A NIR Biosensor for the Detection of Silver Ions Based on a Single-Chirality Carbon Nanotube with DNA Wrapping

Silver ion (Ag+) contamination constitutes a critical environmental and public health challenge, necessitating advanced detection technologies capable of fast response, high sensitivity, and selectivity. Single-chirality carbon nanotubes (SWCNTs) showed ideal potential in specific biosensing owing to their unique near-infrared II signal and minimal spectral overlap, which are recognized as potential biosensing materials for monitoring complex water samples. This research presents a NIR probe, combining C-rich DNA sequences with a purified single-chirality SWCNT (8, 4). Based on the interaction of Ag–C and the subsequent NIR response of (8, 4), we successfully established a fast-response and selective biosensor for the detection of silver ions. An impressively fast signal was achieved right after Ag+ was exposed to our DNA-(8, 4) NIR probe, and compared with unspecific metal ions, Ag+ generated a dramatically higher NIR signal. Finally, a linear detection range (R2 = 0.998) from 30 nM to 60 μM Ag+ was achieved. Moreover, we demonstrated its high recovery rates (97.2%–107.6%) and favorable precision (RSD 1.7%–6.3%, n = 3) when analyzing real water samples. In this work, we systematically investigated the assembly mechanisms and structural switch of DNA–SWCNT hybrids during Ag+ combination, establishing a foundational understanding for further optimization of the biological functionalization of CNT and applications in biosensing, especially for the detection of heavy-metal ions, which has significant implications for environmental preservation and public health.