Wafer-scale nanocracks enable single-molecule detection and on-site analysis.

Large-area surface-enhanced Raman spectroscopy (SERS) sensing platforms displaying ultrahigh sensitivity and signal uniformity have potentially enormous sensing applicability, but they are still challenging to prepare in a scalable manner. In this study, silver nanopaste (AgNPA) was employed to prepare a wafer-scale, ultrasensitive SERS substrate. The self-generated, high-density Ag nanocracks (NCKs) with small gaps could be created on Si wafers via a spin-coating process, and provided extremely abundant hotspots for SERS analyses with ultrahigh sensitivity-down to the level of single molecules (enhancement factor: ca. 10; detection limit: ca. 10 M)-and great signal reproducibility (variation: ca. 3.6%). Moreover, the Ag NCK arrays demonstrated broad applicability and practicability for on-site detection when combined with a portable 785 Raman spectrometer. This method allowed the highly sensitive detection of a diverse range of analytes (benzo[a]pyrene, di-2-ethylhexyl phthalate, aflatoxins B1, zearalenone, ractopamine, salbutamol, sildenafil, thiram, dimethoate, and methamidophos). In particular, pesticides are used extensively in agricultural production. Unfortunately, they can affect the environment and human health as a result of acute toxicity. Therefore, the simultaneous label-free detection of three different pesticides was demonstrated. Finally, the SERS substrates are fabricated through a simple, efficient, and scalable process that offers new opportunities for mass production.