Magnetic nanofluid based non-enzymatic sensor for urea detection

We demonstrate a simple, inexpensive and non-enzymatic optical probe for the detection of urea using functionalized magnetic nanofluid. The nanofluid used here is an oil-in-water magnetic nanoemulsion containing superparamagnetic iron oxide nanoparticles of size similar to 10 nm. Under a constant magnetic field (similar to 90 G), the magnetic emulsion, forms a one dimensional Bragg diffraction grating with a fixed interparticle spacing. In the presence of urea, the probe showed a large wavelength shift in the visible wavelength range of 880-600 nm, due to complexation of urea with the functional moieties that dramatically changes the electrostatic repulsion between emulsion droplets or conformation of adsorbed polymer. The functional moieties, sodium dodecyl sulphate, poly acrylic acid and poly(ethylene oxide)block-poly(propylene oxide)-block-poly(ethylene oxide) copolymer are found to be suitable for the measurement of urea in the concentrations range 0.003-0.6, 0.18-33.3 and 2.4-334 g/L, respectively. PAA stabilized emulsion is found to be suitable for the selective detection of urea in the presence of biologically important cations such as Na+ and Ca2+. The fast response time of the sensor (less than a second) and the wide urea detection capability are the unique features of the new sensor. (C) 2017 Elsevier B.V. All rights reserved.