本研究以自由基聚合法合成一系列含有不同螢光單體比例之共聚高分子poly[(N-isopropylacrylamide)-co-(N-hydroxymethylacrylamide)-co-(3-hydroxy-4-(2-(3'-(N-(4'-phenylcarbonyl)-4-morpholine-1,8-naphthalimide)piperazino)-6'-(diethylamino)-3-oxospiro[isoindoline-1,9'-xanthene]-2-yl)hydrazonomethyl)phenyl methacrylate)] [poly(NIPAAm-co-NMA-co-RM), PRM]，並透過靜電紡絲技術(electrospinning technique)將其加工成具有高比表面積之靜電紡絲奈米纖維，作為固態螢光感測器，對Cu2+進行感測。此PRM共聚高分子是由三種單體共聚而成的，具有溫度敏感性質之NIPAAm使纖維具有收縮-膨潤之特性，化學可交聯之NMA可經由加熱產生交聯而使纖維不會回溶於溶劑，RM則為本研究所合成具有Cu2+感測性之naphthalimide-rhodamine-based螢光單體，其與Cu2+螯合後可使rhodamine基團之螺內醯胺(spirolactam)開環，產生rhodamine之吸收峰，但rhodamine之放光則會因為Cu2+之螢光淬滅效應無法觀察到，因此改藉由觀察naphthalimide基團之放光強度變化作為與Cu2+作用之依據，形成一ON-OFF螢光感測機制。
PRM高分子在溶液態與固態(奈米纖維和薄膜)中均表現其對Cu2+之高識別性，可直接透過肉眼觀察到從淺黃色到粉紅色之明顯顏色變化。根據Stern-Volmer plots之定量分析結果，PRM奈米纖維之螢光淬滅常數(KSV)於[Cu2+]= 0.1~1 µM區間展現高靈敏度，於[Cu2+]= 1~10 µM區間雖比溶液態低了一點，但比薄膜態高得多，證實同樣作為具有方便攜帶、簡易操作特點之固態感測器，具有較高比表面積之奈米纖維其感測能力優於傳統高分子薄膜。此外，PRM奈米纖維與Cu2+之作用在化學上是可逆的，為可重複使用之感測器。

In this study, a series of Cu2+-sensing fluorescent nanofibers with high surface-to-volume ratio has been successfully prepared by electrospinning of poly(NIPAAm-co-NMA-co-RM) (PRM). These PRM copolymers were synthesized by free radical polymerization of three monomers, thermo-responsive NIPAAm (facilitated nanofibers capable of shrinking/swelling in aqueous solutions), chemically crosslinkable NMA (maintained the morphology of nanofibers in aqueous solutions by thermal curing) and Cu2+-sensing RM monomer, which was constructed by coupling a naphthalimide donor with a rhodamine acceptor. The chelation between RM and Cu2+ could trigger the transformation process of rhodamine moieties from ring-closed spirolactam form to ring-opened amide, and lead to a remarkable increase in the absorption of rhodamine. In particular, the rhodamine moieties showed high absorbance but low fluorescence after Cu2+ recognition due to the fluorescence quenching effect of Cu2+. Herein, we observed the emission intensity change of naphthalimide moieties to show that the addition of Cu2+ can promote the ring-opened reaction of the rhodamine moieties of RM, which displayed ON-OFF fluorescence toward Cu2+.
The PRM copolymers showed highly recognition toward Cu2+ both in solution and in solid state (nanofibers and thin films), and a significant color changed from pale yellow to pink could be observed by naked eyes. From the quantitative analysis via Stern-Volmer plots, PRM nanofibers exhibited much higher Stern-Volmer quenching constant (KSV) values than those of PRM solutions and thin films at Cu2+ concentration range of 0.1 to 1 µM, but lower than those of PRM solutions at Cu2+ concentration range of 1 to 10 µM. In addition, the binding of PRM with Cu2+ is chemically reversible with the treatment of Na4EDTA.

1.Tang, J.; Ma, S.; Zhang, D.; Liu, Y.; Zhao, Y.; Ye, Y., Highly sensitive and fast responsive ratiometric fluorescent probe for Cu2+ based on a naphthalimide-rhodamine dyad and its application in living cell imaging. Sensors and Actuators B: Chemical 2016, 236, 109-115.
2.Guan, X.; Lin, W.; Huang, W., Development of a new rhodamine-based FRET platform and its application as a Cu2+ probe. Org Biomol Chem 2014, 12 (23), 3944-9.
3.Masters, B. R., Molecular fluorescence: principles and applications. Journal of Biomedical Optics 2013, 18 (3), 039901.
4.Fereja, T. H.; Hymete, A.; Gunasekaran, T., A Recent Review on Chemiluminescence Reaction, Principle and Application on Pharmaceutical Analysis. ISRN Spectroscopy 2013, 2013, 1-12.
5.AbouElhamd, A.; Al-Sallal, K.; Hassan, A., Review of Core/Shell Quantum Dots Technology Integrated into Building’s Glazing. Energies 2019, 12 (6).
6.Akash, M. S. H.; Rehman, K., Ultraviolet-Visible (UV-VIS) Spectroscopy. In Essentials of Pharmaceutical Analysis, Springer Singapore: Singapore, 2020; pp 29-56.
7.Lakowicz, J. R., Quenching of Fluorescence. In Principles of Fluorescence Spectroscopy, Lakowicz, J. R., Ed. Springer US: Boston, MA, 2006; pp 277-330.
8.Behera, P.; Mukherjee, T.; Mishra, A., Simultaneous presence of static and dynamic component in the fluorescence quenching for substituted naphthalene—CCl4 system. Journal of luminescence 1995, 65 (3), 131-136.
9.Sharma, H.; Kaur, N.; Singh, N., Sensing in aqueous medium: mechanism and its application in the field of molecular recognition. Analytical Methods 2015, 7 (17), 7000-7019.
10.Kaur, N.; Chopra, S.; Singh, G.; Raj, P.; Bhasin, A.; Sahoo, S. K.; Kuwar, A.; Singh, N., Chemosensors for biogenic amines and biothiols. J Mater Chem B 2018, 6 (30), 4872-4902.
11.Jung, H. S.; Verwilst, P.; Kim, W. Y.; Kim, J. S., Fluorescent and colorimetric sensors for the detection of humidity or water content. Chem Soc Rev 2016, 45 (5), 1242-56.
12.Carter, K. P.; Young, A. M.; Palmer, A. E., Fluorescent sensors for measuring metal ions in living systems. Chem Rev 2014, 114 (8), 4564-601.
13.Liu, M.; Yu, X.; Li, M.; Liao, N.; Bi, A.; Jiang, Y.; Liu, S.; Gong, Z.; Zeng, W., Fluorescent probes for the detection of magnesium ions (Mg2+): from design to application. RSC Advances 2018, 8 (23), 12573-12587.
14.Tripathy, M.; Subuddhi, U.; Patel, S., An Azo Dye Based D‐π‐A Chromogenic Probe for Selective Naked‐Eye Detection of Hg2+ Ion: Application in Logic Gate Operation. ChemistrySelect 2020, 5 (16), 4803-4815.
15.Huang, C. B.; Li, H. R.; Luo, Y.; Xu, L., A naphthalimide-based bifunctional fluorescent probe for the differential detection of Hg2+ and Cu2+ in aqueous solution. Dalton Trans 2014, 43 (21), 8102-8.
16.Wu, Y.-S.; Li, C.-Y.; Li, Y.-F.; Li, D.; Li, Z., Development of a simple pyrene-based ratiometric fluorescent chemosensor for copper ion in living cells. Sensors and Actuators B: Chemical 2016, 222, 1226-1232.
17.Wu, L.; Huang, C.; Emery, B. P.; Sedgwick, A. C.; Bull, S. D.; He, X. P.; Tian, H.; Yoon, J.; Sessler, J. L.; James, T. D., Forster resonance energy transfer (FRET)-based small-molecule sensors and imaging agents. Chem Soc Rev 2020, 49 (15), 5110-5139.
18.Aich, K.; Goswami, S.; Das, S.; Mukhopadhyay, C. D.; Quah, C. K.; Fun, H. K., Cd2+ Triggered the FRET "ON": A New Molecular Switch for the Ratiometric Detection of Cd2+ with Live-Cell Imaging and Bound X-ray Structure. Inorg Chem 2015, 54 (15), 7309-15.
19.Ge, Y.; Zheng, X.; Ji, R.; Shen, S.; Cao, X., A new pyrido[1,2-a]benzimidazole-rhodamine FRET system as an efficient ratiometric fluorescent probe for Cu2+ in living cells. Anal Chim Acta 2017, 965, 103-110.
20.Dujols, V.; Ford, F.; Czarnik, A. W., A long-wavelength fluorescent chemodosimeter selective for Cu (II) ion in water. Journal of the American Chemical Society 1997, 119 (31), 7386-7387.
21.Fan, J.; Zhan, P.; Hu, M.; Sun, W.; Tang, J.; Wang, J.; Sun, S.; Song, F.; Peng, X., A fluorescent ratiometric chemodosimeter for Cu2+ based on TBET and its application in living cells. Organic letters 2013, 15 (3), 492-495.
22.Li, Y.; Qi, S.; Xia, C.; Xu, Y.; Duan, G.; Ge, Y., A FRET ratiometric fluorescent probe for detection of Hg2+ based on an imidazo[1,2-a]pyridine-rhodamine system. Anal Chim Acta 2019, 1077, 243-248.
23.Maity, D.; Karthigeyan, D.; Kundu, T. K.; Govindaraju, T., FRET-based rational strategy for ratiometric detection of Cu2+ and live cell imaging. Sensors and Actuators B: Chemical 2013, 176, 831-837.
24.Hu, Z.; Hu, J.; Cui, Y.; Wang, G.; Zhang, X.; Uvdal, K.; Gao, H. W., A facile "click" reaction to fabricate a FRET-based ratiometric fluorescent Cu2+ probe. J Mater Chem B 2014, 2 (28), 4467-4472.
25.Yu, C.; Wen, Y.; Qin, X.; Zhang, J., A fluorescent ratiometric Cu2+ probe based on FRET by naphthalimide-appended rhodamine derivatives. Anal. Methods 2014, 6 (24), 9825-9830.
26.Li, S.; Zhang, D.; Wang, M.; Ma, S.; Liu, J.; Zhao, Y.; Ye, Y., Synthesis and Properties of a Novel FRET-Based Ratiometric Fluorescent Sensor for Cu2+. J Fluoresc 2016, 26 (3), 769-74.
27.Duan, G.; Zhang, G.; Yuan, S.; Ji, R.; Zhang, L.; Ge, Y., A pyrazolo[1,5-a]pyridine-based ratiometric fluorescent probe for sensing Cu2+ in cell. Spectrochim Acta A Mol Biomol Spectrosc 2019, 219, 173-178.
28.Wang, Y.; Ding, H.; Wang, S.; Fan, C.; Tu, Y.; Liu, G.; Pu, S., A ratiometric and colorimetric probe for detecting Hg2+ based on naphthalimide–rhodamine and its staining function in cell imaging. RSC Advances 2019, 9 (21), 11664-11669.
29.Wei, M.; Gao, Y.; Li, X.; Serpe, M. J., Stimuli-responsive polymers and their applications. Polymer Chemistry 2017, 8 (1), 127-143.
30.Kyritsis, A.; Laschewsky, A.; Papadakis, C. M., Self-assembling of Thermo-Responsive Block Copolymers: Structural, Thermal and Dielectric Investigations. In Thermodynamics and Biophysics of Biomedical Nanosystems: Applications and Practical Considerations, Demetzos, C.; Pippa, N., Eds. Springer Singapore: Singapore, 2019; pp 397-444.
31.Dong, Y.; Pamukcu, S., Synthesis of Surface-Modified Sands with Thermoresponsive Wettability. Journal of Materials in Civil Engineering 2020, 32 (9), 04020271.
32.Chuang, W.-J.; Chiu, W.-Y., Thermo-responsive nanofibers prepared from poly(N-isopropylacrylamide-co-N-methylol acrylamide). Polymer 2012, 53 (14), 2829-2838.
33.Chen, B.-Y.; Kuo, C.-C.; Cho, C.-J.; Liang, F.-C.; Jeng, R.-J., Novel fluorescent chemosensory filter membranes composed of electrospun nanofibers with ultra-selective and reversible pH and Hg2+ sensing characteristics. Dyes and Pigments 2017, 143, 129-142.
34.Sun, Y.; Cheng, S.; Lu, W.; Wang, Y.; Zhang, P.; Yao, Q., Electrospun fibers and their application in drug controlled release, biological dressings, tissue repair, and enzyme immobilization. RSC Advances 2019, 9 (44), 25712-25729.
35.Lin, X.; Tang, D.; Yu, Z.; Feng, Q., Stimuli-responsive electrospun nanofibers from poly (N-isopropylacrylamide)-co-poly (acrylic acid) copolymer and polyurethane. Journal of Materials Chemistry B 2014, 2 (6), 651-658.
36.Ghosal, K.; Chandra, A.; G, P.; S, S.; Roy, S.; Agatemor, C.; Thomas, S.; Provaznik, I., Electrospinning over Solvent Casting: Tuning of Mechanical Properties of Membranes. Sci Rep 2018, 8 (1), 5058.
37.Burger, C.; Hsiao, B. S.; Chu, B., Nanofibrous Materials and Their Applications. Annual Review of Materials Research 2006, 36 (1), 333-368.
38.Haider, A.; Haider, S.; Kang, I.-K., A comprehensive review summarizing the effect of electrospinning parameters and potential applications of nanofibers in biomedical and biotechnology. Arabian Journal of Chemistry 2018, 11 (8), 1165-1188.
39.Fong, H.; Chun, I.; Reneker, D. H., Beaded nanofibers formed during electrospinning. Polymer 1999, 40 (16), 4585-4592.
40.Josef, E.; Guterman, R., Designing Solutions for Electrospinning of Poly(ionic liquid)s. Macromolecules 2019, 52 (14), 5223-5230.
41.Bhushan, B., Encyclopedia of Nanotechnology. 2012.
42.Cloupeau, M.; Prunet-Foch, B., Electrostatic spraying of liquids in cone-jet mode. Journal of electrostatics 1989, 22 (2), 135-159.
43.Shao, H.; Fang, J.; Wang, H.; Lin, T., Effect of electrospinning parameters and polymer concentrations on mechanical-to-electrical energy conversion of randomly-oriented electrospun poly(vinylidene fluoride) nanofiber mats. RSC Advances 2015, 5 (19), 14345-14350.
44.Yuan, X.; Zhang, Y.; Dong, C.; Sheng, J., Morphology of ultrafine polysulfone fibers prepared by electrospinning. Polymer International 2004, 53 (11), 1704-1710.
45.Yang, G. Z.; Li, H. P.; Yang, J. H.; Wan, J.; Yu, D. G., Influence of Working Temperature on The Formation of Electrospun Polymer Nanofibers. Nanoscale Res Lett 2017, 12 (1), 55.
46.Nezarati, R. M.; Eifert, M. B.; Cosgriff-Hernandez, E., Effects of humidity and solution viscosity on electrospun fiber morphology. Tissue Eng Part C Methods 2013, 19 (10), 810-9.
47.El-Betany, A. M.; McKeown, N. B., The synthesis and fluorescence properties of macromolecular components based on 1, 8-naphthalimide derivatives and dimers. Tetrahedron Letters 2012, 53 (7), 808-810.
48.Kumawat, L. K.; Abogunrin, A. A.; Kickham, M.; Pardeshi, J.; Fenelon, O.; Schroeder, M.; Elmes, R. B. P., Squaramide-Naphthalimide Conjugates as "Turn-On" Fluorescent Sensors for Bromide Through an Aggregation-Disaggregation Approach. Front Chem 2019, 7, 354.
49.Kim, J. S.; Quang, D. T., Calixarene-derived fluorescent probes. Chemical Reviews 2007, 107 (9), 3780-3799.
50.Haenni, D.; Zosel, F.; Reymond, L.; Nettels, D.; Schuler, B., Intramolecular distances and dynamics from the combined photon statistics of single-molecule FRET and photoinduced electron transfer. The Journal of Physical Chemistry B 2013, 117 (42), 13015-13028.
51.Shrivastava, A.; Gupta, V. B., Methods for the determination of limit of detection and limit of quantitation of the analytical methods. Chronicles of young scientists 2011, 2 (1), 21-25.