Bio-sensing of metal ions by a novel 3D-printable smartphone spectrometer

The first lens-free smartphone spectrometer capable of observation and analysis of reaction kinetics and point measurements without additional electronics is demonstrated in this paper. The reaction rate is calculated and plotted in adjustable intervals by a smartphone app. The only additional materials needed for the spectrometer are produced by 3D-printing. The flashlight LED and the ambient light sensor of the smartphone are used for the absorbance measurements. The smartphone spectrometer is capable of measuring reaction rates by monitoring changes in the absorbance at wavelengths of approximately 425-560 and 625-675 nm. The restriction on specific wavelength is caused by the nonhomogeneous emission spectra of the smartphone's flashlights LED. As a demonstration, the spectrometer and the individually programmed analysis software are used for reading and processing the signal of a urease bioassay developed for the detection and measurement of enzyme inhibitors. The inhibition caused by heavy metal ions is assessed by the smartphone through measurement of urease activity to a minimum activity of approximately 1 Uml(-1). For a detailed investigation of cumulative inhibition effects by lowcost analytical smartphone equipment, the results of mixed inhibition by heavy metals is compared to Bliss independence and Loewe additivity model theories. The study shows that cumulative inhibition effects of multi-component heavy metal solutions and different surface and supply water samples do not follow the conventional models of mixed inhibition effects. However, toxicity of mixed and single heavy metal ions in multi-component solutions, surface water samples, and supply water samples can be determined by the urease bioassay and the smartphone spectrometer. General water quality can also be rated using the same bioassay and equipment. (C) 2017 Elsevier B.V. All rights reserved.