Near-infrared band Gold nanoparticles-Au film “hot spot” model based label-free ultratrace lead (II) ions detection via fiber SPR DNAzyme biosensor

Heavy metal lead ion (Pb2+) detection takes more and more attention due to its synergistic toxicity to human health and undegradability in environment. Currently, there are urgent demands for portable, anti-interference and economical Pb2+ sensors with high sensitivity and selectivity for environmental monitoring as well as modern healthcare in clinic. In this article, via compact and high performed titled fiber Bragg grating (TFBG) surface plasmon resonance (SPR) sensing platform, we present a novel DNAzyme biosensor for ultratrace Pb2+ detection on the basis of “hot spot” effect in near-infrared band. A gold nanoparticle (GNP)-on-Au film construction was built by DNAzyme and its substrate strand. When Pb2+ with high catalytic activity cleave the DNAzyme linked rA (ribonucleotide adenosine) containing substrate strand, making DNA double helix structure transform to a single strand, the GNPs that connected with DNAzyme fall down to the sensor surface. By FDTD simulation, we have demonstrated that the appearing “hot spot” effect due to the narrow gap (<2 nm) will eventually result in enhancement of the spectrum signal response which is directly related to the Pb2+ concentration. In experiments, the proposed fiber biosensor exhibits a competitive low limit of detection ∼ 8.56 pM, excellent selectivity against other environmentally related metal ions and the large dynamic response range from 10−11 M to 10−6 M. More significantly, clinical human serum samples were used to verify the practicability of this TFBG-SPR-DNAzyme-GNPs biosensor showing great potential value in various clinical applications as a high efficiency, portable and easy to miniaturization point-of-care testing technology.