Fluorescent sensors guest editor issue

---

Abstract

This issue provides a definitive view of this exciting field and contains 43 articles and 3 reviews from the leading international research groups. Guest editors A. P. de Silva and P. Tecilla introduce the themed issue and provide an overview of Fluorescent Sensors, with key references.

---

The regulatory pressure for monitoring of chemical species (and even properties) will continue to increase as Governments take note of the heightened awareness of their voters about what is happening inside their bodies and in their external environment.

These monitoring needs can be neatly filled by well-designed fluorescent sensors in many instances. Such designs can also shed light on the fields of molecular switches and supramolecular photochemistry. The vitality and usefulness of the research field of fluorescent sensors are not in doubt. In fact, the field is growing so well that it is outgrowing the books, reviews and themed journal issues which have been devoted to it in the past. The Royal Society of Chemistry was keen to devote a themed issue of J. Mater. Chem. to the topic and to apply its resources to make this issue as complete as possible. What you are looking at is the result. We hope you will find much to interest you in these pages. For those of you wishing for a deep immersion in the literature of this field, we also offer a selected bibliography (ref. 1–4).

We invited the leaders of the fluorescent sensor community (irrespective of their background) to join us to create a definitive snapshot of how the field stands in 2005. The response was generous indeed, with about 50 articles. We hoped this would be an occasion which would further strengthen the field of fluorescent sensors and increase its visibility. Our hope appears to have been fulfilled when we run our eyes over what is on offer within these pages. We are most grateful to all of the authors who made this possible. The laboratories from which these papers originate represent many countries, including Belgium, Canada, France, Germany, India, Ireland, Italy, Japan, Netherlands, People's Republic of China, Portugal, Spain, Turkey, United Kingdom and United States of America.

We are delighted that a fluorescent sensor pioneer (Wolfbeis) casts his authoritative eye over the whole field, i.e. molecules, materials and mechanisms, to produce a Feature article to educate us all. Industrial laboratories with track records in real-life sensing contribute the two Application articles (He and Tusa, Whitten) as well as one of the Research articles (Orellana).

The fluorescent sensor community is so wide that it encompasses molecules in homogeneous media (the large part of papers herein) as well as molecules embedded in heterogeneous situations from nanoparticles (Tonellato and Tecilla, Montalti and Prodi) through meso-scale solids (Valeur, Martinez-Manez, Garcia-Espana, Pina, Shinkai) and gels (Shinkai, Iwai) to bulk membranes (Orellana). Microheterogeneous situations regarding lipid membranes (Sasaki, Smith) are also part of this spectrum, as are materials-based nanoparticles (Nocera and Bawendi). It is evident that the fundamental properties of molecular sensors in solution although relatively well-established are still vigorously pursued, with those systems responding to biologically relevant targets being particularly popular. In contrast, the development of new materials for fluorescent sensing with their fascinating properties promises applications in real life.

Though titled ‘Fluorescent Sensors’ for brevity, the themed issue also contains reports of sensing concerning the sister technique of phosphorescence arising from metal complexes whether they be d-block (Orellana, Beer) or f-block (Nocera and Bawendi). The field is not only concerned with reversible monitoring but also with irreversible ‘once-only’ measurements, especially of otherwise intractable targets. These are fluorescent reagents or chemdosimeters (Imai, Tian, Anslyn).

Since modularity assists this enterprise, it is clear that important modern research in the field can arise from the combination of tried-and-tested fluorophores and receptors. The fluorophores are represented by anthracene (Campagna, Desvergne, James, K. Kubo, Martinez-Manez, S. A. de Silva), pyrene (Teramae, Sasaki), aminonaphthalimide and derivatives (Samanta, Qian, He and Tusa, Tian, Fabbrizzi), diaminonaphthylsulfonyl (Corradini, Valeur, Montalti and Prodi), naphthalenes with simpler substituents (Balzani and Voegtle, Habib-Jiwan and Soumillion, Hamai, Pu), coumarins (Smith, Habib-Jiwan and Soumillion, Anslyn, S. A. de Silva), benzidine (Costero), flavylium (Pina), benzofurazan (Imai), alizarin (Y. Kubo), indole (Garcia-Espana), seminaphthofluorescein (Lippard), oligo/polyphenylenes with/without metal centers (Whitten, De Cola, Swager), polypyridyls with/without metal (Orellana, Beer, Shinkai), metallated porphyrins (Papkovsky, Koepelman) and libraries thereof (Crego-Calama and Reinhoudt). Newer fluorophores are subphthalocyanine (Tian), carbonyldipyrrinone (Akkaya), merocyanine photo-produced from spiropyran (Mihara). These molecular examples are also joined by quantum dots (Nocera and Bawendi).

Plate1 From Tian et al., DOI: 10.1039/b501234a (Fig. 1).

The receptors target analytes such as alkali and alkaline earth metal ions (Costero, Teramae, Desvergne, Akkaya, Habib-Jiwan and Soumillion, Yam, He and Tusa), various transition and post-transition metal ions (Samanta, Costero, Qian, Y. Kubo, K. Kubo, Garcia-Espana, Lippard, Sasaki, Balzani and Voegtle, Crego-Calama and Reinhoudt, Montalti and Prodi, Tonellato and Tecilla), fluoride (Tian, Tian, Y. Kubo), carboxylates (Fabbrizzi), ATP and simpler phosphates (Martinez-Manez, Garcia-Espana, Beer), membrane-bound phosphatidylserine (Smith), ssDNA (Krull, Whitten), proteins (Whitten, Mihara), hydrocarbons (Hamai, Orellana, Nocera and Bawendi). Enantiomers of amino acids (Corradini), hydroxy acids (Pu) and sugar alcohols (James) are also tackled. pH also receives attention, particularly because it can launch complex fluorescence switching phenomena (S. A. de Silva, Campagna, Balzani and Voegtle, Shinkai, Garcia-Espana, Pina). The selectivity profile and the level of analytes which are sensed can be adjusted in many of these cases by structural variation of the receptor. The amplification of detection levels of analytes is specifically addressed by drawing on phenomena as different as lasing (Nocera and Bawendi), catalytic action (Anslyn), and ion accumulation near surfaces (Sasaki, Montalti and Prodi, Martinez-Manez, Valeur, Tonellato and Tecilla). Reactive groups rather than receptors are used to target peptide thiols (Imai). No receptors at all, in a supramolecular sense, are involved in the monitoring of molecular oxygen (Papkovsky, Koepelman, De Cola, Swager) and temperature (Iwai).

Plate2 From Wolfbeis et al. DOI: 10.1039/b501536g (Fig. 1).

Though mechanistic assignments are inherently open to re-interpretation, signal transduction mechanisms encountered include photoinduced electron transfer (PET) (Samanta, Corradini, Smith, Qian, Pu, Campagna, Teramae, Desvergne, James, Whitten, K. Kubo, Martinez-Manez, Garcia-Espana, Lippard, Balzani and Voegtle, Tonellato and Tecilla, Montalti and Prodi, S. A. de Silva, He and Tusa), internal charge transfer (ICT) (Costero, Pina, Imai, Shinkai, Tian, Tian, Akkaya, Habib-Jiwan and Soumillion, Lippard, Mihara, Valeur, Iwai, Krull, Fabbrizzi), excited state intramolecular proton transfer (ESIPT) (Pina, Pu, Krull), metal to ligand charge transfer (MLCT) (Yam, Beer, Orellana), electron energy transfer (EET) (Corradini, Garcia-Espana, Tonellato and Tecilla, Montalti and Prodi), excimers (Pu, Hamai, Martinez-Manez, Sasaki, Balzani and Voegtle) and exciplexes (Teramae, Balzani and Voegtle). Twisting of excited states is also used for this purpose (Costero). The confirmation of mechanism in any given case will require fundamental studies on the photophysical properties of model systems as an essential part of the effort in this field.

Plate3 From Nocera et al., DOI: 10.1039/b503026a (Fig. 9).

When a large undertaking such as this nears its completion, a few more thanks and apologies are in order. First, we acknowledge our error of omission to any leaders of the field who we failed to invite. Second, we are sorry that the practicalities of putting together a large themed issue and the deadlines imposed meant that we could not include all of the work we would have liked. A few papers that missed the deadlines will appear in later issues of the journal. We hope that the people not represented in the issue will continue to build our field, along with the other key players, into something that benefits all. Next, we wish to place on record our thanks to Sophia Anderton, Rachel Hopper, Kate Nussey and Graham McCann in the Editorial team, and Michelle Canning, Carole Nerney and the Organic and Materials Production team, who guided this project through to the end in spite of challenges along the way. A final word of thanks to Maurizio Prato for challenging us to compile this themed issue.

We would like to thank all the contributors to the issue for providing excellent articles for publication and also thank the referees for their invaluable contribution. The real long-term success of this project will be the many hearts and minds that will be touched by the sensor science offered here.

A. P. de Silva, Queen’s University, Belfast

Plate4 A. P. de Silva

Paolo Tecilla, University of Trieste

Plate5 Paolo Tecilla

References

1. Reviews: (a) G. F. Kirkbright, in Indicators, ed. E. Bishop, Pergamon, Oxford, 1972, p. 685; (b) A. J. Bryan, A. P. de Silva, S. A. de Silva, R. A. D. D. Rupasinghe and K. R. A. S. Sandanayake, Biosensors, 1989, 4, 169; (c) R. A. Bissell, A. P. de Silva, H. Q. N. Gunaratne, P. L. M. Lynch, G. E. M. Maguire and K. R. A. S. Sandanayake, Chem. Soc. Rev., 1992, 21, 187; (d) R. Y. Tsien, Am. J. Physiol., 1992, 263, C723; (e) R. A. Bissell, A. P. de Silva, H. Q. N. Gunaratne, P. L. M. Lynch, G. E. M. Maguire, C. P. McCoy and K. R. A. S. Sandanayake, Top. Curr. Chem., 1993, 168, 223; (f) A. W. Czarnik, Adv. Supramol. Chem., 1993, 3, 131; (g) A. W. Czarnik, Acc. Chem. Res., 1994, 27, 302; (h) L. Fabbrizzi and A. Poggi, Chem. Soc. Rev., 1995, 24, 197; (i) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, C. P. McCoy, P. R. S. Maxwell, J. T. Rademacher and T. E. Rice, Pure Appl. Chem., 1996, 68, 1443; (j) T. D. James, K. R. A. S. Sandanayake and S. Shinkai, Angew. Chem., Int. Ed., 1996, 35, 1911; (k) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M. Huxley, C. P. McCoy, J. T. Rademacher and T. E. Rice, Chem. Rev., 1997, 97, 1515; (l) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson, A. J. M. Huxley, C. P. McCoy, J. T. Rademacher and T. E. Rice, Adv. Supramol. Chem., 1997, 4, 1; (m) L. Fabbrizzi, M. Licchelli and P. Pallavicini, Acc. Chem. Res., 1999, 32, 846; (n) A. P. de Silva, D. B. Fox, A. J. M. Huxley, N. D. McClenaghan and J. Roiron, Coord. Chem. Rev., 1999, 185–186, 297; (o) H. Kojima and T. Nagano, Adv. Mater., 2000, 12, 763; (p) K. Rurack, Spectrochim. Acta, Part A, 2001, 57, 2161; (q) S. L. Wiskur, H. Ali-Haddou, J. J. Lavigne and E. V. Anslyn, Acc. Chem. Res., 2001, 34, 963; (r) A. P. de Silva, D. B. Fox, T. S. Moody and S. M. Weir, Pure Appl. Chem., 2001, 73, 503; (s) K. Rurack and U. Resch-Genger, Chem. Soc. Rev., 2002, 31, 116; (t) T. D. James and S. Shinkai, Top. Curr. Chem., 2002, 218, 159; (u) R. Martinez-Manez and F. Sancenon, Chem. Rev., 2003, 103, 4419; (v) L. Pu, Chem. Rev., 2004, 104, 1687; (w) P. Jiang and Z. Guo, Coord. Chem. Rev., 2004, 248, 205; (x) L. Prodi, New J. Chem., 2005, 29, 20; (y) J. M. Haider and Z. Pikramenou, Chem. Soc. Rev, 2005, 34, 120; (z) T. Gunnlaugsson, Chem. Commun., 2005 10.1039/b418196d, in press.
2. Books: (a) Biochemical Fluorescent Concepts, ed. R. F. Chen and H. Edelhoch, Dekker, New York, 1976; (b) Fluorescent Probes, ed. G. S. Beddard and M. A. West, Academic, London, 1981; (c) G. G. Guilbault, Practical Fluorescence, 2nd edn., Dekker, New York, 1990; (d) B. M. Krasovitski and B. M. Bolotin, Organic Luminescent Materials, VCH, Weinheim, 1989; (e) Fibre Optic Chemical Sensors and Biosensors, ed. O. S. Wolfbeis, CRC Press, Boca Raton, FL, 1991; (f) Fluorescent Chemosensors of Ion and Molecule Recognition, ed. A. W. Czarnik, American Chemical Society, Washington DC, 1993; (g) Chemosensors of Ion and Molecule Recognition, ed. A. W. Czarnik and J.-P. Desvergne, Kluwer, Dordrecht, 1997; (h) J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 2nd edn., Plenum, New York, 1999; (i) B. Valeur, Molecular Fluorescence, Wiley-VCH, Weinheim, 2001; (j) Molecular and Supramolecular Photochemistry, ed. V. Ramamurthy and K. S. Schanze, Dekker, New York, 2001, vol. 7; (k) V. Balzani, M. Venturi and A. Credi, Molecular Devices and Machines, Wiley-VCH, Weinheim, 2003; (l) Handbook of Photochemistry and Photobiology, ed. H. S. Nalwa, American Scientific Publishers, Stevenson Ranch, CA, 2003; (m) Encyclopedia of Supramolecular Chemistry, ed. J. L. Atwood and J. W. Steed, Dekker, New York, 2004; (n) Optical Sensors: Industrial, Environmental and Diagnostic Applications, ed. R. Narayanaswamy and O. S. Wolfbeis, Springer, Berlin, 2004.
3. Book series: (a) Modern Fluorescence Spectroscopy, ed. E. L. Wehry, Plenum, New York, 1976– 1981, vol. 1–4; (b) Molecular Luminescence Spectroscopy. Methods and Applications, ed. S. G. Schulman, Wiley, New York, 1985 (part 1), 1993 (part 3); (c) Topics in Fluorescence Spectroscopy, ed. J. R. Lakowicz, Plenum, New York, 1992, (vol. 3), 1994 (vol. 4); (d) Fluorescence Spectroscopy: New Methods and Applications, ed. O. S. Wolfbeis, Springer, Berlin, 1993; (e) R. P. Haugland, The Handbook—A Guide to Fluorescent Probes and Labeling Technologies, Invitrogen, Eugene, OR, 2005, 10th edn.
4. Themed issues: (a) D. Parker, Analyst, 1996, 121, 1749; (b) L. Fabbrizzi, Coord. Chem. Rev., 2000, 205, 1; (c) E. V. Anslyn, Tetrahedron, 2004, 60, 11055; (d) R. Badugu and C. D. Geddes, J. Fluoresc., 2004, 14, 475.

---