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Nano-OptoMechanical Systems for Biological Sensors

Periodic Reporting for period 1 - NOMBIS (Nano-OptoMechanical Systems for Biological Sensors)

Reporting period: 2016-11-01 to 2018-10-31

Early identification of the pathogens causing an infection is critical to provide the most effective drugs to the patient, as well as to avoid costly and inefficient treatments that can potentially lead to the development of further resistances. Clinical diagnosis demands the development of novel technologies that significantly improve the effectiveness and robustness, while reducing the analysis time. The emergence of antibiotic resistance is one of the major challenges in microbiology and medicine today. Only in the European Union, antibiotic resistance results in 25.000 deaths per year and €1.5 billion in additional healthcare costs and productivity loss.

NOMBIS has allowed the development of a novel technique, the mechanical spectroscopy based on optomechanical resonator sensors, which allows to mechanically characterized and identify individual and alive bacteria with extraordinary precision. The technique developed during NOMBIS project will reduce the hospitalization cost and time. Importantly, it will allow to advance on the development of more efficient medical treatments, entering in a market that will approach 100 billion USD by 2025. Moreover, NOMBIS will reduce the difference in between low-income and high income countries as low income countries suffer significantly more from infectious diseases.
I have designed and fabricated Gallium Arsenide optomechanical microdisk sensors. I have optimized the fabrication proccess in order to improve their mechanical and optical properties. I have tested the capabilities of individual microdisks of different dimensions, as well as different configurations containing multiple microdisks. Thanks to this study, I have optimized their dimensions in order to be applied for bacteria detection.

I will have designed and assembled a homemade optical system in the near infrared range in order to detect the optical and mechanical modes of optomechanical microdisks. The system reaches a displacement sensitivity bellow 10-18 m/√Hz and a bandwidth of 3 GHz. It allows the detection of the thermomechanical vibrations of the microdisks, in air and liquid environment. In addition, it allows their excitation by means of optomechanical forces, which significantly improve the sensitivity of the devices.
The optical setup assembled during the project possesses two main characteristics that place it beyond the state of the art, thanks to the use of two different tunable lasers.

On one hand, as the system uses one laser to excite the mechanical vibration, and another to measure these vibrations, it allows to obtain a significantly more precise measurement of the mechanical frequencies of the system. It is important to note that it is possible to measure several mechanical modes at the same time. The system has demonstrated relative frequency stabilities of 10-6, 5*10-5 and 2*10-5 for the first, second and third radial breathing mode, respectively.

On the other hand, the system is also able to simultaneously monitor several optical modes of the microdisks, apart from the already commented mechanical modes. By measuring both, optical and mechanical modes, the sensor provides simultaneous access to the optical and mechanical properties of the given analyte. This dual sensing approach is fully innovative and unconventional. Importantly, it significantly improves the biosensor reliability and robustness.

To validate the capabilities offered by this novel sensing approach, I have applied it on detection of environmental changes, particularly temperature and humidity. I have demonstrated that the method allows to decoupled humidity and temperature effects with extraordinary precision, becoming excellent sensors for this propose. Moreover, I have also used this approach for the detection and identification of bacteria thus, characterizing both their mechanical and optical properties.

This project has demonstrated the enormous potential of optomechanical resonators as biological sensors, for the first time. I have demonstrated that optomechanical microdisks allows not only to identify individual and alive bacteria but also their different life stages.
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