Ultrathin Gold for Robust Multi‐Element Surface Plasmon Resonance Biosensing

Abstract Recently, great progress is achieved in fabricating ultrathin metals that complete 2D family of atomic materials. Here the first application of ultrathin gold in robust multi‐element surface plasmon resonance (SPR) biosensing is reported. Multi‐element SPR delivers several key advantages. It makes use of non‐noble metals that provide enhanced SPR sensitivity. Multi‐element architecture allows one to tune SPR to any desirable wavelength, while ultrathin covering layer gold (graphene) makes possible usage of different functionalization technique. However, multi‐element SPR chips based on 2D materials are not stable in phosphate‐buffered saline (PBS) and survive bio‐functionalization only in small areas. To address this issue, in this work robust stable multi‐element, selective and ultrasensitive SPR chips based on ultrathin gold are fabricated. A usage of 2D materials combined with a biocompatible Ti layer guarantees long time stability of a plasmonic copper film in PBS improving amplitude and phase SPR sensitivity by an order of magnitude. Two types of multi‐element SPR chips are tested: Cu(25.5nm)/Ti(4nm)/Graphene and Cu(25nm)/Ti(3nm)/CuO(0.7nm)/Au(5nm). The stability and sensitivity of the SPR chips are demonstrated by detecting 4‐Carboxybenzenesulfonamide concentration in PBS at the level of 50 pM (10 mL⁻ 1 ) in a reversible bio‐reaction.