Synergistic nanoparticle enhancement LIBS and indirect ablation for ultrasensitive quantification of trace metals in μL oil samples

Abstract

Accurate monitoring of trace wear metals in lubricants is critical for predictive maintenance of mechanical systems, yet remains challenging due to the inadequate sensitivity of conventional techniques with microliter samples. We demonstrate a novel strategy combining nanoparticle-enhanced laser-induced breakdown spectroscopy (NELIBS) with indirect ablation on metal substrates for ultrasensitive quantification of trace metals in engine oil. This approach overcomes fundamental limitations in viscous liquid analysis—including signal instability, matrix effects, and splashing—by leveraging laser ablation of conductive substrates coupled with localized surface plasmon resonance (LSPR) of gold nanoparticles. Crucially, metal substrates (Al) enable synergistic plasma enhancement where semiconductor substrates (Si) fail. Remarkably, the method achieves a 10-fold signal enhancement for target wear metals (Mg), with detection limits of 0.36 ppm (Mg), 0.19 ppm (Ca), and 0.47 ppm (Ba), and excellent linearity (R² > 0.99) validates quantification robustness. This non-contact technique provides a rapid, cost-effective solution for real-time engine health assessment, with significant implications for industrial oil monitoring and failure prediction.