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The combination of a photonic crystal with graphene offers a window of opportunity to develop a highly sensitive sensor that at the same time enhances the simplicity and cost-effectiveness of the sensing device. Recently Iterio Degli-Eredi successfully presented his PhD research results on this new generation of biosensors and obtained the title of Doctor in Engineering.
Biosensors are monitoring devices that are currently used in a wide range of applications, such as in the measurement of blood glucose levels or in the detection of pollutants in water and gas. In his PhD, Iterio keeps his focus on one type of biosensors, namely, the Bloch Surface Wave (BSW) based refractive-index optical biosensors.
The BSW is an optical mode that propagates in a dielectric one-dimensional photonic crystal (PC) and its propagation is affected by the refractive index of the sample – and the corresponding concentration of the analyte to be sensed – above the PC. While BSW sensors already offer many advantages such as label-free operation, compactness, a high sensitivity and low optical losses, attaining high resolutions while keeping the sensor setup relatively simple and cheap is still a challenge.
His work aims to resolve this issue by combining the PC with graphene – an extra-ordinary 2D carbon material whose optical properties are electrically tuneable – and with specific focus on glucose sensing.
The research starts by experimentally demonstrating the suitability of graphene as an interface for glucose refractive index sensing, and discusses the advantageous light-matter interactions when combining graphene with BSW-based sensors as compared to other structures.
Then a new formalism for the design of PCs in BSW-based biosensors is derived. Iterio shows that his design rules enable us to conveniently design and optimise a multilayer sensor in terms of sensitivity and resolution. The used method represents an important advance compared to the state-of-the-art where sensors are typically designed by means of brute-force numerical optimisations. The calculations presented also allow him to study the properties of BSWs in PCs that are combined with graphene.
With this formalism, Iterio designs a 'voltage interrogated' BSW sensor – a PC covered with 2 graphene sheets separated with a dielectric material – that detects the sample’s refractive index and corresponding glucose concentration by means of applying a voltage over the graphene sheets. He theoretically shows his sensor has the potential to measure glucose concentrations with sufficiently high resolution within the required dynamic range as imposed by the clinical standards for blood glucose measurements.
In his PhD, Iterio thus has contributed to the design of a new type of glucose sensor based on electrically tuneable graphene-enhanced PCs. Considering the simplicity of the device and the relatively low price of the components required in the operation, this new sensor opens a novel practical approach for monitoring blood glucose levels or in the detection of other (bio)molecules.