Increase In Rct Research Articles

Associations between Milk Coagulation Properties and Microbiological Quality in Sheep Bulk Tank Milk.

This study conducted a seasonal analysis of bulk tank milk from 77 sheep farms to establish relationships between the concentration of major microbial groups and milk coagulation properties. The investigated milk traits included composition (pH, fat, casein, lactose), coagulation properties (curd firmness: A60-, rennet clotting time: RCT-, curd firming time: k20-, curd yield: CY-), and somatic cell score (SCS). The main microbial groups analyzed were total mesophilic bacteria (SPC), thermodurics (THERMO), psychrotrophs (PSYCHRO), Pseudomonas spp. (PSEUDO), lactic acid bacteria (LAB), catalase-negative gram-positive cocci (GPCNC), Escherichia coli (ECOLI), coliforms other than Escherichia coli (COLI), coagulase-positive staphylococci (CPS), coagulase-negative staphylococci (CNS), and spores of lactate-fermenting Clostridium (BAB). Mixed linear models were used to explore associations between coagulation properties and the aforementioned variables. Results demonstrated that incorporating microbial loads into the models improves their fit and the relative quality of the outcomes. An important seasonality is demonstrated by an increase in CY and A60, along with a decrease in RCT and k20 during autumn and winter, contrasting with spring and summer. BAB concentration resulted in a reduction of A60 and an increase in RCT, whereas SPC concentration led to an enhancement of A60 and a reduction in RCT. An increase in GPCNC concentration was associated with an increase in k20 and a decrease in CY.

Evaluation of ionic liquids based imidazolium salts as an environmentally friendly corrosion inhibitors for carbon steel in HCl solutions

The features of this work on corrosion inhibition have been investigated based on the ecological awareness and according to the strict environmental legislations. This was done by studying how different imidazolium derivatives ionic liquids containing different alkyl chains R8, R10 and R12 affected the corrosion reaction of carbon steel specimen immersed in 1 M hydrochloric acid at various temperatures. Weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy were utilized to examine the corrosion inhibition behavior on carbon steel. In addition, FT-IR spectroscopy was used to analyze the coated film that has been formed on the metal surface. The prepared ionic liquids showed effective inhibition efficiency, where the corrosion rate after the using of 100 ppm of R8-IL, R10-IL and R12-IL was decreased from 5.95 (µg cm−2 min−1) to 0.66, 0.56, and 0.44 (µg cm−2 min−1), respectively at 20 °C. In the polarization curves, the corrosion current, Icorr, decreases by ILs addition and suggest that ILs act as mixed type inhibitors. From EIS findings, the increase in Rct and decrease in Cdl values proves the adherence of inhibitor molecules on carbon steel surface. The temperature effect was also studied on the film formed, where increasing the temperature from 20 to 50 °C, the corrosion rate increased and the inhibitors efficacy decreased. The increasing in the length of the attached alkyl chain, the efficacies of the prepared inhibitors increases. Various thermodynamic parameters such as the reaction activation free energy (ΔG*), the entropy of activation (ΔS*), and the enthalpy of activation (ΔH*), as well as the adsorption isotherm were investigated in order to interpret the mechanism and obtain the most accurate perception.

Effect of Deposition Potential on ZnNi Coating Corrosion Behaviour

ZnNi coatings were deposited using the electrochemical deposition method. In this study, the effect of potential electrodeposition on deposited properties, morphology, and size of ZnNi alloy nanoparticles was investigated in detail. The as-synthesized products were characterized by ZnNi coating properties is characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectroscopy (EIS). The result indicated that the electrodeposition processes of ZnNi were governed by a nucleation process controlled by diffusion. XRD results showed that the phase structure of both alloy and composite coatings was single ZnNi phase. Potential increase influences the larger crystal size and the surface of coating was compact and uniform, the Rct increase, and greater the icorr so that the possibility of corrosion is higher.

Effect of Ti addition on mechanical properties and corrosion resistance of X80 pipeline steel

In this study, the effects of Ti addition on the mechanical properties and corrosion resistance of X80 pipeline steel were investigated using tensile impact, electrochemical and neutral salt spray tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results show that the addition of Ti can promote the formation of acicular ferrite (AF), resulting in significant grain refinement. It can improve the tensile strength, yield strength and impact toughness of X80 pipeline steel, with the highest value of tensile strength at 0.04 wt % Ti content, which is 8% higher than the original; yield strength is 18% higher; and impact work is 9% higher. The best corrosion resistance of the pipeline steel is achieved at a Ti addition of 0.04 wt %, with a reduced corrosion weight loss rate, 28% less than the original. The Tafel curve is shifted forward, the self-corrosion potential Ecorr increases and the corrosion current density Icorr decreases, improving by 10% from the original. The capacitive arc radius and Rct increase, the resistance to corrosion reaction increases. The corrosion products are mainly loose and porous γ-FeOOH and β-FeOOH in the early stage of corrosion, and more α-FeOOH and Fe3O4 are generated in the later stage.

Impedimetric Bacterial Detection Using Random Antimicrobial Peptide Mixtures.

The biosensing of bacterial pathogens is of a high priority. Electrochemical biosensors are an important future tool for rapid bacteria detection. A monolayer of bacterial-binding peptides can serve as a recognition layer in such detection devices. Here, we explore the potential of random peptide mixtures (RPMs) composed of phenylalanine and lysine in random sequences and of controlled length, to form a monolayer that can be utilized for sensing. RPMs were found to assemble in a thin and diluted layer that attracts various bacteria. Faradaic electrochemical impedance spectroscopy was used with modified gold electrodes to measure the charge-transfer resistance (RCT) caused due to the binding of bacteria to RPMs. Pseudomonas aeruginosa was found to cause the most prominent increase in RCT compared to other model bacteria. We show that the combination of highly accessible antimicrobial RPMs and electrochemical analysis can be used to generate a new promising line of bacterial biosensors.

Electrochemical Impedimetric Real-Time Polymerase Chain Reactions Using Anomalous Charge Transfer Enhancement.

We developed a new electrochemical impedimetric method for the real-time detection of polymerase chain reactions (PCR) based on our recent discovery that the DNA intercalator, [Ru(bpy)2DPPZ]2+, anomalously enhances charge transfer between redox mediators, K4[Fe(CN)6]/K3[Fe(CN)6], and a carbon electrode. Three mM [Fe(CN)6]3-/4- and 5 μM [Ru(bpy)2DPPZ]2+ were added to the PCR solution, and electrochemical impedance spectroscopy (EIS) measurements were performed at each elongation heat cycle. The charge transfer resistance (Rct) was initially low due to the presence of [Ru(bpy)2DPPZ]2+ in the solution. As PCR progressed, amplicon dsDNA was produced exponentially, and intercalated [Ru(bpy)2DPPZ]2+ ions, which could be detected as a steep Rct, increased at specific heat cycles depending on the amount of template DNA. The Rct increase per heat cycle, ΔRct, showed a peak at the same heat cycle as optical detection, proving that PCR can be accurately monitored in real time by impedance measurement. This simple method will enable a cost-effective and portable PCR device.

Microbial fuel cell (MFC)-based biosensor for combined heavy metals monitoring and associated bioelectrochemical process

To explore the feasibility and related mechanism of MFC biosensor for wastewater detection under the action of combined heavy metals. Cyclic voltammetry (CV) and scanning electrochemical impedance spectroscopy (EIS) were used to explore the related bioelectrochemical process. The response of the reactor to single/combined heavy metals, low/high heavy metal concentrations, and the differences in ohmic resistance (Rs) and charge transfer resistance (Rct) were investigated using Ni as the core heavy metal and the combined action of Cd, Cu and Zn. The results indicated that there was a linear relationship between the concentration and output voltage of the MFC biosensor under the action of combined heavy metals (R2 = 0.8803–0.973). However, the internal resistance (Rint) of the MFC biosensor under the action of single heavy metal was far less than that of the combined heavy metal group, and the power density (19.849 W m−3) was 4 times that of the combined heavy metal group (3.109–4.589 W m−3). The Rs of the biosensors in the combined heavy metal group were 0.868Ω and 0.860, which were higher than 0.768Ω of the single heavy metal sensor. With the increase of the concentration of heavy metals in the influent, the increase of Rct was more obvious in the combined group, while the Rs in the single group significantly increased (P < 0.05). The results imply that it is possible for MFC biosensors to be used in the detection of actual water polluted by various heavy metals, but the biosensor performance is mainly limited by Rct, which needs to be further improved.

Construction and analysis of photovoltaic directly coupled conditions in PEM electrolyzer

The Markov model and the PEM electrolyzer system model for directly coupled photovoltaic are combined to construct an efficient and reliable working condition that fits the fluctuation characteristics of solar energy. The working condition is designed through genetic algorithm so that the average coupling efficiency of the system can reach 98.8%. Then, the durability and recovery test are conducted on the basis of the constructed conditions. It is found that the attenuation rate at the current density of 1A/cm2 under the photovoltaic fluctuating condition reached 7.8mV/h, which is twice that under the constant current condition. The charge transfer impedance (Rct) is the main factor leading to the degradation. It is proved by the recovery experiment that the increase of Rct is related to the pollution of metal ions. After pickling to remove some metal ions, Rct can be significantly reduced by 46.8% and 65.2%, respectively. After the durability test, the voltammetric charges under the photovoltaic fluctuating condition and the constant current condition are reduced by 48.3% and 19.1% It indicates that the photovoltaic fluctuation condition will accelerate the attenuation of the effective reaction area of MEA, which is irreversible even after pickling. It can be observed from the SEM images that the catalyst layer of MEA has more obvious peeling under the photovoltaic fluctuation condition, which is not conducive to material transmission and destroys the transmission channel of ions and electrons. This result can provide a reliable reference for the coupling design of PEM electrolyzer and renewable energy in the future.

Essence - A New Electrochemical Platform

There is a great demand for a fast, on-site screening test, especially during the COVID-19 pandemic. However, most point-of-care (POC) sensors usually suffer from insufficient sensitivity and selectivity. Often these devices have a very high rate of false positives and false negatives. The incorrect data could result in low customer usage (both the patient and the doctor) due to decreased confidence in the results. Portable ELISA-based kits can have low rates of false-positive and false negatives. However, ELISA is inherently complicated and often requires a specialist on-site to ensure the success of each sample's high costs and time.Here we show a new electrochemical platform called ESSENCE. ESSENCE is an Electrochemical Sensor that uses a Shear-Enhanced, flow-through Nanoporous Capacitive Electrode. ESSENCE can overcome current electrochemical sensors' selectivity and sensitivity limitations. The ESSENCE sensor architecture is a microfluidic channel sandwiched between two gold micro-electrode glass slides, formed a non-planar interdigitated porous electrode that improved electric field penetration compared with the traditional planar interdigitated electrode. The porous electrode structure used in this research has a high Zeta potential compared to the bare glass surface. This results in a significantly smaller Debye double-layer (EDL) length than in a clear channel. Due to a smaller EDL length, the relaxation frequency increases, which shifts the EIS signal to a higher frequency range (1kHz to 100MHz) and results in a fast response with a higher signal-to-noise ratio in Electrochemical Impedance Spectroscopy(EIS) measurements.Further, the modular fabrication of the ESSENCE chip allows ESSENCE to target different biomolecules from DNAs to protein cancer biomarkers by simply changing the packed transducer material. However, the packing material’s conductivity represents a significant challenge to the electrochemical response of ESSENCE. The high conductivity of the transducer material shorts the system leading to a pure resistive response. Impedance spectroscopy (EIS) response of ESSENCE cannot be distinguished enough to determine if the sensor is working. ESSENCE has a switchable electrode system for usage in multiple configurations like a material electrode, clear electrode, and working electrode to overcome these limitations. For carbon nanotube (CNT) transducers with functionalized oligos on the CNT, a 20-fold jump in the signal is noticed from the working electrode configuration compared to the other configurations. It is worthwhile to note that depending on the biomolecule (DNA or Protein), the surface charge transfer resistance (Rct) in the EIS signal of ESSENCE can either show a decrease (DNA) or increase (protein) on the binding of the target bio-molecule (target DNA to DNA or target protein to protein). The change in the Rct depends on the charge of the molecule. It has been seen that on the binding of a target protein, the active area of the electrode surface decreased, leading to a reduction in current and a concomitant increase in Rct. On binding of the target DNA, the capture-target DNA pair essentially becomes a part of the electrode due to its charge. This increase in charge is more significant than any reduction in the surface area due to the DNA's binding. This leads to an increase in current to the packed electrode, leading to a concomitant decrease in Rct.The fluid flow through the porous electrode increases mixing, minimizes diffusion, and generates a significantly enhanced fluidic shear force. This force e can unbind most of the false-positive signals generated by non-specific binding, such as physical adhesive or biofouling. The porous electrode also provides a high surface area to volume ratio to capture the target analyte leading to increased sensitivity. We have an automatic fluidic control system in ESSENCE that minimized any errors in the operation of ESSENCE. Our system has high selectivity and sensitivity for DNA (fM sensitivity, selective against non-target DNA), breast cancer biomarker proteins (p53, pg/L sensitivity, selective against non-target HER2). Figure 1

Neural Conduction Along Postretinal Visual Pathways in Glaucoma.

Purpose: This study was conducted in order to evaluate retinal ganglion cell (RCG) function and the neural conduction along the postretinal large and small axons and its correlation with retinal nerve fiber layer thickness (RNFL-T) in open-angle glaucoma (OAG) eyes.Methods: Thirty-seven OAG patients (mean age: 51.68 ± 9.83 years) with 24–2 Humphrey mean deviation (MD) between −2.5 and −20 dB and IOP <21 mmHg on pharmacological treatment (OAG group) and 20 age-matched controls (control group) were enrolled. In both groups, simultaneous pattern electroretinograms (PERG) and visual evoked potentials (VEP), in response to checks stimulating macular or extramacular areas (the check edge subtended 15′ and 60′ of visual arc, respectively), and RNFL-T (measured in superior, inferior, nasal, and temporal quadrants) were assessed.Results: In the OAG group, a significant (ANOVA, p < 0.01) reduction of 60′ and 15′ PERG P50-N95 and VEP N75-P100 amplitudes and of RNFL-T [overall (average of all quadrants) or temporal] with respect to controls was found; the values of 60′ and 15′ PERG P50 and VEP P100 implicit times and of retinocortical time (RCT; difference between VEP P100 and PERG P50 implicit times) were significantly (p < 0.01) increased with respect to control ones. The observed increased RCTs were significantly linearly correlated (Pearson’s test, p < 0.01) with the reduced PERG amplitude and MD values, whereas no significant linear correlation (p < 0.01) with RNFL-T (overall or temporal) values was detected.Conclusions: In OAG, there is an impaired postretinal neural conduction along both large and small axons (increased 60′ and 15′ RCTs) that is related to RGC dysfunction, but independent from the RNFL morphology. This implies that, in OAG, the impairment of postretinal neural structures can be electrophysiologically identified and may contribute to the visual field defects, as suggested by the linear correlation between the increase of RCT and MD reduction.

Enzyme-free impedimetric biosensor-based molecularly imprinted polymer for selective determination of L-hydroxyproline

This study first reported enzyme-free impedimetric biosensor-based molecularly imprinted polymers for selective and sensitive determination of L-hydroxyproline (L-hyp), a biomarker for the early diagnosis of bone diseases. In recent study, utilizing a single 3-aminophenylboronic acid (3-APBA) to create imprinted surfaces could result in a strong interaction and difficulty in removal of a template molecule. Hence, a mixture of monomer solution containing 3-APBA and o-phenylenediamine (OPD) in the presence of the L-hyp molecule was co-electropolymerized onto the screen-printed electrode using cyclic voltammetry (CV) to eradicate this mentioned limitation. The detection principle of this sensor is relied on alteration of mediator's charge transfer resistance (Rct) that could be obstructed by L-hyp occupied in imprinted surface. The successfully fabricated biosensor was explored by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and confocal scanning microscopy. Furthermore, the effect of polymer composition on the Rct response was systematically investigated. The result exhibited that the mixture of monomers could provide the highest change of Rct due to high selectivity from esterification of 3-APBA and from hydrogen bond of OPD surrounding the template. The sensor showed a significant increase in Rct in the presence of L-hyp, whereas no observable resistance change was detected in the absence thereof. The calibration curve was obtained in the range from 0.4 to 25 μg mL−1 with limits of detection (3SDblank/Slope) and quantification (10SDblank/Slope) of 0.13 and 0.42 μg mL−1, respectively. This biosensor exhibited high selectivity and sensitivity and was successfully applied to determine L-hyp in human serum samples with satisfactory results.

Electrochemical Impedimetric Study of Non-Watson-Crick Base Pairs of DNA.

Electrochemical impedance spectroscopy (EIS) was used to detect non-Watson-Crick base pairs of DNA. Thiol-modified DNA as a probe and mercaptohexanol (MCH) were co-immobilized to form a DNA/MCH mixed self-assembled monolayer on a gold electrode surface and then hybridized with complementary DNAs. The DNA layers were measured by the EIS method and interpreted by equivalent circuits. Every terminal base mismatch of the DNA duplex brought about an increase in the charge-transfer resistance (Rct), unlike the case with a fully matched DNA duplex. The value of Rct was highly sensitive to the number of base mismatches for both unpaired and overhang DNA at the terminal. For internal base mismatches, however, no significant increase in Rct was observed. These experimental results proved that the charge transfer of redox molecules to the electrode surface is largely hindered by an end fraying motion due to base unpairing and dangling overhang. EIS was able to detect these steric properties of DNA strands. Furthermore, an electrode modified with G-quadruplex (G4) DNA demonstrated the influences of bulkiness and loop structure on the accessibility of the redox probe to the electrode.

Experimental and theoretical (MDS and FMO) study of 1-Benzylimidazole for mild steel in 0.1 N H2SO4 at normal and elevated temperatures: An efficient anti-pitting and anti-cracking agent

1-Benzylimidazole (BI) was tested as an anti-pitting and anti-cracking agent for mild steel (MS) in 0.1 N sulphuric acid by experimental and theoretical techniques. Gravimetric, electrochemical impedance spectroscopy and potentiodynamic polarization techniques were used to find corrosion rate and percentage corrosion inhibition efficiency in the presence and absence of BI at three different temperatures. The molecular dynamics simulation and Frontier molecular orbital studies were carried out by using density functional theory. The surface study was performed by Langmuir and Frumkin adsorption isotherms, scanning electron microscopy, and metallurgical imaging techniques. Frequency calculation study was carried out on the geometry optimized structure of BI and corresponding theoretical IR spectra was obtained. Chemical reactivity parameters like global hardness, electronegativity, electrophilicity, nucleophilicity, electron releasing and accepting tendency, work function, back donation energy, proton affinity, metal inhibitor interaction, binding energies, etc., were calculated. Morphological study confirms the even and non-porous film on the MS supported by a decrease in Icorr and an increase in Rct with the concentration of BI. BI shows 93.31% inhibition efficiency at 1000 ppm for MS when exposed to 0.1 N H2SO4. BOD and COD of wastewater was found to be within the permissible limit.

Ultrasensitive electrochemical detection of digoxin using graphite oxide and Au-NPs composites

Digoxin is a cardiac glycoside which is widely used as medication in treatment of congestive heart failure and arrhythmias. Unfortunately, digoxin has small therapeutic range (2 ng/mL), excess digoxin concentration in blood plasma can cause intoxication. Therefore, simple and sensitive procedure is required for strict monitoring of digoxin in blood level to minimize the risk of toxicity. In this paper, we report detection of digoxin using Au-NPs and GO composites synthesized with wet chemistry. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy were employed for the confirmation of Au-NPs attachment on the surface of GO. The synthesized Au-NPs-GO composites were deposited on the surface of glassy carbon electrode (GCE) for electrochemical characterization. The electrodes were further incubated with mercaptoacetic acid (MAA) and digoxin antibody (Ab) for the formation of Ab-MAA-Au-NPs-GO modified electrode. MAA conjugation resulted in a 35 % increase in Ipc and 63 % decrease in charge transfer resistance (Rct). Antibody immobilization on MAA modified electrode resulted a sudden drop in both the cathodic peak (anodic peak) currents Ipc(Ipa). Increase in Rct (940 Ω) after Ab functionalization was due to its proteinic nature, which confirmed the formation of Ab-MAA-Au-NPs-GO modified GCE sensors. Work was further extended to probe the charge transfer characteristics in different dilution of digoxin. 17 % (10 %) decrease in Ipc(Ipa) as the digoxin drug was increased from 0.1 ng/mL to 1000 ng/mL. Linear sweep voltammetry (LSV) was also performed at the end for analytic performance of Ab modified sensor for various digoxin drug dilutions. Two linear regressions for current response against digoxin drug dilution were recorded, which confirmed sensitivity of the sensor was governed by interaction between Ab and digoxin drug coordinated by potassium ions at the electroactive sites. The sensitivity was 154.81 μAcm−2 ng-1 for 2-0.1 ng range and 10.71 μAcm−2 ng-1 in the range of 1000−2 ng. The limit of detection (LoD) was 0.19 ng/mL, which suggested that proposed Ab-MAA-Au-NPs-GO modified GCE electrochemical sensor can be successfully applied for future digoxin drug detection applications.

Corrosion inhibition and adsorption of imidazolium based ionic liquid over P110 steel surface in 15% HCl under static and dynamic conditions: Experimental, surface and theoretical analysis

The present paper deals with the corrosion inhibition evaluation of imidazoline based ionic liquid, namely 1-Decyl-3-methylimidazolium chloride (DMIC) on P110 steel in 15% HCl under static and dynamic conditions. The influence of KI addition was also examined over the inhibition performance (ɳ%). EIS results reveal that Rct increase with increases in DMIC concentration. PDP suggests that the inhibition action of DMIC is a mixed type inhibitor. The inhibitive performance of DMIC is less, and its maximum inhibition efficiency is 68.61% at 400 mg/L. Addition of KI (0.5 mM) + DMIC (400 mg/L) enhanced the corrosion inhibition efficiency to 90.15%. The performance of DMIC and DMIC+KI decreases with an increase in temperature. The adsorption of DMIC obeys the El-Awady isotherm. The performance of DMIC is better under hydrodynamic conditions as compared to static conditions. The performance of DMIC decreases when the rotation speed is higher than 1500 rpm. Density functional theory (DFT) suggests that both anionic/cationic parts help in the DMIC adsorption. Molecular dynamic simulation (MD) reveals that neutral DMIC adsorbed flatly over P110 steel while protonated adsorbed in a twisted manner.

Optimization of Fc-Thiolate SAMs for Electrochemically Mediated Bacterial Biosensors

Alkanethiol Self-Assembled Monolayers (SAMs), typically deposited on Au substrates, have been commonly utilized to immobilize receptor biomolecules in the construction of a variety of biosensors, such as the detection of glucose oxidase by the immobilization of calixarenes thiols 1. The appeal of using SAMs derives from their ease of fabrication and component flexibility, allowing for more than one alkanethiol to be deposited in a single monolayer. This results in the formation of SAMs in which each thiol component adds a different property or role, thus introducing versatility to the construction and operation of resulting sensors 2.In our recent work, alkanethiol SAMs, composed of three different thiol molecules, were constructed for use as an electrochemical Toll-Like Receptor 4 (TLR4)-based sensor that can detect Gram-negative bacteria. TLRs are a family of immunoproteins in the innate immune system, which are able to detect a broad category of pathogens, rather than specific targets, as is the case with the adaptive system (e.g., antibodies). In our published work 3, SAMs consisted of a carboxylic acid terminated thiol that allowed for the conversion to a nitrilotriacetic (NTA) group. This moiety could then chelate a Ni2+ cation, followed by attachment of the TLR4 immunoprotein via its His-tag. The second thiol in the SAM contained a terminal ferrocene (Fc) group, where the Fc group was bound to the C11 chain via an amide group. Here, the Fc group serves as a mediator for charge transfer between ferrocyanide in solution and the Au substrate, resulting in relatively high current signals, thus making the sensor potentially field deployable. The third thiol in these SAMs was a hydroxy-terminated thiol, added as a diluent between the immobilized TLR4 receptors. SAMs were prepared by co-deposition on sputter Au on glass.Electrochemical testing involved cyclic voltammetry (CV) studies in pH 7 buffer solution in order to determine the amount of Fc-thiol present, as well as CV and electrochemical impedance spectroscopy (EIS) studies in ferrocyanide solutions to examine its redox-mediation response and to obtain a measure of the charge transfer rate. In the presence of lysed bacteria, the immobilized TLR4 dimerizes, which blocks electrochemical mediation between ferrocyanide and the surface bound Fc. This results in an increase in RCT which is our biosensor signal. However, a key problem with these sensors is that their RCT increased with electrochemical testing in the absence of lysed bacteria, producing signal drift. Thus, in the present work, the reasons for sensor signal drift and methods to overcome it were explored.It was found in recent work that the drift of the full TLR4 sensor was correlated with the loss in the Fc redox signal, although it was not clear if underlying SAM was at the root of the problem. If so, then it was necessary to determine if the loss in the Fc redox activity was caused by the physical loss of the Fc thiol from the Au surface or deactivation of the Fc surface complex and/or its electrochemistry. To determine which of these options was responsible for signal drift, the relative % v/v fraction of the three thiols was varied, and in later work, based on chemical considerations, the Fc molecule containing an amide group was replaced with a C11 chain bonded directly to the Fc. It was found that this latter strategy led to a very stable SAM, showing negligible drift in the Fc CV charges and in the RCT values in ferrocyanide solutions, with or without the TLR4 receptor attached on the outer surface of the SAM.This presentation will focus on presenting the electrochemistry of the various binary and ternary thiol SAMs investigated in this work and examining the Fc CV peak charges, potential, and kinetics, as well as the double layer capacitance, to better understand how and why the Fc redox response was stabilized. This is important because this correlates directly with the stability of the TLR4/Gram-negative bacteria sensor, as will be demonstrated for a TLR2 biosensor tested against Gram-positive bacteria cell wall ligands.

Aptamer-modified pencil graphite electrodes for the impedimetric determination of ochratoxin A

Ochratoxin A (OTA), a widespread food contaminant, is considered as one of the most hazardous mycotoxins commonly occurring in beer. Herein, we describe a novel impedimetric aptasensor based on Pencil Graphite Electrodes (PGE) for the analysis of OTA. Taking advantage of its affordability and high active surface area, a PGE was modified with a specific aptamer, to achieve sensitive detection of OTA. This strategy relies on the target-induced increase in the electron transfer resistance (Rct) upon OTA recognition using ferro/ferricyanide as a redox probe. With the addition of OTA, the formation of OTA–aptamer complex resulted in an increase of Rct. The change of Rct strongly depends on OTA concentration, which is applied for mycotoxin quantification. An acceptable linear range was obtained from 0.1 to 2.0 ng mL−1 with a very good limit of detection as low as 0,1 ng mL−1. This simple-to-design aptasensor was successfully tested in spiked beer samples, with OTA concentrations in the range of 0.4–1.6 ng mL−1, attesting a recovery percentage of 93.4 ± 6.6%. It also showed a high level of stability and reproducibility thanks to the electro-grafting method via in-situ generation of 4-carboxyphenyl diazonium salts. This PGE-based platform is a versatile approach for the design of low-cost aptasensors for food safety control.

Development of a Novel Tyrosinase Amperometric Biosensor Based on Tin Nanoparticles for the Detection of Bisphenol A (4.4-Isopropylidenediphenol) in Water

Highly crystalline poly-vinyl pyrrolidone (PVP) capped Sn nanocrystals with good size and shape uniformity was synthesized by a hydrothermal process. A highly sensitive amperometric biosensor for the detection of Bisphenol A (BPA) was developed by immobilizing Tyrosinase on to glassy carbon electrode (GCE) modified with Sn nanoparticles. The fabricated amperometric biosensor exhibited excellent electroactivity towards BPA oxidation catalysed by enzymatic reaction of tyrosinase together with good conductivity of Sn nanoparticles. The developed biosensor displayed linear range from 0.01 to 0.10 μmol L-1 and a detection limit (DL) of 1.8 nmol L-1 with a correlation coefficient of 0.989. Electrochemical impedance spectroscopy (EIS) obtained in buffer solution for Tyrosinase/SnNP/GCE had the lowest charge transfer resistance (Rct) value of 219 Ω, which indicated low charge transfer. There was an increase in Rct for Tyrosinase/GCE, SnNP/GCE and Bare GCE which was 316 Ω, 638 Ω and 598 Ω respectively. This indicated a strong resistance to charge transfer. It is reported for the first time the use of Sn nanoparticles modified on GCE and tyrosinase for detection of BPA.

Molecular Imprinted Polymer Based Impedimetric Sensor for Trace Level Determination of Digoxin in Biological and Pharmaceutical Samples

Background: Molecularly Imprinted Polymers (MIPs) are used as artificial receptors in biosensors for the detection of a wide range of analytes from small drug molecules to large molecular weight biomolecules. Quantification of Digoxin (DIG) in human serum and pharmaceutical samples has very high importance due to its low margin of safety. In this report, a highly sensitive molecularly imprinted polymer for DIG is prepared and the detection of analyte was conducted using electrochemical impedance spectroscopy. Methods: Bulk polymerization method was chosen for the preparation of MIP because of its better preservation of the pockets formed during the polymerization. DIG imprinted polymer was prepared by thermal polymerization of Methacrylic Acid (MAA) cross-linked with Ethyleneglycol Dimethacrylate (EGDMA) in the presence of DIG. The molecular interactions via hydrogen bonding between template and monomer in MIP and Non-Imprinted Polymer (NIP) were confirmed using Fourier Transform Infrared (FTIR) spectroscopy. Morphological studies were performed before and after extraction of the template using Scanning Electron Microscopy (SEM). MIP modified carbon paste electrode (MIPCPE) was fabricated by mixing optimized quantities of graphite, the polymer, and eicosane. The change in charge transfer Resistance (Rct) at the electrode-electrolyte (MIPCPE-electrolyte) interface before and after addition of DIG solution was studied using electrochemical impedimetric sensing of DIG. Results: The surface morphology of the MIPCPE shows better porosity in comparison to non-imprinted polymer CPE (NIPCPE) and MIPCPE before extraction of the template. In contrast to NIPCE, the fabricated MIPCPE shows a significant increase in Rct after addition of DIG. The MIPCPE based impedimetric sensor is able to detect DIG over a wide range of concentration from 1.0 × 10-9 M to 0.5 × 10-7 M with a detection limit 6.95 × 10-11 M. The selectivity coefficients obtained for the MIPCPE and NIPCPE reveal specific recognition MIPCPE sensor towards DIG. The recovery rates of DIG from the spiked blood serum and pharmaceutical samples are in the range of sensor 89-101%. Conclusion: In the present work, the capability of MIPs as molecular recognition elements is proved by reporting a selective and sensitive impedimetric sensor for DIG. The selectivity coefficients (K) of MIPCPE and NIPCPE obtained for the DIG and interferents show better selectivity of the sensor towards DIG in the presence of interferents. The proposed sensor also shows satisfactory stability, reproducibility, and repeatability for DIG. The proposed sensor was successfully applied for the quantitative estimation of DIG in serum and pharmaceutical samples with appreciable recoveries. Keywords: Digoxin, molecularly imprinted polymer, free-radical polymerization, scanning electron microscope, electrochemical impedance spectroscopy, Carbon paste electrode.

Phenotypic and genetic relationships between indicators of the mammary gland health status and milk composition, coagulation, and curd firming in dairy sheep

The present study investigated the effect of somatic cell count, lactose, and pH on sheep milk composition, coagulation properties (MCP), and curd firming (CF) parameters. Individual milk samples were collected from 1,114 Sarda ewes reared in 23 farms. Milk composition, somatic cell count, single point MCP (rennet coagulation time, RCT; curd firming time, k20; and curd firmness, a30, a45, and a60), and CF model parameters were achieved. Phenotypic traits were statistically analyzed using a mixed model to estimate the effects of the different levels of milk somatic cell score (SCS), lactose, and pH, respectively. Additive genetic, herd, and residual correlations among these 3 traits, and with milk composition, MCP and CF parameters, were inferred using a Bayesian approach. From a phenotypic point of view, higher SCS levels caused a delayed gelification of milk. Lactose concentration and pH were significant for many milk quality traits, with a very intense effect on both coagulation times and curd firming. These traits (RCT, RCT estimated using the curd firming over time equation, and k20) showed an unfavorable increase of about 20% from the highest to the lowest level of lactose. Milk samples with pH values lower than 6.56 versus higher than 6.78 were characterized by an increase of RCT (from 6.00 to 14.3 min) and k20 (from 1.65 to 2.65 min) and a decrease of all the 3 curd firmness traits. From a genetic point of view, the marginal posterior distribution of heritability estimates evidenced a large and exploitable variability for all 3 phenotypes. The mean intra-farm heritability estimates were 0.173 for SCS, 0.418 for lactose content, and 0.206 for pH. Lactose (favorably), and SCS and pH (unfavorably), at phenotypic and genetic levels, were correlated mainly with RCT and RCT estimated using the curd firming over time equation and scarcely with the other curd firming traits. The SCS, lactose, and pH were significantly correlated with each other's. In conclusion, results reported in the present study suggest that SCS, pH, and lactose affect, contemporarily and independently, milk quality and MCP. These phenotypes, easily available during milk recording schemes measured by infrared spectra prediction, could be used as potential indicators traits for improving cheese-making ability of ovine milk.