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With a sensitivity of 800 nm/RIU, this highly sensitive device responds efficiently to changes in refractive index of the medium (which indicates how light or other electromagnetic waves propagate through a material), making it an excellent tool for measuring small concentrations of a wide range of molecules, as well as for use in environmental monitoring or chemical analysis.

 

"The sensor works by measuring the reflection from the active area of the device. The plasmonic resonances (sudden drops in reflectivity) observed in the reflectance spectrum are highly sensitive to the ambient medium and its refractive index. As this changes, the location of the resonant peak in the spectrum also changes," says one of the sensor's developers, FTMC PhD student Kernius Vilkevičius.

 

Below is the reflectance spectrum for s- and p-polarized light incident on the sensor at an angle of 15 degrees in air, water and solutions of different concentrations of glycerol (a thick transparent liquid). From the measured peak shift, it is possible to determine the presence of the molecules to be tested at the surface of the sensor and to calculate their concentrations.

 

 

 

The sensor is called hybrid for several reasons. Firstly, the device is composed of a coating of two metals, silver and gold. Secondly, the active area of the sensor is laser-made by a series of repeating formations (special 'bumps') which exhibit a hybrid plasmonic mode - a kind of surface electromagnetic wave which is further amplified at each periodically arranged formation.

 

"This reduces the propagation loss of the electromagnetic wave and extends its propagation range. The longer propagation distance allows the surface electromagnetic wave to interact with a larger number of molecules on the surface, making hybrid plasmonic mode sensors more sensitive and capable of detecting smaller concentration of molecules with a more stable and accurate response," explains Dr. Evaldas Stankevičius, one of the authors of the sensor.

 

 

The hybrid plasmonic sensor has been tested with different concentrations of glycerol, according to the researcher:

 

"The study confirmed that even with a small change in the refractive index of the fluid (less than one thousandth), a resonance shift is observed.

 

In the future, we plan to test the developed sensor for the detection of specific proteins that are related to the diagnosis of cancer or other diseases. In addition, we will aim to improve the sensitivity and stability of the developed sensor by using different coating compositions and optimising the arrangement of the derivatives."