Glucose: Detection and analysis

Colorimetric detection of glucose based on gold nanoparticles coupled with silver nanoparticles

We have coupled gold nanoparticles (AuNPs) with silver nanoparticles (AgNPs) to assemble a plasmonic sensing platform for colorimetric detection of glucose. In this system, small AuNPs (~4nm) can act as glucose oxidase (GOD) mimic enzyme to catalytically oxidize glucose in the presence of oxygen, producing hydrogen peroxide, which dissolves AgNPs to lead the color changes. Glucose can be detected not only by naked eyes (from yellow to red) but also by spectrophotometer in the concentration range of 5-70μM, with detection limit of 3μM. More importantly, we found that l-cysteine added in the system can markedly improve the selectivity for the detection of glucose. The proposed method was used to application for the detection of glucose in human serum with satisfactory results. This system is simple and low cost without using any enzymes and organic chromogenic agents.

A bioinspired ionic liquid tagged cobalt-salophen complex for nonenzymatic detection of glucose

The development of efficient and cost effective nonenzymatic biosensors with remarkable sensitivity, selectivity and stability for the detection of biomolecules, especially glucose is one of the major challenges in materials- and electrochemistry. Herein, we report the design and preparation of nonenzymatic biosensor based on an ionic liquid tagged cobalt-salophen metal complex (Co-salophen-IL) immobilized on electrochemically reduced graphene oxide (ERGO) for the detection of glucose via an electrochemical oxidation. The bioinspired Co-salophen-IL complex has been synthesized and immobilized on ERGO, which was previously deposited on a screen printed carbon electrode (SPE) to form the Co-salophen-IL/ERGO/SPE nonenzymatic biosensor. The electrochemical behaviour of this modified electrode was studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Notably, the Co-salophen-IL/ERGO/SPE biosensor exhibited excellent electrocatalytic activity towards glucose oxidation in 0.1M NaOH, based on which an amperometric sensor has been developed. The modified electrode has shown prominent performance towards glucose detection over a wide linear range from 0.2µM to 1.8mM with a detection limit and sensitivity of 0.79µM and 62µAmM^-1 respectively. The detection was carried out at 0.40V and such a less working potential excludes the interference from the coexisting oxidizable analytes. The role of Co-salophen, IL and ERGO in the electrocatalytic activity has been systematically investigated. Furthermore, the biosensor demonstrated high stability with good reproducibility.

Feasibility of Fraction Collection in HPLC Systems with Evaporative Light Scattering Detector: Analysis of Pectinatella magnifica

The use of a liquid chromatography (LC) splitter inserted between an HPLC column and an evaporative light scattering detector (ELSD) is described. This paper aims to show the feasibility of using the splitter in an HPLC-ELSD system to fractionate a model mixture of analytes, namely salicin (2-(hydroxymethyl)-phenyl-β-d-glucopyranoside) and glucose. The retention factors and efficiency of the separation were studied under various temperatures and water contents in the mobile phase in order to clarify the mechanism of polyols separation on a diol column under the conditions of hydrophilic liquid chromatography (HILIC). Finally, the system was applied to a biological sample (a lyophilized colony gel of Pectinatella magnifica), where the presence of fructose and glucose was confirmed.

Effect of Debagging Time on Pigment Patterns in the Peel and Sugar and Organic Acid Contents in the Pulp of ‘Golden Delicious’ and ‘Qinguan’ Apple Fruit at Mid and Late Stages of Development

This study examined the effect of debagging time on color and flavor / taste compounds in the non-red apple cultivar ‘Golden Delicious’ and red cultivar ‘Qinguan’ at mid and late stages of fruit development. Debagging briefly improved the red color in both cultivars, the peel of ‘Golden Delicious’ presenting pale-pink hue. However, rapid anthocyanin accumulation occurred in apple peel at a specific time (after 179 days after flowering (DAF) in ‘Qinguan’) and was unaltered by debagging time in the red cultivar ‘Qinguan’. Furthermore, untimely debagging had a detrimental effect on the content of anthocyanin. All sugars increased and organic acids decreased in apple pulp at mid to late stages of development. Bagging treatment reduced the content of most sugars and organic acids, as well as, the overall total. However, glucose and citric acid contents were higher in bagged fruit than non-bagged fruit; the maximum occurred in T7 treatment that was no-debagging at DAF 159 / 196 (‘Golden delicious’ / ‘Qinguan’), i.e., 24.35 and 0.07 mg g^-1 FW in ‘Golden delicious’, and 38.86 and 0.06 mg g^-1 FW in ‘Qinguan’, respectively. In a word, bagging treatment can alter the pattern of peel color development in apple fruit; however, it remains difficult to alter the timing of rapid anthocyanin accumulation as it is regulated solely by development. Moreover, bagging treatment reduced the total accumulation of sugars and organic acids, and even the over total in pulp, but increased the glucose and citric acid contents in apple pulp.

An electrochemical biosensor for rapid detection of E. coli O157:H7 with highly efficient bi-functional glucose oxidase-polydopamine nanocomposites and Prussian blue modified screen-printed interdigitated electrodes

The presence of pathogenic bacteria in foods has always been a great threat to the wellbeing of people and the revenue of food manufacturers. Therefore, the demand for advanced detection methods that can sensitively and rapidly detect these pathogens has been of great importance. This study reports an electrochemical biosensor for rapid detection of E. coli O157:H7 with the integration of bifunctional glucose oxidase (GOx)-polydopamine (PDA) based polymeric nanocomposites (PMNCs) and Prussian blue (PB) modified screen-printed interdigitated microelectrodes (SP-IDMEs). The core-shell magnetic beads (MBs)-GOx@PDA PMNCs were first synthesized by the self-polymerization of dopamine (DA). Gold nanoparticles (AuNPs) were dispersed on the surface of PMNCs through biochemical synthesis to achieve further highly efficient adsorption of antibodies (ABs) and GOx. The final product ABs/GOxext/AuNPs/MBs-GOx@PDA PMNCs served as the carrier to separate target bacteria from food matrices as well as the amplifier for electrochemical measurement. The unbound PMNCs were separated by a filtration step and transferred into glucose solution to allow the enzymatic reaction to occur. The change of the current response was measured with an electrochemical detector using PB-modified SP-IDMEs. The constructed biosensor has been proven to be able to detect E. coli O157:H7 with the detection limit of 10(2) cfu ml(-1). The bifunctional PMNCs contain a high load of enzyme and can optimally utilize the binding sites on bacterial cells, which efficiently amplify the signals for measurement. The biosensor in this study exhibited good specificity, reproducibility, and stability and is expected to have a great impact on applications in the detection of foodborne pathogens.

Optical and surface band bending mediated fluorescence sensing properties of MoS2 quantum dots

Band bending assisted fluorescence sensing of glucose and bovine serum albumin using MoS₂ quantum dots.