Highly sensitive detection of Pb²⁺ with a non-contact, near-infrared responsive hydrogel-functionalized optical fiber...

Most sensors use acidic eluent to realize the desorption of Pb²⁺, which inevitably causes damage to the sensing membrane. A near-infrared responsive hydrogel sensing membrane (PNIPAm/PVA/GO) was prepared by free radical polymerization, which was modified on U-shaped optical fiber sensors for the selective determination of Pb²⁺. Graphene oxide (GO) is the functional recognition monomer, and the double-crosslinked network of polyvinyl alcohol (PVA) and Poly(N-isopropylacrylamide) (PNIPAm) acts as the mechanical stress skeleton while increasing the Pb²⁺ adsorption sites and inhibiting the agglomeration of GO. The "self-healing" of the sensing membrane achieves non-destructive desorption without causing secondary pollution to the environment by utilizing the high photothermal conversion efficiency of GO and the temperature response characteristics of PNIPAm. The sensor exhibited a sensitivity of 0.2191 nm/ppb in the 0-100 ppb range; the limit of detection was calculated to be 0.27 ppb. The experimental results show that the sensor has good reproducibility, stability, and selectivity. Further, the proposed signal analysis method based on convolutional neural networks realizes the measurement of Pb²⁺ at different pH values. This method can effectively solve the problem of increased selectivity while leading to desorption difficulties and provides a new idea for realizing green, clean, and efficient detection of Pb²⁺.