Water absorption of mid-infrared (MIR) radiation severely limits the options for vibrational spectroscopy of the analytes–including live biological cells–that must be probed in aqueous environments. While internal reflection elements, such as attenuated total reflection prisms and metasurfaces, partially overcome this limitation, such devices have their own limitations: ATR prisms are difficult to integrate with multiwell cell culture workflows, while metasurfaces suffer from a limited spectral range and small penetration depth into analytes. In this work, we introduce an alternative live cell biosensing platform based on metallic nanogratings fabricated on top of elevated dielectric pillars. For the MIR wavelengths that are significantly longer than the grating period, reflection-based spectroscopy enables broadband sensing of the analytes inside the trenches separating the dielectric pillars. Because the depth of the analyte twice-traversed by the MIR light excludes the highly absorbing thick water layer above the grating, we refer to the technique as inverted transflection spectroscopy (ITS). The analytic power of ITS is established by measuring a wide range of protein concentrations in solution, with the limit of detection in the single-digit mg mL^–1. The ability of ITS to interrogate live cells that naturally wrap themselves around the grating is used to characterize their adhesion kinetic.

中文翻译：

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使用高架纳米柱上的金属光栅对活细胞进行倒转反射光谱分析

中红外 (MIR) 辐射的水吸收严重限制了必须在水环境中探测的分析物（包括活生物细胞）振动光谱的选择。虽然内反射元件（例如衰减全反射棱镜和超表面）部分克服了这一限制，但此类设备也有其自身的局限性：ATR棱镜难以与多孔细胞培养工作流程集成，而超表面的光谱范围有限且穿透深度小转化为分析物。在这项工作中，我们介绍了一种基于在高架电介质柱顶部制造的金属纳米光栅的替代活细胞生物传感平台。对于明显长于光栅周期的中红外波长，基于反射的光谱能够对分隔介电柱的沟槽内的分析物进行宽带传感。由于中红外光两次穿过分析物的深度不包括光栅上方高吸收性的厚水层，因此我们将该技术称为反半透反射光谱 (ITS)。 ITS 的分析能力是通过测量溶液中的各种蛋白质浓度来确定的，检测限为个位数 mg mL ^–1。 ITS 能够询问自然包裹在光栅周围的活细胞，从而表征它们的粘附动力学。