(179f) Biosensors Using Metamaterial-Inspired Ring Resonators

In the recent times, metamaterial based resonators have been actively pursued for variety of applications such as super-lenses, filters, and invisibility cloaks ^1-3. Sensors are one more application area, in which significant studies have been done, using metamaterials, in very recent times. Arrays of split-ring resonators (SRRs) and complementary split-ring resonators (CSRRs) have been used in their dimensions comparable to the wavelength of radiation incident on them, and the negative refractive index materials have been realised using either the electrical or magnetic, or electro-magnetic metamaterials. These structures have their dimensions extremely small (much lesser than l/2), thereby having significance as miniaturized devices.

Our group has put in efforts to use these structures, as unit-cell components, and has applied them for their use in gas sensing, hazardous molecule (explosives and propellants) detection and adulterated fuel detection ^4-6. Explicit dielectric constants and the permittivity values of the sensing moiety, well defined resonance frequency of the sensor and high selectivity imparted by further functionalisation strategy becomes the main driving thrust for such ultrafast, selective, recoverable and highly sensitive sensor ⁷.

Through this presentation, metamaterial-inspired SRR structures are projected to sense various bio-entities such as bacteria (gram positive and gram negative), viruses (Dengue infections), Nitric oxide (NO) (for harmful immunological responses and carcinogenesis) and hydrogen sulphide sensing. Depending upon the type of detection, the CSRR structure was duly functionalised with either a nanomaterial or an antibody to achieve better selectivity.

The CSRR sensor is etched on the ground plane of a micro-strip line using printed circuit board technology. The resonant frequency was tuned to 434 MHz using appropriate unit cell dimensions, which was also confirmed, initially, using COMSOL simulation software. For Dengue virus detection, an NS1 antibody layer (via a linker molecule such as EDC) was deposited on the top of SRR structure, for H₂S detection, gold nanoparticles were functionalised over this structure and for bacteria (gram-positive or gram-negative), poly L-Lysine was coated over the resonator structure. The moiety to-be-tested was subjected to the appropriate sensor bed, in the known quantities. Vector network analyser was used to send (and detect) the radio frequencies through the micro-strip line of the sensor. The sensing mechanism is based on perturbance of electromagnetic field around the resonator which leads to a shift in the resonance frequency (or power) of the signal, and this shift depends on the dielectric constant of the material under test. Extremely fast, recoverable, selective biosensor is hence demonstrated.

This sensor is further converted into a compact portable device for on-site detection by integrating the sensor with an appropriate radio-frequency source and detector of ~ 434 MHz. The results are interpreted in terms of the interaction of the electromagnetic radiations with the changing characteristics of the sensor environment, typically with the antigen-antibody interactions or selective interactions of the nanoparticles.

¹ J.B. Pendry, A.J. Holden, D.J. Robbins, and W.J. Stewart, 47, 2075 (1999).

² T.J. Yen, W.J. Padilla, N. Fang, D.C. Vier, D.R. Smith, J.B. Pendry, D.N. Basov, and X. Zhang, Science (80-. ). 303, 1494 (2004).

³ J. García-García, F. Martín, F. Falcone, J. Bonache, J.D. Baena, I. Gil, E. Amat, T. Lopetegi, M.A.G. Laso, J.A.M. Iturmendi, M. Sorolla, and R. Marqués, IEEE Trans. Microw. Theory Tech. 53, 1997 (2005).

⁴ V. Rawat, S. Dhobale, and S.N. Kale, J. Appl. Phys. 116, 1 (2014).

⁵ V. Rawat, R. Kitture, D. Kumari, H. Rajesh, S. Banerjee, and S.N. Kale, J. Magn. Magn. Mater. 415, 77 (2016).

⁶ V. Rawat, V. Nadkarni, and S.N. Kale, Appl. Phys. A Mater. Sci. Process. 123, 2 (2017).

⁷ Sohini Roy Choudhury, Vaishali Rawat, A.H. Jalal, S.N. Kale, Shekhar Bhansali, Biosensors and Bioelectronics, 86, 595 (2016)