Metasurfaces provide opportunities for wavefront control, flat optics, and subwavelength light focusing. We developed an imaging-based nanophotonic method for detecting mid-infrared molecular fingerprints and implemented it for the chemical identification and compositional analysis of surface-bound analytes. Our technique features a two-dimensional pixelated dielectric metasurface with a range of ultrasharp resonances, each tuned to a discrete frequency; this enables molecular absorption signatures to be read out at multiple spectral points, and the resulting information is then translated into a barcode-like spatial absorption map for imaging. The signatures of biological, polymer, and pesticide molecules can be detected with high sensitivity, covering applications such as biosensing and environmental monitoring. Our chemically specific technique can resolve absorption fingerprints without the need for spectrometry, frequency scanning, or moving mechanical parts, thereby paving the way toward sensitive and versatile miniaturized mid-infrared spectroscopy devices.

Infrared spectroscopy resolves the structure of molecules by detecting their characteristic vibrational fingerprints. Subwavelength light confinement and nanophotonic enhancement have extended the scope of this technique for monolayer studies. However, current approaches still require complex spectroscopic equipment or tunable light sources. Here, we introduce a novel metasurface-based method for detecting molecular absorption fingerprints over a broad spectrum, which combines the device-level simplicity of state-of-the-art angle-scanning refractometric sensors with the chemical specificity of infrared spectroscopy. Specifically, we develop germanium-based high-Q metasurfaces capable of delivering a multitude of spectrally selective and surface-sensitive resonances between 1100 and 1800 cm−1. We use this approach to detect distinct absorption signatures of different interacting analytes including proteins, aptamers, and polylysine. In combination with broadband incoherent illumination and detection, our method correlates the total reflectance signal at each incidence angle with the strength of the molecular absorption, enabling spectrometer-less operation in a compact angle-scanning configuration ideally suited for field-deployable applications.

Low-loss nanostructured dielectric metasurfaces have emerged as a breakthrough platform for ultrathin optics and cutting-edge photonic applications, including beam shaping, focusing, and holography. However, the static nature of their constituent materials has traditionally limited them to fixed functionalities. Tunable all-dielectric infrared Huygens' metasurfaces consisting of multi-layer Ge disk meta-units with strategically incorporated non-volatile phase change material Ge 3 Sb 2 Te 6 are introduced. Switching the phase-change material between its amorphous and crystalline structural state enables nearly full dynamic light phase control with high transmittance in the mid-IR spectrum. The metasurface is realized experimentally, showing postfabrication tuning of the light phase within a range of 81% of the full 2π phase shift. Additionally, the versatility of the tunable Huygen's metasurfaces is demonstrated by optically programming the spatial light phase distribution of the metasurface with single meta-unit precision and retrieving high-resolution phase-encoded images using hyperspectral measurements. The programmable metasurface concept overcomes the static limitations of previous dielectric metasurfaces, paving the way for "universal" metasurfaces and highly efficient, ultracompact active optical elements like tunable lenses, dynamic holograms, and spatial light modulators.

Dielectric metasurfaces have emerged as a powerful platform for novel optical biosensors. Due to their low optical loss and strong light–matter interaction, they demonstrate several exotic optical properties, including sharp resonances, strong near-field enhancements, and the compelling capability to support magnetic modes. They also show advantages such as CMOS-compatible fabrication processes and lower resonance-induced heating compared to their plasmonic counterparts. These unique characteristics are enabling the advancement of cutting-edge sensing techniques for new applications. In this Perspective, we review the recent progress of dielectric metasurface sensors. First, the working mechanisms and properties of dielectric metasurfaces are briefly introduced by highlighting several state-of-the-art examples. Next, we describe the application of dielectric metasurfaces for label-free sensing in three different detection schemes, namely, refractometric sensing, surface-enhanced spectroscopy through Raman scattering and infrared absorption, and chiral sensing. Finally, we provide a perspective for the future directions of this exciting research field.

Molecular spectroscopy provides unique information on the internal structure of biological materials by detecting the characteristic vibrational signatures of their constituent chemical bonds at infrared frequencies. Nanophotonic antennas and metasurfaces have driven this concept towards few‐molecule sensitivity by confining incident light into intense hot spots of the electromagnetic fields, providing strongly enhanced light‐matter interaction. In this Minireview, recently developed molecular biosensing approaches based on the combination of dielectric metasurfaces and imaging detection are highlighted in comparison to traditional plasmonic geometries, and the unique potential of artificial intelligence techniques for nanophotonic sensor design and data analysis is emphasized. Because of their spectrometer‐less operation principle, such imaging‐based approaches hold great promise for miniaturized biosensors in practical point‐of‐care or field‐deployable applications.

Metasurfaces have emerged as a breakthrough platform for manipulating light at the nanoscale and enabling on‐demand optical functionalities for next‐generation biosensing, imaging, and light‐generating photonic devices. However, translating this technology to practical applications requires low‐cost and high‐throughput fabrication methods. Due to the limited choice of materials with suitable optical properties, it is particularly challenging to produce metasurfaces for the technologically relevant mid‐infrared spectral range. These constraints are overcome by realizing functional metasurfaces on almost completely transparent free‐standing metal‐oxide membranes. A versatile nanofabrication process is developed and implemented for highly efficient dielectric and plasmonic mid‐infrared metasurfaces with wafer‐scale and complementary metal–oxide–semiconductor (CMOS)‐compatible manufacturing techniques. The advantages of this method are revealed by demonstrating highly uniform and functional metasurfaces, including high‐Q structures enabling fine spectral selectivity, large‐area metalenses with diffraction‐limited focusing capabilities, and birefringent metasurfaces providing polarization control at record‐high conversion efficiencies.  Aluminum plasmonic devices and their integration into microfluidics for real‐time and label‐free mid‐infrared biosensing of proteins and lipid vesicles are further demonstrated. The versatility of this approach and its compatibility with mass‐production processes bring infrared metasurfaces markedly closer to commercial applications, such as thermal imaging, spectroscopy, and biosensing.

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Techniken der molekularen Absorptionsspektroskopie liefern einzigartige Informationen über die innere Zusammensetzung biologischer Materie, indem sie die charakteristischen Infrarot‐Vibrationsbanden der beteiligten Moleküle detektieren. Durch den Einsatz von nanophotonischen Antennen und Metaoberflächen lässt sich einfallendes Licht auf der Nanoskala bündeln, was zu starker Licht‐Materie‐Wechselwirkung führt und es erlaubt, dieses Sensorkonzept bis hin zur Detektion weniger Moleküle auszudehnen. In diesem Kurzaufsatz werden wir neuartige Metaoberflächen‐basierte Ansätze der molekularen Biosensorik vorstellen und mit traditionellen Konzepten vergleichen. Ein besonderes Augenmerk liegt auf der kürzlich eingeführten Kombination von dielektrischen Metaoberflächen mit bildgebender Detektion, sowie auf dem Potential von künstlicher Intelligenz für das Design nanophotonischer Sensoren und die Datenanalyse. Solche Methoden erlauben die Messung molekularer Signaturen ohne Verwendung klassischer IR‐Spektrometer oder durchstimmbarer Laserquellen und stellen somit einen Durchbruch für miniaturisierte Sensoren in der Umweltanalytik und der patientennahen Labordiagnostik dar.