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Abstract The performance of surface‐enhanced Raman spectroscopy (SERS) is determined by the interaction between highly diluted analytes and boosted localized electromagnetic fields in nanovolumes. Although superhydrophobic surfaces are developed for analyte enrichment, i.e., to concentrate and transfer analytes toward a specific position, it is still challenging to realize reproducible, uniform, and sensitive superhydrophobic SERS substrates over large scales, representing a major barrier for practical sensing applications. To overcome this challenge, a superhydrophobic SERS chip that combines 3D‐assembled gold nanoparticles on nanoporous substrates is proposed, for a strong localized field, with superhydrophobic surface treatment for analyte enrichment. Intriguingly, by concentrating droplets in the volume of 40 µL, the sensitivity of 1 nmis demonstrated using 1,2‐bis(4‐pyridyl)‐ethylene molecules. In addition, this unique chip demonstrates a relative standard deviation (RSD) of 2.2% in chip‐to‐chip reproducibility for detection of fentanyl at 1 µg mL^–1concentration, revealing its potential for quantitative sensing of chemicals and drugs. Furthermore, the trace analysis of fentanyl and fentanyl‐heroin mixture in human saliva is realized after a simple pretreatment process. This superhydrophobic chip paves the way toward on‐site and real‐time drug sensing to tackle many societal issues like drug abuse and the opioid crisis. 

Abstract Reliability, shelf time, and uniformity are major challenges for most metallic nanostructures for surface‐enhanced Raman spectroscopy (SERS). Due to the randomness of the localized field supported by silver and gold nanopatterns in conventional structures, the quantitative analysis of the target in the practical application of SERS sensing is a challenge. Here, a superabsorbing metasurface with hybrid Ag–Au nanostructures is proposed. A two‐step process of deposition plus subsequent thermal annealing is developed to shrink the gap among the metallic nanoparticles with no top‐down lithography technology involved. Because of the light trapping strategy enabled by the hybrid Ag–Au metasurface structure, the excitation laser energy can be localized at the edges of the nanoparticles more efficiently, resulting in enhanced sensing resolution. Intriguingly, because more hot spots are excited over a given area with higher density of small nanoparticles, the spatial distribution of the localized field is more uniform, resulting in superior performance for potential quantitative sensing of drugs (i.e., cocaine) and chemicals (i.e., molecules with thiol groups in this report). Furthermore, the final coating of the second Au nanoparticle layer improves the reliability of the chip, which is demonstrated effective after 12 month shelf time in an ambient storage environment.