MT-I/AuNP-Based Fiber-Optic SPR Biosensor for Ultralow Limit Triglyceride Detection and On-Site Hydrolysis

Triglyceride (TG) is a critical biomarker in lipid metabolism and its trace-level detection and hydrolytic processes are important for human health management. Here, we present a novel approach involving the functionalization of a tilted fiber Bragg grating (TFBG) with Au–MT-I/AuNPs/lipase for plasmonic fiber-optic spectral comb technology, enabling rapid response and ultrasensitive TG detection as well as on-site hydrolysis. Through the utilization of Au–S bond self-assembly, the thiol groups derived from cysteine residues within metallothionein-I (MT-I) are utilized to create a functional modification layer on the gold-coated TFBG surface. Subsequently, the carboxyl groups of MT-I are activated using carbodiimide/N-hydroxysuccinimide (EDC/NHS) chemistry and covalently linked to the amine groups of gold nanoparticles–NH2 (AuNPs–NH2) via amide bond formation. Finally, the carboxyl groups of lipases are conjugated to the amine groups of AuNPs–NH2. Leveraging the molecular bridging capability and high specific surface area of AuNPs–NH2, both MT-I and lipase are covalently immobilized onto the nanoparticle surface, creating a “gold film–MT-I/AuNPs/lipase” composite sensing interface. The experimental results indicate that the proposed sensor exhibits a sensitivity of 0.346 dB/lg­(mM) and a low limit of detection (LOD) of 4.192 μM, surpassing previous reports by over 4 orders of magnitude. In addition, the lipase in the sensing membrane can catalyze the hydrolysis of triglyceride into glycerol and free fatty acids by gradually breaking the ester bonds to achieve complete hydrolysis. The “protein-nanoparticle-enzyme” synergistic sensing system established by this sensor offers valuable insights and serves as a reference for the design and development of dual-functional biosensors capable of monitoring enzymatic reactions and biosensing detection.