Xanthan/chitosan gold chip for metal enhanced protein biomarker detection

Protein microarrays for disease diagnostics are required to accurately quantify analytes in the low pg/mL range. This task is hampered by weak signal strengths and too low detector sensitivity. Herein we present reflective gold chips coated with polyelectrolyte multilayers (PEMs) for signal enhancement in immunoassays for melanoma-relevant biomarkers. Among tested (semi)natural polysaccharides (xanthan, chitosan, carboxymethylcellulose, hyaluronic acid) PEMs composed of xanthan and chitosan performed best in terms of detection of low analyte concentrations (ED10), spot morphology, fluorescence background and variability (<10%). Fluorescence signals on gold slides with a 75 nm coating of seven crosslinked polyelectrolyte double layers were up to 50 times higher than on bare glass slides. In comparison to commercial substrates the signal to noise ratio is enhanced by up to factor 11. Furthermore sandwich assays for interleukins 6, 8, 10, tumour necrosis factor alpha (TNFα), vascular endothelial growth factor A (VEGF-A) and S100B show working ranges which cover significantly lower concentrations (up to 38-fold). Not limited to above assays the presented substrates, which combine a biocompatible interface with metal-based signal amplification, are a valuable tool in a variety of biosensor applications.