Systematic Study of Fluorescein-Functionalized Macrophotoinitiators for Colorimetric Bioassays

Substituent Effects of Fluorescein on Photoredox Initiating Performance under Visible Light

We demonstrated the effects of substituents in fluorescein on the photoredox catalytic performance under visible light. For the systematic investigation, the phenyl ring of fluorescein was substituted with six different functional groups (i.e., amine, amide, isothiocyanate, aminomethyl, bromo, or nitro group) at the 5- or 6-position. The fluorescein derivatives were carefully characterized through photophysical and electrochemical analyses. The substituent effects were estimated by comparing the photopolymerization of poly(ethylene glycol) diacrylate (PEGDA) and N-vinylpyrrolidone (VP) in the presence of triethanolamine (TEOA) under aerobic conditions to that of intact fluorescein. As a result, the amine and nitro groups exhibited the lowest performances, presumably due to intramolecular photoinduced electron transfer (PET) promoted by the strong electron push-pull effect. The others, representative moderate or weak deactivators and activators, exhibited inferior performances than intact fluorescein, presumably owing to the more negative ΔGPET values, resulting in a decreased rate of intermolecular PET. These results are crucial for understanding the structure-performance relationship and the development of visible-light photoredox catalysts with improved performance and functionality.

Visible-Light-Mediated Radical Arylations Using a Fluorescein-Derived Diazonium Salt: Reactions Proceeding via an Intramolecular Forth and Back Electron Transfer

Functionalizations of arenes and alkenes via additive-free radical reactions using highly photosensitive, fluorescein-derived diazonium salts are described. The particular properties of the diazonium salts enable unique Meerwein-type carbohydroxylations of non-activated alkenes, which can be rationalized by a reaction mechanism involving forth and back electron transfer from and to the xanthene subunit of the fluorescein moiety.

Photoinitiated Free-Radical Polymerization of 4,5,6,7-Tetrahalogenated Fluoresceins

We demonstrated the photoredox catalytic performances of fluorescein derivatives, bearing heavy halogen atoms (Br or I) on a benzoic acid group, using photoinitiated free-radical polymerization. 4,5,6,7-Tetrabromofluorescein and 4,5,6,7-tetraiodofluorescein were used as visible-light-photoredox catalysts to initiate polymerization of poly(ethylene glycol) diacrylate and N-vinylpyrrolidone in the presence of triethanolamine under aerobic conditions. Their photocatalytic performances were evaluated by the hydrogelation of photopolymerization both on the surface of an agarose film and in a liquid solution. The polymerization degree increased considerably in the following order: tetraiodofluorescein<tetrabromofluorescein<fluorescein. This result was different from fluorescein derivatives containing the heavy halogen atoms on a xanthene core ring. Consequently, the location of the heavy halogen atoms was crucial in the photocatalytic performance of fluorescein derivatives.

Naked-eye detection of Hg(ii) ions by visible light-induced polymerization initiated by a Hg(ii)-selective photoredox catalyst

A selective turn-on photoredox catalyst extends the applications of visible light-induced polymerization.

Applications of gold nanoparticles in ELISA, PCR, and immuno-PCR assays: A review

Development of state-of-the-art assays for sensitive and specific detection of disease biomarkers has received significant interest for early detection and prevention of various diseases. Enzyme Linked Immunosorbent assays (ELISA) and Polymerase Chain Reaction (PCR) are two examples of proteins and nucleic acid detection assays respectively, which have been widely used for the sensitive detection of target analytes in biological fluids. Recently, immuno-PCR has emerged as a sensitive detection method, where high specificity of sandwich ELISA assays is combined with high sensitivity of PCR for trace detection of biomarkers. However, inherent disadvantages of immuno-PCR assays limit their application as rapid and sensitive detection method in clinical settings. With advances in nanomaterials, nanoparticles-based immunoassays have been widely used to improve the sensitivity and simplicity of traditional immunoassays. Owing to facile synthesis, surface functionalization, and superior optical and electronic properties, gold nanoparticles have been at the forefront of sensing and detection technologies and have been extensively studied to improve the efficacies of immunoassays. This review provides a brief history of immuno-PCR assays and specifically focuses on the role of gold nanoparticles to improve the sensitivity and specificity of ELISA, PCR and immuno-PCR assays.

Radical polymerization reactions for amplified biodetection signals

This review summarizes various radical polymerization chemistries for amplifying biodetection signals and compares them from the practical point of view.

Gold nanoparticle triggered siloxane formation for polymerization based amplification in enzyme free visual immunoassay

Herein, we report a new signal amplification scheme for quantitative biochemical analysis based on gold nanoparticle (GNPs) catalyzed polymerization of transparent silane solution to milky white and turbid siloxane. Using immunoassay as a proof of concept, GNP labeled immunoprobe was used to bind captured antigen and catalyse the polymerization reaction allowing sensitive biochemical investigation. The polymerization reaction was optimized for standard 96 well polystyrene microtiter plates and we discovered that sodium lactate acts as an enhancer in the polymerization reaction as it reduces detection time to merely 30 min. The sensing strategy was applied to detection and quantification of Salmonella Typhimurium in water and egg samples and the platform showed excellent visibly quantifiable analytical response up to 100 cells mL^-1. Furthermore, clinical utility and potential of the method was validated by detecting Vi capsular polysaccharide (Vi antigen) responsible for typhoidal Salmonellosis in human serum in sandwich format with a detection limit of 1 ng mL^-1. The method serves as the first report towards nanoparticle triggered polymerization for development of rapid and low cost quantitative biochemical assay.

Liposome-Enhanced Polymerization-Based Signal Amplification for Highly Sensitive Naked-Eye Biodetection in Paper-Based Sensors

Polymerization-based signal amplification (PBA) is a material-based approach to improving the sensitivity of paper-based diagnostic tests. Eosin Y is used as an assay label to photo-initiate free-radical polymerization to produce colored hydrogels in the presence of target analytes captured by bioactive paper. PBA achieves high-contrast and time-independent signals, but its nanomolar detection limit makes it impractical for early diagnosis of many diseases. In this work, we demonstrated efficient localization of large quantities of eosin Y per captured target analyte by incorporating eosin Y-loaded liposomes into PBA. This new "materials approach" allowed 30-fold signal enhancement compared to conventional PBA. To further improve the detection limit of liposome-enhanced PBA, we used a continuous flow-through assay format with 100 μL of analyte solution, achieving sub-nanomolar detection limits with high-contrast signals that were easily discernible to the unaided eye.

The heavy-atom effect on xanthene dyes for photopolymerization by visible light

Heavy halogen atoms on the xanthene ring significantly increase the photoredox catalytic performance for visible-light-induced photopolymerization.

Cell-Surface Engineering for Advanced Cell Therapy

Stem cells opened great opportunity to overcome diseases that conventional therapy had only limited success. Use of scaffolds made from biomaterials not only helps handling of stem cells for delivery or transplantation but also supports enhanced cell survival. Likewise, cell encapsulation can provide stability for living animal cells even in a state of separateness. Although various chemical reactions were tried to encapsulate stolid microbial cells such as yeasts, a culture environment for the growth of animal cells allows only highly biocompatible reactions. Therefore, the animal cells were mostly encapsulated in hydrogels, which resulted in enhanced cell survival. Interestingly, major findings of chemistry on biological interfaces demonstrate that cell encapsulation in hydrogels have a further a competence for modulating cell characteristics that can go beyond just enhancing the cell survival. In this review, we present a comprehensive overview on the chemical reactions applied to hydrogel-based cell encapsulation and their effects on the characteristics and behavior of living animal cells.

Comparison of eosin and fluorescein conjugates for the photoinitiation of cell-compatible polymer coatings

Targeted photopolymerization is the basis for multiple diagnostic and cell encapsulation technologies. While eosin is used in conjunction with tertiary amines as a water-soluble photoinitiation system, eosin is not widely sold as a conjugate with antibodies and other targeting biomolecules. Here we evaluate the utility of fluorescein-labeled bioconjugates to photopolymerize targeted coatings on live cells. We show that although fluorescein conjugates absorb approximately 50% less light energy than eosin in matched photopolymerization experiments using a 530 nm LED lamp, appreciable polymer thicknesses can still be formed in cell compatible environments with fluorescein photosensitization. At low photoinitiator density, eosin allows more sensitive initiation of gelation. However at higher functionalization densities, the thickness of fluorescein polymer films begins to rival that of eosin. Commercial fluorescein-conjugated antibodies are also capable of generating conformal, protective coatings on mammalian cells with similar viability and encapsulation efficiency as eosin systems.

Backfilling-Free Strategy for Biopatterning on Intrinsically Dual-Functionalized Poly[2-Aminoethyl Methacrylate-co-Oligo(Ethylene Glycol) Methacrylate] Films

We demonstrated protein and cellular patterning with a soft lithography technique using poly[2-aminoethyl methacrylate-co-oligo(ethylene glycol) methacrylate] films on gold surfaces without employing a backfilling process. The backfilling process plays an important role in successfully generating biopatterns; however, it has potential disadvantages in several interesting research and technical applications. To overcome the issue, a copolymer system having highly reactive functional groups and bioinert properties was introduced through a surface-initiated controlled radical polymerization with 2-aminoethyl methacrylate hydrochloride (AMA) and oligo(ethylene glycol) methacrylate (OEGMA). The prepared poly(AMA-co-OEGMA) film was fully characterized, and among the films having different thicknesses, the 35 nm-thick biotinylated, poly(AMA-co-OEGMA) film exhibited an optimum performance, such as the lowest nonspecific adsorption and the highest specific binding capability toward proteins.

The Role of Surface Receptor Density in Surface-Initiated Polymerizations for Cancer Cell Isolation

Fluid biopsies potentially offer a minimally invasive alternative to traditional tissue biopsies for the continual monitoring of metastatic cancer. Current established technologies for isolating circulating tumor cells (CTCs) suffer from poor purity and yield and require fixatives that preclude the collection of viable cells for longitudinal analyses of biological function. Antigen specific lysis (ASL) is a rapid, high-purity method of cell isolation based on targeted protective coatings on antigen-presenting cells and lysis depletion of unprotected antigen-negative cells. In ASL, photoinitiators are specifically labeled on cell surfaces that enable subsequent surface-initiated polymerization. Critically, the significant determinants of process yield have yet to be investigated for this emerging technology. In this work, we show that the labeling density of photoinitiators is strongly correlated with the yield of intact cells during ASL by flow cytometry analysis. Results suggest ASL is capable of delivering ∼25% of targeted cells after isolation using traditional antibody labeling approaches. Monomer formulations of two molecular weights of PEG-diacrylate (Mn ∼ 575 and 3500) are examined. The gelation response during ASL polymerization is also investigated via protein microarray analogues on planar glass. Finally, a density threshold of photoinitiator labeling required for protection during lysis is determined for both monomer formulations. These results indicate ASL is a promising technology for high yield CTC isolation for rare-cell function assays and fluid biopsies.

Using photo-initiated polymerization reactions to detect molecular recognition

Radical polymerization reactions initiated by light can be used to provide signal amplification in molecular binding assays.

Protective Polymer Coatings for High-Throughput, High-Purity Cellular Isolation

Cell-based therapies are emerging as the next frontier of medicine, offering a plausible path forward in the treatment of many devastating diseases. Critically, current methods for antigen positive cell sorting lack a high throughput method for delivering ultrahigh purity populations, prohibiting the application of some cell-based therapies to widespread diseases. Here we show the first use of targeted, protective polymer coatings on cells for the high speed enrichment of cells. Individual, antigen-positive cells are coated with a biocompatible hydrogel which protects the cells from a surfactant solution, while uncoated cells are immediately lysed. After lysis, the polymer coating is removed through orthogonal photochemistry, and the isolate has >50% yield of viable cells and these cells proliferate at rates comparable to control cells. Minority cell populations are enriched from erythrocyte-depleted blood to >99% purity, whereas the entire batch process requires 1 h and <$2000 in equipment. Batch scale-up is only contingent on irradiation area for the coating photopolymerization, as surfactant-based lysis can be easily achieved on any scale.

Characterization of molecular transport in ultrathin hydrogel coatings for cellular immunoprotection

PEG hydrogels are routinely used in immunoprotection applications to hide foreign cells from a host immune system. Size-dependent transport is typically exploited in these systems to prevent access by macromolecular elements of the immune system while allowing the transport of low molecular weight nutrients. This work studies a nanoscale hydrogel coating for improved transport of beneficial low molecular weight materials across thicker hydrogel coatings while completely blocking transport of undesired larger molecular weight materials. Coatings composed of PEG diacrylate of molecular weight 575 and 3500 Da were studied by tracking the transport of fluorescently labeled dextrans across the coatings. The molecular weight of dextran at which the transport is blocked by these coatings are consistent with cutoff values in analogous bulk PEG materials. Additionally, the diffusion constants of 4 kDa dextrans across PEG 575 coatings (9.5 × 10(-10)-2.0 × 10(-9) cm(2)/s) was lower than across PEG 3500 coatings (5.9-9.8 × 10(-9) cm(2)/s), and these trends and magnitudes agree with bulk scale models. Overall, these nanoscale thin PEG diacrylate films offer the same size selective transport behavior of bulk PEG diacrylate materials, while the lower thickness translates directly to increased flux of beneficial low molecular weight materials.

Investigation of dendrimers functionalized with eosin as macrophotoinitiators for polymerization-based signal amplification reactions

Water-soluble macrophotoinitiators with up to 24 eosin substituents and one protein per dendrimer were assessed in interfacial binding assays.

Interfacial polymerization for colorimetric labeling of protein expression in cells

Determining the location of rare proteins in cells typically requires the use of on-sample amplification. Antibody based recognition and enzymatic amplification is used to produce large amounts of visible label at the site of protein expression, but these techniques suffer from the presence of nonspecific reactivity in the biological sample and from poor spatial control over the label. Polymerization based amplification is a recently developed alternative means of creating an on-sample amplification for fluorescence applications, while not suffering from endogenous labels or loss of signal localization. This manuscript builds upon polymerization based amplification by developing a stable, archivable, and colorimetric mode of amplification termed Polymer Dye Labeling. The basic concept involves an interfacial polymer grown at the site of protein expression and subsequent staining of this polymer with an appropriate dye. The dyes Evans Blue and eosin were initially investigated for colorimetric response in a microarray setting, where both specifically stained polymer films on glass. The process was translated to the staining of protein expression in human dermal fibroblast cells, and Polymer Dye Labeling was specific to regions consistent with desired protein expression. The labeling is stable for over 200 days in ambient conditions and is also compatible with modern mounting medium.