in situ synthesis of cuonp into polyvinyl alcohol-borax hydrogel sensor for determination of tryptophan using a smart phone

Tryptophan is an essential amino acid consisting an α-amino group, an α-carboxylic acid group and a side chain indole which converts it to a non-polar aromatic amino acid [1]. the human body is unable to produce it and must be supplied through the consumption of foods containing l-tryptophan.when tryptophan is improperly metabolized, it produces a waste product in the brain that is toxic and causes hallucinations and delusions. many methods are currently used to measure tryptophan, such as high performance liquid chromatography, spectrophotometry, and electrochemical methods. chromatographic methods are often tedious and time consuming and require complex tools and a skilled operator, and are practically not simple methods. spectroscopic methods involve difficult and slow steps with tryptophan modification by countless reagents [2]. today, smartphone-based colorimetric quantification is becoming more and more widespread. in this work, a user-friendly, non-instrumental, cost-effective and portable method was developed that can rapidly determine tryptophan concentration by digital image processing-based colorimetric method. in this study, a red, green, blue (rgb) color sensor was used for quantitative optical analysis of tryptophan using copper oxide nanoparticles synthesized in borax polyvinyl alcohol hydrogel matrix. the hydrogel was characterized by edx-map, ft-ir, uv–vis spectrometry and sem. by photographing the sensor and analyzing the images using photoshop software, the relationship between the mean of the signals obtained by the rgb channels from the pixels of the experimental area for different concentrations of tryptophan. in order to increase the sensitivity and selectivity of the method, the effective factors in the tryptophan measurement were optimized using design expert software. under optimal conditions, mean of rgb channels sensor was linearly related to the tryptophan concentration in the range of 5-100 ng ml-1 with a correlation coefficient of r=0.9967 and the detection limit was 1.43 ng ml-1. from 7 repeated measurements at concentrations of 20 ng ml-1 and 60 ng ml-1 of tryptophan, the relative standard deviation was calculated to be 2.02% and 1.07%, respectively. the proposed sensor was successfully applied to the determination of tryptophan in chickpea, barley and milk samples.