Advancing Chloride Ion Detection in Edible Oils: Enhanced

Sensitivity with NCQD/Ag Nanotriangles via Localized Surface

Plasmon Resonance

Muhammad Qayyum Othman

, Mohd Hafiz Abu Bakar

2,*

, Nur Hidayah Azeman

Nadhratun Naiim Mobarak

and Ahmad Ashrif A. Bakar

1,4,*

Photonics Technology Laboratory, Department of Electrical, Electronic and Systems Engineering, Faculty of Engineering

and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor

Institute of Power Engineering, Universiti Tenaga Nasional, 43000 Kajang, Selangor, Malaysia

Department of Chemical Sciences, Faculty of Science and Technology,

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor

Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Keywords: Carbon Quantum Dots, Localized Surface Plasmon Resonance, Silver Nanotriangle, Edible Oil, Chloride Ion.

Abstract: Chloride ion detection in edible oil is crucial for food safety and preventing harmful compounds like 3-MCPD

during refining. This study presents a novel method utilizing Nitrogen-Doped Carbon Quantum Dots

(NCQDs) combined with Silver Nanotriangles (AgNTs) through Localized Surface Plasmon Resonance

(LSPR) for chloride ion detection. The chemical properties of AgNT-NCQD enhance sensor performance by

improving stability and biocompatibility while providing new binding sites for chloride ions. LSPR allows

precise monitoring of the interaction between AgNT-NCQD and chloride ions, resulting in a distinct LSPR

peak for accurate detection. The synergy between surface plasmon resonance and NCQDs increases

sensitivity, with significant LSPR peak shifts upon chloride exposure. This technology offers a wider dynamic

range and lower detection limits, demonstrating excellent selectivity for chloride ions in edible oil. The

enhanced properties of NCQDs make this sensing platform vital for food quality assurance and consumer

health protection.

1 INTRODUCTION

The discovery of various contaminants in edible oils

that pose health risks has raised significant concerns

about their quality and safety. Contaminants like 3-

monochloropropane- 1,2-diol (3-MCPD) esters are

particularly concerning due to their potential

carcinogenicity (Jong-Sun et al., 2020). 3-MCPD are

byproducts formed as impurities during high-

temperature oil refining. 3- MCPD was classified as

a possible human carcinogen (Group 2B) by The

International Agency for Research on Cancer (IARC)

(Panel & Chain, 2016). These compounds are

produced during the deodorization process of oils and

have been linked to tumor development in animal

studies. According to EFSA (2016), palm oil contains

significantly higher levels of 3- MCPD than regular

fat margarine (Panel & Chain, 2016). 3-MCPD has

been known to form as a contaminant in processed

foods, including refined oils, since the 1980s (Cheng

et al., 2017). The presence of 3-MCPD has raised

global safety concerns especially in refined edible

oils. The synthesis of 3-MCPD esters is primarily

influenced by chloride, acylglycerols, pH,

temperature, and time (Kuntom et al., 2006).

Frequency depends on the nanoparticles’ material,

shape, and surrounding environment (Bakar et al.,

2022) (Abdullah et al., 2018). Moreover, gold and

silver are popular choices for these nanoparticles,

which can come in various shapes. Gold

nanoparticles (AuNPs) are favored for their stability

and biocompatibility. However, triangular silver

nanotriangles (AgNTs), with their sharp edges, are

particularly useful for enhancing electric fields in

surface-based spectroscopic techniques (Zannotti et

al., 2020)

that offer greater sensitivity. Yet, to

Othman, M. Q., Bakar, M. H. A., Azeman, N. H., Mobarak, N. N. and Bakar, A. A. A.

Advancing Chloride Ion Detection in Edible Oils: Enhanced Sensitivity with NCQD/Ag Nanotriangles via Localized Surface Plasmon Resonance.

DOI: 10.5220/0013131100003902

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 13th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2025), pages 74-78

ISBN: 978-989-758-736-8; ISSN: 2184-4364

selectively detect low concentrations of target

molecules, these nanoparticles often require

additional modifications with specific materials

(Azeman et al., 2020) (Rahman et al., 2019) (Abu

Bakar et al., 2020).

Carbon quantum dots (CQDs) are tiny (less than

10 nm) fluorescent particles made of carbon with

unique properties. Their core is carbon, but their

surface has elements such as oxygen, hydrogen, and

nitrogen. CQDs can be improve by attaching specific

chemical groups (amino, hydroxyl, carboxyl) to their

surface, making them more reactive and water-

soluble (Nazri et al., 2022). Different materials such

as chitosan or branched polyethyleneimine can be

used for this. By attaching certain groups like

polyamines, CQDs can be made to selectively bind to

specific ions (Yoo et al., 2019). For instance, Nazri et

al. in 2022, used CQDs with amino groups and silver

nanoparticles to detect chlorophyll in water. The

author’s study showed that improved CQDs

(NCQDs) were much better at detecting chlorophyll

(Nazri, 2022).

In this study, we evaluate the potential of

functionalized carbon quantum dots (CQDs) for

chloride ion detection using a localized surface

plasmon resonance (LSPR)-based optical sensor.

Amino-functionalized CQDs (NCQDs) were

synthesized via a two-step hydrothermal method

employing polyethyleneimine as the amino group

precursor. The composite film comprised of these

functionalized CQDs and triangular silver

nanotriangles (AgNTs) served to enhance the

sensitivity of the LSPR sensor. The introduction of

amine groups on the CQD surface facilitated

improved chloride ion interaction through

electrostatic interactions. The performance of the

sensor was assessed by monitoring the wavelength

shift of the LSPR spectrum across varying chloride

ion concentrations. This analysis aimed to establish

the sensor's linearity, range, sensitivity, and detection

limit

2 EXPERIMENTAL SECTION

2.1 Materials

Citric acid, polyethyleneimine, silver nitrate, sulfuric

acid (98%), hydrogen peroxide (H

), trisodium

citrate, sodium borohydride (NaBH

), 3-

aminopropyltrimethoxysilane (97%) (APTES),

polyvinyl alcohol, ethanol, and acetone were

purchased from Sigma Aldrich. Ethylenediamine,

heavy metals, iso-propyl, and ammonia solution

(30%) were purchased from R&M Chemicals, and

edible oil was purchased from the local market

2.2 Experimental Setup

Building on prior research, this work utilizes

triangular silver nanoparticles (AgNT) synthesized

via a room- temperature chemical reduction process.

The synthesis utilizes readily available chemicals

such as silver nitrate, trisodium citrate, sodium

borohydride, and water. The composite sensing

material AgNT-NCQD morphology was

characterized by HRTEM and FESEM. Figure 1(a)

shows triangular-shaped nanoparticles with a scale

bar for 50nm. Conversely, Figure 1(b) obtained using

FESEM demonstrates that the NCQDs possess a

spherical morphology and are smaller than 10

nanometers

Figure 1: Surface morphology using HRTEM and FESEM

showing the structure of a) AgNT b) NCQD.

Experimental setup comprised an HR4000CG-

UV-NIR spectrometer from Ocean Optics interfaced

with a reflection probe boasting a numerical aperture

of 0.22. This configuration facilitated the

Figure 2: Detection of chloride ion using localized surface

plasmon resonance (LSPR) setup.

Advancing Chloride Ion Detection in Edible Oils: Enhanced Sensitivity with NCQD/Ag Nanotriangles via Localized Surface Plasmon

Resonance

measurement of the reflectivity spectra of both

AgNTs and AgNT-NCQDs in edible oil containing

10 ppm chloride ions. The measurements

encompassed a wavelength range of 350-850 nm and

were swiftly captured following spectra acquisition.

To ensure optimal signal acquisition, the probe was

meticulously positioned above the sample as

illustrated in Figure 2.

3 RESULT AND DISCUSSION

The study evaluated the fabricated AgNT-NCQD film

sensor's ability to quantitatively detect chloride ions

in edible oil by compared its efficiency and sensitivity

to AgNT alone, using edible oil as the baseline for all

sensor materials. Figure 3(a) shows when AgNTs

were exposed to chloride ion, the wavelength value

was shifted from baseline (450 nm) to 448.37, 447.06,

Figure 3: The reflectance spectra of the LSPR sensor in the

presence of chloride ion with different concentrations

ranging from 2-50 ppm of (a) AgNT, (b) AgNT-NCQD.

453.09, 448.11, and 447.32 nm for 2, 6, 10, 20, and

50 ppm of chloride ion concentrations, respectively.

The wavelength shift (Δλ) values change to 2.10,

3.41, 2.62, 2.36, and 3.15 nm. In contrast, Figure 3(b)

shows the response of AgNT-NCQD to different

chloride concentrations. Here, we observed a distinct

trend: a narrow peak with increasing intensity as the

chloride concentration rises

Figure 3(b) reveals a critical observation as the

concentration of chloride ions in edible oil increases,

the reflectance peak associated with AgNT-NCQD

film undergoes a noticeable shift. At the outset, with

edible oil as the baseline, the peak is measured at

343.45 nm and exhibits minimal reflectance.

Interestingly, a positive correlation between the

concentration of chloride ions and the peak's spectral

position were observed. In simpler terms, the higher

the chloride ion concentration, the greater the shift

towards higher wavelengths observed in the

reflectance peak. Thus, the measured Δλ values for 2,

6, 10, 20, and 50 ppm of chloride ion are 0.79, 5.30,

7.68, 11.92, and 12.98 nm, respectively. The observed

wavelength shift can conclude that it is through

plausible electrostatic interaction due to positively-

charged NCQD and negatively-charged Cl.

Traditionally, oppositely charged molecules

experience stronger attraction due to electrostatic

forces, leading to faster diffusion and interaction. The

reversibility of the AgNT-NCQD sensor is supported

by the non-covalent nature of electrostatic interactions,

where chloride ions bind to the functional groups on

the NCQD surface. These interactions are relatively

weak and temporary, allowing chloride ions to detach

when rinsed or exposed to a neutralizing environment,

and subsequently reattach during reuse. However, in

our study, the LSPR sensor using AgNTs displayed an

unexpected result where the wavelength shift wasn't

consistent. This finding challenges our understanding

of how the shape and size of AgNTs affect the sensor's

response. As reported by previous studies by Azeman

and co. in 2022, the sharp corners of triangular AgNTs

typically cause a redshift (longer wavelength) in

reflectance peaks compared to spherical shapes.

Multiple arrangements within the triangular AgNT

might weaken this effect, leading to less pronounced

redshift peaks (Bakar et al., 2022).

Figure 4 depicts the calibration plots for both

AgNT and AgNT-NCQD across three separate

experiments, all encompassing chloride ion

concentrations ranging from 2 ppm to 50 ppm. The

graph clearly illustrates that the Δλ for AgNT exhibits

a gradual rise proportional to increasing chloride ion

concentrations. In contrast, the Δλ for the AgNT-

NCQD composite shows a significantly steeper rise.

PHOTOPTICS 2025 - 13th International Conference on Photonics, Optics and Laser Technology

Figure 4: Calibration curve AgNT and AgNT-NCQD.

Furthermore, Figure 4 shows a graph comparing

the linear regressions of AgNT and AgNT-NCQD.

Notably, when detecting varying chloride ion

concentrations, the linear regression for AgNT-

NCQD appears to consist of two distinct lines. These

two lines correspond to concentration ranges: 0-6

ppm and 6-50 ppm. It shows a high correlation

coefficient (R2 = 0.9625) for 0-6ppm and AgNT-

NCQD range 6-50ppm correlation coefficient (R2 =

0.6793) compared to the AgNT range 0-6ppm and 6-

50ppm for R2 = 0.8992 and 0.1359, respectively. The

sensitivity of the sensor can be determined by

analyzing the slope of the lines in Figure 4. The

steeper the slope, the higher the sensitivity. The film

sensors exhibits optimal sensitivity up to 20 ppm of

chloride concentration, beyond which the sensor's

binding sites become saturated, leading to a plateau in

the response curve and reduced sensitivity. In this

case, the slope of the AgNT-NCQD composite's

calibration line is significantly steeper compared to

AgNT, indicating a greater increase in Δλ for each

increment in chloride ion concentration. This

translates to a higher detection accuracy for the

AgNT-NCQD composite, signifying its superior

performance as an LSPR sensor for chloride ion

detection in edible oil

The analysis confirms that the AgNT-NCQD

sensor is remarkably more sensitive than the AgNT

sensor for detecting chloride ions in edible oil. The

sensitivity of AgNT-NCQD was measured to be 0.92

nm ppm-1 (0-6ppm) and 0.21 nm ppm-1 (6-50ppm),

whereas AgNT's sensitivity was only 0.53 nm ppm-1

(0-6ppm) and 0.01 nm ppm-1 (6- 50ppm). This

significant improvement can be attributed to the

NCQDs in the composite sensor. NCQDs likely

provide more binding sites for chloride ions, allowing

for a greater response from the sensor and a more

precise measurement. The performance of AgNT-

NCQD compared to AgNT strongly suggests that

incorporating NCQDs significantly enhances the

sensitivity of LSPR sensors for chloride ion detection.

This work obtained a high sensitivity with the

detection range (0-6ppm), primarily due to the

addition of NCQDs as the sensor layer of chloride ion

detection compared to pure AgNT. However, the

AgNT-NCQD range (6-50ppm) has lower sensitivity

than the AgNT-NCQD range (0-6ppm). The readily

available positively charged sites on the NCQD

surface might be limited at higher chloride

concentrations, hindering their interaction with the

chloride ions. This findings demonstrated that

AgNT–NCQD outperforms AgNT as a sensing

material for chloride ion detection. It is important to

note that this sensor is designed for use with vegetable

oils that have properties similar to palm oil, such as

olive oil and canola oil.

4 CONCLUSIONS

This study investigated a sensor for detecting chloride

ions using triangular silver nanoparticles (AgNTs)

film and nitrogen-doped carbon quantum dots

(NCQDs). It compared the performance of this AgNT-

NCQD film sensor to the sensors using only AgNTs.

It analyzed the sensors by measuring the shift in

reflected light wavelength as the chloride ion

concentration increased. Presence of amino in the

NCQDs creates more active sites for chloride ions to

bind, enhancing the sensor's capability. This binding

likely occurs through electrostatic interactions. The

AgNT-NCQD film sensor positively responds to

increasing chloride ion concentrations within a

specific range (potentially 0 to 6 ppm). The sensor

demonstrated a value of 0.92 nm ppm

-1

. Additionally,

it showed a strong linear relationship between the

reflected light shift and chloride concentration (R² =

0.9625). However, the Limit of Detection (LOD) was

calculated to be 4.12 ppm, suggesting room for

improvement in detecting very low chloride

concentrations. In addition, considering the potential

of LSPR, this simple and efficient detection technique

could be applied to total chlorine in edible oil where it

provides a potential real-time detection for total

chlorine utilizing AgNT-NCQD films on LSPR to

achieve easy and fast detection in the food safety

fields.

ACKNOWLEDGEMENTS

The authors would like to thank the Photonics

Advancing Chloride Ion Detection in Edible Oils: Enhanced Sensitivity with NCQD/Ag Nanotriangles via Localized Surface Plasmon

Resonance

Laboratory of the Department of Electrical,

Electronic & Systems Engineering, Faculty of

Engineering and Built Environment, Faculty of

Science and Technology, and the Centre for Research

and Instrument Management (CRIM), Universiti

Kebangsaan Malaysia (UKM) for all amenities

provided. The author acknowledges the Fundamental

Research Grant Scheme (FRGS), grant number

FRGS/1/2023/TK07/UKM/02/2, funded by Ministry

of Education Malaysia and Research University

Grant (GUP), grant number GUP-2023-043, funded

by the Universiti Kebangsaan Malaysia (UKM),

Malaysia.

REFERENCES

Abdullah, S., Azeman, N. H., Mobarak, N. N., Zan, M. S.

D., & Ahmad, A. A. (2018). Sensitivity enhancement of

localized SPR sensor towards Pb(II) ion detection using

natural bio-polymer based carrageenan. Optik,

168(May), 784–793. https://doi.org/10.1016/j.ijleo.

2018.05.016

Abu Bakar, M. H., Azeman, N. H., Mobarak, N. N.,

Mokhtar, M. H. H., & Bakar, A. A. A. (2020). Effect of

active site modification towards performance

enhancement in biopolymer κ-Carrageenan derivatives.

Polymers, 12(9), 1–13. https://doi.org/10.

3390/POLYM12092040

Azeman, N. H., Arsad, N., & Bakar, A. A. A. (2020).

Polysaccharides as the sensing material for metal ion

detection-based optical sensor applications. Sensors

(Switzerland), 20(14), 1–22. https://doi.org/10.

3390/s20143924

Bakar, M. H. A., Azeman, N. H., Mobarak, N. N., Nazri, N.

A. A., Abdul Aziz, T. H. T., Zain, A. R. M., Arsad, N.,

& Bakar, A. A. A. (2022). Succinyl-κ-carrageenan

Silver Nanotriangles Composite for Ammonium

Localized Surface Plasmon Resonance Sensor.

Polymers, 14(2), 1–17. https://doi.org/10.3390/

polym14020329

Blumhorst, M. R., Collison, M. W., Cantrill, R., Shiro, H.,

Masukawa, Y., Kawai, S., & Yasunaga, K. (2013).

Collaborative study for the analysis of glycidyl fatty

acid esters in edible oils using LC-MS. JAOCS, Journal

of the American Oil Chemists’ Society, 90(4), 493–500.

https://doi.org/10.1007/s11746-012-2187-7

Cheng, W. W., Liu, G. Q., Wang, L. Q., & Liu, Z. S. (2017).

Glycidyl Fatty Acid Esters in Refined Edible Oils: A

Review on Formation, Occurrence, Analysis, and

Elimination Methods. Comprehensive Reviews in Food

Science and Food Safety, 16(2), 263–281.

https://doi.org/10.1111/1541-4337.12251

EFSA. (2018). Revised safe intake for 3-MCPD in

vegetable oils and food. EUROPEAN FOOD SAFETY

AUTHORITY. https://efsa.europa.eu/en/press/news/

180110

Jędrkiewicz, R., Kupska, M., Głowacz, A., Gromadzka, J.,

& Namieśnik, J. (2016). 3-MCPD: A Worldwide

Problem of Food Chemistry. Critical Reviews in Food

Science and Nutrition, 56(14), 2268–2277.

https://doi.org/10.1080/10408398.2013.829414

Jong-Sun, L., Ji-Won, H., Munyhung, J., Kwang-Won, L.,

& Myung-Sub, C. (2020). Effects of Thawing and

Frying Methods on the Formation of Acrylamide and

Polycyclic Aromatic. Foods, 9(5), 573.

Kuntom, A., Balasundram, N., & Lin, S. W. (2006). Esters

in Refined Edible Oils and Fats. 7–10.

Mehrotra, P. (2016). Biosensors and their applications - A

review. Journal of Oral Biology and Craniofacial

Research

, 6(2), 153–159. https://doi.org/10.

1016/j.jobcr.2015.12.002

Nazri, N. A. A. (2022). Chlorophyll Detection by Localized

Surface Plasmon Resonance Using Functionalized

Carbon Quantum Dots Triangle Ag Nanoparticles.

Nanomaterials, 12(17). https://doi.org/10.3390/nano

12172999

Nazri, N. A. A., Azeman, N. H., Bakar, M. H. A., Mobarak,

N. N., Luo, Y., Arsad, N., Aziz, T. H. T. A., Zain, A. R.

M., & Bakar, A. A. A. (2022). Localized surface

plasmon resonance decorated with carbon quantum

dots and triangular ag nanoparticles for chlorophyll

detection. Nanomaterials, 12(1). https://doi.org/

10.3390/nano12010035

Panel, E., & Chain, F. (2016). Risks for human health related

to the presence of 3- and 2-monochloropropanediol

(MCPD), and their fatty acid esters, and glycidyl fatty

acid esters in food. EFSA Journal, 14(5).

https://doi.org/10.2903/j.efsa.2016.4426

Rahman, W. B. W. A., Azeman, N. H., Kamaruddin, N. H.,

Menon, P. S., Shabaneh, A. A., Mahdi, M. A., Mokhtar,

M. H. H., Arsad, N., & Bakar, A. A. A. (2019). Label-

free detection of dissolved carbon dioxide utilizing

multimode tapered optical fiber coated zinc oxide

nanorice. IEEE Access, 7(2008), 4538–4545.

https://doi.org/10.1109/ACCESS.2018.2888626

Yoo, D., Park, Y., Cheon, B., & Park, M. H. (2019). Carbon

Dots as an Effective Fluorescent Sensing Platform for

Metal Ion Detection. Nanoscale Research Letters,

14(1). https://doi.org/10.1186/s11671-019-3088-6

Zannotti, M., Vicomandi, V., Rossi, A., Minicucci, M.,

Ferraro, S., Petetta, L., & Giovannetti, R. (2020).

Tuning of hydrogen peroxide etching during the

synthesis of silver nanoparticles. An application of

triangular nanoplates as plasmon sensors for Hg2+ in

aqueous solution. Journal of Molecular Liquids, 309,

113238. https://doi.org/10.1016/j.molliq.2020.113238.

PHOTOPTICS 2025 - 13th International Conference on Photonics, Optics and Laser Technology