Gold Nanoparticles and Surfactant-Based Electrochemical Sensing Platform for the Detection and Electroanalysis of the Anticancer Drug Oxoplatin

In the current work surface of a glassy carbon electrode (GCE) is purposely modified with a suitable modifier to enhance its sensing characteristics. A composite of surfactant 1-(2, 4-initrophenyl)-dodecanoylthiourea (DAN) and gold nanoparticles (AuNPs) was employed as modified for the sensitive detection of oxoplatin (OXP), an extensively used anticancer drug. It enters into water bodies through improper handling in underdeveloped countries where drug disposal precautions are not fully respected. The designed platform (DAN/AuNPs/GCE) displays remarkable sensitivity 6.35 μA nM−1 and senses OXP with LOD of 14.5 pM under optimized conditions. The sensor was characterized by electrochemical techniques mainly cyclic voltammetry, electrochemical impedance spectroscopy, and square wave voltammetry. The response of OXP was also examined in the artificial serum sample. The modified electrode was found to have extraordinary discrimination ability for the selected drug even in the presence of a 100-fold higher concentration of several interfering agents and displayed remarkable repeatability and reproducibility with RSD up to 3%. The role of the electrode modifier in enhancing the concentration of OXP near the transducer surface and consequently intensifying the oxidation signal of OXP was validated from experimental and computational studies.

Oxoplatin (cis-dichlorodiamminedihydroxoplatin (IV) is extensively used for cancer treatment.Due to improper disposal of OXP, it enters into water bodies.The major contributor to the entrance of drug into water bodies is the manufacturing industry.After excretion, OXP and its metabolites make their way into wastewater treatment plants.Hence, its detection in wastewater is essential for protecting life beneath the water.The current work is focused on the designing of a sensitive method for the determination of OXP in an aqueous system.
2][3] Even after the therapeutic course has ended, this medication still has anticancer effects that continue for a long time.Most experts agree that the drug's mode of action involves hydrolysis first, followed by covalent bonds with mitochondrial DNA, RNA, and proteins.Additionally, oxoplatin has a high therapeutic index and inhibits the growth of solid and ascitic tumors.In order to control the pharmacokinetics of the medicine in a patient, it is crucial to identify the hydrolysis products of OXP.OXP detection is also important for environmental reasons since hospital wastes containing it may collect in the ecosystem as soluble platinum complexes because these toxic compounds are not biodegradable.][8][9][10][11] These catalytic properties of the nano modifiers intensify the current intensity and increase the selectivity and sensitivity for the targeted analytes.In comparison to other techniques like spectroscopy and chromatography, electrochemical methods are more affordable, less complicated, and easier to use.
Many analytical techniques, including high-performance liquid chromatography (HPLC), mass spectrometry, and electrochemical sensors, have been proposed to identify and quantitatively detect the anticancer drugs including mitoxanthrone, cisplatin, oxaloplatin, and oxaliplatin in biological, synthetic serum and pharmaceutical fluids.
Chromatographic techniques have been employed for this purpose for a long time, but they come with drawbacks such as the use of hazardous solvents, the requirement for a competent operator, and the impossibility to convert portable kits. 12Due to this, surfactantbased materials have been proposed that enhanced the electrocatalytic behavior of several toxic analytes.Due to their low cost of synthesis, abundance, high stability, and low environmental impact, surfactants are now considered promising materials for the detection of drugs.These compounds have been used along with the nanoparticles in a wide range of sensing applications with remarkable results.A variety of biological and pharmaceutical chemicals, particularly anticancer medications in biological samples can be determined using electrochemical methods, which are both sensitive and effective.One of the nanomaterials' distinctive characteristics is their high electrical conductivity, which has made it easier to develop sensitive electrochemical sensors.The high electrical conductivity of thiourea surfactant-based nanomaterials was one of these, and they have recently been suggested for the production of various electrochemical sensors. 13,14he host molecules that interact with the target guest molecules are attached to electrodes for electrode modification.Modification can be done by using a variety of materials including ligands, polymers, and biological molecules like DNA and enzymes.Surfactants, however, are preferred due to their superior electrode anchoring capacity and effective electro-catalytic function.Due to the formation of micelles, surfactants are important in the solubilization process.6][17][18][19][20][21][22][23] Surfactants immobilized over the electrode surface function as redox mediators between the transducer and analytes. 17,18,24Surfactants are amphiphilic molecules with lipophilic and hydrophilic parts that can alter the electrode/solution interface and the electrochemical process occurring there through adsorption at the electrode surface. 24Surfactants such as SDS oxidation sites are found on the tail's terminal hydrocarbons, while its reduction sites are found on oxygen (especially the oxygen atom that serves as a bridge between the tail and the head group, and oxidation sites are found on the terminal hydrocarbons of the tail group. 25Surfactant-based nanomaterials have distinguished themselves as superior electrode materials for z E-mail: afzals_qau@yahoo.comECS Advances, 2023 2 040506 sensing applications due to their strong electrocatalytic activity and electrical conductivity.Recent research has shown that the incorporation of surface functionalities, in particular, N, S, and O functionalities in nanomaterials has provided active sites that favor the oxidation process for various drugs such as ascorbic and uric acid, Hybrid materials have also been investigated for their potential to produce functional electrode materials with outstanding sensitivity and selectivity towards electrooxidation of various pharmaceutical products. 26,279][30] The chemical, optical, electrical, and catalytic properties of AuNPs are remarkable.2][33] Au nanoparticles in particular have been extensively used as electrode modifiers among a variety of nanomaterials due to the catalytic provision of active sites to the protein redox centers. 34Au nanoparticles also show excellent stability over a broad pH range of the electrolyte.A promising strategy for accumulating Au nanoparticles onto the electrode surface is through sulfhydryl or amine-ended functional groups to bind them since thiol and ammine-tailed groups have a strong attraction to Au nanoparticles. 35-mercaptopropyl trimethoxysilane (3-MPTMS) was used to immobilise Au nanoparticles on the Indium tin oxide (ITO) electrode surface.According to Yagati et al., 36 Au NPs acted as a bridge between cytochrome c (cyt c) and the electrode substrate, exhibiting excellent electrocatalytic activity for the determination of H 2 O 2 .In another study Karimi-Maleh, H. et al. utilized AuNPs/PPy/Ti 3 C 2 T x for the selective and sensitive detection of Pb 2+ up to the concentration of 0.01 pm.37 Furthermore, AuNPs were immobilised on the carbon paste electrode (CPE) surface using physical adsorption and electrodeposition techniques to facilitate the electron transfer of heme proteins for the detection of hydroquinone, nitrites, phenols, dopamine, hydrogen peroxide, and glucose.15,[37][38][39] In this study, a thiourea-based surfactant and Au NPs have been utilised to increase the catalytic property of the electrode surface.16,40 1-(2, 4-dinitrophenyl)-dodecanoylthiourea (DAN) and NPs can function as an electrocatalyst for the detection of analytes based on the unique interaction of the chosen surfactant.DAN contains sulphur, amine, and carbonyl, which may be able to bind to drug molecules via hydrogen, ionic, and coordination covalent bonds.[41][42][43] Thus, in the present work, DAN /AuNPs were utilized to fabricate an electrochemical sensor using a glassy carbon electrode (DAN/AuNPs/GCE) for the determination of the picomolar concentration of oxoplatin (OXP).
Oxoplatin was purchased from the pharmaceutical company Eczacıbaşı (Ankara, Turkey).A stock solution of 1 mM OXP and 1 mM of DAN surfactant was prepared in ultrapure water.The modification solution was prepared by mixing 1 ml of DAN in 1 ml of AuNPs.
Instruments.-PalmSens 5 with software PS Trace 5.4 was utilized for electrochemical measurements.Polynomial order with nonlinear baseline has been applied to every curve using PalmSens software.All pH measurements were performed by using a pH meter.pH meter Model 538 (WTW, Austria).A model K64 PARC electrochemical cell was used for the experiments.4-5 14/20andard taper ports were present on the cell cap's top for the insertion of electrodes (WE, CE,, and RE) as well as the inlet of inert gas.Through a side opening, the cell is connected to the LAUDA K-4R thermostat, which maintains a constant temperature throughout the measurements.The electrochemical cell has a 10 ml volume capacity.As a reference electrode, silver chloride (Ag/AgCl) enclosed in saturated 3 M KCl was used.As a counter/auxiliary electrode, platinum was used.Working electrodes included bare and modified glassy carbon electrodes.

Schematics of DAN/AuNPs/GCE for the detection of OXP.-
The surface area of the GCE was 0.07 cm 2 and it was cleaned by polishing the electrode surface area with 0.05 mm alumina slurry and then rinsed with doubly distilled water.DAN/AuNPs solution of optimum concentration was immobilized on the surface.The droplet of a 10 μl solution of DAN/Au nanoparticles (1:1) was immobilized onto the surface of GCE by micropipette, and then followed by drying of the droplet using the dryer.The DAN/AuNPs/GCE was then dropped into the electrochemical cell for the electrochemical investigations as shown in Scheme 1.The following parameters were used to get the square wave voltammograms (SWVs): accumulation time: 120 s and deposition potential: −0.8 V, 0.025 V modulation amplitude, 0.005 V step potential, and 0.5 s of Scheme 1. Electrode modification by using DAN/AuNPs for the electrochemical detection of Oxoplatin.
ECS Advances, 2023 2 040506 interval duration.Impedance spectra were obtained at the potential of 0.7 V vs Ag/AgCl in the frequency range of 1 Hz to 10 kHz with the voltage signal amplitude of 10 mV.
Analysis of OXP in artificial serum.-For the detection of OXP, square wave voltammetry was performed in the synthetic serum sample. 1 ml of OXP and 5.4 ml of acetonitrile solution were added in the 3.6 ml of serum sample under optimum pH in the centrifuged tubes and centrifuged at 2500 rpm for 30 min.The clear solution was obtained after centrifugation and then the solution was subjected to an electrochemical analysis.To determine the reliability and sensitivity of the designed sensor the calibration plot for drugs in the synthetic serum was also obtained using the standard addition method.
Computational details.-The interaction between the modifiers and the analytes was investigated using Amsterdam Density Functional (ADF) software provided Quaid-i-Azam University, Islamabad.For the theoretical calculations, the DFTB/B3LYP basis set was used.All of the structures undergo geometry optimization before the binding energy calculations.After geometry optimization, DFTB single-point energy was used to determine the interaction energy between the modifier (DAN/AuNPs) and the analyte (OXP).
Electrochemical impedance spectroscopy (EIS).-EISwas performed to probe the catalytic behavior of modified and unmodified electrodes in a solution of 5.0 mM potassium ferricyanide. 44The Nyquist plots for the DAN/AuNPs modified GCE and the bare GCE are shown in Fig. 1A The Nyquist plot has a diffusion-controlled linear and semi-circular region corresponding to the charge transfer region.The semicircle portion corresponds to the high frequency region for electron transfer (ET) process.The diameter of the semicircle portion corresponds to the R ct .The diffusion-controlled process is indicated by the linear region in the lower frequency range.The diffusion of the redox probe at the electrode surface is correlated with the R W (Warburg resistance).The R ct is a critical parameter for identifying the interfacial characteristics of a modified electrode.The high charge transfer resistance of GCE as compared to DAN/AuNPs/GCE shows the lower ET of the redox species at the electrode surface.The lower value of R ct of the redox probe by using DAN/AuNPs/GCE indicates the electroconductive nature of the DAN and AuNPs, which facilitates the ET rate.Therefore, the fast ET rate of the redox probe at the DAN/AuNPs/GCE also signifies the successful modification of the electrode surface.The EIS parameters that were calculated by fitting the experimental data with the Randles circuit are displayed in Table I.
Chronocoulometry (CC) is an electroanalytical technique that is mostly used to calculate the effective electrode surface area, diffusion coefficients, the amount of charge adsorbed, and the identification and orientation of species adsorbed on the electrode surface.Choronocoulometry experiment was conducted to characterize the surface area of the electrode by using Anson equation.(see Fig. 1B) Area occupied by a single molecule 10 N 3 16 av

= / Γ [ ]
Where A is the electrode's area, Q dl is the charge of the electrical double layer, Q represents total charge, n the number of electrons transferred per molecule, F the Faraday constant, C the concentration of the analyte, D the diffusion coefficient, and t the time.Table II contains a list of the parameters that were determined by using chronocoulometry.These parameters show that due to an increase in charge density and charge transfer of electrons on the surface of DAN/AuNPs/GCE, the surface area, diffusion coefficient, and surface coverage values of DAN/AuNPs are higher than the unmodified GCE electrode.The results also suggest that the area of the DAN/ AuNPs is greater than the area of the bare electrode.This increased  electroactive active sites for Oxoplatin has also improved the charge transfer rate and current response.These findings show that DAN/ AuNPs/GCE has a greater accumulation capacity than a bare electrode.The orientation (vertical, bent or laydown) of molecules on the electrode surface was predicted from the area occupied by the molecules on the electrode surface. 45,46sults and Discussion Characterization of DAN/AuNPs by using cyclic and square wave voltammetry.-Cyclicvoltammetry (CV) was performed to characterize the redox behaviors of OXP by using the unmodified and modified electrode as shown in the Fig. 2A.It can be seen that well defined oxidation peak was observed for the OXP.The hydrogen production range is in the reduction region, so the oxidation region is selected for further electrochemical experiments.The intensified current signals of the oxidation of OXP were observed by using the DAN/AuNPs as compared to bare electrode signify the catalytic behavior of the DAN/AuNPs.The use of DAN/ Au nanoparticles to modify the electrode for OXP oxidation is advantageous due to several reasons.For example, the surfactant and Au nanoparticles enhance the sensitivity of electrode by increasing the surface area.In addition, the modifier DAN/Au can also improve the stability of the electrode by forming a protective layer and preventing interference from other compounds.The Au nanoparticles particularly enhance the electrical properties of electrodes as well.Moreover, the combination of DAN and Au nanoparticles is also expected to improve the selectivity of GCE, as the layers of modifier on the electrode can provide a controlled environment for detecting a particular analyte.
SWV was performed to further probe the oxidation behaviour of OXP on the GCE, DAN/GCE, and DAN/AuNPs/GCE.The voltammetric study was carried out in an acetate buffer at pH 3. Due to the slow electron transfer rate, the current response at the GCE is relatively low (see Fig. 2B).The catalytic action of DAN and AuNPs is responsible for the increase in peak current (I p ) of OXP at the DAN/GCE and AuNPs/GCE, which is visible from the curve.When DAN and AuNPs were employed to immobilise on the surface of the electrode in the optimal concentration (1:1), the amplitude of peak current (I p ) rose 6-fold times over that of DAN/GCE and AuNPs/ GCE.This synergistic impact of DAN and AuNPs could be related to the presence of moieties in the thiourea-based surfactant.The introduction of a thiourea-based surfactant with moieties (S, O, and N groups) that have an Au nano-dimensional structure may be responsible for this synergistic action of DAN and AuNPs by providing more binding sites for the OXP.Moreover, it increases the electrode surface's surface area (A) as the area of the bare ECS Advances, 2023 2 040506 electrode is 0.07 cm 2 and the area of DAN/AuNPs/GCE is found to be 0.17 cm 2 .Hence, the conductivity of DAN/AuNPs/GCE can act as a superior sensing surface for OXP.Half peak width is utilized for the calculation on the number of electrons involved in the oxidation process. 47

W
3.52RT nF Effect of modifier.-Theinfluence of the modifier concentration on the current intensity of OXP was probed.For this purpose, different ratio of surfactant and AuNPs were applied on the surface of electrode.SWVs were recorded to acquire the optimum concentration of modifier which gives maximum peak intensity of the drug OXP. Figure 2C illustrates the resultant I p with various combination ratios of modifiers immobilized over the GCE.Maximum current response was found with 1:1 (DAN: AuNPs).Beyond the optimized ratio decrease in peak current was observed.This may be due to the saturation of electrode surface at the higher concentration of DAN/ AuNPs.Hence, further experiments were performed using 1:1 of DAN:AuNPs.
Effect of pH and supporting media.-Theeffect of the pH and the supporting electrolyte on the peak current intensity of OXP was investigated through SWVs.The pH of the medium is a significant parameter for the detection of the analyte.To find out the best pH for the electrochemical sensing of OXP, a pH range of 2-10 was prepared by the use of several electrolytes such as acetate, phosphate, and BRB buffers.The variation of peak current with pH is displayed in Fig. 3A where it can be seen that the highest current intensity is observed in the acidic medium.With the increase in pH of the solution the peak current started decreasing indicating good conductivity of the medium for more facile electron transfer between OXP and the electrode surface in acidic medium than in basic medium.The most intense and well resolved peak of OXP appeared in a medium of pH 3.
We also evaluated the effect of the nature of electrolyte on the peak intensity of OXP (irrespective of the pH) as supporting electrolyte is also an important factor in analyte detection.For this purpose, 0.25 M of electrolytes such as acetate buffer (pH 3.0), H 3 PO 4 (pH 2), H 2 SO 4 (pH 1), HCl (pH 1), NaOH (pH 13), and HNO 3 (pH 1) were utilized to record the SWVs of OXP.As seen in Fig. 3B, the maximum peak signal with a good peak resolution of OXP was obtained in acetate buffer using DAN/AuNPs/GCE and it was considered the most acceptable supporting electrolyte for further studies.It was found that peak form, signals, and position changed significantly with the variation of the supporting medium.This is because the peak current of the analyte is affected by the ionic strength, ion mobility, charge, and the chemical interactions of various electrolytes.Ionic strength and ionic mobility of electrolyte has an impact to increase the peak current of the analyte.The charge of electrolytes can support or hinder the electrochemical sensing of the analyte (e.g., it can compete with oxidation/reduction). Similarly, chemical interactions such as complexation and adsorption, can also hinder or enhance the peak current.We have not delved into the details of these effects, however the study of the effect of supporting electrolytes enabled us to identify the best system for electrochemical sensing of OXP.
Effect of scan rate.-Thescan rate effect in electrochemical investigations can be used to explore information about the processes of oxidation/reduction, the nature of the reaction on the electrode surface, whether it is regulated by diffusion or adsorption, and kinetics parameters.Therefore, CV was used to assess the impact of scan rates on the oxidation peak currents of OXP using DAN/AuNPs/GCE, The scan rate's impact on the OXP peak current showed increase in peak current with the increase of scan rate and the peak potentials (E P ) shifted towards higher positive values.The positive shift in the peaks potentials with the increase in scan rate is  I p stands for the maximum current in amps, A for electrode area (cm 2 ), V for scan rate (V/s), D for diffusion coefficient (cm 2 /s), n for number of electrons participating in a redox reaction, and C for concentration of redox probe (mole/cm 3 ) in this equation.From the peak width value we calculated the number of electrons (n = 2) participating in the chemical equation.The diffusion value of the OXP is found to be 8 × 10 −6 cm 2 s −1 as obtained from Eq. 2 using slope value of the plot shown in Fig. 4A.According to a literature study, a plot between the log I p against log v, the slope value near to 0.5 indicates a diffusion-controlled electrode process, whereas a slope value close to 1 indicates an adsorption-controlled process.The slope value of the plot shown in Fig. 4B is close to the reported values of 0.5 indicating that the redox process is diffusion-controlled process.A linear relationship between peak current vs ѵ 1/2 also suggesting the oxidation process of OXP utilizing DAN/AuNPs/ GCE is diffusion-controlled process.
To calculate the coverage of the adsorbed molecules on the electrode surface following equation was utilized; Where n = the number of electrons, Ґ is the surface area occupied by molecules that have been adsorbed on the electrode surface.The remaining symbols all have their usual meanings.The estimated value of Ґ for the DAN/AuNPs/GCE is 4.36 × 10 −8 mol.cm 2 .
Effect of the deposition potential and time.-SWVswere recorded to check the effect of accumulation time and potential (V) on the peak current I p of OXP at the modified GCE as depicted in Fig. 5.With the increase of negative deposition potential the amplitude of peak current gradually increases up to −0.8 V.The maximum peak current was obtained at −0.8 V and after that with the further increase of negative potential the peak current of OXP started to decrease.The impact of accumulation time on the OXP peak current was also investigated.Peak current increased with the increase of accumulation time up to 120 s after which it started to decrease due to saturation on modified electrode surface (Fig. 5B).Hence, the optimum parameters i.e. deposition potential − 0.8 V and accumulation time 120 s were selected for further voltammetric study owing to the maximum OXP electrooxidation under these conditions.
Analytical characterization of DAN/AuNPs/GCE for the detection of OXP.-The important parameters to characterize the electrochemical sensors are the detection range and LOD.As a result, square wave voltammograms of various OXP concentrations were attained at the DAN/AuNPs under ideal conditions.The peak current I p intensity increased with an increase in concentration as shown in Figs.6A and 6B, which indicates a linear connection between the I p and concentration of OXP at the DAN/AuNPs/GCE in pH 3 solution from 1 to 50 nM.The following formulae were used to compute the limit of quantification (LOQ) and LOD. 47   Where σ is the standard deviation of peak current (I p) of the blank, and m is the slope value of the linear calibration plot.
Table II provides a summary of the calibration plot's parameters.The proposed sensor's LOD suggests that the proposed method will be effective to detect OXP levels with exceptional sensitivity.As listed in Table II, DAN/AuNPs/GCE exhibits a linear concentration for OXP detection with a broad range and lower LOD values in the proposed work.The sensitivity and LOD of the proposed electrode is found to be 6.35 μA nM −1 and 14.5 pM respectively which is quite remarkable The LOD up to a picomolar concentration demonstrates the potential of the suggested sensor as a sensing platform.The synthesis of the modifier and the fabrication of the electrode are also very easy, simple, and inexpensive.
Repeatability and reproducibility.-TheDAN/AuNPs/GCE repeatability and reproducibility were confirmed with RSD values less than 3.5%.Three consecutive SWVs at various OXP concentrations were recorded to test inter-and intra-repeatability.The reproducibility of the proposed sensor DAN/AuNPs/GCE for OXP detection was checked by fabricating three modified electrodes using the same modification technique on different days as shown in Fig. 7.These results validate the DAN/AuNPs/GCE excellent repeatability and reproducibility for OXP detection, as shown in Table III.][55] In order to determine the long term stability of the DAN/AuNPs/ GCE, the electrode was stored under ambient conditions over a period of two weeks.The DAN/AuNPs/GCE retained 97.5% of its initial anodic peak signal for three different concentrations of OXP These findings indicate the good stability of the DAN/AuNPs/GCE.
The comparison of the performance of our designed sensor with the previous reported sensors for the detection of Platinum-based anticancerous drugs as they are structurally related to oxoplatin is shown in Table IV.The LOD values suggested that our desired sensor has lower limit of detection as compared to previously proposed sensors which clearly shows the remarkable efficacy of our designed sensor.
Interference study.-Theinfluence of various interfering agents on the SWVs of OXP were investigated to determine the selectivity of the developed sensor.To determine their effects on the peak intensity of the OXP at DAN/AuNPs/GCE different excipients such as dopamine, ascorbic acid, carbonate, bicarbonate, uric acid, glucose, and sucrose were added individually in the ratios of (1:100) to the solution of OXP.Fig. 8 displays the 30 μM OXP oxidation peak signal in both the presence and absence of interferents.It is obvious that despite a 100-fold concentration of interfering chemicals, no appreciable changes in the OXP peak current were recorded. 59These results, therefore, show that the Table III.Parameters obtained from the calibration plot of OXP through SWVs in standard solution, confidence limit is (p<0.10,n = 3) with confidence interval of 95%.

Parameters
Drug (OXP)  ECS Advances, 2023 2 040506 interfering agents have no significant impact on the proposed sensor, and it is therefore very selective towards the determination of OXP.
Practical applicability of the proposed method.-TheDAN/ AuNPs/ GCE applicability was investigated by employing the standard addition method in a serum based OXP solution.First, the serum's standard calibration curve was obtained.The unknown concentrations of OXP and recovery studies were obtained by using the calibration curve.Three times each measurement was made.Table V. includes the RSD values and recovery percentages.The obtained RSD values are less than 2%, demonstrating the sensor's incredible precision.Furthermore, good recoveries suggest the effectiveness and reliability of the proposed method for future medical analysis. 60,61mputational study of the interaction of OXP with modifier.-Molecularorbitals calculations were performed to understand the interactions of the drug OXP with modifier DAN and AuNPs by using ADF software.The quantum parameters were used to calculate the program using DFTB/B3LYP.Following optimization of the geometry, the binding energies of the analyte OXP with sensing material AuNPs and DAN, were calculated (see Figs. 9A and 9B).For the purpose of calculating interaction energy, the binding energy of a combined structure was determined by bonding all three structures-DAN, AuNPs, and OXP-as a single unit using the DFTB approach, as illustrated in (Fig. 9C).Hence, both computational and experimental findings can be used to compare the oxidation of OXP.The interaction energy predicts the feasibility of the reaction between the modifier and the analyte.The high negative value of E int suggests that strong interaction exists between DAN/AuNPs and OXP and, which also suggests potential for a spontaneous reaction.These findings imply that theoretical calculations favours the experimental finding.
Redox mechanism of oxoplatin.-TheSWVs of oxoplatin in a wide pH range were recorded.The pH dependent electrochemical behavior of oxoplatin can be used to propose its oxidation mechanism.The peak width at half height (W 1/2 ) and plot of peak potential as a function of pH shown in Fig. 10 suggest a consecutive two steps one electron transfer oxidation mechanism of oxoplatin.The shift in peak potential with increase in pH of the medium suggests that electron transfer is coupled with proton transfer.A proposed mechanism in acidic pH is depicted in Scheme 2.

Conclusions
DAN/AuNPs/GCE was utilized as a modifier to investigate the electrochemical oxidation and analytical detection of OXP in water and artificial serum.The results depicted that under optimized conditions, DAN/AuNPs/GCE has a high sensitivity for the detection of OXP with a LOD value of 1.45 × 10 −11 M. Excellent recovery from spiked samples and negligible interference from interferents validated the selectivity and reliability of the developed sensor.To calculate the binding energy between the OXP and the electrode modifier, computational investigations were carried out using the DFTB program.The negative interaction energy suggested that strong interactions occurred between DAN/AuNPs and OXP.The outcomes of computational investigations supported those of the experimental analysis.The electroanalytical applications of the developed sensors were tested on artificial serum samples, and the results showed amazing recoveries, indicating the practical usability of the suggested sensors in the analysis of artificial serum sample.These surfactant-based nano sensors are therefore more efficient at detecting OXP in biological samples due to the simple, inexpensive, and environmentally friendly fabrication process, which also meet the requirements of low sample volume, high sensitivity, selectivity, and reproducibility.By performing voltammetric analysis to detect OXP at concentrations as low as picomolar levels, the current research effectively addresses the previously identified research gap in this area.

Future Perspective
The development of novel electrochemical sensors with enhanced sensitivity and selectivity for drugs's detection is a significant research area for future study.The could entail the development of novel surfactant-based nanomaterials that are better at detecting platinum ions, like graphene or conductive polymers.To improve the sensor's performance and lower the LOD, researchers may also investigate the use of various electrode materials or surface modifications.Future studies might also focus on using electrochemical sensors to find other platinum-based medicines or their metabolites.This could include several types of chemotherapy medications based on platinum that are frequently used to treat cancer, including Pt-DNA adducts, which are significant indicators for medication efficiency and toxicity.Future research might concentrate on integrating existing electrochemical sensors into portable devices for testing in biological fluids which could provide useful information about the pharmacokinetics of the drug.This could make it possible to identify OXP quickly and precisely, which could have significant effects on cancer diagnosis and therapy.Thus, the detection of unexamined OXP using electrochemical analysis marks a major step in the detection of novel analytical methods for platinum-based pharmaceuticals.

Figure 1 .
Figure 1.A Nyquist plot showing EIS response in a 5 mM K 3 Fe(CN) 6 solution.Frequency range is from (1 Hz to 10 kHz).Impedance spectra were obtained at the potential of 0.7 V vs Ag/AgCl in the frequency range of 0.01 Hz to 104 Hz, applying an amplitude for the voltage signal of 10 mV.B. Chronocoulometry of 5 mM K 3 Fe(CN) 6 at GCE, DAN/GCE and AuNP/ DAN/GCE.

Figure 3 .
Figure 3.Effect of (A) pH on the peak current of 0.1 μM solution of OXP using SWV under optimized concentration (B) Supporting electrolyte on peak current of 0.4 μM solution of OXP by using SWV.Deposition potential −0.8 V and accumulation time 90 s.The error bars represent the standard deviation of three independent measurements.

Figure 4 .
Figure 4. (A) (Plot of anodic peak current of 100 μM OXP versus square root of scan rate ranging from 100-1000 mV s −1 .(C) Logarithm of anodic peak current versus logarithm of scan rate.

Figure 5 .
Figure 5.The effect of deposition potential and time on the oxidation I p of 40 μM solution of OXP in acetate buffer pH 3 by using SWV under these conditions; step potential: 0.005 V; modulation amplitude: 0.025 V; modulation time: 0.05 s; interval time: 0.5 s.The error bars represent the standard deviation of three independent measurements.

Figure 6 .
Figure 6.(A) SWVs of pH 3 containing different concentrations of OXP (B) Plot of I p versus concentrations of OXP at scan rate of 100 mV/s under optimum experimental conditions using modified GCE.; step potential: 0.005 V; modulation amplitude: 0.025 V; modulation time: 0.05 s; interval time: 0.5 s t ac = 120 s, Deposition potential= −0.8 V.The error bar represents the standard deviation of three independent measurements.

Figure 7 .
Figure 7. Reproducibility studies at three different GCE modified with DAN/Au/GCE in 10 nM at a scan rate of 100 mV/s under optimized experimental conditions.

Figure 8 .
Figure 8. Peak currents of OXP in the presence of 100 folds concentration of (A) ascorbic acid (B) uric acid (C) carbonates (D) bicarbonates(E) dopamine (F) glucose (G) measured sucrose through SWVs.under optimum conditions.Deposition potential −0.8 V and accumulation time = 120 s.

Figure 10 .
Figure 10.(A) SWVs of OXP solutions in the pH range of 2-10.Depostion potential −0.8 V; Accumulation time 120 s (B) Plot of E p vs pH under optimum condition.

Table I .
Parameters obtained from EIS by using modified and unmodified GCE.

Table II .
Parameters obtained from Choronocoulometry by using GCE, DAN, and DAN/AuNPs/GCE.

Table IV .
Comparison of proposed method with the reported method for the detection of platinum based anticancerous drug. 62,63