Comparison of different noble metal-based screen-printed sensors for detection of PIK3CA point-mutations as biomarker for circulating tumor DNA

Screen-printed electrochemical sensors are of particular interest for point-of-care diagnostic applications due to their high sensitivity, short analysis times, and cost-efficient large-scale fabrication. Especially noble metal-based sensors offer the possibility of easy surface modification via self-assembly of thiol-labelled compounds. We examined silver, gold, and palladium as electrode materials regarding their suitability for highly specific and sensitive DNA detection with a chronoamperometric enzyme-amplified electrochemical assay. Modification with either gold nanoparticles or silver-coated microbeads was tested as a possibility to improve the performance of the electrochemical sensors. The sensors were characterized regarding surface topography, sensitivity towards the redox-active substrate TMB, efficiency of capture probe immobilization, as well as mutation specificity. The highest sensitivity for oxidized TMB was observed for gold sensors that yielded a limit of detection of 2.1 mu M, while no improvement in sensitivity was observed for sensors modified with gold nanoparticles or silver-coated microbeads. DNA probe immobilization and multiplexed target DNA detection was successful with all tested electrode materials. However, modification with silver-coated microbeads led to both reduced probe immobi-lization efficiency and hybridization specificity. Gold nanoparticle modification of both silver and of gold sensors induced a highly porous sensor surface after sintering, which increases the surface area of the electrodes. The gold nanoparticle modified sensors showed particularly appreciable results in terms of improved hybridization specificity, as demonstrated by successful multiplexed detection of three PIK3CA point-mutations (H1047R, E545K, and E542K). Average discrimination factors D of 2.7 and 2.1 were obtained for gold and silver sensors modified with one layer of gold nanoparticles, respectively.