Designing a template by ۳D printer for construction of lab-on-paper chemical sensor containing silver nanoparticles for the measurement of thiosulfate in water samples using smartphone

The chemical sensors are laboratory equipment that play important role in environmental, chemical, and biological measurements, and have become smaller in size and dimensions called lab-on-chip devices [۱]. Many features such as small size, biodegradability, and ability to use micro volumes samples in the detection zone of analysis have made the paper as a substrate for such sensors [۲]. The basis of paper based analytical devices (PAD) and also lab-on-paper was introduced by Whiteside et al. [۳]. In this research, we designed a template for the construction of lab-on-paper chemical sensors containing silver nanoparticles for measurement of thiosulfate ion in aqueous solutions. We designed a pattern in solid works software and then printed the template in the ۳D printer device, and used it to make PADs by wax dipping method, which resulted in PADs with good performance. The detection zones of PADs containing silver nanoparticle (AgNPs) are yellow but in the presence of different concentrations of thiosulfate ions turn red because of the interaction of AgNPs and thiosulfate ion and are darker at higher concentrations of thiosulfate. The detection zones are photographed and the mean color intensity of the zones is determined in Photoshop software. These color intensity changes were used as analytical signals for the determination of thiosulfate. The experimental conditions such as synthesis of AgNPs, sodium hydroxide concentration, number of injecting AgNPs on the paper were optimized to achieve maximum analytical signals. By applying the optimal conditions, a linear calibration graph in the range of ۰.۰۵-۲۲.۶۰ μg mL-۱ was obtained and the limit of detection was ۰.۰۲۵ μg mL-۱. The relative standard deviation (RSD) for ۸ replicate measurements of ۰.۲۳ and ۴.۵۲ μg mL-۱ were ۴.۱۷ and ۲.۲۰, respectively. This system was used to determine thiosulfate in water and wastewater samples with good recoveries.