Optical System Based on Nafion Membrane for the Detection of Ammonia in Blood Serum Samples

Abstract

The blood ammonia (NH3) level is one of the most important hepatic biomarkers for the diagnosis and monitoring of liver pathologies and infections. In this work, we developed an optimized optical biosensing method to extract and quantify the ammonia contained in complex-matrix samples emulating the blood serum. First, the approach was tested with solutions of phosphate-buffered saline (PBS) and ammonia chloride. Then, further trials were carried out with solutions of fetal bovine serum (FBS). The ammonia was extracted from the tested samples through a customized cell, and it was optically quantified by exploiting the indophenol reaction. The extraction cell included a cation-exchange membrane in Nafion, which was chemically pre-treated through cleaning procedures of sulfuric acid and hydrogen peroxide to keep a basic pH in the ammonia solution and to avoid contaminants in the membrane. From the NH3 solution, the indophenol reaction produced light-reactive indophenol dye molecules, which were used as colorimetric indicators. Through absorbance measurements of the indophenol dye solution at 670 nm wavelength, we were able to detect and quantify the ammonia level in the samples both with a spectrophotometer and a customized miniaturized read-out system, obtaining a detection limit of 0.029 µmol/mL.

SPECTRA: A Novel Compact System for Surface Plasmon Resonance Measurements

“…Mirrors and lens are protected by a plastic cover to ease the device handling. The mirrors are positioned in an L shape in order to focalize the light beam firstly on the tested device surface and then on the spectrophotometer detector (7). The horizontal optical system (Figure 1c) is similarly composed of a rectangular planar support (1) and four mirrors (2).…”

“…Surface plasmon resonance (SPR) is a valuable optical analytic tool used as a sensing technique in a wide range of applications including studies of biomolecular interactions [1,2], drug discovery [3,4], and pathogen detection [5,6]. In recent years, there has been an evergrowing interest in optical detection techniques such as absorbance [7][8][9] and SPR [10][11][12], since they guarantee high sensitivity, immunity to external disturbance, stability, and low noise [13]. The SPR measurements allow rapid, sensitive, real-time, and label-free analysis, and they can also be applied in an array to detect analytes simultaneously [14].…”

Surface plasmonic biosensors: principles, designs and applications

“…Pasqualotto et al have developed a new SPR inspection equipment system called SPECTRA. 59 Unlike traditional complex instruments, it can quickly detect the presence of analytes and changes in surface properties in both static and dynamic setups at a lower cost.…”

Paper-based colorimetric hyperammonemia sensing by controlled oxidation of plasmonic silver nanoparticles

“… 13 A custom optical detection module was subsequently designed by Pasqualotto et al for readout of the Berthelot reaction from such a Nafion separation system. 14 However, the reliance on the Berthelot reaction with indophenol and sodium nitroprusside again limits the applicability of this system in point-of-care settings. For point-of-care testing, inexpensive single-use colorimetric sensors are highly attractive, a requirement which the rapid developments in paper-based sensors aim to address.…”