Imaging agents

Christopher J. Chang

Christopher J. Chang is the Class of 1942 Chair Professor in the Departments of Chemistry and Molecular and Cell Biology at UC Berkeley, Howard Hughes Medical Institute Investigator, and Faculty Scientist in the Chemical Sciences Division of Lawrence Berkeley National Laboratory. He is a Senior Editor of ACS Central Science. Chris received his BS and MS from Caltech in 1997, was a Fulbright scholar in Strasbourg, France, and received his PhD from MIT in 2002 with Dan Nocera. After postdoctoral studies with Steve Lippard, he joined UC Berkeley in 2004. His research is focused on chemical biology and inorganic chemistry, with interests in molecular imaging and catalysis applied to neuroscience and sustainable energy. He has obtained awards from the Dreyfus, Beckman, Sloan, and Packard Foundations, Amgen, AstraZeneca, and Novartis, Technology Review, ACS (Cope Scholar, Eli Lilly, Nobel Laureate Signature, Baekeland), Royal Society of Chemistry (Transition Metal Chemistry), and SBIC.

Thorfinnur Gunnlaugsson

Thorfinnur (Thorri) Gunnlaugsson, MRIA holds a Personal Chair in Chemistry (Professor of Chemistry) in the School of Chemistry, University of Dublin, Trinity College. He is a Principle Investigator in the Trinity Biomedical Sciences Institute (TBSI) and an elected Member of the Royal Irish Academy (2011). His research interests lie broadly within the fields of medicinal chemistry and organic and inorganic supramolecular chemistry, with emphasis on the development of functional self-assemblies and nanostructures for applications in biology. He has published over 180 papers to date. He was the recipient of the Royal Society of Chemistry Bob Hay Award in 2008 and the Erskin Fellowship (University of Canterbury, NZ) in 2009, and in 2014 he was awarded The Institute of Chemistry of Ireland (ICI) Annual Award for Chemistry (Eva Philbin Lecturer).

Tony D. James

Tony D. James is a Professor at the University of Bath, he obtained his BSc from UEA in 1986, PhD in 1991 from the University of Victoria, and worked as a PDRF in Japan from 1991–1995 with Seiji Shinkai. From 1995 to 2000 he was a Royal Society Research Fellow at the School of Chemistry at the University of Birmingham, moving to the Department of Chemistry at the University of Bath in September 2000. He has been a visiting Professor at Tsukuba, Osaka and Kyushu Universities, an AMADEus invited Professor at the University of Bordeaux and is a guest Professor at East China University of Science and Technology, Xiamen University, Shandong Normal University, Nanjing University, and is a Hai-Tian (Sea-Sky) Scholar at Dalian University of Technology. In 2013 he was awarded a Daiwa Adrian Prize. His research interests include boronic acid based receptors for the fluorescence sensing of saccharides.

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We are delighted to write these editorials on what has been a very exciting project involving world leading experts on the development of sensors and imaging agents for these two themed issues on sensor targets and imaging agents. Through the coordination and editing of these two issues we were able to take advantage of each other's extensive knowledge in the areas of sensing and imaging.^1–10

The choice of who to invite to contribute to the issues was an enjoyable one and included established and up and coming researchers in the overlapping areas of sensing and imaging. We were delighted by the overwhelming and positive response from invitees and their willingness to contribute cutting edge highlight articles, tutorial reviews and critical reviews to Chemical Society Reviews. Chemical Society Reviews is a premier journal for critical, tutorial and highlight research articles. Therefore, while we invited contributions from researchers who we felt would enhance the journal, the final selection of manuscripts needed to pass the strict refereeing criteria. During this process, some of the reviews we would have liked to include in these themed issues on sensor targets and imaging agents unfortunately didn't make it through the peer review process. However, we are confident and anticipate that those articles will soon be published in other review formats. In summary, as readers you can be assured that the articles contained in these two compilations are of the highest quality and have been rigorously and fairly evaluated by Chemical Society Reviews prior to publication. The final compilations consist of diverse selections of articles, which we are confident will encourage new researchers and established researchers working on the development of new sensors and imaging agents to achieve even more outstanding results and fill the remaining blanks in the sensing and imaging areas.

For the imaging issue, 18 articles have been published in diverse areas of imaging from A (Anion) to Z (Zinc).

Kikuchi and co-workers (DOI: 10.1039/C5CS00030K) describe the use of BODIPY-based fluorescence probes for cellular and in vivo imaging. BODIPY fluorophores are particularly useful since they have high fluorescence quantum yields, sharp emission and high photostability. In addition, their fluorescence can be switched from OFF to ON by target molecules via Förster resonance energy transfer (FRET) or photoinduced electron transfer (PET) processes.

Koide and co-workers (DOI: 10.1039/C4CS00323C) discuss the imaging of palladium and platinum in biological systems. In addition to being imaging targets, palladium and platinum have been used to label biomolecules with fluorophores. The importance of platinum-based drugs has led to the development of fluorescent tags.

Monitoring the formation and changes in concentration of anions within living systems is of critical importance. In their critical review, Ashton, Jolliffe and Pfeffer (DOI: 10.1039/C4CS00372A) discuss the development of fluorescence probes that can aid in the interpretation of the exact biological roles and effects of anions such as fluoride, chloride, iodide, cyanide, pyrophosphate, bicarbonate, hydrosulphide, peroxynitrite, hypochlorite and hypobromite.

Wolfbeis (DOI: 10.1039/C4CS00392F) provides an extensive overview of the various kinds of nanoparticles (NPs) that are widely used for purposes of fluorescence imaging of cells and tissues. The review discusses the surface modification of NPs and examples of use for (a) fluorescence imaging of cells, (b) targeted imaging, (c) imaging of chemical species and (d) imaging of temperature. The review ends with a discussion on multimodal imaging (such as fluorescence/NMR) and imaging in combination with drug delivery and theranostics.

Amoroso and Pope (DOI: 10.1039/C4CS00293H) present a review on the use of trivalent lanthanide ions in the design of bio-imaging agents and their application in both optical and magnetic resonance imaging. In particular, the importance of molecular design in the development of probes and multimodal imaging systems with appropriate bio-compatibility are discussed.

Metals are required to sustain life, but misregulation of spatial and temporal homeostasis is connected to many disease states. Qian and Xu (DOI: 10.1039/C4CS00292J) describe recent advances in the applications of fluorescence metal probes to help gain a better understanding as to how they contribute to disease, as well as to the potential for metal indicators to serve as disease diagnostics.

Graphene-based materials, including graphene oxides (GOs), reduced graphene oxides (rGOs) and graphene quantum dots (GQDs), have become increasing popular for applications in basic biology and medical science because of their biocompatibility, environment-friendly nature and attractive optical properties. Hong and co-workers (DOI: 10.1039/C5CS00072F) summarize the state-of-the-art in this area, focusing on NIR-responsive cancer therapy and fluorescence bio-imaging, and additionally provide future perspectives.

Semiconductor quantum dots (QDs) have emerged as bright, tunable, and photostable platforms for in vitro and in vivo bio-imaging research. Hildebrandt and Wegner (DOI: 10.1039/C4CS00532E) review the properties of QDs in terms of synthesis, surface conjugation and characterization, as well as recent literature on the design and application of QD-bioconjugates for bio-imaging from the single-molecule to whole organism level.

Zinc is an essential transition metal in biology, serving as a cofactor in all six classes of enzymes. He, Guo and their co-workers (DOI: 10.1039/C5CS00005J) summarize recent results in the maturing area of photoluminescence zinc sensing and their application for imaging Zn²⁺ in living systems.

Carbon-based nanomaterials, particularly carbon nanotubes, nanohorns, nanoonions, nanodiamonds and different graphene derivatives, have emerged as useful detection platforms for biomedical imaging. Giordani and colleagues (DOI: 10.1039/C4CS00306C) explore the use of this diverse array of organic materials for fluorescence and Raman imaging.

Caltagirone and co-workers (DOI: 10.1039/C4CS00270A) describe recent advances in the development of imaging agents based on silica nanoparticles. The review covers magnetic resonance imaging, optical imaging, positron emission tomography, X-ray computed tomography, and ultrasound imaging. They also discuss the potential extension of the systems to personalised healthcare via a combination of imaging techniques in order to enable simultaneous imaging and therapy.

Xian, Chang and co-workers (DOI: 10.1039/C4CS00298A) review chemical probes for imaging and the detection of hydrogen sulfide and reactive sulfur species. The review discusses the approaches used to detect hydrogen sulfide including azide and nitro group reduction, nucleophilic attack, and CuS precipitation. The detection of other reactive sulfur species (RSS), including sulfite and bisulfite, as well as sulfane sulfur species and related modifications such as S-nitrosothiols are also covered.

A tutorial review by Cheon and co-workers (DOI: 10.1039/C4CS00345D) discusses recent advances in the use of magnetic nanoparticles for magnetic resonance imaging (MRI) contrast agents. Emerging magnetic imaging techniques including magnetic particle imaging (MPI), magneto-motive ultrasound imaging (MMUS) and magneto-photoacoustic imaging (MPA) are also introduced.

Chiu and Peng (DOI: 10.1039/C4CS00294F) have reviewed the use of soft fluorescent nanomaterials as biological imaging agents. In particular, the in vitro imaging, in vivo imaging, and cellular-process imaging of soft fluorescent nanoparticles (NPs), including dye-doped polymer NPs, semiconducting polymer NPs, small-molecule organic NPs, nanogels, micelles, vesicles and biomaterial-based NPs are discussed.

In their review, Yoon and colleagues (DOI: 10.1039/C4CS00275J) discuss recent advances in the design and development of fluorescence probes for the bio-imaging of alkali metal and alkaline earth metal cations, including lithium, sodium, potassium, magnesium and calcium, and pH.

The review by Montalti and co-workers (DOI: 10.1039/c4cs00486h) describes the use of silicon quantum dots (Si QDs) and fluorescent nanodiamonds (FNDs) for fluorescence bio-imaging. Si QDs and FNDs are particularly useful bio-imaging probes given that they display minimal photobleaching under physiological conditions and are non-toxic and biocompatible, making them ideal diagnostic tools and potential vectors for the delivery of therapeutic agents.

In their review, Prodi and co-workers (DOI: 10.1039/c4cs00394b) cover the use of nanoparticles with long wavelength emission properties as multimodal imaging agents. The review concentrates on lanthanide-based nanocrystals which are particularly interesting due to their brightness and ability to up-convert light.

Thomas (DOI: 10.1039/c5cs00070j) provides an introductory perspective discussing the current challenges facing the development of optical imaging probes. This excellent highlight also proposes areas where improvements could and should be made.

We hope that you enjoy reading these great reviews as much as we did when preparing this themed issue on Imaging Agents.

References

1. R. M. Duke, E. B. Veale, F. M. Pfeffer, P. E. Kruger and T. Gunnlaugsson, Chem. Soc. Rev., 2010, 39, 3936–3953.
2. E. Galbraith and T. D. James, Chem. Soc. Rev., 2010, 39, 3831–3842.
3. A. R. Lippert, G. C. Van de Bittner and C. J. Chang, Acc. Chem. Res., 2011, 44, 793–804.
4. J. Chan, S. C. Dodani and C. J. Chang, Nat. Chem., 2012, 4, 973–984.
5. S. Banerjee, E. B. Veale, C. M. Phelan, S. A. Murphy, G. M. Tocci, L. J. Gillespie, D. O. Frimannsson, J. M. Kelly and T. Gunnlaugsson, Chem. Soc. Rev., 2013, 42, 160.
6. S. D. Bull, M. G. Davidson, J. M. H. van den Elsen, J. S. Fossey, A. T. A. Jenkins, Y.-B. Jiang, Y. Kubo, F. Marken, K. Sakurai, J. Zhao and T. D. James, Acc. Chem. Res., 2013, 46, 312–326.
7. V. S. Thoi, Y. Sun, J. R. Long and C. J. Chang, Chem. Soc. Rev., 2013, 42, 2388–2400.
8. X. Wu, Z. Li, X.-X. Chen, J. S. Fossey, T. D. James and Y.-B. Jiang, Chem. Soc. Rev., 2013, 42, 8032–8048.
9. J. P. Byrne, J. A. Kitchen and T. Gunnlaugsson, Chem. Soc. Rev., 2014, 43, 5302–5325.
10. Y. Kubo, R. Nishiyabu and T. D. James, Chem. Commun., 2015, 51, 2005–2020.

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