Voltammetric Determination Research Articles

Highly sensitive molecularly imprinted polymer-based electrochemical sensor for voltammetric determination of Adenine and Guanine in real samples using gold screen-printed electrode

Novel screen-printed gold electrodes (AuSPE) modified with molecularly imprinted (MIP) polyphenol were fabricated to detection of guanine (GU) and Adenine (AD) in the presence of each other species. The electrochemical polymerization method in the presence of specific analyte (GU or AD) as template molecules was used for synthesize of MIP thin layer on AuSPE surface. To investigate the effect of the presence of a molecular template in the surface layer via the produce of binding sites, MIP electrodes were compared with non-imprinted (NIP) electrodes. The fabricated MIP sensors (GU-MIP-AuSPE and AD-MIP-AuSPE) were used in the detection of GU and AD by differential pulse voltammetry (DPV) in 0.1 M phosphate buffer solution at pH 7.0 as optimized pH. Anodic peak currents for AD and GU show two linearity intervals in the range of 5 to 50 nM and 50 to 500 nM for GU and 5 to 50 nM and 50 to 700 nM for AD. Also, the values of limit of detection (LOD = 3Sb/m) and the limit of quantification (LOQ = 10Sb/m) were calculated as 0.37 × 10−9 M and 1.25 × 10−9 M for GU and 0.24 × 10−9 M and 0.80 × 10−9 M for AD, respectively. On the other hand, he fabricated MIP sensors exhibited high sensitivity, good repeatability and long-term stability. The MIP sensors were successfully utilized for the measurement of GU and AD in real human serum samples.

COF-42 as sensory material for voltammetric determination of Cu(II) ion: optimizing experimental condition via central composite design

COF-42 as sensory material for voltammetric determination of Cu(II) ion: optimizing experimental condition via central composite design

An electrochemical sensor for capsaicin based on two-dimensional titanium carbide (MXene)-doped titania-Nafion composite film

Two-dimensional titanium carbide (called MXene) has been utilized to fabricate a highly sensitive electrochemical sensor for the determination of capsaicin. In the present work, Ti3C2Tx MXene was dispersed in the composite solution of sol–gel derived titania and Nafion. The as-prepared MXene-titania-Nafion composite solution was drop-cast on the surface of a glassy carbon (GC) electrode. Due to the electrostatic interaction between positively charged capsaicin at pH 1.0 and negatively charged MXene-titania-Nafion composite film, capsaicin was selectively adsorbed onto the present electrochemical sensor. The introduction of MXene in the titania-Nafion composite film on GC electrode significantly increased the oxidation current of capsaicin compared to that at a bare GC electrode and the titania-Nafion composite-modified GC electrode, which could be attributed to the synergistic effect of Ti3C2Tx MXene and mesoporous titania-Nafion composite film. The experimental parameters affecting the detection capability of capsaicin (i.e., pH, MXene loading amount and accumulation time) were optimized. Using the linear sweep adsorptive stripping voltammetry, the present electrochemical sensor based on the MXene-titania-Nafion composite film can detect capsaicin from 5.0 × 10−8 M to 2.5 × 10−5 M with a detection limit of 2.5 × 10−8 M (S/N = 3). Furthermore, the present electrochemical sensor exhibited good selectivity towards capsaicin against interfering species like glucose and organic acids. Recovery tests for spiked capsaicin in a real pepper sample showed good recoveries. Therefore, the present electrochemical sensor based on the MXene-titania-Nafion composite could be applied to the voltammetric determination of capsaicin in food and pharmaceuticals.

The Experimental Design Approach in Square‐Wave Voltammetric Determination of Tamoxifen by NiO‐CPE**

AbstractDue to the explosive global increase of various cancers, the need to introduce/develop novel catalysts/sensors for quantitative determination of cancer drugs is emphasized. Nickel oxide nanoparticles (NiO‐NPs) calcined at 200 °C were used as a modifier of carbon paste electrode (CPE) to quantify tamoxifen (TAM) in an aqueous solution. The square wave voltammetry (SqW) was used due to its high sensitivity. The modified NiO‐CPE showed an SqW anodic peak current with a peak potential of about 420 mV in the NaOH‐supporting electrolyte. This peak current was decreased when TAM analyte was added to the test solution. Thus, this reduced peak current (Δi) was used to quantify TAM in solution. The experimental design used the response surface methodology (RSM) approach to study the simultaneous interaction effects between the influencing variables. The optimized run was associated with a 10 % NiO ingredient in the CPE, 0.3 M NaOH, an amplitude of 200 mV, a step potential of 3 mV, and a frequency of 25 Hz. A proportional behavior was obtained between the mentioned Δi and TAM concentration in the range of 10–60 nM. The detection (LOD) and quantification (LOQ) limits were 1.81±0.35 and 6.05±0.24 nM, respectively. Interfering and recovery results confirmed the applicability of the proposed NiO‐CPE electrode for TAM determination in complex matrixes and the direct assay of the drug in human serum.

Recent development of eco-friendly nanocomposite carbon paste electrode for voltammetric determination of Cd(II) in real samples

Using eco-friendly, cheap, and available adsorbents is promising for the determination of metal ions. So, this study focuses on the modification of graphite reinforcement carbon paste electrode (GRCPE) with mango seed kernel (MSK) for voltammetric determination of Cd(II). Moreover, to increase the surface area of this adsorbent, it was prepared in nanosized that formed nanoparticles of mango seed kernel (MSK-NPs). The developed nanocomposite electrode of carbon paste electrode modified with nanoparticles of mango seed kernel (MSK-NPs@GRCPE) was characterized using Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM). The effect of pH, buffer solution, and supporting electrolyte as experimental conditions were optimized through differential pulse adsorptive anodic stripping voltammetric method (DPAdASV). Britton-Robinson buffer pH = 3.9 at Eacc = – 1400 mV, tacc = 30 s, pulse width = 10 ms and sampling time = 8 ms were the optimum conditions for determination of Cd(II). The LOD and LOQ of MSK-NPs@GRCPE were calculated at 5.44 × 10–9 and 1.65 × 10–8 M, respectively. Compared with bare graphite reinforcement carbon paste electrode (BGRCPE), the nanocomposite MSK-NPs@GRCPE has a lower detection limit, indicating that the presence of MSK-NPs could greatly improve the response to Cd(II). The practical applicability of the electrode was verified by the determination of Cd(II) in chocolate and white rice samples. The results show high selectivity and sensitivity for Cd(II) in real samples.Graphical abstract

Voltammetric determination of Molnupiravir used in treatment of the COVID-19 at magnetite nanoparticle modified carbon paste electrode

To reduce the progression of the viral process in patients infected with COVID-19, new treatments and drug active substances are needed. One of these drugs is Molnupiravir (MNP) which has a direct antiviral effect and has also proven to be highly effective in reducing the azopharyngeal SARS-CoV-2 infectious virus and viral RNA. Due to the importance and frequent use of this drug in the treatment of COVID-19, its accurate, quick, and cheap detection in pharmaceutical or biological samples is crucial. In this work, electrochemical behavior and sensitive voltammetric determination of MNP are described using a magnetite nanoparticle modified carbon paste electrode (Fe3O4@CPE) for the first time. Fe3O4 nanoparticles (NPs) were characterized by recording their transmission electron microscopy (TEM) images, energy dispersive X-ray (EDX), and X-ray diffraction (XRD) spectra. Cyclic voltammetric measurements showed that MNP was irreversibly oxidized at Fe3O4@CPE at 760 mV in pH 2.0 Britton Robinson buffer solution (BRBS). The peak current of MNP was increased approximately threefold at Fe3O4@CPE compared to bare CPE due to a good electrocatalytic efficiency of Fe3O4 NPs. According to differential pulse voltammetric studies, the fabricated electrode exhibited a linear range (LR) between 0.25 and 750 µM with sensitivity and limit of detection (LOD) of 4591.0 µA mM−1 cm−2 and 0.05 µM, respectively. On the other hand, although lower sensitivity (327.3 µA mM−1 cm−2) was obtained from CV compared to DPV, a wider linear calibration curve between 0.25 and 1500 µM was obtained in CV. Studies performed in tablet samples confirmed that the Fe3O4@CPE exhibits high applicability for selective and accurate voltammetric determination of MNP in real samples.

Voltammetric Determination of Favipiravir Used as an Antiviral Drug for the Treatment of Covid-19 at Pencil Graphite Electrode.

This work describes the sensitive voltammetric determination of favipiravir (FAV) based on its reduction for the first time with a low-cost and disposable pencil graphite electrode (PGE). In addition, the determination of FAV was also performed based on its oxidation. Differential pulse (DP) voltammograms recorded in 0.5 M H2SO4 for the reduction of FAV show that peak currents increase linearly in the range of 1.0 to 600.0 μM with a limit of detection of 0.35 μM. The acceptable recovery values (98.9-106.0 %) obtained from a pharmaceutical tablet, real human urine, and artificial blood serum samples spiked with FAV confirm the high accuracy of the proposed method.

Tip-porous microneedle: A highly stable sensing platform for direct determination of labile metals in natural seawater

Nanomaterial-functionalized voltammetric microsensors are promising tools for detecting trace metals at low concentrations in the complex environment of natural seawater. However, the sensitivity reduction caused by the loss of modified nanomaterials in the detection process has always been a major problem. Herein, to fabricate a highly stable sensing platform, a microneedle electrode with a hierarchical porous tip was prepared through electrochemical etching technology to firmly embed nanoparticles. Using copper (Cu) as a model trace metal, a micro-cluster needle sensor based on a gold nanoparticle (AuNP)-embedded tip-porous microneedle electrode (P-MNE) was fabricated for the direct voltammetric determination of labile Cu in natural seawater. The porous structure of P-MNE not only provided a larger specific surface area and active sites for AuNPs which had excellent electrocatalytic performance for Cu2+ determination, but also protected from their loss during the detection process in seawater. Therefore, this novel micro-cluster needle sensor exhibited significantly improved stability with a relative standard deviation (RSD) of 1.5% for 30 detections. The linear range of Cu2+ on this micro-cluster needle sensor was from 0.1 to 1000 nM with a detection limit of 0.03 nM. More importantly, this micro-cluster needle sensor was successfully used for directly detecting labile Cu in natural seawater samples without any preaccumulation treatment or reagent addition to obtain the contribution proportions of the labile fraction in total dissolved Cu. Furthermore, this sensing platform might also be extended to the reliable determination of other labile metals in seawater by changing the functional nanoparticles embedded in the nanopores.

Validation of Voltammetric Methods for Online Analysis of Platinum Dissolution in a Hydrogen PEM Fuel Cell Stack

Platinum dissolution in PEM fuel cells is an increasingly important indicator for the state-of-health and lifetime prediction of fuel cells in real applications. For this reason, portable online analysis tools are needed that can detect and quantify platinum with high sensitivity, selectivity, and accuracy in the product water of fuel cells. We validated the hanging mercury drop electrode (HMDE) and non-toxic bismuth film electrodes for the voltammetric determination of platinum for this purpose. Bismuth films were prepared by reductive deposition on both a glassy carbon solid state electrode and on a screen-printed electrode (film on-chip electrode). Both bismuth film electrodes could be successfully validated for the determination of platinum by adsorptive stripping voltammetry. An LOD of 7.9 μg/L and an LOQ of 29.1 μg/L were determined for the bismuth film solid state electrode, values of 22.5 μg/L for the LOD and of 79.0 μg/L for the LOQ were obtained for the bismuth film on-chip electrode. These numbers are still much higher than the results measured with the HMDE (LOD: 0.76 ng/L; LOQ: 2.8 ng/L) and are not sufficient to detect platinum in the product water of a fuel cell run in different load tests. The amount of dissolved platinum produced by a 100 W fuel cell stack upon dynamic and continuous high load cycling, respectively, was in the range of 2.9–4.1 ng/L, which could only be detected by the HMDE.

Electrocatalytic response of chitosan modified multiwall carbon nanotube paste electrode toward iodide: A facile voltammetric method for determination of iodide in biological sample

Herein we report, a simple operable, sensitive, and highly selective, voltammetric method for the determination of iodide (Iˉ) using chitosan modified multiwall carbon nanotube paste electrode (chit-MWCNTPE). It is established that chit-MWCNTPE exhibited a pronounced response toward Iˉ oxidation. The peak potential of Iˉ is recorded at 0.69 V vs SCE. The conditions such as scan rate (V.s−1), accumulation time (ta), and pH are thoroughly optimized for the voltammetric determination of Iˉ. A wide range linear response is observed between oxidation peak current and Iˉ concentration (0.1–100 μM). The limit of detection (LOD) for Iˉ on chit-MWCNTPE is found to be 0.03 μM. The developed method is highly selective for Iˉ detection in the presence of various interfering ions. The method is successfully applied for the determination of Iˉ in urine samples. The method has high selectivity for Iˉ detection at comparably low potential as well as amiable LOD and Linear range.

Gold Nanoparticles Decorated with Multi-Walled Carbon Nanotubes/Graphene Oxide for Voltammetric Determination of Dopamine in the Presence of Acetaminophen

We developed an electrochemical sensor by combination of Graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) then decorated with Au-nanoparticles (AuNPs) by an electrodeposition process for detection of dopamine (DP) in the presence of acetaminophen (AC). The electrochemical properties of MWCNT/GO- AuNPs/GCE were characterized by scanning electron microscopy (SEM) and cyclic voltammetry (CV).The results displayed that Au nanoparticles were well jointed onto MWCNT/GO nanocomposite. The electrochemical responses displayed the prepared sensor showed enhanced electrocatalytic activity for the detection of DP inthe presence of acetaminophen (AC). Under optimum conditions, the proposed sensorpresented a linear response based on the DP concentration in the range of 1.0 to 165 μM with a detection limit of 0.07 μM using the differential pulse voltammogram (DPV) method.Moreover, this proposed sensor displayed a linear range concentration of AC ranging from 3 to 200.0 μM and detection limit of 0.061 μM. Also, the prepared sensor indicated excellent sensitivity and selectivity for the DP determination in the presence of AC in real samples.

Voltammetric trace determination of Vanadium ions and their removal from industrial effluents by using biosorbent

Vanadium is extensively utilized in a variety of industries, including textiles, chemical manufacturing, metal plating, and many more. Pentavalent Vanadium is a highly toxic and carcinogenic substance when present in high concentrations. Therefore, eliminating it from industrial effluents before it can reach any water supply or land is critical. In the present research, the determination of trace V(V) by Differential pulse polarography (DPP) and its removal from industrial effluents by using Annona squamosa leaves as biosorbent has been analyzed. The mercury electrode is used as working electrode for DPP analysis. The reference and auxiliary electrodes were Ag/AgCl and platinum wire respectively. The biosorbent capacity of Annona squamosa leaves were analyzed by using different parameters like pH, concentration, contact time, biosorbent dosage, and temperature. The V(V) showed a sharp DP peak at -1.19V in presence of Ammonia-Ammonium phosphate buffer. The maximum V(V) adsorption was 8.1mg/g and 85%with respect to contact time and concerning temperature respectively. The present study concluded that the determination of V(V) by DPP are in good agreement with that of results obtained from UV-VIS technique. Further the biosorbent so prepared from Annona squamosa leaves is likely to be a cost-effective, economically feasible, and easily available material for removing V(V)from industrial effluents.

Chitosan/genipin modified electrode for voltammetric determination of interleukin-6 as a biomarker of sepsis

Ultrasensitive electroanalytical monitoring of interleukin-6 levels in serum samples has emerged as a valuable tool for the early diagnosis of inflammatory diseases. Despite its advantages, there is a lack of strategies for the label-free voltammetric determination of cytokines. Here, a novel chitosan/genipin modified fluorine tin oxide electrode was developed providing an in-situ hydrogel formation (FTO/CSG). This platform was applied for the detection of interleukin-6, a major pro-inflammatory cytokine. Transmission electron microscopy (TEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) indicated genipin serves as an efficient green cross-linker to build the immunosensing platform (FTO/CSG/anti-IL-6). EIS showed an increase in charge transfer resistance from 326 to 1360 kΩ after the immobilization of anti-IL-6 antibodies. By square wave voltammetry, this method achieved a detection limit of 0.03 pg mL−1 with a wide linear range of 0.05–1000 pg mL−1. Additionally, it displayed a high selectivity index when tested in the presence of three inflammatory cytokines as interfering proteins: IL-12, IL-1β, and TNF-α. The sample matrix effect showed a peak current variation lower than 5 %. The novel method was applied for the quantification of IL-6 in serum samples of septic mice. No statistical differences were observed between the standard ELISA and the proposed method using a confidence level of 95 %.

Prospects of Application of Ultramicroelectrode Ensembles for Voltammetric Determination of Compounds with Close Standard Electrode Potentials and Different Diffusion Coefficients

The spherical diffusion that occurs when using ultramicroelectrodes (i.e., electrodes with a characteristic size of 1–10 µm) contributes to a higher mass transfer rate. This leads to equalization of the depletion rates of the near-electrode layer due to the electrochemical reaction and to the supply of the product from the solution depth. This is the reason why, for ultramicroelectrodes, a limiting size of the spherical layer exists in which the concentration gradient is localized (diffusion layer). Thus, a stationary mass transfer mode is achieved, which is expressed in the sigmoidal CV curve’s shape. In ultramicroelectrode arrays, when the diffusion hemispheres are separated, a steady-state diffusion is realized. However, with a decrease in the interelectrode distance, which leads to the diffusion spheres intersection, a mixed regime arises, which is not fully time-independent. The resulting voltammogram’s shape change can serve as an analytical signal in the study of substances with differing diffusion coefficients, since the diffusion layer growth rate and, consequently, the area of intersection of neighboring spheres, depends on it. This work shows the applicability of voltammetry using ensembles of ultramicroelectrodes operating in the transient mode for the analysis of mixtures of electrochemically active compounds with close electrode reaction parameters, such as exchange currents and electrode potential. Ferrocenemethanol esters are used as an example. The applicability of cyclic voltammetry on the UME array for analysis of mixtures was illustrated by means of finite element modelling. The reliability of the modelling results was experimentally proved for ferrocenemethanol esters with glycine and triglycine.

Voltammetric Determination of 3-Methylmorphine Using Glassy Carbon Electrode Modified with rGO and Bismuth Film.

This work reports the development and application of a simple, rapid and low-cost voltammetric method for the determination of 3-methylmorphine at nanomolar levels in clinical and environmental samples. The proposed method involves the combined application of a glassy carbon electrode modified with reduced graphene oxide, chitosan and bismuth film (Bi-rGO-CTS/GCE) via square-wave voltammetry using 0.04 mol L−1 Britton–Robinson buffer solution (pH 4.0). The application of the technique yielded low limit of detection of 24 × 10−9 mol L−1 and linear concentration range of 2.5 × 10−7 to 8.2 × 10−6 mol L−1. The Bi-rGO-CTS/GCE sensor was successfully applied for the detection of 3-methylmorphine in the presence of other compounds, including paracetamol and caffeine. The results obtained also showed that the application of the sensor for 3-methylmorphine detection did not experience any significant interference in the presence of silicon dioxide, povidone, cellulose, magnesium stearate, urea, ascorbic acid, humic acid and croscarmellose. The applicability of the Bi-rGO-CTS/GCE sensor for the detection of 3-methylmorphine was evaluated using synthetic urine, serum, and river water samples through addition and recovery tests, and the results obtained were found to be similar to those obtained for the high-performance liquid chromatography method (HPLC)—used as a reference method. The findings of this study show that the proposed voltammetric method is a simple, fast and highly efficient alternative technique for the detection of 3-methylmorphine in both biological and environmental samples.

Strategic Electrochemical Determination of Nitrate over Polyaniline/Multi-Walled Carbon Nanotubes-Gum Arabic Architecture.

Significant agricultural and industrial activities necessitate the regular monitoring of nitrate (NO3−) ions levels in feed and groundwater. The current comparative study discloses an innovative user-friendly electrochemical approach for the determination of NO3− over polyaniline (PAni)-based modified electrodes. The electrochemical sensors concocted with PAni, multi-walled carbon nanotubes (CNT), and gum arabic (GA). The unique electrode material GA@PAni-CNT was synthesized by facile one-pot catalytic polymerization of aniline (Ani) with FeCl3/H2O2 in the presence of CNT and GA as integral components. As revealed by cyclic voltammetry (CV), the anchoring/retention of NO3− followed by reduction is proposed to occur when a GA@PAni-CNT electrode is immersed in phosphate buffer electrolyte containing NO3− that eventually results in a significantly higher redox activity of the GA@PAni-CNT electrode upon potential scan. The mechanism of NO3− anchoring may be associated with the non-redox transition of leucomeraldine salt (LS) into emeraldine salt (ES) and the generation of nitrite (NO2−) ions. As a result, the oxidation current produced by CV for redox transition of ES ↔ pernigraniline (PN) was ~9 times of that obtained with GA@PAni-CNT electrode and phosphate buffer electrolyte, thus achieving indirect NO3− voltammetric determination of the GA@PAni-CNT electrode. The prepared GA@PAni-CNT electrode displayed a higher charge transfer ability as compared to that of PAni-CNT and PAni electrodes. The optimum square wave voltammetric (SWV) response resulted in two linear concentration ranges of 1–10 (R2 = 0.9995) and 15–50 µM (R2 = 0.9988) with a detection limit of 0.42 µM, which is significantly lower. The GA@PAni-CNT electrode demonstrated the best detection, sensitivity, and performance among the investigated electrodes for indirect voltammetric determination of NO3− that portrayed the possibility of utilizing GA—stabilized PAni and CNT nanocomposite materials in additional electrochemical sensing applications.

Screen-Printed Graphite Electrode Modified with Graphene-Co3O4 Nanocomposite: Voltammetric Assay of Morphine in the Presence of Diclofenac in Pharmaceutical and Biological Samples.

This work focuses on the development of a novel electrochemical sensor for the determination of morphine in the presence of diclofenac. The facile synthesis of graphene-Co3O4 nanocomposite was performed. The prepared material (graphene-Co3O4 nanocomposite) was analyzed by diverse microscopic and spectroscopic approaches for its crystallinity, composition, and morphology. Concerning the electrochemical determinations, after drop-casting the as-fabricated graphene-Co3O4 nanocomposite on the surface of a screen-printed graphite electrode (SPGE), their electrochemical performance was scrutinized towards the morphine detection. It was also found that an SPGE modified by a graphene-Co3O4 nanocomposite exhibited better electrocatalytic activity for morphine oxidation than unmodified electrode. Under optimal conditions, the differential pulse voltammetry (DPV) was employed to explore the present sensor (graphene-Co3O4/SPGE), the findings of which revealed a linear dynamic range as broad as 0.02–575.0 µM and a limit of detection (LOD) as narrow as 0.007 μM. The sensitivity was estimated to be 0.4 µM/(µA cm2). Furthermore, the graphene-Co3O4/SPGE sensor demonstrated good analytical efficiency for sensing morphine in the presence of diclofenac in well-spaced anodic peaks. According to the DPV results, this sensor displayed two distinct peaks for the oxidation of morphine and diclofenac with 350 mV potential difference. In addition, the graphene-Co3O4/SPGE was explored for voltammetric determination of diclofenac and morphine in pharmaceutical and biological specimens of morphine ampoule, diclofenac tablet, and urine, where recovery rates close to 100% were recorded for all of the samples.

Nanomaterial-based sandwich-type electrochemical aptasensor platform for sensitive voltammetric determination of leptin.

A sandwich-type electrochemical aptasensor was designed for sensitive detection of leptin in biological samples, including human serum and human plasma. The developed aptasensor was produced by electrodeposition of gold nanoparticles on a screen-printed electrode modified with zinc oxide nanoparticles. The synergy effect of zinc oxide and gold nanoparticles improved the electrocatalytic activity of the aptasensor. The obtained high surface area allowed more aptamer molecules to be loaded on the electrode surface. Signal amplification significantly increases the detection sensitivity of a developed biosensor. Although the use of nanomaterials is the most preferred detection tool for this purpose, as an alternative, enzyme-catalyzed signal amplification is widely used in the construction of a biosensor due to its specificity and high catalytic efficiency. Therefore, both nanomaterial-supported and an alkaline phosphatase-based aptasensor design were developed, which can produce in situ electroactive product by enzymatic hydrolysis of the inactive substrate to achieve a higher signal-to-background ratio. Under optimal conditions, the developed aptasensor exhibited a wide linear concentration range from 0.01 pg mL-1 to 100.0 pg mL-1 with a detection limit of 0.0035 pg mL-1. While the developed aptasensor provided excellent selectivity in the presence of some interfering compounds, it possessed outstanding reproducibility and stability. In addition, the developed aptasensor has been applied with good recoveries in the range 96.31 to 108.79% in human serum and plasma samples. In conclusion, all the obtained results showed the feasibility of the developed aptasensor for practical applications.

A novel ion-imprinted polymer based on pyrrole as functional monomer for the voltammetric determination of Hg(II) in water samples

A novel selective ion-imprinted polymer (IIP) was synthesized, characterized, and used as part of a carbon paste electrode (CPE) for the electrochemical analysis of Hg(II) in real water samples by differential pulse anodic stripping voltammetric (DPASV). Hg-IIP (mercury-ion imprinted polymer) was synthesized using pyrrole for the first time as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as a cross-linker agent, and sodium persulfate as initiator. The CPE was modified with IIP (CPE-IIP) with a composite mixture of Hg-IIP (10%), graphite (90%), and 0.08 g of paraffin oil. A notable difference in the Hg(II) Iap (anodic peak current) between a CPE, CPE-IIP and CPE-NIP (non-imprinted polymer) was observed when optimizing the differential pulse anodic stripping voltammetry (DPASV) parameters by a Box-Behnken design. When analyzing a 50 µmol l−1 Hg(II) solution, the optimal conditions (step potential: 0.11 V, amplitude: 0.15 s, modulation time: 0.005 s, and interval time: 0.15 s) allowed an Iap of 144 µA with a %RSD < 10% for the CPE-IIP response, in comparison to the Iap of 1.47 µA obtained with the CPE-NIP, Iap confirming the existence and performance of the recognition cavities in the IIP. The proposed methodology presents a limit of detection (LOD) of 0.02 mg l−1 within a linear range of 0.09 mg l−1 to 20.05 mg l−1. The inter-day and intra-day precision were measured in two concentration levels (1 mg l−1 and 10 mg l−1) with %RSD < 10%. The developed methodology was successfully applied to determine Hg(II) in three spiked samples (10 mg l−1) of natural water sources without acid digestion, obtaining percentage recoveries close to 99.74%, which demonstrates that digestion treatment is not required for this kind of samples.

Molecularly imprinted polymer specific to creatinine complex with copper(II) ions for voltammetric determination of creatinine.

Synthesis of creatinine-imprinted polymer is challenging because of its insolubility in aprotic solvents, traditionally utilized for synthesizing molecularly imprinted polymer (MIP). Moreover, creatinine is not electroactive at conventional electrodes, and thus, introducing an electrochemical sensing platform for its determination is a difficult target. This study addressed the above-cited issues to introduce a novel creatinine voltammetric sensor with high selectivity and sensitivity. Creatinine-copper complex was found to be soluble in acetonitrile and was utilized as a template for the MIP synthesis. Methacrylic acid, ethylene glycol dimethacrylate, and azobisisobutyronitrile were used as functional monomers, cross-linker, and initiator, respectively. The MIP holding creatinine sites were used to modify the carbon paste electrode. Since creatinine did not exhibit a significant voltammetric signal, an indirect sensing technique was employed. This was based on using Cu(II) ion as an electrochemical probe. The MIP-modified electrode signal for copper ion was significantly improved in the presence of creatinine. However, the introduction of creatinine in the Cu(II) solution did not affect the NIP-modified electrode response to copper ion. The proposed sensor indicated a linear current response in the range 1 × 10-7-1 × 10-5mol L-1 with adetection limit of 5.9 × 10-8mol L-1 (S/N = 3). Moreover, this method presents excellent performance in real sample analysis, with values of favorable creatinine recovery in plasma. The system exhibits acceptable precision (RSD = 4.04) and favorable selectivity toward creatinine.