Clean and Open Yo-Yo-Shaped Nanoparticle with Large and Sensitive Hot Space Enhanced Raman Spectroscopy in Ultradilute Colloids

The pursuit of more hot spots and smaller hot spot spacing has long been a key research direction in the field of Surface-Enhanced Raman Spectroscopy (SERS). However, researchers increasingly recognize that simply increasing the number of hot spots or reducing interparticle spacing does not necessarily advance SERS technology. Instead, there is a growing consensus that the ultimate goal for SERS is to efficiently deliver analyte molecules into hot spots and construct open nanostructures with a uniform field intensity to achieve higher sensitivity and stability. Here, we report a facile strategy to fabricate yo-yo-shaped nanoparticles. By removing surfactants through a combination of solvent washing and chloride ion substitution in ultradilute colloidal solutions, we achieve the formation of clean and open yo-yo-shaped nanoparticles. These features facilitate the easy entry of analytes into the homogeneous field of the hot spot zone, resulting in high sensitivity and stability. The connected hot spot zones with clean and open characteristics, as well as large and uniform field intensity in yo-yo-shaped nanoparticles, have been termed "hot space". This yo-yo-shaped nanoparticle colloid strategy demonstrates excellent uniformity, with a relative standard deviation (RSD) of within 10% for the anticancer drug 5-fluorouracil (5-FU). This performance can be attributed to the homogeneous hot space geometry and the availability of clean hot space. Notably, for real serum samples from 27 tumor patients who received intravenous injections of 5-FU, the recovery rate reached 101.25%. It is no exaggeration to say that this yo-yo-shaped nanoparticle colloid strategy can be widely applied in SERS quantitative detection for fluid sensing, providing a valuable reference for clinical diagnosis.