'Urease immobilized single-kit' for sensing of thiourea-glucose pair employing fluorescence 'Turn off - Turn on' and as an efficient sorbent for selective sample cleanup of thiourea.

The tenfold lowering in binding energy for TU-Tyrosine in immobilized urease (K: 4.7 × 10) with respect to the native enzyme (K: 6.5 × 10) begets easy desorption of thiourea (TU) by glucose (GL) with an eventual formation of a more strong TU- GL adduct; that rejuvenates the kit-material ready for the subsequent cycle(s). The sorption-desorption heeds fluorescence turn-off and turn-on in DCM for selective sensing of TU- GL pair at their respective linear range of concentration 2.5-26.1 ppm and 2.36-11.57 ppm. The process was found to be static (K ≥ 2.25 × 10 L mol), exothermic (ΔH: -0.08 kJ mol), spontaneous (ΔG: -21.1 kJ mol) and marginally entropy gaining (ΔS: 0.07 kJ mol K). The 'bulk material' (200 ± 20 μm) brilliantly preconcentrates TU with an enrichment factor of 106.2 after its selective extraction at near-neutral pH from a large volume sample (800 mL) of low concentration (30 ppm). A very dilute solution (0.05 mmol L) of GL at minimum volume (6 mL) acts as a stripping agent and provides a longer life (200 cycles with good extraction efficiency) to the material. The method was found to be efficient in the analysis of fruit juice as a real sample.