Follow up of the prostate cancer treatment based on a novel sensing method for anti-prostate cancer drug (flutamide).

In this work, novel modified electrode (MXene/MIL-101(Cr)/GCE) are manufactured through simple layer-by-layer immobilization procedure. The fabricated electrochemical sensor was utilized for electrochemical sensing of flutamide in biological fluids. The immobilization of both MXene and metal-organic framework (MOF) materials on the electrode surface could improve the electrochemical performance of the modified glassy carbon electrode (GCE) towards flutamide due to the synergic effects. The established sensor illustrated the significant sensing ability for the determination of flutamide. The influence of solution pH and volume ratio of MXene/MIL-101(Cr) on electrochemical performance of the modified GCE was researched and optimized. The sensor demonstrated a favorable detection limit of 0.009 µM and a linear range of 0.025-100 µM using differential pulse voltammetry (DPV) technique. The suggested assay illustrated an excellent sensing efficiency towards flutamide in body fluids with recoveries ranging from 97.7% to 102.5%, which indicates its potential in real matrices. In addition, the MXene/MIL-101(Cr)/GCE was illustrated some advantages including simple preparation, good selectivity and reproducibility, and rapid flutamide detection.

Stereoselective Voltammetric Biosensor for Myo-Inositol and D-Chiro-Inositol Recognition.

This paper describes the development of a simple voltammetric biosensor for the stereoselective discrimination of myo-inositol (myo-Ins) and D-chiro-inositol (D-chiro-Ins) by means of bovine serum albumin (BSA) adsorption onto a multi-walled carbon nanotube (MWCNT) graphite screen-printed electrode (MWCNT-GSPE), previously functionalized by the electropolymerization of methylene blue (MB). After a morphological characterization, the enantioselective biosensor platform was electrochemically characterized after each modification step by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The results show that the binding affinity between myo-Ins and BSA was higher than that between D-chiro-Ins and BSA, confirming the different interactions exhibited by the novel BSA/MB/MWCNT/GSPE platform towards the two diastereoisomers. The biosensor showed a linear response towards both stereoisomers in the range of 2-100 µM, with LODs of 0.5 and 1 µM for myo-Ins and D-chiro-Ins, respectively. Moreover, a stereoselectivity coefficient α of 1.6 was found, with association constants of 0.90 and 0.79, for the two stereoisomers, respectively. Lastly, the proposed biosensor allowed for the determination of the stereoisomeric composition of myo-/D-chiro-Ins mixtures in commercial pharmaceutical preparations, and thus, it is expected to be successfully applied in the chiral analysis of pharmaceuticals and illicit drugs of forensic interest.

Highly sensitive voltammetric determination of NADH based on N-CQDs decorated SnO2/ionic liquid/carbon paste electrode.

A highly sensitive and selective modified electrode was successfully developed for the monitoring of nicotinamide adenine dinucleotide (NADH) in the presence of folic acid. In this regard, a carbon paste electrode (CPE) was functionalized by the nitrogen-doped carbon quantum dots/tin oxide (N-CQDs/SnO2) nanocomposite and 1-butyl-2,3-dimethyl imidazolium hexafluorophosphate ([C4DMIM][PF6]) ionic liquid (IL). The structure and surface morphology of the nanocomposite were characterized by various methods, including field emission scanning electron microscopy, energy dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD). The modified electrode displayed powerful and long-lasting electron mediating activity, with well-separated NADH and folic acid oxidation peaks. The sensing response of the developed [C4DMIM][PF6]/N-CQDs/SnO2/CPE platform was evaluated by determining NADH via the voltammetric technique under the optimized operating conditions. The current peaks of the square wave voltammograms of NADH and folic acid increased linearly with enhancing its concentrations within the ranges of 0.003-275µM NADH and 0.4-380µM folic acid. The detection limits for NADH and folic acid were obtained at 0.8 nM and 0.1µM, respectively. Interference species such as glucose, urea, tryptophan, glycine, methionine, and vitamin B12had no influence on the ability of the fabricated modified electrode to detect the target species. The low detection limit, high sensitivity, excellent selectivity, superior stability, and cost-effectiveness made it suitable for the quantification of NADH in the real biological samples with the recovery percent values in the range of 97.5%-103%.

Ultrasensitive voltammetric detection of SARS-CoV-2 in clinical samples.

In every pandemic, it is critical to test as many people as possible and keep track of the number of new cases of infection. Therefore, there is a need for novel, fast and unambiguous testing methods. In this study, we designed a sandwich-type voltammetric immunosensor based on unlabeled- and labeled with a redox probe antibodies against virus spike protein for fast and ultrasensitive detection of SARS-CoV-2. The process of the preparation of the sensor layer included chemisorption of cysteamine layer and covalent anchoring of antibody specific for the S1 subunit of the S protein. The source of the voltametric signal was the antibody labeled with the redox probe, which was introduced onto biosensor surface only after the recognition of the virus. This easy-to-handle immunosensor was characterized by a wide analytical range (2.0·10-7 to 0.20 mg·L-1) and low detection limit (8.0·10-8 mg·L-1 ≡ 0.08 pg·mL-1 ≡ 4 virions·µL-1). The utility of the designed device was also evidenced by the detection of SARS-CoV-2 in the clinical samples. Moreover, the main advantage and a huge novelty of the developed device, compared to those already existing, is the moment of generating the analytical signal of the redox probe that appears only after the virus recognition. Thus, our diagnostic innovation may considerably contribute to controlling the COVID-19 pandemic. The as-developed immunosensor may well offer a novel alternative approach for viral detection that could complement or even replace the existing methods.

Sensitive Determination of Trace 4-Nitrophenol in Ambient Environment Using a Glassy Carbon Electrode Modified with Formamide-Converted Nitrogen-Doped Carbon Materials.

Sensing trace amounts of 4-nitrophenol (4-NP) as a harmful substance to organisms even in small quantities is of great importance. The present study includes a sensitive and selective electrochemical sensor for detecting 4-NP in natural water samples using formamide-converted nitrogen-carbon materials (shortened to f-NC) as a new material for electrode modification. The structure and morphology of the f-NC were set apart by SEM, TEM, XRD, XPS, FTIR, Raman, and the electrochemical performance of the f-NC were set apart by CV, EIS and CC. We studied the electrochemical behaviour of 4-NP on the glassy carbon electrode modified with f-NC before and after pyrolysis treatment (denoted as f-NC1/GCE and f-NC2/GCE). In 0.2 M of H2SO4 solution, the f-NC2/GCE has an apparent electrocatalytic activity to reduce 4-NP. Under the optimal conditions, the reduction peak current of 4-NP varies linearly, with its concentration in the range of 0.2 to 100 mM, and the detection limit obtained as 0.02 mM (S/N = 3). In addition, the electrochemical sensor has high selectivity, and the stability is quite good. The preparation and application of the sensor to detect 4-NP in water samples produced satisfactory results, which provides a new method for the simple, sensitive and quantitative detection of 4-NP.

Construction of an electrochemical sensor with graphene aerogel doped with ZrO2 nanoparticles and chitosan for the selective detection of luteolin.

A simple, fast and sensitive method for the detection of luteolin is proposed based on the chitosan/reduced graphene oxide aerogel with dispersed ZrO2 nanoparticles modified glassy carbon electrode (ZrO2/CS/rGOA-GCE) as an electrochemical sensor. The ZrO2/CS/rGOA composite was prepared by one pot synthesis from a mixture of GO, CS and zirconyl chloride octahydrate, and subsequently be freeze-dried. Scanning electron microscope images showed a typical thin, wrinkled and fluctuant morphology of graphene nanosheets and the polymerized CS and ZrO2 nanoparticles deposited on the surface of rGOA. Cyclic voltammetry and differential pulse voltammetry were used to measure the electrochemical response of ZrO2/CS/rGOA composite-based biosensor towards luteolin at the working potential window (-0.8-0.8 V). The improved performance of this biosensor was attributed to efficient electron transfer and large surface area of 3D rGOA, and high specific activity of Zr towards adjacent hydroxyl groups. Under optimized conditions, the analytical performance of this method towards luteolin was investigated with a detection limit of 1 nM and a linear range from 5 nM to 1000 nM.. Finally, the ZrO2/CS/rGOA-GCE electrochemical method coupled with solid phase extraction was used for the detection of luteolin in real samples. Recoveries of  spiked samples with different concentrations were in the range 78.6-103.3% with a relative RSD lower than 12.0%. Graphical abstract Schematic representation of the preparation of the ZrO2 nanoparticles and chitosan doped graphene aerogel modified electrode. The electrode was employed for the detection of luteolin coupled with the solid-phase extraction technique.

Intertwined Carbon Nanotubes and Ag Nanowires Constructed by Simple Solution Blending as Sensitive and Stable Chloramphenicol Sensors.

Chloramphenicol (CAP) is a harmful compound associated with human hematopathy and neuritis, which was widely used as a broad-spectrum antibacterial agent in agriculture and aquaculture. Therefore, it is significant to detect CAP in aquatic environments. In this work, carbon nanotubes/silver nanowires (CNTs/AgNWs) composite electrodes were fabricated as the CAP sensor. Distinguished from in situ growing or chemical bonding noble metal nanomaterials on carbon, this CNTs/AgNWs composite was formed by simple solution blending. It was demonstrated that CNTs and AgNWs both contributed to the redox reaction of CAP in dynamics, and AgNWs was beneficial in thermodynamics as well. The proposed electrochemical sensor displayed a low detection limit of up to 0.08 µM and broad linear range of 0.1-100 µM for CAP. In addition, the CNTs/AgNWs electrodes exhibited good performance characteristics of repeatability and reproducibility, and proved suitable for CAP analysis in real water samples.

A fast method for the detection of irinotecan in plasma samples by combining solid phase extraction and differential pulse voltammetry.

In this paper, a fast method for the detection of irinotecan (CPT-11) in plasma samples was investigated. CPT-11 is widely used in a number of chemotherapeutic treatments of several solid tumors. The method is based on the combination of a solid phase extraction and an electrochemical detection step. The extraction of CPT-11 from plasma was performed using solid phase extraction (SPE) columns and acetonitrile as eluent. The procedure included also a cleaning step to eliminate interference due to plasma endogenous compounds and the co-therapeutics 5-fluoroacil (5-FU) and folinic acid (FA). The latter are administered together with CPT-11 in the FOLFIRI regimen. The detection of CPT-11 was performed by differential pulse voltammetry at a glassy carbon electrode (GCE) in basified acetonitrile media. Under these conditions, a well-defined peak due to the oxidation of the tertiary ammine end of CPT-11, also free from interference due to main metabolites, was obtained. Calibration plots showed a good linear response with limit of detection and quantification of 1.10 × 10-7 and 3.74 × 10-7 M, respectively. The suitability of the method proposed here for clinical applications was verified by determining the concentration of CPT-11 in plasma samples of an oncological patient, collected after 30 and 180 min from the infusion of the drug. Graphical abstract.

Polymerase incorporation of 4-nitrophenyl modified 2'-deoxyuridine-5'-triphosphates into double-stranded DNA for direct electrochemical detection.

Three novel 2'-deoxyuridine-5'-triphosphates modified with 4-nitrophenyl groups via various linkers (dUTP-N1, dUTP-N2, and dUTP-N3) were tested as bearers of reducible electroactive labels as well as substrates suitable for enzymes used in polymerase chain reaction (PCR) and recombinase polymerase amplification (RPA) with a potential application to direct electrochemical detection of double-stranded deoxyribonucleic acid (dsDNA). In cyclic and square wave voltammograms on carbon screen printed electrodes, the labeled dUTP have demonstrated distinct reduction peaks at potentials of -0.7 V to -0.9 V (phosphate buffer, pH 7.4). The reduction peak currents of dUTP-N derivatives were found to increase with their molar concentrations. The dUTP-N3 with a double bond in the linker had the lowest reduction potential (about 100 mV less negative) among the derivatives studied. Further, dUTP-N nucleotides were tested as substrates in PCR and RPA to incorporate the electroactive labels into 90, 210, or 206 base pair long dsDNA amplicons. However, only a dUTP-N1 derivative with a shorter linker without the double bond demonstrated satisfactory compatibility with both PCR and RPA, though with a low reaction output of modified dsDNA amplicons (at 100% substitution of dTTP). The dsDNA amplicons produced by PCR with 85% substitution of dTTP by the dUTP-N1 in the reaction mixture were successfully detected by square wave voltammetry at micromolar concentrations at high square wave frequency.

Quantitative determination of dopamine in the presence of interfering substances supported by machine learning tools.

In the field of neuroscience as well as in the clinical setting, the neurotransmitter dopamine (DA) is an analyte which is important for research as well as medical purposes. There are plenty of methods available to measure dopamine quantitatively, with voltammetric ones such as differential pulse voltammetry (DPV) being among the most convenient and simple ones. However, dopamine often occurs, either naturally or because of the requirements of involved enzymatic systems, alongside substances that can influence the signal it produces upon electrochemical conversion. An example for such substances is the magnesium ion, which itself is not electrochemically active in the potential range needed for DA oxidation, but influences the dopamine signal. We have characterized the properties of DPV signals subject to the interaction between DA and Mg2+ and show that, although these properties are changing in a nonlinear fashion when both concentrations are varying, relatively simple linear mathematical models can be used to determine dopamine concentrations quantitatively in the presence of magnesium ions. The focus of this study is thus, the mathematical treatment of experimental data in order to overcome an analytical problem and not the investigation of the chemical background of DA-Mg2+ interaction.

Polymerase incorporation of fluorescein or rhodamine modified 2'-deoxyuridine-5'-triphosphates into double-stranded DNA for direct electrochemical detection.

The 2'-deoxyuridine-5'-triphosphates modified with fluorescein (dUTP-Fl) or rhodamine (dUTP-Rh) were tested as bearers of electroactive labels and as proper substrates for polymerases used in polymerase chain reaction (PCR) and isothermal recombinase polymerase amplification (RPA) with the aim of electrochemical detection of double-stranded DNA (dsDNA) amplification products. For this purpose, electrochemical behavior of free fluorescein and rhodamine as well as the modified nucleotides, dUTP-Fl and dUTP-Rh, was studied by cyclic (CV) and square wave (SWV) voltammetry on carbon screen printed electrodes. Both free fluorescein and dUTP-Fl underwent a two-step oxidation at the peak potentials (Ep) of 0.6-0.7 V and 0.8-0.9 V (phosphate buffer, pH 7.4). The reduction peaks of fluorescein and dUTP-Fl were registered between -0.9 V and -1 V, but they did not depend on concentration. The free rhodamine and dUTP-Rh have demonstrated the well-defined oxidation peaks at 0.8-0.9 V. In addition, the distinct reduction peaks at Ep between -0.8 V and -0.9 V were registered for both rhodamine and dUTP-Rh. The dUTP-Fl and dUTP-Rh were further tested as substrates to incorporate an electroactive label into 210 or 206 base pair long dsDNA amplicons generated either by PCR or RPA. Among two dUTP derivatives tested, dUTP-Fl revealed significantly better compatibility with PCR and RPA, producing the full-size amplicons at 50-90% substitution of dTTP in the reaction mixture. In the PCR, the best compromise between amplicon output and labeling was achieved at the dUTP-Fl : dTTP and dUTP-Rh : dTTP molar ratios of 70% : 30% and 20% : 80% in the PCR mixture, respectively, allowing the direct electrochemical detection of amplicons at micromolar concentrations. Alongside with fluorescence DNA assays, the fluorescein and rhodamine modified dUTP appear as promising electroactive labels to develop direct electrochemical DNA assays for detecting PCR and RPA products.

Electrochemical detection of carmoisine in the presence of tartrazine on the surface of screen printed graphite electrode modified with nickel-cobalt layered double hydroxide ultrathin nanosheets.

Toxic effluents containing azo dyes are discharged from various industries and they adversely affect water resoures, soil and aquatic ecosystems. Also, excessive use of food azo dyes can be carcinogenic, toxic, and adversely affect human health. Therefore, the determination of food azo dyes is significant from the perspective of human health and aquatic organisms. In the present work, nickel-cobalt layered double hydroxide nanosheets were prepared and analyzed by various techniques (field emission-scanning electron microscopy, X-ray diffraction, and Fourier Transform-Infrared spectroscopy). Then, the screen printed graphite electrode modified with nickel-cobalt layered double hydroxide nanosheets was used for the detection of carmoisine. The nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode significantly improved the oxidation of carmoisine by increasing the response current and lowering potentials compared to unmodified screen printed graphite electrode. Based on the findings from differential pulse voltammetry, the nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode sensor response towards carmoisine was linear (0.3-125.0 µM) with a detection limit of 0.09 µM. A sensitivity of 0.3088 µA µM-1 was achieved. Also, the nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode was used for voltammetric detection of carmoisine in the presence of tartrazine. Due to the catalytic activity of prepared layered double hydroxide, the prepared sensor exhibited remarkable separation of the peaks when carmoisine and tartrazine coexist. In addition, the prepared sensor showed good stability. Finally, the proposed sensor had promising applicability for analysis of study analytes in powdered juice and lemon juice, with commendable recoveries between 96.9%-104.8%.

Nanosponges by the oxo-Michael polyaddition of cyclodextrins as sorbents of water pollutants: the o-toluidine case.

Hydrophilic cyclodextrin nanosponges were prepared by the oxo-Michael polyaddition in an aqueous solution at pH > 10 of α-, ß-, and γ-cyclodextrin with 1,4-bisacryloylpiperazine or 2,2-bisacrylamidoacetic acid. These nanosponges and, for comparison purposes, their precursor cyclodextrins were tested as sorbents of o-toluidine, a carcinogenic wastewater contaminant, by monitoring the depletion of o-toluidine from a 10-4 M (10 ppm) aqueous solutions. To this aim, an innovative analytical procedure was used: The voltammetric peak currents of o-toluidine in linear sweep voltammetry experiments were registered using multi-walled carbon nanotubes-modified glassy carbon electrodes. The experimental sorption curves fitted a mono-exponential kinetic model, and the residual o-toluidine was 0.16 ppm, one order of magnitude lower than those of all other sorbents reported so far. The sorption capacities ranged from 88 to 199 µmol g-1 (10-21.3 mg g-1), equal to or higher than those of the parent cyclodextrins. All nanosponges were completely regenerated by extracting with methanol. After regeneration, the sorption capacity slightly improved, suggesting a rearrangement of the nanosponge network. Overall, it may be reasonably concluded that the cyclodextrin nanosponges reported in this paper warrant potential as o-toluidine exhaustive sorbents.

Effective voltammetric tool for simultaneous detection of MMP-1, MMP-2, and MMP-9; important non-small cell lung cancer biomarkers.

Simultaneous detection of multiple biomarkers can allow to reduce the costs of medical diagnostics, and thus improve the accuracy and effectiveness of disease diagnosis and prognosis. Here, for the first time, we present a low-cost, simple, and rapid method for simultaneous detection of three matrix metalloproteinases (MMP-1, MMP-2, and MMP-9) that play important roles in the progression of lung cancer. The sensor matrix was constructed using a G2 polyamidoamine dendrimer (PAMAM) containing amino, carboxyl, and sulfhydryl groups. The recognition process was based on specific enzymatic cleavage of the Gly-Ile peptide bond by MMP-1, Gly-Leu bond by MMP-2, and Gly-Met bond by MMP-9, and monitoring was done by square wave voltammetry. The activity of metalloproteinases was detected based on the change of current signals of redox receptors (dipeptides labeled with electroactive compounds) covalently anchored onto the electrode surface. The conditions of the biosensor construction, including the concentration of receptors on the sensor surface and the time of interaction of the receptor with the analyte, were carefully optimized. Under optimal conditions, the linear response of the developed method ranged from 1.0⋅10-8 to 1.0 mg⋅L-1, and the limit of detection for MMP-1, MMP-2, and MMP-9 was 0.35, 0.62, and 1.10 fg⋅mL-1, respectively. The constructed biosensor enabled us to efficiently profile the levels of active forms of MMP-1, MMP-2, and MMP-9 in tissue samples (plasma and lung and tumor extracts). Thus, the developed biosensor can aid in the early detection and diagnosis of lung cancer.

Electrochemically-functionalized CNT/ABTS nanozyme enabling sensitive and selective voltammetric detection of microalbuminuria.

Developing a cost-effective and reliable sensing platform for the routine screening of microalbuminuria and early diagnosis of chronic kidney disease is of great importance. Herein, we report on the high specificity and electrocatalytic activity of CNT/ABTS(CV) nanozyme, derived from the electrochemical functionalization of the carbon nanotube/2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) nanocomposite CNT/ABTS), towards electrochemical oxidation of human serum albumin (HSA) in urine. The potential cycling of CNT/ABTS electrode resulted in the surface functionalization with imine and carbonyl functional groups, which enhances electrode's affinity towards the electroactive tyrosine and tryptophan amino acids and thus facilitates the adsorption and subsequent electrochemical oxidation of HSA. The developed CNT/ABTS(CV) nanozyme modified electrode showed promising sensing characteristics for the point-of-care diagnosis of microalbuminuria without any sample pretreatment and inclusion of additional label or redox probes during measurement, including a practical sensing range up to 1.50 µM, a low detection limit of 60 nM, good reusability (>5 cycles), good long-term stability (>28 days), and high accuracy (error <15%) for the detection of HSA in urine. This work opens a new avenue for the detection and quantification of proteins in physiological conditions.

Disposable Electrochemical Biosensor Based on the Inhibition of Alkaline Phosphatase Encapsulated in Acrylamide Hydrogels.

The present work describes the development of an easy-to-use portable electrochemical biosensor based on alkaline phosphatase (ALP) as a recognition element, which has been immobilized in acrylamide-based hydrogels prepared through a green protocol over disposable screen-printed electrodes. To carry out the electrochemical transduction, an electroinactive substrate (hydroquinone diphosphate) was used in the presence of the enzyme and then it was hydrolyzed to an electroactive species (hydroquinone). The activity of the protein within the matrix was determined voltammetrically. Due to the adhesive properties of the hydrogel, this was easily deposited on the surface of the electrodes, greatly increasing the sensitivity of the biosensor. The device was optimized to allow the determination of phosphate ion, a competitive inhibitor of ALP, in aqueous media. Our study provides a proof-of-concept demonstrating the potential use of the developed biosensor for in situ, real-time measurement of water pollutants that act as ALP inhibitors.

Sensitive voltammetric quantification of carminic acid in candies using selenium dioxide nanoparticles based electrode.

Carminic acid is a food colorant which concentration has to be controlled due to the possible negative health effects. Sensitive voltammetric method is developed for carminic acid determination using electrode modified with SeO2 nanoparticles (SeO2 NPs) and hexadecyltriphenylphosphonium bromide (HDTPPB) acting as dispersive agent for nanoparticles and electrode surface co-modifier. SeO2 NPs of 37-45 nm are uniformly distributed at the electrode increasing its electroactive area (41 ± 2 vs. 8.9 ± 0.2 mm2 for bare glassy carbon electrode (GCE)). Electrochemical impedance spectroscopy data confirm an 18.3-fold decrease of charge transfer resistance compared to GCE (12.7 ± 0.3 vs. 232 ± 7 kΩ, respectively). In differential pulse mode, the linear dynamic ranges of carminic acid are 0.010-2.5 and 2.5-10 µmol L-1 with a detection limit of 3.4 nmol L-1. The method is successfully employed in candies and lozenges for sore throat treatment. The approach is simple, reliable, and can be used as an alternative to chromatography in routine analysis.

Enzymatic cleavage of specific dipeptide conjugated with ferrocene as a flexible ultra-sensitive and fast voltammetric assay of matrix metalloproteinase-9 considered a prognostic cancer biomarker in plasma samples.

Studies over the last decade have shown that matrix metalloproteinases (MMPs) play a key role in the growth and metastasis of cancer. This zinc-dependent family of endopeptidases is crucial for the degradation of extracellular matrix (ECM), as well as serves as important ECM transducers which have been recognized as early biomarkers for both cancer diagnosis and treatment. In this study, we designed a new type of voltammetric biosensor, composed of a glycine-methionine dipeptide conjugated covalently to ferrocene (Gly-Met-Fc), for fast and ultrasensitive detection of the active form of MMP-9 in plasma samples. The detection was based on specific enzymatic cleavage of the Gly-Met peptide bond, which was monitored by voltammetry and gravimetry measurements. The ferrocene units act as voltammetric visualizers for the detection process. The cysteamine layer directly anchored to the gold surface ensured that the packing density of Gly-Met-Fc in the receptor layer was appropriate for the sensitive detection of MMP-9 in its active form. The developed biosensor was characterized by the widest analytical range (2.0·10-6 - 5.0 µg⋅mL-1) and low detection limit (0.04 pg⋅mL-1). Another valuable feature of the proposed biosensor is that it can be applied directly to the plasma samples without any additional preparation step and thus speeds up the analysis.

Semi-circular sweep voltammetry. Bio-analytical applications.

A novel voltammetric method applying a semi-circular potential sweep is applied to the simultaneous electroanalytical determination of solutions containing two components with similar oxidation potentials which precludes their resolution using conventional voltammetric methods including linear sweep, square wave and pulse voltammetries. Three such biologically important mixtures, ascorbic acid/acetaminophen, glucose/ethanol and hydroquinone/catechol were studied, analytical methods developed and the method of semi-circular sweep voltammetry shown to give notable advantages over the other conventional analytical voltammetries in terms of signal resolution and the sensitivity of the detection. Favourable accuracy was obtained using electrodes with either simple or no modification in the established linear detection ranges.

An Electrochemical Sensor Based on a Nitrogen-Doped Carbon Material and PEI Composites for Sensitive Detection of 4-Nitrophenol.

A glassy carbon electrode (GCE) was modified with nitrogen-doped carbon materials (NC) and polyethyleneimine (PEI) composites to design an electrochemical sensor for detecting 4-nitrophenol (4-NP). The NC materials were prepared by a simple and economical method through the condensation and carbonization of formamide. The NC materials were dispersed in a polyethyleneimine (PEI) solution easily. Due to the excellent properties of NC and PEI as well as their synergistic effect, the electrochemical reduction of the 4-NP on the surface of the NC-PEI composite modified electrode was effectively enhanced. Under the optimized conditions, at 0.06-10 µM and 10-100 µM concentration ranges, the NC-PEI/GCE sensor shows a linear response to 4-NP, and the detection limit is 0.01 µM (the signal-to-noise ratio is three). The reliability of the sensor for the detection of 4-NP in environmental water samples was successfully evaluated. In addition, the sensor has many advantages, including simple preparation, fast response, high sensitivity and good repeatability. It may be helpful for potential applications in detecting other targets.