvent which created vacancies of Cd (II) ions on the surface of CDs (stage 2). These vacancies were occupied selectively by the Cd (II) ions upon treatment with analyte solution containing Cd (II) ions (stage 3), resulting in a decrease in fluorescence intensity.

3. The PSS-Cd-CDs, as claimed in claims 1-2, appeared quasi spherical, with an average size of -5.56 nm and the morphology remain unchanged while undergoing the three stages mentioned above.

4. The PSS-Cd-CDs, as claimed in claims 1-3, are fluorescent nanoparticlcs showing excitation dependent emissions.

5. The PSS-Cd-CDs as claimed in claim 1-4 were studied throughout the three stages of ionimprinting using ' X-ray photoelectron spectroscopy (XPS) and Atomic absorption spectroscopy (AAS), which clearly indicated the rebinding of Cd (II) ions tethered to the surface of CDs.

6. The PSS-Cd-CDs as claimed in claim 1-5 with the vacancies on the surface of CDs showed fluorescence quenching selectively to the Cd (II) ions (40.2% quenching upon adding 20 pM of cadmium) as compared to other metal ions and found to be sensitive with LOD of 118 nM.

7. The PSS-Cd-CDs, as claimed in claims 1-6 presents a novel, efficient and time-saving
means to detect Cd (11) ions. ,
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosure will be elucidated with additional particularity and detail with the following figures in which:

[0013] Figure 1 is the schematic representation of the proposed ion-imprinting mechanism in accordance with an embodiment of the invention.

[0014] Figure 2 represents the HRTEM images and size distribution histogram of PSS-Cd- CDs in accordance with an embodiment of the invention.
[0015] Figure 3 is the XPS survey spectrum of all the three stages of ion-imprinting process in accordance with an embodiment of the invention.
[0016] Figure 4 represents the optical characteristics of PSS-Cd-CDs in accordance with an embodiment of the invention.
[0017] Table 1 represents the AAS data of all the three stages of ion-imprinting process.
[0018] Figure 5 represents the FT-IR. spectrum and XRD plot of all the three stages of ionimprinting process in accordance with an embodiment of the invention.
[0019] Figure 6 depicts the PL response of PSS-CDs to various metal ions in accordance with an embodiment of the invention.
[0020] Figure 7 is the sensitivity of PSS-CDs to Cd (11) ions in accordance with an embodiment of the invention
[0021] Figure S represents the selectivity in PL response of PSS-Cd-CDs to Cd (II) ions in accordance with an embodiment of the invention.

[0022] Figure 9 is the sensitivity of PSS-Cd-CDs to Cd (II) ions in accordance with an embodiment of the invention.
[0023] Figure 10 represents the fluorescence response to all the three stages of ion-imprinting
process.

DETAILED DESCRIPTION OF THE INVENTION
[0024] In order to promote a better understanding of the features of the present disclosure, references will now be made to the embodiment illustrated in the figures, and specific language will be used to describe them. It will nonetheless be comprehended that no limitation of the scope of the disclosure is therefore purposed. Such further applications of the features of the disclosure as would naturally occur to those skilled in the art are to be interpreted as being within the scope of the present disclosure

10025] Appearances of the phrase "in an embodiment", "in another embodiment," and similar language throughout this specification may. but not necessarily do, all refer to the same embodiment. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. The system and methods provided herein are only illustrative and not intended to be limiting.

(0026] In the following specification and the claims, reference will be made to a number of tenns, which shall be defined to have the following meanings. The singular forms "a". "an", and "the" include plural references unless the context clearly dictates otherwise.

[0027] Embodiments of the present invention provide details on the ion-imprinting mechanism of PSS-Cd-CDs and the various characterizations of the same to prove the imprinting process on PSS-Cd-CDs. The details of the structural, optical characterizations of PSS-Cd-CDs and its selectivity and sensitivity to Cd (II) ions are also included.

[0028] Figure 1 is the schematic representation of the proposed ion-imprinting mechanism. The proposed method involves a three-step modification of CDs that, evaluates the fluorescence response at each stage. In the first stage, Cd (II) ions tethered CDs are synthesized by hydrothermally treating PSS in the respective metal solution. Subsequently, Cd (II) ions bound to the CD surface are removed via precipitation using suitable eluting solvent in the stage two. In the stage three, Cd (11) ions are reintroduced to these vacancies on the CD surface demonstrates the potential of this technique.

[0029] Figure 2 represents high-resolution transmission electron microscope (HRTEM) images of the PSS-Cd-CDs in accordance with an embodiment of the invention. Figure 2a represents the HRTEM image of the PSS-Cd-CDs appeared quasi spherical in morphology. Figure 2b depicts the.PSS-Cd-CDs with an average size of 5.56 nm. Figure 2c represents the lattice fringes of 0.24 nm which are the characteristics of (002) plane of the graphitic interlayer, affirming PSS-Cd-CDs.

(00301 Figure 3 represents the XPS survey spectrum of all the three stages of ion-imprinting process. Figure 3a represents the survey spectrum of PSS-CDs alone. Figure 3 (b,c,d) is the survey spectrum of stage 1,2 and 3 respectively. Figure 3b indicates that Cd (II) ions are successfully been tethered to the surface of CDs. Figure 3c signifies the vacancy been created on the surface of the CDs and the vacancy been occupied by the Cd (II) ions can be seen in the figure 3d.

[0031J Figure 4 represents the optical characteristics of all the three stages of ion-imprinting process. Figure 4a is the UV-visible plot of all the three stages corresponding to 11- n* and n- 11 *transitions in the absorption spectra. Figure 4b is the plot of PL excitation and emission of PSS-Cd-CDs. Figure 4c represents the plot of excitation wavelength dependent PL emissions of PSS-Cd-CDs. Figure 4d is the plot of fluorescence lifetime of all the three stages of ionimprinting process.

[0032] Table 1 represents the AAS data of all the three stages of ion-imprinting process. From the AAS data it is clear that in stage 1 the Cd (II) ions are tethered to the surface of CDs. In the stage 2 the concentration of Cadmium is low which indicates that the vacancy is been created on the surface of CDs, which was then occupied selectively by Cd (II) ions in stage 3.

[0033] Figure 5 represents the structural characterizations of all the three stages of ion - imprinting process in accordance with an embodiment of the invention. Figure 5a is the FT- IR spectrum of all the three stages of ion-imprinting reveals the presence of various functional groups on the surface of the CDs. Figure 5b is the XRD plot of all the three stages of ion-imprinting. The peak at 23.8 degrees corresponds to the graphitic (002) facet of PSS- Cd-CDs.

[0034] Figure 6 is the fluorescence based studies of the PSS-CDs. Figure 6 represents the PL response of PSS-CDs to various metal ions of same concentration (20 pM). Io and I are the PL intensities at 315 nm (^=260 nm) in the absence and presence of metal ions, respectively. It is evident from image 6 that the amount of quenching response of PSS-CDs towards Cd (11) ions is less as compared to PSS-Cd-CDs towards Cd (II) ions which shows the potential of PSS-Cd-CDs to detect Cd (II) ions through ion-imprinting technique.

[0035] Figure 7 represents the fluorescence based studies of PSS-CDs. Figure 7a is the PL spectra of the PSS-CDs dispersions in the presence of various concentrations of Cd (II) ions at 315 nm, Xw=260 nm. Figure 7b is the plot of I/Io against the concentration of Cd (II), inset shows the fitted linear plot in the lower concentrations of PSS-CDs.

[0036] Figure 8 is the fluorescence based studies of the PSS-Cd-CDs with vacancies. Figure 8 represents the PL response of PSS-Cd-CDs with vacancies to various metal ions of same concentration (20 pM). Io and I are the PL intensities at 315 nm (Xex=260 nm) in the absence and presence of metal ions, respectively. It is evident from image 8 that PSS-Cd-CDs have the capability to detect selectively Cd (II) ions compared to various other metal ions.

[0037] Figure 9 represents the fluorescence based studies of PSS-Cd-CDs with vacancies. Figure 9a is the PL spectra of the PSS-Cd-CDs with vacancies, dispersions in the presence of various concentrations of Cd (II) ions at 315 nm, Xcx=260 nm. Figure 9b is the plot of I/Io against the concentration of Cd (II), inset shows the fitted linear plot in the lower concentrations of PSS-Cd-CDs.

(0038] Figure 10 represents the fluorescence response to the three stages of ion-imprinting process. It is clear from the figure 10 that the Cd (II) ions were tethered on the surface of the CDs in the first stage and were eluted using suitable eluting agent in,the stage 2 and were occupied by fne Cd (II) ions selectively in the stage 3. Thus figure 10 demonstrates the potential of ion-imprinting strategy on the surface of CDs based on the fluorescence mechanism.

[0039] The various embodiments of the preparation of ion-imprinted carbon dots from PSS as precursor, through hydrothermal process involving Alteration and dialysis, is a novel method which facilitates the applications of PSS-Cd-CDs and also the use of time saving and efficient method which helps in building a sustainable environment. The XPS and AAS data reveals the importance and potential of ion-imprinting strategy on the surface of CDs. The particle size through HR-TEM gives an insight to the surface morphology of PSS-Cd-CDs. The fluorescence quenching behaviour of PSS-Cd-CDs selectively toward Cd (II) ions through ion-imprinting techniques makes PSS-Cd-CDs as a fluoroprobe to detect Cd (11) ions in the solution.

[0040] The ion-imprinted carbon dots synthesized from PSS acts as a fluoroprobe to selectively detect Cd (11) ions with the limits of detection 118 nM.

[0041] The language used in the disclosure is specific, but the limitations arising from it are hot intended. A skilled person can modify the method to implement the inventive concept taught in this document.

[0042] The figures and the description above give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element'. Alternatively, certain features may be split into different functional elements. It is also viable that the elements from one embodiment may be appended to another embodiment. Additionally, the actions of any flow diagram need not be implemented in the order depicted, nor do all of the acts need to be necessarily performed. Also, those acts that are independent of other actions may be carried out in parallel with the other actions. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes, to fall within the true spirit of the invention.

Signature
(1) AISHWARYA JOJI MATHEW (2) VINOD T.P.

TITLE OF INVENTION
ION-IMPRINTING IN CARBON DOTS FOR THE DETECTION OF CADMIUM (II) IONS

Figure 1. Proposed ion-imprinting mechanism

Figure 2. (a,c) HR-TEM images and (b) size distribution histogram of PSS-Cd-CDs.

Figure 3. XPS survey spectrum of (a) PSS-CDs, (b) stage l, (c) stage 2 and (d) stage 3 of.
ion-imprinting process.

Figure 4. (a) UV-visible absorption of all three stages of ion-imprinting process, (b) The plot
of PL excitation and emission of PSS-Cd-CDs, (c) The plot of excitation wavelength dependent PL emissions of PSS-Cd-CDs, (d) Plot of fluorescence lifetime of all 3 stages of ion-imprinting process .

Table 1. Atomic absorption spectroscopy (AAS) data of all the three stages of ion-imprinting
process

Samples Absorbance Concentration of
Cd (11) ions (ppm).
Stage 1 . . 1.485 0.752
Stage 2 .0.129 0.065
Stage 3 1.207 0.611

Figure 6. The PL response of PSS-CDs to various metal ions of same concentration (20 pM).
Io and I are the PL intensities at 315 nm (%ex=260 nm) in the absence and presence of metal ions, respectively

Figure 7. (a) The PL spectra of the PSS-CDs dispersions in the presence of various
concentrations (0-50 pM) of Cd (II) ions at 315 nm, Xcx=260 nm. (b) Plot of I/Io against the
concentration of cd (II) ions, inset shows the fitted linear plot in the lower concentrations

Figure 8. The PL response of PSS-Cd- CDs with vacancies, to various metal ions of same
concentration (20 pM). Io and I are the PL intensities at 315 nm Q^-26Q nm) in the absence
and presence of metal ions, respectively

Figure 9. (a) The PL spectra of the PSS-Cd-CDs with vacancies, dispersions in the presence
of various concentrations (0-50 pM) of Cd (II) ions at 315 nm, Xcx=260 nm. (b) Plot of I/Io
against the concentration of cd (II) ions, inset shows the fitted linear plot in the lower
concentrations

Figure 10. The fluorescence response to the three stage of ion-imprinting process.

TITLE OF INVENTION
ION-IMPRINTING IN CARBON DOTS FOR THE DETECTION OF CADMIUM (II) IONS

CLAIM
[0100J We claim,
1. The Cd (II) ions tethered CDs (PSS-Cd-CDs) were synthesized through hydrothermal treatment of Poly (styrene sulphonate) [PSS] in the corresponding metal ion solution (stage 1).

2. The PSS-Cd-CDs, as claimed in claim 1, were treated with a suitable eluting solvent which created vacancies of Cd (II) ions on the surface of CDs (stage 2). These vacancies were occupied selectively by the Cd (II) ions upon treatment with analyte solution containing Cd (II) ions (stage 3), resulting in a decrease in fluorescence intensity.

3. The PSS-Cd-CDs, as claimed in claims 1-2, appeared quasi spherical, with an average size of -5.56 nm and the morphology remain unchanged while undergoing the three stages mentioned above.

4. The PSS-Cd-CDs, as claimed in claims 1-3, are fluorescent nanoparticles showing excitation dependent emissions.

5. The PSS-Cd-CDs as claimed in claim 1-4 were studied throughout the three stages of ion imprinting using X-ray photoelectron spectroscopy (XPS) and Atomic Absorption Spectroscopy (AAS), which clearly indicated the rebinding of Cd (II) ions tethered to the surface of CDs.

6. The PSS-Cd-CDs as claimed in claim 1-5 with the vacancies on the surface of CDs showed fluorescence quenching selectively to the Cd (II) ions (40.2% quenching upon adding 20 pM of cadmium) as compared to other metal ions and found to be sensitive with LOD of 118 nM.

7. The PSS-Cd-CDs, as claimed in claims 1-6 presents a novel, efficient and time-saving means to detect Cd (II) ions.

Documents