A portable microfluidic device-based Fe3O4-urease nanoprobe-enhanced colorimetric sensor for the detection of heavy metals in fish tissue

A portable microfluidic device with highly sensitive enzyme nanoprobe (Fe(3)O(4)MNPs-urease, average size 34.6 nm) was demonstrated for the analysis of heavy metals ions (Hg2+, Cd(2+)and Pb2+) in fish gill and muscle tissue. The immobilized urease nanoprobe (K-m= 0.05 mM) exhibited twofold sensitivity over the free enzyme assay (apparentK(m)= 0.1 mM). The nanoprobe was characterized using SEM, EDAX, PSA and FT-IR. The inhibition measurements were carried out for individual as well as the mixture of metal ions (CRM standards of 9 elements (CRMmix-9)). The lower limit of quantification (LOQ) (0.5, 0.1, and 0.1 ng L(-1)for Hg2+, Cd2+, and Pb2+) and lower limit of detection (LOD) was achieved at 0.1 ng L(-1)with sensitivity 8-14% per decade for Hg2+, Cd2+, and Pb(2+)ions. A visual result can be observed by the naked eye through the microfluidic device as well as with 96 transparent microwell plates. The order of relative inhibition was found to be CRMmix-9> (Hg2++ Cd2++ Pb2+) > (Cd2++ Pb2+) > (Pb2++ Hg2+) > (Hg2++ Cd2+) > Pb2+> Cd2+> Hg2+, respectively. The recovery % in fish tissues were found to be 88-98% for Hg2+, Cd(2+)and Pb(2+)ions.