Bifunctional Laser-Induced Graphene Platforms for Integrated Electrochemical Sensing and Matrix-Free LDI-MS Quantitation of Sarcosine.

This work introduces a dual-modality analytical platform based on laser-induced graphene (LIG) for the label-free, noninvasive detection of the prostate cancer biomarker sarcosine in human urine. The tunable porosity and high conductivity of LIG enable its bifunctional application as both a sensitive electrochemical electrode and an efficient matrix for laser desorption/ionization mass spectrometry (LDI-MS). Functionalized with sarcosine oxidase and gold nanoparticles (AuNPs), the platform leverages the strengths of both modalities: the AuNPs/LIG electrode provides rapid electrochemical screening with a low limit of detection (LOD) of 2 μM, while the LDI-MS modality offers highly selective, matrix-free confirmation with an enhanced ultralow LOD of 500 nM. Both modalities share a wide linear range (5-50 μM), falling well below the clinical urinary threshold of 20 μM. By combining speed and simplicity from electrochemical sensing with the high sensitivity and molecular specificity of MS analysis on a single device, this platform demonstrates the orthogonal capabilities of LIG for robust, pretreatment-free cancer biomarker diagnostics.