Achieving Highly Sensitive In Situ Detection of Trace Starch with a Hydrogel-Functionalized MZI Optical Fiber Biosensor.

To address the critical concern about trace starch residues in cleaning water within the food industry, which can lead to cross-contamination and water eutrophication, a label-free optical fiber biosensor designed for high-sensitivity, specific in situ detection of starch was proposed. The sensor was constructed as an Multimode-No-core-Multimode (MNM) structure by cascading multimode fiber (MMF) and no-core fiber (NCF), which was functionalized with a hydrogel-based sensing layer. A key innovation involved the covalent immobilization of α-amylase onto the NCF surface via a glutaraldehyde-CS cross-linking method, creating a highly specific recognition interface for starch. Experimental results showed outstanding sensing performance within a linear range of 0-7 mg/mL, and the sensor achieved an excellent sensitivity of 3.74 nm/(mg/mL) and a low detection limit (LOD) of 0.034 mg/mL. This work successfully realized a sensing platform capable of label-free, highly sensitive, and specific detection of starch at trace levels, enabling precise detection of minute concentration changes. The proposed sensor offered an effective solution for in situ starch residue detection in food processing applications.