{Development of ciprofloxacin sensor using iron-doped graphitic carbon nitride as transducer matrix: Analysis of ciprofloxacin in blood samples:} http://dx.doi.org/10.5599/jese.1112 59 J. Electrochem. Sci. Eng. 12(1) (2022) 59-70; http://dx.doi.org/10.5599/jese.1112 Open Access : : ISSN 1847-9286 Original scientific paper Development of ciprofloxacin sensor using iron-doped graphitic carbon nitride as transducer matrix: Analysis of ciprofloxacin in blood samples Hattna Shivarudraiah Vedhavathi1; Ballur Prasanna Sanjay1; Mahesh Basavaraju2; Beejaganahalli Sangameshwara Madhukar1 and Ningappa Kumara Swamy1, 1Department of Chemistry, JSS Science and Technology University, Mysuru- 570006, Karnataka, India 2Department of Chemistry, JSS Academy of Technical Education, Bengaluru- 560060, Karnataka, India Corresponding author: kumaryagati@gmail.com; Phone: +91-9741027970, Fax: 0821-2548290 Received: September 15, 2021; Accepted: November 6, 2021; Published: November 17, 2021 Abstract In the present work, we have synthesized an iron-decorated graphitic carbon nitride (Fe@g-C3N4) composite and employed it for electrochemical sensing of ciprofloxacin (CFX). The physicochemical characteristics of the Fe@g-C3N4 composite were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray diffraction (EDX) spectroscopy methods. Further, the pencil graphite electrode (PGE) was modified with Fe@g-C3N4 composite to get PGE/Fe@g-C3N4 electrode and characterized the resultant electrode by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Differential pulse voltammetry (DPV) was employed to determine the effect of concentration and interferents. The modified PGE/Fe@g-C3N4 electrode demonstrated the exceptional electrochemical performance for CFX identification and quantification with a LOD of 5.4 nM, a wide linear range of 0.001-1.0 µM, and high sensitivity of 0.0018 µA mM-1 cm-2. Besides, Fe@g-C3N4 modified PGE showed remarkable recovery results in qualitative analysis of CFX in human blood specimens. This research advocates that the Fe@g-C3N4 composite acts as an excellent transducer material in the electrochemical sensing of CFX in blood and standard samples. Further, the proposed strategy deduces that the PGE/Fe@g-C3N4 sensor can be a prospective candidate for the dynamic determination of CFX in blood serum and possibly ratified as an exceptional drug sensor for therapeutic purposes. Keywords quinolone, drug sensor, electrochemical sensor, electrode matrix, differential pulse voltammetry Introduction The quinolones are a class of broad spectrum of drugs due to their excellent activity against gram- negative pathogens. They are the choice for patients with intra-abdominal infections together with anti-anaerobic agents [1-3]. Ciprofloxacin (CFX) continues to be the most efficient quinolone in http://dx.doi.org/10.5599/jese.1112 http://dx.doi.org/10.5599/jese.1112 mailto:kumaryagati@gmail.com J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 CIPROFLOXACIN SENSOR 60 veterinary and human medication [4]. An immoderate dosage of CFX residues can purport significant antagonistic effects besides causing the ailments such as skin and respiratory infections, chronic bacterial prostatitis, and nosocomial pneumonia [5]. The European Union has set the maximum residue level of ciprofloxacin in milk [6] to be 100 ng mL-1. The presence of CFX and other antimicrobials in the environment is a ground for attention, owing to the possible genesis of resistance to antibiotics. Therefore, developing alternate sensitive and precise sensors to examine the antibiotics in the biological samples (blood) is a dynamic field of the probe [7]. To ascertain the CFX analytical models, like high-performance liquid chromatography, spectro- photometry, capillary electrophoresis, liquid chromatography-mass spectroscopy, spectrofluorimetry, immunoassays, chemiluminescence, impedance spectroscopy, and voltammetry, are performed. Although these methods are sensitive, they are usually elaborate and time-consuming. Moreover, continued specimen pretreatment is essential for the test. Electrochemical methods (impedance spectroscopy, voltammetry) are methods of choice due to their low energy requirement, affordable costs, extraordinary sensitivity, expeditious, and user-friendliness [8-11]. Many biomolecules, including active ingredients in pharmacological formulations and human body fluids, were analysed by electrochemical methodology [12–18]. Diverse designs, procedures, and materials are engaged to promote the sensitivity and selectivity of an electrochemical sensor [15,16]. In the improving electro- chemical sensor, nanomaterials were frequently used as transducer elements [19-27]. Previously, carbon-based nanomaterials such as graphene, graphene oxide (GO), multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), graphene nanoribbons (GNRs), single-walled carbon nanotubes (SWCNTs), and carbon nanofibers began multiple favourable traits to drive direct electron transfer within the transducer and the electrode surface [28]. Among them, g-C3N4 is one of the most promising materials attributable to its unusual two-dimensional graphene-like structure, non-toxicity, extraordinary chemical endurance, easy accesssibility, and photo- responsivity in the visible-light region [29]. Concurrently, metallic nanoparticles (MNPs) in conjunction with carbonaceous substances in various domains like sensors, batteries, drug delivery, medical, solar cells, etc. MNPs possess unique attributes like charge surface-to-volume ratio, superior conductivity, and the capacity to function as an electron-conducting tunnel to magnify the direct electron transfer in an electrochemical sensor [30,31]. Iron (Fe) nanoparticles are acknowledged for their excellent electrocatalytic activity, low cost, non-toxicity, high stability, and fair conductivity, indicating that combining Fe with g-C3N4 might improve the sensitivity of the intended sensor [31]. The combination of iron and g-C3N4 can potentially magnify the electrochemical sensing characteristics of the electrode surface. The decoration of Fe on the g-C3N4 surface can demonstrate a stable sensing platform with good electron transfer characteristics, which ideally suit the construction of novel electrochemical sensing systems. An electrochemical sensor was described with this motivation by modifying a pencil graphite electrode (PGE) with Fe@g-C3N4 nanomaterials. This work demonstrates a new promising electroactive drug sensor for the qualitative and quantitative detection of CFX using g-C3N4 and Fe@g-C3N4. The proposed sensor manifested an extensive linear detection range, high sensitivity, low detection limit, and selectivity concerning the detection of CFX. Moreover, the sensor considers high accuracy, extensive shelf-life, and reproducibility, indicating that the Fe@g-C3N4 is a proper matrix for the sensor fabrication. The real- time application of the advanced sensor is further validated with the analysis of CFX in human blood specimens. Finally, a comprehensive comparison with earlier sensors highlighted the performance H. S. Vedhavathi et al. J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 http://dx.doi.org/10.5599/jese.1112 61 of PGE/Fe@g-C3N4. Therefore, it is anticipated that the drug sensor can be a useful tool for biomedical and diagnostic applications. Experimental Reagents and equipment Analytical grade CFX was procured from Sigma-Aldrich (99 %), whereas urea (98 %), Ferric (II) chloride (98 %), acetone (99 %), ascorbic acid (AA) (99 %), uric acid (UA) (99 %) and glucose (99 %) were acquired from Fischer scientific and used as such without further purification. The morphology and elemental composition of the developed sensor were described by scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX), and the suggested g-C3N4 and Fe@ g- C3N4 samples were characterized by a powder X-ray diffractometer (PROTO - AXRD) to authenticate the physical traits like structure, crystallinity, lattice planes, etc. All the voltammetric readings (CV, EIS, and DPV) are conducted utilizing a Biologic Science potentiostat (model SP-150) with the three- electrode configuration. Synthesis of Fe@g-C3N4 The synthesis of g-C3N4 was carried out by urea pyrolysis (20 g) using a lid crucible (Isotemp Programmable Muffle Furnace 650-750 Series, Fisher Scientific) in a muffle furnace at 550 °C for 3 h [31]. Finally, the doping of Fe on g-C3N4 nanosheets was made by mixing calculated quantities of ferric(II) chloride and 0.6 g of g-C3N4 nanosheets in 50 mL of acetone with constant stirring. The resulting suspension was agitated for two hours at ambient temperature, centrifuged for 15 min at around 6000 rpm, and rinsed many times with acetone to eliminate aggregates. The color of the withered specimens slightly shifted from pale yellow to imperceptibly reddish-brown upon the doping of iron [29]. Fabrication of CFX sensor with Fe@g-C3N4 A cylindrically shaped pencil graphite rod with a diameter of 3 mm (surface area: 0.07068 cm2) was utilized as a working electrode. Further, the electrode was modified by taking a tiny portion of the rod and polished along one face. A copper wire was fastened to secure the electrical contact flanked by the electrode and the potentiostat. To obtain a shiny surface, PGE was polished using emery paper (80 and 300 Grit) and consequently, with the electrode polishing solution containing alumina and silica using electrode polishing tool kit (PK-3 brand kit). Then, the polished PGE was sonicated and eventually washed with milli-Q water and dried at room temperature to eliminate loosely bounded shreds. The prepared bare PGE was further deposited with 3 µl of 5 mg mL-1 stock solution of Fe@ g-C3N4 by drop-casting method and eventually, the electrode was dried at ambient temperature to get the working electrode PGE/Fe@g-C3N4. Electrochemical studies The electrochemical investigations were performed in a three-electrode cell, where PGE was used as a working electrode (surface area: 0.07068 cm2), saturated calomel electrode as the reference electrode, and platinum wire as the counter electrode. All electrochemical characteristics of bare and modified PGEs were performed in phosphate buffer solution (PBS) of pH 7.0. The charge transfer at the electrode/electrolyte interface of the altered electrode was studied in the frequency range of 100 kHz to 0.1 Hz using the EIS technique, with 5 mM [Fe(CN)6]3-/4- as the electrochemical probe. The probe of EIS had operated in 0.1M PBS (pH 7.0) constituting 1 mM [Fe(CN)6]4-/3-, and at an amplitude of 5 mV and frequencies within 100 kHz and 0.1Hz range. http://dx.doi.org/10.5599/jese.1112 J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 CIPROFLOXACIN SENSOR 62 Preparation of sample for real analysis The serum samples collected from normal individuals (taking their inscribed consent) were refrigerated till examination. 5 mL of serum was treated with an equivalent volume of methanol as a serum desaturating and precipitating agent. The conduits were vortexed for 10 min and then centrifuged for 40 min at 5000 rpm to eliminate the protein residues. The supernatants were diluted up to 10 mL with the 0.1 M PBS buffer solution of pH 7.0. The standard addition method was employed for calculating the recoveries of the spiked CFX in human serum. The percentage recovery and detection precision were computed based on the known amount of spiked CFX (R) and empirical values (E) using equations 1 and 2. Accuaracy, % 100 R E R − = (1) Recovery, % 100 R E = (2) Results and discussion X-ray diffraction and FT-IR studies Figure 1A shows XRD patterns of the nanosheets of the integrated g-C3N4 and Fe@g-C3N4. A strong diffraction peak at 27.3o demonstrates strong interlayer interactions of aromatic rings, indexed as the (002) planes for g-C3N4. The smaller diffraction signal at around 13.1o, listed as (100), is associated with the in-plane structural perpetual motif, i.e., the continuous tri-s-triazine structures [32]. Besides, the depth of the (002) peak had substantially diminished and expanded for g-C3N4 nanosheets [33]. The resulting doping with Fe evidenced no change of the crystal phase of g-C3N4. The location of diffraction peaks for nanosheets Fe@g-C3N4 switched to a steadily higher angle for nanosheets of g-C3N4. The peak intensity diminished, and the diffraction peak width broadened for iron content, implying the presence of excess Fe species caused the host-guest interactions and polymeric condensation inhibition. It is further evident that the iron is chemically coordinated to g-C3N4 via Fe-N bonds [34]. . 2 / o Wavenumber, cm-1 Figure 1. A - XRD data of g-C3N4 and Fe@g-C3N4, and B - IR spectrum of g-C3N4 and Fe@g-C3N4 Figure 1B shows the FT-IR spectra of the g-C3N4 and Fe@g-C3N4 nanosheets. From Figure 1B, the extended absorption band at nearly 3155 cm-1, assigned to the stretching vibrational modes of surplus N–H components connected with uncondensed amino groups [35,36], can be identified. The H. S. Vedhavathi et al. J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 http://dx.doi.org/10.5599/jese.1112 63 peak at 1633 cm-1 is classified as vibrational stretching mode, whereas aromatic C-N stretching vibra- tions of heterocyclic rings matched with the bands at 1415, 1400, and 1234 cm-1 [26]. The specific particular peak at 807 cm-1 confirmed the s-triazine ring system [37]. Further, it is evidenced from Figure 1B that the intensity of the peaks reduced with an increase in Fe content in the Fe@g-C3N4, and the principal characteristic bands of g-C3N4 nanosheets change to smaller wavenumbers (redshift) intimates that the C-N and C=N bonds are weakened [29] SEM and EDS analysis The g-C3N4 and Fe@g-C3N4 synthesis was demonstrated by SEM and EDS study. Figures 2A and 2B denote the SEM image of integrated g-C3N4 and Fe@g-C3N4 nanocomposite. The micrographs were obtained at 3,000 magnifications by an expediting voltage of 5.0 kV LED. The sheets-like morphology evidences a greater surface area for the catalytic reactions between target and transducer interface [38]. Figure 2C shows the EDS spectrum of the synthesized material, and it reveals elemental composition. The EDS data illustrated the presence of carbon (C) 51.92 %, nitrogen (N) 31.24 %, oxygen (O) 2.96 %, and iron (Fe) 13.88 % in the Fe@g-C3N4 sample, indicating that Fe-doped g-C3N4 has a pretty high rate of purity, and it comprises solely four elements. These essential considerations made on EDS interpretation insinuate the purity of the substance. Energy, keV Figure 2. A - SEM image of g-C3N4, B - SEM image of Fe@g-C3N4, (C) EDX of Fe@g-C3N4, (Inset: elemental composition) Electrochemical assessment of the modified PGE The electrochemical response of the modified PGE was monitored by CV using a 5 mM [Fe(CN)6]3- /4- as an electrochemical mediator in 0.1 M PBS buffer (pH 7.0). The CV of the bare PGE shows a In te n si ty , a .u . http://dx.doi.org/10.5599/jese.1112 J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 CIPROFLOXACIN SENSOR 64 well-defined quasi reversible oxidation and reduction peaks with a peak-to-peak separation (ΔEp) of 201.6 mV (Figure 3A, curve a). The peak current increased after the deposition of 3 µl Fe@g-C3N4, which resulted in peak separation (ΔEp) of 271.2 mV (Figure 3A, curve b). The increase in current response and stability of the CV curve suggests the successful deposition of Fe@g-C3N4 on the PGE electrode surface. EIS spectra of PGE and PGE/Fe@g-C3N4 recorded in 1 mM [Fe(CN)6]4-/3- PBS solution Figure 3B are displayed in the Nyquist diagram. From the EIS data, the charge transfer resistance (Rct) could be calculated from the best fit of the Randles electrical equivalent circuit. The Rct for bare PGE is 78.73 kΩ, and after the addition of Fe@g-C3N4, Rct is reduced to 19.41 kΩ on account of the higher rate of electron transfer between the redox probe and electrode surface. Reduction in Rct values on the deposition of Fe@g-C3N4 is clearly in agreement with CV results, and it further confirms the successful electrode deposition. Randles–Sevcik equation (Equation 3) was used to validate the improved catalytic response of modified PGE in terms of increased active electrode surface area [39]. Ip = (2.69 105)n3/2A0DR1/2v1/2 (3) where Ip is the anodic peak current of PGE/Fe@g-C3N4 (Ip = 1.38×10-4 A), and n is the number of electrons transferred in the redox reaction of CFX (n = 2). A / cm2 is the electroactive surface area to be determined, DR (cm2/s) is the solution diffusion coefficient (6×10-6 for [Fe (CN)6]4-). C0 (mol/cm3) is the concentration of the reaction species in the electrolyte (10-6 for [Fe (CN)6]4-), and ν (V/s) is the scan rate [40]. From this equation, the PGE/Fe@g-C3N4 active electrode surface area was calculated to 3.94 cm2, ensuring the high electrocatalytic surface area for the modified electrode [41]. Figure 3. A - CVs of 5 mM [Fe(CN)6]3-/4- solution obtained held at (a) bare PGE, (b) PGE/Fe@g-C3N4(3 µl); B - Nyquist diagrams of EIS data of (a) bare PGE, (b) PGE/Fe@g-C3N4 (3 µl) Effect of scan rate and pH Figure 4A shows the effect of the scan rate on the modified PGE/Fe@g-C3N4 for various scan rates like from 25 up to 375 mV s-1 in 10 μM solution of CFX. The oxidation peak current increases with the scan rate. Figure 4B shows the linear relationship between the current peak height and the square root of the scan rate with the regression coefficient of R2=0.9966. It is because the larger surface area facilitates faster electron transfer. Further, the regression analysis of log Ip versus log ν plot gives a relation of log Ip=0.7601 log ν + + 1.7926; R2= 0.9973 with the slope close to 1. The value of slope of log Ip versus log v confirms that the electrode process is dominantly diffusion-controlled [41]. H. S. Vedhavathi et al. J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 http://dx.doi.org/10.5599/jese.1112 65 To know the effect of pH on the electrochemical properties of the proposed sensor, the electro- chemical performance of the Fe@g-C3N4 decorated PGE electrode was investigated in different pHs in the range 3 - 9) in the presence of 10 μM CFX in PBS buffer solution. From Figure 4C, the current response of the sensor at different pH values reveals that the oxidation peak reached the maximum at pH 7.0. Therefore, pH 7.0 was adopted for all further analyses. Potential, V vs. SCE v1/2 / mV s-1)1/2 Figure 4. A - CVs of PGE/Fe@g-C3N4 in 0.1 M PBS (pH 7) containing 10 μM CFX at different scan rates; B - Plot of Anodic peak current vs. v-1/2 (c) Effect of pH on the response of PGE/Fe@gC3N4 modified electrode Electrochemical determination of CFX Figure 5A shows cyclic voltammograms of PGE/Fe@g-C3N4 in the presence of different concentrations of CFX (1-100 µM) in nitrogen saturated PBS (pH 7.0) at a scan rate of 50 mV s-1. With the increase in the concentration of CFX, the oxidation peak current proportionately increases at the Fe@g-C3N4 modified electrode. Oxidation of CFX is the electrochemical reaction occurring at the electrode/electrolyte interface, as shown in Scheme 1. The anodic peak current increased linearly from 1 to 100 µM of CFX with a correlation coefficient (R2) of 0.9675. Hence, this proves the authenticity of the sensor performance. The DPV experiment was conducted in 0.1 PBS solution in the potential range -0.1 to 1.5 V at smaller concentrations of CFX. Fig 5B illustrates the DPV current response from 1 to 1000 nM of CFX, and it is clear from Fig 5B that there is a linear relationship between current and CFX concentration with a correlation coefficient of R2 = 0.9968. The data from DPV experiments were used to compute the analytical quantities of the sensor i.e., the limit of detection (LOD), sensitivity, and quantification limit (LOQ) (equations 4, 5, and 6) [42]. C u rr e n t, m A http://dx.doi.org/10.5599/jese.1112 J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 CIPROFLOXACIN SENSOR 66 Potential, V vs. SCE Potential, V vs. SCE Figure 5. A - CVs of PGE/Fe@g-C3N4 electrode at various CFX concentrations (1 to 100 µM) in 0.1M PBS at pH 7, Inset: calibration plot of current Vs CFX concentration; B - DPVs of the PGE/Fe@g-C3N4 electrode in the presence of varying CFX concentrations (1 to 1000 nM) in 0.1 M PBS solution; Inset: peak current Vs CFX concentration Scheme 1. The electrocatalytic interaction at the interface is represented using chemical equations LOD = 3 / S (4) Sensitivity = I / A (5) LOQ = 10 / S (6) Here, σ represents the standard deviation of the blank, and S indicates the slope of the calibration plot (Inset: Figure 5B). The sensitivity, LOQ, linear range, and LOD determined using the above experimental data are 0.0596 µA mM-1cm-2, 0.0018 µM, 0.001 to 1.0 µM, and 5.4 nM, respectively. The overall analytical performance of the suggested Fe@g-C3N4 based sensor is in accordance with those already reported in the literature (Table 1) [43-47]. The superior performance characteristics exhibited by the PGE/Fe@g-C3N4 sensor are explicitly related to the composite matrix's synergic effects [48]. This suggests that the as-developed sensor can be a promising tool in the analysis of CFX. Table 1. Comparison of different electrochemical sensors for the determination of CFX Matrix Linear range of detection of CFX, µM LOD, nM References MgFe2O4-MWCNT/GCE 0.1 - 1000 10 [43] MWCNT-GCE 40 - 1000 6000 [44] TiO2/PB/AuNPs/CMK3/Nafion/GE 1 - 10 108 [45] β–CD/MWCNT/GC 10 - 80 5 [46] Boron doped diamond electrode 0.15 - 2.11 50 [47] PGE/Fe@g-C3N4 0.001-1.0 5.4 Proposed work Effects of interferents The proposed sensor was subjected to radical scavenging experiments to affirm its selectivity. The DPV responses were recorded after the additions of 50 µM of some common interferents like AA, UA, H. S. Vedhavathi et al. J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 http://dx.doi.org/10.5599/jese.1112 67 glucose, Ca2+, and Mg2+ to 10 µM CFX in 0.1 PBS buffer solution. The obtained DPV responses are exhibited in Figure 6. Figure 6 discloses no significant variation in the current peaks despite the residence of interferents, implying the selectivity and robustness of the sensor for field purposes. Potential, V vs. SCE Figure 6. DPVs of PGE/Fe@g-C3N4 electrode in the presence of 10 µM CFX and 50 µM additions of interferents such as uric acid, ascorbic acid, glucose, Ca2+, and Mg2+ in PBS buffer (pH 7.0) Repeatability, reproducibility, and stability These experiments are crucial to argue on the sensor’s practical applicability and reliability. The repeatability of the sensor performance was tested by measuring the CV response for 10 µM CFX in 0.1M PBS solution for twenty electro-analytical cycles between −0.1 to 1.5 V at a scan rate of 50 mV s-1. Further, we examined the reproducibility of the PGE/Fe@g-C3N4 electrodes by preparing a set of five distinct electrodes using a method described in the experimental section. The current response of these electrodes was measured by CV in 0.1 M PBS comprising 10 µM CFX. The estimated magnitude of the current response under identical circumstances depicts comparable electro- chemical properties for the sensor with a suitable shift in peak current, demonstrating an agreeable reproducibility as apparent from Fig 7A. Figure 7. A - The peak current measured for 10 µM CFX in 0.1M PBS (pH) with five separately tailored PGE/Fe@g-C3N4 to symbolize the sensor’s repeatability; B - Stability of the sensor in the presence of 10 µM CFX The storage stability of the PGE/Fe@g-C3N4 electrode had been determined steadily for up to twenty days, and the results are shown in Figure 7B. The current response for 10 µM CFX was http://dx.doi.org/10.5599/jese.1112 J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 CIPROFLOXACIN SENSOR 68 monitored at regular intervals, and the developed sensor retained 100, 98.01, 97.13, 97.02, and 96 % of the initial current response after 0, 5, 10, 15, and 20 days of storage, respectively, suggesting that the developed sensor exhibits a high level of stability in the detection of CFX. Real sample analysis The potency of the proposed sensor in practical applications was ascertained by analyzing CFX in human blood specimens. The actual samples were diluted with PBS in equal proportions, accompanied by spiking a known quantity of CFX to them. The responses were measured, and the observed percentage of the recovery is registered in Table 2. As noted, the results attained are good, with insignificant errors and hence the developed sensor might be used for the determination of CFX in biological fluids. It ratifies the generated sensor for primary specimen analysis. The worthy administration characteristics buttressed by the PGE/Fe@g-C3N4 sensor are completely ascribed to the synergic effect of the composite matrix. Table 2. Detection of CFX using proposed Fe@g-C3N4 sensor in blood samples Sample Amount of CFX spiked, nM Amount of CFX found, nM Recovery, % Accuracy, % A 100 98.9 100.5 100.1 B 100 100.6 99.7 99.8 Conclusion In the present work, we developed an electrochemical sensor using Fe@g-C3N4 composite as a working electrode matrix. The physical, chemical and electrochemical investigations of the Fe@g-C3N4 matrix confirmed the sensor's stability, conductivity, and electrocatalytic nature. It has the advantage of a low detection limit (5.4 nM) and a wide linear range (0.001-1.0 µM) in the detection of CFX. The offered sensor manifested an exceptional selectivity, sensitivity (0.0596 µA mM-1 cm-2) and reproducibility regarding the CFX determination. This sensor proved comparatively improved performance than various CFX sensors reported earlier in the literature. Remarkably, the success had interlaced by the cost-effective matrix and optimized material usage of the sensor. The parameters including storage stability, reproducibility, and repeatability were studied. The PGE/Fe@g-C3N4 sensor may be an alternative to the reported sensors for detecting and quantifying CFX in blood, environmental and industrial specimens. Acknowledgments: The authors successfully acknowledge the colossal support from the Department of Chemistry, JSS Science and Technology University, Mysuru-570006, India and Department of Chemistry and Principal, JSSATE Bengaluru, Karnataka, India References [1] J. S. Solomkin, H. H. Reinhart, E. P. Dellinger, J. M. Bohnen, O. D. Rotstein, S. B. Vogel, H. H. Simms, C. S. Hill, H. S. Bjornson, D. C. Haverstock, H. O. Coulter, R. M. Echols, Annals of Surgery 223 (1996) 303-315. https://doi.org/10.1097/00000658-199603000-00012 [2] A. R. Abadia, J. J. Aramayona, M. J. Muńoz, J. M. P. Delfina, M. A. Bregante, Journal of Vete- rinary Medicine 42 (1995) 505-511. https://doi.org/10.1111/j.1439-0442.1995.tb00405.x [3] R. Davis, A. Markham, J. A. Balfour, Drugs 51 (1996) 1019-1074. https://doi.org/10.2165/ 00003495-199651060-00010 [4] H. H. H. Mohammed, G. E.-D. A. A. Abuo-Rahma, S. H. Abbas, E. S. M. N. Abdelhafez, Current Medicinal Chemistry 26 (2018) 3132-3149. https://doi.org/10.2174/09298673256661802 14122944 https://www.ncbi.nlm.nih.gov/pubmed/?term=Reinhart%20HH%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Dellinger%20EP%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Bohnen%20JM%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Rotstein%20OD%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Vogel%20SB%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Simms%20HH%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Simms%20HH%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Hill%20CS%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Bjornson%20HS%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://www.ncbi.nlm.nih.gov/pubmed/?term=Haverstock%20DC%5BAuthor%5D&cauthor=true&cauthor_uid=8604912 https://doi.org/10.1097/00000658-199603000-00012 https://doi.org/10.1111/j.1439-0442.1995.tb00405.x https://doi.org/10.2165/00003495-199651060-00010 https://doi.org/10.2165/00003495-199651060-00010 https://doi.org/10.2174/0929867325666180214122944 https://doi.org/10.2174/0929867325666180214122944 H. S. Vedhavathi et al. J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 http://dx.doi.org/10.5599/jese.1112 69 [5] B. Huang, Y. Yin, L. Lu, H. Ding, L. Wang, T. Yu, J. J. Zhu, X. D. Zheng, Y. Z. Zhang, Journal of Zheijang University Science B 11 (2010) 812-818. https://doi.org/10.1007/s10967-010-0571-z [6] M. Tumini, O. Nagel, M. P. Molina, R. Althaus, International Dairy Journal 64 (2017) 9–13. https://doi.org/10.1016/j.idairyj.2016.08.008 [7] J. B. Xiao, C. S. Yang, F. L. Ren, X. Y. Jiang, M. Xu, Measurement Science and Technology 18 (2007) 859-866. https://doi.org/10.1088/0957-0233/18/3/039 [8] H. Karimi-Maleh, F. Karimi, L. Fu, A. L. Sanati, M. Alizadeh, C. Karaman, Y. Orooji, Journal of Hazardous Materials 423 (2022) 127058. https://doi.org/10.1016/j.jhazmat.2021.127058 [9] H. Karimi-Maleh, Y. Orooji, F. Karimi, M. Alizadeh, M. Baghayeri, J. Rouhi, S. Tajik, H. Beitollahi, S Agarwal, V. K. Gupta S. Rajendran, Biosensors and Bioelectronics 184 (2021) 113252. https://doi.org/10.1016/j.bios.2021.113252 [10] H. Karimi-Maleh, M. L. Yola, N. Atar, Y. Orooji, F. Karimi, P. S. Kumar, J. Rouhi, M. Baghayeri, Journal of Colloid and Interface Science 592 (2021) 174-185. https://doi.org/10.1016/j.jcis. 2021.02.066 [11] C. Karaman, O. Karaman, B. B. Yola, I. Ulker, N. Atar, M. L. Yola, New Journal of Chemistry 45 (2021) 11222-11233. https://doi.org/10.1039/D1NJ02293H [12] C. Karaman, O. Karaman, N. Atar, M. L. Yola, Microchimica Acta 188 (2021) 182. https://doi.org/10.1007/s00604-021-04838-6 [13] R. N. Goyal, V. K. Gupta, S. Chatterjee, Electrochimica Acta 53 (2008) 5354-5360. https://doi.org/10.1016/j.electacta.2008.02.059 [14] R. N. Goyal, V. K. Gupta, N. Bachheti, Analytica Chimica Acta 597 (2007) 82-89. https://doi.org/ 10.1016/j.aca.2007.06.017 [15] H. Bagheri, A. Shirzadmehr, M. Rezaei, Journal of Molecular Liquids 212 (2015) 96-102. https://doi.org/10.1016/j.molliq.2015.09.005 [16] H. Bagheri, A. Afkhami, Y. Panahi, H. Khoshsafar, A. Shirzadmehr, Materials Science and Engineering C 37 (2014) 264-270. https://doi.org/10.1016/j.msec.2014.01.023 [17] N. Ozcan, C. Karaman, N. Atar, O. Karaman, M. L. Yola, Journal of Solid State Science and Technology 9(12) (2020) 121010. https://doi.org/10.1149/2162-8777/abd149 [18] C. P. Boke, O. Karaman, H. Medetalibeyoglu, C. Karaman, N. Atar, M. L. Yola, Microchemical Journal 157 (2020) 105012. https://doi.org/10.1016/j.microc.2020.105012 [19] M. Baghayeri, H. Veisi, H. Veisi, B. Maleki, H. Karimi-Maleh, H. Beitollahi, RSC Advances 4(91) (2014) 49595-49604. https://doi.org/10.1039/C4RA08536A [20] M. A. Khalilzadeh, H. Karimi-Maleh, A. Amiri, F. Gholami, Chinese Chemical Letters 21(12) (2010) 1467-1470. https://doi.org/10.1016/j.cclet.2010.06.020 [21] A. A. Ensafi, E. Khoddami, B. Rezaei, H. Karimi-maleh, Colloids and Surfaces B 81(1) (2010) 42- 49. https://oi.org/10.1016/j.colsurfb.2010.06.020 [22] H. Medetalibeyoğlu, M. Beytur, S. Manap, C. Karaman, F. Kardaş, O. Akyıldırım, M. L. Yola, ECS Journal of Solid State Science and Technology 9(10) (2020) 101006. https://doi.org/10.1149/ 2162-8777/abbe6a [23] C. Somaye, A. Mohammad H. Taher, H. Karimi-Maleh, K. Fatmeh, S. N. Mehdi, A. Marzieh, A.O. Amani, E. Nevin, K. Praveen, R. Yegya, K. Ceren, Chemosphere 287(2) (2022) 132187. https://doi.org/10.1016/j.chemosphere.2021. 132187 [24] A. A. ENSAFI, D. T. Samira, K. M. Hassan, Analytical Sciences 27(4) (2011) 409. https://doi.org/ 10.2116/analsci.7.409 [25] J. A. Cruz-Navarro, F. Hernandez-Garcia, G. A. Alvarez Romero, Coordination Chemistry Reviews, 412 (2020) 213263. https://doi.org/10.1016/j.ccr.2020.213263. [26] J. A. Cruz-Navarro, F. Hernández-García, L. H. Mendoza-Huizar, V. Salazar-Pereda, J. Á. Cobos- Murcia, R. Colorado-Peralta, G. A. Álvarez-Romero, Solids 2 (2021) 212-231. https://doi.org/ 10.3390/solids2020014 http://dx.doi.org/10.5599/jese.1112 https://doi.org/10.1007/s10967-010-0571-z https://doi.org/‌10.1016/j.idairyj.2016.08.008 https://doi.org/10.1088/0957-0233/18/3/039 https://doi.org/10.1016/j.jhazmat.2021.127058 https://doi.org/10.1016/j.bios.2021.113252 https://pubs.rsc.org/en/results?searchtext=Author%3ACeren%20Karaman https://pubs.rsc.org/en/results?searchtext=Author%3AOnur%20Karaman https://pubs.rsc.org/en/results?searchtext=Author%3ABahar%20Banko%C4%9Flu%20Yola https://pubs.rsc.org/en/results?searchtext=Author%3A%C4%B0zzet%20%C3%9Clker https://pubs.rsc.org/en/results?searchtext=Author%3ANecip%20Atar https://doi.org/10.1039/D1NJ02293H https://pubs.rsc.org/en/results?searchtext=Author%3ACeren%20Karaman https://doi.org/10.1007/s00604-021-04838-6 https://doi.org/10.1016/j.electacta.2008.02.059 https://doi.org/10.1016/‌j.aca.2007.06.017 https://doi.org/10.1016/‌j.aca.2007.06.017 https://doi.org/10.1016/j.molliq.2015.09.005 https://doi.org/10.1149/2162-8777/abd149 https://doi.org/10.1016/j.microc.2020.105012 https://doi.org/10.1039/C4RA08536A https://doi.org/10.1016/j.cclet.2010.06.020 https://doi.org/10.1016/j.colsurfb.2010.06.020 https://doi.org/10.1149/2162-8777/abbe6a https://doi.org/10.1149/2162-8777/abbe6a https://doi.org/10.1016/‌j.chemosphe‌re.20‌21.%20132187 https://doi.org/10.2116/analsci.7.409 https://doi.org/10.2116/analsci.7.409 https://www.sciencedirect.com/science/journal/00108545 https://www.sciencedirect.com/science/journal/00108545 https://doi.org/10.1016/j.ccr.2020.213263 https://doi.org/10.3390/solids2020014 https://doi.org/10.3390/solids2020014 J. Electrochem. Sci. Eng. 12(1) (2022) 59-70 CIPROFLOXACIN SENSOR 70 [27] S. Sandeep, A. S. Santhosh, N. K. Swamy, G. S. Suresh, J. S. Melo, N. A. Chamaraja, New Journal of Chemistry 42 (2018) 16620–16629. https://doi.org/10.1039/C8NJ02325E [28] H. Ishiguro, Y. Yao, R. Nakano, M. Hara, K. Sunada, K. Hashimoto, J. Kajioka, A. Fujishima, Y. Kubota, Applied Catalysis B 129 (2013) 56-61. https://doi.org/10.1016/j.apcatb.2012.09.012 [29] K. Sunada, T. Watanabe, K. Hashimoto, Environmental Science & Technology 37 (2003) 4785- 4789. https://doi.org/10.1021/es034106g [30] J. Liu, T. Zhang, Z. Wang, G. Dawson, W. Chen, Journal of Materials Chemistry 21 (2011) 14398. https://doi.org/10.1039/C1JM12620B [31] F. Goettmann, A. Fischer, M. Antonietti, A. Thomas, Angewandte Chemie 45 (2006) 4467-4471. https://doi.org/10.1002/anie.200600412 [32] X. Zhang, X. Xie, H. Wang, J. Zhang, B. Pan, Y. Xie, Journal of the American Chemical Society 135 (2013) 18–21. https://doi.org/10.1021/ja308249k [33] X. Wang, X. Chen, A. Thomas, X. Fu, M. Antonietti, Advanced Materials 21 (2009) 1609-1612. https://doi.org/10.1002/adma.200802627 [34] G. Zhang, J. Zhang, M. Zhang, X. Wang, Journal of Materials Chemistry 22 (2012) 8083. https://doi.org/10.1039/C2JM00097K [35] S. C. Yan, Z. S. Li, Z. G. Zou, Langmuir 25 (2009) 10397-10401. https://doi.org/10.1021/la900923z [36] K. S. Siddegowda, B. Mahesh, N. A. Chamaraja, B. Roopashree, N. Kumara Swamy, G. S. Nanjundswamy, Electroanalysis 32 (2020) 2183–2192. https://doi.org/10.1002/elan.202000010 [37] Y. Li, J. Zhang, Q. Wang, Y. Jin, D. Huang, Q. Cui, G. Zou, Journal of Physical Chemistry B 114 (2010) 9429-9434. https://doi.org/10.1021/jp103729c [38] S. Sarkar, N. Kamboj, M. Das, T. Purkait, A. Biswas, R. S. Dey, Inorganic Chemistry 59 (2020) 1332-1339. https://doi.org/10.1021/acs.inorgchem.9b03042 [39] B. P. Sanjay, N. Kumara Swamy, S. R. Yashas, S. Sandeep, Journal of the Electrochemical Society 168 (2021) 076511. https://doi.org/10.1149/1945-7111/ac1495P [40] P. Zhu Y. Zhao, Materials Chemistry and Physics 233 (2019) 60-67. https://doi.org/10.1016/ j.matchemphys.2019.05.034 [41] N. P. Shetti, S. J. Malode, S. T. Nandibewoor, Analytical Methods 7 (2015) 8673-8682. https://doi.org/10.1039/C5AY01619C [42] B. P. Sanjay, S. Sandeep, A. S. Santhosh, C. S. Karthik, D. N. Varun, N. Kumara Swamy, P. Mallu, K. S. Nithin, J. R. Rajabathar, K. Muthusamy, Chemosphere 287 (2022) 132153. https://doi.org/10.1016/j.chemosphere.2021.132153 [43] S. R. Yashas, S. Sandeep, B. P. Shivakumar, N. K. Swamy, Analytical Methods 11 (2019) 4511- 4519. https://doi.org/10.1039/C9AY01468C [44] A. A. Ensafi, A. R. Allafchian, R. Mohammadzadeh, Analytical Sciences 28 (2012) 705-710 (2012). https://doi.org/10.2116/analsci.28.705 [45] L. Fotouhi, M. Alahyari, Colloids Surfaces B Biointerfaces 81 (2010) 110-114. https://doi.org/ 10.1016/j.colsurfb.2010.06.030 [46] A. Pollap, K. Baran, N. Kuszewska, J. Kochana, Journal of Electroanalytical Chemistry 878 (2020) 114574. https://doi.org/10.1016/j.jelechem.2020.114574 [47] J. M. Garrido, M. Melle-Franco, K. Strutynski, F. Borges, C. M. Brett, E. M. P. Garrido, Journal of Environmental Science and Health 52 (2017) 313-319. https://doi.org/10.1080/10934529. 2016.1258864 [48] K. S. Siddegowda, B. Mahesh, N. Kumara Swamy, Sensors and Actuators A 280 (2018) 277- 286. https://doi.org/10.1016/j.sna.2018.07.049 ©2021 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (https://creativecommons.org/licenses/by/4.0/) https://doi.org/10.1039/C8NJ02325E https://doi.org/10.1016/j.apcatb.2012.09.012 https://doi.org/10.1021/es034106g https://doi.org/‌10.1039/C1JM12620B https://doi.org/‌10.1002/anie.200600412 https://doi.org/10.1021/ja308249k https://doi.org/10.1002/adma.200802627 https://doi.org/10.1039/‌C2JM00097K https://doi.org/10.1039/‌C2JM00097K https://doi.org/10.1021/jp103729c https://doi.org/10.1021/acs.inorgchem.9b03042 https://doi.org/10.1149/1945-7111/ac1495 https://doi.org/10.1016/j.matchemphys.2019.05.034 https://doi.org/10.1016/j.matchemphys.2019.05.034 https://doi.org/‌10.1039/‌C5AY01619C https://doi.org/10.1016/j.chemo‌sphere.2021.‌132153 https://doi.org/10.1016/j.chemo‌sphere.2021.‌132153 https://doi.org/10.1039/C9AY01468C https://doi.org/10.2116/analsci.28.705 https://doi.org/10.1016/j.jelechem.2020.114574 https://doi.org/10.1080/‌10934529.‌2016.1258864 https://doi.org/10.1080/‌10934529.‌2016.1258864 https://doi.org/10.1016/j.sna.2018.07.049 https://creativecommons.org/licenses/by/4.0/)