The thiourea group modulates the fluorescence emission decay of fluorescein-labeled molecules

Uptake Quantification of Antigen Carried by Nanoparticles and Its Impact on Carrier Adjuvanticity Evaluation

Nanoparticles have been identified in numerous studies as effective antigen delivery systems that enhance immune responses. However, it remains unclear whether this enhancement is a result of increased antigen uptake when carried by nanoparticles or the adjuvanticity of the nanoparticle carriers. Consequently, it is important to quantify antigen uptake by dendritic cells in a manner that is free from artifacts in order to analyze the immune response when antigens are carried by nanoparticles. In this study, we demonstrated several scenarios (antigens on nanoparticles or inside cells) that are likely to contribute to the generation of artifacts in conventional fluorescence-based quantification. Furthermore, we developed the necessary assay for accurate uptake quantification. PLGA NPs were selected as the model carrier system to deliver EsxB protein (a Staphylococcus aureus antigen) in order to testify to the feasibility of the established method. The results showed that for the same antigen uptake amount, the antigen delivered by PLGA nanoparticles could elicit 3.6 times IL-2 secretion (representative of cellular immune response activation) and 1.5 times IL-12 secretion (representative of DC maturation level) compared with pure antigen feeding. The findings above give direct evidence of the extra adjuvanticity of PLGA nanoparticles, except for their delivery functions. The developed methodology allows for the evaluation of immune cell responses on an antigen uptake basis, thus providing a better understanding of the origin of the adjuvanticity of nanoparticle carriers. Ultimately, this research provides general guidelines for the formulation of nano-vaccines.

NIR-Fluorescent Multidye Silica Nanoparticles with Large Stokes Shifts for Versatile Biosensing Applications

We have synthesized and characterized of a series of single and multidye copolymerized nanoparticles with large to very large Stokes shifts (100 to 255 nm) for versatile applications as standalone or multiplexed probes in biological matrices. Nanoparticles were prepared via the Stöber method and covalently copolymerized with various combinations of three dyes, including one novel aminocyanine dye. Covalently encapsulated dyes exhibited no significant leakage from the nanoparticle matrix after more than 200 days of storage in ethanol. Across multiple batches of nanoparticles with varying dye content, the average yields and average radii were found to be highly reproducible. Furthermore, the batch to batch variability in the relative amounts of dye incorporated was small (relative standard deviations <2.3%). Quantum yields of dye copolymerized nanoparticles were increased 50% to 1000% relative to those of their respective dye-silane conjugates, and fluorescence intensities were enhanced by approximately three orders of magnitude. Prepared nanoparticles were surface modified with polyethylene glycol and biotin and bound to streptavidin microspheres as a proof of concept. Under single wavelength excitation, microsphere-bound nanoparticles displayed readily distinguishable fluorescence signals at three different emission wavelengths, indicating their potential applications to multicolor sensing. Furthermore, nanoparticles modified with polyethylene glycol and biotin demonstrated hematoprotective qualities and reduced nonspecific binding of serum proteins, indicating their potential suitability to in vivo imaging applications.

Isothiocyanyl Alanine as a Synthetic Intermediate for the Synthesis of Thioureayl Alanines and Subsequent Aminotetrazolyl Alanines

The synthesis of unnatural amino acids with small side-chain functionalities usable for further transformations is highly demanding for the expansion of the genetic code and other possible biotechnological applications. To this end, we wanted to report the utility of an unexplored unnatural amino acid, isothiocyanyl alanine (^NCSAla = Ita), for the synthesis of another class of unnatural amino acids, thioureayl alanines (^TUAla = Tua). The synthesis of a third class of unnatural amino acids, amino tetrazolyl alanines (^ATzAla = Ata), in a very good yield was subsequently achieved utilizing thioureayl alanines. Thus, a variety of aliphatic- and aromatic-substituted thioureayl alanines and aromatic-substituted amino tetrazolyl alanines were successfully synthesized in good to excellent yields. The photophysical properties of three of the fluorescent unnatural amino acids from two classes were also studied and presented herein.

A convenient, bio-inspired approach to the synthesis of multi-functional, stable fluorescent silica nanoparticles using poly(ethylene-imine)

Branched poly(ethylene-imine) can be tagged with luminescent dyes (e.g., fluorescein isothiocyanate and tetramethylrhodamine isothiocyanate) and used to precipitate spherical silica particles from 10s-to-100s of nm diameter size under mild conditions. These dye-PEI/SiO₂ nanoparticles are highly compatible with polar solvents to give bright fluorescent suspensions, and detailed photophysical characterization reveals well-separated dye moieties with an approximately homogeneous dispersion of dye-PEI conjugate throughout the SiO₂ matrix. Reaction of PEI amine groups incorporated at the particle surface affords a simple method for post-synthesis functionalization of these materials, and the formation of FITC/Eosin-Y fluorescence resonance energy transfer pair-tagged particles and SiO₂@Au core-shell nanocomposites using this strategy is demonstrated. This bio-inspired approach to multi-functional SiO₂ nanoparticles provides a range of potential advantages over traditional "inorganic" syntheses of similar materials, as it proceeds through a scalable, single-step reaction using inexpensive reagents, enables efficient incorporation of luminescent species into the resulting particles with very limited dye aggregation, and provides nanoparticles that do not require post-synthesis modification for further conjugation with species of interest. The method offers a simple means to generate complex nanocomposites, whereby a host of desired species can be incorporated both inside and on the surface of biocompatible SiO₂ nanoparticles.

The interaction of Hg2+and trivalent ions with two new fluorescein bio-inspired dual colorimetric/fluorimetric probes

Two new bio-inspired fluorescein derivatives were successfully synthesized and both the compounds showed a “turn on” fluorescence in the presence of trivalent (Al³⁺, Fe³⁺, Ga³⁺, Cr³⁺) and Hg²⁺metal ions, forming mononuclear complexes in acetonitrile.

A novel fluoro-chromogenic click reaction for the labelling of proteins and nanoparticles with near-IR theranostic agents

Binding of red-absorbing porphycene isothiocyanates to proteins and nanoparticles leads to near-IR fluorescent and photosensitising conjugates.

Complex coacervate core micelles as diffusional nanoprobes

Because of their ease of preparation and versatile modification opportunities, complex coacervate core micelles (C3Ms) may be a good alternative for expensive diffusional probes, such as dendrimers. However, C3Ms are unstable at high salt concentrations and may fall apart in contact with other polymers or (solid) materials. Therefore, we designed and characterized small (15 nm radius), stable fluorescent C3Ms. These were formed by electrostatic interactions between poly(ethylene oxide-methacrylic acid) (PEO-PMAA) and fluorescently labelled poly(allylamine hydrochloride) (PAH) and irreversible cross-linking of the core through amide bonds. We compared the properties of the cross-linked and non-cross-linked micelles. The radii of the two types of micelles were quite similar and independent of the ionic strength. Surprisingly, both were found to be stable at salt concentrations as high as 1.5 M. However, unlike the non-cross-linked C3Ms, the stability of the cross-linked C3Ms is independent of the pH. As a first example of their application as diffusional nanoprobes, we present results on the diffusion of the fluorescent micelles measured in xanthan solutions using fluorescence recovery after photobleaching (FRAP).

Thioamide quenching of fluorescent probes through photoinduced electron transfer: mechanistic studies and applications

Previously we have shown that thioamides can be incorporated into proteins as minimally perturbing fluorescence-quenching probes to study protein dynamics, folding, and aggregation. Here, we show that the spontaneity of photoinduced electron transfer between a thioamide and an excited fluorophore is governed by the redox potentials of each moiety according to a Rehm-Weller-type model. We have used this model to predict thioamide quenching of various common fluorophores, and we rigorously tested more than a dozen examples. In each case, we found excellent agreement between our theoretical predictions and experimental observations. In this way, we have been able to expand the scope of fluorophores quenched by thioamides to include dyes suitable for microscopy and single-molecule studies, including fluorescein, Alexa Fluor 488, BODIPY FL, and rhodamine 6G. We describe the photochemistry of these systems and explore applications that demonstrate the utility of thioamide quenching of fluorescein to studying protein folding and proteolysis.

Development of novel fluorescent probes for the analysis of protein interactions under physiological conditions with medical devices

In this article, a method to analyze protein adsorption on porous, clinically relevant samples under physiologically relevant conditions is described. The use of fluorescent probes was identified as a methodology that would facilitate analysis under a range of conditions including fully competitive conditions where a protein of interest may be labeled in isolation and then allowed to compete with unlabeled proteins on samples that require no specialized surface pretreatment. As a first step, this article describes the covalent labeling of isolated bovine serum albumin (BSA) with fluorescent fluoresceinthioureidoaminocaproic acid, FTCA, giving FTCA-BSA. The fluorescence intensity of FTCA-BSA was then used to monitor the adsorption and desorption of the protein under noncompetitive conditions with two forms of hydroxyapatite discs (silicate-substituted, SA and stoichiometric, HA) in phosphate-buffered saline (PBS) and minimum essential Eagles' medium (MEM). Noncompetitive conditions were used to facilitate the validation of the technique in which data obtained from these experiments were corroborated against data obtained using an established total protein assay method (Quant-IT kit, Invitrogen). These experiments demonstrated that the FTCA-BSA probe had several advantages including a greater sensitivity at lower concentrations and a considerably longer lifetime. The results also demonstrated that the interaction of BSA with SA and HA was also highly temperature- and media-dependent. Under the most physiologically relevant conditions of MEM at 37 °C, BSA was more readily adsorbed to SA with significant differences between biomaterials, but no differences were observed during the desorption process. The use of this method to analyze adsorption under competitive conditions will be the subject of further investigations.

Fluorescence correlation spectroscopy reveals strong fluorescence quenching of FITC adducts on PEGylated gold nanoparticles in water and the presence of fluorescent aggregates of desorbed thiolate ligands

Colloidal gold particles functionalised with oligoethylene-glycolated disulfide ligands and fluorescent moieties derived from fluorescein isothiocyanate (FITC) have been prepared and studied in aqueous suspension using fluorescence correlation spectroscopy (FCS). FCS probes the dynamics of the particles at the single object level, and reveals the desorption of fluorescent ligands which subsequently aggregate into larger (slower diffusing) objects. Cross-correlation spectroscopy of the FITC fluorescence and the Rayleigh-Mie scattering (RM-FCCS) of the gold cores shows that the only detectable fluorescent objects are free ligands and aggregates not associated with a gold particle. The fluorescence of bound fluorophores is quenched making their fluorescence too weak to be detected. FCS and RM-FCCS are useful tools for characterising functionalised noble metal particles in solution, under conditions similar to those used in optical bio-imaging. Desorption of thiolates from gold nanoparticles needs to be taken into account when working with these materials at low concentration.

Probing the interactions between disulfide-based ligands and gold nanoparticles using a functionalised fluorescent perylene-monoimide dye

The binding of disulfides to gold nanoparticles was investigated using fluorescence spectroscopy and a perylene-monoimide dye coupled to a dissymmetric disulfide via a tetraethyleneglycolalkyl chain (PMImSS). Quantum chemical calculations using the polarizable continuum model (PCM) predict a strong quenching of perylene-monoimide fluorescence by gold nanoparticles as a result of efficient excitation energy transfer from the dye to the particle. Such quenching is indeed observed when unfunctionalised gold nanoparticles are added to a solution of PMImSS. The fluorimetric titration curves show behaviour indicative of the existence of an equilibrium between free and bound ligands (association constant 5 x 10(5) M(-1)), whereas the affinity of thiols and disulfide for gold surfaces is in general assumed to be much higher. Gold nanoparticles fully functionalised with PMImSS were synthesised and purified. Fluorescence correlation spectroscopy shows the appearance of free PMImSS ligands in dilute (approx. pM) suspensions of these PMImSS-functionalised nanoparticles over a period of several days.

Optical properties of fluorescein-labeled organoclay

We report the preparation of aminopropyl-functionalized magnesium phyllosilicate (Mg-organoclay) conjugated to fluorescein isothiocyanate (FITC) functionality (FITC-organoclay) by one-pot sol-gel synthesis. The physical characteristics of the Mg- and FITC-organoclays were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR and UV-Vis spectrophotometry. X-ray fluorescence and elemental analysis were conducted to confirm the composition of the Mg-organoclay. The FITC-organoclay particles were polydispersed with an average particle size of approximately 50 nm, as determined from SEM images. The XRD patterns of FITC-organoclay exhibited broad peaks and reduced basal d(001) indicating a less condensed and more disordered structure than was observed for Mg-organoclay. The conjugation between FITC- and Mg-organoclay was characterized by FT-IR spectroscopy. Fluorescence excitation and emission spectral data demonstrated the successful conjugation of FITC dye molecules to the Mg-organoclay. The time-resolved fluorescence measurements revealed that FITC had a lifetime of 4.58 ns, whereas the lifetime of FITC-organoclay required a double exponential fit (tau(1,2) = 0.72 and 2.68 ns). As a result, the lifetime of the FITC-organoclay was shorter than that of FITC in ethanol and indicated moderate photostability in the solution state. The cellular uptake of FITC-organoclay in human lung alveolar carcinoma epithelial cells (A549) was quantified and characterized.