Towards ultra-sensitive and rapid near-source wastewater-based epidemiology.

Wastewater-based epidemiology is emerging as a powerful early-warning public health surveillance tool. However, gold-standard PCR necessitates transporting samples to laboratories, with significant reporting delays (24-72 h), prompting growing interest in rapid, near-source tests for resource-limited settings. Research has focused on gold nanoparticle dipsticks, but these typically lack sensitivity in wastewater. Herein, we explore two complementary nanomaterial based approaches, using SARS-CoV-2 as an exemplar: 1) visually-read carbon black dipsticks; 2) spin-enhanced fluorescent nanodiamond dipsticks, exploiting selective separation from background autofluorescence. The assay provides a 2-hour turnaround from sample preparation to result with minimal equipment and achieves a limit of detection down to 7 copies per assay. A pilot study with samples from the Welsh National WBE programme finds 80% sensitivity and 100% specificity for carbon black, and 100% sensitivity, specificity for nanodiamonds. A proof-of-concept lab-in-a-suitcase nanodiamond assay tests raw, unprocessed wastewater samples. These findings lay the foundations for near-source WBE early-warning quantum sensors in the environment.