Enhanced label-free SERS detection of uremic toxins in clinical spent dialysate

β2-microglobulin (β2-m) and leptin are key biomarkers for assessing the progression of chronic kidney disease and the efficacy of dialysis. Traditional biochemical assays are often time-consuming or require expensive consumables. Due to the low surface-enhanced Raman spectroscopy (SERS) activity of the characteristic functional groups of β2-m or leptin, the enhancement intensity of substrate-based label-free SERS may be weak. This work designs a method that combines modified Ag NPs (mAg NPs) with Au NPs/ZrO₂ substrate (Au NPs/fZrO₂ or Au NPs/pZrO₂) to approach target species and constructs a feature recognition system for the detection of β2-m and leptin in clinical spent dialysate.

SERS spectral analysis of purified β2-m and leptin was performed using mAg NPs with Au NPs/ZrO₂ to investigate their Raman characteristic peaks. First, reference and indicator peaks were identified to distinguish β2-m and leptin. Importantly, the major species Trp⁹⁵ of β2-m was likely located near the mAg NPs, while the minor species Trp⁶⁰ was located near the protein core, similar to the major species Leu⁵¹ and Phe⁴¹ in leptin.

This constructed detection system utilizes synergistic plasmon coupling between Au NPs on a substrate and mAg NPs surrounding the target species to enhance the Raman signal and generate local hotspots, thereby improving signal reproducibility and detection sensitivity even in complex clinical media. Characteristic peak enhancement is most pronounced near the major species Trp⁹⁵ of β2-m, but less noticeable with less exposure in the protein core or target species. It is significant to evaluate dialysis performance and contribute to dialysis monitoring.