There are only a few systematic rules about how to selectively control the formation of DNA-templated metal nanoparticles (NPs) by varying sequence combinations of double-stranded DNA (dsDNA), although many attempts have been made. Herein, we develop a facile method for sequence-dependent formation of fluorescent CuNPs by using dsDNA as templates. Compared with random sequences, AT sequences are better templates for highly fluorescent CuNPs. Other specific sequences, for example, GC sequences, do not induce the formation of CuNPs. These results shed light on directed DNA metallization in a sequence-specific manner. Significantly, both the fluorescence intensity and the fluorescence lifetime of CuNPs can be tuned by the length or the sequence of dsDNA. In order to demonstrate the promising practicality of our findings, a sensitive and label-free fluorescence nuclease assay is proposed.

Developing plasmon‐enhanced fluorescence (PEF) technology for identifying important biological molecules has a profound impact on biosensing and bioimaging. However, exploration of PEF for biological application is still at a very early stage. Herein, novel PEF‐based core–shell nanostructures as a near‐infrared fluorescent turn‐on sensor for highly sensitive and selective detection of pyrophosphate (PPi) in aqueous solution are proposed. This nanostructure gold nanorod (AuNR)@SiO2@meso‐tetra(4‐carboxyphenyl) porphyrin (TCPP) contains a gold nanorod core with an aspect ratio of 2.3, a silica shell, and TCPP molecules covalently immobilized onto the shell surface. The silica shell is employed a rigid spacer for precisely tuning the distance between AuNR and TCPP and an optimum fluorescence enhancement is obtained. Due to the quenching effect of Cu2+, the copper porphyrin (TCPP‐Cu2+) results in a weak fluorescence. In the presence of PPi, the strong affinity between Cu2+ and PPi can promote the disassembly of the turn‐off state of TCPP‐Cu2+ complexes, and therefore the fluorescence can be readily restored. By virtue of the amplified fluorescence signal imparted by PEF, this nanosensor obtains a detection limit of 820 × 10−9m of PPi with a good selectivity over several anions, including phosphate. Additionally, the potential applicability of this sensor in cell imaging is successfully demonstrated.

Optical antennas with anisotropic metal nanostructures are widely used in the field of fluorescence enhancement based on localized surface plasmons (LSPs). They overcome the intrinsic defects of low brightness of near-infrared (NIR) dyes and can be used to develop sensitive NIR sensors for bioapplications. Here, we demonstrate a novel NIR plasmon-enhanced fluorescence (PEF) system consisting of elongated gold nanobipyramids (Au NBPs) antennas, silica, and NIR dyes. Silica was chosen as the rigid spacer to regulate the distance between the metal nanostructures and dyes. Maximum enhancement was observed at a distance of approximately 17 nm. The enhanced fluorescence could be quenched by Cu and recovered by pyrophosphate (PPi) owing to the strong affinity between PPi and Cu. Thus, the Au NBP@SiO@Cy7 nanoparticles (NPs) detect PPi via "switch-on" fluorescence signals, with a detection limit of 80 nM in the aqueous phase. The probe not only detects PPi in living cells but also can be used for a microRNA assay with a detection limit of 8.4 pM by detecting PPi in rolling circle amplification (RCA). Additionally, gold nanorods (Au NRs) with the same longitudinal plasmon resonance wavelength (LPRW) as the Au NBPs were prepared to synthesize Au NR@SiO@Cy7 NPs for comparison. The experimental and finite-different time-domain (FDTD) simulation results indicate that the stronger electric fields of Au NBPs contribute to a fluorescence enhancement that is several times higher than that of Au NRs, confirming the superior properties of Au NBPs as novel ideal substrates to develop PEF biosensors.

No abstract

No abstract