Title : High sensitive biosensor based on topological darkness in hybrid thin filmgraphene nanostructure
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 ~50nm metallic films and the possibility to functionalize the surface of the metal in order to achieve selectivity. However, sensitivity of the most advanced plasmonic biosensors has fundamental limitation caused by losses in metals and/or geometry of biochips. Here, we introduce a new paradigm in optical biosensing associated with the phenomenon of topological darkness. Main feature of the nanostructures possessed topological darkness (TD) is the absence of reflection/transmission provided by spectral properties of optical constants of constituted materials and the positioning of the zero reflection/transmission surfaces. Importantly, the generation of TD in hybrid thin film-graphene nanostructures can lead to extreme singularities of phase of light, which can be used in phase interrogation schemes to improve the sensitivity of plasmonic label-free biosensors by several orders of magnitude. We create and utilise the TD using two different methods: (i) fabricate grapheneprotected copper nanostructures with strong surface plasmon resonance (SPR) and a jump of phase for reflection of p-polarized light under Kretschmann prism geometry and its strong response to variations of refractive index of the environment compared to amplitude parameters; (ii) the TD for both s- and p-polarizations of incident light can be realised in flat layered nanostructures with thinnest active metallic and graphene layers beyond the plasmonic metamaterials based on interference principle for enhancing of optical sensitivity and immobilization efficiency of label-free biosensors. In suggested biosensor the graphene works as a biomolecular recognition element for enhancing the surface adhesion and consequently improving the sensitivity of TD in hybrid thin filmgraphene nanostructures and plays a dual role. First, graphene protects thin metal film from oxidation during biosensing which often requires liquid environment accelerating corrosion. Second, graphene is used as a bio-functionalized surface that also provides selectivity of biosensing. In our studies it was shown that graphene-protected copper SPR exhibits great advantages on biosensing if use the phase which is more sensitive to the presence of DNA-like analytes at the sensor surface achieves the detection limit to 2.4pM (pico-mole). Such sensor sensitivity is compatible with the ones checked through current popular diagnoses. We have demonstrated a realtime, label-free, highly sensitive and relative cost-effective graphene-enhanced SPR sensor for malarial plasmodium parasite (malaria disease). The phase sensitivity of our graphene-enhanced SPR sensor exceeded by about two orders of magnitude of analogous optical biosensors and provides the detection limit of malaria hybridization probes at the level of 12 pM (100 pg/ ml). We have realised the Reichert Company protocol, which works fine for Au chips, and we found that amplitude (spectral) and phase sensitivities of our chips (Cu(Ag)@Graphene are 8 and 12 times, respectively,better than the conventional ones. Using graphene-protected copper SPR biosensors allows sheddinglight on the detection of important molecules in many different applications, such as human health,food and environmental safety.
