Sumaira Ashraf

pH-Sensitive Capsules as Intracellular Optical Reporters for Monitoring Lysosomal pH Changes Upon Stimulation

The concept of a long-term sensor for ion changes in the lysosome is presented. The sensor is made by layer-by-layer assembly of oppositely charged polyelectrolytes around ion-sensitive fluorophores, in this case for protons. The sensor is spontaneously incorporated by cells and resides over days in the lysosome. Intracellular changes of the concentration of protons upon cellular stimulation with pH-active agents are monitored by read-out of the sensor fluorescence at real time. With help of this sensor concept it is demonstrated that the different agents used (Monensin, Chloroquine, Bafilomycin A1, Amiloride) possessed different kinetics and mechanisms of action in affecting the intracellular pH values.

Particle-Based Optical Sensing of Intracellular Ions at the Example of Calcium - What Are the Experimental Pitfalls?

Colloidal particles with fluorescence read-out are commonly used as sensors for the quantitative determination of ions. Calcium, for example, is a biologically highly relevant ion in signaling, and thus knowledge of its spatio-temporal distribution inside cells would offer important experimental data. However, the use of particle-based intracellular sensors for ion detection is not straightforward. Important associated problems involve delivery and intracellular location of particle-based fluorophores, crosstalk of the fluorescence read-out with pH, and spectral overlap of the emission spectra of different fluorophores. These potential problems are outlined and discussed here with selected experimental examples. Potential solutions are discussed and form a guideline for particle-based intracellular imaging of ions.

Gold-Based Nanomaterials for Applications in Nanomedicine

In this review, an overview of the current state-of-the-art of gold-based nanomaterials (Au NPs) in medical applications is given. The unique properties of Au NPs, such as their tunable size, shape, and surface characteristics, optical properties, biocompatibility, low cytotoxicity, high stability, and multifunctionality potential, among others, make them highly attractive in many aspects of medicine. First, the preparation methods for various Au NPs including functionalization strategies for selective targeting are summarized. Second, recent progresses on their applications, ranging from the diagnostics to therapeutics are highlighted. Finally, the rapidly growing and promising field of gold-based theranostic nano-platforms is discussed. Considering the great body of existing information and the high speed of its renewal, we chose in this review to generalize the data that have been accumulated during the past few years for the most promising directions in the use of Au NPs in current medical research.

Synthesis and functionalization of monodisperse near-ultraviolet and visible excitable multifunctional Eu3+, Bi3+:REVO4 nanophosphors for bioimaging and biosensing applications

Near-ultraviolet and visible excitable Eu- and Bi-doped NPs based on rare earth vanadates (REVO4, RE = Y, Gd) can be used for bioimaging and biosensing applications.

Zwitterionic surface coating of quantum dots reduces protein adsorption and cellular uptake.

We have studied the effect of the zwitterionic surface coating of quantum dots (QDs) on their interaction with a serum supplemented cell medium and their internalization by human cervical carcinoma (HeLa) cells. Zwitterionic QDs showed negligible adsorption of human serum albumin (HSA) selected as a model serum protein, in contrast to similar but negatively charged QDs. The incorporation of zwitterionic QDs by HeLa cells was found to be lower than for negatively charged QDs and for positively charged QDs, for which the uptake yield was largest. Our results suggest that the suppression of protein adsorption, here accomplished by zwitterionic QD surfaces, offers a strategy that allows for reducing the cellular uptake of nanoparticles.

Fluorescence-based ion-sensing with colloidal particles

Particle-based fluorescence sensors for the quantification of specific ions can be made by coupling ion-sensitive fluorophores to carrier particles, or by using intrinsically fluorescent particles whose fluorescence properties depend on the concentration of the ions. Despite the advantages of such particle-based sensors for the quantitative detection of ions, such as the possibility to tune the surface chemistry and thus entry portal of the sensor particles to cells, they have also some associated problems. Problems involve for example crosstalk of the ion-sensitive fluorescence read-out with pH, or spectral overlap of the emission spectra of different fluorescent particles in multiplexing formats. Here the benefits of using particle-based fluorescence sensors, their limitations and strategies to overcome these limitations will be described and exemplified with selected examples.

Engineering of nanoparticle size via electrohydrodynamic jetting

Abstract Engineering the physical properties of particles, especially their size, is an important parameter in the fabrication of successful carrier systems for the delivery of therapeutics. Here, various routes were explored for the fabrication of particles in the nanosize regime. It was demonstrated that the use of a charged species and/or solvent with high dielectric constant can influence the size and distribution of particles, with the charged species having a greater effect on the size of the particles and the solvent a greater effect on the distribution of the particles. In addition to the fabrication of nanoparticles, their fractionation into specific size ranges using centrifugation was also investigated. The in vitro particle uptake and intracellular transport of these nanoparticles was studied as a function of size and incubation period. The highest level of intralysosomal localization was observed for the smallest nanoparticle group (average of 174 nm), followed by the groups with increasing sizes (averages of 378 and 575 nm), most likely due to the faster endosomal uptake of smaller particles. In addition, the internalization of nanoparticle clusters and number of nanoparticles per cell increased with longer incubation periods. This work establishes a technological approach to compartmentalized nanoparticles with defined sizes. This is especially important as relatively subtle differences in size can modulate cell uptake and determine intercellular fate. Future work will need to address the role of specific targeting ligands on cellular uptake and intracellular transport of compartmentalized nanoparticles.