Periodic Reporting for period 1 - TWODPS (TWO-Dimensional nanomaterial-based metasurfaces for enhanced Plasmonic Sensing) Reporting period: 2018-06-15 to 2020-06-14 Summary of the context and overall objectives of the project The convergence of nanotechnology, biology, and photonics opens the possibility of detecting and manipulating atoms and molecules that promises to revolutionize diagnostics and therapy at the cellular and even molecular level. As a result, a large variety of biosensors, which incorporate biological probes coupled to a transducer, have been developed during the last two decades for environmental, industrial, and biomedical diagnostics. Biosensors are usually based on systems that can detect electronic or optical signals in terms of the concentrations of biological molecules, where molecular interactions can be monitoring by the signal change. Useful applications include DNA analysis, glucose concentration test in human blood, and sensing of toxins in the water, food, and atmosphere. Current challenges for biosensors, especially for handheld devices that can be deployed at the point of care, are to improve their detection sensitivity, and reduce their size and operating cost. The rapid development of the fabrication techniques for different types of nanomaterials has allowed many breakthroughs on the optical and electronics properties, e.g. high charge carrier mobility, negative refraction, hyperbolic dispersion. Typical examples are the discovery of monolayer graphene and metamaterial/metasurfaces, which showed to us how the properties and performances for optoelectronic sensing and imaging devices can be improved by engineering the materials at the nanoscale and even atomic scale. They are promising materials for the plasmonic field as the sensing substrate to realize the zero-reflection for the phase singularity. The objective of this project is to design and fabricate ultrasensitive plasmonic biosensors with the integration of atomically thin perovskite nanomaterials on metasurfaces, reaching a detection limit up to 10^-10 refractive index unit (RIU) for the target sample solutions. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far In this project, the Fellow has collaborated with Dr. Sylvain Vedraine, Prof. Bernard Ratier (Plasmonic solar cell group, Xlim) and Prof. N. Yu (Columbia University, USA) and firstly designed a highly sensitive plasmonic metasensors based on atomically thin perovskite/graphene nanomaterials for the target sample solutions. The top layer graphene could insulate the 2D perovskite from oxygen and contaminations, and will also enhance the adsorption efficiency of the targeted biological molecules through pi-stacking forces. Through both numerical and analytical modeling, the Fellow has improved the phase singularity detection with the Goos–Hänchen (GH) effect. The GH shift is known to be closely related to the optical phase signal changes. And it is much more sensitive and sharp than the phase signal at the plasmonic condition while the experimental measurement setup is much more compact than that of the commonly used interferometer scheme to exact the phase signals. The atomically thin perovskite nanomaterials with high absorption rate enable the precise tuning of the depth of the plasmonic resonance dip. As such, one can optimize the structure to reach near zero-reflection at the resonance angle and the associated sharp phase singularity, which leads to a strongly enhanced GH lateral shift at the sensor interface. By integrating the 2D perovskite nanolayer into a metasurface structure, a strong localized electric field enhancement can be realized and the GH sensitivity was further improved. This result has been published in Nanomaterials-Basel. For the experimental demonstration of the tunibility of atomically thin 2D materials, the Fellow has collaborated with her colleague Dr. Aurelian Crunteanu (Leader of Microelectronics group, XLIM) and Prof. H.P. Ho (CUHK, Hong Kong). We fabricated an optimized multi-layered metallic sensing substrate based on 2D Ge2Sb2Te5 (GST) phase change nanomaterials (2 nm) and gold thin film (40 nm). Both the experimental and theoretical results show that the sensitivity in Goos-Hänchen (GH) shift has been greatly enhanced compared to pure gold substrate by more than one order of magnitude. Small biotin molecules with low concentrations ranging from 10 fM to 10 μM have been successfully detected. These results led to 2 CLEO-US conference papers and 3 journal articles have been published. In addition to the research work, during the project, the Fellow has also given oral presentations at International Conference (NanoP2018), Rome, 1-3 Oct, 2018 and MRS Fall, Boston (Nov 25-30, 2018) and have learned/exchanged plasmonic ideas with some of the distinguished professors and their group members, including Prof. Laura Na Liu (Max Planck Institute for Intelligent Systems), Stefan Maier (Universität München) and Javier Garcia De Abajo (ICFO, Spain). The Fellow has been invited to give a talk at 8th FOAN International Conference on Optics, Sarajevo Sep. 2019 and at SPIE-Photonics West, San Francisco, USA. Jan. 2019. She also has been interviewed through invitation and featured by: Nanowerk News. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) Plasmonic sensors or surface plasmon resonance (SPR) sensors are some of the most commonly-used optical sensing devices for real-time monitoring of chemical and biomolecular interactions. SPR sensors have been commercialized for more two decades, and they represent the current 'gold standard' for label-free biosensing. These sensors have been applied in various areas including food quality control, environmental monitoring, drug screening, and early-stage disease diagnosis. However, SPR-based sensing is not sufficiently sensitive for the most demanding tasks: 1) Sensing small target analytes with a molecular weight less than 400 Dalton especially for cancer biomarkers, antibiotics, thyroid hormones, peptides, steroids, and bacterial pathogens in infectious diseases; and 2) detecting biological and chemical molecules with low concentration levels (i.e. < 10-15 mol/L) in complex matrices such as urine, saliva, and blood serum.The use of optical phase singularity could be a powerful solution to address these two challenges. Plasmonic resonances typically take the form of broadened Lorentz curves due to optical losses of metallic substrates or nanoparticles. Plasmonic detection based on phase singularity is not dependent upon angular scanning and not affected by the broad resonance curves.Based on these results, one can optimize the structure to reach near zero-reflection at the resonance angle and the associated sharp phase singularity, which leads to a strongly enhanced position lateral shift at the sensor interface. The enhanced electric field together with the significantly improved GH shift will enable single molecular or even submolecular detection for hard-to-identify chemical and biological markers, including single nucleotide mismatch in the DNA sequence, toxic heavy metal ions, and tumor necrosis factor-α (TNFα). The development of plasmonic sensors that can achieve multiplexed detection for different cancer biomarkers on a single chip will benefit the real life applications for the healthcare. Also, this study will provide a significant impact on the nonlinear optical response with the 2D hybrid plasmonic metasurfaces to obtain a more significant sensing signal.