A regenerable electrochemical DNA biosensor based on a new type of acrylic microspheres and gold nanoparticles (AuNPs) composite coated onto a screen printed electrode (SPE) has been successfully developed for specific determination of the 35 S promoter from cauliflower mosaic virus (CaMV 35S) gene in soybean. DNA probe was immobilised onto acrylic microspheres via covalent bonding. The presence of modified gene in soybean can be detected via hybridisation of CaMV 35S gene-modified DNA with immobilised DNA probe, which was monitored by differential pulse voltammetry of anthraquinone-2sulfonic acid monohydrate sodium salt (AQMS) as redox indicator during hybridisation event. The peak current signal of AQMS was linearly related to the target CaMV 35S gene concentration over the range of 2 x 10(-15) to 2 x 10(-9) M (R-2 = 0.982) with a very low concentration detect limit (7.79 x 10(-16) M). The recovery test showed satisfactory results of 94.6 +/- 5.1-105.4 +/- 4.9% (n = 5) when the biosensor was used for the determination of genetically modified (GM) DNA sequences extracted from GM soybean samples. The DNA biosensor showed good reproducibility (relative standard deviation (RSD) below 5.0%, n = 5) and regenerability (RSD below 5.0%, n = 7). The biosensor response was stable up to 45 days of storage period at 4 degrees C. The main advantages of this biosensor design are very low detection limit and capability of reusing the biosensor for at least seven times after regeneration with mild sodium hydroxide. (c) 2013 The Authors. Published by Elsevier B. V. All rights reserved.