Abstract
Plasmonic biosensing has emerged as the most sensitive label-free technique to detect various molecular species in solutions and has already proved crucial in drug discovery, food safety and studies of bio-reactions. This technique relies on surface plasmon resonances in ~50 nm metallic films and the possibility to functionalize the surface of the metal in order to achieve selectivity. At the same time, most metals corrode in bio-solutions, which reduces the quality factor and darkness of plasmonic resonances and thus the sensitivity. Furthermore, functionalization itself might have a detrimental effect on the quality of the surface, also reducing sensitivity. Here we demonstrate that the use of graphene and other layered materials for passivation and functionalization broadens the range of metals which can be used for plasmonic biosensing and increases the sensitivity by 3-4 orders of magnitude, as it guarantees stability of a metal in liquid and preserves the plasmonic resonances under biofunctionalization. We use this approach to detect low molecular weight HT-2 toxins (crucial for food safety), achieving phase sensitivity~0.5 fg/mL, three orders of magnitude higher than previously reported. This proves that layered materials provide a new platform for surface plasmon resonance biosensing, paving the way for compact biosensors for point of care testing.
Highlights
The unique properties of graphene and related layered materials (GRMs) are promising for applications in many areas[1,2,3]
layered material (LM) protected surface plasmon resonance (SPR) biosensors could solve this problem by providing unprecedented phase sensitivity to binding events[17,18]
Graphene protected metal thin films (Cu is taken as an example, more combinations of layered LMs oxides and metals are described in Supplementary Materials) in which high (
Summary
The unique properties of graphene and related layered materials (GRMs) are promising for applications in many areas[1,2,3]. By bringing the functional sensing groups very close to the sensing metal surface, GRM monolayers offer very good protection against corrosion[11], removing the need to functionalize the metal surface (which might damage the plasmonic properties of the metal) by being themselves bio-functionalized This broadens the possible avenues for bio-functionalization and opens new opportunities for SPR biosensing, which, at present, lacks the sensitivity required to detect small (~1 fg/mL) concentrations of drugs, vitamins, antigens and viruses, as these can be deadly or pathogenic even in this ultra-low quantities. We fabricate ultrasensitive SPR sensor functionalized with an anti-HT-2 toxin Fab fragment (HT2-10) and detected HT-2 toxin (~424 Da) with an amplitude detection limit ~1 pg/mL, 3 orders of magnitude better than currently available methods[12,13] and a phase sensitivity limit ~0.5 fg/mL, which is comparable with label techniques This paves the way to LM-based label-free SPR biosensing of small bio-objects at ultra-low concentrations. LM functionalization (in contrast to conventional Au functionalization) provides new avenues in achieving selectivity of bio-detection
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