Citrate-capped gold nanoparticles as a sensing probe for determination of cetyltrimethylammonium surfactant using FTIR spectroscopy and colorimetry

Targeted synthesis of gold nanorods and characterization of their tailored surface properties using optical and X-ray spectroscopy

In recent years, nanophotonics have had a transformative impact on harnessing energy, directing chemical reactions, and enabling novel molecular dynamics for thermodynamically intensive applications. Plasmonic nanoparticles have emerged as a tool for confining light on nanometer-length scales where regions of intense electromagnetic fields can be precisely tuned for controlled surface chemistry. We demonstrate a precision pH-driven synthesis of gold nanorods with optical resonance properties widely tunable across the near-infrared spectrum. Through controlled electrostatic interactions, we can perform selective adsorbate molecule attachment and monitor the surface transitions through spectroscopic techniques that include ground-state absorption spectrophotometry, two-dimensional X-ray absorption near-edge spectroscopy, Fourier-transform infrared spectroscopy, and surface-enhanced Raman spectroscopy. We elucidate the electronic, structural, and chemical factors that contribute to plasmon-molecule dynamics at the nanoscale with broad implications for the fields of energy, photonics, and bio-inspired materials.

Development and validation of colorimetric-assisted chemometrics methods based on the localized gold nanoparticles surface plasmon resonance for fast simultaneous estimation of anti-hepatitis C virus drugs in their combined dosage form: A comparative study with HPLC method

The present work describes a developed analytical method based on a colorimetric assay using gold nanoparticles (AuNPs) along with chemometric techniques for the simultaneous estimation of sofosbuvir (SOF) and ledipasvir (LED) in their synthetic mixtures and tablet dosage form. The applied chemometric approaches were continuous wavelet transform (CWT) and least squares support vector machine (LS-SVM). Characterization of AuNPs and AuNPs in combination with the drug was performed by UV-vis spectrophotometer, transmission electron microscopy (TEM), dynamic light scattering (DLS), and Fourier transform infrared (FTIR) spectroscopy. In the CWT method, the zero amplitudes were determined at 427 nm with Daubechies wavelet family for SOF (zero crossing point of LED) and 440 nm with Symlet wavelet family for LED (zero crossing point of SOF) over the concentration range of 7.5-90.0 μg/L and 40.0-100.0 μg/L with coefficients of determination (R2) of 0.9974 and 0.9907 for SOF and LED, respectively. The limit of detection (LOD) and limit of quantification (LOQ) of this method were found to be 7.92, 9.96 μg/L and 12.02, 30.2 μg/L for SOF and LED, respectively. In the LS-SVM model, the mean percentage recovery of SOF and LED in synthetic mixtures was 98.29 % and 99.25 % with root mean square error of 2.392 and 1.034, which were obtained by the optimization of regularization parameter (γ) and width of the function (σ) based on the cross-validation method. The proposed methods were also applied for the determination concentration of SOF and LED in the combined dosage form, recoveries were higher than 95 %, and relative standard deviation (RSD) values were lower than 0.4 %. The achieved results were statistically compared with those obtained from the high-performance liquid chromatography (HPLC) technique for the concurrent estimation of components through one-way analysis of variance (ANOVA), and no significant difference was found between the suggested approaches and the reference one. According to these results, simplicity, high speed, lack of time-consuming process, and cost savings are considerable benefits of colorimetry along with chemometrics methods compared to other ways.

Integrated magneto-plasmonic nanostructures-based immunoassay for galectin-3 detection

Cardiovascular diseases remain a leading cause of global mortality, highlighting the need for accurate diagnostic tools and the detection of specific cardiac biomarkers. Surface-enhanced Raman scattering (SERS) spectroscopy has proved to be a promising alternative diagnostic tool to detect relevant biomarkers compared to traditional methods. To our knowledge, SERS methodology has never been used to detect galectin-3 (Gal-3), a crucial biomarker for cardiovascular conditions. Our study aimed to develop plasmonic and magneto-plasmonic nanoplatforms for the sensitive immunodetection of Gal-3 using SERS. Spherical gold nanoparticles (AuNPs) were synthesized and functionalized with 11-mercaptoundecanoic acid (MUDA) to enable antibody binding and 4-mercaptobenzoic acid (4MBA) that served as a Raman reporter due to its intense Raman signal. Following bioconjugation with Gal-3 antibody, the AuNPs were employed in the immunodetection of Gal-3 in phosphate-buffer saline (PBS) solution, offering a limit of detection (LOD) of 12.2 ng mL-1 and a working range up to 120 ng mL-1. Furthermore, our SERS-based immunosystem demonstrated selectivity for Gal-3 (40 ng mL-1) in the presence of other biomolecules such as α-amylase, bovine serum albumin and human C-reactive protein. As a proof of concept, we developed magneto-plasmonic nanoparticles composed of silica-coated magnetite decorated with the bioconjugated AuNPs aimed at enhancing the uptake and detection of Gal-3 via SERS coupled with Raman imaging. Our findings underscore the potential of SERS-based techniques for the sensitive and specific detection of biomarkers, holding significant implications for improved diagnosis and surveillance of cardiovascular diseases. Future research will focus on further optimizing these nanoplatforms and their translation into clinical settings.

Rapid and naked-eye colorimetric detection of ultra trace sumatriptan in drinking water, saliva, and human urine samples based on the aggregation of gold nanoparticles

In this study, the determination of sumatriptan (SUM) was performed using a simple, rapid, and precise colorimetric method based on the surface plasmon resonance (SPR) feature of gold nanoparticles (AuNPs). By adding SUM, the aggregation was observed in AuNPs with red-to-blue color shifts. The size distribution of NPs was estimated before and after adding SUM via dynamic light scattering (DLS), which was found to be 15.34 and 97.45 nm, respectively. Characterization of AuNPs, SUM, and AuNPs in combination with SUM was investigated using transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Examining the effect of pH, the volume of buffer, the concentration of AuNPs, interaction time, and ionic strength revealed that their optimal values were 6, 100 μL, 5 μM, 14 min, and 12 μg L-1, respectively. The suggested method was able to determine the amount of SUM in a linear range of 10 to 250 μg L-1 with a limit of detection (LOD) and limit of quantification (LOQ) of 0.392 and 1.03 μg L-1, respectively. This approach was successfully applied to determine SUM in drinking water, saliva, and human urine samples with relative standard deviations (RSD) lower than 0.03%, 0.3%, and 1.0%, respectively.

On the role of polymeric hydrogels in the thermal response of gold nanorods under NIR laser irradiation

Hydrogels are 3D cross-linked networks of polymeric chains designed to be used in the human body. Nowadays they find widespread applications in the biomedical field and are particularly attractive as drug delivery vectors. However, despite many good results, their release performance is sometimes very quick and uncontrolled, being forced by the high in vivo clearance of body fluids. In this direction, the development of novel responsive nanomaterials promises to overcome the drawbacks of common hydrogels, inducing responsive properties in three-dimensional polymeric devices. In this study, we synthesized and then loaded gold nanorods (Au NRs) within an agarose-carbomer (AC)-based hydrogel obtained from a microwave-assisted polycondensation reaction between carbomer 974P and agarose. The photothermal effect of the composite device was quantified in terms of maximum temperature and spatial-temporal temperature distribution, also during consecutive laser irradiations. This work shows that composite Au NRs loaded within AC hydrogels can serve as a stable photothermal treatment agent with enhanced photothermal efficiency and good thermal stability after consecutive laser irradiations. These results confirm that the composite system produced can exhibit an enhanced thermal effect under NIR laser irradiation, which is expected to lead to great therapeutic advantages for the localized treatment of different diseases.

Coagulation of Hydrophobic Ionic Associates of Cetyltrimethylammonium Bromide and Carrageenan

In aqueous solutions, cetyltrimethylammonium cations bind to carrageenan polyanions, and the resulting ionic associates form macroscopic aggregates due to hydrophobic interaction. At certain ratios of cetyltrimethylammonium to carrageenan, the resulting colloidal particles auto-flocculate. According to visual observations, the ratio ranges from 1 to 3 mmol/g; otherwise the suspensions are stable. By measuring the sedimentation rate and particle size distribution, the most extensive flocculation was found to be from 1.7 to 2.3 mmol/g. The ratio corresponding to the fastest auto-flocculation was precisely determined by titrating the reagents with small increments and recording the turbidity. The turbidimetric titration plots contain distinct break points corresponding to the most extensive flocculation. These break points occur at the same ratio of carrageenan to cetyltrimethylammonium over a wide range of reagent concentrations. The precise values of the critical ratio were found to be 1.78 and 1.53 mmol/g, respectively, during the titration of cetyltrimethylammonium with carrageenan and vice versa. The number of anionic sulfate groups in carrageenan was measured by ICP OES and found to be 1.35 mmol/g. This value is consistent with the critical ratio of the auto-flocculation.

Determination of ketamine using melamine-modified gold nanoparticles

Ketamine is used in medicine because of its anaesthetic and antidepressant effects at low doses. Unfortunately, due to its narcotic effect when used at high doses, its abuse among young people is increasing. It is also one of the most common drugs used in rape. Therefore, there is a need for fast and inexpensive tests that can be performed on-site. With the advancement of nanotechnology, nanoparticle-based approaches have found their place in selective analyses as in many fields. In the developed method, firstly gold nanoparticles were modified with melamine (AuNPs@Mel). Under optimized conditions, hydrogen bonds formed between ketamine and AuNPs@Mel cause the red colour of AuNPs@Mel to shift to blue-purple (i.e. aggregation-induced surface plasmon absorption shift). The association between absorbance and concentration produced a calibration line (curve) having a linearity correlation coefficient of 0.9981 for ketamine concentrations ranging from 4.76 to 47.6 mg L-1. The detection limit of the proposed method was 1.5 mg L-1 and the RSD (relative standard deviation) values of concentrations were changed ranging from 5.2% to 8.2%. The intra-assay and inter-assay measurements using the suggested method resulted in coefficients of variation (CVs) of 5.7% and 8.5%, respectively. Scan transmission electron microscopy (STEM), UV-vis spectrophotometry and FTIR spectroscopy were used to characterize the synthesized and modified AuNPs. Additionally, the procedure was successfully carried out with some interference materials and a real sample of fetal bovine serum. Lastly, using the Student t-test and F tests, the suggested technique was compared to and confirmed against an LC-MS/MS procedure previously published.

Role of Tunable Gold Nanostructures in Cancer Nanotheranostics: Implications on Synthesis, Toxicity, Clinical Applications and Their Associated Opportunities and Challenges

The existing diagnosis and treatment modalities have major limitations related to their precision and capability to understand several stages of disease development. A superior therapeutic system consists of a multifunctional approach in early diagnosis of the disease with a simultaneous progressive cure, using a precise medical approach towards complex treatment. These challenges can be addressed via nanotheranostics and explore suitable approaches to improve health care. Nanotechnology in combination with theranostics as an unconventional platform paved the way for developing novel strategies and modalities leading to diagnosis and therapy for complex disease conditions, ranging from acute to chronic levels. Among the metal nanoparticles, gold nanoparticles are being widely used for theranostics due to their inherent non-toxic nature and plasmonic properties. The unique optical and chemical properties of plasmonic metal nanoparticles along with theranostics have led to a promising era of plausible early detection of disease conditions, and they enable real-time monitoring with enhanced non-invasive or minimally invasive imaging of several ailments. This review aims to highlight the improvement and advancement brought to nanotheranostics by gold nanoparticles in the past decade. The clinical use of the metal nanoparticles in nanotheranostics is explained, along with the future perspectives on addressing the key applications related to diagnostics and therapeutics, respectively. The scope of gold nanoparticles and their realistic potential to design a sophisticated theranostic system is discussed in detail, along with their implications in clinical advancements which are the needs of the hour. The review concluded with the challenges, opportunities, and implications on translational potential of using gold nanoparticles in nanotheranostics.

The Antimelanoma Biological Assessment of Triterpenic Acid Functionalized Gold Nanoparticles

One of several promising strategies for increasing the bioavailability and therapeutic potential of high-lipophilic biologically active compounds is gold nanoparticle formulation. The current study describes the synthesis and biological antimelanoma evaluation of three triterpen-functionalized gold nanoparticles, obtained using our previously reported antimelanoma benzotriazole-triterpenic acid esters. Functionalized gold nanoparticle (GNP) formation was validated through UV-VIS and FTIR spectroscopy. The conjugate's cytotoxic effects were investigated using HaCaT healthy keratinocytes and A375 human melanoma cells. On A375 cells, all three conjugates demonstrated dose-dependent cytotoxic activity, but no significant cytotoxic effects were observed on normal HaCaT keratinocytes. GNP-conjugates were found to be more cytotoxic than their parent compounds. After treatment with all three GNP-conjugates, 4,6'-diamidino-2-phenylindole (DAPI) staining revealed morphological changes consistent with apoptosis in A375 melanoma cells. Quantitative real-time polymerase chain reaction (RT-qPCR) analysis revealed that the triterpene-GNP conjugate treated A375 melanoma cells had a fold change increase in Bcl-2-associated X protein (BAX) expression and a fold change decrease in B-cell lymphoma 2 (Bcl-2) expression. In A735 melanoma cells, high-resolution respirometry studies revealed that all three GNP-conjugates act as selective inhibitors of mitochondrial function. Furthermore, by examining the effect on each mitochondrial respiratory rate, the results indicate that all three conjugates are capable of increasing the production of reactive oxygen species (ROS), an apoptosis trigger in cancer cells.

Cationic Polystyrene Resin Bound Silver Nanocomposites Assisted Fourier Transform Infrared Spectroscopy for Enhanced Catalytic Reduction of 4-Nitrophenol in Aqueous Medium

The present work reported a novel strategy to construct supported cationic-polystyrene-resin-bound silver nanocomposites for enhanced catalytic reduction of 4-nitrophenol in an aqueous medium. The Fourier transform infrared spectroscopy (FTIR) was used as a model instrument for the study of catalytic reduction of 4-nitrophenol using cationic-polystyrene-resin-bound silver nanocomposite materials. The mechanism is based on the reduction of 4-nitrophenol to 4-aminophenol due to the electron transfer process that occurred between donor borohydride (BH4−) and acceptor 4-nitrophenol. The polystyrene resin provides support and surface area to increase the catalytic activity of silver nanoparticles. The diffused reflectance-Fourier transform infrared spectroscopy revealed the binding of silver particles onto the surface of cationic polystyrene resin beads. Furthermore, the catalyst was easily separated by the filtration and drying process and was able to reuse. A quantitative analysis of this work has also been performed. The linearity range, the limit of detection, and the limit of quantification obtained for the present method were 0.1 × 10−4 to 1.0 M, 0.6 M, and 2.1 M, respectively. Moreover, a good catalytic efficiency was found to be 96.8%. The advantages of the current method are its simplicity, sensitivity, rapidity, low cost, ease of preparation, and excellent catalytic efficiency to reduce 4-nitrophenol from an aqueous solution.

The Anti-Melanoma Effect of Betulinic Acid Functionalized Gold Nanoparticles: A Mechanistic In Vitro Approach

Implementing metallic nanoparticles as research instruments for the transport of therapeutically active compounds remains a fundamentally vital work direction that can still potentially generate novelties in the field of drug formulation development. Gold nanoparticles (GNP) are easily tunable carriers for active phytocompounds like pentacyclic triterpenes. These formulations can boost the bioavailability of a lipophilic structure and, in some instances, can also enhance its therapeutic efficacy. In our work, we proposed a biological in vitro assessment of betulinic acid (BA)-functionalized GNP. BA-GNP were obtained by grafting BA onto previously synthesized citrate-capped GNP through the use of cysteamine as a linker. The nanoformulation was tested in HaCaT human keratinocytes and RPMI-7951 human melanoma cells, revealing selective cytotoxic properties and stronger antiproliferative effects compared to free BA. Further examinations revealed a pro-apoptotic effect, as evidenced by morphological changes in melanoma cells and supported by western blot data showing the downregulation of anti-apoptotic Bcl-2 expression coupled with the upregulation of pro-apoptotic Bax. GNP also significantly inhibited mitochondrial respiration, confirming its mitochondrial-targeted activity.

Adsorption kinetics for the removal of toxic Congo red dye by polyaniline and citrus leaves as effective adsorbents

This study focusses on the synthesis of polyaniline (PANI) and polyaniline base adsorbent utilizing Citrus limon leaves (CL) powder. The polyaniline base adsorbent with C. limon was synthesized using the same process as polyaniline synthesis, but with the addition of leaves powder. PANI and PANI based adsorbent with C. limon leaves powder (PANI/CL) were characterized by Fourier Transform Infra-Red (FTIR), UV-Visible spectroscopy and Scanning Electron Microscopy (SEM). This synthesized material was employed for the removal of congo red (CR) dye from industrial wastewater. Furthermore, the Langmuir, Temkin and Freundlich isotherms were also applied to evaluate experimental results. PANI is an efficient adsorbent for CR removal with 71.9 mg/g, while PANI/CL is an efficient adsorbent with 80 mg/g removal of dye according to a comparison of maximal adsorption capabilities. The data concludes that the prepared adsorbents could possibly be employed for the removal of toxic dyes from industrial effluents at large scale and ultimately could help in improving the environment.

Citrate functionalized gold nanoparticles assisted micro extraction of L-cysteine in milk and water samples using Fourier transform infrared spectroscopy

This paper describes the sensing application of citrate functionalized gold nanoparticles (AuNPs) employing for the determination of L-cysteine in food and water samples. It is established with diffuse reflectance Fourier transform infrared (DRS-FTIR) spectroscopic analysis. The disappearance of the thiol (-SH) band in the FTIR spectra and the shift in the peaks of the amino group (NH₃⁺) and carboxylate group (-COO^-) indicated the Au-S interaction and the aggregation of the NPs. The signal intensity of L-cysteine was enhanced due to hot-spots formed by the aggregation of AuNPs producing the effective absorption of electromagnetic radiation in the IR region for molecular vibration. The relationship between AuNPs and L-cysteine was theoretically investigated by the Density Function Theory (DFT) based on LANL2DZ with the aid of the Gaussian 09 (C.01) software. Interaction between AuNPs and L-cysteine molecules resulted to a shift to higher wavelengths in the plasmon bands, further verified by transmission electron microscopes (TEM), which have indicated random aggregated particles. Further dynamic light scattering (DLS) measurements showed a relatively high degree of polydispersity confirming the aggregation of the particles. Under optimized conditions, the calibration curve showed a good linearity range from 20 to 150 μg mL^-1 with a correlation coefficient (R²) 0.990. The limit of detection and quantification were 1.04 and 3.44 μg mL^-1, respectively by DRS-FTIR. This modified AuNPs sample was used successfully in milk and water samples with adequate results to determine L-cysteine.

Resin immobilized gold nanocomposites assisted surface enhanced infrared absorption (SEIRA) spectroscopy for improved surface assimilation of methylene blue from aqueous solution

In the present work, we report the adsorption of the methylene blue (MB) dye from an aqueous solution employing resin immobilized gold nanocomposites (R-AuNCs) assisted surface-enhanced infrared absorption (SEIRA) spectroscopy. The appropriate adsorption isotherm models, including the Langmuir, Freundlich, and Temkin are tested to reveal the interactive behavior between the adsorbent (R-AuNCs) and adsorbed (MB). Interestingly, Fourier transform infrared spectroscopy (FTIR) in combination with R-AuNC materials could be another approach through which the analysis of adsorption-desorption of MB on the surface of nanocomposite adsorbents is possible in a more precise way with high sensitivity and adsorptivity. In addition, a 10-fold enhancement of the signal intensity of MB dye was obtained due to the electrostatic interaction and H-bonding interaction between COO^- groups of adsorbent and the positively charged active sites of the dye molecules. The value of % removal efficiency and % adsorption obtained in the present method was 77.64% and 186.61%, respectively. Desorption of MB from adsorbent surface was also carried out using 0.1 M cetylpyridinium chloride as cationic surfactant; resulting process shows for 'n' number of cyclic process. The maximum desorption capacity for MB found in the present investigation was 44.38 mg/g, The advantages of current method are its simplicity, sensitivity, rapidity, ease to fabrication and excellent adsorption efficiencies to remove MB dye from aqueous solution.

A Simple and Sensitive Nanogold RRS/Abs Dimode Sensor for Trace As3+ Based on Aptamer Controlled Nitrogen Doped Carbon Dot Catalytic Amplification

Using citric acid (CA) and ethylenediamine (EDA) as precursors, stable nitrogen-doped carbon dots (CD) nanosols were prepared by microwave procedure and characterized in detail. It was found that CD_Ns catalyze ethanol (Et)-HAuCl₄ to generate gold nanoparticles (AuNPs), which have strong surface plasmon resonance, Rayleigh scattering, (RRS) and a surface plasmon resonance (SPR) absorption (Abs) effect at 370 nm and 575 nm, respectively. Compled the new catalytic amplification indicator reaction with the specific As³⁺ aptamer reaction, a new RRS/Abs dual-mode aptamer sensor for the assay of trace As³⁺ was developed, based on the RRS/Abs signals increasing linearly with As³⁺ increasing in the ranges of 5-250 nmol/L and 50-250 nmol/L, whose detection limits were 0.8 nmol/L and 3.4 nmol/L As³⁺, respectively. This analytical method has the advantages of high selectivity, simplicity, and rapidity, and it has been successfully applied to the detection of practical samples.

A simple and cost-effective paper-based and colorimetric dual-mode detection of arsenic(iii) and lead(ii) based on glucose-functionalized gold nanoparticles

We report a simple and cost-effective paper-based and colorimetric dual-mode detection of As(iii) and Pb(ii) based on glucose-functionalized gold nanoparticles under optimized conditions. The paper-based detection of As(iii) and Pb(ii) is based on the change in the signal intensity of AuNPs/Glu fabricated on a paper substrate after the deposition of the analyte using a smartphone, followed by processing with the ImageJ software. The colorimetric method is based on the change in the color and the red shift of the localized surface plasmon resonance (LSPR) absorption band of AuNPs/Glu in the region of 200-800 nm. The red shift (Δλ) of the LSPR band observed was from 525 nm to 660 nm for As(iii) and from 525 nm to 670 nm for Pb(ii). The mechanism of dual-mode detection is due to the non-covalent interactions of As(iii) and Pb(ii) ions with glucose molecule present on the surface AuNPs, resulting in the aggregation of novel metal nanoparticles. The calibration curve gave a good linearity range of 20-500 μg L-1 and 20-1000 μg L-1 for the determination of As(iii) and Pb(ii) with the limit of detection of 5.6 μg L-1 and 7.7 μg L-1 for both metal ions, respectively. The possible effects of different metal ions and anions were also investigated but did not cause any significant interference. The employment of AuNPs/Glu is successfully demonstrated for the determination of As(iii) and Pb(ii) using paper-based and colorimetric sensors in environmental water samples.

A simple and convenient dry-state SEIRS method for glutathione detection based on citrate functionalized silver nanoparticles in human biological fluids

Graphical representation for determination of glutathione using citrate functionalized AgNPs enriched dry-state SEIRS method.

L-cysteine modified silver nanoparticles for selective and sensitive colorimetric detection of vitamin B1 in food and water samples

The use of L-cysteine modified silver nanoparticles (Cys-capped AgNPs) as a colorimetric probe for determination of vitamin B1 (thiamine) is described in the present work. This method is based on the measurement of red shift of localized surface plasmon resonance (LSPR) band of Cys-capped AgNPs in the region of 200–800 nm. The color of Cys-capped AgNPs was changed from yellow to colorless by the addition of vitamin B1. The mechanism for detection of vitamin B1 is based on the electrostatic interaction between positively charged vitamin B1, which causes the red shift of LSPR band from 390 nm to 580 nm. The interaction between Cys-capped AgNPs and vitamin B1 was theoretically explored by density function theory (DFT) using LANL2DZ basis sets with help of Gaussian 09 (C.01) program. The morphology, size distribution and optical properties of Cys-capped AgNPs were characterized by transmission electron microscope (TEM), UV-Visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS) techniques. The method is linear in the range of 25–500 μg mL⁻¹ with correlation coefficient (R²) 0.992 and limit of detection of 7.0 μg mL⁻¹. The advantages of using Cys-capped AgNPs as a chemical sensor in colorimetry assay are being simple, low cost and selective for detection of vitamin B1 from food (peas, grapes and tomato) and environmental (river, sewage and pond) water samples.

A KBr-impregnated paper substrate as a sample probe for the enhanced ATR-FTIR signal strength of anionic and non-ionic surfactants in an aqueous medium

Herein, we report a KBr-impregnated paper substrate as a sample probe to enhance the attenuated total reflection-Fourier transform infrared (ATR-FTIR) signal strength of anionic surfactants (AS) and non-ionic surfactants (NS) in an aqueous solution. The mechanism for the sensing of AS and NS is based on the strong interaction of surfactants with the silicate groups (SiO₄⁴⁻) of the KBr-impregnated paper substrate. The role of SiO₄⁴⁻ on the surface of the paper is to enhance the adsorption of AS and NS, resulting in improved IR signal intensities for the target analytes. The improved signal intensity at 1253 cm⁻¹ (SO₄²⁻, symmetric stretching) for AS and 1114 cm⁻¹ (C–O–C, stretching vibration) for NS were selected for quantification. SEM-EDX was employed to determine the elemental compositions of pre- and post-adsorbed AS and NS on glass fibre filter paper (GFF). The linear range for the determination of AS and NS was 10–100 μg L⁻¹ with a method detection limit (MDL) of 4 μg L⁻¹ and method quantification limit (MQL) of 12 μg L⁻¹. The good relative recovery of 71.4–109.7% and the interference studies showed the selectivity of the method for the determination of AS and NS in environmental water and commodity samples. The advantages of this method include its cost-effectiveness, enhanced sensitivity, disposability and accessibility of the paper substrate.

Flow diagram of the procedures for the analysis of surfactants using modified GFF paper substrate.