Plasmon‐Enhanced Fluorescence‐Based Core–Shell Gold Nanorods as a Near‐IR Fluorescent Turn‐On Sensor for the Highly Sensitive Detection of Pyrophosphate in Aqueous Solution

Abstract

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.

Recent Progress on Plasmon-Enhanced Fluorescence

“…Recently, several works have reported that the result of investigations of the distance and plasmon wavelength dependent fluorescence of fluorophore via nanorod or nanoparticle substrate [85,86]. In particular, core-shell configuration, precisely controlling the distance between fluorophore and plasmonic nanostructure, have been widely used in the investigation of PEF effect recently [87][88][89][90]. It is found that by introduction of silica shell with various thicknesses to isolated fluorophore Au nanoparticles (AuNPs) and four different target molecules with different absorbance properties, the investigation of fluorescence quenching effect from complete quenching to no coupling was comprehensively carried out.…”

Plasmon‐Enhanced Fluorescent Sensor based on Aggregation‐Induced Emission for the Study of Protein Conformational Transformation

“…SiO 2 ‐Apt‐PrP Sc ‐BSNVA NPs are used as control sample because they do not affect the fluorescence of dyes, hence serving as a common method to observe PEF. [16c,26]…”

“…The enhanced local EM fields around plasmonic nanostructures can dramatically modify the optical properties of adjacent fluorescent molecules, known as PEF. [16a] PEF is considered as an attractive biosensing technique as it can improve detection sensitivity of target molecules. The plasmon metallic NPs are key factors in PEF because they can serve as antennas providing enhanced EM field .…”

“…Au NCs, with multiple sharp corners and edges of “hot spots”, are considered as suitable materials for PEF. [16d] In this work, Au NCs with an average diameter of about 50 nm were prepared by a seed‐growth method, which possessed a surface plasmon absorption at 540 nm ( Figure A,E). When the distance between the dyes and the metallic nanostructures is less than 10 nm, the fluorescence of dyes is quenched due to fluorescence resonance energy transfer .…”

“…PEF can improve the fluorescence performance of fluorescent molecules and the detection sensitivity of target molecules. At present, a variety of fluorescent molecules have achieved fluorescence enhancement through the PEF effect, including porphyrin dyes, cyanine dyes, nucleic acid stain, and fluorescein . However, these conventional dyes usually undergo serious self‐quenching when they are concentrated or bounded to biological macromolecules due to the intermolecular π–π stacking interactions, which greatly limits their applications in biological macromolecular detection.…”