Surface Plasmon Resonance-Based Highly Sensitive Optical Fiber Sensor for Detection of Urease Enzyme in Soil: Real-World Application and Binding Insights With Inhibitor

Urease is an enzyme found in soil, which plays a crucial role in soil’s health by catalyzing the hydrolysis of urea. Surface plasmon resonance (SPR)-based optical fiber sensors have been widely popular for the detection of a large number of molecules with benefits like miniaturization and real-time monitoring. This study presents the development of a fiber-optic SPR (FO-SPR) sensor for precisely detecting urease enzymes. The sensor has a detection range of 0–10 pM and a sensitivity of 1.91 nm/pM. A high figure of merit (FOM) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.67\times 10^{{9}}$ </tex-math></inline-formula> pM<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula> and a very low limit of detection (LOD) of 0.63 pM has been achieved. This sensor was successfully utilized in quantifying urease concentrations for three distinct soil samples, with the results confirmed through surface-enhanced Raman spectroscopy (SERS). A linear response was observed when the sensor was applied to spiked real-world soil samples, highlighting its effectiveness in complex environments. Further control experiments were conducted to investigate the efficiency of N-(n-butyl) thiophosphoric triamide (NBPT) as a urease inhibitor, determining the optimal pH conditions for their enhanced binding. The sensor not only enables accurate urease detection in environmental matrices but also provides valuable insights into the nature and optimal ambiance pH for inhibitor-enzyme interaction, offering applications in agriculture monitoring.