Differential Pulse Voltammetry Peak Currents Research Articles

Bio-Inspired Molecularly Imprinted Polymer Electrochemical Sensor for Cortisol Detection Based on O-Phenylenediamine Optimization.

This paper presents a comprehensive investigation of the various parameters involved in the fabrication of a molecularly imprinted polymer (MIP) sensor for the detection of cortisol. Parameters such as monomer concentration, electropolymerization cycles, pH, monomer-template ratio, template removal technique, and rebinding time were optimized to establish a more consistent and effective method for the fabrication of MIP sensors. Under the optimized conditions, the MIP sensor demonstrated a proportional decrease in differential pulse voltammetry peak currents with increasing cortisol concentration in the range of 0.1 to 100 nM. The sensor exhibited excellent sensitivity, with a limit of detection of 0.036 nM. Selectivity experiments using a non-imprinted polymer sensor confirmed the specific binding affinity of the MIP sensor for cortisol, distinguishing it from other steroid hormones. This study provides crucial insights into the development of a reliable and sensitive strategy for cortisol detection using O-PD-based MIPs. These findings laid the foundation for further advancements in MIP research.

Construction of a dual-mode biosensor for electrochemiluminescent and electrochemical sensing of alkaline phosphatase

We demonstrate the construction of a dual-mode biosensor based on fully-π conjugated covalent organic framework (COF) and cobalt oxyhydroxide (CoOOH) nanoflakes for electrochemiluminescent (ECL) and electrochemical sensing of alkaline phosphatase (ALP). The fully-π conjugated COF with sp2 carbon-linkage is synthesized through Knoevenagel polycondensation of 2, 5-dimethoxy-terephthalaldehyde (DMTA) and 1,3,5-tris(4-cynomethylphenyl)benzene (TCPB), and it acts as an efficient ECL emitter whose signal is 41 and 125-fold higher than those of TCPB and DMTA. The ECL signal of TCPB-DMTA-COF may be quenched by CoOOH nanoflakes through electrochemiluminescent resonance energy transfer, and meanwhile CoOOH promotes the oxidation of o-phenylenediamine (o-PD) to generate a high differential pulse voltammetry (DPV) signal. When ALP is present, it hydrolyzes L-ascorbic acid-2-phosphate (AAP) to produce L-ascorbic acid (AA). AA can reduce CoOOH to Co2+, resulting in the decomposition of the CoOOH nanoflakes and consequently the recovery of ECL signal and the decrease of DPV peak current. This dual-mode biosensor can efficiently eliminate the errors associated with personnel operation and experimental factors, leading to more reliability and accuracy than single-mode biosensor. Moreover, this dual-mode biosensor can be applied for specifically sensing ALP in human serums and screening the inhibitors, with potential applications in biomedical researches.

Ultrasensitive Electrochemical Detection of Carcinoembryonic Antigen with a Label‐Free Immunosensor Using Gold Nanoparticle‐Decorated Poly(pyrrole‐co‐3,4‐ethylenedioxythiophene)

AbstractIn this study, an electrochemical immunosensor was developed using gold nanoparticles (AuNPs), 3,4‐ethylenedioxythiophene (EDOT), and pyrrole (Py) to detect carcinoembryonic antigen (CEA) sensitively. Firstly, the electrocopolymerization of PPy and EDOT was carried out on a pencil graphite electrode (PGE) by the chronoamperometry method (p(Py‐co‐EDOT)/PGE). Then, gold nanoparticles were electrochemically deposited on the prepared p(Py‐co‐EDOT)/PGEs by the chronoamperometry method. The characterizations of the developed label‐free immunosensor (AuNPs/p(Py‐co‐EDOT)/PGE) were carried out using CV, EIS, XPS, SEM, EDX, and FTIR methods. Antibody concentration, antibody immobilization time, and immunocomplex time were optimized using differential pulse voltammetry (DPV). After optimal conditions are determined, the DPV peak current of the immunosensor decreases linearly with increasing CEA concentration of 0.001–100 ng mL−1. The detection limit was calculated as 0.741 pg mL−1 from the calibration graph (S/N=3). The developed sensor showed excellent anti‐interference ability against ascorbic acid, bovine serum albumin, dopamine, and glucose. The applicability of the developed sensor to real samples was investigated, and good recovery values were obtained. As a result, the AuNPs/p(Py‐EDOT)/PGE provides low‐cost, selective, and rapid detection of CEA. Our findings suggest the present immunosensor is a good candidate for application in clinical screening.

Smartphone-based electrochemical system with multi-walled carbon nanotubes/thionine/gold nanoparticles modified screen-printed immunosensor for cancer antigen 125 detection

In the paper, a smartphone-based electrochemical system with differential pulse voltammetry (DPV) measurement was developed for cancer antigen 125 (CA125) detection. The system was composed of screen-printed immunosensor, miniaturized electrochemical detector and Android smartphone. Combined with multi-walled carbon nanotubes (MWCNTs)/ thionine (Thi)/ gold nanoparticles (AuNPs) modified screen-printed immunosensor, miniaturized electrochemical detector realized high accuracy detection of CA125. The datum were transmitted to Android smartphone through Bluetooth. The detector was powered by audio jack of smartphone, which also used 3.3 V button cell and USB as additional power supply. Android application (APP) running on a smartphone served to control detection process and show detection results. The experimental results indicated that there had good linear relationship between DPV peak currents and the logarithm of CA125 concentrations in the range from 1.3 U mL−1 to 260 U mL−1. The limit of detection (LOD) was 2 mU mL−1. The smartphone-based electrochemical system was also evaluated for the analysis of human serum sample. The detection results showed good agreement with the Roche electrochemicalluminescenceimmunoassay (ECLIA) tests. The proposed system provided a new method for tumor marker detection in remote medicine centre or developing area.

Electrochemical Immunosensing of Interleukin-6 in Human Cerebrospinal Fluid and Human Serum as an Early Biomarker for Traumatic Brain Injury.

In this work, we develop a label-free electrochemical immunosensor for the detection of interleukin-6 (IL-6) in human cerebrospinal fluid (CSF) and serum for diagnostic and therapeutic monitoring. The IL-6 immunosensor is fabricated from gold interdigitated electrode arrays (IDEAs) that are modified with IL-6 antibodies for direct antigen recognition and capture. A rigorous surface analysis of the sensor architecture was conducted to ensure high structural fidelity and performance. Electrochemical characterization was conducted by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and sensing was performed using differential pulse voltammetry (DPV). The DPV peak current was used to quantify IL-6 in buffer, CSF, and serum in the range 1 pg mL-1 < [IL-6] < 1 μg mL-1. The IL-6 IDEA sensor achieved a limit of detection (LOD) of 1.63 pg mL-1 in PBS, 2.34 pg mL-1 in human CSF, and 11.83 pg mL-1 in human serum. The sensor response is linear in the concentration range 10 pg mL-1 < [IL-6] < 10 ng mL-1, and the sensor is selective for IL-6 over other common cytokines, including IL-10 and TNF-α. EIS measurements showed that the resistance to charge transfer, R CT, decreases upon IL-6 binding, an observation attributed to a structural change upon Ab-Ag binding that opens up the architecture so that the redox probe can more easily access the electrode surface. The IL-6 IDEA sensor can be used as a point-of-care diagnostic tool to deliver rapid results (∼3 min) in clinical settings for traumatic brain injury, and potentially address the unmet need for effective diagnostic and prognostic tools for other cytokine-related illnesses, such as sepsis and COVID-19 induced cytokine storms. Given the interdigitated electrode form factor, it is likely that the performance of the sensor can be further improved through redox cycling.

Ratiometric electrochemical biosensor for ultrasensitive and highly selective detection of p53 gene based on nicking endonuclease-assisted target recycling and rolling circle amplification

Tumor suppressor p53 gene is one vital anticancer gene that plays critical role in the prevention, diagnosis, and prognosis evaluation of cancers. Specific recognition and sensitive detection of p53 gene is important for early cancer screening and diagnosis. A ratiometric electrochemical biosensor is developed for ultrasensitive detection of tumor suppressor p53 gene in this work. Hairpin capture probe (Fc-HP-SH) is labeled with ferrocene (Fc) at the 3′ termini and thiol group at the 5′ termini. Fc-HP-SH was self-assembled on the surface of gold electrode through Au-S binding, while 6-mercaptohexanol was used to block the unoccupied sites on electrode surface. At the presents of p53 gene and nicking endonuclease, p53 gene specifically hybridizes with the loop sequences of Fc-HP-SH to unwind the hairpin structure. Nicking endonuclease subsequently cleaves DNA duplex to release p53 gene for target recycling. Residual single-stranded oligonucleotide is prolonged with the help of phi29 DNA polymerase via rolling circle amplification, leading to the increased gathering of electroactive probe methylene blue (MB) on long polynucleotide. Such variations cause the alterations of the differential pulse voltammetry peak currents of Fc at + 0.32 V (vs. Ag/AgCl) and MB at − 0.25 V (vs. Ag/AgCl), resulting in an obvious enhancement of the ratiometric signal of two peak currents. Under optimum experimental conditions, this biosensor has a response that covers the 1 fM to 10 pM p53 gene concentration range, and the detection limit is 0.23 fM (for S/N = 3). This biosensor highly recognized p53 gene over its mutants and was successfully applied in human serum samples. This approach shows excellent reproducibility, acceptable stability, good selectivity, and ultrahigh sensitivity toward p53 gene detection.

Highly sensitive electrochemical sensor based on Pt nanoparticles/carbon nanohorns for simultaneous determination of morphine and MDMA in biological samples

Morphine and 3,4-methylenedioxymethamphetamine (MDMA or Ecstasy) are two majorly abused drugs worldwide, which are harmful to human health and social stability. Therefore, it is necessary to detection morphine and MDMA rapidly and sensitively. In this study, a highly sensitive electrochemical sensor for simultaneous determination of morphine and MDMA was developed based on high surface area carbon nanohorns decorated with Pt nanoparticles (CNHs@PtNPs). Under the optimized conditions, CNHs@PtNPs nanocomposite with three-dimensional structure exhibits good electrocatalytic activity toward morphine and MDMA. Differential pulse voltammetry peak currents increase linearly with analyte concentration. At the potential of 0.2 V and 1.0 V (vs. SCE), the fabricated electrode shows excellent sensing performance for morphine and MDMA with a wide linear range between 0.05 and 25.4 μmol L−1, and detection limit of 0.02 μmol L−1 and 0.018 μmol L−1, respectively. Furthermore, the sensor exhibits good selectivity, repeatability and stability. Our developed method is also successfully applied to the highly sensitive determination of morphine and MDMA in human serum and urine samples with satisfactory results.

Simultaneous electrochemical determination of nuc and mecA genes for identification of methicillin-resistant Staphylococcus aureus using N-doped porous carbon and DNA-modified MOF.

The detection of Staphylococcus aureus specific gene in combination with the mecA gene is vitally important for accurate identification of methicillin-resistant Staphylococcus aureus (MRSA). A homogeneous electrochemical DNA sensor was fabricated for simultaneous detection of mecA and nuc gene in MRSA. Metal-organic framework (type UiO-66-NH2) was applied as nanocarrier. Two electroactive dyes, methylene blue (MB) and epirubicin (EP), were encapsulated in UiO-66-NH2,respectively, and were locked by the hybrid double-stranded DNA. Based on the target-response electroactive dye release strategy, once target DNA exists, it completely hybridizes with displacement DNA (DEP and DMB). So DEP and DMB is displaced from the MOF surface, causing the release of electroactive dyes. Co-Zn bimetallic zeolitic imidazolate framework-derived N-doped porous carbon serves for electrode modification to improve electrocatalytic performance and sensitivity. The differential pulse voltammetry peak currents of MB and EP were accurately detected at - 0.14V and - 0.53V versus the Ag/AgCl reference electrode, respectively. Under the optimal conditions, the detection limits of mecA gene and nuc gene were 3.7fM and 1.6fM, respectively. Combining the effective application of MOFs and the homogeneous detection strategy, the sensor exhibited satisfactory performance for MRSA identification in real samples. The recovery was 92.6-103%, and the relative standard deviation was less than 5%. Besides, MRSA and SA can also be distinguished. This sensor has great potential in practical applications.

Molecularly Imprinted Sensor for Ascorbic Acid Based on Gold Nanoparticles and Multiwalled Carbon Nanotubes

Background: L-Ascorbic acid (AA) is a kind of water soluble vitamin, which is mainly present in fruits, vegetables and biological fluids. As a low cost antioxidant and effective scavenger of free radicals, AA may help to prevent diseases such as cancer and Parkinson’s disease. Owing to its role in the biological metabolism, AA has also been utilized for the therapy of mental illness, common cold and for improving the immunity. Therefore, it is very necessary and urgent to develop a simple, rapid and selective strategy for the detection of AA in various samples. Methods: The molecularly imprinted poly(o-phenylenediamine) (PoPD) film was prepared for the analysis of L-ascorbic acid (AA) on gold nanoparticles (AuNPs) - multiwalled carbon nanotubes (MWCNTs) modified glass carbon electrode (GCE) by electropolymerization of o-phenylenediamine (oPD) and AA. Experimental parameters including pH value of running buffer and scan rates were optimized. Scanning electron microscope (SEM), fourier-transform infrared (FTIR) spectra, cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were utilized for the characterization of the imprinted polymer film. Results: Under the selected experimental conditions, the DPV peak currents of AA exhibit two distinct linear responses ranging from 0.01 to 2 μmol L-1 and 2 to 100 μmol L-1 towards the concentrations of AA, and the detection limit was 2 nmol L-1 (S/N=3). Conclusion: The proposed electrochemical sensor possesses excellent selectivity for AA, along with good reproducibility and stability. The results obtained from the analysis of AA in real samples demonstrated the applicability of the proposed sensor to practical analysis.

Electrochemical determination of glutathione in hemolysed erythrocytes

The physiological significance of determining glutathione (GSH) and its oxide form is obvious from their applications in clinical practices such as diagnostic experiments for diabetes, Parkinson’s disease, and cancers. Such an important detemination still needs the development of certain experimental procedures that are easy, fast, and cheap enough to implement. These procedural advantages can be provided through electrochemical methods. Therefore, in this study, at the surface of a glassy carbon electrode (GCE), a composite of functionalized multi-walled carbon nanotubes (MWCNTs) and formazon was used as a mediator to determine GSH electrochemically. The results indicated that this modified GCE is electrocatalytically very active for glutathione oxidation. Several techniques including cyclic voltammetry (CV), scanning electron microscopy (SEM), and differential pulse voltammetry (DPV) were used to characterize the electrode. Also, such kinetic parameters as the charge transfer rate constant and the transfer coefficient were calculated. In optimized conditions, there was a linear relationship between the DPV peak current of GSH oxidation and GSH concentration in the ranges of 1.0-100.0 and 100.0-800.0 µM at pH 7.0. As for the detection limit, it was found to be 0.73 µM.

A ratiometric electrochemical aptasensor for ultrasensitive determination of adenosine triphosphate via a triple-helix molecular switch.

A ratiometric electrochemical aptamer-based assay is described for the ultrasensitive and highly specific determination of adenosine triphosphate (ATP). It is based on ATP aptamer-mediated triple-helix molecular switch (THMS). The method uses (a) a hairpin DNA (MB-DNA-SH) labeled with the redox probe Methylene Blue (MB) at the 3' end, and a thiol group at the 5' end, and (b) a single strand ATP aptamer modified with two ferrocenes at each end (Fc-DNA-Fc). The labeled probe of type MB-DNA-SH was self-assembled onto the surface of a gold electrode via gold-thiol binding. On exposure to Fc-DNA-Fc, it will hybridize with MB-DNA-SH to form a stable THMS structure on electrode surface. In the presence of ATP, it hybridizes with the loop portion of Fc-DNA-Fc, and this results in the unwinding of the THMS structure. Such variation caused the changes of the differential pulse voltammetry (DPV) peak currents of both MB (at around -0.25V) and Fc (at around 0.39V; both vs. Ag/AgCl). A significant enhancement is found for the ratio of the two DPV peaks. Under the optimum experimental conditions, this assay has a response that covers the 0.05 to 100 pM ATP concentration range, and the detection limit is 5.2 fM (for S/N= 3). The method is highly selective for ATP over its analogs. Graphical abstract Schematic presentation of a novel ratiometric electrochemical aptasensor for ATP via triple-helix molecular switch (THMS) strategy. MB-DNA-SH was self-assembled on GE surface through gold-thiol binding. Fc-DNA-Fc hybridized with MB-DNA-SH to form THMS structure. ATP specifically bond with its aptamer sequence of Fc-DNA-Fc to unwind the THMS structure. The ratio of DPV peak currents of MB and Fc was applied to monitor the concentration of ATP in real samples over its analogs.

Synthesis and characterization of NiFe2O4 nanoparticles using the hydrothermal method as magnetic catalysts for electrochemical detection of norepinephrine in the presence of folic acid

AbstractIn this article, we present a simple and efficient method to synthesize a magnetic NiFe2O4 nanocatalyst under hydrothermal conditions. Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X‐ray spectroscopy (EDX) analyses confirmed the synthesis of NiFe2O4 nanoparticles. These nanoparticles showed satisfactory catalytic activity for determination of norepinephrine (NE) in the presence of folic acid (FA) using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. Differential pulse voltammetry peak currents of NE increased linearly with their concentrations in the range of 1.0 × 10−7–5.0 × 10−4 M, and the detection limit for NE was 2.3 × 10−8 M, respectively. The modified electrode displayed strong function for resolving the overlapping voltammetric responses of NE and FA into two well‐defined voltammetric peaks. In the mixture containing NE and FA, the two compounds can well separate from each other with a potential difference of 510 mV between NE and FA, which was large enough to determine NE and FA individually and simultaneously. Additionally, the prepared electrochemical sensor demonstrated a practical feasibility for real sample determination.

An ultrasensitive electrochemical anti-lysozyme aptasensor with biorecognition surface based on aptamer/amino-rGO/ionic liquid/amino-mesosilica nanoparticles

In this work, a novel method based on aptamers is proposed for electrochemical measurement of lysozyme. To this end, screen-printed carbon electrode (SPCE) was modified with a nanocomposite made from amino-reduced graphene oxide (Amino-rGO) synthesized from natural graphite powder, an ionic liquid (IL), and amino-mesosilica nanoparticles (Amino-MSNs). The composition of the nanocomposite (Amino-rGO/IL/Amino-MSNs) results in high thermal and chemical stability, conductivity, surface-to-volume ratio, cost efficiency, biocompatibility, and great bioelectrocatalysis characteristics. Presence of numerous amino groups, as well as remaining oxygen defects in rGO, provides a suitable site for immobilization of aptamers. Furthermore, use of this nanocomposite leads to considerable enhancement of the electrochemical signal and improved method sensitivity. Covalent coupling of aptamer’s amino groups with that of the nanocomposite using glutaraldehyde (GLA) as a linker helps immobilize amino-linked lysozyme aptamers (Anti-Lys aptamers) on nanocomposite. The modified electrode was characterized using electrochemical methods such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The immobilized aptamer selectively adsorbs lysozyme (Lys) on the electrode interface, leading to increased Charge Transfer Resistance (RCT) in EIS and decrease in the DPV peak currents which are used as analytical signals. Two separate calibration curves were drawn using the data acquired from EIS and DPV. The prepared anti-Lys aptasensor has two very low LODs equal to 2.1 and 4.2 fmol L−1 with wide detection ranges of 10 fmol L−1 to 200 nmol L−1, and 20 fmol L−1 to 50 nmol L−1 for EIS and DPV calibration curves, respectively. The SPCE/Amino-rGO/IL/Amino-MSNs/APT also showed high reproducibility, specificity, sensitivity, and rapid response to Lys which has various applications in fields of bioengineering and biomedicine.

Carvacrol electrochemical reaction characteristics on screen printed electrode modified with La2O3/Co3O4 nanocomposite

Electrochemical characteristics of carvacrol were investigated on a screen-printed electrode (SPE) modified with La2O3/Co3O4 nanocomposite by using voltammetric techniques, which displayed a well-defined peak for sensitive carvacrol determination in phosphate buffer solution (PBS) at pH 7.0. La2O3/Co3O4 nanoparticles demonstrated suitable catalytic activity for carvacrol determination by differential pulse voltammetry (DPV) technique. Besides, determination of carvacrol in a real samples was recognized in the light of electrochemical findings and a validated voltammetric technique for quantitative analysis of carvacrol in a real formulation was proposed. The DPV peak currents were found to be linear in the concentration range of 10.0 to 800.0 μM. The limit of detection (LOD) was found to be 1.0 μM.

DNA concatemer-silver nanoparticles as a signal probe for electrochemical prostate-specific antigen detection.

In this study, we report a metallobioassay for ultrasensitive electrochemical detection of prostate-specific antigen (PSA) based on DNA hybridization chain reaction (HCR) for amplifying the signal, which is derived from silver nanoparticles (Ag NPs) on DNA concatemers. The assay mainly consists of primary antibody (Ab1), secondary antibody (Ab2) with primer, and a signal probe. In the presence of PSA, a sandwich structure with DNA concatemers was formed, and numerous Ag NPs were loaded on the DNA concatemers, resulting in a strong signal, which appeared within the applied potential (-0.2 V to 0.3 V) in the phosphate-buffered saline (PBS). Differential pulse voltammetry (DPV) was employed to evaluate the analytical performance. Under optimal conditions, the DPV peak current of Ag NPs at about +0.09 V (vs. SCE) increased linearly as the logarithm of PSA concentration increased from 0.1 pg mL-1 to 75 ng mL-1, and the detection limit of PSA was estimated to be 0.033 pg mL-1 at the signal to noise ratio of 3. In addition, the assay was evaluated with human serum samples, and satisfying results were obtained, indicating that the assay can achieve PSA detection in the serum sample.

Highly Sensitive Label-Free Electrochemical Aptasensor Based on Screen-Printed Electrode for Detection of Cadmium (II) Ions

In this study, a simple but highly sensitive label-free aptasensor based on a screen-printed electrode (SPE) was developed for detection of Cd2+. As crucial biorecognizer, the Cd2+ aptamer (issAP08-Cd2+) was first screened out using the isothermal titration calorimetric method, which showed that the equilibrium dissociation constant (KD) of Cd2+ binding with issAP08-Cd2+ was 2.9 μM. Then, the issAP08-Cd2+, which is a single-stranded DNA with 25 nucleotides, was modified with thiol and assembled on gold screen-printed electrode. After that, the electrochemical aptasensor was used for Cd2+ detection by dropping Cd2+ solution on the SPE. The electrochemical properties were characterized by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under the optimal conditions, the change of DPV peak currents density values (Δi) increased linearly with the logarithm of Cd2+ concentrations from 0.1 ng/mL to 1000 ng/mL. The regression coefficient was 0.9914 and the limit of detection (LOD) was 0.05 ng/mL (S/N = 3). This outcome supported the conclusion that the electrochemical aptasensor not only showed good sensitivity and selectivity but also obtained satisfactory reproducibility and stability results and performance on applications in real samples. More importantly, the composition of this aptasensor is very simple, and it has promising potential for rapid field detection of Cd2+.

Nanoraspberry-like copper/ reduced graphene oxide as new modifier for simultaneous determination of benzenediols isomers and nitrite

In this study, immobilized nanoraspberry-like copper on the reduced graphene oxide (NRCu-rGO) was synthesized and used for modification of glassy carbon electrode (GCE) for selective and sensitive simultaneous determination of benzenediols isomers; hydroquinone (HQ), catechol (CC), resorcinol (RS) as well as nitrite (NO2−). A detailed investigation such as field emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction as well as electrochemistry methods such as cyclic voltammetry, electrochemical impedance spectroscopy, differential pulse voltammetry (DPVs) and chronoamperometry are performed in order to elucidate the preparation process and properties of the NRCu-rGO/GCE. DPVs peak currents increased linearly with the analytes concentrations within the ranges of 0.13–131.5 μM for HQ, CC, RS and 0.3–131.5 μM for NO2− with a detection limits 49, 52, 60 and 100 nM for HQ, CC, RS and NO2−, respectively. The proposed modified electrode was successfully used for simultaneous determination of HQ, CC, RS and NO2− in real samples.

Preparation and characterization of a carbon nanotube-based ceramic electrode and its potential application at detecting sulfonamide drugs

In this work, we report the construction, characterization, and the potential application of carbon-ceramic electrodes prepared with functionalized multi-walled carbon nanotubes (CCE/f-MWCNT) to detect two sulfonamide drugs: sodium sulfacetamide (SFC) and sulfadiazine (SFD). Prior to the construction of CCE/f-MWCNT, MWCNT samples were functionalized by using an acid treatment (HNO3/HClO4), and then characterized by FTIR spectroscopy, XRD, FESEM, and Raman spectroscopy. These techniques were also employed to characterize the prepared carbon-ceramic electrodes, and the obtained results demonstrated that the MWCNT were properly dispersed in the silica matrix. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy experiments showed that the f-MWCNT could enhance the electrochemical performance of the electrodes, as a consequence of its high electrical conductivity and large surface area. The antibacterial drugs were determined with CCE/f-MWCNT by employing CV and differential pulse voltammetry (DPV). A linear relationship between DPV peak currents and SFC and SFD concentrations was verified separately in the range from 9.9 to 177.0 µmol L− 1 in 0.04 mol L− 1 BR buffer solution pH 6.0. Detection and quantification limits were found to be 1.06 and 3.54 µmol L− 1 for SFC and 2.31 and 7.71 µmol L− 1 for SFD, respectively. Besides the good sensitivity, the CCE/f-MWCNT showed reproducibility and specificity, since its response was not significantly affected by the presence of electroactive interfering compounds. The promising analytical performance of the CCE/f-MWCNT was confirmed by determining SFC and SFD in commercial veterinary formulations, with percent recoveries ranging from 99.9 to 101.1% for SFC and from 99.8 to 102.2% for SFD.

Highly Sensitive Nanostructured Electrochemical Sensor Based on Carbon Nanotubes-Pt Nanoparticles Paste Electrode for Simultaneous Determination of Levodopa and Tyramine

A multicomponent electrochemical sensor, with two nanometer-scale components in sensing matrix/electrode, was used to simultaneous determination of levodopa (LD) and tyramine (TR) in pharmaceutical and diet samples. Multiwall carbon nanotubes (MWCNTs) were used as carbonaceous materials in the electrode construction. 5-amino-3',4'-dimethoxy-biphenyl-2-ol (5ADMB) was used as electron mediator and Pt nanoparticles (nPt) as a catalyst. The 5ADMB catalyzes the oxidation of LD to the corresponding catecholamine, which is electrochemically reduced back to LD. Preparation of this electrode was very simple and modified electrode showed good properties at electrocatalytic oxidization of LD and TR. Using differential pulse voltammetry (DPV), a highly selective and simultaneous determination of LD and TR has been explored at the modified electrode. Differential pulse voltammetry peak currents of LD and TR increased linearly with their concentrations at the ranges of 0.50–100.0 μM and 0.60–100.0 μM, respectively. Also, the detection limits for LD and TR were 0.31 and 0.52 μM, respectively. The electrode exhibited an efficient catalytic response with good reproducibility and stability.

Ultrasensitively electrochemical detection activity of DNA methyltransferase using an autocatalytic and recycling amplification strategy

Herein, we report a novel approach to the ultrasensitive detection of DNA methyltransferase (MTase) in terms of a dual-signal recycling amplification strategy assisted by an autocatalytic and exonuclease III (Exo III). A duplex DNA probe was designed by G-quadruplex-forming oligomer (S1) hybridizing with ferrocene (Fc)-labeled DNA (S2) modified on Au electrode. With DNA adenine methylation (Dam) MTase, the response of the hairpin probe to methylation is methylated. Then it can be cleaved by the methylation-sensitive restriction endonuclease Dpn I, releasing S3. The released S3 sequence hybridizes with the dangling end of S2 sequence, forming a new duplex DNA. Then the Exo III can cleave the S2 sequence step by step, with the release of Fc from the sensing interface and autonomous generation of new secondary S3 for successive hybridization and cleavage. Meanwhile, S1 sequences on the electrode surface are folded into G-quadruplex-hemin complexes by adding K+ and hemin to give a remarkable electrochemical response. Such conformational changes result in the decrease of differential pulse voltammetry (DPV) peak current of Fc and increase of the DPV peak current of G-quadruplex-hemin complexes. The dual-signal changes are linear with the concentration of DNA MTase. This novel, single electrode-based dual-signal assay strategy is superior to previous Dam assays using single electrochemical signal as output.