Skin-Conformal Sandwich-Structured SERS Superlattice Platform for Non-Invasive Depression Detection

Flexible wearable biochemical sensors hold great promise for personalized health monitoring. However, achieving ultrahigh molecular sensitivity, conformal skin adhesion, and efficient sweat handling within a single device remains a critical challenge. Here, we present a fully integrated wearable sweat-sensing platform that seamlessly combines a biocompatible adhesive hydrogel, an ultrasensitive sandwich-structured surface-enhanced Raman scattering (SERS) architecture, and microfluidic sweat-collection channels for non-invasive monitoring of dopamine, a key biomarker associated with depression. The central component of the system is a dual-layer heterogeneous superstructure. Specifically, a highly ordered Au nanoparticle (Au NP) superlattice forms the bottom layer, offering uniform and dense plasmonic hotspots, while the top layer is based on double-shelled hollow Au@Au-Ag nanocages functionalized with Raman reporters and aptamer sequences. Furthermore, DNA-guided hybridization forms a robust "nanolock" junction that ensures strong interparticle coupling and provides excellent specificity. This configuration yields an exceptional SERS enhancement factor of 1.57 × 10¹¹, enabling nanomole-level dopamine detection (limit of detection: 3.78 × 10^-14 M) with excellent reproducibility (RSD = 9.02%) and high chemical specificity. To adapt the sensing unit for on-body use, the SERS chip is embedded within an adhesive, deformable, and biocompatible polyethylene glycol hydrogel. Featuring engineered microfluidic channels, this hydrogel autonomously transports sweat to the sensing area, thereby guaranteeing precise detection alongside consistent conformal contact and comfort. This multifunctional, integrated platform has the potential to overcome longstanding limitations in sensitivity, stability, biocompatibility, and sweat management that hinder conventional wearable sensors. It provides a powerful route toward a versatile design framework for next-generation wearable bioelectronics.