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A sensitive detection strategy for ascorbic acid (AA), using sodium alginate reduced/stabilized gold nanoparticles (SA-AuNPs) as the optical probe, is reported. The SA-AuNPs were prepared by mixing gold salt and SA under stirring for 2 h at room temperature, without any further steps. The mixture was aged at 4 °C overnight, after which a faint-purple colloidal solution of SA-AuNPs was obtained. Characterization shows that the synthesis is incapable of reducing all Au 3+ to Au°, but rather to mixture of Au°/Au + . The addition of AA to the SA-AuNPs probe reduced completely all Au + to new AuNPs which were deposited on the pre-formed SA-AuNPs seed, leading to size increment and absorption spectra enhancement. The assay exhibited a good linearity between 12.5 and 150.0 μM AA and low limit of quantification of 11.2 μM. It was further used for AA quantitation in vitamin C injection and fruit juice with satisfactory accuracy and precision., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The silver/poly(3-aminophenyl boronic acid)/sodium alginate nanogel (Ag@PABA-SA) was fabricated through green, in situ chemical oxidative polymerization method. 3-Aminophenyl boronic acid (APBA) served as the room temperature reductant of AgNO 3 which acted as an oxidant towards the polymerization of APBA to its conducting polymeric form (PABA). Importantly with SA present, PABA will bind to hydroxyl groups of SA through covalent bonding to generate PABA-SA semi-interpenetrating network, on which AgNPs were concomitantly deposited. This results highly stable, dispersed polymer based AgNPs. The morphology, size, surface charge, composition and thermal stability of nanogel was characterized by UV-vis, Raman and FTIR spectroscopy, TEM, FESEM, EDX, XRD, DLS and zeta potential analysis, TGA and DTG. The Ag@PABA-SA nanogel was investigated as colorimetric probe towards H 2 O 2 detection. Wide linearity from 5 to 1000 μM H 2 O 2 , with low limit of detection of 1.0 μM in addition to satisfactory precision (< 3.5 %) and recovery (95-105 %) and high selectivity was achieved., Competing Interests: Declaration of Competing Interest The authors declare no competing financial interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)