Locking the GFP Fluorophore to Enhance Its Emission Intensity

The Green Fluorescent Protein (GFP) and its analogues have been widely used as fluorescent biomarkers in cell biology. Yet, the chromophore responsible for the fluorescence of the GFP is not emissive when isolated in solution, outside the protein environment. The most accepted explanation is that the quenching of the fluorescence results from the rotation of the aryl-alkene bond and from the Z/E isomerization. Over the years, many efforts have been performed to block these torsional rotations, mimicking the environment inside the protein β-barrel, to restore the emission intensity. Molecule rigidification through chemical modifications or complexation, or through crystallization, is one of the strategies used. This review presents an overview of the strategies developed to achieve highly emissive GFP chromophore by hindering the torsional rotations.

Engineering surface patterns on nanoparticles: New insights on nano-bio interactions

The surface properties of nanoparticles affect their fates in biological systems. Based on nanotechnology and methodology, pioneering works have explored the effects of chemical surface patterns on the behavior of...

Green fluorescent protein inspired fluorophores

Green fluorescence proteins (GFP) are appealing to a variety of biomedical and biotechnology applications, such as protein fusion, subcellular localizations, cell visualization, protein-protein interaction, and genetically encoded sensors. To mimic the fluorescence of GFP, various compounds, such as GFP chromophores analogs, hydrogen bond-rich proteins, and aromatic peptidyl nanostructures that preclude free rotation of the aryl-alkene bond, have been developed to adapt them for a fantastic range of applications. Herein, we firstly summarize the structure and luminescent mechanism of GFP. Based on this, the design strategy, fluorescent properties, and the advanced applications of GFP-inspired fluorophores are then carefully discussed. The diverse advantages of bioinspired fluorophores, such as biocompatibility, structural simplicity, and capacity to form a variety of functional nanostructures, endow them potential candidates as the next-generation bio-organic optical materials.

Combination of [12]aneN3 and Triphenylamine-Benzylideneimidazolone as Nonviral Gene Vectors with Two-Photon and AIE Properties

Three nonviral gene vectors, TPA-BI-A/B/C, have been designed and synthesized by the combination of one or two hydrophilic [12]aneN₃ moieties and two-photon fluorescent triphenylamine-benzylideneimidazolone (TPA-BI) units through different ester linkage. Spectroscopic characterization demonstrated that TPA-BI-A/B/C had strong aggregation-induced emissions (AIE), large Stokes shifts (230, 284, and 263 nm), and large two-photon absorption cross sections (δ_2PA) (67, 592, and 80 GM). Gel electrophoresis indicated that the three compounds completely condensed DNA at 15 μM in the presence of DOPE, and showed the lipase- and pH-triggered reversible release of DNA and the fluorescent recognition of the different lengths of ssDNA and dsDNA. The optimal TPA-BI-C/DOPE-mediated luciferase and GFP activity was 146% and 290% higher than those of Lipo2000. The transfection process of DNA could be traced clearly through one- and two-photon fluorescence spectra, and displayed in a 3D-video. TPA-BI-C/DOPE successfully transfected the GFP gene into zebrafish, which was superior to Lipo2000 (192%). In conclusion, TPA-BI-C/DOPE is the first nonviral gene vector with the abilities of pH/lipase enzyme responsiveness, one/two-photon fluorescent tracking of intracellular delivery of DNA, and successful transfection in vivo and in vitro, even better than Lipo2000.

Nanomanufacture of Free-Standing, Porous, Janus-Type Films of Polymer-Plant Virus Nanoparticle Arrays

We present a facile method for preparing hierarchical assemblies of cowpea mosaic virus (CPMV) nanoparticles adsorbed onto patterned polypyrrole copolymer arrays, which can be released as a freely standing and microporous polymer-protein membrane with a Janus-type structure. The patterning protocol is based on colloidal sphere lithography wherein a sacrificial honeycomb pattern composed of colloidal polystyrene (PS) microspheres is assembled on an electrode. A thin layer of polypyrrole film is electropolymerized within the interstices of the template and monitored using an electrochemical quartz crystal microbalance with dissipation (EC-QCM-D) and microscopy. Dissolving the PS template reveals an inverse opaline pattern capable of electrostatically capturing the CPMV particles. Through an electrochemical trigger, the polypyrrole-CPMV delaminates from the surface producing a self-sustaining polymer-protein membrane that can potentially be used for sensing and nanocargo applications.

DNA mimics of red fluorescent proteins (RFP) based on G-quadruplex-confined synthetic RFP chromophores

Red fluorescent proteins (RFPs) have emerged as valuable biological markers for biomolecule imaging in living systems. Developing artificial fluorogenic systems that mimic RFPs remains an unmet challenge. Here, we describe the design and synthesis of six new chromophores analogous to the chromophores in RFPs. We demonstrate, for the first time, that encapsulating RFP chromophore analogues in canonical DNA G-quadruplexes (G4) can activate bright fluorescence spanning red and far-red spectral regions (Em = 583-668 nm) that nearly match the entire RFP palette. Theoretical calculations and molecular dynamics simulations reveal that DNA G4 greatly restricts radiationless deactivation of chromophores induced by a twisted intramolecular charge transfer (TICT). These DNA mimics of RFP exhibit attractive photophysical properties comparable or superior to natural RFPs, including high quantum yield, large Stokes shifts, excellent anti-photobleaching properties, and two-photon fluorescence. Moreover, these RFP chromophore analogues are a novel and distinctive type of topology-selective G4 probe specific to parallel G4 conformation. The DNA mimics of RFP have been further exploited for imaging of target proteins. Using cancer-specific cell membrane biomarkers as targets, long-term real-time monitoring in single live cell and two-photon fluorescence imaging in tissue sections have been achieved without the need for genetic coding.

Mussel-Inspired Polydopamine Coating on Tobacco Mosaic Virus: One-Dimensional Hybrid Nanofibers for Gold Nanoparticle Growth

One-dimensional (1D) hybrid nanofibers with surface-deposited gold nanoparticles (AuNPs) have been fabricated by self-assembly of rod-like tobacco mosaic virus (TMV) with mussel-inspired polymerization of dopamine and in situ reduction of gold ion, providing a method for sensing the endocytic pathway of nanomaterial.

A metal–organic framework as a flask: photophysics of confined chromophores with a benzylidene imidazolinone core

Photophysics and dynamics of chromophores with a benzylidene imidazolinone core, responsible for emission of green fluorescent protein variants, were studied as a function of host topology by three approaches.

Emission enhancement of GFP chromophore in aggregated state via combination of self-restricted effect and supramolecular host–guest complexation

The emission response of GFP chromophore in aggregated state is greatly enhanced more than 100-fold due to the inhibition of conformational motion and the reduction of strong π–π interaction.

Self-Restricted Green Fluorescent Protein Chromophore Analogues: Dramatic Emission Enhancement and Remarkable Solvatofluorochromism

The confinement effect of the β-barrel defines the emission profiles of the chromophores of the green fluorescent protein (GFP) family. Here, we describe the design strategy and mimicking of confinement effects via the chromophore itself, termed the self-restricted effect. By systematically tailoring the GFP core, a family of 2,5-dialkoxy-substituted GFP chromophore analogues is found to be highly emissive and show remarkable solvatofluorochromism in fluid solvents. Fluorescence quantum yield (QY) and lifetime measurements, in combination with theoretical calculations, illustrate the mechanism relying on inhibition of torsional rotation around the exocyclic CC bond. Meanwhile, theoretical calculations further reveal that the electrostatic interaction between the solvent and the imidazolinone oxygen can contribute to suppress the radiationless decay channel around the exocyclic C═C double bond. Our findings put forward a universal approach toward unlocked highly emissive GFPc analogues, potentially promoting the understanding of the photophysics and biochemical application of GFP chromophore analogues.

Photophysics of GFP-related chromophores imposed by a scaffold design

In this paper, a rigid scaffold imposes the photophysics of chromophores with a benzylidene imidazolidinone core by mimicking the β-barrel structure of the green fluorescent protein (GFP) and its analogs.