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Metals are essential for sustaining all forms of life, but alterations in their cellular homeostasis are connected to severe human disorders, including cancer, diabetes and neurodegenerative diseases. Fluorescent small molecules that respond to metal ions in the cell with appropriate selectivity and sensitivity offer the ability to probe physiological and pathological consequences of the cell biology of metals with spatial and temporal fidelity. Molecular imaging of normal and abnormal cellular metal ion pools using these new chemical tools provides a host of emerging opportunities for visualizing, in real time, aspects of metal accumulation, trafficking, and function or toxicity in living systems. This review presents a brief survey of available synthetic small-molecule sensor types for fluorescence detection of cellular metals.

Presented here is a cytocompatible covalently adaptable hydrogel uniquely capable of mimicking the complex biophysical properties of native tissue and enabling natural cell functions without matrix degradation. Demonstrated is both the ability to control elastic modulus and stress relaxation time constants by more than an order of magnitude while predicting these values based on fundamental theoretical understanding and the simulation of muscle tissue and the encapsulation of myoblasts.

Metallic copper surfaces rapidly and efficiently kill bacteria. Cells exposed to copper surfaces accumulated large amounts of copper ions, and this copper uptake was faster from dry copper than from moist copper. Cells suffered extensive membrane damage within minutes of exposure to dry copper. Further, cells removed from copper showed loss of cell integrity. Acute contact with metallic copper surfaces did not result in increased mutation rates or DNA lesions. These findings are important first steps for revealing the molecular sensitive targets in cells lethally challenged by exposure to copper surfaces and provide a scientific explanation for the use of copper surfaces as antimicrobial agents for supporting public hygiene.

We present the synthesis, properties, and biological applications of Peroxy Lucifer 1 (PL1), a new fluorescent probe for imaging hydrogen peroxide produced in living cells by a ratiometric response. PL1 utilizes a chemoselective boronate-based switch to detect hydrogen peroxide by modulation of internal charge transfer (ICT) within a 1,8-naphthalimide dye. PL1 features high selectivity for hydrogen peroxide over similar reactive oxygen species, including superoxide, and nitric oxide, and a 65 nm shift in emission from blue-colored fluorescence to green-colored fluorescence upon reaction with peroxide. Two-photon confocal microscopy experiments in live macrophages show that PL1 can ratiometrically visualize localized hydrogen peroxide bursts generated in living cells at immune response levels.

Dynamic fluxes of s-block metals like potassium, sodium, and calcium are of broad importance in cell signaling. In contrast, the concept of mobile transition metals triggered by cell activation remains insufficiently explored, in large part because metals like copper and iron are typically studied as static cellular nutrients and there are a lack of direct, selective methods for monitoring their distributions in living cells. To help meet this need, we now report Coppersensor-3 (CS3), a bright small-molecule fluorescent probe that offers the unique capability to image labile copper pools in living cells at endogenous, basal levels. We use this chemical tool in conjunction with synchotron-based microprobe X-ray fluorescence microscopy (XRFM) to discover that neuronal cells move significant pools of copper from their cell bodies to peripheral processes upon their activation. Moreover, further CS3 and XRFM imaging experiments show that these dynamic copper redistributions are dependent on calcium release, establishing a link between mobile copper and major cell signaling pathways. By providing a small-molecule fluorophore that is selective and sensitive enough to image labile copper pools in living cells under basal conditions, CS3 opens opportunities for discovering and elucidating functions of copper in living systems.fluorescent sensor | molecular imaging | mobile metals | transition metal signaling M etals are essential components of all living cells, and in many cases cells trigger and utilize dynamic metal movements for signaling purposes. Such processes are well established for alkali and alkaline earth metals like potassium, sodium, and calcium (1-3) but not for transition metals like copper and iron, which are traditionally studied for their roles as static cofactors in enzymes (4-6). We have initiated a program aimed at exploring the concept of mobile transition metals and their contributions to cell physiology and pathology, and in this context, brain neurons offer an attractive model for this purpose owing to their widespread use of potassium and sodium ion channels and calcium release for signaling events (7), as well as a high requirement for copper and iron to meet their steep oxidative demand (8-12). Indeed, the brain needs much higher levels of copper compared to other parts of the body under normal physiological conditions (9, 12), but at the same time mishandling of neuronal copper stores and subsequent oxidative stress and damage events are connected to a variety of neurodegenerative ailments, including Menkes and Wilson's diseases (13, 14), Alzheimer's disease (15-17), familial amyotrophic lateral sclerosis (18,19), and prionmediated encephalopathies (20,21). Previous work hints at the importance of exchangeable copper in neurophysiology, including observations of 64 Cu efflux from stimulated neurons (22, 23), export of Cu from isolated synaptosomes (24), and elevated susceptibility of neurons to excitotoxic insult with copper chelation (25), but none of these reports show direct, live-cell mon...

We identified a Cu accumulating structure with a dynamic role in intracellular Cu homeostasis. During Zn limitation, Chlamydomonas reinhardtii hyperaccumulated Cu, dependent on the nutritional Cu sensor CRR1, but was functionally Cu-deficient. Visualization of intracellular Cu revealed major Cu accumulation sites coincident with electron-dense structures that stained positive for low pH and polyphosphate, suggesting that they are lysosome-related organelles. NanoSIMS showed colocalization of Ca and Cu, and X-ray absorption spectroscopy (XAS) was consistent with Cu+ accumulation in an ordered structure. Zn resupply restored Cu homeostasis concomitant with reduced abundance of these structures. Cu isotope labeling demonstrated that sequestered Cu+ became bio-available for the synthesis of plastocyanin, and transcriptome profiling indicated that mobilized Cu became visible to CRR1. Cu trafficking to intracellular accumulation sites may be a strategy for preventing protein mis-metallation during Zn deficiency and enabling efficient cuproprotein (re)-metallation upon Zn resupply.

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