Versatile and high performance in-paper flexible SERS chips for simple and in-situ detection of methylene blue in river water and thiram on apple skin

In-paper flexible SERS chips were simply prepared by immersing pieces of filter paper into colloidal silver nanoparticle (e-AgNP) solution for 24 h and drying naturally at room temperature. Characteristic properties of cellulose fibers allowed the paper-based chips to be available for two sample collecting approaches. Being hydrophilic but insoluble in water, the chips were convenient to be dipped into aqueous media to collect soluble target analytes. Besides, they could “stick” on wet surfaces and bend along them to grab analytes. Hence, they were employed for in-situ detection of methylene blue dye in river water using “dip and dry” method and thiram pesticide on apple skin using “paste and peel off” procedure, resulting in detection limit of 10−10 M with excellent recovery rates of 93–104% and 86–93%, respectively. Therefore, the e-AgNPs-based in-paper SERS chips have served as a versatile tool for a large range of samples. More importantly, simple procedures of SERS chip preparation and sample collecting do not require the use of any complex equipment or expert operators. It can bring SERS techniques a step closer to real applications.