Spectrophotometric and Spectrofluorimetric Quantification of Urea via Silver Nanoparticles Prepared by Wet Chemical Method
School of Environmental Science and Engineering, North China Electric Power University, 102206, Beijing, China
Academic Editor: Narendra Kumar
Special Issue: Nanoparticles and Nanotechnologies in Catalysis
Received: November 09, 2022 | Accepted: February 28, 2023 | Published: March 15, 2023
Catalysis Research 2023, Volume 3, Issue 1, doi:10.21926/cr.2301014
Recommended citation: Ismail M. Spectrophotometric and Spectrofluorimetric Quantification of Urea via Silver Nanoparticles Prepared by Wet Chemical Method. Catalysis Research 2023; 3(1): 014; doi:10.21926/cr.2301014.
© 2023 by the authors. This is an open access article distributed under the conditions of the Creative Commons by Attribution License, which permits unrestricted use, distribution, and reproduction in any medium or format, provided the original work is correctly cited.
Nanotechnology is concerned with synthesizing, characterizing, and using diverse materials by regulating the form and size of dimensions less than 100 nanometers [1,2,3]. Many researchers have been drawn to the development of ecologically benign methods for the synthesis of metallic nanoparticles, particularly silver, which has a wide range of applications in textiles, electronics, the environment, and the medicinal sectors [4,5,6]. Ag NPs are made by reducing silver salt using a variety of processes, including chemical, biogenic, photo-reduction, thermal and radiation [7,8,9,10]. These silver nanomaterials are used as a research tool in various sectors, like photodegradation of environmental pollutants, photocatalysts for removing hazardous substances, especially dyes, gases and biomedical wastes, cancer cells treatment and removal of heavy metals from water bodies [11,12,13,14,15]. Moreover, Ag NPs are utilized in biosensing to assess several chemical substances in environmental, laboratorial, and clinical serums [16,17,18]. Due to their cheapness, low operating time, and sensitivity, spectrometric methods for quantifying pharmaceuticals, heavy metal ions, urea, etc., are now being researched [19,20,21]. Urea makes up between 80 and 90 percent of the nitrogen excreted by humans [22,23,24,25]. On the other side, if the body cannot get rid of it, it might cause serious health issues including uremic syndrome or azotemia [26,27,28,29]. Because of its importance, researchers have paid close attention to urea analysis; it supports disease detection, controls biological processes, and facilitates the delivery of medications and formulations [30,31,32,33].
In this work, silver nanoparticles were prepared by reducing the salt of silver nitrate solution with sodium borohydride stabilized by DIPO. The produced silver nanoparticles were then used to detect urea by complexation utilizing a much simpler, quick, and more reliable approach that included spectrophotometry and spectrofluorimetry along with accuracy and precision. This study aims to efficiently and reliably apply the silver nanoparticles for quantifying urea in two spectrometric ways to find a better detection method in the scientific and medical sectors.
All stirring was done on the Sh-4 model ceramic magnetic stirrer using cylindrical magnetic stirring bars. All absorbance measurements were performed on a UV-1602 UV-visible spectrophotometer (photodiode array) using a quartz cuvette with an optical path of 1 cm. All fluorescence measurements were obtained on a spectrofluorimeter (Perkin-Elmer LS55). SEM images of the prepared silver nanoparticles were acquired on SEM JEOL (JSM-5910, 20 kV). X-ray diffractometer acquired XRD pattern (adv. Bruker-D8, Cu Kα, 1.5418 Å).
All reagents were of analytical grade and were not purified further. Throughout our investigation, deionized water was used to make all the solutions. Solutions prepared are: 1 mM silver nitrate AgNO3 (Merck) solution, 1 mM DIPO solution (synthesized by Gero’s method ), 1 mM sodium borohydride NaBH4 (Merck), 1 mM Urea (Agrium) solution, dilute 1% HCl and NaOH (Merck) solution.
2.3 Preparation of Silver Nanoparticles
10 mL AgNO3 (1 mM) solution was stirred for 15 minutes on a magnetic stirrer along 10 mL DIPO (1 mM) solution, followed by the addition of 0.5 mL NaBH4 solution was dropped and stirred again for 15 more minutes, which led to Ag NPs conversion of whole solution from transparent to yellowish color that gives an initial indication of Ag NPs being prepared. The as-prepared silver nanoparticles were scanned on a UV-visible spectrophotometer in the 300-800 nm range and a spectrofluorimeter in the range of 250-650 nm with a 435 nm excitation wavelength. The schematic preparation of silver nanoparticles is illustrated in Scheme 1.
Scheme 1 Schematic presentation of synthetic procedure of Ag NPs.
2.4 Preparation of Ag NP-urea Complex
Firstly, prepared silver nanoparticles were used as a blank to record their UV-vis. Absorbance and fluorescence emission spectra have 300-800 nm and 250-650 nm with a 435 nm excitation wavelength, respectively. After that, 10 mL of prepared silver nanoparticles were combined with 10 mL urea (1 mM) solution, stirred for 15 minutes and the complex absorbance and fluorescence spectra were recorded.
2.5 Determination of Urea
Urea concentrations of 0.1-15 mM were mixed with prepared Ag NPs in a ratio of 10:1 (nanoparticle: urea). An absorbance and emission spectra at 435 nm were recorded and a regression equation was applied to both methods to calculate the concentration of urea once the calibration curves were formed. Recovery experiments were conducted following the addition of a known quantity of pure urea to the different pre-analyzed urea concentration formulations to accurately and precisely analyze the suggested approach. Followed by the determination of the limit of detection (LOD), the limit of quantification (LOQ), the percent recovery, the standard deviation (SD) and the relative standard deviation (RSD).
3. Results and Discussion
3.1 Confirmation of Ag NPs Synthesis
The conversion of a solution containing silver nitrate and DIPO to dark yellow after adding NaBH4 indicated the formation of Ag NPs. This was confirmed by the UV-vis spectrum showing an absorbance band at 406 nm, as seen in Figure 1 (a). This peak is, because of the metallic silver nanoparticles surface plasmon resonance (SPR) effect that verifies the Ag NPs formation. Additionally, spectrofluorimetric confirmation was performed at an excitation wavelength of 406 nm, showing emission spectra at 471 nm, as shown in Figure 1 (b).
Figure 1 UV–Visible absorbance (a) and Fluorescence emission (b) spectra of Ag NPs.
3.2 Morphology Analysis of Ag NPs
SEM was used to examine the surface morphology and particle size of the as-prepared Ag NPs. Figures 2 (a) and Figure 2 (b) show Ag NPs as randomly dispersed particles having rough surfaces with irregular shapes. ImageJ software was used to determine the nanoparticle size, which was between 27 and 39 nm in size, with an average size of 32.9 nm.
Figure 2 SEM images of Ag NPs (a and b).
Furthermore, the confirmation and phase purity of the prepared Ag NPs was analyzed by XRD; the result is depicted in Figure 3. The XRD pattern is matching with the powder diffraction file (# 04-0783) with lattice planes at 2 theta values of 38, 44, 64 and 74° indicating diffraction peaks (111), (200), (220) and (311), respectively. The XRD pattern showed no impurities, supporting the effective formation of Ag NPs.
Figure 3 XRD pattern of prepared Ag NPs.
3.3 Complexation of Prepared Ag NPs with Urea
The formation of a complex between silver nanoparticles and urea was confirmed through UV-visible and spectrofluorimetric emission spectrum. Figure 1 (a) illustrates an absorption spectrum showing a red shift from 435 to 450 nm. This may be due to the complex formation between silver nanoparticles and urea. Besides, Figure 1 (b) displays an emission spectrum, showing a quenching of Ag NPs due to urea molecules from 450 to 490 nm. This may result from the new, non-fluorescent ground state (Ag NPs-urea complex) that absorbs radiation and returns within less time to the ground state without photon emission, which leads to quenching of emission spectra.
3.4 Determination of Urea
The urea concentration was quantified from both methods by Beer's-Lambert law. The maximum absorbance wavelength of 445 nm and fluorescence emission wavelength of 471 nm was chosen for plotting the calibration curves.
A linear correlation was obtained between absorbance/emission and urea concentration at the optimum conditions. Beer’s law was obeyed in the 0.1-15 mM concentration range.
The spectrophotometric method calibration curve was plotted as shown in Figure 4 (a) obtaining slope 0.0065, intercept 0.0078 and correlation coefficient 0.96. SD, RSD, LOD, and LOQ from the calibration curve were calculated as 0.27 mM, 36.18%, 0.89 mM, and 2.72 mM respectively.
Similarly, a standard calibration curve was drawn for the spectrofluorimetric method from the urea concentration against the emission followed by applying the linear regression equations as shown in Figure 4 (b). The calibration curve shows slope 0.0073, correlation coefficient 0.99, SD 0.02 mM, RSD 9.60%, LOD 0.04 mM and LOQ 0.16 mM.
Figure 4 Calibration curve of Ag NPs by (a) UV-visible (b) Fluorescence.
Table 1 provides the summarized results for the urea determination. The results demonstrated that the suggested method may be used to determine urea satisfactorily.
For analysis of recovery studies, the same sample of 0.5, 1, and 5 mM were tested three times each. The SD and RSD values were used to calculate the method's precision. The method's accuracy is demonstrated by the low SD and RSD results. % Recovery and RSD found by the spectrophotometric method shows 88.00 ± 19.7%, 96.67 ± 21.5%, and 130.80 ± 1.3%, respectively Table 2). Similarly, Table 3 demonstrates the % Recovery and RSD found by the spectrofluorimetric method, showing 102.30 ± 12.7%, 97.26 ± 5.6% and 111.40 ± 3.8%, respectively. The RSD values from both methods were satisfactory, indicating improved reproducibility of the suggested approaches. However, the spectrofluorimetric method shows good percent recovery with a small RSD suggesting high accuracy for determining urea.
The current work on silver nanoparticle synthesis is easy and inexpensive, and its function in urea determination is highlighted by simple, selective, sensitive, and low-cost approaches. The prepared silver nanoparticles were successfully employed to determine urea in pure samples using spectrophotometric and spectrofluorimetric methods, yielding good results. Both results revealed that the proposed methods for urea determination might be used successfully. From both methods, good RSD values were found, indicating improved repeatability. The suggested technique for determining urea is highly accurate since it has a high percent recovery and minimal RSD. Urea determination by spectrofluorimetric method shows a good result compared to the UV-visible method showing a good % recovery and less RSD, as shown in Table 4. Besides, our results have been compared with the previously reported methods, as shown in Table 5. From the table, it can be seen that the detection limit and LOD from our work are least as compared to other values previously reported having, the smaller value was found through the spectrofluorimetric method as compared to spectrophotometry. These techniques can be developed further and applied in further study for application in general and industrial analysis.
The authors are grateful to North China Electric Power University's (College of Energy Dynamics and Mechanical Engineering) in Beijing, China, for its assistance and supporting this work.
The author confirms sole responsibility for the study conception, design, data collection, analysis, interpretation of results, and manuscript preparation.
The project did not receive any funding.
The author declares no conflict of interests.
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