Search

Hybrid instruments combining Optical Tweezers (OT) with Raman spectroscopy (Raman Tweezers, RT) are becoming increasingly popular, as they enable measurements of size and composition of micro and nanoparticles in a contact-less fashion. RTs are gaining attention as a unique analytical tool for environmental sciences and food analysis, capable to detect and chemically identify micro- and nano-plastics (MNPs). Here we show optical trapping and chemical identification of sub-20 μm plastics, down to the 50 nm range by RT [1]. Analysis at the single particle level allows us to unambiguously discriminate plastics from organic matter and mineral sediments, overcoming the capacities of standard Raman spectroscopy in liquid, intrinsically limited to ensemble measurements. Applications are demonstrated on both model particles and naturally aged environmental samples, made of common plastic pollutants, including polyethylene, polypropylene, nylon, and polystyrene, also in the presence of a thin eco-corona. Finally the analysis is extended to samples of tire and road wear particles collected from a brake test platform, where we highlight the presence of sub-micrometric agglomerates of rubber and brake debris, thanks to the presence of additional spectral features other than carbon [2]. Either used to trap & analyse single particles or coupled to field-flow fractionation techniques, RT have the potential to fill the technological gap in MNP detection. In the next years research & development will be oriented towards the exploration of the full potential and limits of RT in terms of sensitivity, size limitations, multispectral analysis and chemical information that can be extracted from contaminated MNPs and in complex environments. [3] [1] Gillibert et al. Environ. Sci. Technol. 2019, 53, 15, 9003 [2] Gillibert et al. Environ. Sci.: Nano, 2022, 9, 145 [3] Volpe et al. Roadmap for Optical Tweezers, arXiv preprint arXiv:2206.13789 (2022) Also see: https://micro2022.sciencesconf.org/425821/document, In MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nano

Background: The terahertz spectroscopy has attracted enormous attention for label free chemical and biological sensing, due to the presence of molecular fingerprints and remote sensing capabilities. However, because of the strong absorption of THz waves in aqueous solutions, detecting liquid-phase biological samples by THz spectroscopy has encountered strong constraints. Results: Here, we demonstrate for the first time a rapid and label-free sensing for liquid-phase biological samples using THz spectroscopy based on microfluidic metasensors. The metasensors were integrated with microfluidic chip to precisely control the liquid sample thickness within 220 nanometer (MMS-N) and 50 micrometer (MMS-U). The metasensors include a periodic split ring resonator (SRR) with two resonant peaks in the THz range. The sensitivity(S) and corresponding figure of merit (FOM) of the two resonance peaks of MMS-N and MMS-U are analyzed with respect to different refractive index matching solution. Both the two resonance peaks of the metasensors are sensitive to the varies refractive index environment and high-frequency resonant of MMS-N shows the best sensitivity(~136GHz/RIU). In addition, the label-free biological sensing capability was conducted through qualitative and quantitative LDL and ox-LDL, where a shift of resonance frequency was observed as the LDL and ox-LDL concentration increased. Conclusions: The results indicated nanofluidic metasensor presented excellent sensing capability for liquid-phase molecular analysis by THz spectroscopy, and the proposed sensing system has the potentials to be developed as a rapid, label-free and highly sensitive detection tool for molecular analysis by THz sensing.