Synthetic Serum Samples Research Articles

Development of a green-synthesized molecularly imprinted polymer-based electrochemical nanosensor for the determination of N-nitrosodimethylamine (NDMA) in serum and tap water.

N-nitrosodimethylamine (NDMA) was determined using a molecularly imprinted polymer (MIP)-based electrochemical sensor.Green-synthesized silver nanoparticles were functionalized with cysteamine to enhance their integration into the electrode surface, which was used to modify a glassy carbon electrode (GCE). Furthermore, a MIP-based electrochemical sensor was constructed via electropolymerization of 3-aminophenyl boronic acid (3-APBA) as a conjugated functional monomer in the presence of lithium perchlorate (LiClO4) solution as a dopant, chitosan as a carrier natural polymer, and NDMA as a template/target molecule. The polymer film was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The analytical performance of the silver nanomaterial-based MIP-based electrochemical (AgNPs@Chitosan/3-APBA@MIP-GCE) sensor was evaluated under optimized conditions. The linear range of NDMA was 1.0 × 10-13-1.0 × 10-12M (0.1-1.0pM), with a limit of detection (LOD) of 3.63 × 10-15M (3.63 fM) using differential pulse voltammetry (DPV). Method validation figured out that the developed MIP-based electrochemical nanosensor exhibited excellent selectivity, accuracy, and precision, which was shown by the analysis of synthetic serum samples and tap water. The LOD and LOQ in serum samples were 17.8 fM and 59.5 fM,respectively,which were in agreement with the developed method. Good recovery results confirm the successful application of the method in serum and tap water samples. The selectivity of the developed AgNPs@Chitosan/3-APBA@MIP-GCE sensor for NDMA was demonstrated in the presence of NDEA, sartans (valsartan, losartan, irbesartan, candesartan, telmisartan), and potential interferents that arepossibly present in biological fluids (dopamine, ascorbic acid, uric acid) besides ionic species (sodium, chloride, potassium, nitrate, magnesium, sulfate) and common analgesic paracetamol.

Design of a Novel Electrochemical Immunosensor for Toxoplasma gondii Detection Based on Gold Nanoparticle/Chitosan Decorated Screen Printed Electrode

Toxoplasma gondii is an intracellular parasite that primarily utilizes cats as its definitive host. This parasite, which is spread through cat feces, can be transmitted to other animals and, from there, to humans through various routes. In healthy individuals, this parasite may not cause severe illness, but it can be fatal, especially in individuals with weakened immune systems due to factors like chemotherapy or organ transplantation, as well as in fetuses developing in the womb. Given its relatively common occurrence worldwide, controlling the spread of this parasite is imperative. In this study, an antibody-based electrochemical biosensor was developed to directly detect Toxoplasma, offering potential applications in disease surveillance and management. The biosensor was designed using screen-printed electrodes, and the electrode surface was modified with chitosan and gold nanoparticles. Anti-Toxoplasma gondii antibodies were immobilized onto the modified electrode surface using glutaraldehyde as a cross-linking agent. Changes in surface properties were investigated using various techniques, including differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. The surface morphology of the developed immunosensor was visualized using scanning electron microscopy. Subsequently, the biosensor's linear working range and detection limit were determined, followed by its application in the detection of Toxoplasma gondii in synthetic serum samples. This innovative approach holds promise for the development of sensitive and specific diagnostic tools for Toxoplasma gondii infection, which is crucial for effective disease management and prevention, particularly in vulnerable populations.

Fabrication of molecularly imprinted electrochemical sensors for sensitive codeine detection

Codeine (COD) is a natural opiate alkaloid obtained from hashish or prepared by methylation from morphine, widely used as an analgesic, antitussive, and antidiarrheal drug. A sensitive and selective electrochemical sensor based on molecular imprinting polymer (MIP) was developed to detect COD in tablet form and biological fluid samples. The polymeric thin film on the glassy carbon electrode (GCE) surface was formed using template molecule COD, a functional monomer based on amino acid N-methacryloyl-L-tryptophan (MA-Trp), basic monomer 2-hydroxyethyl methacrylate (HEMA), cross-linker ethylene glycol dimethacrylate (EGDMA), and the pore-making sacrificial material zinc oxide (ZnO). The developed MIP-based electrochemical sensor (MA-Trp@MIP/GCE) was characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) methods. The electrochemical properties of the sensor were examined using differential pulse voltammetry (DPV). Under optimum experimental conditions, the dynamic linear range of the developed sensor was calculated as 0.1–1.0 pM and the detection limit of 0.0150 pM. The current electrochemical sensor technique also demonstrated outstanding recovery in human urine, synthetic serum samples, and tablet form, with relatively high recoveries of 98.5%, 101.4%, and 101.5%, respectively. Moreover, the MA-Trp@MIP/GCE sensor exhibited good reproducibility, repeatability, stability, and fast response time for the electrochemical analysis of COD. The presented sensor successfully determined COD in tablet and biological fluid samples.

Digital microfluidic platform assembled into a home-made studio for sample preparation and colorimetric sensing of S-nitrosocysteine.

Digital microfluidics (DMF) is a versatile lab-on-a-chip platform that allows integration with several types of sensors and detection techniques, including colorimetric sensors. Here, we propose, for the first time, the integration of DMF chips into a mini studio containing a 3D-printed holder with previously fixed UV-LEDs to promote sample degradation on the chip surface before a complete analytical procedure involving reagent mixture, colorimetric reaction, and detection through a webcam integrated on the equipment. As a proof-of-concept, the feasibility of the integrated system was successfully through the indirect analysis of S-nitrosocysteine (CySNO) in biological samples. For this purpose, UV-LEDs were explored to perform the photolytic cleavage of CySNO, thus generating nitrite and subproducts directly on DMF chip. Nitrite was then colorimetrically detected based on a modified Griess reaction, in which reagents were prepared through a programable movement of droplets on DMF devices. The assembling and the experimental parameters were optimized, and the proposed integration exhibited a satisfactory correlation with the results acquired using a desktop scanner. Under the optimal experimental conditions, the obtained CySNO degradation to nitrite was 96%. Considering the analytical parameters, the proposed approach revealed linear behavior in the CySNO concentration range between 12.5 and 400μmolL-1 and a limit of detection equal to 2.8μmolL-1. Synthetic serum and human plasma samples were successfully analyzed, and the achieved results did not statistically differ from the data recorded by spectrophotometry at the confidence level of 95%, thus indicating the huge potential of the integration between DMF and mini studio to promote complete analysis of lowmolecular weight compounds.

A Novel Strategy for Selective Thyroid Hormone Determination Based on an Electrochemical Biosensor with Graphene Nanocomposite.

This article presents a novel and selective electrochemical bioassay with antibody and laccase for the determination of free thyroid hormone (free triiodothyronine, fT3). The biosensor was based on a glassy carbon electrode modified with a Fe3O4@graphene nanocomposite with semiconducting properties, an antibody (anti-PDIA3) with high affinity for fT3, and laccase, which was responsible for catalyzing the redox reaction of fT3. The electrode modification procedure was investigated using a cyclic voltammetry technique, based on the response of the peak current after modifications. All characteristic working parameters of the developed biosensor were analyzed using differential pulse voltammetry. Obtained experimental results showed that the biosensor revealed a sensitive response to fT3 in a concentration range of 10-200 µM, a detection limit equal to 27 nM, and a limit of quantification equal to 45.9 nM. Additionally, the constructed biosensor was selective towards fT3, even in the presence of interference substances: ascorbic acid, tyrosine, and levothyroxine, and was applied for the analysis of fT3 in synthetic serum samples with excellent recovery results. The designed biosensor also exhibited good stability and can find application in future medical diagnostics.

Investigation of SARS-CoV-2 RNA contamination in water supply resources of Tabriz metropolitan during a peak of COVID-19 pandemic.

It is crucial to have access to clean water resources during the COVID-19 pandemic for hygiene, since virus infection through wastewater leaks in metropolitan areas can be a threat. Accurate monitoring of urban water resources during the pandemic seems to be the only way to confirm safe and infected resources. Here, in this study, the amount of Severe Acute Respiratory Syndrome Coronavirus 2's Ribonucleic Acid (SARS-CoV-2 RNA) in the Tabriz urban water network located in the northwest of Iran was investigated by an extensive sampling of the city's water sources at a severe peak of the COVID-19 pandemic. The sampling process comprised a range of water sources, including wells, qanats, water treatment facilities, dams, and reservoirs. For each sample, a combination of polyethylene glycol (PEG) and sodium chloride (NaCl) was used for concentration and a laboratory RNA-based method was conducted for quantification. Before applying the extraction and quantification procedure to real samples, the proposed concentration method was verified with synthetic serum samples for the first time. After the concentration, RNA extraction was done by the BehPrep extraction column method, and Reverse Transcription Polymerase Chain Reaction(RT-PCR) detection of the virus was done by Covitech COVID-19 RT-PCR kit. In none of the water supply resources, SARS-COV-2 RNA has been detected except in a sample grabbed from a well adjacent to an urban wastewater discharge point downstream. The results of molecular analysis for the positive sample showed that the CT value and concentration of the virus genome were equal to 32.57 and 5720copies/L, respectively. Quantitative analysis of real samples shows that the city's water network was safe at the time of the study. However, given that the positive sample was exposed to wastewater leakage, periodic sampling from wells and qanats is suggested during the pandemic until it can be proven that the leakage to these water sources is impossible.

A sensitive and selective electrochemical sensor based on molecularly imprinted polymer for the assay of teriflunomide

In this work, pyrrole-histidine has been designed, synthesized and, used as a novel functional monomer to fabricate a molecularly imprinted electrochemical sensor for the selective and sensitive detection of teriflunomide (TER). The molecularly imprinted thin film of electrochemical sensor was constructed by directly electropolymerization of co-polymer of pyrrole-histidine (PyHis) with pyrrole in the presence of a template, TER, on a glassy carbon electrode (GCE). After electropolymerization, the structure and morphology of the fabricated MIP sensor were characterized by Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and its electrochemical parameters such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). The poly (pyrrole-co-pyrrole-histidine) [Poly (Py-co-PyHis)]@MIP/GCE sensor have a linear TER concentration in the of 0.1–1.0 pM with a low detection limit of 11.38 fM. The present strategy for electrochemical sensor have been also showed excellent recovery in synthetic serum samples and tablet dosage form with the recoveries 97.56% and 100.35%, respectively. The developed [Poly (Py-co-PyHis)]@MIP/GCE sensor exhibited an excellent electrochemical response for TER due to the synergistic effect of conducting polymer and molecularly imprinting techniques.

RGO/ReO3 nano composite modified electrode for the ultra-sensitive determination of dopamine and uric acid

Development of suitable modified electrode in generating the electrochemical signals from dopamine (DA), uric acid (UA) and ascorbic acid (AA) has remained challenging issue even after decades of research in the related field. Under the present investigation the perovskite type metal oxide nano particle has been used in the form of composite with the reduced graphene oxide (rGO) as the active material for sensing. The superior electrical conductivity of Rhenium oxide (ReO3) combined with the adsorptive and conducting nature of rGO has been utilised in enhancing the electrochemical responses form the molecules. Thin films of Nafion was used over the rGO/ReO3 composite materials for stabilization of the modification. The electron transfer property of the molecules has been evaluated from the cyclic voltammetry and electrochemical impedance measurements. The standard electron transfer rate constants have been obtained from the Laviron formulations of the cyclic voltammetry measurements. Simultaneous electrochemical response has been obtained from the three molecules over the rGO/ReO3 nano composite modified electrode, the analytical method has been developed with the detection limit (S/N = 3) of 0.08 nM, 0.06 μM and 0.89 μM for DA, UA and AA respectively. For simultaneous determination however, the determination of DA and UA has been proposed and the interference test was carried out through simultaneous detection of the signals of the molecules. The analytical method has been applied for the detection of analytical signals of DA and UA in synthetic serum samples through spiked recovery test.

Selective nanosensor based on folic acid imprinted nanostructures.

Folic acid, which provides the transfer of single carbon atoms in synthesis reactions and metabolic cycles in metabolism, is very important for metabolism. Folic acid also plays an important role in nucleotide synthesis and methylation reactions. There are many disorders caused by defective folic acid metabolism and lack of folic acid. Today, innovative, cost-effective methods are needed to develop folic acid determination methods. The main objective of this study is the development of surface-printed carbon electrodes (SPCE) modified with folic acid imprinted nanostructures (FA-Imp-poly(MPTS-rGO-co-NAT), which will be used for the first time for folic acid determination in commercially human blood serum. For this purpose, the synthesis of nanostructures has been carried out and characterized by FTIR, SEM-EDS, and AFM. Then, a new chemically modified nanosensor was fabricated for the determination of folic acid using folic acid imprinted nanostructures. Differential pulse voltammetry (DPV) and circular voltammetry (CV) methods were used as electrochemical methods in the FA-imprinted-nanosensor studies. Measurements in differential pulse voltammetry were performed at an application speed of 0.005 volts per second in the potential range of -0.4 to 0.6 volts. As a result of the circular voltammetric method, an idea about the surface was obtained with the voltammograms obtained. The detection limit (LOD) of the developed FA-imprinted-nanosensor was 7.54 ng/mL and the determination limit (LOQ) was 25.14 ng/mL. FA analytical (10 and 20 ng/mL) was added to commercial synthetic serum samples by the standard adding method and RSD values of 0.092% and 0.734% were found in the DPV technique and measurements respectively. This manuscript demonstrated a novel, simple, selective, and rapid FA-imprinted-nanosensor for determining the FA in the biological samples.

A sensitive electrochemical detection of metronidazole in synthetic serum and urine samples using low-cost screen-printed electrodes modified with reduced graphene oxide and C60

Monitoring the concentration of antibiotics in body fluids is essential to optimizing the therapy and minimizing the risk of bacteria resistance, which can be made with electrochemical sensors tailored with appropriate materials. In this paper, we report on sensors made with screen-printed electrodes (SPE) coated with fullerene (C60), reduced graphene oxide (rGO) and Nafion (NF) (C60-rGO-NF/SPE) to determine the antibiotic metronidazole (MTZ). Under optimized conditions, the C60-rGO-NF/SPE sensor exhibited a linear response in square wave voltammetry for MTZ concentrations from 2.5 × 10−7 to 34 × 10−6 mol/L, with a detection limit of 2.1 × 10−7 mol/L. This sensor was also capable of detecting MTZ in serum and urine, with recovery between 94% and 100%, which are similar to those of the standard chromatographic method (HPLC-UV). Because the C60-rGO-NF/SPE sensor is amenable to mass production and allows for MTZ determination with simple principles of detection, it fulfills the requirements of therapeutic drug monitoring programs.

Enhanced and selective adsorption of urea and creatinine on amine-functionalized mesoporous silica SBA-15 via hydrogen bonding

In this study, mesoporous silica SBA-15 particles were synthesized using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and tetraethoxysilane as the precursors and were subsequently modified with 3-aminopropyl triethoxysilane (APTES). The amine-functionalized particles were characterized using field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, N2 sorptiometry, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy, and thermogravimetric analysis. The prepared materials were subsequently used for the adsorption removal of small uremic toxins, namely urea, creatinine, and hippuric acid. The adsorption of these single toxins from synthetic serum samples on SBA-15–based adsorbents followed a pseudo-second-order kinetic model, and the adsorption was well described by the Langmuir isotherm. It was determined that the adsorption capacity of SBA-15 for urea and creatinine was increased after APTES functionalization. The highest adsorption capacities of SBA-15 modified with 0.2 mol/L APTES in toluene for urea and creatinine were 1644.7 and 181.7 mg/g, respectively, at 37 °C, whereas the highest adsorption capacity of pristine SBA-15 for hippuric acid was 111.7 mg/g. Preferential and competitive hydrogen bonding-promoted adsorption of urea over hippuric acid in binary mixtures occurred for the APTES-modified SBA-15 adsorbents, as demonstrated using the FTIR spectra of the adsorbents before and after adsorption.

A selective and molecular imaging approach for anticancer drug: Pemetrexed by nanoparticle accelerated molecularly imprinting polymer

A new molecularly imprinting polymer (MIP) based sensor was developed for the selective detection of pemetrexed (PMX) by the electropolymerization of ortho phenylenediammine (o-PD) on carbon quantum dot modified screen printed carbon electrode (CQD/SPCE). The surface characterization was performed with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The conditions such as casting amount of CQD, incubation time, removal time for successful polymerization were tested. The selectivity of developed sensor also tested with similar compounds with PMX. The results showed that the developed sensor could achieve to detection of PMX from synthetic serum sample with high recovery 99.3%. From the computational perspective of view, PMX was also optimized at B3LYP/6-311 G∗//DFT level using the Gaussian 09 program package. Molecular electrostatic potential surface (MESP) was performed to investigate effects of the electronic and structure properties of PMX.

Paper-based colorimetric spot test utilizing smartphone sensing for detection of biomarkers

The need for a continuous, real-time monitoring of specific diseases represents an unmet scientific need. Evidently, cancer is one of the most important diseases where it is crucial to increase the rates of patient survival and monitor disease prognosis. Herein, a novel type of immunoassay was developed for detection of cancer biomarkers, using alpha-fetoprotein (AFP) and mucin-16 (MUC16) as model analytes. Using gold nanoparticle (AuNP) bioconjugates as a signal production tool, relevant antibody (Ab)-conjugated AuNPs were prepared on the nitrocellulose (NC) membrane. To construct a spot-like point-of-care (POC) immunoassay, cysteamine conjugated AuNPs (AuNP-Cys) were immobilized on the NC membrane and antibodies were conjugated to the nanoparticle on the detection pad, following a treatment with the samples that contains AFP or MUC16 which are well-known protein biomarkers for liver and ovarian cancer. By using the change in the colorimetric properties of AuNPs, detection of tumor markers was achieved by using a smartphone image and color analysis software at the final stage. Image J application was used for the evaluation of color changes depending on the biomarker concentration in buffer or spiked synthetic serum samples. The linear range was found as 0.1 ng/mL-100 ng/mL for AFP and 0.1–10 ng/mL for MUC16. Limit-of-detection (LOD) was calculated as 1.054 ng/mL and 0.413 ng/mL for AFP and MUC16, respectively. Interferent molecules, Her2, Immunoglobulin G (IgG) and bovine serum albumin (BSA) were tested on the system. Furthermore, synthetic serum samples spiked with selected analyte molecule were applied on the system and measured successfully.

A novel gold nanocluster–based fluorometric biosensor for measuring prooxidant activity with a large Stokes shift

A chicken egg white protein−protected gold nanocluster (CEW−AuNC) based fluorogenic biosensor, where protein was used as both reducing and protecting agent, was developed to determine the Cu(II)−induced prooxidant activity of natural antioxidants abundant in food and biological samples. Gold nanoclusters, prepared using egg white proteins, exhibited strong fluorescence. The prooxidant activity of the tested antioxidants was indirectly measured by their reducing action on Cu(II) to Cu(I), and the reduced cuprous ion was bound to the thiol groups in the CEW−AuNC structure, causing a decrease in fluorescence intensity. Epicatechin, catechin, epigallocatechin gallate, morin, rutin, quercetin, gallic, chlorogenic, and rosmarinic acids, glutathione, cysteine, N−acetyl cysteine, bilirubin, resveratrol, and α-tocopherol were studied as natural antioxidants. A fluorometric method showing a large Stokes shift with excitation/emission maxima at 360∕640 nm was developed to sensitively measure the decrease in the fluorescence of CEW−AuNC associated with the binding of copper(I) to the protein structure. Total prooxidant activities of the binary, ternary, and quaternary synthetic mixtures and of some food and synthetic serum samples were determined. The biosensor response was statistically compared to that of its spectrophotometric counterpart. This method can be used for the control of the oxidative stability of foods with a prolonged shelf life.

An Electrochemical Biosensor Platform for Testing of Dehydroepiandrosterone 3‐Sulfate (DHEA−S) as a Model for Doping Materials

AbstractEndogenous steroids such as dehydroepiandrosterone (DHEA) and dehydroepiandrosterone 3‐sulfate (DHEA−S) have commonly used as doping materials by athletes and to date novel techniques are needed for detection of these molecules. In this study, antibody‐based electrochemical biosensor has developed for testing level of the DHEA−S. For this aim, gold surfaces were initially modified with cysteamine (Cys) and then, DHEA−S antibody was immobilized on the surface via glutaraldehyde (GA) as a crosslinking agent. The stepwise modification of electrode surface was monitored by using various electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Linear range was determined as 2.5–100 ng/mL DHEA−S using differential pulse voltammetry (DPV) technique, as well. Moreover, repeatability (±S.D.), coefficient of variation (%) and limit of detection (LOD) values were calculated as 0.033, 1.030 and 3.971, respectively. Also, DHEA−S in synthetic serum and urine samples were successfully determined with standard addition method and confirmation analysis were performed with liquid chromatography quadrupole‐time of flight mass spectrometry (LC‐QTOF/MS) system. The selectivity was studied with the addition of some interfering molecules (testosterone, bovine serum albumin (BSA), cholesterol, uric acid, lactic acid, codein (COD), ascorbic acid, DHEA). Consequently, this work is proposed as practical, innovative and cost‐effective technique that can be easily adapted for the miniaturized form for the analysis of other doping substances as well as DHEA−S for the future works.

Silver Nanoparticles‐Silsesquioxane Nanomaterial Applied to the Determination of 4‐Nitrophenol as a Biomarker

AbstractA novel silsesquioxane material was synthetized and used as a stabilizing agent for silver nanoparticles. This hybrid material was characterized by FTIR, 29Si CP‐MAS NMR, 13C DEPT 135° NMR and TGA techniques and the silver nanoparticles were characterized from DLS, UV‐Vis spectroscopy, zeta‐potential, TEM and SAXS results. The silver nanoparticles obtained were spherical in shape with a diameter of 3.74 nm. The nanomaterial was successfully applied in the modification of a glassy carbon electrode and a pronounced current response was obtained in the determination of the biomarker 4‐nitrophenol. Quantum chemical calculations, using density functional theory, were also performed in order to evaluate the redox properties of the analyte. Two different linear ranges were obtained applying optimal square wave voltammetry conditions. The reduction peak currents obtained were linear for 4‐NP concentrations in the ranges of 0.29 to 1.50 μmol L−1 (Ed=−0.6 V and td=20 s) and 2.75 to 31.5 μmol L−1, with a theoretical (signal to noise=3) limit of detection of 0.05 μmol L−1 (td=20 s). The proposed method was successfully applied to the determination of 4‐NP in synthetic serum samples at different levels of 4‐NP with a recovery range of 94–101 %. Validation was performed using a comparative method through the capillary electrophoresis (CE) technique.

An impedimetric molecularly-imprinted biosensor for Interleukin-1β determination, prepared by in-situ electropolymerization on carbon screen-printed electrodes

This work reports the first electrochemical molecularly imprinted polymer (MIP) sensor for Interleukin-1beta (IL-1β) detection, based on modified commercial screen-printed carbon electrode (SPCE) was successfully demonstrated. For this purpose, the carbon support was modified with a PEDOT/4-aminothiophenol layer prior to the MIP film to enhance sensitivity and signal stability. The MIP layer was constructed on top of this by electropolymerization of Eriochrome black T (EBT) in the presence of IL-1β. The several steps of the biosensor assembly was followed by Raman spectroscopy and electroanalytical techniques.Using electrochemical impedance spectroscopy (EIS), a linear response in the range of 60 pM to 600 nM, with a LOD of 1.5 pM with (S/N = 3) was obtained in neutral PBS. Selectivity tests of the MIP biosensor made in spiked synthetic serum samples as well as against other structurally related (Myoglobin, of similar shape and size) or competing compounds (Immunoglobulin G, also present in the human serum) confirmed the good selectivity of the biosensor.Overall, the biosensor described herein has the potential to provide a simple and quick way for on-site screening of IL-1β, with low sample/reagent consumption and enabling direct serum analysis, which constitutes a valuable alternative to other conventional methods.

Novel optical sensor-based method for determining total tocopherol content in serum

Lipid-soluble endogenous antioxidants, such as tocopherols, protect biological structures from oxidative damage through their chain-breaking ability and thus the development of a simple method for tocopherol determination is important. In this study, a novel optical sensor-based method was proposed for determining total tocopherol content (TTC) of serum, with selectivity for $\alpha $-tocopherol over $\beta $-carotene. The proposed method is based on the use of a copper(II)-neocuproine complex (Cu(II)-Nc) reagent immobilized onto a Nafion membrane, and the absorbance changes associated with the formation of Cu(I)-Nc chelate on the membrane strip as a result of reaction with serum tocopherols were measured at 450 nm. The calibration graph of $\alpha $-tocopherol was linear with a slope of 1.96 x 10$^{4}$ L mol$^{-1}$ cm$^{-1}$. The limit of detection and limit of quantification for tocopherol in the proposed method were found as 0.50 and 1.67 μM, respectively. The TTC value of synthetic serum samples was determined with the use of the proposed method, and the obtained results were comparable to those of the CUPRAC spectrophotometric method. The proposed method enables simple, rapid, and in situ determination of total tocopherol content of serum by taking advantage of optical sensors.

A simple automated microplate method for determining reducing sugars in food extracts and synthetic serum using cupric-neocuproine as reductant

In the present work, a simple automated microplate method based on cupric ion reduction is described for determining total reducing sugars in food extracts and synthetic serum. The reaction of Cu(II)-Nc (cupric-neocuproine) with reducing sugars was performed in alkaline medium in microplates, and the absorbance of the formed highly colored Cu(I)-Nc chelate in a plate reader at 450 nm was recorded. The proposed method was applied to reducing sugars (glucose, fructose, galactose, maltose, and lactose) and their linear calibration curves were constructed. The detection and quantification limits (LOD and LOQ) for glucose were 0.14 and 0.46 $\mu $M, respectively. Absorbances of glucose were linear within the concentration range 2.5-54.2 $\mu $M and the method showed high linearity (r = 0$.$9998) over a relatively broad concentration range of analyte. This automated microplate method was validated through linearity, additivity, precision (RSD%, 2.33-6.65), and recovery (101%-103%), revealing that the method is reliable and robust for determining reducing sugars. Total reducing sugar contents of synthetic sugar mixtures, fruit juices, milk, and synthetic serum samples were successfully determined with the proposed method. The results were compared to those of the conventional alkaline Cu(II)-Nc spectrophotometric method. The proposed method offers many advantages when compared to classical methods, such as (sample and reagent) volume reduction (20-fold), simplicity, multiple sample analysis (32 samples in 4 h), and environmental friendliness.

Synthesis and application of a “plastic antibody” in electrochemical microfluidic platform for oxytocin determination

By means of molecular imprinting of a conducting polymer, molecular cavities selective for oxytocin nonapeptide, an autism biomarker, were designed. Embedding of the oxytocin template, and then its extracting from the molecularly imprinted polymer (MIP) was confirmed by the XPS analysis. AFM imaging of the MIP film surface indicated changes in mechanical properties of the film after template extraction. The MIP synthetic receptor was deposited by potentiodynamic electropolymerization as a thin film on an Au film electrode in an electrochemical miniaturized microfluidic cell. The use of this cell allowed to shorten analysis time and to decrease the sample volume. The linear dynamic concentration range extended from 0.06 to 1mM with the limit of detection of 60µM (S/N = 3). Advantageously, sensitivity of the diagnostic microfluidic platform devised for oxytocin determination in both synthetic serum samples and in aqueous solutions was similar and, moreover, it was selective to common interferences, such as oxytocin analogs and potential metabolites.