Marc Vendrell

Intracellular glutathione detection using MnO2-nanosheet-modified upconversion nanoparticles

We report a novel design, based on a combination of lanthanide-doped upconversion nanoparticles and manganese dioxide nanosheets, for rapid, selective detection of glutathione in aqueous solutions and living cells. In this approach, manganese dioxide (MnO(2)) nanosheets formed on the surface of nanoparticles serve as an efficient quencher for upconverted luminescence. The luminescence can be turned on by introducing glutathione that reduces MnO(2) into Mn(2+). The ability to monitor the glutathione concentration intracellularly may enable rational design of a convenient platform for targeted drug and gene delivery.

Combinatorial Strategies in Fluorescent Probe Development

Marc Vendrell,*,†,⊥ Duanting Zhai,‡ Jun Cheng Er,‡,§ and Young-Tae Chang*,†,‡ †Laboratory of Bioimaging Probe Development, Singapore Bioimaging Consortium, Agency for Science, Technology and Research (A*STAR), 11 Biopolis Way, 138667 Singapore ‡Department of Chemistry and MedChem Program for Life Sciences, National University of Singapore, 3 Science Drive 3, 117543 Singapore Graduate School for Integrative Sciences and Engineering, National University of Singapore, Centre for Life Sciences, #05-01, 28 Medical Drive, 117456 Singapore

Surface-enhanced Raman scattering in cancer detection and imaging.

Technologies that use surface-enhanced Raman scattering (SERS) have experienced significant growth in biomedical research during the past 4 years. In this review we summarize the progress in SERS for cancer diagnostics, including multiplexed detection and identification of new biomarkers, single-nucleotide polymorphisms, and circulating tumor cells. SERS is also used as a non-invasive tool for cancer imaging with immunoSERS microscopy, histological analysis of biopsies, and in vivo detection of tumors. We discuss the future of SERS probes compatible with multiple imaging modalities and their potential for clinical translation (e.g., endoscope-based and intraoperative imaging as tools for surgical guidance). Moreover, we highlight the potential of SERS agents for targeted drug delivery and photothermal therapy.

Synthesis of a BODIPY Library and Its Application to the Development of Live Cell Glucagon Imaging Probe

The first BODIPY library (BD) was synthesized, and a highly selective glucagon sensor, Glucagon Yellow (BD-105), was discovered by fluorescence image-based screening method. BD library was synthesized via a Knoevenagel-type condensation reaction with 160 benzaldehydes and the 1,3 dimethyl-BODIPY scaffold. Using BD compounds, a fluorescence image-based screening was performed against three cell lines including AlphaTC1 and BetaTC6 cells which secret glucagon and insulin, respectively, and HeLa as control cells. Out of the 160 candidate probes, one compound, Glucagon Yellow, exhibited selective staining only in AlphaTC1 cells. The selectivity of Glucagon Yellow toward glucagon was confirmed in vitro by comparison of its fluorescence intensity change against 19 biologically relevant analytes. Subsequent immunostaining experiments revealed that Glucagon Yellow and the glucagon antibody colocalized in pancreas tissue, showing a high quantitative correlation analysis by the Pearsons coefficient constant (R(r) = 0.950). These results demonstrated the potential application of Glucagon Yellow as a glucagon imaging agent in live cells and tissues.

Multicomponent Reactions for de Novo Synthesis of BODIPY Probes: In Vivo Imaging of Phagocytic Macrophages

Multicomponent reactions are excellent tools to generate complex structures with broad chemical diversity and fluorescent properties. Herein we describe the adaptation of the fluorescent BODIPY scaffold to multicomponent reaction chemistry with the synthesis of BODIPY adducts with high fluorescence quantum yields and good cell permeability. From this library we identified one BODIPY derivative (PhagoGreen) as a low-pH sensing fluorescent probe that enabled imaging of phagosomal acidification in activated macrophages. The fluorescence emission of PhagoGreen was proportional to the degree of activation of macrophages and could be specifically blocked by bafilomycin A, an inhibitor of phagosomal acidification. PhagoGreen does not impair the normal functions of macrophages and can be used to image phagocytic macrophages in vivo.

MegaStokes BODIPY-triazoles as environmentally sensitive turn-on fluorescent dyes

A novel class of triazole-derivatized BODIPY compounds have been synthesized on solid-phase by employing mild reaction conditions based on the copper-catalyzed azide–alkyne cycloaddition. The resulting BODIPY-triazoles exhibited MegaStokes shifts (up to 160 nm) and remarkable environmentally sensitive quantum yield increments that asserted their potential as turn-on fluorescent sensors. Out of a library of 120 compounds, we identified BDC-9 as a fluorescent chemosensor with high sensitivity and remarkable species-selectivity towards human serum albumin. These results validate MegaStokes BODIPY dyes as new fluorophores for the development of environmentally sensitive fluorescent probes.

Fluorescent Dye Cocktail for Multiplex Drug-Site Mapping on Human Serum Albumin

Elucidating how molecules bind to HSA is fundamental for predicting drug incompatibilities. Through combinatorial screening, we identified a novel fluorescent dye (BD140) with turn-on fluorescence emission and specific binding at HSA drug site 2. We further combined it with dansylamide to develop a fluorescent dye cocktail for high-throughput mapping of the interaction between therapeutics at HSA drug-binding sites.

Synthesis of a Novel BODIPY Library and Its Application in the Discovery of a Fructose Sensor

We prepared a new library of 160 compounds by conjugation of a BODIPY core to a collection of aldehydes. This library was screened against 52 biologically relevant analytes and we identified one fluorescent sensor of fructose (Fructose Orange). Fructose Orange showed a 24-fold fluorescence increase upon recognition of fructose and an outstanding selectivity among 24 different saccharides. NMR studies confirmed that five different binding interactions were formed between the sensor and fructose. Furthermore, Fructose Orange was applied to the quantification of fructose in soft drinks, being the most selective fluorescent sensor for fructose reported to date.

Modern Synthetic Avenues for the Preparation of Functional Fluorophores

Abstract Biomedical research relies on the fast and accurate profiling of specific biomolecules and cells in a non‐invasive manner. Functional fluorophores are powerful tools for such studies. As these sophisticated structures are often difficult to access through conventional synthetic strategies, new chemical processes have been developed in the past few years. In this Minireview, we describe the most recent advances in the design, preparation, and fine‐tuning of fluorophores by means of multicomponent reactions, C−H activation processes, cycloadditions, and biomolecule‐based chemical transformations.

Spacer-free BODIPY fluorogens in antimicrobial peptides for direct imaging of fungal infection in human tissue

Fluorescent antimicrobial peptides are promising structures for in situ, real-time imaging of fungal infection. Here we report a fluorogenic probe to image Aspergillus fumigatus directly in human pulmonary tissue. We have developed a fluorogenic Trp-BODIPY amino acid with a spacer-free C-C linkage between Trp and a BODIPY fluorogen, which shows remarkable fluorescence enhancement in hydrophobic microenvironments. The incorporation of our fluorogenic amino acid in short antimicrobial peptides does not impair their selectivity for fungal cells, and enables rapid and direct fungal imaging without any washing steps. We have optimized the stability of our probes in human samples to perform multi-photon imaging of A. fumigatus in ex vivo human tissue. The incorporation of our unique BODIPY fluorogen in biologically relevant peptides will accelerate the development of novel imaging probes with high sensitivity and specificity.