Photoswitchable dual-color fluorescent polymeric nanoparticles for self-erased time-resolved information encryption and anti-counterfeiting
Hong Wang , Yong Tian , Tiancheng Wu , Shun He , Jiaxi Cui , Jian Chen , Xudong Chen
Photoswitchable fluorescent polymeric nanoparticles (PFPNs) that can regulate their fluorescence color through the non-destructiveness and spatial-controllability of light, and thus shows great application potential in bioimaging, security inks, data storage, rewritable patterning, information encryption and anti-counterfeiting [1-6]. Recently, many PFPNs with excellent photoswitchable performance including high fluorescence contrast, fast photo-responsibility, and photo-reversibility were developed to expand their applications in information encryption and anti-counterfeiting [2, 4, 7-10]. However, these PFPNs can only rely on the fluorescence or color of the stable state induced by light to achieve information encryption and anti-counterfeiting, resulting in the low security and easy replication. Despite significant progress in information encryption and anti-counterfeiting, the development of dynamic information encryption and anti-counterfeiting with the high security remains challenging.
To address, time-resolved encryption technology were developed and integrated into polymer systems to enable pre-designed correct information to be observed at a specific time period, resulting in the high security of information encryption and anti-counterfeiting [11-22]. In these technologies, all kinds of stimuli (e.g., light, heat, water, and pH) were utilized to induce a dynamic change in the fluorescence, color, transparency, etc. By contrast, introducing time-resolved encryption technology into PFPNs was a more desired strategy because the non-destructiveness and spatial-controllability of light as stimuli could induce a thermodynamically driven dynamic process in fluorescence or color [23-25]. These works usually made use of the feature of photochromic molecules (i.e., photochromic spiropyrane or spiroxazine derivatives) that exhibited different thermal isomerization rates in polymer substrates with different glass transition temperatures (Tg) to implement time-resolved information encryption and anti-counterfeiting. Owing to the flexibility of design and easy preparation and functionalization, photoswitchable fluorescent polymeric nanoparticles containing photochromic spiropyran derivatives were designed for time-resolved information encryption [23-25]. Although these materials shown excellent time-resolved responsiveness and photoresponsiveness, the photo-fatigue effect of spiropyran itself resulted in poor photo-reversibility. Therefore, introducing photochromic spiroxazine derivatives into nanoparticles systems to fabricate PFPNs with prominent photoreversibility was crucial for the development of advanced information encryption and anti-counterfeiting system with the high security.
Herein, we described photoswitchable dual-color fluorescent polymeric nanoparticles (PDFPNs) with high fluorescence contrast, the fast photo-response, and excellent photoreversibility for self-erased time-resolved information encryption and anti-counterfeiting. In this system, 4-ethoxy-9-allyl-1, 8-naphthalimide (EANI), 10-(diethylamino)-5-oxo-5H-benzo-[a]phenoxazin-2-yl-methacrylate (NRME), and 1, 3, 3-trimethylspiro[indoline-2, 3′-naphtho [2, 1-b], [1, 4]oxazin]-9′-yl-acrylate (SOMA) were covalently integrated into polymeric nanoparticles by a simple one-pot miniemulsion polymerization with methacrylate/butyl acrylate. There were two light-induced fluorescence resonance energy transfer (FRET) process between EANI and SOMA, NRME and SOMA (Fig. 1). Because the significantly different thermo-induced isomerization rates of SOMA in different polymethacrylate (PMMA, rigid polymer) or poly(butyl acrylate) (PBA, flexible polymer) substrates, PDFPNs exhibited the time-resolved fluorescence change process from blue to red. These excellent features prompted us to apply PDFPNs in time-resolved information encryption and anti-counterfeiting.
Fig. 1 showed our design concept via employing rigid PMMA and flexible PBA as matrixes, blue EANI and red NRME with the outstanding photostability as FRET donors, and SOMA as FRET acceptors with excellent photo-reversibility to fabricate PDFPNs [26-28]. The ring-closed form of photochromic SOMA (SOMA-c, Fig. 1b) has no absorption band between 450 nm and 700 nm. After ultraviolet light (UV) irradiation, the ring-opened merocyanine state (MC) of SOMA (SOMA-o, Fig. 1b) exhibited an obvious absorption. A poor spectral overlap between the fluorescence emission of EANI and the absorbance of MC form of SOMA and a large spectral overlap between the fluorescence emission of NRME and the absorbance of MC form of SOMA could ensure that PDFPNs has a light-induced fluorescent color change from red to blue. The thermo-induced isomerization rate of SOMA from MC state to SP state depended on the Tg of polymers, resulting in the programmable decoloration rates. The rigid PMMA (high Tg) in nanoparticles would cause the MC state of SOMA to present a slow thermo-induced isomerization process, whereas flexible PBA (low Tg) in nanoparticles would induce a fast thermo-induced isomerization process (Figs. 1a and b). Therefore, when we created the information encryption units using a different flexible polymer matrix containing the same concentration EANI, NRME, and SOAM, the displayed information including the false interference information induced by UV were gradually recovered in the dark. Over time, only the correct information was displayed, and eventually all the information disappears, resulting in the self-erased time-resolved information encryption (Fig. 1c).
EANI, NRME, and SOMA were synthesized via our reported methods [26-28]. UV absorption spectra for EANI and NRME in different solvents (dichloromethane (DCM), N, N-dimethylformamide (DMF), hexane (Hex), methanol (MeOH), tetrahydrofuran (THF)) were tested. EANI and NRME showed the polarity dependence from Hex to MeOH (Fig. S1 in Supporting information). There were integrated into PMMA- or PBA-based nanoparticles via a simple miniemulsion polymerization (Fig. S2a in Supporting information). The nanoparticles presented a regular spherical structure based on the dynamic light scattering (DLS) and atomic force microscope (AFM) (d = 76.7 nm, Figs. S2b and c, Table S1 in Supporting information), and transmission electron microscope (TEM, d = 72 nm, Fig. S3 in Supporting information). The fluorescence and absorbance properties of PDFPNs containing only EANI or NRME were firstly investigated. The absorbance spectrum of NP-9 and NP-10 revealed that EANI and NRME shown a remarkable absorbance peak at 366 and 565 nm, respectively (Fig. S4 in Supporting information). Absorbance and fluorescence spectrum of NP-9 and NP-10 indicated that EANI or NRME (> 90%, Table S2 in Supporting information) were successfully embedded into the nanoparticle via covalent bonds (Figs. S5a and b in Supporting information), respectively [3, 26, 27]. A change in fluorescence emission of NP-11 and NP-12 demonstrated two typical FRET process between EANI and SOMA-o, NRME and SOMA-o (Figs. S5c and d in Supporting information). The mass ratio between EANI and NRME were investigated. When the mass of NRME were fixed (1 mg, Table S1 and Fig. S6 in Supporting information), the fluorescence intensity of EANI and NRME obviously increased with the enhancement of EANI (Fig. S6). Considering fluorescence intensity between EANI and NRME, NP-2 with the similar fluorescence intensity between 430 nm (EANI) and 610 nm (NRME) was chosen.
Subsequently, the different amount of SOMA were introduced into nanoparticles containing EANI and NRME (NP-2) to explore FRET process between EANI and SOMA, and NRME and SOMA. As depicted in Figs. 2a–c, upon the increase of SOMA in nanoparticles, the FRET efficiency between EANI and the MC form of SOMA enhanced from 22.1% to 47.2%, whereas the FRET efficiency between NRME and the MC form of SOMA rose from 77.6% to 95.6%. This difference should be attributed to the fact that the different spectral overlap (Fig. S7 in Supporting information). Considering FRET efficiency, the feed of SOMA, and fluorescence color, NP-5 was chosen as typical sample to study the fluorescence properties.
The previous work indicated that the higher Tg could induce a slower discoloration rate [23, 25, 28]. We thus chosen MMA as rigid monomer and BA as flexible monomer to prepare three polymer nanoparticles (MMA: BA= 1:0, 1:1, 0:1) for exploring their photoswitchable properties. We further calculated the molecular volume of SOMA before and after UV irradiation to explore its thermo-induced isomerization rates in the polymer matrix with different rigidity. The spatial structure and molecular volume of SOMA after UV irradiation showed an obvious enhancement, especially in the Y-axis direction (Fig. S8 in Supporting information). Therefore, the photoisomerization process required a free space. In nanoparticles, a lower Tg can ensure a more free space inside the polymer to induce an easy photoisomerization process the from SP state to the MC form, whereas high Tg may not provide enough space to facilitate this photoisomerization process. As shown in Fig. 2d, with the enhancement of BA fractions in polymers, Tg decreased significantly from ~105 ℃ to ~−49 ℃. Such change in Tg resulted in a noteworthy enhancement in FRET efficiency (26.2% to 54.6%) between EANI and SOMA-o and a slight increase in FRET efficiency (89.6% to 93.7%) between NRME and SOMA-o (Figs. 2b, e, and f). This arresting change in FRET efficiency between EANI and SOMA-o should be attributed to the synergistic action between the increase of spectral overlap due to the EANI spectral redshift (430 nm to 435 nm, Fig. S9 and Table S3 in Supporting information) induced by the increase of BA fractions and the enhanced uniform dispersion of SOMA in flexible polymer matrix (Figs. S10 and S11, Table S3 in Supporting information).
Subsequently, the self-erased time-resolved fluorescence switching property of PDFPNs was investigated by UV irradiation and storage in a dark condition (25 ℃) for the different times. When the samples (NP-5) containing PMMA were exposed to UV and then storage in the dark (25 ℃), the fluorescence intensity of EANI and NRME can be restored to the initial state within 6 h (Fig. 3a). The fluorescence intensity at 610 nm was selected to make a fitting curve to observe decoloration rate constant (kD, Fig. 3b). During this recovery process, the fluorescence color gradually changes from blue to red because of the absence of FRET (Fig. 3c). In contrast, NP-7 containing PMMA and PBA (nMMA/nBA: 1/1) and NP-8 containing PBA took less time to restore to the initial state (3 min (Figs. 3d–f) and 24 s (Figs. 3g–i)), accompanying with the increase kD (from 0.015 s−1 to 3.582 s−1). This phenomenon should to be fact that the hard polymers (PMMA) can limit the isomerization rate of SOMA and induce slower coloration/decoloration rates. This process was consistent with the kinetics of described decoloration (Eq. S1 in Supporting information) [28].
Obviously, there were two different photo-induced FRET processes in this system: a weak FRET process between EANI and SOMA-o because of a poor spectral overlap between the fluorescence emission of EANI and the absorbance of SOMA-o, and a strong FRET process between NRME and SOMA-o due to a large spectral overlap between the fluorescence emission of NRME and the absorbance of SOMA-o. We thus implemented the change of photo-induced average fluorescence lifetime of PDFPNs (NP-7) by using the time-correlated single-photon counting (TCSPC) technique. When NP-7 was exposed to UV, the average fluorescence lifetime of EANI in nanoparticles showed a 35% reduction (from 5.22 ns to 3.38 ns, Fig. S12a in Supporting information), while NRME's average fluorescence lifetime in nanoparticles exhibited a 50% decrease (from 4.22 ns to 2.11 ns, Fig. S12b in Supporting information), implied two different FRET processes.
The photoswitchable performance was an important index to evaluate PDFPNs system. We thus evaluated photoswitchable properties of NP-7. As depicted in Fig. 4a, when NP-7 were exposed to UV light, the fluorescent intensity at 610 nm decreased significantly within 0.5 min and then remained stable because of the absence of FRET process between NRME and SOMA-o. Subsequently, NP-7 were transferred to a dark condition (25 ℃), the fluorescence intensity gradually returned to the initial state within 4 min. In addition, we also implemented the photoreversibility of NP-7. When the sample were alternately stored in UV light (0.5 min) and dark environments (4 min), no obvious fluorescence attenuation after 30 cycles were observed (Fig. 4b), indicated that NP-7 possessed the satisfactory photoreversibility. These results implied that PDFPNs have the great application potential in anti-counterfeiting and information encryption.
The desired self-erased time-resolved properties allowed us to utilize PDFPNs to fabricate the high security of advanced information encryption and anti-counterfeiting systems. We thus employed PDFPNs (NP-5, NP-7, NP-8) as functional units to prepared the anti-counterfeiting labels. As depicted in Fig. 5a, NP-5, NP-7, and NP-8 were used to fabricate different parts of the number "8" (NP-5 ("1"), NP-7 (≡), NP-8 ("1")). All parts exhibited the red fluorescence in the original state (Figs. 5a and b). When they were exposed to UV light, the fluorescence of number "8" changed from red to blue. Subsequently, the number was stored in a dark condition for 20 s (25 ℃), a red fluorescence information (the number "1" prepared by NP-8) revealed emerged because higher flexibility of PBA can induce an easy isomerization to cause a faster discoloration rate. In contrast, the other parts still showed blue fluorescence due to the slower discoloration rate. Over time, red information ("3") occurred. Finally, all information disappeared. In addition, when we used them to prepare others anti-counterfeiting labels (Chinese character ("1"), Fig. S13 in Supporting information), similarly, the Chinese character ("1") with red fluorescence were observed, whereas the blue fluorescent Chinese characters appeared after UV irradiation. Subsequently, Chinese characters with blue fluorescence gradually changed from "1" to "2" (20 s) and "3" (2 min). This result indicated PDFPNs can be used to develop advanced anti-counterfeiting technology with high security.
Information security has been widely concerned because of its importance in national and personal property security [4, 29, 30]. Based on the excellent performances including self-erased time-resolved, high fluorescence contrast, fast photo-responsibility, photoreversibility, and photostability, we thus attempted the application of PDFPNs in self-erased time-resolved information encryption. As revealed in Fig. 5c, we prepared the information encryption units by coating PDFPNs (NP-5, NP-7, NP-8) onto the circular filter papers. The whole system did not show any useful information before and after UV irradiation (Fig. 5d). When it was stored in a dark condition, the primary information "1" displayed at 20 s. Subsequently, the information "I" appeared at 2 min (Fig. 5d). Eventually, the all information disappeared, implying a complex information encryption process with simple operation. In addition, we chose NP-2, NP-5, NP-7, and NP-8 as the corresponding basic units that were infused in a 96-well plate for the construction of self-erased time-resolved information encryption. All information remained in an encrypted state after UV exposure (Fig. S14 in Supporting information). When it was exposed to UV light, the primary information "OOO" displayed (Fig. S14). Subsequently, it was stored in a dark environment, information "MAN" and "LAD" are emerged at 20 s and 2 min, respectively (Fig. S14). These results demonstrated that PDFPNs can be used to develop the high security of multilevel information encryption systems.
In conclusion, we described a strategy of PDFPNs for self-erased time-resolved information encryption and anti-counterfeiting. Two photo-induced FRET processes between EANI and SOMA, NRME and SOMA were presented in nanoparticles. A time-resolved fluorescence switching between red and blue can be achieved via tuning chain flexibility (Tg) to induce the photochromic behavior of SOMA, which improved information encryption security. Thanks to the some excellent properties, including the self-erased time-resolved photoswitchable dual-color fluorescence, fast photo-responsibility, photostability, and photoreversibility, we thus demonstrated their potential in the high security of self-erased time-resolved information encryption and anti-counterfeiting via facile decoding way. We envision that the self-erased time-resolved dual-color fluorescence switching strategy can be applied in developing advanced multilevel information encryption and anti-counterfeiting systems with high security.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Hong Wang: Writing – review & editing, Writing – original draft, Visualization, Supervision, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Yong Tian: Writing – review & editing, Writing – original draft, Visualization, Validation, Project administration, Methodology, Investigation, Formal analysis, Data curation. Tiancheng Wu: Writing – review & editing, Writing – original draft, Visualization, Methodology, Investigation, Formal analysis, Data curation. Shun He: Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. Jiaxi Cui: Writing – review & editing, Writing – original draft, Visualization, Formal analysis, Conceptualization. Jian Chen: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Data curation, Conceptualization. Xudong Chen: Writing – review & editing, Writing – original draft, Supervision, Conceptualization.
This work was financially supported by the National Key R & D Program of China (Nos. 2023YFB3812400, 2023YFB3812403), National Natural Foundation of China (Nos. 52273206, 52350233), Hunan Provincial Natural Science Foundation (No. 2021JJ10029), Huxiang High-level Talent Gathering Project (No. 2022RC4039).
Supplementary material associated with this article can be found, in the online version, at doi:
K. Peng, F. Lv, H. Lu, et al., Chin. Chem. Lett. 31 (2020) 755–758.
A. Abdollahi, B. Ghasemi, S. Nikzaban, et al., ACS Appl. Mater. Interfaces 15 (2023) 7466–7484. doi: 10.1021/acsami.2c22532
H. Wang, P. Zhang, B.P. Krishnan, et al., J. Mater. Chem. C 6 (2018) 9897–9902. doi: 10.1039/c8tc03757d
Z. Quan, Q. Zhang, H. Li, S. Sun, Y. Xu, Coord. Chem. Rev. 493 (2023) 215287.
W. Wan, M. -Q. Zhu, Z. Tian, A.D.Q. Li, J. Am. Chem. Soc. 137 (2015) 4312–4315. doi: 10.1021/jacs.5b01007
Z. Yao, X. Wang, J. Liu, et al., Chem. Commun. 59 (2023) 2469–2472. doi: 10.1039/d2cc06707b
J. Li, M. Tian, H. Xu, X. Ding, J. Guo, Part. Part. Syst. Char. 36 (2019) 1900346.
S. Lin, Y. Tang, W. Kang, et al., Nat. Commun. 14 (2023) 3005.
M. Yu, P. Zhang, B.P. Krishnan, et al., Adv. Funct. Mater. 28 (2018) 1804759.
Y. Zhuang, X. Ren, X. Che, et al., Adv. Photon. 3 (2021) 014001.
J. Tan, Q. Li, S. Meng, et al., Adv. Mater. 33 (2021) 2006781.
D. Guo, X. Le, H. Shang, et al., Chin. Chem. Lett. 34 (2023) 108347.
D. Feng, Q. Guo, Z. Huang, et al., Adv. Mater. 36 (2024) 2314201.
Q. Wang, Z. Qi, Q. -M. Wang, et al., Adv. Funct. Mater. 32 (2022) 2208865.
X. Le, H. Shang, H. Yan, et al., Angew. Chem. Int. Ed. 60 (2021) 3640–3646. doi: 10.1002/anie.202011645
Z. Zou, J. Wang, Y. Sun, Q. Wang, D.H. Qu, Chin. Chem. Lett. 35 (2024) 108972.
Y. Zhang, X. Zhang, Z. Feng, et al., ACS Appl. Mater. Interfaces 13 (2021) 44797–44805. doi: 10.1021/acsami.1c12647
J. Zhou, D. Liu, L. Li, et al., Chin. Chem. Lett. 35 (2024) 109929.
D. Li, Z. Feng, Y. Han, et al., Adv. Sci. 9 (2022) 2104790.
Z. Gao, S. Qiu, F. Yan, et al., Chem. Sci. 12 (2021) 10041–10047. doi: 10.1039/d1sc03105h
Y. Ma, Y. Yu, P. She, et al., Sci. Adv. 6 (2020) eaaz2386.
D. Lou, Y. Sun, J. Li, et al., Angew. Chem. Int. Ed. 61 (2022) e202117066.
M. Tao, X. Liang, J. Guo, et al., ACS Appl. Mater. Interfaces 13 (2021) 33574–33583. doi: 10.1021/acsami.1c09677
Y. Xie, M.C. Arno, J.T. Husband, M. Torrent-Sucarrat, R.K. O'Reilly, Nat. Commun. 11 (2020) 2460.
M.H. Sharifian, A.R. Mahdavian, H. Salehi-Mobarakeh, Langmuir 33 (2017) 8023–8031. doi: 10.1021/acs.langmuir.7b01869
H. Wang, P. Zhang, J. Chen, et al., Sens. Actuators B: Chem. 242 (2017) 818–824.
Z. Lin, H. Wang, M. Yu, et al., J. Mater. Chem. C 7 (2019) 11515–11521. doi: 10.1039/c9tc04054d
T. Wu, Y. Tian, J. Wu, et al., Dyes. Pigments 212 (2023) 111119.
L. Shi, L. Ding, Y. Zhang, S. Lu, Nano Today 55 (2024) 102200.
Y. Wu, X. Chen, W. Wu, Small 19 (2023) 2206709.
Figure 1 Design of photoswitchable dual-color fluorescent polymeric nanoparticles (PDFPNs). (a) Concept and self-erased process of PDFPNs. (b) Schematic illustration of EANI, NRME, polymer, photochromism of SOMA, and FRET process. (c) Schematic illustration of self-erased time-resolved information encryption.
Figure 2 Photoswitchable fluorescence property of PDFPNs. Fluorescence response of NP-4 (a), NP-5 (b), NP-6 (c) under UV (365 nm, 2.36 mW/cm2) irradiation for 2 min, and storage in a dark condition for 6 h (25 ℃). (d) Tg of NP-5, NP-7, NP-8. Fluorescence response of NP-7 (e) and NP-8 (f) under UV (365 nm, 2.36 mW/cm2) irradiation for 2 min, and storage in a dark condition for 44 min (25 ℃). Scale bar: 5 mm.
Figure 3 The self-erased property of PDFPNs. Fluorescence response (a) and normalized fluorescence intensity at 610 nm (b) of NP-5 containing MMA as monomers after treating with UV (365 nm, 2.36 mW/cm2) for 2 min, and storage in a dark condition for 6 h (25 ℃), and the corresponding photographs (c). Fluorescence response (d) and normalized fluorescence intensity at 610 nm (e) of NP-7 containing MMA and BA (nMMA/nBA: 1/1) as monomers after treating with UV (365 nm, 2.36 mW/cm2) for 2 min, and storage in a dark condition for 3 min (25 ℃), and the corresponding photographs (f). Fluorescence response (g) and normalized fluorescence intensity at 610 nm (h) of NP-8 containing BA as monomers after treating with UV (365 nm, 2.36 mW/cm2) for 2 min, storage in a dark condition for 0.4 min (25 ℃), and the corresponding photographs (i). Scale bar: 5 mm.
Figure 4 The photoswitchable fluorescence property of PDFPNs. (a) Fluorescence response of NP-7 under UV irradiation and storage in a dark. (b) Photo-induced switching cycles of NP-7 under alternative illumination of UV for 30 s and storage in a dark for 3 min.
Figure 5 Self-erased time-resolved anti-counterfeiting and information encryption. (a) Schematic illustration of multi-level information encryption by using NP-5, NP-7, NP-8 as different part of the number "8". (b) The photograph of the number "8" irradiated by UV stored in dark for the different times (20 s, 2 min, 3 h). (c) Schematic illustration of multi-level binary information encryption. (d) The photograph of the binary information irradiated by UV stored in dark for the different times (20 s, 2 min, 3 h). Scale bar: 1 cm.
扫一扫看文章
扫一扫关注我们
DownLoad:
下载:
下载: