The morphology and adhesion strength of the autocatalytic electroless nickel phosphorus (Ni-P) film, deposited at 40 ºC on polished alumina (Al2O3 99.6%) substrate, pretreated by sulfur/nitric solution, sensitizing with acid stannous chloride and activated using palladium chloride solutions, was studied using contact angle (CA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), mechanical profilometer (DekTak), and direct laser writer (“maskless lithography”). The results showed that after treatment of the polished Al2O3 substrate, it presented a high performance in the electroless deposition of Ni-P thin-film at low temperature (40 ºC). It was obtained a more compact and continuous film, with small grain size and strong adherence.

This work proposes a novel approach for colorimetric assays using ubiquitous and inexpensive water beads (WBs) made of a superabsorbent polymer (sodium polyacrylate). The high-water absorption capacity by the WBs was exploited for the preconcentration of iron ions from samples of tap, well, and lake waters. Moreover, the WBs also worked as a substrate for colorimetric detection of iron by the classical reaction of formation of Fe(II)-phenanthroline complex. Digital images acquired with a smartphone were used to obtain the color intensity of the WBs containing the orange color complex. The WBs were able to uptake and preconcentrate iron ions, allowing colorimetric detection with good linearity (R2 = 0.9978) and limits of detection (LOD) and quantification (LOQ) of 0.02 and 0.07 mg L-1, respectively. The proposed method provided recoveries ranging from 93 to 111% for a sample of well water spiked with 0.15 mg L-1 of iron.