Excellent Analytical Characteristics Research Articles

Homojunction-Incorporated Oxygen Vacancy Functionalized Spherical TiO2 Nanocrystals for the Electrochemical Detection of Chemical Oxygen Demand.

Chemical oxygen demand (COD) is a critical criterion for the analytical assessment of the degree of organic contaminants in an aqueous system. Typically, toxic and expensive reagents are employed in standardized COD analysis methods, leading to secondary pollution. In this work, we developed a rapid electrochemical method for COD detection based on the oxidation of hydroxyl radicals for organics in water by using oxygen vacancy doped anatase/rutile-TiO2 nanoparticles as electrooxidation catalysts. Homojunction interface generated increasing oxygen vacancies for enhancing electron-transfer rate and accelerating H2O oxidation to substantially improve ·OH yield. Oxygen vacancy further increased the oxygen evolution potential of the material. Initially, glucose was chosen as a standard analyte to evaluate electrochemical responses, and water from urban wastewater treatment plants was assessed as real samples subsequently. Excellent analytical characteristics were achieved with the A/R-TiO2 sensor under the optimal conditions, exhibiting a linear range from 1 to 300 mg L-1 and detection limit of 0.1 mg L-1 COD. The estimated COD values obtained from the samples were highly consistent with those determined using the conventional standard dichromate method. We have presented a fast, cost-effective, and ecologically sustainable method that outperforms the standard COD analysis method and holds great potential for the accurate determination of COD and boasts high detection sensitivity and a broad linear range.

Hybridization-driven fluorometric platform based on metal-organic frameworks for the identification of the highly homologous viruses

A novel fluorometric strategy for the simultaneous identification of SARS-CoV-2 and SARS-CoV was successfully established based on a hybridization-induced signal on–off-on mechanism. Here, one part of the probe (P1) of SARS-CoV-2 (P = P1/P2) is partially related to SARS-CoV, while the other part (P2) is completely irrelevant to SARS-CoV. They as smart gatekeepers were anchored on NH2-MIL-88(Fe) (MOF@P1/P2) to turn off its catalytic performance. Only the specific SARS-CoV-2 genetic target can strongly restore the peroxidase-like activity of MOF@P1/P2. In the presence of o-phenylenediamine, SARS-CoV-2 can be efficiently detected with high sensitivity, accuracy, and reliability. This strategy demonstrated excellent analytical characteristics with a linear range (10-9 M ∼ 10-6 M) under the limit of detection of 0.11 nM not only in buffer but also in 10 % serum, which partly shows its practicability. Most importantly, with the help of the auxiliary test of MOF@P1 and MOF@P2, SARS-CoV-2 and SARS-CoV can be efficiently quantified and distinguished. This novel strategy has provided a breakthrough in the development of such identification. In the whole process, only a simple one-step experiment was involved. This circumvents the trouble of pretreatment experiments in traditional methods, including complex enzymatic mixtures, specialized experimental equipment, many primers optimization as well as reverse transcriptase. Additionally, this novel strategy is rapid, low-cost, and easy-to-use tools.

Conducting Matrices of the Poly(-O-Toluidine, PTOL) Film for Immobilizing Uricase

Polyaniline, PANI as conducting polymer has been used as enzyme immobilization matrix in biosensors due to its excellent stability and electrochromic effects, conductivity, and redox reversibility. However, at pH above 4, the electron transfer ability and redox activity decrease, henceit is necessary to modify the PANI structure to increase the PANI pH range. In this study, the PANI derivative, the poly(-o-toluidine, PTOL) film was produced for the uricase immobilization matrix. This study aimed to develop a supporting material that maintains catalytic activity uricase with a facile and inexpensive procedure. The PTOL was prepared by using the chemical oxidative polymerization technique with ammonium persulfate (dissolved in 1.0 M HCl) as an oxidizing agent. The FTIR spectra confirmed the success of PTOL formation by the appearance of its characteristic peaks. The UV-Vis spectra indicated that PTOL was in an emeraldine state with a semi-crystalline structure that was shown by its XRD pattern. While, SEM analysis described that the PTOL film was uniform with some granular aggregation in its surface morphology, but there is no holes or porosity were found. The use of PTOL film as a uricase matrix could maintain the uricase activity against the substrate (uric acid, UA) with excellent analytical characteristics. Therefore, PTOL film could be used as conducting matrices for immobilizing enzymes (e.g. biosensors).

Colloidal lithography as a novel approach for the development of Ni-nanocavity insulin sensor

In this study, a highly sensitive, fast, and selective enzyme-free electrochemical sensor based on the deposition of Ni cavities on conductive glass was proposed for insulin detection. Considering the growing prevalence of diabetes mellitus, an electrochemical sensor for the determination of insulin was proposed for the effective diagnosis of the disease. Colloidal lithography enabled deposition of nanostructured layer (substrate) with homogeneous distribution of Ni cavities on the electrode surface with a large active surface area. The morphology and structure of conductive indium tin oxide glass modified with Ni cavities (Ni-c-ITO) were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The diameter of the resulting cavities was approximately 500 nm, while their depth was calculated at 190 ± 4 nm and 188 ± 18 nm using AFM and SEM, respectively. The insulin assay performance was evaluated by cyclic voltammetry. Ni-c-ITO exhibited excellent analytical characteristics, including high sensitivity (1.032 µA µmol−1 dm3), a low detection limit (156 µmol dm−3), and a wide dynamic range (500 nmol dm−3 to 10 µmol dm−3). Finally, the determination of insulin in buffer with interferents and in real blood serum samples revealed high specificity and demonstrated the practical potential of the method.

Portable amperometric method for selective determination of caffeine in samples with the presence of interfering electroactive chemical species

• Simple protocol to improve the selectivity of flow systems with amperometric detection. • Selective amperometric determination of compounds only oxidizable at high potentials. • Amperometric determination of caffeine in the presence of different interfering electroactive chemical substances. • Practical tool for the development of simple portable amperometric methods. In the present paper, we show that caffeine (only electrochemical oxidizable at high potentials) can be selectively determined in complex samples using a portable flow system with amperometric detection. The selective determination of caffeine was possible in several samples and in the presence of different interfering electroactive chemical species after a simple sample pretreatment step (dissolution and/or dilution in a supporting electrolyte). The results obtained were statistically similar (P > 0.05) to those acquired using an analytical separation technique (capillary electrophoresis). In addition to the improvement in selectivity, the developed method presented excellent analytical characteristics such as low limit of detection (0.26 µmol L −1 ), wide linear range (10 to 1445 µmol L −1 ; r = 0.999), high analytical frequency (130 injections h −1 ) and, adequate recovery values (108 ± 10%). The protocol proposed here shows great potential to improve the selectivity of portable amperometric methods.

Starch-Based Carbon Dots for Nitrite and Sulfite Detection.

Nitrite and sulfite play important roles in human health and environmental science, so it is desired to develop a facile and efficient method to evaluate NO2 - and SO3 2- concentrations. In this article, the use of green alternatives with the potential of multi-functionality has been synthesized to detect nitrite and sulfite based on fluorescent probe. The carbon dots (CDs) with starch as only raw materials show fluorescence turn “on-off-on” response towards NO2 - and SO3 2- with the limits of detection of 0.425 and 0.243 μМ, respectively. Once nitrite was present in the solution, the fluorescence of CDs was quenched rapidly due to the charge transfer. When sulfite was introduced, the quenching fluorescence of CDs was effectively recovered because of the redox reaction between NO2 - and SO3 2-, and thus providing a new way for NO2 - and SO3 2- detection. Owing to their excellent analytical characteristics and low cytotoxicity, the “on-off-on” sensor was successfully employed for intracellular bioimaging of NO2 - and SO3 2-.

Mesoporous onion-like carbon nanostructures from natural oil for high-performance supercapacitor and electrochemical sensing applications: Insights into the post-synthesis sonochemical treatment on the electrochemical performance

Although onion-like carbon nanostructures (OLCs) are attractive materials for energy storage, their commercialization is hampered by the absence of a simple, cost-effective, large-scale synthesis route and binder-free electrode processing. The present study employs a scalable and straightforward technique to fabricate sonochemically tailored OLCs-based high-performance supercapacitor electrode material. An enhanced supercapacitive performance was demonstrated by the OLCs when sonicated in DMF at 60 °C for 15 min, with a specific capacitance of 647 F/g, capacitance retention of 97% for 5000 cycles, and a charge transfer resistance of 3 Ω. Furthermore, the OLCs were employed in the electrochemical quantification of methylene blue, a potential COVID-19 drug. The sensor demonstrated excellent analytical characteristics, including a linear range of 100 pM to 1000 pM, an ultralow sensitivity of 64.23 pM, and a high selectivity. When used to identify and quantify methylene blue in its pharmaceutical formulation, the sensor demonstrated excellent reproducibility, high stability, and satisfactory recovery.

Effect of nisin and potassium sorbate additions on lipids and nutritional quality of Tan sheep meat

Nisin and potassium sorbate as preservatives are used in a broad range of meat. A lipidomic evaluation was performed on Tan sheep meat treated by two types of preservatives. The addition of potassium sorbate resulted in higher lipid losses compared with nisin treatment. Furthermore, 106 significant lipids of 12 lipid classes (PC, PS, LPS, LPC, PE, PI, LPE, TG, Cer, DG, SM, Sph) with variable importance in projection scores greater than 1.0 were detected and qualified to distinguish different preservatives added meat using UHPLC-Q-Orbitrap MS/MS. LOD and LOQ were 0.12–0.32 μg kg−1 and 0.35–0.89 μg kg−1, indicating high sensitivity and excellent analytical characteristics in the study. Nisin was confirmed to be the better preservative for prolonging the shelf life of Tan sheep meat while reducing the loss of nutrients. These results could provide a strong cornerstone for future research on preservatives in meat products.

Fast and Sensitive Determination of the Fungicide Carbendazim in Fruit Juices with an Immunosensor Based on White Light Reflectance Spectroscopy.

Carbendazim is a systemic benzimidazole-type fungicide with broad-spectrum activity against fungi that undermine food products safety and quality. Despite its effectiveness, carbendazim constitutes a major environmental pollutant, being hazardous to both humans and animals. Therefore, fast and reliable determination of carbendazim levels in water, soil, and food samples is of high importance for both food industry and public health. Herein, an optical biosensor based on white light reflectance spectroscopy (WLRS) for fast and sensitive determination of carbendazim in fruit juices is presented. The transducer is a Si/SiO2 chip functionalized with a benzimidazole conjugate, and determination is based on a competitive immunoassay format. Thus, for the assay, a mixture of an in-house developed rabbit polyclonal anti-carbendazim antibody with the standards or samples is pumped over the chip, followed by biotinylated secondary antibody and streptavidin. The WLRS platform allows for real-time monitoring of biomolecular interactions carried out onto the Si/SiO2 chip by transforming the shift in the reflected interference spectrum caused by the immunoreaction to effective biomolecular adlayer thickness. The sensor is able to detect 20 ng/mL of carbendazim in fruit juices with high accuracy and precision (intra- and inter-assay CVs ≤ 6.9% and ≤9.4%, respectively) in less than 30 min, applying a simple sample treatment that alleviates any “matrix-effect” on the assay results and a 60 min preincubation step for improving assay sensitivity. Excellent analytical characteristics and short analysis time along with its small size render the proposed WLRS immunosensor ideal for future on-the-spot determination of carbendazim in food and environmental samples.

Specific Features of the Design and Operation of Magnetic Resonance Mass Spectrometers

Magnetic resonance mass spectrometers (MRMSs), developed in the second half of the 20th century at the Ioffe Institute, have still possessed such a complex of parameters that they have no alternative for solving many analytical problems, in particular, in the isotopy of helium. With the resolution of one of the devices several thousand at the base of the 3He+ mass peak, its absolute sensitivity is <106 atoms of this isotope in the volume of the mass analyzer chamber (~2.5 L), and the 3He/4He isotope ratio measured in a single experiment can be as low as 109 and even 1010. Another device of this type demonstrated resolution of more than 150 000 at the base of the mass peak, which ensured the detection of a 3He+–3T+ doublet. Excellent analytical characteristics of the MRMSs make it possible to use them to study the isotopy of helium in natural and man-made samples (solid, liquid, or gaseous) in meteorites and lunar soil, ferromanganese nodules from the bottom of seas and oceans, in ice cores from the well of Lake Vostok in Antarctica, in water from mountain streams of Mongolia and geysers of Iceland, in volcanic gases of Kamchatka and gases released from structural materials of a modern thermonuclear installation. In this work, we consider the principle and modes of operation of an MRMS and its design. The focus is on the details that distinguish these instruments from other instruments and ensure extremely high analytical performance, which is partly presented in the article.

A green and efficient pseudotargeted lipidomics method for the study of depression based on ultra-high performance supercritical fluid chromatography-tandem mass spectrometry

The pseudotargeted lipidomics method integrates the advantages of untargeted andtargeted lipidomics methods as a novel emerging approach. In this study, a green andefficient pseudotargeted lipidomics method based on ultra-high performancesupercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS) wasdeveloped. The tandem mass spectra of the analytes were obtained by using UHPSFCwith quadrupole-time of flight MS (Q-TOF MS) in MS E mode and the multiplereaction monitoring (MRM) transitions of the lipidome were defined. Then, thecandidate MRM transitions were verified by UHPSFC with triple quadrupole massspectrometry (QqQ MS) in the scheduled MRM mode. In total, 758 potential lipidscorresponding to 509 and 249 MRM transitions were detected within 8 min in positiveand negative modes, respectively. The established pseudotargeted lipidomics methodwas validated to have excellent analytical characteristics. Compared with thepseudotargeted method based on ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), the UHPSFC-MS/MS-basedpseudotargeted method not only reduced the analytical time by half but also improvedthe sensitivity and resolution for most analytes, especially had better separation forlipid isomers. Besides, the UHPSFC-MS/MS-based pseudotargeted method showedhigher sensitivity and better repeatability for most analytes than the UHPSFC-MS/MS-based untargeted method. The established method was finally applied to investigatingthe lipid profiles of the plasma from the depressed rats and 33 differential variableswere screened, which related to three metabolic pathways. The results indicated thatthe UHPSFC-MS/MS-based pseudotargeted method is reliable and efficient and couldbe used in the lipidomics studies.

Electrochemical Micropyramid Array-Based Sensor for In Situ Monitoring of Dopamine Released from Neuroblastoma Cells.

Abnormal dopamine neurotransmission is associated with several neurological and psychiatric disorders such as Parkinson's disease, schizophrenia, attention deficiency and hyperactivity disorder, and addiction. Developing highly sensitive, selective, and fast dopamine monitoring methods is of high importance especially for the early diagnosis of these diseases. Herein, we report a new ultrasensitive electrochemical sensing platform for in situ monitoring of cell-secreted dopamine using Au-coated arrays of micropyramid structures integrated directly into a Petri dish. This approach enables the monitoring of dopamine released from cells in real-time without the need for relocating cultured cells. According to the electrochemical analyses, our dopamine sensing platform exhibits excellent analytical characteristics with a detection limit of 0.50 ± 0.08 nM, a wide linear range of 0.01-500 μM, and a sensitivity of 0.18 ± 0.01 μA/μM. The sensor also has remarkable selectivity toward DA in the presence of different potentially interfering small molecules. The developed electrochemical sensor has great potential for in vitro analysis of neuronal cells as well as early diagnosis of different neurological diseases related to abnormal levels of dopamine.

Electrochemical Microfluidic Micromotors-Based Immunoassay for C-Reactive Protein Determination in Preterm Neonatal Samples with Sepsis Suspicion.

Online coupling of a micromotor-based immunoassay and a microfluidic electrochemical detection was explored as a new approach for C-reactive protein (CRP) determination in serum and preterm neonatal plasma samples with sepsis suspicion. The approach combines the advantages of micromotors (self-fluid mixing capabilities leading to a faster assay in low sample volumes) and electrochemical microfluidic (flow-controlled ultraminiaturized electrochemical detection, high sensitivity, and low-cost) technologies. Both technologies elegantly meet the point of care testing or bed side device requirements such as low analysis times, miniaturization and simplification, and single use. Anti-CRP functionalized micromotors (anti-CRP-rGO(reduced graphene oxide)/Ni/PtNPs (platinum nanoparticles))-based immunoassay coupled to thin layer Au-based electrochemical microfluidics operating at -0.20 V under controlled fluidic detection operations (30 μL min-1) allowed the sensitive (LOD = 0.54 μg/mL) and accurate CRP determination using very low volume preterm neonatal clinical samples (<10 μL) in just 8 min of total assay time. These excellent analytical characteristics obtained linked to the full automatization of the immunoassay allowed the fast and accurate determination of CRP in hardly available clinical samples as those coming from preterm infants with suspected sepsis. These results demonstrated the usefulness of the approach which meets the clinical requirements as a future point-of-care device for clinical analysis.

ZnS/C/MoS2 Nanocomposite Derived from Metal-Organic Framework for High-Performance Photo-Electrochemical Immunosensing of Carcinoembryonic Antigen.

A hexafluorophosphate ionic liquid is used as a functional monomer to prepare a metal-organic framework (Zn-MOF). Zn-MOF is used as a template for MoS2 nanosheets synthesis and further carbonized to yield light-responsive ZnS/C/MoS2 nanocomposites. Zn-MOF, carbonized-Zn-MOF, and ZnS/C/MoS2 nanocomposites are characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray diffraction pattern, scanning electron microscopy (SEM), element mapping, Raman spectroscopy, X-ray photoelectron spectroscopy, fluorescence, and nitrogen-adsorption analysis. Carcinoembryonic antigen (CEA) is selected as a model to construct an immunosensing platform to evaluate the photo-electrochemical (PEC) performances of ZnS/C/MoS2 nanocomposites. A sandwich-type PEC immunosensor is fabricated by immobilizing CEA antibody (Ab1 ) onto the ZnS/C/MoS2 /GCE surface, subsequently binding CEA and the alkaline phosphatase-gold nanoparticle labeled CEA antibody (ALP-Au-Ab2 ). The catalytic conversion of vitamin C magnesium phosphate produces ascorbic acid (AA). Upon being illuminated, AA can react with photogenerated holes from ZnS/C/MoS2 nanocomposites to generate a photocurrent for quantitative assay. Under optimized experimental conditions, the PEC immunosensor exhibits excellent analytical characteristics with a linear range from 2.0 pg mL-1 to 10.0 ng mL-1 and a detection limit of 1.30 pg mL-1 (S/N = 3). The outstanding practicability of this PEC immunosensor is demonstrated by accurate assaying of CEA in clinical serum samples.

Rapid and sensitive label-free determination of aflatoxin M1 levels in milk through a White Light Reflectance Spectroscopy immunosensor

A miniaturized optical immunosensor based on White Light Reflectance Spectroscopy (WLRS) for the rapid and label-free detection of aflatoxin M1 (AFM1) in milk samples has been developed. WLRS sensing system consists of the measurement set-up and the biochip. The first encompasses the reflection probe, the light source and the spectrometer, while the latter is a Si chip with a SiO2 layer on top where an AFM1-bovine serum albumin conjugate has been immobilized. The assay was performed by running mixtures of rabbit polyclonal anti-AFM1 antibody with the calibrators or the samples, followed by reaction with biotinylated anti-rabbit IgG antibody and streptavidin. The assay cycle was completed in 25 min, the limit of detection was 6 pg/mL, and the linear working range extended from 0.012 to 2.0 ng/mL. The assay was repeatable (intra-and inter-assay coefficients of variation ranged from 2.1 to 6.3% and 3.5 to 8.2%, respectively) and accurate (percent recovery values ranged from 92.5 to 110%). AFM1 could be detected with the immunosensor developed in both processed and unprocessed milk of different animal species without any dilution. The excellent analytical characteristics and the small instrument size make the proposed sensor suitable for accurate low-cost AFM1 determination in milk samples at the point-of-need.

A critical evaluation of the Beckman Coulter Access hsTnI: Analytical performance, reference interval and concordance

IntroductionWe investigated the analytical performance, outlier rate, carryover and reference interval of the Beckman Coulter Access hsTnI in detail and compared it with historical and other commercial assays. Materials and methodsWe compared the imprecision, detection capability, analytical sensitivity, outlier rate and carryover against two previous Access AccuTnI assay versions. We established the reference interval with stored samples from a previous study and compared the concordances and variances with the Access AccuTnI+3 as well as with two commercial assays. ResultsThe Access hsTnI had excellent analytical sensitivity with the calibration slope 5.6 times steeper than the Access AccuTnI+3. The detection capability was markedly improved with the SD of the blank 0.18–0.20 ng/L, LoB 0.29–0.33 ng/L and LoD 0.58–0.69 ng/L. All the reference interval samples had a result above the LoB value. At a mean concentration of 2.83 ng/L the SD was 0.28 ng/L (CV 9.8%). Carryover (0.005%) and outlier (0.046%) rates were similar to the Access AccuTnI+3. The combined male and female 99th percentile reference interval was 18.2 ng/L (90% CI 13.2–21.1 ng/L). Concordance amongst the assays was poor with only 16.7%, 19.6% and 15.2% of samples identified by all 4 assays as above the 99th, 97.5th and 95th percentiles. Analytical imprecision was a minor contributor to the observed variances between assays. ConclusionThe Beckman Coulter Access hsTnI assay has excellent analytical sensitivity and precision characteristics close to zero. This allows cTnI measurement in all healthy individuals and the capability to identify numerically small differences between serial samples as statistically significant. Concordance in healthy individuals remains poor amongst assays.

Rapid C-reactive protein determination in whole blood with a White Light Reflectance Spectroscopy label-free immunosensor for Point-of-Care applications

The fast and accurate determination of C-reactive protein (CRP) in human whole blood samples employing a white light reflectance spectroscopy sensing platform is demonstrated. Each assay cycle was completed in 12 min, including 5-min reaction with the diluted whole blood samples, 3-min with the biotinylated anti-CRP antibody, and 4-min with streptavidin solution. The effect of whole blood on the assay performance was evaluated, and it was found that dilutions as low as 50-times could be employed. Thus, taking into account that the assay had a detection limit of 2.2 μg/L CRP in 50-times diluted sample, whole blood concentrations as low as 110 μg/L could be determined. In addition, due to the implementation of a two-step sandwich immunoassay, high-dose hook-effect was avoided. The accuracy of the assay was determined through recovery experiments by spiking whole blood samples with exogenous CRP. Mean recovery values ranging from 92 to 108% were obtained, indicating the accuracy of measurements performed with the developed immunosensor. The excellent analytical characteristics, the short analysis time and the compact instrument size support the applicability of the immunosensor developed for point-of-care CRP determinations.

A New Targeted CFTR Mutation Panel Based on Next-Generation Sequencing Technology

Searching for mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR) is a key step in the diagnosis of and neonatal and carrier screening for cystic fibrosis (CF), and it has implications for prognosis and personalized therapy. The large number of mutations and genetic and phenotypic variability make this search a complex task. Herein, we developed, validated, and tested a laboratory assay for an extended search for mutations in CFTR using a next-generation sequencing-based method, with a panel of 188 CFTR mutations customized for the Italian population. Overall, 1426 dried blood spots from neonatal screening, 402 genomic DNA samples from various origins, and 1138 genomic DNA samples from patients with CF were analyzed. The assay showed excellent analytical and diagnostic operative characteristics. We identified and experimentally validated 159 (of 188) CFTR mutations. The assay achieved detection rates of 95.0% and 95.6% in two large-scale case series of CF patients from central and northern Italy, respectively. These detection rates are among the highest reported so far with a genetic test for CF based on a mutation panel. This assay appears to be well suited for diagnostics, neonatal and carrier screening, and assisted reproduction, and it represents a considerable advantage in CF genetic counseling.

Gold-Ruthenium Alloy Nanoparticles Modified Glassy Carbon Electrode as a Sensing Platform for the Trace Level Detection of Indol-3-Carbaldehyde

In the present work we have proposed a novel strategy for the detection of indol-3-carbaldehyde (I3C) using Au-Ru alloy nanoparticles (NPs) modified glassy carbon electrode. The work is focused on achieving the optimum conditions for getting robust signal of I3C over NPs modified electrode surface. The alloy NPs of Au-Ru were synthesized by polyols method and characterized by XRD and UV-visible spectroscopy. Cyclic, square wave and differential pulse voltammetry were used for investigating the performance of the designed sensor for the electroanalysis of I3C. The developed sensor showed nice voltammetric response in media of different pH and demonstrated remarkable electrocatalytic activity and anti-interference ability. A linear calibration curve for indol-3-carbaldehyde was obtained in the concentration range of 20–100 μM with a correlation coefficient of 0.99. The results revealed that 1.89 μM concentration of I3C can be reliably detected at Au-Ru modified glassy carbon electrode. Moreover, the designed sensor showed excellent analytical characteristics such as high selectivity, reproducibility, wide linearity range and lower limit of detection.

Single-walled carbon nanotubes covalently functionalized with polytyrosine: A new material for the development of NADH-based biosensors

We report for the first time the use of single-walled carbon nanotubes (SWCNT) covalently functionalized with polytyrosine (Polytyr) (SWCNT-Polytyr) as a new electrode material for the development of nicotinamide adenine dinucleotide (NADH)-based biosensors. The oxidation of glassy carbon electrodes (GCE) modified with SWCNT-Polytyr at potentials high enough to oxidize the tyrosine residues have allowed the electrooxidation of NADH at low potentials due to the catalytic activity of the quinones generated from the primary oxidation of tyrosine without any additional redox mediator. The amperometric detection of NADH at 0.200V showed a sensitivity of (217±3)µAmM−1cm−2 and a detection limit of 7.9nM. The excellent electrocatalytic activity of SWCNT-Polytyr towards NADH oxidation has also made possible the development of a sensitive ethanol biosensor through the immobilization of alcohol dehydrogenase (ADH) via Nafion entrapment, with excellent analytical characteristics (sensitivity of (5.8±0.1)µAmM−1cm−2, detection limit of 0.67µM) and very successful application for the quantification of ethanol in different commercial beverages.