4D-printed, NIR-actuated, and power-controlled stream selector for automated solid-phase extraction of multiple trace metals

An automated solid-phase extraction (SPE) device using a digital light processing 4DP technique combined with graphene-incorporated N-isopropylacrylamide resins has been developed. The device comprised flow manifolds, a monolithic packing, and a cantilever featuring a channel connected to a near-infrared (NIR)-actuated thermoresponsive actuator composed of a graphene-incorporated layer and a nonresponsive layer. Power-controlled NIR irradiation increased the temperature of the graphene-incorporated layer above its volume phase transition temperature, causing it to deswell and creating an imbalance between the two layers that induced stepwise bending of the cantilever. This manipulation enabled multiple streams to sequentially pass through the monolithic packing, thereby facilitating the automation of the SPE scheme. Coupling the optimized 4D-printed NIR-actuated stream selector-SPE device with inductively coupled plasma mass spectrometry enabled highly sensitive and reliable determination of Mn, Co, Ni, Cu, Zn, Cd, and Pb ions, with method detection limits ranging from 0.1 to 0.3 ng L^- 1. The reliability and applicability of this analytical method were validated by determining the metal ions in four reference materials (CASS-6, SLRS-5, 1643f, and Seronorm™ Trace Elements Urine L-2), as well as in environmental water and human urine samples. Our results demonstrate the capability and versatility of 4DP technologies to advance the fabrication of smart analytical devices and automate conventional SPE schemes while maintaining competitive analytical performance.