Editorial pubs.acs.org/acssensors
Should ACS Sensors Publish Papers on Fluorescent Sensors for Metal Ions at All?
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events, environmental changes, or onset of disease? Finally, how do cells regulate metal dynamics, and how do metal dynamics impact cellular function?” It is the potential to answer questions such as these that excites us about fluorescent metal ion sensors. It seems harder to justify the research effort in the first category because we have many technologies that can detect metals in the environment that work exceptionally well. This does again mean that papers in this category would need to demonstrate an advantage of the fluorescent sensors over existing technologies: for example, in dynamic speciation analysis, the assessment of chemical gradients in situ, and the imaging of chemical fluxes in the vicinity of microenvironments and sediments. So, what types of papers are we looking for in relation to fluorescent sensors for metal ions? The first few issues of ACS Sensors all have papers on this class of sensor that may serve as examples. But broadly speaking, we are looking for fluorescent sensors that provide new information, or the potential to provide new information, and where the conditions in which they operate are fit-for-purpose. This last point is where we see many papers fall down. As stated in the review by Li and coworkers,3 “for real applications of luminescent chemodosimeters, especially in bioimaging, water solubility is essential. Although most reported chemodosimeters can function well in organic solvents, their water solubility is often poor, which limits their application to real systems.” If these sensors are for biological applications, or water monitoring for that matter, it is hard to see how the sensor is fit-for-purpose, if it is not watersoluble. If one attempts to monitor a biological process in cells that have been exposed to a sensor dissolved in a 50:50 mixture of an organic solvent and buffer, to what extent is one now monitoring a perturbed biological process? In this case, how robust are the conclusions the sensor is coming to? Similarly, to demonstrate that the sensor can work in an intracellular environment, a common strategy is to incubate the cells in buffer containing the metal ions and then show that the metals are inside the cell. We can appreciate the merits of this strategy as a starting point, but it seems imperative to us that one needs to demonstrate not only the functionality of the sensor at the concentrations found within the cell, but also the ability to monitor changes in the ion concentrations as a result of normal biological processes. This last characteristic mandates that the sensors operate reversibly, and not as irreversible probes. Too many authors tend to disregard the difference between the two. We believe that the field of fluorescent sensors for monitoring metal ions is going to go from strength to strength. The power of a good metal ion sensor is shown by the success of the first intracellular fluorescence sensors for metals, the calcium sensor for live cell imaging by Tsien and co-workers5 in
he title of this editorial is perhaps provocative, but based on what we see in the vast majority of sensing journals, the question is not without merit. The field of fluorescent molecular probes, in general, and for metal ions in particular, is attracting intense interest. Traditionally this area tends to be more the domain of organic chemistry journals when papers are reporting the existence of a new chromogenic receptor or biological journals when a new optical probe is developed to answer specific biological questions. So far, however, the majority of sensing journals seldom publish such manuscripts. Considering that the very first ACS Editors’ Choice paper of ACS Sensors was from the Lippard group on an intracellular sensor for zinc,1 we do believe that such papers are within the scope of ACS Sensors. Indeed, contributions in this area are a popular submission topic at this timeand an active topic of discussion for the editors of ACS Sensors. So, why does this field of sensing even warrant such a question being asked? It is natural in any emerging field that different communities that enter the field have different views on what science is encompassed within the new term. So, in the case of sensors, we have heard it emphatically suggested more than once that something isor is nota sensor. And yes, we have heard such statements pertaining to fluorescent sensors for metals! At ACS Sensors we take a very liberal view on what a chemical or biological sensor is. This view is not without a basis. It is compatible with the definition of a sensor by the International Union of Pure and Applied Chemistry (IUPAC) from a 1991 paper2 which stated, “A chemical sensor is a device that transforms chemical information, ranging from the concentration of a specific sample component to total composition analysis, into an analytically useful signal. The chemical information, mentioned above, may originate from a chemical reaction of the analyte or from a physical property of the system investigated.” The paper goes on to say that “chemical sensors contain two basic functional units: a receptor part and a transducer part”. If we look at fluorescent sensors, they clearly have these two components where there is a receptor that provides the sensor with selectivity for the target species, and the fluorophore, and its interaction with the metal gives rise to a detectable signal. Research activity in this field is intense, as demonstrated by two recent reviews in Chemical Reviews that deal with this topic.3,4 The submissions we receive on fluorescent sensors for metals can approximately be subdivided into two broad categoriesthose that eventually aim to detect ions in the environment, and those for monitoring intracellular ion concentration. The case for fluorescent ion sensors in the intracellular environment is compelling. This is because there may be no other existing method for answering a range of fundamental biological questions. To use the words from the review by Palmer and co-workers,4 “some of these basic unanswered questions include: What is the amount and speciation of metals in cells? Where are metals located? How do metal ion concentrations change in response to cellular © 2016 American Chemical Society
Received: March 29, 2016 Published: April 22, 2016 324
DOI: 10.1021/acssensors.6b00213 ACS Sens. 2016, 1, 324−325
ACS Sensors
Editorial
1982. There are many such examples that have followed since. In particular, we are excited about the potential for sensors that provide subcellular information, sensors that exploit superresolution and other state-of-the-art microscopies in their transduction, and, above all, sensors that can provide new ways to answer important chemical or biological questions. We look forward to receiving more submission along the lines we have described.
J. Justin Gooding, Editor-in-Chief The University of New South Wales, Sydney, Australia
Eric Bakker, Associate Editor The University of Geneva, Switzerland
Shana Kelley, Associate Editor
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The University of Toronto, Canada
AUTHOR INFORMATION
Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
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REFERENCES
(1) Zastrow, M. L.; Radford, R. J.; Chyan, W.; Anderson, C. T.; Zhang, D. Y.; Loas, A.; Tzounopoulos, T.; Lippard, S. J. ReactionBased Probes for Imaging Mobile Zinc in Live Cells and Tissues. ACS Sens. 2016, 1 (1), 32−39. (2) Hulanicki, A.; Glab, S.; Ingman, F. Chemical Sensors − Definitions and Classifications. Pure Appl. Chem. 1991, 63, 1247− 1250. (3) Yang, Y.; Zhao, Q.; Feng, W.; Li, F. Luminescent Chemodosimeters for Bioimaging. Chem. Rev. 2013, 113, 192−270. (4) Carter, K. P.; Young, A. M.; Palmer, A. E. Fluorescent Sensors for Measuring Metal Ions in Living Systems. Chem. Rev. 2014, 114, 4564− 4601. (5) Tsien, R. Y.; Pozzan, T.; Rink, T. J. Calcium homeostasis in intact lymphocytes: cytoplasmic free calcium monitored with a new, intracellularly trapped fluorescent indicator. J. Cell Biol. 1982, 94, 325−334.
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DOI: 10.1021/acssensors.6b00213 ACS Sens. 2016, 1, 324−325
