Signal amplification using Ab-AuNPs integrated with LDI-MS analysis for diabetes screening in urine and saliva

The global prevalence of diabetes is rising at an alarming rate, making it the third leading cause of death worldwide. This study presented a user-friendly, straightforward, and non-invasive method for screening diabetes. Various antibody-conjugated boronic acid-modified gold nanoparticles (Ab-AuNPs) were prepared, including anti-HbA1c, anti-HBA1, anti-HSA, anti-gHSA, and anti-insulin, to enable the specific recognition of their corresponding antigens in single droplet samples of urine and saliva on nitrocellulose membranes, with subsequent analysis performed using laser desorption/ionization mass spectrometry (LDI-MS). Ab-AuNPs absorbed ultraviolet laser light, leading to the direct desorption and ionization of Au ions. This process eliminated the need for an additional organic matrix in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), effectively reduced interference from matrix-related ions, and significantly amplified the detection signal of Au ions at trace levels for targeted antigens in urine and saliva. The developed method revealed elevated levels of glycated proteins, including glycated hemoglobin (HbA1c) and glycated human serum albumin (gHSA), as well as human serum albumin (HSA), in diabetic patients compared to healthy individuals. In contrast, insulin levels were notably lower in diabetic patients. By analyzing these biomarker changes, we successfully identified the presence of diabetes. The reported method for screening diabetes in biological fluids provides a practical approach and holds significant promise for analyzing other diseases as corresponding biomarkers are discovered and their antibodies are developed and acquired in the future.