Theranostic Fluorescent Probes.

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Metal-organic framework (MOF) hybridized gold nanoparticles as a bifunctional nanozyme for glucose sensing.

Inspired by natural enzymes that possess multiple catalytic activities, here we develop a bifunctional metal-organic frame-work (MOF) for biosensing applications. Ultrasmall gold nano-particles (AuNPs) are grown in the internal cavities of an iron (Fe) porphyrin-based MOF to produce a hybridized nanozyme, AuNPs@PCN-224(Fe), in which AuNPs and PCN-224(Fe) exhibit the catalytic activity of glucose oxidase (GOx) and horseradish peroxidase (HRP), respectively. We established that the bifunctional nanozyme was capable of a cascade reaction to generate hydrogen peroxide in the presence of d-glucose and oxygen in situ, and subsequently activate a colorimetric or chemiluminescent substrate through HRP-mimicking catalytic activity. The nanozyme was selective over a range of other saccharides, and 93% of the catalytic activity was retained after being recycled five times.

Human serum albumin-based supramolecular host-guest boronate probe for enhanced peroxynitrite sensing.

Peroxynitrite (ONOO-) is an important oxygen/nitrogen reactive species implicated in a number of physiological and pathological processes. However, due to the complexity of the cellular micro-environment, the sensitive and accurate detection of ONOO- remains a challenging task. Here, we developed a long-wavelength fluorescent probe based on the conjugation between a TCF scaffold and phenylboronate; the resulting conjugate is capable of supramolecular host-guest assembly with human serum albumin (HSA) for the fluorogenic sensing of ONOO-. The probe exhibited an enhanced fluorescence over a low concentration range of ONOO- (0-9.6 µM), whist the fluorescence was quenched when the concentration of ONOO- exceeded 9.6 µM. In addition, when human serum albumin (HSA) was added, the initial fluorescence of the probe was significantly enhanced, which enabled the more sensitive detection of low-concentrations of ONOO- in aqueous buffer solution and in cells. The molecular structure of the supramolecular host-guest ensemble was determined using small-angle X-ray scattering.

Phenotyping of Methicillin-Resistant Staphylococcus aureus Using a Ratiometric Sensor Array.

Chemical tools capable of classifying multidrug-resistant bacteria (superbugs) can facilitate early-stage disease diagnosis and help guide precision therapy. Here, we report a sensor array that permits the facile phenotyping of methicillin-resistant Staphylococcus aureus (MRSA), a clinically common superbug. The array consists of a panel of eight separate ratiometric fluorescent probes that provide characteristic vibration-induced emission (VIE) profiles. These probes bear a pair of quaternary ammonium salts in different substitution positions around a known VIEgen core. The differences in the substituents result in varying interactions with the negatively charged cell walls of bacteria. This, in turn, dictates the molecular conformation of the probes and affects their blue-to-red fluorescence intensity ratios (ratiometric changes). Within the sensor array, the differences in the ratiometric changes for the probes result in "fingerprints" for MRSA of different genotypes. This allows them to be identified using principal component analysis (PCA) without the need for cell lysis and nucleic acid isolation. The results obtained with the present sensor array agree well with those obtained using polymerase chain reaction (PCR) analysis.

Targeted photothermal release of antibiotics by a graphene nanoribbon-based supramolecular glycomaterial.

Here, we report the simple construction of a supramolecular glycomaterial for the targeted delivery of antibiotics to P. aeruginosa in a photothermally-controlled manner. A galactose-pyrene conjugate (Gal-pyr) was developed to self-assemble with graphene nanoribbon-based nanowires via π-π stacking to produce a supramolecular glycomaterial, which exhibits a 1250-fold enhanced binding avidity toward a galactose-selective lectin when compared to Gal-pyr. The as-prepared glycomaterial when loaded with an antibiotic that acts as an inhibitor of the bacterial folic acid biosynthetic pathway eradicated P. aeruginosa-derived biofilms under near-infrared light irradiation due to the strong photothermal effect of the nanowires accelerating antibiotic release.

Metabolically Specific In Situ Fluorescent Visualization of Bacterial Infection on Wound Tissues.

The ability to effectively detect bacterial infection in human tissues is important for the timely treatment of the infection. However, traditional techniques fail to visualize bacterial species adhered to host cells in situ in a target-specific manner. Dihydropteroate synthase (DHPS) exclusively exists in bacterial species and metabolically converts p-aminobenzoic acid (PABA) to folic acid (FA). By targeting this bacterium-specific metabolism, we have developed a fluorescent imaging probe, PABA-DCM, based on the conjugation of PABA with a long-wavelength fluorophore, dicyanomethylene 4H-pyran (DCM). We confirmed that the probe can be used in the synthetic pathway of a broad spectrum of Gram-positive and negative bacteria, resulting in a significantly extended retention time in bacterial over mammalian cells. We validated that DHPS catalytically introduces a dihydropteridine group to the amino end of the PABA motif of PABA-DCM, and the resulting adduct leads to an increase in the FA levels of bacteria. We also constructed a hydrogel dressing containing PABA-DCM and graphene oxide (GO), termed PABA-DCM@GO, that achieves target-specific fluorescence visualization of bacterial infection on the wounded tissues of mice. Our research paves the way for the development of fluorescent imaging agents that target species-conserved metabolic pathways of microorganisms for the in situ monitoring of infections in human tissues.

Targeted delivery of maytansine to liver cancer cells via galactose-modified supramolecular two-dimensional glycomaterial.

A two-dimensional (2D) glycomaterial for targeted delivery of maytansine to liver cancer cells was developed. Host-guest interaction between a galactosyl dye and human serum albumin (HSA) produces supramolecular galactoside-HSA conjugates, which are then used to coat 2D MoS2. The 2D glycomaterial was shown to be capable of the targeted delivery of maytansine to a liver cancer cell line that highly expresses a galactose receptor, resulting in greater cytotoxicity than maytansine alone.

Tuning the Solid- and Solution-State Fluorescence of the Iron-Chelator Deferasirox.

Deferasirox, an FDA-approved iron chelator, has gained increasing attention for use in anticancer and antimicrobial applications. Recent efforts by our group led to the identification of this core as an easy-to-visualize aggregation-induced emission platform, or AIEgen, that provides a therapeutic effect equivalent to deferasirox (J. Am. Chem. Soc. 2021, 143, 3, 1278-1283). However, the emission wavelength of the first-generation system overlapped with that of Syto9, a green emissive dye used to indicate live cells. Here, we report a library of deferasirox derivatives with various fluorescence emission profiles designed to overcome this limitation. We propose referring to systems that show promise as both therapeutic and optical imaging agents as "illuminoceuticals". The color differences between the derivatives were observable to the unaided eye (solid- and solution-state) and were in accord with the Commission Internationale de L'Eclairage (CIE) chromaticity diagram 1913. Each fluorescent derivative successfully imaged the respective spherical and rod shapes of methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. They also displayed iron-dependent antibiotic activity. Three derivatives, ExNMe2 (3), ExTrisT (11), and ExDCM (13), display emission features that are sufficiently distinct so as to permit the multiplex (triplex) imaging of both MRSA and P. aeruginosa via stimulated emission depletion microscopy. The present deferasirox derivatives allowed for the construction of a multi-fluorophore sensor array. This array enabled the successful discrimination between Gram-positive/Gram-negative and drug-sensitive/drug-resistant bacteria. Antibiotic sensitivity and drug-resistant mutants from clinically isolated strains could also be identified and differentiated.

Near-Infrared Light-Triggered Bacterial Eradication Using a Nanowire Nanocomposite of Graphene Nanoribbons and Chitosan-Coated Silver Nanoparticles.

Bacterial infection is a major threat to human health. However, many antibacterial agents currently used are severely limited due to drug-resistance, and the development of side effects. Herein, we have developed a non-antibiotic nanocomposite consisting of chitosan (ChS) coated silver nanoparticles (AgNPs) and graphene nanoribbon (GNR)-based nanowires for light-triggered eradication of bacteria. The presence of AgNP/ChS significantly enhanced the interactions of the GNR nanowires with Pseudomonas aeruginosa, a clinically common Gram-negative bacterium. Which enables the highly effective photothermal eradication of bacteria by GNR upon near-infrared light irradiation. The nanocomposite was shown to be applicable for the light-triggered eradication of bacterial biofilms and the inhibition of bacterial growth on medical patches used for abdominal-wall hernia surgery.

Correction: Fluorescent glycoconjugates and their applications.

Correction for 'Fluorescent glycoconjugates and their applications' by Baptiste Thomas et al., Chem. Soc. Rev., 2020, 49, 593-641, DOI: 10.1039/C8CS00118A.

Low-dimensional nanomaterials for antibacterial applications.

The excessive use of antibiotics has led to a rise in drug-resistant bacteria. These "superbugs" are continuously emerging and becoming increasingly harder to treat. As a result, new and effective treatment protocols that have minimal risks of generating drug-resistant bacteria are urgently required. Advanced nanomaterials are particularly promising due to their drug loading/releasing capabilities combined with their potential photodynamic/photothermal therapeutic properties. In this review, 0-dimensional, 1-dimensional, 2-dimensional, and 3-dimensional nanomaterial-based systems are comprehensively discussed for bacterial-based diagnostic and treatment applications. Since the use of these platforms as antibacterials is relatively new, this review will provide appropriate insight into their construction and applications. As such, we hope this review will inspire researchers to explore antibacterial-based nanomaterials with the aim of developing systems for clinical applications.

Deferasirox (ExJade): An FDA-Approved AIEgen Platform with Unique Photophysical Properties.

Deferasirox, ExJade, is an FDA-approved iron chelator used for the treatment of iron overload. In this work, we report several fluorescent deferasirox derivatives that display unique photophysical properties, i.e., aggregation-induced emission (AIE), excited state intramolecular proton transfer, charge transfer, and through-bond and through-space conjugation characteristics in aqueous media. Functionalization of the phenol units on the deferasirox scaffold afforded the fluorescent responsive pro-chelator ExPhos, which enabled the detection of the disease-based biomarker alkaline phosphatase (ALP). The diagnostic potential of these deferasirox derivatives was supported by bacterial biofilm studies.

A glycoconjugate-based gold nanoparticle approach for the targeted treatment of Pseudomonas aeruginosa biofilms.

In this study, "core-shell" gold nanoparticles (AuNPs) have been functionalised using a simple one-pot approach to form fucose-based glycoconjugate AuNPs (Fuc-AuNPs) and galactose-based glycoconjugate AuNPs (Gal-AuNPs), respectively. Owing to the selective carbohydrate-based recognition of the key virulence factors of P. aeruginosa, LecB (fucose-specific lectin)/LecA (galactose-specific lectin), Fuc-AuNPs and Gal-AuNPs-based imaging and therapeutic strategies were evaluated towards P. aeruginosa. Both Fuc-AuNPs and Gal-AuNPs were non-covalently loaded with the fluorophore dicyanomethylene 4H-pyran (DCM) to afford two highly selective fluorescence imaging agents for the visualisation of P. aeruginosa. The loading of Fuc-AuNPs and Gal-AuNPs with the known antibiotic Ceftazidime (CAZ) exhibited an enhanced therapeutic effect, illustrating the significance of this targeted drug delivery strategy. Exploiting the phototherapeutic properties of AuNPs, photoirradiation (600 nm) of Fuc-AuNP@CAZ/Gal-AuNP@CAZ provided both photothermal and photodynamic therapeutic (PTT/PDT) effects, which facilitated the release of CAZ. Fuc-AuNP@CAZ and Gal-AuNP@CAZ were shown to be effective photo/chemotherapeutics resulting in almost complete eradication of P. aeruginosa biofilms formed on clinically relevant surfaces (glass slides and steel surface).

Photochromic Fluorescent Probe Strategy for the Super-resolution Imaging of Biologically Important Biomarkers.

Here, we report a ß-galactosidase (ß-Gal)-responsive photochromic fluorescent probe, NpG, that was designed to prebind to human serum albumin (HSA) to form the probe/protein hybrid, NpG@HSA. The formation of NpG@HSA led to an increase in fluorescence emission (520 nm) corresponding to the binding of the fluorescent naphthalimide unit with HSA. In addition, this enabled visualization of the spiropyran fluorescence emission in aqueous media. Our probe/protein hybrid approach afforded a unique imaging platform with enhanced cell permeability and solubility that was capable of visualizing the cellular uptake of NpG@HSA before its activation by ß-Gal. The ß-Gal-mediated cleavage of the galactose unit within the NpG@HSA hybrid resulted in the formation of NpM@HSA and an increase in red fluorescence emission (620 nm). The resultant merocyanine unit was then able to undergo photoisomerization (merocyanine ↔ spiropyran) to facilitate STORM (i.e., stochastic optical reconstruction microscopy) imaging with minimal phototoxicity and excellent photostability/reversibility. Using STORM, NpG@HSA was able to determine the subcellular distribution of ß-Gal activity between cell lines with nanoscale precision. We believe that this system represents a versatile imaging platform for the design of photochromic fluorescent probes suitable for illuminating the precise location of disease-specific biomarkers in various cellular processes.

Fluorescent glycoconjugates and their applications.

Glycoconjugates and their applications as lectin ligands in biology have been thoroughly investigated in the past decades. Meanwhile, the intrinsic properties of such multivalent molecules were limited essentially to their ability to bind to their receptors with high selectivity and/or avidity. The present review will focus on multivalent glycoconjugates displaying an additional capability such as fluorescence properties not only for applications toward imaging of cancer cells and detection of proteins or pathogens but also for drug delivery systems toward targeted cancer therapy. This review is a collection of research articles discussed in the context of the structural features of fluorescent glycoconjugates organized according to their fluorescent core scaffold and with their representative applications.

Cyclodextrin-Based Peptide Self-Assemblies (Spds) That Enhance Peptide-Based Fluorescence Imaging and Antimicrobial Efficacy.

As a result of their high specificity for their corresponding biological targets, peptides have shown significant potential in a range of diagnostic and therapeutic applications. However, their widespread use has been limited by their minimal cell permeability and stability in biological milieus. We describe here a hepta-dicyanomethylene-4H-pyran appended ß-cyclodextrin (DCM7-ß-CD) that acts as a delivery enhancing "host" for 1-bromonaphthalene-modified peptides, as demonstrated with peptide probes P1-P4. Interaction between the fluorescent peptides P1-P3 and DCM7-ß-CD results in the hierarchical formation of unique supramolecular architectures, which we term supramolecular-peptide-dots (Spds). Each Spd (Spd-1, Spd-2, and Spd-3) was found to facilitate the intracellular delivery of the constituent fluorescent probes (P1-P3), thus allowing spatiotemporal imaging of an apoptosis biomarker (caspase-3) and mitosis. Spd-4, incorporating the antimicrobial peptide P4, was found to provide an enhanced therapeutic benefit against both Gram-positive and Gram-negative bacteria relative to P4 alone. In addition, a fluorescent Spd-4 was prepared, which revealed greater bacterial cellular uptake compared to the peptide alone (P4-FITC) in E. coli. (ATCC 25922) and S. aureus (ATCC 25923). This latter observation supports the suggestion that the Spd platform reported here has the ability to facilitate the delivery of a therapeutic peptide and provides an easy-to-implement strategy for enhancing the antimicrobial efficacy of known therapeutic peptides. The present findings thus serve to highlight a new and effective supramolecular delivery approach that is potentially generalizable to overcome limitations associated with functional peptides.

A Supramolecular-Based Dual-Wavelength Phototherapeutic Agent with Broad-Spectrum Antimicrobial Activity Against Drug-Resistant Bacteria.

With the ever-increasing threat posed by the multi-drug resistance of bacteria, the development of non-antibiotic agents for the broad-spectrum eradication of clinically prevalent superbugs remains a global challenge. Here, we demonstrate the simple supramolecular self-assembly of structurally defined graphene nanoribbons (GNRs) with a cationic porphyrin (Pp4N) to afford unique one-dimensional wire-like GNR superstructures coated with Pp4N nanoparticles. This Pp4N/GNR nanocomposite displays excellent dual-modal properties with significant reactive-oxygen-species (ROS) production (in photodynamic therapy) and temperature elevation (in photothermal therapy) upon light irradiation at 660 and 808 nm, respectively. This combined approach proved synergistic, providing an impressive antimicrobial effect that led to the complete annihilation of a wide spectrum of Gram-positive, Gram-negative, and drug-resistant bacteria both in vitro and in vivo. The study also unveils the promise of GNRs as a new platform to develop dual-modal antimicrobial agents that are able to overcome antibiotic resistance.

Self-Assembled 2D Glycoclusters for the Targeted Delivery of Theranostic Agents to Triple-Negative Breast Cancer Cells.

Triple-negative breast cancer (TNBC) is a devastating disease worldwide, for which targeted imaging and therapeutic agents remain elusive. There has been growing awareness that carbohydrates are valuable as drug candidates and targeting agents for a variety of human diseases, including cancers that overexpress carbohydrate receptors on the cell surface. Here, we develop a two-dimensional (2D) glycocluster by means of simple, stepwise self-assembly for the targeted delivery of theranostic agents to TNBC cells that express mannose receptors (MRs) on the cell surface. Human serum albumin, which contains a variety of hydrophobic pockets capable of accommodating small molecules, was used to simultaneously encapsulate a mannose-based glycoprobe and a commercial photosensitizer (i.e., Ce6). The multicomponent "neoglycoprotein" formed was used to self-assemble with 2D MnO2, producing 2D glycoclusters, which could be selectively internalized by a TNBC cell line (MDA-MB-231) as facilitated by binding to the transmembrane MR. The intracellular degradation of the 2D MnO2 backbone by biothiols then released Ce6 for cell imaging and, subsequently, photodynamic therapy. This study provides insights into the development of carbohydrate-based materials for targeted, stimuli-responsive theranostics of TNBC.

Self-Assembled Thin-Layer Glycomaterials With a Proper Shell Thickness for Targeted and Activatable Cell Imaging.

The construction of targeted and activatable materials can largely improve the precision of disease diagnosis and therapy. However, the currently developed systems either target a transmembrane antigen or are activatable to release imaging and/or therapeutic reagents intracellularly. Here, we develop a simple thin-layer glycomaterial through the self-assembly between fluorescent glycoprobes, in which the carbohydrate-targeting reagent and the fluorophore are linked to each other by polyethylene glycol with a suitable chain length, and thin-layer manganese dioxide. The fluorogenic material developed is both capable of targeting a transmembrane glycoprotein receptor and fluorescently activatable by intracellular biothiols. The shell thickness of the material was determined to be important for achieving the biothiol-induced activation of fluorescence. This research might provide insight into the development of precision-enhanced self-assembled materials for disease theranostics.