A hybrid composite of Polypyrole/carboxymethyl cellulose/MWCNT fiber with antimicrobial properties and Sb3+ determination on a glassy carbon electrode

ABSTRACT

In order to prepare fiber-type nanohybrid composites for electrochemical and antimicrobial applications, polypyrrole was combined with carboxymethylcellulose and multiwalled carbon nanotubes (PPy/CMC/MWCNTS). These composite materials were synthesized using ultrasonication and in situ polymerization. By using analytical methods, the structure and morphology of the synthesized nanohybrid composite material were confirmed. Slurry of fiber-type PPY/CMC/MWCNT composites synthesized in ethanol was deposited as a thin-uniform layer with conductive nafion (5% ethanolic solution of nafion) binder. Based on electrochemical measurements in a phosphate buffer medium, Sb³⁺ ions have linear responses between 0.1 nM and 0.01 mM, which is known as linear dynamic range (LDR). A sensor’s sensitivity (22.4304 µAµM⁻¹cm⁻²) is calculated using the LDR slope by considering the GCE surface area (0.0316 cm²). A signal-to-noise ratio of 3 is used to estimate the lower limit of detection which is equal to 96.82 ± 4.84 pM. Moreover, the antibacterial activity of the obtained polypyrrole/carboxymethylcellulose/MWCNT composite has also been evaluated “against Gram-positive bacteria B. subtilis along with S. aureus, as well as Gram-negative bacteria, P. aeruginosa along with Escherichia coli by utilizing” autoclave of agar media. In electrochemical analysis, the proposed Sb³⁺ cationic sensor exhibits appreciable reproducibility, response time, stability, and outstanding outcome in analysis of real samples. In the field of metal ion sensor, this reliable method might be prospective in the recent future.

摘要

为了制备用于电化学和抗菌应用的纤维型纳米杂化复合材料, 将聚吡咯与羧甲基纤维素和多壁碳纳米管（PPy/CMC/MWCNTS）相结合. 这些复合材料是通过超声处理和原位聚合合成的. 通过分析方法, 证实了合成的纳米杂化复合材料的结构和形态. 将在乙醇中合成的纤维型PPY/CMC/MWCNT复合材料浆料与导电nafion（5%的nafion乙醇溶液）粘合剂沉积为均匀的薄层. 根据在磷酸盐缓冲介质中的电化学测量,Sb3+离子具有0.1 nM和0.01 mM之间的线性响应, 这被称为线性动态范围（LDR）. 通过考虑GCE表面积（0.0316 cm2）, 使用LDR斜率计算传感器的灵敏度（22.4304 µAµM-1 cm-2）. 使用3的信噪比来估计检测的下限,该下限相等96.82 ± 4.84 pM. 此外,还评估了所获得的聚吡咯/羧甲基纤维素/MWCNT复合物的抗菌活性,“通过使用”琼脂培养基的高压釜“对抗革兰氏阳性菌枯草芽孢杆菌和金黄色葡萄球菌, 以及革兰氏阴性菌、铜绿假单胞菌和大肠杆菌.” 在电化学分析中,所提出的Sb3+阳离子传感器在实际样品的分析中表现出可观的再现性、响应时间、稳定性和出色的结果. 在金属离子传感器领域,这种可靠的方法在最近的将来可能是有前景的.

KEYWORDS:

• Composites PPY/CMC/MWCNTS Fiber
• Sb³⁺ ion sensor
• electrochemical method
• glassy carbon electrode
• antimicrobial study
• environmental safety

关键词:

• 复合材料PPY/CMC/MWCNTS纤维
• Sb3+离子传感器
• 电化学方法
• 玻璃碳电极
• 抗菌研究
• 环境安全

Introduction

Our daily lives involve a wide variety of nano composites, depending on our needs, which are also found in nature due to their polymer content. Biopolymers such as cellulose are prevalent on earth and present in animals and plants. Many different resources have been used to extract cellulose, including pineapples, corn cobs, soy hulls, hemp fibers, rice husks, etc. (Costa et al. 2013; Dai, Fan, and Collins 2013; Johar, Ahmad, and Dufresne 2012; Silverio et al. 2013). It is the most abundant renewable organic raw material in the world and a biodegradable complex polysaccharide. Natural linear homopolysaccharides (polysaccharides) like cellulose are made up of D-glucopyranose rings linked by β-(1–4)-glycosidic chains (Nishino 2004). Cellulose has some limitations in its application due to its strong hydrogen bonding, including its difficulty in solubilizing. It has been proposed to overcome the problem of non-derivatizing solvents for cellulose, which do not interact chemically with the hydroxyl groups (Pinkert et al. 2009; Vitz et al. 2009). There have been several suggestions for overcoming this problem (Gousse et al. 2002, 2004; Grunert and Winter 2002; Ifuku et al. 2007; Yuan et al. 2006). Several methods have been proposed for chemically modifying cellulosic fillers, including using acetic anhydride, alkenyl succinic anhydrides, chlorosilanes, or hexamethyldisilazane. It was the first-time cellulose whisker-based composites were produced (Favier, Chanzy, and Cavaille 1995). In the following years, many more studies were carried out using polylactide (Espino-Perez et al. 2013), polymethylmethacrylate (Dong et al. 2012; Fahma et al. 2013; Thakur, Singh, and Misra 2011) and polyvinyl acetate (Garcia de Rodriguez, Thielemans, and Dufresne 2006).

In CMC, some carboxymethyl groups are attached to hydroxyl groups in cellulose. Sodium carboxymethyl groups give cellulose its soluble and chemically reactive properties (Jackson et al. 2011; Tongdesoontorn et al. 2011). The properties of CMC include chemical resistance, membrane formation, and binding. A variety of technological applications can be derived from its interesting properties. Due to its hydroxyl groups and bonded water molecules, CMC is soluble in water and environmentally friendly. A carbon nanotube has a much finer scale than a common fiber. It’s made up of fullerene hemispheres that are rolled around graphene sheets (Foldyna, Foldyna, and Zeleňák 2016). CNTs show a lot of interesting properties due to sp2 hybridization of carbon – carbon bonds. Recently, dispersing carbon nanomaterials in nanocellulosic matrixes has enabled the development of functional hybrid composite (Bacakova et al. 2020; Chen et al. 2018; Du et al. 2017; Durairaj et al. 2021; Koga et al. 2013; Nguyen et al. 2019; Wang et al. 2020; Yu et al. 2020). Researcher have found that MWCNTs that contain a high concentration of negatively charged sulfate functional groups exhibit different behavior in the composite electrode when attached to negatively charged sulfate molecules (Durairaj et al. 2019). Over the past few years, nanocellulose/nanocarbon composites have become increasingly popular for electrochemical applications (Anirudhan et al. 2018; Khan 2020; Ortolani et al. 2019; Shalauddin et al. 2019; Zhao et al. 2020).Various anthropogenic sources contain antimony (Sb) as a trace element in the environment. In the mining, processing, and casting industries including pewter and tin, this element is extremely abundant. The element is also used in solder, lead storage batteries, bearings, sheet metal, castings, and pewter alloys. As well as being an excellent fire retardant, antimony can be found in the formulation of textiles, plastics, paints, paper, and rubber. It is antimony trisulfide that produces explosives, antimony salts, pigments, and ruby glass (Nam, Yang, and An 2009; Zanetti et al. 2002). The semiconductor industry uses antimony to produce optoelectrical devices and integrated circuits (Bustamante et al. 1997) in the form of gallium antimonide (GaSb) and indium antimonide (InSb). It has been found that antimony cation (Sb³⁺) can be used to treat AIDs, HPA-23 and tropical diseases (billarziosis, leishmaniasis, trypanosomiasis, and schistosomiasis) (Lonard and Gerber 1996; Rozenbaum et al. 1985). Environmental contamination is a high risk due to antimony’s excessive industrial use. When humans are exposed to antimony they may suffer damage to their organs, specifically their hearts, livers, kidneys, and lungs. Antimony may cause DNA damage or cancer through long-term occupational exposure (Kanematsu, Hara, and Kada 1980; Kuroda et al. 1991). Long term occupational exposure through drinking water or inhalation has been reported as causing lung tumors (Nikula et al. 1995). Trivalent antimony has been linked to cardiovascular disease, hemolytic anemia, and acute renal failure (Su et al. 2014; Vinhal et al. 2016). To ensure a safe and healthy workplace, antimony monitoring should also be implemented in the drinking water supply. The detection of Sb3+ cations has been carried out using conventional analytical methods, including capillary electrophoresis (Casiot et al. 1998), UV-Vis spectrophotometer (El-Sharjawy and Amin 2016), inductively coupled plasma optical emission spectrometry (Hansen and Pergantis 2006), laser-induced fluorescence (Enger et al. 1995), spectrofluorimetric (Yu et al. 2009) and HPLC-HGAFS (high-performance liquid chromatography coupled with hydride generation and atomic fluorescence spectrometry (De Gregori et al. 2007). The electrochemical (I-V) method is becoming more and more popular because it has several disadvantages compared to these conventional methods such as being expensive, heavy, complicated, time-consuming, and difficult to import. There have been numerous research studies to detect numerous heavy metal ions using an electrochemical approach (Hussein et al. 2018, 2019; Khan et al. 2016, 2017, 2018, 2019; Rahman et al. 2018a, 2018b). and these studies are based on organometallic composites. Thus, the purpose of this study is to develop an electrochemical sensor based on biodegradable composites for the detection of heavy and environmentally unsafe toxic metal ions. The combination of cellulose and carbon nanoparticles possesses several advantages over materials containing cellulose nanoparticles or carbon nanoparticles alone. In addition to increasing the mechanical strength of nanocellulose materials, adding carbon nanoparticles can further enhance their properties (Liu et al. 2017; Zhu, Liu, and Mathew 2017). Adding these compounds to diamond nanoparticles, graphene, carbon nanotubes, or graphene-containing nanocellulose can improve their electrical properties (Abol-Fotouh et al. 2019; Buzid et al. 2019; Siljander et al. 2018). A variety of industrial and technological applications can be made with nanocellulose/nanocarbon composites, such as the purification of water and the separation of atoms and molecules (Alizadehgiashi et al. 2018; Liang et al. 2019; Vetrivel et al. 2018). A polypyrrole/polysaccharide composite system can be considered an interesting area of research because of its low cost, stable redox properties, and interesting nanomorphologies. A conjugated polymer that is most prominent is polypyrrole, which is a promising conducting polymer in electronic, biological, and medical applications because it can be easily polymerized, stable in the environment, and highly conductible by altering doping levels (Ferenets and Harlin 2007). A nanohybrid composite of polypyrrole, carboxymethylcellulose, and multiwalled carbon nanotubes was developed for antimicrobial and electrochemical applications. A composite was confirmed using structural, morphological, and electrochemical sensor applications developed by GCE. An electrochemical sensor for detecting Sb³⁺ cation has been developed by electrochemically coating biodegradable composites of PPY/CMC/MWCNTS with GCE. Five analytical characteristics are calculated for the selective detection of antimony with fabricated sensor probe such as sensitivity, LDR, DL, reproducibility, and response time. A Sb³⁺ ion sensor was evaluated by analyzing real samples, which are collected from different locations of environmental sources. Consequently, it is the easiest and most facile method of constructing a metal ionic sensor probe based on PPY/CMC/MWCNTS/GCE, which could also demonstrate to be a novel approach for advancing metal ion sensors in a broad scale in the fields of environmental and health.

Experimental section

Materials and methods

The cellulose used was carboxymethyl cellulose (Fluka) that was not purified further. MWCNT was received from Applied Science Innovations, India. Nitric acid, and ethanol. The study required the use of chemicals of analytical grade, including HgCl₂, Y(NO₃)₃, Ba(NO₃)₂, MgCl₂, AsCl₃, SnCl₂, SbCl₃, FeCl₃, CrCl₃ and AgNO₃ were parched from Sigma-Aldrich company (USA) and without further refinement used directly. Nafion (5% suspension in ethanol) was used in this study in combination with monosodium and disodium phosphate buffers. PPy/CMC/MWCNT composite morphology has been obtained by using a JEOL JSM-7610 FPLUS model USIF, AMU Aligarh at various amplifications. The nutrient agar plate was prepared, by the pour plate technique after the autoclave sterilizer machine (JSR Autoclave, JSAC-80 Korea). The Keithley electrometer which is fabricated in the USA was applied to electrochemical (I-V) analysis.

Synthesized of PPY/CMC/MWCNT composite

During this study, pyrrole was polymerized in situ in the presence of a dispersion of CMC/MWCNT in water. PPY/CMC/MWCNT composites were prepared using the same CMC/MWCNTs in our previous studies (Khan 2020). The CMC/MWCNT composite was first dispersed in de-ionized water for 50 ml using a sonicator. Pyrrole was then added to the CMC/MWCNT composite under sonication for 1 hour to load the pyrrole into the CMC/MWCNT composite. The reaction solution was mixed with 30 mL of FeCl₃ solution in DDW to polymerize pyrrole in situ within CMC/MWCNT composite. As a result of filtration, washes with ethanol and distilled water, and transfer to an alumina crucible, the precipitate was formed into a hybrid composite. After this, the PPY/CMC/MWCNT was placed in an oven overnight to dry. PPY/CMC/MWCNT had been sufficiently characterized and was ready for use.

Assessment of antibacterial activity of PPY/CMC/MWCNT composite

Zone inhibition assay

The synthetic materials were tested for their antibacterial properties against Gram-positive bacteria S. aeruginosa and B. subtilis, and Gram-negative bacteria P. aeruginosa and E. coli. These bacterial cultures were grown in Luria Bertani broth, and a loopful culture was inoculated into the 100 ml liquid broth and brooded in a rotatory incubator for optimum growth acquisition. A fresh culture of each strain was obtained by the re-culturing method in the same media and optimum condition. The nutrient agar plate was prepared, by the pour plate technique after the autoclave of media at the ideal temperature of 121°C and pressure at 15 psi for 20 min in a sterilizer machine (JSR Autoclave, JSAC-80 Korea). After the media pouring into the Petri plates wait 10 min, the media becomes solidified. From the fresh culture tubes, each bacterial strain was spread on the media plates and held up for 10 min to retain the way of life by the plate’s media. Further, 6 mm wells were set up in each plate for an explicit sum of 25, 50, and 100 µg suspensions of the newly synthesized compound were added into the wells. The compound from the media wells becomes diffused into the surrounding media and uncovers the antimicrobial activity around the wells after the optimum brooding overnight at 37°C. Standard antibiotic amoxicillin was utilized as a control.

PPY/CMC/MWCNT composite MIC and MBC determination

The newly synthesized MWCNT/cellulose composite effect on bacterial growth in broth was assayed and determined the minimum inhibitory concentration and minimum bactericidal concentration. Newly synthesized MWCNT/cellulose composite was suspended in the mili Q water, and vertex was further utilized as an antibacterial agent against selected test microorganisms. To determine whether bacteria can survive or not against a test agent or composite material, the broth dilution method is commonly used. The synthesized composite material was supplemented at a varying concentration from 0 to 100 µg/ml. First, 100 ml broth media was set up into twenty 500 ml flasks and autoclaved concurring measures techniques in the sterilizer. Further, the four sets taught by test strains and 25 to 100 µg/ml amount of compound were supplemented in the medium and incubated at a rotatory incubator at 37°C for overnight. The bacterial culture was standardized according to the McFarland 0.5 protocol for testing the antimicrobial susceptibility of compounds. The serial dilutions of the composite materials were done with a broth medium and then 5 × 10⁶ CFU containing bacterial culture was inoculated for a 16 h incubation period. After the incubation period, bacterial culture turbidity and plate count were measured.

Fabrication of working electrode by PPY/CMC/MWCNTS composite

This study focuses on developing a working electrode for the proposed sensor. A thick fiber-type slurry of synthesized PPY/CMC/MWCNTS NCs was suspended in ethanol, formed into a thin uniform layer, and deposited on GCE (surface area 0.0316 cm²). Once the modified GCE had dried with PPY/CMC/MWCNTS, Nafion was added as a conductor coating binder between composite and electrode. An hour was needed for the product to completely dry in the oven. Keithley electrometers were used to assemble the electrochemical sensor, with the modified GCE and Pt wires connected in series. In order to implement the desired analyte, a sequence of solutions ranging in concentration from 0.1 mM to 0.1 nM were prepared from the stock (0.1 mM) solution of Sb³⁺ ion. Sb³⁺ ion concentration vs. current was explored in a plot known as calibration. GCE’s surface area and the slope of the calibration curve were used to calculate the sensitivity. A signal-to-noise ratio of 3 was used to estimate the sensor’s detection limit. I-V analysis was carried out using 10.0 mL of buffer solution in the detection beaker throughout the investigation. Keithley electrometer-based sensors rely on two electrodes for their operation.

Results and discussion

In Figure 1, the steps for the preparation of PPY/CMC/MWCNTS are shown. PPY is produced by the oxidative chemical polymerization of ferric chloride in an aqueous solution that contains CMC/MWCNTS. In the process of separating the solution from the reaction product, ethanol and distilled water were used to wash the product. This was done to yield a dark dispersion that could then be precipitated. After drying and washing in ethanol, it was examined by SEM. As-synthesized materials can be identified by analyzing their shape, size, growth, and morphology through SEM. SEM graphs of PPY/CMC/MWCNTS composites (Figure 2) show that the particles are mostly spherical, like PPY that settles on CMC/MWCNTS fibers in irregular clusters. PPY molecules conformation and rearrangement are greatly influenced by the extent of hydrogen bonding between and within a composite material. A PPY chain forms a pi–pi stack in sp² carbon of MWCNTs when it is attached to carboxylic and hydroxyl groups, but it forms inter/intra hydrogen bonds between its hydrogen atoms in CMC molecules (Janaki et al. 2013). In order to understand material properties, XRD techniques are widely used. The results of XRD analysis of the composite PPY/CMC/MWCNTS are shown in Figure 3. The sharp peaks at 2θ = 25.8° indicate parallel and perpendicular lattice periodicity in the composite and might indicate a certain degree of crystallinity. In accordance with previous studies (Zavadskii 2004), PPy/CMC/MWCNT composite exhibits broad and weak peaks due to its PPY shell layers. Higher peaks at 2θ = 42–44◦ may be attributed to MWCNTs, indicating successful synthesis of PPY/CMC/MWCNTS composite (El-Shishtawy et al. 2018; Khan et al. 2019).

Figure 1. Schematic representation of electrochemical detection by PPY/CMC/MWCNTS Cs/binder/GCE, as well as the antibacterial activity by PPY/CMC/MWCNTS composite.

Figure 2. SEM images of the PPY/CMC/MWCNTS composite.

Figure 3. The XRD pattern of the PPY/CMC/MWCNTS composite.

Electrochemical detection of Sb³⁺ with PPY/CMC/MWCNTS NCs/binder/GCE

PPY/CMC/MWCNTS NCs were successfully synthesized and used to develop an electrochemical sensor selective to Sb³⁺ in phosphate buffer with pH 7.0. NCs in ethanol were deposited as thin films onto the flat top of the GCE (0.0316 cm²) with a conducting nafion (5% suspension in ethanol) binder to improve its stability. Nafion, known as a conductive copolymer, has been applied as a binding agent. This has improved the binding strength between NCs and GCE, as well as increased the electron transfer rate of working sensors. Previous reports (Alam et al. 2019; Rahman, Alam, and Asiri 2019) have reported similar observations relating to the detection of various metal ions and chemicals using the I-V method. PPY/CMC/MWCNTS NCs/binder/GCE thin films are electrochemically analyzed at the applied potential by measuring the resulted current and holding time in the electrometer at 1.0 s. This study aims to detect selectivity first. An electrochemical sensor based on PPY/CMC/MWCNTS NCs/binder/GCE was recently assembled to analyze a number of heavy metal ions of 0.1 M concentration, including Hg²⁺, Y³⁺, Ba²⁺, Mg²⁺, As³⁺, Sn²⁺, Sb³⁺, Fe³⁺, Cr³⁺, and Ag⁺ in phosphate buffer medium of pH 7.0 as illustrated in Figure 4(a). As shown in Figure 4(a), considering that the antimony (Sb³⁺) ion exhibits a very high I-V response, sensor assembly toxic metal ions may be defined as selective toxic metal ions. The I-V analysis of the Sb³⁺ ion was carried out with various concentrations ranging from 0.1 nM to 0.1 mM, and the results are shown in Figure 4(b).Fig. 4(b) shows that the measurements were performed in a potential range of 0 ~ +1.5 V in a phosphate buffer of pH 7.0. There was a sequence of I-V responses from lower to higher concentrations of Sb³⁺ ions. As a result, it has been shown that the I-V responses during the analysis of Sb3+ are directly related to its concentration, and an electrochemical approach has been used to detect a wide range of toxic chemicals in previous articles of ours (Karim et al. 2019; Rahman et al. 2018).

Figure 4. Analysing the electrochemical behavior of PPY/CMC/MWCNTS Cs in the presence of binders/GCEs. (a) Using 0.1 µM concentration of analytes at potential 0 ~ +1.5 V, (b) the electrochemical response (I-V) to Sb³⁺, (c) the calibration of the Sb³⁺ ion sensor, (d) current vs. log[Sb³⁺] ion.

Based on the linear relationship of current vs. concentration of Sb³⁺ ions shown in Figure 4(c), a calibration plot was constructed to determine the calibration of the Sb³⁺ cationic sensor. To explore the current vs. concentration of Sb³⁺ ions, the currents at potential +1.5 V from the experiment shown in Figure 4(b), are collected. Figure 4(c) clearly displays linear dynamic range (LDR) defined as data scattered between 0.1 nM and 0.01 mM on a line, and the equation of this line can be expressed by the equation y = 0.7088×+35.842. Based on the calibration curve slope (0.7088 µAµM⁻¹) and the area of the GCE (0.0316 cm²), the calculated sensitivity is 22.4304 AM⁻¹cm⁻², which is an impressive value. In an experiment with a signal-to-noise ratio of 3, 96.82 ± 4.84 pM was calculated as the detection limit and a satisfactory lower limit of detection was determined.

Based on PPY/CMC/MWCNTS NCs/binders/GCE, the proposed Sb³⁺ ion sensor must prove to be reliable. As demonstrated in Figure 5, various experiments were conducted to compare the I-V responses of coated and bare GCEs, response time, reproducibility, and long-term performance under identical conditions. An electrochemical study with 0.01 M Sb³⁺ ion solution at 0.1 V potential in phosphate buffer was performed with coated and bare GCEs in Figure 5(a). Obviously, the GCE coated with PPY/CMC/MWCNTS NCs shows the highest intensity. It is very relevant to measure the response time of an electrochemical sensor in order to evaluate its efficiency. It is a measure of the time required for a full I-V response to develop at steady state. Therefore, the response time of Sb³⁺ ion sensor was performed with 0.1 µM Sb³⁺ ion solution in phosphate buffer medium as illustrated in Figure 5(b). As illustrated in Figure 5(b), the projected Sb³⁺ ion sensor has a very short response time to analyze Sb³⁺ ions.

Figure 5. Based on PPY/CMC/MWCNTS Cs/binders/GCE, tests are performed to establish the reliability of the Sb³⁺ ion sensor. Among them are: (a) an I-V comparison between coated and bare GCE for 0.1 M Sb³⁺ ion in phosphate buffer medium, (b) an evaluation of the proposed Sb³⁺ ion sensor with 0.1 M Sb³⁺ ion, (c) a reproducibility test, and (d) a long-term performance evaluation.

Response of electrochemical sensors must be reproducible, which is defined as the ability to produce similar I-V responses under identical conditions. In the phosphate buffer medium, pH 7.0, 0.1 µM Sb³⁺ ions were used as a sensor calibration sample for a reproducibility analysis in Figure 5(c). Seven consecutive runs produced no distinctive or dispersed results and the coated GCE returned the same results after each run, even after being washed. As a result of this test, it has been confirmed that all real samples can be used to measure the selective Sb³⁺ ions. In terms of percentage of relative standard deviation (%RSD), the precision of the I-V responses of the reproducibility test has been measured within 0 to +1.5 V potential and is found as 0.56%. The performance of real-time applications must be high for a long period of time, while maintaining the same level of precision. A reproducibility test was performed on the proposed sensor under identical conditions for around 7 days. The observation from Figure 5(d) shows the same result as in the reproducibility performances. Therefore, the Sb³⁺ ion can be assumed to be stable for a long period of time in the phosphate buffer phase. The scientific acceptability of this study is demonstrated and presented in Table 1, which represents the analytical performance of the Sb³⁺ ion sensor, including its sensitivity, LDR, and DL. Table 1 shows that the Sb³⁺ ionic sensor based on PPY/CMC/MWCNTS NCs/binder/GCE provides appreciable outstanding performance.

Table 1. Sensors analytical performance toward Sb³⁺ cation compared with other composite materials.

Modified GCE	DL	LDR	Sensitivity	Ref.
NDNA/GCE	75.0 pM	0.1 ~ 10.0 mM.	12.66 × 10^-4 µAμM^−1cm^−2	(Rahman et al. 2018).
PPY/CMC/MWCNTS NCs/GCE	96.89 pM	0.1 nM ~0.01 mM	22.43 µAµM^-1cm^-2	This work

Investigation of real samples by fabricated sensor assembly

Finally, using the recovery method, it was examined a number of real samples such as tap-water, well-water, sea-water, and mineral-water for the detection of Sb³⁺ with fabricated PPY/CMC/MWCNTS NCs/binders/GCE as a sensor probe by electrochemical method. The results are presented in Table 2 which seem quite satisfactory.

Table 2. Validation of environmental samples analyses using PPY/CMC/MWCNTS BCs, binders, and GCE sensors.

Samples	Added Sb^3+ ion conc. (µM)	Determined Sb^3+ conc.^a by NCs/GCE (µM)			Average recovery^b (%)	RSD^c (%) (n = 3)
		R1	R2	R3
Tap water	0.01000	0.00981	0.00975	0.00969	97.50	0.62
Well water	0.01000	0.01032	0.01021	0.01020	102.43	0.65
Sea water	0.01000	0.00987	0.00989	0.00993	98.97	0.31
Mineral water	0.01000	0.01001	0.00989	0.00988	99.27	0.73

^aPPy/PPY/CMC/MWCNTS/NCs/GCE is the mean of three repeated determinations (signal to noise ratio 3)^.b Determined/taken concentration of Sb³⁺ ion. (Unit: µM). ^c The relative standard deviation is an indication of the degree of precision among three measurements (R1,R2,R3).

PPY/CMC/MWCNTS composite for antibacterial performance

An antimicrobial test was performed on the newly synthesized composite PPY/CMC/MWCNTS against gram-negative and gram-positive strains of bacteria. This composite material showed incredible antimicrobial activities against both grams of positive and negative bacterial strains. Gram-positive bacterial strain was more significantly affected than Gram-negative bacterial strain in both assays. The bacterial strain of S. aureus and B. subtilis growth was significantly influenced and developed a bacterial growth hindrance zone around the well, where the compound diffused into the surrounding media. Dissemination of antimicrobial mixes on media controls the growth and development of bacterial growth layers on media plates. The most significant effect in the form of zone inhibition range 22 ± 0.50 and 19 ± 0.25 mm appeared against S. aureus and B. subtilis separately and 18 ± 0.25 and 17 ± 0.5 mm zone inhibition was recorded against E. coli and P. aeruginosa at 100 µg/ml concentration (Table 3). These outcomes were more critically contrasted with the standard antibiotic. Further, antimicrobial action was checked in a broth and analyzed MIC and MBC. The inhibitory concentration of up to 30 ± 5 and 100 ± 10 µg/ml against Gram-positive and Gram-negative strains respectively was observed. All test microorganisms’ development was effectively influenced when increasing dose concentration in liquid media connected to the media plate and observing the bacterial survivability against drugs (Figure 6). Overall, the newly synthesized composite material has an antimicrobial activity that makes it rust-free and applicable in the medical device coating.

Figure 6. Antimicrobial effect of PPY/CMC/MWCNTS composite against both grams of positive and negative bacterial strains. Image showing excellent dose-response, increasing concentration significantly retard the bacterial.

Table 3. Zone inhibition Table of PPY/CMC/MWCNTS BCs against pathogens.

Type	Test microorganism	Zone of inhibition (mm)				MIC (µg/ml)
		at different dose
		25 (µg/ml)	50 (µg/ml)	75 (µg/ml)	100 (µg/ml)
G +ve	S. aureus	12 ± 0.25	16 ± 0.50	18 ± 0.50	22 ± 0.50	30
	B. subtilis	12 ± 0.40	15 ± 0.55	16 ± 0.25	19 ± 0.25	35
G ‒ve	E. coli	10 ± 0.25	13 ± 0.35	15 ± 0.35	18 ± 0.25	50
	P. aeruginosa	10 ± 0.20	12 ± 0.25	14 ± 0.25	17 ± 0.50	60

Conclusion

The present study attempted to assess the efficiency of PPY/CMC/MWCNTS composite for the Sb³⁺ cationic sensor and their potential application for antimicrobial activities. GCE coated with PPY/CMC/MWCNTS composite fabricated the Sb³⁺ cationic sensor and nafion binder and the detailed investigation in reliable I-V approach was elaborately investigated. The assembled sensor showed appreciable results such as sensitivity, long-term stability, LDR, DL, response time, and reproducibility. Besides this, the sensor probe exhibited very good performance in the investigation of real sample for validation. Simultaneously, the antibacterial property of PPY/CMC/MWCNTS composite is estimated against four pathogenic bacteria, such as B. subtilis along with S. aureus of (G +ve) and P. aeruginosa along with E. coli for (G -ve) by using autoclave of agar media. The proposed technique is ideal for quality management laboratories along with scientific studies wherein time and economic systems are important.

Highlights

• A fiber-type nanohybrid PPY/CMC/MWCNTS composite was prepared for electrochemical and antimicrobial applications.

• To investigate the Sb3+ cationic sensor using the I-V method on a glassy carbon electrode coated with PPY/CMC/MWCNTS composite.

• Antibacterial study results showed that PPY/CMC/MWCNTS composite was most effective against Bacillus bacteria, as well as Staphylococcus aureus, respectively.

• A lower limit of detection is equal to 96.82 ± 4.84 pM at the signal-to-noise ratio at an SNR of 3 (signal-to-noise ratio).

Acknowledgements

This research work was funded by the Institutional Fund Project under grant no. (IFPHI-279-130-2020). Therefore, authors gratefully acknowledge technical and financial support from the Ministry of Education and King Abdulaziz University, DSR, Jeddah, Saudi Arabia.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by the King Abdulaziz University [IFPHI-279-130-2020].