An enzyme-sensitive probe for photoacoustic imaging and fluorescence detection of protease activity

Abstract

A gold nanocage and dye conjugate has been demonstrated for use with photoacoustic imaging and fluorescence detection of protease activity. The detection sensitivity could be maximized by using gold nanocages with a localized surface plasmon resonance peak away from the emission peak of the dye. These hybrids can be potentially used as multimodal contrast agents for molecular imaging.

Gold-nanoparticle-based biosensors for detection of enzyme activity

“…Severing the link between the GNP and the fluorophore, thereby restoring the fluorescence of the fluorophore, is the basic detection principle in these assays ( Figure 1C, Table 1). However, it is important to take into consideration that the fluorescence intensity of the free dye strongly depend on the GNP concentration in solution and on the spectral overlap between fluorophore emission and the GNP surface plasmon absorption peak [14]. In one study, for example, fluorescent dyes were attached to the surface of gold nanocages via protease cleavable peptides [14].…”

“…Surprisingly none of the currently reported GNP-based enzyme assays takes advantage of these favorable optical characteristics. Only a few designs utilizing nanorods [33,34] or nanocages [14] have been applied to optimize the sensitivity of GNP-based assays by exploiting the tunability of surface plasmon absorption peak.…”

“…However, it is important to take into consideration that the fluorescence intensity of the free dye strongly depend on the GNP concentration in solution and on the spectral overlap between fluorophore emission and the GNP surface plasmon absorption peak [14]. In one study, for example, fluorescent dyes were attached to the surface of gold nanocages via protease cleavable peptides [14]. In the presence of the protease, the peptides were cleaved, the dye molecules were released from the surface of the nanocage, and the fluorescence was recovered.…”

Noninvasive Detection and Imaging of Matrix Metalloproteinases for Cancer Diagnosis

“…And the energy transfer distances is nearly twice as long as the typical FRET distance (\10 nm) [22]. A MMP-2-sensitive gold nanocage conjugated with a FITC-labeled peptide showed MMP-responsive ability and good NSET quenching efficiency (96.6%) [32]. A gold nanoprobe containing activatable fluorogenic peptide (GNP-ActFP) was developed to specifically detect the expression level and proteolytic activity of membrane type-1 matrix metalloproteinase (MT1-MMP or MMP-14) in cancer cells by protease-mediated endocytosis [33].…”

Plasmonic Nanostructures for Biomedical and Sensing Applications

“…"Click chemistry" is another particularly appealing conjugation route, due to the orthogonality of the functional groups involved [123]. Additionally, these covalent linkages can be designed to respond to a variety of external or internal stimuli such as irradiation [124], pH change [125,126], or exposure to biomolecules [117], enabling controlled release [127]. Covalent bonds offer relatively stable conjugates with low leakage during transport in the circulatory system.…”