Molecular receptors integrated bimodal porous polymer scaffolds as portable solid-state optical ion-sensors and extractors for the selective capturing of ultra-trace toxic copper ions.

Background: Environmental contamination by heavy metal ions has caused growing ecological and public health concerns. In this line, monitoring of copper toxicity gains importance due to its application in industrial, agricultural, domestic, medical and technological sectors. Although noteworthy breakthroughs were made, critical issues, such as portability, the need for well-trained personnel, costly/complex instrumentations, long response time, and the introduction of secondary contaminants, required attention. Hence, developing a low-cost, user-friendly, real-time, portable analytical platform for rapid and on-site analysis remained imperative. Solid-state colorimetric sensors have gained widespread popularity due to their low cost, ease of use, and brilliant sensitivity/selectivity.

Results: We have successfully unfolded an ultra-portable azomethine-infused structurally interwoven polymer monolith as the solid-state chromatic sensor for the quantitative naked-eye detection of ultra-trace Cu in industrial/environmental samples. For the sensor fabrication, non-hygroscopic conjugated Schiff-base receptors, namely N-(1E,2E)-3-(4-dimethylamino)phenyl)allylidene)-3-nitrobenzohydrazide (DPAN) and 2,3-bis(((1E,2E)-3-(4-dimethylamino)phenyl)allylidene)amino)malononitrile (DPAM) were synthesized in-house and voluminously immobilized onto a crack-free porous poly(4VP-co-EGDMA) monolith framework. The topological structure and functionalities of the porous polymer monolith and chromatic sensor materials were examined using various surface analytical and microscopic techniques. The excellent surface area and intriguing interlaced porosity features of the tailor-made polymer monolith facilitated the voluminous anchoring of the chromatic receptors for the selective/sensitive targeting of Cu. The DPAN and DPAM receptor-loaded poly(4VP-co-EGDMA) sensors exhibited a linear range of 0-150 μg/L, with the limit of detection of 0.11 and 0.13 μg/L for Cu, respectively. The sensors manifested Cu specificity amidst concomitant matrix ions to highlight the relevance of the proposed solid-state sensor.

Significance: The sensor materials offered a reliable approach for detecting and quantifying environmentally toxic and industrially pertinent Cu from aqueous samples, with the prospect of large-scale production, owing to the sensor's integrated compact design that can be reused for repeated real-time surveillance. The sensor's ability to sense/trap traces of toxic Cu can provide an early warning about the growing toxicity in a particular resource, thereby providing an opportunity to initiate remediation protocols for speedy decontamination.