Molecular form-specific immunoassays for neutrophil gelatinase-associated lipocalin by surface-enhanced Raman spectroscopy

Neutrophil gelatinase-associated lipocalin (NGAL) with its great potential in clinical applications is a promising biomarker for the early diagnosis of acute kidney injury (AKI). Detection capability of immunoassays for versatile molecular forms of NGAL will affect the clinical performance of NGAL as biomarker for AKI. Here a molecular form-specific immunoassay for the detection of NGAL is developed by surface-enhanced Raman spectroscopy (SERS). 4-mercaptobenzoic acid (MBA)-modified silver chips are used as SERS-active substrates for capturing NGAL antibodies via amide bonds. The typical SEAS band frequency of MBA is highly sensitive to different molecular forms of NGAL. The SERS-based immunoassay has obvious advantages over other conventional enzyme-based methods in sample preparation and detection procedure. This is a first attempt to apply SEAS to detect AKI biomarkers, and the results demonstrate the proposed method has potential applications in the immunoassays for not only monomer NGAL, but also homodimer NGAL.