Mimicking tricks from nature with sensory organic-inorganic hybrid materials

Design strategies for (bio)chemical systems that are inspired by nature's accomplishments in system design and operation on various levels of complexity are increasingly gaining in importance. Within the broad field of biomimetic chemistry, this article highlights various attempts toward improved and sophisticated sensory materials that rely on the combination of supramolecular (bio)chemical recognition principles and nanoscopic solid structures. Examples range from more established concepts such as hybrid sensing ensembles with improved sensitivity and selectivity or for target analytes for which selectivity is hard to achieve by conventional methods, which were often inspired by protein binding pockets or ion channels in membranes, to very recent approaches relying on target-gated amplified signalling with functionalised mesoporous inorganic supports and the integration of native biological sensory species such as transmembrane proteins in spherically supported bilayer membranes. Besides obvious mimicry of recognition-based processes, selected approaches toward chemical transduction junctions utilizing artificially organized synapses, hybrid ensembles for improved antibody generation and uniquely colour changing systems are discussed. All of these strategies open up exciting new prospects for the development of sensing concepts and sensory devices at the interface of nanotechnology, smart materials and supramolecular (bio)chemistry. © 2011 The Royal Society of Chemistry.Martínez Mañez, R.; Sancenón Galarza, F.; Biyikal, M.; Hecht, M.; Rurack, K. (2011). Mimicking tricks from nature with sensory organic-inorganic hybrid materials. Journal of Materials Chemistry. 21(34):12588-12604. doi:10.1039/c1jm11210dS12588126042134Ma, M. (2007). Encoding Olfactory Signals via Multiple Chemosensory Systems. Critical Reviews in Biochemistry and Molecular Biology, 42(6), 463-480. doi:10.1080/10409230701693359Leinders-Zufall, T., Lane, A. P., Puche, A. C., Ma, W., Novotny, M. V., Shipley, M. T., & Zufall, F. (2000). Ultrasensitive pheromone detection by mammalian vomeronasal neurons. Nature, 405(6788), 792-796. doi:10.1038/35015572Serezani, C. H., Ballinger, M. N., Aronoff, D. M., & Peters-Golden, M. (2008). Cyclic AMP. American Journal of Respiratory Cell and Molecular Biology, 39(2), 127-132. doi:10.1165/rcmb.2008-0091trShimada, T. (2006). Xenobiotic-Metabolizing Enzymes Involved in Activation and Detoxification of Carcinogenic Polycyclic Aromatic Hydrocarbons. Drug Metabolism and Pharmacokinetics, 21(4), 257-276. doi:10.2133/dmpk.21.257Duncan, M. C., Ho, D. G., Huang, J., Jung, M. E., & Payne, G. S. (2007). Composite synthetic lethal identification of membrane traffic inhibitors. Proceedings of the National Academy of Sciences, 104(15), 6235-6240. doi:10.1073/pnas.0607773104Helmreich, E. J. M. (2002). Environmental influences on signal transduction through membranes: a retrospective mini-review. Biophysical Chemistry, 100(1-3), 519-534. doi:10.1016/s0301-4622(02)00303-4Anslyn, E. V. (2007). Supramolecular Analytical Chemistry. The Journal of Organic Chemistry, 72(3), 687-699. doi:10.1021/jo0617971Descalzo, A. B., Martínez-Máñez, R., Sancenón, F., Hoffmann, K., & Rurack, K. (2006). The Supramolecular Chemistry of Organic–Inorganic Hybrid Materials. Angewandte Chemie International Edition, 45(36), 5924-5948. doi:10.1002/anie.200600734Martínez-Máñez, R., Sancenón, F., Hecht, M., Biyikal, M., & Rurack, K. (2010). Nanoscopic optical sensors based on functional supramolecular hybrid materials. Analytical and Bioanalytical Chemistry, 399(1), 55-74. doi:10.1007/s00216-010-4198-2Koshland, D. E. (1958). Application of a Theory of Enzyme Specificity to Protein Synthesis. Proceedings of the National Academy of Sciences, 44(2), 98-104. doi:10.1073/pnas.44.2.98Hammes, G. G. (2002). Multiple Conformational Changes in Enzyme Catalysis†. Biochemistry, 41(26), 8221-8228. doi:10.1021/bi0260839Lin, V. S.-Y., Lai, C.-Y., Huang, J., Song, S.-A., & Xu, S. (2001). Molecular Recognition Inside of Multifunctionalized Mesoporous Silicas: Toward Selective Fluorescence Detection of Dopamine and Glucosamine. Journal of the American Chemical Society, 123(46), 11510-11511. doi:10.1021/ja016223mRadu, D. R., Lai, C.-Y., Wiench, J. W., Pruski, M., & Lin, V. S.-Y. (2004). Gatekeeping Layer Effect: A Poly(lactic acid)-coated Mesoporous Silica Nanosphere-Based Fluorescence Probe for Detection of Amino-Containing Neurotransmitters. Journal of the American Chemical Society, 126(6), 1640-1641. doi:10.1021/ja038222vDescalzo, A. B., Rurack, K., Weisshoff, H., Martínez-Máñez, R., Marcos, M. D., Amorós, P., … Soto, J. (2005). Rational Design of a Chromo- and Fluorogenic Hybrid Chemosensor Material for the Detection of Long-Chain Carboxylates. Journal of the American Chemical Society, 127(1), 184-200. doi:10.1021/ja045683nComes, M., Marcos, M. D., Martínez-Máñez, R., Sancenón, F., Soto, J., Villaescusa, L. A., … Beltrán, D. (2004). Chromogenic Discrimination of Primary Aliphatic Amines in Water with Functionalized Mesoporous Silica. Advanced Materials, 16(20), 1783-1786. doi:10.1002/adma.200400143(s. f.). doi:10.1021/ol052298García-Acosta, B., Comes, M., Bricks, J. L., Kudinova, M. A., Kurdyukov, V. V., Tolmachev, A. I., … Amorós, P. (2006). Sensory hybrid host materials for the selective chromo-fluorogenic detection of biogenic amines. Chem. Commun., (21), 2239-2241. doi:10.1039/b602497aComes, M., Marcos, M. D., Martínez-Máñez, R., Millán, M. C., Ros-Lis, J. V., Sancenón, F., … Villaescusa, L. A. (2006). Anchoring Dyes into Multidimensional Large-Pore Zeolites: A Prospective Use as Chromogenic Sensing Materials. Chemistry - A European Journal, 12(8), 2162-2170. doi:10.1002/chem.200500932Comes, M., Rodríguez-López, G., Marcos, M. D., Martínez-Máñez, R., Sancenón, F., Soto, J., … Beltrán, D. (2005). Host Solids Containing Nanoscale Anion-Binding Pockets and Their Use in Selective Sensing Displacement Assays. Angewandte Chemie International Edition, 44(19), 2918-2922. doi:10.1002/anie.200461511Comes, M., Marcos, M. D., Martínez-Máñez, R., Sancenón, F., Soto, J., Villaescusa, L. A., & Amorós, P. (2008). Hybrid materials with nanoscopic anion-binding pockets for the colorimetric sensing of phosphate in water using displacement assays. Chemical Communications, (31), 3639. doi:10.1039/b804396eComes, M., Aznar, E., Moragues, M., Marcos, M. D., Martínez-Máñez, R., Sancenón, F., … Amorós, P. (2009). Mesoporous Hybrid Materials Containing Nanoscopic «Binding Pockets» for Colorimetric Anion Signaling in Water by using Displacement Assays. Chemistry - A European Journal, 15(36), 9024-9033. doi:10.1002/chem.200900890Vašák, M. (2005). Advances in metallothionein structure and functions. Journal of Trace Elements in Medicine and Biology, 19(1), 13-17. doi:10.1016/j.jtemb.2005.03.003Slocik, J. M., & Wright, D. W. (2003). Biomimetic Mineralization of Noble Metal Nanoclusters. Biomacromolecules, 4(5), 1135-1141. doi:10.1021/bm034003qLee, J.-W., & Helmann, J. D. (2007). Functional specialization within the Fur family of metalloregulators. BioMetals, 20(3-4), 485-499. doi:10.1007/s10534-006-9070-7Lee, M. H., Lee, S. J., Jung, J. H., Lim, H., & Kim, J. S. (2007). Luminophore-immobilized mesoporous silica for selective Hg2+ sensing. Tetrahedron, 63(48), 12087-12092. doi:10.1016/j.tet.2007.08.113Song, C., Zhang, X., Jia, C., Zhou, P., Quan, X., & Duan, C. (2010). Highly sensitive and selective fluorescence sensor based on functional SBA-15 for detection of Hg2+ in Aqueous Media. Talanta, 81(1-2), 643-649. doi:10.1016/j.talanta.2009.12.047Métivier, R., Leray, I., Lebeau, B., & Valeur, B. (2005). A mesoporous silica functionalized by a covalently bound calixarene-based fluoroionophore for selective optical sensing of mercury(ii) in water. Journal of Materials Chemistry, 15(27-28), 2965. doi:10.1039/b501897hLee, S. J., Lee, J.-E., Seo, J., Jeong, I. Y., Lee, S. S., & Jung, J. H. (2007). Optical Sensor Based on Nanomaterial for the Selective Detection of Toxic Metal Ions. Advanced Functional Materials, 17(17), 3441-3446. doi:10.1002/adfm.200601202Palomares, E., Vilar, R., & Durrant, J. R. (2004). Heterogeneous colorimetric sensor for mercuric saltsElectronic supplementary information (ESI) available: Materials and methods. See http://www.rsc.org/suppdata/cc/b3/b314138a/. Chemical Communications, (4), 362. doi:10.1039/b314138aWang, Y., Li, B., Zhang, L., Liu, L., Zuo, Q., & Li, P. (2010). A highly selective regenerable optical sensor for detection of mercury(ii) ion in water using organic–inorganic hybrid nanomaterials containing pyrene. New Journal of Chemistry, 34(9), 1946. doi:10.1039/c0nj00039fLi, L.-L., Sun, H., Fang, C.-J., Xu, J., Jin, J.-Y., & Yan, C.-H. (2007). Optical sensors based on functionalized mesoporous silica SBA-15 for the detection of multianalytes (H+ and Cu2+) in water. Journal of Materials Chemistry, 17(42), 4492. doi:10.1039/b708857dZhang, H., Zhang, P., Ye, K., Sun, Y., Jiang, S., Wang, Y., & Pang, W. (2006). Mesoporous material grafted with luminescent molecules for the design of selective metal ion chemosensor. Journal of Luminescence, 117(1), 68-74. doi:10.1016/j.jlumin.2005.04.009Gao, L., Wang, J. Q., Huang, L., Fan, X. X., Zhu, J. H., Wang, Y., & Zou, Z. G. (2007). Novel Inorganic−Organic Hybrid Fluorescence Chemosensor Derived from SBA-15 for Copper Cation. Inorganic Chemistry, 46(24), 10287-10293. doi:10.1021/ic7008732Wang, J.-Q., Huang, L., Xue, M., Wang, Y., Gao, L., Zhu, J. H., & Zou, Z. (2008). Architecture of a Hybrid Mesoporous Chemosensor for Fe3+ by Covalent Coupling Bis-Schiff Base PMBA onto the CPTES-Functionalized SBA-15. The Journal of Physical Chemistry C, 112(13), 5014-5022. doi:10.1021/jp7099948Gao, L., Wang, Y., Wang, J., Huang, L., Shi, L., Fan, X., … Li, Z. (2006). A Novel ZnII-Sensitive Fluorescent Chemosensor Assembled within Aminopropyl-Functionalized Mesoporous SBA-15. Inorganic Chemistry, 45(17), 6844-6850. doi:10.1021/ic0516562Balaji, T., Sasidharan, M., & Matsunaga, H. (2005). Naked eye detection of cadmium using inorganic–organic hybrid mesoporous material. Analytical and Bioanalytical Chemistry, 384(2), 488-494. doi:10.1007/s00216-005-0187-2Balaji, T., El-Safty, S. A., Matsunaga, H., Hanaoka, T., & Mizukami, F. (2006). Optical Sensors Based on Nanostructured Cage Materials for the Detection of Toxic Metal Ions. Angewandte Chemie International Edition, 45(43), 7202-7208. doi:10.1002/anie.200602453El-Safty, S. A., Ismail, A. A., Matsunaga, H., & Mizukami, F. (2007). Optical Nanosensor Design with Uniform Pore Geometry and Large Particle Morphology. Chemistry - A European Journal, 13(33), 9245-9255. doi:10.1002/chem.200700499El-Safty, S. A., Ismail, A. A., Matsunaga, H., Hanaoka, T., & Mizukami, F. (2008). Optical Nanoscale Pool-on-Surface Design for Control Sensing Recognition of Multiple Cations. Advanced Functional Materials, 18(10), 1485-1500. doi:10.1002/adfm.200701059Ros-Lis, J. V., Casasús, R., Comes, M., Coll, C., Marcos, M. D., Martínez-Máñez, R., … Rurack, K. (2008). A Mesoporous 3D Hybrid Material with Dual Functionality for Hg2+Detection and Adsorption. Chemistry - A European Journal, 14(27), 8267-8278. doi:10.1002/chem.200800632Lee, S. J., Bae, D. R., Han, W. S., Lee, S. S., & Jung, J. H. (2008). Different Morphological Organic–Inorganic Hybrid Nanomaterials as Fluorescent Chemosensors and Adsorbents for CuII Ions. European Journal of Inorganic Chemistry, 2008(10), 1559-1564. doi:10.1002/ejic.200701073Lee, H. Y., Bae, D. R., Park, J. C., Song, H., Han, W. S., & Jung, J. H. (2009). A Selective Fluoroionophore Based on BODIPY-functionalized Magnetic Silica Nanoparticles: Removal of Pb2+ from Human Blood. Angewandte Chemie International Edition, 48(7), 1239-1243. doi:10.1002/anie.200804714Haupt, K., & Mosbach, K. (2000). Molecularly Imprinted Polymers and Their Use in Biomimetic Sensors. Chemical Reviews, 100(7), 2495-2504. doi:10.1021/cr990099wWulff, G. (2002). Enzyme-like Catalysis by Molecularly Imprinted Polymers. Chemical Reviews, 102(1), 1-28. doi:10.1021/cr980039aSellergren, B. (1997). Noncovalent molecular imprinting: antibody-like molecular recognition in polymeric network materials. TrAC Trends in Analytical Chemistry, 16(6), 310-320. doi:10.1016/s0165-9936(97)00027-7D�az-Garc�a, M. E., & La�n�o, R. B. (2004). Molecular Imprinting in Sol-Gel Materials: Recent Developments and Applications. Microchimica Acta, 149(1-2), 19-36. doi:10.1007/s00604-004-0274-7Bossi, A., Bonini, F., Turner, A. P. F., & Piletsky, S. A. (2007). Molecularly imprinted polymers for the recognition of proteins: The state of the art. Biosensors and Bioelectronics, 22(6), 1131-1137. doi:10.1016/j.bios.2006.06.023Nicholls, I. A., & Rosengren, J. P. (2001). Bioseparation, 10(6), 301-305. doi:10.1023/a:1021541631063Chang, Y.-S., Ko, T.-H., Hsu, T.-J., & Syu, M.-J. (2009). Synthesis of an Imprinted Hybrid Organic−Inorganic Polymeric Sol−Gel Matrix Toward the Specific Binding and Isotherm Kinetics Investigation of Creatinine. Analytical Chemistry, 81(6), 2098-2105. doi:10.1021/ac802168wBass, J. D., & Katz, A. (2003). Thermolytic Synthesis of Imprinted Amines in Bulk Silica. Chemistry of Materials, 15(14), 2757-2763. doi:10.1021/cm021822tCarlson, C. A., Lloyd, J. A., Dean, S. L., Walker, N. R., & Edmiston, P. L. (2006). Sensor for Fluorene Based on the Incorporation of an Environmentally Sensitive Fluorophore Proximal to a Molecularly Imprinted Binding Site. Analytical Chemistry, 78(11), 3537-3542. doi:10.1021/ac051375bShughart, E. L., Ahsan, K., Detty, M. R., & Bright, F. V. (2006). Site Selectively Templated and Tagged Xerogels for Chemical Sensors. Analytical Chemistry, 78(9), 3165-3170. doi:10.1021/ac060113mTrammell, S. A., Zeinali, M., Melde, B. J., Charles, P. T., Velez, F. L., Dinderman, M. A., … Markowitz, M. A. (2008). Nanoporous Organosilicas as Preconcentration Materials for the Electrochemical Detection of Trinitrotoluene. Analytical Chemistry, 80(12), 4627-4633. doi:10.1021/ac702263tMakote, R., & Collinson, M. M. (1998). Template Recognition in Inorganic−Organic Hybrid Films Prepared by the Sol−Gel Process. Chemistry of Materials, 10(9), 2440-2445. doi:10.1021/cm9801136Makote, R., & Collinson, M. M. (1998). Dopamine recognition in templated silicate films. Chemical Communications, (3), 425-426. doi:10.1039/a705536fFireman-Shoresh, S., Avnir, D., & Marx, S. (2003). General Method for Chiral Imprinting of Sol−Gel Thin Films Exhibiting Enantioselectivity. Chemistry of Materials, 15(19), 3607-3613. doi:10.1021/cm0340734Marx, S., Zaltsman, A., Turyan, I., & Mandler, D. (2004). Parathion Sensor Based on Molecularly Imprinted Sol−Gel Films. Analytical Chemistry, 76(1), 120-126. doi:10.1021/ac034531sTurner, N. W., Jeans, C. W., Brain, K. R., Allender, C. J., Hlady, V., & Britt, D. W. (2006). From 3D to 2D: A Review of the Molecular Imprinting of Proteins. Biotechnology Progress, 22(6), 1474-1489. doi:10.1002/bp060122gXie, C., Liu, B., Wang, Z., Gao, D., Guan, G., & Zhang, Z. (2008). Molecular Imprinting at Walls of Silica Nanotubes for TNT Recognition. Analytical Chemistry, 80(2), 437-443. doi:10.1021/ac701767hTan, J., Wang, H.-F., & Yan, X.-P. (2009). Discrimination of Saccharides with a Fluorescent Molecular Imprinting Sensor Array Based on Phenylboronic Acid Functionalized Mesoporous Silica. Analytical Chemistry, 81(13), 5273-5280. doi:10.1021/ac900484xWang, H.-F., He, Y., Ji, T.-R., & Yan, X.-P. (2009). Surface Molecular Imprinting on Mn-Doped ZnS Quantum Dots for Room-Temperature Phosphorescence Optosensing of Pentachlorophenol in Water. Analytical Chemistry, 81(4), 1615-1621. doi:10.1021/ac802375aJentsch, T. J., Stein, V., Weinreich, F., & Zdebik, A. A. (2002). Molecular Structure and Physiological Function of Chloride Channels. Physiological Reviews, 82(2), 503-568. doi:10.1152/physrev.00029.2001Morbach, S., & Krämer, R. (2002). Body Shaping under Water Stress: Osmosensing and Osmoregulation of Solute Transport in Bacteria. ChemBioChem, 3(5), 384. doi:10.1002/1439-7633(20020503)3:53.0.co;2-hWemmie, J. A., Price, M. P., & Welsh, M. J. (2006). Acid-sensing ion channels: advances, questions and therapeutic opportunities. Trends in Neurosciences, 29(10), 578-586. doi:10.1016/j.tins.2006.06.014Bayley, H., & Martin, C. R. (2000). Resistive-Pulse SensingFrom Microbes to Molecules. Chemical Reviews, 100(7), 2575-2594. doi:10.1021/cr980099gJung, Y., Bayley, H., & Movileanu, L. (2006). Temperature-Responsive Protein Pores. Journal of the American Chemical Society, 128(47), 15332-15340. doi:10.1021/ja065827tJenkins, A. T. A., Boden, N., Bushby, R. J., Evans, S. D., Knowles, P. F., Miles, R. E., … Vancso, G. J. (1999). Microcontact Printing of Lipophilic Self-Assembled Monolayers for the Attachment of Biomimetic Lipid Bilayers to Surfaces. Journal of the American Chemical Society, 121(22), 5274-5280. doi:10.1021/ja983968sRose, L., & Jenkins, A. T. A. (2007). The effect of the ionophore valinomycin on biomimetic solid supported lipid DPPTE/EPC membranes. Bioelectrochemistry, 70(2), 387-393. doi:10.1016/j.bioelechem.2006.05.009Tsukube, H., Takagi, K., Higashiyama, T., Iwachido, T., & Hayama, N. (1994). Biomimetic Membrane Transport: Interesting Ionophore Functions of Naturally Occurring Polyether Antibiotics toward Unusual Metal Cations and Amino Acid Ester Salts. Inorganic Chemistry, 33(13), 2984-2987. doi:10.1021/ic00091a043Murillo, O., Suzuki, I., Abel, E., Murray, C. L., Meadows, E. S., Jin, T., & Gokel, G. W. (1997). Synthetic Transmembrane Channels: Functional Characterization Using Solubility Calculations, Transport Studies, and Substituent Effects. Journal of the American Chemical Society, 119(24), 5540-5549. doi:10.1021/ja962694aSakai, N., Brennan, K. C., Weiss, L. A., & Matile, S. (1997). Toward Biomimetic Ion Channels Formed by Rigid-Rod Molecules: Length-Dependent Ion-Transport Activity of Substituted Oligo(p-Phenylene)s. Journal of the American Chemical Society, 119(37), 8726-8727. doi:10.1021/ja971513hRoks, M. F. M., & Nolte, R. J. M. (1992). Biomimetic macromolecular chemistry: design and synthesis of an artificial ion channel based on a polymer containing cofacially stacked crown ether rings. Incorporation in dihexadecyl phosphate vesicles and study of cobalt ion transport. Macromolecules, 25(20), 5398-5407. doi:10.1021/ma00046a042Finn, J. T., Grunwald, M. E., & Yau, K.-W. (1996). Cyclic Nucleotide-Gated Ion Channels: An Extended Family With Diverse Functions. Annual Review of Physiology, 58(1), 395-426. doi:10.1146/annurev.ph.58.030196.002143Levitan, I. B. (2006). Signaling protein complexes associated with neuronal ion channels. Nature Neuroscience, 9(3), 305-310. doi:10.1038/nn1647Goldenberg, L. M., Bryce, M. R., & Petty, M. C. (1999). Chemosensor devices: voltammetric molecular recognition at solid interfaces. Journal of Materials Chemistry, 9(9), 1957-1974. doi:10.1039/a901825eBühlmann, P., Aoki, H., Xiao, K. P., Amemiya, S., Tohda, K., & Umezawa, Y. (1998). Chemical Sensing with Chemically Modified Electrodes that Mimic Gating at Biomembranes Incorporating Ion-Channel Receptors. Electroanalysis, 10(17), 1149-1158. doi:10.1002/(sici)1521-4109(199811)10:173.0.co;2-nSugawara, M., Hirano, A., Bühlmann, P., & Umezawa, Y. (2002). Design and Application of Ion-Channel Sensors Based on Biological and Artificial Receptors. Bulletin of the Chemical Society of Japan, 75(2), 187-201. doi:10.1246/bcsj.75.187Gadzekpo, V. P. Y., Xiao, K. P., Aoki, H., Bühlmann, P., & Umezawa, Y. (1999). Voltammetric Detection of the Polycation Protamine by the Use of Electrodes Modified with Self-Assembled Monolayers of Thioctic Acid. Analytical Chemistry, 71(22), 5109-5115. doi:10.1021/ac990580mGadzekpo, V. P. Y., Bühlmann, P., Xiao, K. P., Aoki, H., & Umezawa, Y. (2000). Development of an ion-channel sensor for heparin detection. Analytica Chimica Acta, 411(1-2), 163-173. doi:10.1016/s0003-2670(00)00740-6Bandyopadhyay, K., Liu, H., Liu, S.-G., & Echegoyen, L. (2000). Self-assembled monolayers of bis-thioctic ester derivatives of oligoethyleneglycols: remarkable selectivity for K+/Na+ recognition. Chemical Communications, (2), 141-142. doi:10.1039/a905839gFlink, S., Schönherr, H., Vancso, G. J., Geurts, F. A. J., van Leerdam, K. G. C., van Veggel, F. C. J. M., & Reinhoudt, D. N. (2000). Cation sensing by patterned self-assembled monolayers on gold. Journal of the Chemical Society, Perkin Transactions 2, (10), 2141-2146. doi:10.1039/b002606iAOKI, H., UMEZAWA, Y., VERTOVA, A., & RONDININI, S. (2006). Ion-channel Sensors Based on ETH 1001 Ionophore Embedded in Charged-alkanethiol Self-assembled Monolayers on Gold Electrode Surfaces. Analytical Sciences, 22(12), 1581-1584. doi:10.2116/analsci.22.1581Aoki, H., Hasegawa, K., Tohda, K., & Umezawa, Y. (2003). Voltammetric detection of inorganic phosphate using ion-channel sensing with self-assembled monolayers of a hydrogen bond-forming receptor. Biosensors and Bioelectronics, 18(2-3), 261-267. doi:10.1016/s0956-5663(02)00177-xAoki, H., & Umezawa, Y. (2003). Trace analysis of an oligonucleotide with a specific sequence using PNA-based ion-channel sensors. The Analyst, 128(6), 681. doi:10.1039/b300465aKatayama, Y., Ohuchi, Y., Higashi, H., Kudo, Y., & Maeda, M. (2000). The Design of Cyclic AMP−Recognizing Oligopeptides and Evaluation of Its Capability for Cyclic AMP Recognition Using an Electrochemical System. Analytical Chemistry, 72(19), 4671-4674. doi:10.1021/ac990847hCliment, E., Casasús, R., Marcos, M. D., Martínez-Máñez, R., Sancenón, F., & Soto, J. (2008). Chromo-fluorogenic sensing of pyrophosphate in aqueous media using silica functionalised with binding and reactive units. Chemical Communications, (48), 6531. doi:10.1039/b813199fCliment, E., Calero, P., Marcos, M. D., Martínez-Máñez, R.