Dual-Channel Optical Fiber SPR Sensor: Sensitive Tributyrin Measurement From Trace to High Levels

Tributyrin is widely used in medical treatment, drug development, and other fields. Lipase can decompose one tributyrin into one glycerol and three butyric acids, causing the effective refractive index (RI) and pH to change. Detecting the RI change or pH change during the experiment is usually used to determine the tributyrin in the sample. However, these methods encounter limitations at low or high concentrations. The RI difference detection method is difficult to implement in low-concentration detection, but the pH detection method is difficult to apply in high-concentration detection. In this article, we present an optical fiber sensor with dual channels based on surface plasmon resonance (SPR) to achieve the measurement of tributyrin. Polyacrylic acid (PAA)/chitosan (CS) pH-sensitive material is coated on half of the SPR sensor as channel 1 to monitor tributyrin-induced pH changes, and the lipase is bonded on the polydopamine (PDA)/maleic acid (MA) coated on the fiber as channel 2 to decompose tributyrin. Experimental results show that channel 1 realizes high pH sensitivity (34.52 nm/pH) and the tributyrin sensitivity reaches 12.8 nm/mM with a concentration between 0.1 and 1 mM. In the concentration range of 1–4 mM, channel 2 exhibits a tributyrin sensitivity of 4.85 nm/mM. In addition, the sensor proposed in this article has excellent stability and selectivity. Thus, the dual-channel optical fiber SPR sensor holds significant potential for drug development and biomedicine.