Infrared (IR) Spectroscopy has been developed for centuries and has been widely used to identify molecular structure from the massive information provided by IR fingerprint absorption, reflecting the vibration energy of the chemical bond. Due to the intrinsically weak light-matter interaction, IR spectroscopy serves low sensitivity and sizeable optical interaction length (~mm to ~cm) compared with other optical probes like Raman, florescent, and refractometry technology, which hinder the applications for ultra-sensitive biomolecular screening. Here, we report a new type of IR spectroscopy by wavelength gradient hook nanoantenna integrated with the microfluidic channel, enhancing the IR molecular absorption and bringing in refractometry function with ultrathin (~100 nm) optical interaction length. With the proof-of-concept demonstration of molecular recognition of mixed alcoholic liquids by machine learning and molecular fingerprint retrieving by hyperspectral images in one-time data acquisition, our work paves the way to advance, small-volume, real-time, ultra-sensitive, in-vitro biomolecular dynamic analysis in the aqueous environment.