Compact, lightweight, and on-chip spectrometers are required to develop portable and handheld sensing and analysis applications. However, the performance of these miniaturized systems is usually much lower than their benchtop laboratory counterparts due to oversimplified optical architectures. Here, we develop a compact plasmonic “rainbow” chip for rapid, accurate dual-functional spectroscopic sensing that can surpass conventional portable spectrometers under selected conditions. The nanostructure consists of one-dimensional or two-dimensional graded metallic gratings. By using a single image obtained by an ordinary camera, this compact system can accurately and precisely determine the spectroscopic and polarimetric information of the illumination spectrum. Assisted by suitably trained deep learning algorithms, we demonstrate the characterization of optical rotatory dispersion of glucose solutions at two-peak and three-peak narrowband illumination across the visible spectrum using just a single image. This system holds the potential for integration with smartphones and lab-on-a-chip systems to develop applications for in situ analysis.

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 nm is 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–1 concentration, 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.

Here we report a plasmonic “rainbow” chip for spectroscopic sensing. By analyzing a single image with deep neural network, this image-based system can precisely determine the spectroscopic and polarimetric information of the incident light.

We report a broadband and efficient absorbing substrate composed of self-assembled gold nanoparticles onto a three-dimensional porous membrane for highly sensitive SERS sensing using a superhydrophobic hierarchical nanostructure.

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