Aptamer-Driven Nanoparticles-Coupled Plasmonic Metasurface Biosensing Platform for Ultrasensitive and Quantitative Identification of Heavy Metal Cadmium Ions in Body Fluids

A cost-effective AuNPs-coupled PM platform for highly sensitive and selective cadmium ion (Cd²⁺) detection is developed, in which Cd²⁺-induced conformational switching of aptamers from single-stranded DNA to a stem-loop structure is utilized, preventing AuNPs from binding to the PM surface and reducing wavelength shift. Furthermore, the contribution of localized coupling effects between AuNPs and various positions on the PM surface to the change of the sensing signal is revealed, offering insights into AuNPs-enhanced PM sensing compared to traditional effective refractive index theory. Our proposed sensing platform enables the detection of Cd²⁺ in ultrapure water over a broad concentration range from 10 pg/L to 10 mg/L with excellent linearity, achieving a detection limit of 3.72 pg/L, which is approximately 6 orders of magnitude lower than the clinically required concentration. Moreover, the sensing method demonstrates excellent recovery rates and resistance to interferences in complex Cd²⁺-spiked urine and serum samples. Due to the low-cost, scalability, and ease of fabrication of both AuNPs and PM chips, as well as the universal applicability of aptamers to target various analytes, this biosensing platform holds the potential for high-throughput detection of other heavy metal ions, environmental pollutants, and disease biomarkers.