Mercapto-ordered carbohydrate-derived porous carbon electrode as a novel electrochemical sensor for simple and sensitive ultra-trace detection of omeprazole in biological samples

A platform for microplastic assessment in aquatic environments based on the protein corona-induced aggregation effect

The environmental hazards of microplastics have received widespread attention. However, the in-situ detection of microplastics, particularly in aquatic environments, has been challenged by the limitations of detection methods, the large-scale instruments, and small size. Herein, a photoelectrochemical sensor based on the protein corona-induced aggregation effect is designed for the detection of polystyrene microplastics. The sensor has advantages of high sensitivity, reproducibility, and detection capability. A linear detection range of 0.5-500 μg mL-1, a method detection limit of 0.06 μg mL-1, and a limit of quantification of 0.14 μg mL-1 are achieved. Furthermore, the relative standard deviations of intra-day and inter-day precision, ranging from 0.56% to 4.63% and 0.84%-3.36% are obtained. A digital multimeter was employed to construct a platform for the real-time detection in real water samples, streamlining the detection process and yielding clear results. We believe this sensor provides new insight for the in-situ real-time detection of microplastics and has broad applications for the analysis of microplastic pollution in aquatic environments.

Determination of omeprazole via fluorescence-quenching methodology; application to content uniformity testing

A new, proven, economical spectrofluorimetric approach has been used to determine the proton pump inhibitor omeprazole (OMP). This innovative technique is based on the ability of OMP to quench the native fluorescence of the mercurochrome dye in an acidic (pH 3.6) solution. Because it was discovered that quenching is proportional to the drug concentration, this dye was used as a sensor for OMP detection. The fluorescence intensity was measured at 518/540 nm, and its linear response ranged from 0.2-10.0 μg/mL with a linear coefficient of 0.9999. The computation yielded a limit of quantification (LOQ) of 0.20 μg/mL and a limit of detection (LOD) of 0.07 μg/mL. Every circumstance and element impacting the reaction product was examined in detail. Pharmacopeial standards carried out the validation. The approved method investigated several commercial preparations and formulations, and the results were favorably compared with those provided by a reference method. According to United States Pharmacopeia (USP) rules, content consistency for two distinct formulations was evaluated.

An amplified electrochemical sensor employing one-step synthesized nickel-copper-zinc ferrite/carboxymethyl cellulose/graphene oxide nanosheets composite for sensitive analysis of omeprazole

In this work, a signal amplification strategy was designed by the fabrication of a highly sensitive and selective electrochemical sensor based on nickel-copper-zinc ferrite (Ni0.4Cu0.2Zn0.4Fe2O4)/carboxymethyl cellulose (CMC)/graphene oxide nanosheets (GONs) composite modified glassy carbon electrode (GCE) for determination of omeprazole (OMP). The one-step synthesized Ni0.4Cu0.2Zn0.4Fe2O4/CMC/GONs nanocomposite was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and X-ray diffraction techniques. Then, the Ni0.4Cu0.2Zn0.4Fe2O4/CMC/GONs/GCE was applied to study the electrochemical behavior of the OMP. Electrochemical data show that the Ni0.4Cu0.2Zn0.4Fe2O4/CMC/GONs/GCE exhibits superior electrocatalytic performance on the oxidation of OMP compared with bare GCE, GONs/GCE, CMC/GONs/GCE and MFe2O4/GCE (M = Cu, Ni and Zn including single, double and triple of metals) which can be attributed to the synergistic effects of the nanocomposite components, outstanding electrical properties of Ni0.4Cu0.2Zn0.4Fe2O4 and high conductivity of CMC/GONs as well as the further electron transport action of the nanocomposite. Under optimal conditions, the Ni0.4Cu0.2Zn0.4Fe2O4/CMC/GONs/GCE offers a high performance toward the electrodetermination of OMP with the wide linear-range responses (0.24-5 and 5-75 μM), lower detection limit (0.22 ± 0.05 μM), high sensitivity (1.1543 μA μM-1 cm-2), long-term signal stability and reproducibility (RSD = 2.54%). It should be noted that the Ni0.4Cu0.2Zn0.4Fe2O4/CMC/GONs/GCE sensor could also be used for determination of OMP in drug and biological samples, indicating its feasibility for real analysis.

Electrochemical sensor based on 3D-printed substrate by masked stereolithography (MSLA): a new, cheap, robust and sustainable approach for simple production of analytical platforms

The development of miniaturized, sustainable and eco-friendly analytical sensors with low production cost is a current trend worldwide. Within this idea, this work presents  the innovative use of masked stereolithography (MSLA) 3D-printed substrates for the easy fabrication of pencil-drawn electrochemical sensors (MSLA-3D-PDE). The use of a non-toxic material such as pencil (electrodes) together with a biodegradable 3D printing resin (substrate) allowed the production of devices that are quite cheap (ca. US$ 0.11 per sensor) and with low environmental impact. Compared to paper, which is the most used substrate for manufacturing pencil-drawn electrodes, the MSLA-3D-printed substrate has the advantages of not absorbing water (hydrophobicity) or becoming crinkled and weakened when in contact with solutions. These features provide more reproducible, reliable, stable, and long-lasting sensors. The MSLA-3D-PDE, in conjunction with the custom cell developed, showed excellent robustness and electrochemical performance similar to that observed of the glassy carbon electrode, without the need of any activation procedure. The analytical applicability of this platform was explored through the quantification of omeprazole in pharmaceuticals. A limit of detection (LOD) of 0.72 µmol L^-1 was achieved, with a linear range of 10 to 200 µmol L^-1. Analysis of real samples provided results that were highly concordant with those obtained by UV-Vis spectrophotometry (relative error ≤ 1.50%). In addition, the greenness of this approach was evaluated and confirmed by a quantitative methodology (Eco-Scale index). Thus, the MSLA-3D-PDE appears as a new and sustainable tool with great potential of use in analytical electrochemistry.

Metal-free Sulfur-doped graphitic carbon nitride-modified GCE-based electrocatalyst for the enhanced electrochemical determination of Omeprazole in Drug formulations and Biological Samples

This study presents a novel sulfur-doped graphitic carbon nitride (S@g-C₃ N₄ ) with a wider potential range as electrocatalyst for electrochemical sensor application. The S@g-C₃ N₄ nanosheets were successfully prepared with a ball milling method by mixing appropriate molar concentration required precursors. The as-synthesized heteroatom-doped graphitic carbon nitride is characterized by spectroscopic techniques including PL, DRS-UV, FT-IR, and Brunauer-Emmett-Teller equation. The morphological features were studied by FE-SEM and HR-TEM analysis. Chit-S@g-C₃ N₄ -modified glassy carbon electrode (GCE) was employed for the electrochemical detection of omeprazole (OMZ) use in drug formulations. We have noted an oxidation peak current response at a potential of +0.8 V versus Ag/AgCl in PBS medium (0.1 M, pH 7.0). Differential pulse voltammetry amperometry experimental method can be used to measure the concentration of OMZ for quantitative studies in known samples. Under the optimized experimental condition, the calibration plot was constructed by plotting the peak currents versus OMZ in the linear ranges from 6.0 × 10^-7 to 26 × 10^-5  M. The linear regression equation is estimated to be I_p (μA) = 0.9518 (C/μM) + 0.3340 with a good correlation coefficient of 0.9996. The lower determination limit was found to be 20 nM and the current sensitivity was calculated (31.722 μA μM^-1  cm^-2 ). The developed sensor was utilized successfully to determine the OMZ concentration in drug formulations and biological fluids. These results revealed that the Chit-S@g-C₃ N₄ -modified GCE showed excellent electroanalytical performance for the detection of OMZ at a low LOD, wider linear range, high sensitivity, good reproducibility, long-term storage stability, and selectivity with an acceptable relative standard deviation value.

Multi-template molecularly imprinted polymer hybrid nanoparticles for selective analysis of nonsteroidal anti-inflammatory drugs and analgesics in biological and pharmaceutical samples

The multi-template molecularly imprinted polymers reinforced with hybrid oxide nanoparticles were developed for the selective separation and determination of the trace level of naproxen (NPX), methocarbamol (MTH), and omeprazole (OMZ) simultaneously from biological and pharmaceutical samples. The polymers were constructed by magnetic core@shell molecularly imprinted polymer nanocomposite (Fe₃O₄/ZnO/CuO/MWCNT@MIP). An electrochemical sensor has been fabricated for this purpose. Fe₃O₄/ZnO/CuO/MWCNT nanocomposite was introduced to improve the electron transport capability and increase the sensor surface area, as well as enhance the electronic conductivity. The triple-template MIP-coated layer provides simultaneous selective identification of three analytes by using [Fe (CN)₆]^3-/4-as the redox probe. Electrochemical behavior of MTH, NPX, and OMZ on the modified electrode (Fe₃O₄/ZnO/CuO/MWCNT@MIP) by various techniques such as cyclic voltammetry, differential pulse voltammetry, and chronoamperometry was examined. The morphology of the modified and unmodified carbon paste electrodes was performed by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The average crystal size for fabricated nanoparticles obtained by calculating the X-ray diffraction technique was 17 nm in the Scherer method. The particle size which was determined by SEM was 48 nm. Some electrochemical parameters such as the diffusion coefficient and electron transfer coefficient were determined. The effect of many variables such as the pH and scan rate was also investigated. Under optimal conditions, the sensor is designed in the linear range 5.0 nM-100 μM and 5.0 nM-100 μM and 1.0 nM-130 μM with a detection limit of 1.5 nM, 1.0 nM, and 0.7 nM for measurement OMZ, NPX, and MTH, respectively. The relative standard deviation (RSD) of the five measurements was 1.21%, 2.23%, and 2.56% for NPX, MTH, and OMZ. Finally, the designed sensor was successfully used for simultaneous detection of target analytes in the real samples; tablets, water samples, and biological samples.

A state of the art overview of carbon-based composites applications for detecting and eliminating pharmaceuticals containing wastewater

The growing prevalence of new toxins in the environment continues to cause widespread concerns. Pharmaceuticals, organic pollutants, heavy metal ions, endocrine-disrupting substances, microorganisms, and others are examples of persistent organic chemicals whose effects are unknown because they have recently entered the environment and are displaying up in wastewater treatment facilities. Pharmaceutical pollutants in discharged wastewater have become a danger to animals, marine species, humans, and the environment. Although their presence in drinking water has generated significant concerns, little is known about their destiny and environmental effects. As a result, there is a rising need for selective, sensitive, quick, easy-to-handle, and low-cost early monitoring detection systems. This study aims to deliver an overview of a low-cost carbon-based composite to detect and remove pharmaceutical components from wastewater using the literature reviews and bibliometric analysis technique from 1970 to 2021 based on the web of science (WoS) database. Various pollutants in water and soil were reviewed, and different methods were introduced to detect pharmaceutical pollutants. The advantages and drawbacks of varying carbon-based materials for sensing and removing pharmaceutical wastes were also introduced. Finally, the available techniques for wastewater treatment, challenges and future perspectives on the recent progress were highlighted. The suggestions in this article will facilitate the development of novel on-site methods for removing emerging pollutants from pharmaceutical effluents and commercial enterprises.

A novel non-enzymatic sensor for prostate cancer biomarker sensing based on electrocatalytic oxidation of sarcosine at nanostructured NiMn2O4 impregnated carbon paste electrode

This work addresses the electrocatalytic activity of a binary metal oxide catalyst of NiMn₂O₄ for electroxidation of sarcosine, the well-known prostate cancer biomarker. The nanocatalyst described was prepared via hydrothermal synthesis route, followed by calcination at 800 °C. Field emission scanning electron microscopy and X-ray diffraction were applied to obtain information about the material morphology and structure. A carbon paste electrode modified with nano-NiMn₂O₄ showed unique catalytic activity in sarcosine electroxidation which led to a significant rise in oxidation current (about four times) in comparison with the blank electrode. However, the carbon paste electrodes containing single oxides of NiO and Mn₂O₃ exhibited no considerable enhancement in sarcosine signal. The cyclic voltammetry results indicated that the Mn³⁺/Mn⁴⁺ couple was responsible for sarcosine oxidation, and NiO may enhance the content of Mn⁴⁺species in NiMn₂O₄ material. The carbon paste-based NiMn₂O₄ electrode was applied in the sensitive determination of sarcosine in the concentration range of 0.01-5.0 μM with the relative standard deviation of 3.49% (n = 5). The detection limit and quantification limit of the probe were determined to be 3.8 and 12 nM, respectively. The remarkable sensitivity and high selectivity of the method approved the sensor applicability in measurement of sarcosine content in urine samples.

Bio-inspired Ag nanovilli-based sandwich-type SERS aptasensor for ultrasensitive and selective detection of 25-hydroxy vitamin D3

Vitamin D has been identified as an essential biomarker for various diseases such as rheumatoid arthritis, cancer, and cardiovascular diseases. Recently, many reports have demonstrated a potential link between vitamin D and systemic infections, including coronavirus disease 2019. The villi of the small intestine increase the surface area of the intestinal walls, demonstrating exceptionally efficient absorption of nutrients in the lumen and adding digestive secretions. In this study, based on the villi structure, we developed a bio-inspired silver nanovilli-based sandwich-type surface enhanced Raman scattering aptasensor for the ultrasensitive and selective detection of 25-hydroxy vitamin D₃. The densely packed nanovilli structure enhanced the Raman signal, forming hotspots owing to its large surface area. Using experiments and electromagnetic simulations, we optimized the nanovilli structure as a SERS sensor. The sandwich-type aptasensor was designed using an aptamer and 4-Phenyl-1,2,4-triazoline-3,5-dione-methylene blue complex. The nanovilli-based aptasensor could sensitively detect various concentrations of 25-hydroxy vitamin D₃, ranging from those found in deficient to excess conditions. The detection limit of the nanovilli-based sandwich-type aptasensor for 25-hydroxy vitamin D₃ was 0.001 ng/mL, which is much lower than the deficiency concentration, and was detectable even in the human serum. In addition, our proposed sensor exhibited good repeatability (17.76%) and reproducibility (7.47%). Moreover, the nanovilli-based sandwich-type SERS aptasensor could selectively distinguish 25-hydroxy vitamin D₃ from other vitamins. The silver nanovilli-based sandwich-type surface enhanced Raman scattering aptasensor opens a new avenue for the development of a bio-inspired vitamin-sensing platform.

An electrochemical sensor based on an Eriochrome Black T polymer and deep eutectic solvent for the simultaneous determination of omeprazole and lansoprazole

Here we report the fabrication of an electrochemical sensor for the simultaneous determination of the concentrations of omeprazole (OMZ) and lansoprazole (LAN) in biological fluids and pharmaceuticals in Britton-Robinson buffer solution (pH 6.0). The sensor was prepared by bulk modifying a carbon paste electrode with deep eutectic solvent (DES), followed by carrying out electropolymerization of Eriochrome Black T (EBT) at this electrode. The presence of DES increased the extent of the polymerization of EBT on the surface of the electrode, and this increase led to better OMZ and LAN electron transfer kinetics at the electrode surface. The modified electrode was evaluated and characterized by performing cyclic voltammetry, electrochemical impedance spectroscopy, scanning electronic microscopy, and Fourier-transform infrared spectroscopy. The best responses were obtained in drug-free Britton-Robinson buffer solution (pH 6.0) after 600 s of stirring at the open circuit potential. Linear relationships were obtained between the anodic peak currents and the concentrations of OMZ and LAN in the ranges of 0.010-0.276 and 0.010-0.300 μM, with detection limits of 0.006 and 0.009 μM, respectively. Satisfactory results were also obtained for the analysis of OMZ and LAN in real samples. The excellent sensitivity and easy regeneration and modification of this electrode with DES followed by the polymerization of EBT make this electrode relatively highly applicable for flow methods.

Application of Nanostructured Carbon-Based Electrochemical (Bio)Sensors for Screening of Emerging Pharmaceutical Pollutants in Waters and Aquatic Species: A Review

Pharmaceuticals, as a contaminant of emergent concern, are being released uncontrollably into the environment potentially causing hazardous effects to aquatic ecosystems and consequently to human health. In the absence of well-established monitoring programs, one can only imagine the full extent of this problem and so there is an urgent need for the development of extremely sensitive, portable, and low-cost devices to perform analysis. Carbon-based nanomaterials are the most used nanostructures in (bio)sensors construction attributed to their facile and well-characterized production methods, commercial availability, reduced cost, high chemical stability, and low toxicity. However, most importantly, their relatively good conductivity enabling appropriate electron transfer rates-as well as their high surface area yielding attachment and extraordinary loading capacity for biomolecules-have been relevant and desirable features, justifying the key role that they have been playing, and will continue to play, in electrochemical (bio)sensor development. The present review outlines the contribution of carbon nanomaterials (carbon nanotubes, graphene, fullerene, carbon nanofibers, carbon black, carbon nanopowder, biochar nanoparticles, and graphite oxide), used alone or combined with other (nano)materials, to the field of environmental (bio)sensing, and more specifically, to pharmaceutical pollutants analysis in waters and aquatic species. The main trends of this field of research are also addressed.

A novel Fe-hemin-metal organic frameworks supported on chitosan-reduced graphene oxide for real-time monitoring of H2O2 released from living cells

Herein, a kind of novel hemin-based metal organic frameworks (Fe-hemin-MOFs) with unique peroxidase-like bioactivity was developed for the first time. The synthesized Fe-hemin-MOFs exhibited satisfactory catalytic activity toward hydrogen peroxide (H₂O₂). When it was further supported on Chitosan-reduced graphene oxide (CS-rGO), amplified electrochemical signal could be obtained. The Fe-hemin-MOFs/CS-rGO composite was used to construct a novel H₂O₂ electrochemical sensor. The electrocatalytic reduction of H₂O₂ displayed two segments linearity range from 1 to 61 μM and 61-1311 μM, as well as a low detection limit of 0.57 μM. Furthermore, the proposed sensor was successfully used for real-time monitoring of H₂O₂ released from living cells, which extended the practical application of MOFs-based sensors in monitoring the pathological process in living cells.

Voltammetric Techniques for the Analysis of Drugs using Nanomaterials based Chemically Modified Electrodes

Background:

Electroanalytical techniques play a very important role in the areas of medicinal, clinical as well as pharmaceutical research. Amongst these techniques, the voltammetric methods for the determination of drugs using nanomaterials based chemically modified electrodes (CMEs) have received enormous attention in recent years. This is due to the sensitivity and selectivity they provide on qualitative as well as quantitative aspects of the electroactive analyte under study. The aim of the present review was to discuss the work on nanomaterials based CMEs for the analysis of drugs covering the period from 2000 to present employing various voltammetric techniques for different classes of the drugs.

Methods:

The present review deals with the determination of different classes of drugs including analgesics, anthelmentic, anti-TB, cardiovascular, antipsychotics and anti-allergic, antibiotic and gastrointestinal drugs. Also, a special section is devoted for enantioanalysis of certain chiral drugs using voltammetry. The detailed information of the voltammetric determination for the drugs from each class employing various techniques such as differential pulse voltammetry, cyclic voltammetry, linear sweep voltammetry, square wave voltammetry, stripping voltammetry, etc. are presented in tabular form below the description of each class in the review.

Results:

Various nanomaterials including carbon nanotubes, graphene, carbon nanofibers, quantum dots, metal/metal oxide nanoparticles, polymer based nanocomposites have been used by researchers for the development of CMEs over a period of time. The large surface area to volume ratio, high conductivity, electrocatalytic activity and biocompatibility make them ideal modifiers where they produce synergistic effect which helps in trace level determination of pharmaceutical, biomedical and medicinal compounds. In addition, macrocyclic compounds as chiral selectors have been used for the determination of enantiomeric drugs where one of the isomers captured in the cavities of chiral selector shows stronger binding interaction for one of the enantiomorphs.

Conclusion:

arious kinds of functional nanocomposites have led to the manipulation of peak potential due to drug - nanoparticles interaction at the modified electrode surface. This has facilitated the simultaneous determination of drugs with almost similar peak potentials. Also, it leads to the enhancement in voltammetric response of the analytes. It is expected that such modified electrodes can be easily miniaturized and used as portable, wearable and user friendly devices. This will pave a way for in-vivo onsite real monitoring of single as well as multi component pharmaceutical compounds.

Fabrication of an ultrasensitive and selective electrochemical aptasensor to detect carcinoembryonic antigen by using a new nanocomposite

A lable-free electrochemical aptasensor was successfully developed for the sensitive detection of carcinoembryonic antigen as a tumor biomarker. To do this, a ternary nanocomposite of hemin, graphene oxide and multi-walled carbon nanotubes was used. The aptamer can be attached to the surface of a hemin, graphene oxide and multi-walled carbon nanotubes glassy carbon electrode through -NHCO- covalent bonds to form a sensing surface. Through fourier transform infrared spectroscopy and scanning electron microscopy, it was indicated that hemin can be successfully incorporated into hemin, graphene oxide and multi-walled carbon nanotubes. Hemin, which protects graphene nanosheets, also serves as an in-situ probe owing to its well-defined redox properties. Multi-walled carbon nanotubes in the modifier enhance conductivity and facilitate the electron transfer between hemin and the glassy carbon electrode. In this study, carcinoembryonic antigen got specifically bound to the aptamer, and the current changes were used for selective and specific detection of that antigen. The devised aptasensor proved to have excellent performance with a wide linear range of 1.0 × 10^-15 - 1.0 × 10^-8 gmL^-1 and a detection limit of 0.82 fg mL^-1. The inter-day and intra-day values of RSD% were obtained in the range of 0.10-2.91 and 2.21-4.56 respectively. According to the experiments conducted on real samples, it may be claimed that the proposed label-free electrochemical aptasensor is capable enough of determining carcinoembryonic antigen in clinical diagnostics.

Recent Trends on Electrochemical Sensors Based on Ordered Mesoporous Carbon

The past decade has seen an increasing number of extensive studies devoted to the exploitation of ordered mesoporous carbon (OMC) materials in electrochemistry, notably in the fields of energy and sensing. The present review summarizes the recent achievements made in field of electroanalysis using electrodes modified with such nanomaterials. On the basis of comprehensive tables, the interest in OMC for designing electrochemical sensors is illustrated through the various applications developed to date. They include voltammetric detection after preconcentration, electrocatalysis (intrinsically due to OMC or based on suitable catalysts deposited onto OMC), electrochemical biosensors, as well as electrochemiluminescence and potentiometric sensors.

Mechanistic study of in vitro chemical interaction of trimipramine drug with barbituric derivative after its oxidation: Electrochemical synthesis of new dibenzazepine derivative

Electrochemical oxidation of trimipramine in the absence and presence of 1,3 dimethyl barbituric acid as a nucleophile in aqueous solution has been studied using cyclic voltammetry and controlled-potential coulometry electrolysis. Voltammetric studies of electro-oxidation of trimipramine were realized in a range of pH1.0 to 8.0 in the absence and presence of 1,3 dimethyl barbituric acid. Based on the obtained electrochemical results, dimerization is the main reaction of electro-oxidation of trimipramine in the absence of nucleophile. The voltammetric data indicate that the 1,3 dimethyl barbituric acid participation in Michael addition reaction with the oxidized dimeric form of trimipramine via an ECEC electrochemical mechanisms. On the other hand the results indicate existence of a catalytic (EC') electrochemical mechanism in parallel with ECEC electrochemical mechanism. This method provides a facile and one-pot procedure for the synthesis of new dibenzazepine derivative. Finally, a possible mechanism is proposed for the electrode process, on the basis of the present and previous investigations. The product has been characterized by IR, ¹H NMR, ¹³CNMR and MS methods.

Comparison of unusual carbon-based working electrodes for electrochemiluminescence sensors

In this work, unconventional carbon-based materials were investigated for use in electrochemiluminescence (ECL) working electrodes. Precursors such as bamboo, pistachio shells, kevlar^® fibers and camphor were differently treated and used as working electrodes in ECL experiments. After a proper process they were assembled as electrodes and tested in an electrochemical cell. Comparison among them and with a commercial glassy carbon electrode (GCE) shows a very good response for all of them thus demonstrating their potential use as disposable low-cost electrodes for early detection electrochemical analysis.

Design an aptasensor based on structure-switching aptamer on dendritic gold nanostructures/Fe3O4@SiO2/DABCO modified screen printed electrode for highly selective detection of epirubicin

The present work describes a label free electrochemical aptasensor for selective detection of epirubicin. In this project, 5'-thiole terminated aptamer was self-assembled on carbon screen printed electrode, which modified with electrodeposited gold nanoparticles on magnetic double-charged diazoniabicyclo [2.2.2] octane dichloride silica hybrid (Fe₃O₄@SiO₂/DABCO) by Au-S bond. The interactions of epirubicin with aptamer on the AuNPs/Fe₃O₄@SiO₂/DABCO/SPE have been studied by cyclic voltammetry, linear sweep voltammetry and electrochemical impedance spectroscopy. Under optimized conditions, the peak current of epirubicin increased linearly with increasing epirubicin concentration, due to the switching in the aptamer conformation and formation of aptamer- epirubicin complex instead of aptamer on the modified electrode surface. The Apt/AuNPs/Fe₃O₄@SiO₂/DABCO/SPE is sensitive, selective and has two linear range from 0.07µM to 1.0µM and 1.0µM to 21.0µM with a detection limit of 0.04µM. The applicability of the aptasensor was successfully assessed by determination of epirubicin in a human blood serum sample.

Molecularly imprinted poly(4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid) modified glassy carbon electrode as an electrochemical theophylline sensor

Theophylline is an inexpensive drug employed in asthma and chronic obstructive pulmonary disorder medications and is toxic at higher concentration. The development of a molecularly imprinted polymer based theophylline electrochemical sensor on glassy carbon electrode by the electropolymerization of 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid is being discussed in this work. The MIP modification enhances the theophylline recognition ability and the electron transfer kinetics of the bare electrode. The parameters, controlling the performance of the imprinted polymer based sensor, like number of electropolymerization cycles, composition of the pre-polymerization mixture, pH and immersion time were investigated and optimized. The interaction energy and the most stable conformation of the template-monomer complex in the pre-polymerization mixture were determined computationally using ab initio calculations based on density functional theory. The amperometric measurements showed that the developed sensor has a method detection limit of 0.32μM for the dynamic range of 0.4 to 17μM, at optimized conditions. The transducer possesses appreciable selectivity in the presence of structurally similar interferents such as theobromine, caffeine and doxofylline. The developed sensor showed remarkable stability and reproducibility and was also successfully employed in theophylline detection from commercially available tablets.