Alginate NiFe2O4 Nanoparticles Cryogel for Electrochemical Glucose Biosensor Development

Glucose biosensors based on porous material of alginate cryogel has been developed, and the cryogel provides a large surface area for enzyme immobilization. The alginate cryogel has been supplemented with NiFe2O4 nanoparticles to improve the electron transfer for electrochemical detection. The fabrication parameters and operational conditions for the biosensor have also been optimized. The results showed that the optimum addition of NiFe2O4 nanoparticles to the alginate solution was 0.03 g/mL. The optimum operational conditions for the electrochemical detection were a cyclic voltammetry scan rate of 0.11 V/s, buffer pH of 7.0, and buffer concentration of 150 mM. The fabricated alginate NiFe2O4 nanoparticles cryogel-based glucose biosensor showed a linear response for glucose determination with a regression line of y = 18.18x + 455.28 and R² = 0.98. Furthermore, the calculated detection limit was 0.32 mM and the limit of quantification was 1.06 mM.

Development of an Effective and Economic Biosensor for Diabetic Blood Monitoring Based on MWCNTs, Artificial Redox Mediator Ferrocene, Nafion Polymer and a Local Extracted and Purified Glucose Oxidase Enzyme from Penicillium Notatum F-158 Fungus

Enhancement of the properties of glucose oxidase (GOx) enzyme is still receiving attention due to its extensive applications. Eight different fungal strains were isolated from soil and orange fruit samples for inexpensive GOx production. Penicillium notatum F-158 (P. notatum) strain produced a remarkable amount of GOx. Its culture condition was optimized for optimum GOx production. GOx was purified and its activity, stability and kinetic parameters were studied. An effective biosensor {GCE/[MWCNTs–Fc–GOx(FAD)–NF]} based on layer by layer immbolization of MWCNTs, aritificial ferrocene (Fc) redox mediator, extracted P. notatum GOx enzyme and nafion polymer (NF) on glassy carbon electrode (GCE) surface was developed for glucose determination. Fc acts as an electron relay between enzyme and MWCNTs/GCE. The synergy of MWCNTs and Fc enhances the electrocatalytic action of Fc to the enzymatic oxidation of glucose. Low potential (+0.3V) of Fc applied in amperometric measurements avoids interference of the main electroactive substances present in the real plasma samples. This biosensor showed broad linear ranges {2.80×10-4 to 14.99×10-3 M} and low detection limit (8.68×10-6 M) for glucose determination. The achieved glucose concentrations in six plasma samples are consistent with normal values in human blood indicating that such biosensor could be used clinically.

Fully integrated sampler and dilutor in an electrochemical paper-based device for glucose sensing

An electroanalytical platform capable to take and dilute the sample has been designed in order to fully integrate the different steps of the analytical process in only one device. The concept is based on the addition of glass-fiber pads for sampling and diluting to an electrochemical cell combining a paper-based working electrode with low-cost connector headers as counter and reference electrodes. In order to demonstrate the feasibility of this all-in-one platform for biosensing applications, an enzymatic sensor for glucose determination (requiring a potential as low as −0.1 V vs. gold-plated wire by using ferrocyanide as mediator) was developed. Real food samples, such as cola beverages and orange juice, have been analyzed with the bioelectroanalytical lab-on-paper platform. As a proof-of-concept, and trying to go further in the integration of steps, sucrose was successfully detected by depositing invertase in the sampling strip. This enzyme hydrolyzes sucrose into fructose and glucose, which was determined using the enzymatic biosensor. This approach opens the pathway for the development of devices applying the lab-on-paper concept, saving costs and time, and making possible to perform decentralized analysis with high accuracy. Graphical abstract

Acute supplementation with whey protein or collagen does not alter appetite in healthy women: A randomized double-blind and crossover pilot study

Protein quality has an important role in increasing satiety. Evidence suggests that whey protein (WP) provides satiety via gastrointestinal hormone secretion. Hydrolysed collagen supplementation can also stimulate the production of incretins and influence satiety and food intake. Thus, we sought to compare the effect of acute supplementation of WP or hydrolysed collagen on post-intervention appetite and energy consumption. This was a randomized, double-blind, crossover pilot study with 10 healthy adult women (22.4 y/o) who were submitted to acute intake (single dose) of a beverage containing WP (40 g of concentrated WP) or hydrolysed collagen (40 g). Subjective appetite ratings (feelings of hunger, desire to eat and full stomach) were measured using the Visual Analog Scale (VAS), energy intake was quantified by ad libitum cheese bread consumption 2 hours after supplementation and blood was collected for leptin and glucose determination. There was no difference between treatment groups in the perception of hunger (P = 0.983), desire to eat (p = 0.326), full stomach feeling (p = 0.567) or food consumption (p = 0.168). Leptin concentrations at 60 min post supplementation were higher when subjects received hydrolysed collagen (p = 0.006). Acute supplementation with hydrolysed collagen increased leptin levels in comparison with WP but had no effect on appetite measured by feelings of hunger, desire to eat, full stomach feeling (VAS) or energy consumption.

Validation of two human point-of-care glucometers for glucose concentration determination in rats

Glucose disorders associated with critical illness are common in veterinary medicine and availability of efficient, easy and affordable diagnostic process is vital in combating the menace. Point-of-care glucometers readily come to mind in achieving this goal considering their importance in research and critical case management in veterinary clinics as they are cheap, user friendly, can use small sample quantity and quick generation of results. However, there have been concerns about generation of erroneous results in certain species. This study compared the accuracy and agreement of two point-of-care glucometers for blood glucose determination in rats. Blood samples were obtained from 20 healthy Sprague-Dawley albino rats. Blood (2 ml) was collected through the retro-bulbar plexus and two glucometers were used to determine the blood glucose concentrations immediately. Thereafter, 1 ml was put into a clean test tube treated with ethylene diamine tetracetic acid and the remaining 1 ml was also put into another test tube without anticoagulant. The samples were processed appropriately to harvest the plasma and serum. Blood glucose test kit was used to measure glucose concentrations in plasma and serum by the glucose oxidase method. Data generated were analysed using one way analysis of variance. Results showed that the mean value generated by one glucometer was relatively comparable with the values generated by the laboratory methods while the other significantly overestimated the glucose concentration. This underscores the importance of validation of glucometers before use in any species as unvalidated glucometers can lead to erroneous research conclusions and clinical decisions with dire consequences

Surface-modified Colloid CdTe/CdS Quantum Dots by a Biocompatible Thiazolidine Derivative as Promising Platform for Immobilization of Glucose Oxidase: Application to Fluorescence Sensing of Glucose

This work focuses on the synthesis of novel modified core-shell CdTe/CdS quantum dots (QDs) and develops as a fluorescence sensor for glucose determination. The (E)-2,2'-(4,4'-dioxo-2,2'-dithioxo-2H,2'H-[5,5'-bithiazolylidene]-3,3'(4H,4'H)-diyl)bis(3- mercaptopropanoic acid) (DTM) as a new derivative of thiazolidine was synthesized and characterized and used to surface-modification of CdTe/CdS QDs. DTM-capped CdTe/CdS QDs used to immobilization of glucose oxidase (GOD). The intensity fluorescence emission of the CdSe/CdS-DTM/GOD is highly sensitive to the concentration of H2O2 as a byproduct of the catalytic oxidation of glucose. The experimental results showed that the quenched fluorescence was proportional to the glucose concentration within the range of 10 nM − 0.32 µM under optimized experimental conditions. The limit of detection of this system was found to be 4.3 nM. Compared with most of the existing methods, this newly developed system possesses many advantages, including simplicity, low cost, and good sensitivity.

Glucose Biosensor Based on Dendritic Gold Nanostructures Electrodeposited on Graphite Electrode by Different Electrochemical Methods

In this research, we have demonstrated a one-step electrochemical deposition of dendritic gold nanostructures (DGNs) on a graphite rod (GR) electrode without any template, seeds, surfactants, or stabilizers. Three electrochemical methods, namely, constant potential amperometry (CPA), pulse amperometry, and differential pulse voltammetry, were used for DGN synthesis on GR electrode and further application in enzymatic glucose biosensors. Formed gold nanostructures, including DGNs, were characterized by a field emission scanning electron microscopy. The optimal concentration of HAuCl4 (6.0 mmol L−1), duration of DGNs synthesis (400 s), electrodeposition potential (−0.4 V), and the best electrochemical method (CPA) were determined experimentally. Then the enzyme, glucose oxidase, was adsorbed on the surface of DGNs and covalently cross-linked with glutaraldehyde vapor. The enzymatic glucose biosensor based on DGNs electrodeposited at optimal conditions and modified with glucose oxidase showed a quick response (less than 3 s), a high saturation current (291 μA), appropriate linear range (up to 9.97 mmol L−1 of glucose, R2 = 0.9994), good repeatability (RSD 2.4, 2.2 and 1.5% for 2, 30, 97 mmol L−1 of glucose), low limit of detection (0.059 mmol L−1, S/N = 3) and good stability. Additionally, this biosensor could be successfully applied for glucose determination in real samples with good accuracy. These results proved the principle of enzymatic glucose biosensor development based on DGNs as the basis for further investigations.