DNAzyme-based biosensor for sub ppb lead ions detection using porous silicon Fabry-Pérot interferometer

Herein, we present an optical sensing approach based on nanostructured porous silicon (PSi) Fabry-Pérot interferometers for real-time monitoring of lead (Pb2+) contaminants using DNAzyme, a synthetic DNA sequence with a functional catalytic region. The latter cleaved the complementary DNA/RNA substrate strand in the presence of Pb2+, which resulted in a decrease in the average refractive index of the total porous void. The interfacial optical contrast was enhanced by coupling silica nanoparticles to the complementary strand, thus improving the interferometer’s inherent performance. The catalytic activity of the DNAzyme-modified platform was monitored in real-time using reflective interferometric Fourier transform spectroscopy. The optimized conditions offered means for accurate, rapid (~20 min) and precise detection of Pb2+ in the range of 0.1–25 ppb with a detection limit of 0.49 ppb (2.4 nM). Sufficient selectivity and specificity were attained against other commonly known metallic pollutants in water sources. Finally, the practical applicability of the biosensor’s performance was demonstrated using real samples, such as ground, irrigation, tap water and even plasma, while depicting satisfactory recovery values of 94–103% in compliance with the ICP-MS approach. Overall, the developed sensing platform coupled to optical signal amplification can be easily redesigned for targeting other metal pollutants posing risks to water sources and the environment.