Needle-based sampling coupled with colorimetric reaction catalyzed by layered double hydroxide peroxidase mimic for rapid detection of the change of D-glucose levels with time in bananas

For analyte detection in raw fruits, the conventional sample pretreatment method usually involves mashing (blending or homogenization), extraction, and dilution. This process is time-consuming, solvent-intensive and laborious. Usually, there is also a lot wastage with multiple fruits being combined into composite samples. In this work, a new micro-sampling approach based on a syringe needle is developed; it was coupled with micro liquid-phase extraction to determine and quantify D-glucose in bananas. This sampling and extraction approach was quick, easy and required only minimal use of solvent. The D-glucose in the extracted banana flesh was first oxidized enzymatically with glucose oxidase. The resulting peroxide was then detected colorimetrically via oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of a catalyst. The latter, consisting of an iron (III) enickel (II) layered double hydroxide (LDH[Ni-II-Fe-III]) was synthesized in this work for the purpose. The results of this new detection method for D-glucose in fruits provided low limits of detection (0.025 mu g/mL), wide linear range (0.1-3000 mu g/mL) and good linearity (r(2) = 0.9998). Quantification of D-glucose using this approach was applied to banana samples over a period of 10 days. The results showed that the D-glucose levels in bananas increased as the fruits ripened, as expected. This work demonstrated a new and interesting approach for easy and efficient detection of analytes in raw fruit samples. (c) 2017 Elsevier B.V. All rights reserved.