Monitoring and manipulation of the pH of single cells using infrared spectromicroscopy and a molecular switch

Top-Down N-Doped Carbon Quantum Dots for Multiple Purposes: Heavy Metal Detection and Intracellular Fluorescence

In the present study, we successfully synthesized N-doped carbon quantum dots (N-CQDs) using a top-down approach, i.e., hydroxyl radical opening of fullerene with hydrogen peroxide, in basic ambient using ammonia for two different reaction times. The ensuing characterization via dynamic light scattering, SEM, and IR spectroscopy revealed a size control that was dependent on the reaction time, as well as a more pronounced -NH2 functionalization. The N-CQDs were probed for metal ion detection in aqueous solutions and during bioimaging and displayed a Cr3+ and Cu2+ selectivity shift at a higher degree of -NH2 functionalization, as well as HEK-293 cell nuclei marking.

The reversed intra- and extracellular pH in tumors as a unified strategy to chemotherapeutic delivery using targeted nanocarriers

Solid tumors are complex entities, comprising a wide variety of malignancies with very different molecular alterations. Despite this, they share a set of characteristics known as "hallmarks of cancer" that can be used as common therapeutic targets. Thus, every tumor needs to change its metabolism in order to obtain the energy levels required for its high proliferative rates, and these adaptations lead to alterations in extra- and intracellular pH. These changes in pH are common to all solid tumors, and can be used either as therapeutic targets, blocking the cell proton transporters and reversing the pH changes, or as means to specifically deliver anticancer drugs. In this review we will describe how proton transport inhibitors in association with nanocarriers have been designed to block the pH changes that are needed for cancer cells to survive after their metabolic adaptations. We will also describe studies aiming to decrease intracellular pH in cancer using nanoparticles as molecular cages for protons which will be released upon UV or IR light exposure. Finally, we will comment on several studies that have used the extracellular pH in cancer for an enhanced cell internalization and tumor penetration of nanocarriers and a controlled drug delivery, describing how nanocarriers are being used to increase drug stability and specificity.

Photoactivated release of membrane impermeant sulfonates inside cells

Photouncaging delivers compounds with high spatial and temporal control to induce or inhibit biological processes but the released compounds may diffuse out. We here demonstrate that sulfonate anions can be photocaged so that a membrane impermeable compound can enter cells, be uncaged by photoirradiation and trapped within the cell.

Photocaged sulfonate delivers membrane impermeant compounds to cells.

Microfluidic approaches to synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectral microscopy of living biosystems

A long-standing desire in biological and biomedical sciences is to be able to probe cellular chemistry as biological processes are happening inside living cells. Synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectral microscopy is a label-free and nondestructive analytical technique that can provide spatiotemporal distributions and relative abundances of biomolecules of a specimen by their characteristic vibrational modes. Despite great progress in recent years, SR-FTIR imaging of living biological systems remains challenging because of the demanding requirements on environmental control and strong infrared absorption of water. To meet this challenge, microfluidic devices have emerged as a method to control the water thickness while providing a hospitable environment to measure cellular processes and responses over many hours or days. This paper will provide an overview of microfluidic device development for SR-FTIR imaging of living biological systems, provide contrast between the various techniques including closed and open-channel designs, and discuss future directions of development within this area. Even as the fundamental science and technological demonstrations develop, other ongoing issues must be addressed; for example, choosing applications whose experimental requirements closely match device capabilities, and developing strategies to efficiently complete the cycle of development. These will require imagination, ingenuity and collaboration.

Exogenous control over intracellular acidification: Enhancement via proton caged compounds coupled to gold nanoparticles and an alternative pathway with DMSO

Proton caged compounds exhibit a characteristic behavior when directly dosed into cells or being coupled to gold nanoparticles prior to the dosing. When irradiated in the near ultraviolet region, they release protons that interact with intracellular HCO₃⁻ to yield H₂CO₃. The dissociation of carbonic acid, then, releases CO₂ that can be distinctively singled out in infrared spectra.

In the process of searching a pathway to augment the intracellular uptake of proton caged compounds, we probed the association of 1-(2-nitrophenyl)-ethylhexadecyl sulfonate (HDNS) with DMSO, an agent to enhance the membrane permeability. We found out a different UV-induced protonation mechanism that opens up to new conduits of employing of proton caged compounds. Here, we report the infrared data we collected in this set of experiments.

Synthesis of proton caged disulphide compounds for gold nanoparticle functionalization

Novel proton caged compounds have been synthesized, with a sulphur bridge to bind gold nanoparticles and release protons upon UV irradiation.

Real-time metabolic analysis of living cancer cells with correlated cellular spectro-microscopy

In recent years, major efforts have been devoted to the application of microscopy with mid-infrared light to the study of living cells and tissue. Despite this interest, infrared (IR) microscopy has not realized its full potential in the molecular characterization of living systems. This is partly due to the fact that current approaches for data mining and analysis of IR absorption spectra have not evolved comparably to measurement technology and are not up to the interpretation of the complex spectra of living systems such as cells and tissue. In this work we show that the use of two-dimensional correlation spectroscopy coupled to IR absorption spectro-microscopy allows us to extract the spectral components of individual metabolites from time-resolved IR spectra of living cells. We call this method correlated cellular spectro-microscopy, and we implement it in the study of the glycolytic metabolism of cancer cells. We show that the method can detect intermediates of the glycolytic pathway, quantify their rate of formation, and correlate this with variations in pH, all in a single measurement. We propose the method as a useful tool for the quantitative description of metabolic processes in living cells and for the validation of drug candidates aimed at suppressing glycolysis in cancer cells.

Synchrotron based infrared imaging and spectroscopy via focal plane array on live fibroblasts in D2O enriched medium

We successfully tested the viability of using synchrotron-based full-field infrared imaging to study biochemical processes inside living cells. As a model system, we studied fibroblast cells exposed to a medium highly enriched with D2O. We could show that the experimental technique allows us to reproduce at the cellular level measurements that are normally performed on purified biological molecules. We can obtain information about lipid conformation and distribution, kinetics of hydrogen/deuterium exchange, and the formation of concentration gradients of H and O isotopes in water that are associated with cell metabolism. The implementation of the full field technique in a sequential imaging format gives a description of cellular biochemistry and biophysics that contains both spatial and temporal information.