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)-nickel (II) layered double hydroxide (LDH[Ni-Fe]) 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 μg/mL), wide linear range (0.1-3000 μg/mL) and good linearity (r = 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.