Name: electroactive polymer nanoparticles exhibiting photothermal properties
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Description: Watch this Scientific Journal Video about Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties at JoVE.com

This work was funded in part by the Texas Emerging Technology Fund (Startup to TB), the Texas State University Research Enhancement Program, the Texas State University Doctoral Research Fellowship (to TC), the NSF Partnership for Research and Education in Materials (PREM, DMR-1205670), The Welch Foundation (AI-0045), and National Institutes of Health (R01CA032132).

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The authors have nothing to disclose.

In this work, electroactive polymer NPs have been synthesized as potential PTT agents for cancer treatment. The preparation of the NPs is described, starting with the synthesis of the monomers followed by emulsion polymerization. While the preparation of NPs using electroactive polymers such as EDOT and pyrrole has been described before, this paper describes the preparation of polymeric NPs starting with unique extended conjugation monomers, demonstrating that this process can be extended to larger, more complex monomers.
Two different routes are necessary to synthesize the dialkoxybenzene monomers. While the 1,4-dihexyloxybenzene can be synthesized using KOH/EtOH, that approach is unsuccessful in the synthesis of 1,4-bis(ethyl butanoyloxy)benzene, most likely due to base-promoted ester hydrolysis. When a KI/K2CO3 mixture is used, hydrolysis is avoided, and the product is successfully obtained. Bromination of both dialkoxybenzenes is accomplished using Br2. It is necessary to conduct this experiment under flowing argon to displace HBr formed during the reaction. The gas outlet should vent over a neutralizing NaOH solution to prevent HBr from corroding hood fixtures; note that HBr may cause plastic tubing to harden over time.
BEDOT-B(OR)2 monomers M1 and M2 were synthesized using Negishi coupling. This is an effective method for the carbon-carbon coupling of EDOT with 1,4-dialkoxy-2,5-dibromobenzenes to yield BEDOT-B(OR)2 monomers. It is crucial to chill the EDOT to -78 &#176;C prior to the addition of nBuLi, in order to minimize undesirable side reactions. When all the 1,4-dialkoxy-2,5-dibromobenzene is depleted from the reaction mixture (determined using TLC; this typically takes 3-5 days), the reaction is complete. The reaction is extremely air sensitive, and any exposure to air will affect the yield of the reaction. Thus, when introducing solid compounds (such as the catalyst) into the sealed flask, air exposure should be minimized by increasing argon flow.
Electroactive monomers and polymers are routinely characterized using cyclic voltammetry to determine monomer and polymer oxidation potentials and polymer reduction potentials, and films prepared via electrochemical polymerization are used to determine polymer absorption in the UV-Vis-nIR spectrum in both the oxidized and reduced states. In this work, polymer films were deposited onto both a platinum button and ITO coated glass by electropolymerization. Some of the advantages of electropolymerization are reproducibility and the ability to control the film thickness by monitoring the current of the polymerized film and stopping the electropolymerization when a specific response is achieved.34 Electrochemical experiments must be conducted under an inert atmosphere such as argon; the argon flow should be so slow as to not disturb the surface of the solution to ensure a diffusion-controlled process. Alternatively, the electrochemical experiments can be performed in an inert atmosphere dry box fitted with electrochemical feedthroughs. It is important that none of the three electrodes are touching each other during electropolymerization. Prior to polymer cyclic voltammetry studies, the deposited polymer films must be washed with monomer-free electrolyte solution to remove any unreacted monomer from the films. For all electrochemical studies the potential range needed will depend on the structure of the monomer/polymer; so this range may vary with alternative monomers and polymers. Depending on the structure of the alkoxy substituents, the solvent used to prepare the monomer electrolyte solutions may also dissolve the polymer. In that case, polymer deposition on the electrode during electropolymerization will be slow or non-existent, and the solvent used for polymerization must be changed.
Emulsion polymerization for the preparation of NPs composed of electroactive polymers is an effective method that yields NPs with a uniform morphology. In this work, the emulsion polymerization process utilizes the same oxidative polymerization mechanism utilized during electrochemical polymerization; the major difference is that a chemical oxidant (ferric chloride) is used instead of an applied electrochemical potential. This emulsion polymerization, therefore, produces NPs identical in chemical composition to the films prepared via electrochemical polymerization. While electrochemical polymerization provides a facile means of characterizing the redox properties of the monomers and polymers, emulsion polymerization is a quick, inexpensive, and reproducible process that is easily scalable and can potentially be used with a number of different electroactive polymers. Emulsion polymerization also enables the preparation of NPs from polymers that have low solubility in organic and aqueous solutions that could not be emulsified effectively from the polymeric state. In our emulsion polymerizations, the organic phase was comprised of monomer, organic solvent (hexane), and dodecylbenzene sulfonic acid (surfactant). The aqueous phase was comprised of water, ferric chloride (oxidant), and PSS-co-MA (surfactant). The emulsion polymerization process is preceded by a sonication step to ensure the organic phase is well dispersed in the aqueous phase. During sonication, it is necessary to immerse the emulsion in an ice bath to prevent bulk heating. The surfactants PSS-co-MA and DBSA enable the dispersion of the synthesized NPs in aqueous solutions through inter-particle electrostatic repulsive forces. These surfactants also act as additional charge-balancing dopants and have been shown to produce spherical NP geometry.24 The polymeric NPs remain in the oxidized state, (as evidenced by the peak absorption at 795 nm; Figure 4), which is critical for biomedical applications in which absorption in the NIR range is necessary.24
Zeta potential analysis is commonly performed to assess the stability of NP suspensions. Zeta potential is the potential at the boundary between the Stern layer where ions are strongly associated with the NP surface, and the diffuse layer where ions no longer interact with the NP surface.31 Zeta potential measurements rely on the movement of charged NPs when an electric field is applied to the suspension. Specifically, negatively charged NPs are attracted toward the positive electrode, and vice versa. Colloidal suspensions can be stabilized via electrostatic repulsions. Specifically, suspensions are considered stable when their zeta potential is greater than +/- 30 mV. In our NP formulations, the presence of sulfonate and carboxylate groups from DBSA and PSS-co-MA yields a negative surface charge on the NPs.
Purification of the NPs is a crucial step in order to remove any excess surfactant and any unreacted starting material prior to in vitro cell studies. Ineffective surfactant removal can lead to significant cell death. As for any other in vitro cell assay, it is vital to work in a laminar flow hood and to work under sterile conditions. NPs should also be sterilized prior to use by passing the suspension through a sterile 0.2-&#181;m filter. It is also important to verify the concentration of NP suspensions after sterile filtering. For this purpose, a fraction of the filtered NP suspension of known volume can be freeze dried to obtain the dry mass. The MTT cell viability assay is typically used to study the effect of biomaterials, including NPs, on cultured cells. This simple assay can be adapted to the investigation of the cytocompatibility of NP suspensions with any mammalian cell line. The MTT colorimetric assay is based on the conversion of a yellow tetrazolium dye into purple, insoluble formazan crystals which can then be dissolved in DMSO or acidic alcohol solutions.35,36 When performing in vitro cell assays such as the MTT cell viability assay in multi-well plates, consistency in cell seeding and manipulation is critical to achieve minimal differences between replicate samples. Prior to and during the experiment, the seeded cells should be examined under a microscope to ensure consistent seeding and growth, and also to rule out any contamination. Finally, microscopy can also be utilized to confirm complete dissolution of formazan crystals after addition of DMSO.
Photothermal studies were conducted using a continuous laser at 808-nm. The use of continuous vs. pulsed lasers can heat materials differently. Previous studies have compared photothermal conversion and photothermal ablation with gold nanostructures as PTT agents,37 but more research is needed to investigate photothermal conversion from polymeric NPs like the ones described herein. In this work, the laser was diverged into a convex lens and focused at a 6 mm spot size. It is important to be careful not to disturb the optical system when running experiments to prevent accidental changes in the focal plane that would cause differences in the photothermal conversion results. A hot plate was used to warm and maintain a constant baseline temperature for the study.
In conclusion, a protocol for NP preparation of electroactive polymers suspended in aqueous medium is described. Negishi coupling is an effective method for coupling 1,4-dialkoxy-2,5-dibromobenzenes with 3,4-ethylenedioxythiophene (EDOT). Electropolymerization of the monomers is detailed in this protocol. This proves to be an effective way to rapidly produce polymer films and study their electronic properties. The polymer films are further characterized using UV-Vis-NIR spectroscopy to determine the band gaps of the neutral polymers. Electrochemical emulsion polymerization yields sub-100 nm NPs with uniform spherical morphologies. In addition to photothermal ablation therapy, these NPs have many potential applications in electroactive devices, including energy storage and sensors. The thermal and cytocompatibility studies performed indicate that these NPs could be potential candidates in biomedical applications as photothermal agents.

Electroactive polymers change their properties (color, conductivity, reactivity, volume, etc.) in the presence of an electric field. The rapid switching times, tunability, durability, and lightweight characteristics of electroactive polymers have led to many proposed applications, including alternative energy, sensors, electrochromics, and biomedical devices. Electroactive polymers are potentially useful as flexible, light-weight battery and capacitor electrodes.1 Applications of electroactive polymers in electrochromic devices include glare-reduction systems for buildings and automobiles, sunglasses, protective eyewear, optical storage devices, and smart textiles.2-5 Smart windows can reduce energy requirements by blocking specific wavelengths of light on-demand and protecting interiors of homes and automobiles. Smart textiles can be used in clothing to help protect against UV radiation.6 Electroactive polymers have also begun to be used in medical devices. Among electroactive polymers used in biomedical devices, polypyrrole (PPy), polyaniline (PANI), and poly(3,4-ethylenedioxythiophene) (PEDOT) are among the most common. For example, these types of polymers are commonly used as transducers in biosensor devices.7 Applications in therapeutic delivery have also shown promise; studies have demonstrated the release of drugs and therapeutic proteins from devices prepared from electroactive polymers.8-12 More recently, electroactive polymers have been used as therapeutic agents in photothermal therapy.13-15 In photothermal therapy, photothermal agents must absorb light in the near-infrared (NIR) region (~ 700&#8722;900 nm), also known as the therapeutic window, where light has the maximum depth of penetration in tissue, typically up to 1 cm.16,17 In this range, biological chromophores such as hemoglobin, oxygenated hemoglobin, lipids, and water have little-to-no absorbance, which enables light to penetrate easily. When photothermal agents absorb light in this therapeutic window, the photoenergy is converted to photothermal energy.
Irvin and co-workers have previously reported alkoxy-substituted bis-EDOT benzene monomers that were synthesized using Negishi coupling.18 Negishi coupling is a preferred method for carbon-carbon bond formation. This process has many advantages, including the use of organozinc intermediates, which are less toxic and tend to have higher reactivity than other organometallics used.19,20 Organozinc compounds are also compatible with a wide range of functional groups on the organohalides.20 In the Negishi coupling reaction, an organohalide and organometal are coupled through the use of a palladium(0) catalyst.20 In the work presented herein, this cross coupling method is utilized in the synthesis of 1,4-dialkoxy-2,5-bis(3,4-ethylenedioxythienyl) benzene (BEDOT-B(OR)2) monomers. These monomers can then be easily polymerized electrochemically or chemically to yield polymers that are promising candidates for use in biomedical applications.
Conventional methods for preparation of colloidal polymeric suspensions in aqueous solutions for biomedical applications typically involve the dissolution of bulk polymers followed by nanoprecipitation or emulsion-solvent evaporation techniques.21,22 In order to produce NPs of poly(BEDOT-B(OR)2), a bottom-up approach is demonstrated here where the NPs are synthesized via in situ emulsion polymerization. Emulsion polymerization is a process that is easily scalable and is a relatively fast method for NP preparation.22 Studies using emulsion polymerization to produce NPs of other electroactive polymers have been reported for PPy and PEDOT.15,23,24 PEDOT NPs, for example, have been prepared using spray emulsion polymerization.24 This method is difficult to reproduce, and typically yields larger, micron-sized particles. The protocol described in this article explores the use of a drop-sonication method to reproducibly prepare 100-nm polymer NPs.
In this protocol, electroactive polymers tailored to absorb light in the NIR region similar to previously reported poly(BEDOT-B(OR)2) are synthesized and characterized to demonstrate their potential in electrochromic devices and as PTT agents. First, the protocol for the synthesis of the monomers via Negishi coupling is described. The monomers are characterized using NMR and UV-Vis-NIR spectroscopy. The preparation of NP colloid suspensions via oxidative emulsion polymerization in aqueous media is also described. The procedure is based on a two-step emulsion polymerization process previously described by Han et al. that is applied to the different monomers. A two-surfactant system is used to control the NP monodispersity. A cell viability assay is used to evaluate cytocompatibility of the NPs. Lastly, the potential of these NPs to act as PTT transducers is demonstrated by irradiation with a NIR laser.

<table><tbody><tr><td>2 mm diameter platinum working electrode</td><td>CH Instruments</td><td>CH102</td><td>Polished using very fine sandpaper</td></tr><tr><td>3,4-ethylenedioxythiophene</td><td>Sigma-Aldrich</td><td>483028</td><td>Purified by vacuum distillation</td></tr><tr><td>3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) 98%</td><td>Alfa Aesar</td><td>L11939</td><td></td></tr><tr><td>505 Sonic Dismembrator</td><td>Fisher Scientific&amp;trade;&amp;nbsp;</td><td>FB505110</td><td>1/8&amp;ldquo; tip and rated at 500&amp;nbsp;watts</td></tr><tr><td>808 nm laser diode</td><td>ThorLabs</td><td>L808P1WJ</td><td>Rated at 1 W</td></tr><tr><td>Acetonitrile anhydrous 99%</td><td>Acros</td><td>61022-0010</td><td></td></tr><tr><td>Avanti J-26 XPI</td><td>Beckman Coulter</td><td>393127</td><td></td></tr><tr><td>Bromohexane 98%</td><td>MP Biomedicals</td><td>202323</td><td></td></tr><tr><td>Dialysis (100,000) MWCO</td><td>SpectrumLabs</td><td>G235071</td><td></td></tr><tr><td>Dimethyl sulfoxide 99% (DMSO)</td><td>BDH</td><td>BDH1115</td><td></td></tr><tr><td>Dimethylformamide anhydrous (DMF) 99%</td><td>Acros</td><td>326870010</td><td></td></tr><tr><td>Dodecyl benzenesulfonate (DBSA)&amp;nbsp;</td><td>TCI</td><td>D0989</td><td></td></tr><tr><td>Dulbecco&amp;rsquo;s modified eagle medium (DMEM)&amp;nbsp;</td><td>Corning</td><td>10-013 CV</td><td></td></tr><tr><td>EMS 150 TES sputter coater</td><td>Electron Microscopy Sciences</td><td></td><td></td></tr><tr><td>Ethanol (EtOH) 100%</td><td>BDH</td><td>BDH1156</td><td></td></tr><tr><td>ethyl 4-bromobutyrate (98%)</td><td>Acros</td><td>173551000</td><td></td></tr><tr><td>Ethyl acetate 99%</td><td>Fisher</td><td>UN1173</td><td></td></tr><tr><td>Fetal bovine serum (FBS)</td><td>Corning</td><td>35-010-CV</td><td></td></tr><tr><td>Helios NanoLab 400</td><td>FEI</td><td></td><td></td></tr><tr><td>Hexane</td><td>Fisher</td><td>H306-4</td><td></td></tr><tr><td>Hydrochloric acid (HCl)</td><td>Fisher</td><td>A142-212</td><td></td></tr><tr><td>Hydroquinone 99.5%</td><td>Acros</td><td>120915000</td><td></td></tr><tr><td>Hydrozine anhydrous 98%</td><td>Sigma-Aldrich</td><td>215155</td><td></td></tr><tr><td>Indium tin oxide (ITO) coated galss</td><td>Delta Technologies</td><td>CG-41IN-CUV</td><td>4-8 &amp;Omega;/sq</td></tr><tr><td>Iron chloride 97% FeCl&lt;sub&gt;3&lt;/sub&gt;</td><td>Sigma-Aldrich</td><td>157740</td><td></td></tr><tr><td>Magnesium sulfate (MgSO&lt;sub&gt;4&lt;/sub&gt;)</td><td>Fisher</td><td>593295</td><td>Dried at 100 &amp;#176;C</td></tr><tr><td>SKOV-3</td><td>ATCC</td><td>HTB-26</td><td></td></tr><tr><td>Methanol</td><td>BDH</td><td>BHD1135</td><td></td></tr><tr><td>n-Butlithium (2.5 M)&amp;nbsp;</td><td>Sigma-Aldrich</td><td>230707</td><td>Pyrophoric</td></tr><tr><td>Poly(styrenesulfonate-co-malic acid) (PSS-co-MA) 20,000 MW</td><td>Sigma-Aldrich</td><td>434566</td><td></td></tr><tr><td>Potassium carbonate</td><td>Sigma-Aldrich</td><td>209619</td><td>Dried at 100 &amp;#176;C</td></tr><tr><td>Potassium hydroxide</td><td>Alfa Aesar</td><td>A18854</td><td></td></tr><tr><td>Potassium iodide</td><td>Fisher</td><td>P410-100</td><td></td></tr><tr><td>RO-5 stirplate</td><td>IKA-Werke</td><td></td><td></td></tr><tr><td>SC4000 IR camera</td><td>FLIR</td><td></td><td></td></tr><tr><td>Synergy H4 Hybrid Reader</td><td>Biotek</td><td></td><td></td></tr><tr><td>Tetrabutylammonium perchlorate (TBAP) 99%</td><td>Sigma-Aldrich</td><td>3579274</td><td>Purified by recrystallization in ethyl acetate</td></tr><tr><td>Tetrahydrofuran anhydrous (THF) 99%</td><td>Sigma-Aldrich</td><td>401757</td><td></td></tr><tr><td>tetrakis(triphenylphosphine) palladium(0)</td><td>Sigma-Aldrich</td><td>216666</td><td>Moisture sensitive</td></tr><tr><td>Thermomixer</td><td>Eppendorf</td><td></td><td></td></tr><tr><td>USB potentiostat/galvanostat</td><td>WaveNow</td><td>AFTP1</td><td></td></tr><tr><td>Zetasizer Nano Zs</td><td>Malvern</td><td></td><td>Optical Arrangment 175&amp;#176;</td></tr><tr><td>Zinc chloride (1 M) ZnCl&lt;sub&gt;2&lt;/sub&gt;</td><td>Acros</td><td>370057000</td><td></td></tr></tbody></table>

electroactive polymer nanoparticles exhibiting photothermal properties

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step process that finishes with Negishi coupling. Negishi coupling is a cross-coupling process in which a chemical precursor is first lithiated, followed by transmetallation with ZnCl2. The resultant organozinc compound can be coupled to a dibrominated aromatic precursor to give the conjugated monomer. Polymer films can be prepared via electropolymerization of the monomer and characterized using cyclic voltammetry and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. Nanoparticles (NPs) are prepared via emulsion polymerization of the monomer using a two-surfactant system to yield an aqueous dispersion of the polymer NPs. The NPs are characterized using dynamic light scattering, electron microscopy, and UV-Vis-NIR-spectroscopy. Cytocompatibility of NPs is investigated using the cell viability assay. Finally, the NP suspensions are irradiated with a NIR laser to determine their effectiveness as potential materials for photothermal therapy (PTT).

The reaction protocol yielding M1 and M2 is shown in Figure 1. The monomers can be characterized by 1H and 13C NMR spectroscopy, melting point, and elemental analysis. The 1H NMR spectrum provides information regarding the connectivity of atoms and their electronic environments; thus, it is routinely used to verify that reactions have been completed successfully. Negishi coupling reactions involve coupling of the phenyl ring to the EDOT, causing the phenyl proton peak to shift from 7.1 ppm to 7.8 ppm. The thienyl proton will also shift upfield to 6.5 ppm. The four protons on the ethylenedioxy bridge carbons will split into two sets of multiplets at 4.3 ppm. Protons on aliphatic carbons will not change significantly. The 13C NMR spectrum will exhibit peaks at 170, 145, 140, and 113 for the thienyl carbons, and 150, 120, and 112 for the phenylene carbons. Positions of aliphatic carbons will not change significantly. The chemical structure, 1H NMR, and 13C NMR of M2 are shown in Figure 3.
Electropolymerizations of M2 yielding polymer (P2) and cyclic voltammetry of P2 are shown in Figure 4. In Figure 4A, initially, there is no current response; as potential increases, the onset of oxidation of the M1 monomer (Eon,m) can be seen at + 0.25 V, with the peak oxidation of the monomer (Ep,m) at + 0.61 V. During the first scan, the initial peak observed is indicative of irreversible monomer oxidation, resulting in P2 formation on the surface of the working electrode. During the second scan two oxidation processes are observed: monomer oxidation is still seen at +0.25 V, and polymer oxidation is seen at 0 V. Cyclic voltammetry of P2 (Figure 4B) was conducted at scan rates ranging from 50 to 400 mV/sec. The polymer film is dark blue in the oxidized state and red in the neutral state. Cycling the polymer at a variety of scan rates reveals a linear relationship between scan rate and peak current, indicating that the polymer is electroactive and adhered to the electrode.18 Polymer oxidation (Ea,p) is observed at -0.02 V for P2, and polymer reduction (Ec,p) is observed at -0.3 V when cycled at 100 mV/sec.
The NPs were synthesized as shown in Figure 2 and characterized using UV-Vis-NIR spectroscopy, electron microscopy, and DLS. The UV-Vis-NIR spectra of oxidized and reduced P2 films, and of oxidized P2 NPs, are shown in Figure 5. The oxidized polymer films and NPs exhibit a peak absorbance &#955;max at 1.56 eV (795 nm). When reduced in hydrazine, the film peak absorbance shifts to a &#955;max of 2.3 eV (540 nm). The polymer band gap (Eg) is determined from the onset of the &#960;- &#960;* transition in the neutral polymer, as indicated by the black arrow in Figure 5.
The SEM image of P2 NPs in Figure 6A shows that the NPs are spherical and sub-100 nm in diameter. DLS data in Figure 6B shows a Z-average of the suspensions to be 104 nm in diameter with a polydispersity index (PDI) of 0.13, indicating that the sample is moderately monodispersed. The zeta potential of the P2 NPs was found to be -30.5 mV. Change in temperature when NPs are exposed to NIR radiation demonstrates photothermal conversion. Compared to water controls, which undergo less than a 1 &#176;C increase in temperature, NP suspensions in water are able to convert the absorbed laser energy into heat as demonstrated by the 30 &#176;C increase in temperature of the NP suspensions (Figure 6C). A similar temperature increase (28 &#176;C) is observed when polymer films on ITO glass are irradiated at 808 nm (Figure 6C).
The cytocompatibility of polymer NPs is determined using MTT cell viability assays. Results of cytocompatibility studies for PEDOT:PSS-co-MA NPs are shown in Figure 7. As shown, within the NP concentration range of 0.23 to 56 &#181;g/ml, the NPs do not decrease cell viability to less than 90% of control. Typically, a reduction in cell viability of less than 20% (i.e., up to 80% viability) is considered acceptable for determination of NP cytocompatibility.
<img alt="Figure 1" src="/files/ftp_upload/53631/53631fig1.jpg" /> 
Figure 1. General monomer synthesis starting with the precursor synthesis.&#160;(A) Synthesis of 1,4-dialkoxy-2,5-dibromobenzene. (B) Synthesis of 1,4-dialkoxy-2,5-dibromobenzene containing ester moiety. (C) Cross-coupling reaction of 1,4-dialkoxy-2,5-dibromobenzene with EDOT, yielding monomers M1 and M2. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53631/53631fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53631/53631fig2.jpg" /> 
Figure 2. Polymerization process in which the organic solution is added dropwise to an aqueous solution creating an emulsion. The monomer and the organic solvent may vary. Oxidative polymerization occurs when FeCl3 is added to the emulsion. After purification of the colloidal suspension, the NPs are suspended in the aqueous medium. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53631/53631fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53631/53631fig3.jpg" /> 
Figure 3. NMR spectra of monomer M2.&#160;(A) 1H NMR spectroscopy of M2 where the splitting of the ethylenedioxy protons at 4.32 ppm, the upfield shift of the thienyl protons, and the upfield shift of the phenyl protons are indicative of successful coupling. (B) 13C NMR spectroscopy of M2 showing the thienyl and phenyl carbon peaks. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53631/53631fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/53631/53631fig4.jpg" /> 
Figure 4. (A) Electrochemical polymerization of M2 to P2; five cycles at 100 mV/sec of 0.01 M M2 in 0.1 M TBAP/CH3CN. (B) Cyclic voltammetry of the polymer film in 0.1 M TBAP/CH3CN cycled at 50, 100, 200, 300, and 400 mV/sec. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53631/53631fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/53631/53631fig5.jpg" /> 
Figure 5. UV-Vis-NIR spectra of P2 both as a film and as a suspension of NPs. The spectrum of the oxidized film is shown in blue, the spectrum of the reduced film is shown in red, and the spectrum of the oxidized NP suspension is shown in green. The black arrow corresponds to the tangent line used for determination of the polymer bandgap. Peak absorption wavelengths for the polymers are provided. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53631/53631fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/53631/53631fig6.jpg" /> 
Figure 6. (A) SEM image showing the morphology and size of P2 NPs. (B) Size distribution of P2:PSS-co-MA NP suspension where the Z-average value is 104 nm and the PDI is 0.13. (C) Temperature change of a P2:PSS-co-MA NP suspension at 1 mg/ml (blue) and film (green) when irradiated with NIR light for 300 sec, followed by passive cooling upon completion of laser irradiation. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53631/53631fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/53631/53631fig7.jpg" /> 
Figure 7. Cytocompatibility of PEDOT:PSS-co-MA NP suspensions as determined by the MTT assay. Viability is shown for cells exposed to varying concentrations of NPs as the average percentage relative to that of cells incubated with NP-free media (positive control). Negative control consists of cells killed by exposure to methanol prior to the MTT assay. Error bars represent the standard deviation between replicates (n = 6). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53631/53631fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties at JoVE.com

Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

A protocol is presented for the synthesis and preparation of nanoparticles consisting of electroactive polymers.

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step ...

electroactive-polymer-nanoparticles-exhibiting-photothermal-properties

Nanyang Technological University

Research

JoVE Journal

Engineering

13.7K Views.  Texas State University. A protocol is presented for the synthesis and preparation of nanoparticles consisting of electroactive polymers. 

Video: Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

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Organic dye molecules and oleic acid coated upconverting nanoparticles are not water-soluble. This protocol describes a &#8216;plug and play&#8217; method that enables the transfer of organic dye molecules and upconverting particles from their initial hydrophobic solvent to water.

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This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

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Hybrid interfaces between organic semiconductors and living tissues represent a new tool for in-vitro and in-vivo applications. In particular, conjugated ...

Magnetic and Thermal-sensitive Poly(N-isopropylacrylamide)-based Microgels for Magnetically Triggered Controlled Release

Magnetically and thermally sensitive poly(N-isopropylacrylamide) (PNIPAAm)/Fe3O4-NH2 microgels with the encapsulated anti-cancer drug curcumin (Cur) were designed and fabricated for magnetically triggered release. PNIPAAm-based magnetic microgels with a spherical structure were produced via a temperature-induced emulsion followed with physical-crosslinking by mixing PNIPAAm, polyethylenimine (PEI), and Fe3O4-NH2 magnetic nanoparticles. Because of their dispersity, the Fe3O4-NH2 nanoparticles were embedded inside the polymer matrix. The amine groups exposed on the Fe3O4-NH2 and PEI surface supported the spherical structure by physically crosslinking with the amide groups of the PNIPAAm. The hydrophobic anti-cancer drug curcumin can be dispersed in water after encapsulation into the microgels. The microgels were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and UV-Vis spectral analysis. Furthermore, magnetically triggered release was studied under an external high frequency magnetic field (HFMF). A significant &#34;burst release&#34; of curcumin was observed after applying the HFMF to the microgels due to the magnetic inductive heating (hyperthermia) effect. This manuscript describes the magnetically triggered controlled release of Cur-PNIPAAm/Fe3O4-NH2 encapsulated curcumin, which can be potentially applied for tumor therapy.

Magnetic and Thermal-sensitive PolyN-isopropylacrylamide-based Microgels for Magnetically Triggered Controlled Release

This manuscript describes the preparation of magnetic and thermal-sensitive microgels via a temperature-induced emulsion without chemical reaction. These sensitive microgels were synthesized by mixing poly(N-isopropylacrylamide) (PNIPAAm), polyethylenimine (PEI) and Fe3O4-NH2 nanoparticles for the potential use in magnetically and thermally triggered drug-release.

Magnetically and thermally sensitive poly(N-isopropylacrylamide) (PNIPAAm)/Fe3O4-NH2 microgels with the encapsulated anti-cancer drug curcumin (Cur) were ...

Gold Nanorod-assisted Optical Stimulation of Neuronal Cells

Recent studies have demonstrated that nerves can be stimulated in a variety of ways by the transient heating associated with the absorption of infrared light by water in neuronal tissue. This technique holds great potential for replacing or complementing standard stimulation techniques, due to the potential for increased localization of the stimulus and minimization of mechanical contact with the tissue. However, optical approaches are limited by the inability of visible light to penetrate deep into tissues. Moreover, thermal modelling suggests that cumulative heating effects might be potentially hazardous when multiple stimulus sites or high laser repetition rates are used. The protocol outlined below describes an enhanced approach to the infrared stimulation of neuronal cells. The underlying mechanism is based on the transient heating associated with the optical absorption of gold nanorods, which can cause triggering of neuronal cell differentiation and increased levels of intracellular calcium activity. These results demonstrate that nanoparticle absorbers can enhance and/or replace the process of infrared neural stimulation based on water absorption, with potential for future applications in neural prostheses and cell therapies.

This protocol outlines how to use the transient heating associated with the optical absorption of gold nanorods to stimulate differentiation and intracellular calcium activity in neuronal cells. These results potentially open up new applications in neural prostheses and fundamental studies in neuroscience.

Recent studies have demonstrated that nerves can be stimulated in a variety of ways by the transient heating associated with the absorption of infrared ...

Neuroscience

Hydrothermal Synthesis of Persistent Luminescent Nanoparticles

Synthesis of Persistent Luminescent Nanoparticles for Rewritable Displays and Illumination Applications

Persistent luminescent nanoparticles (PLNPs) possess the capabilities to maintain extended longevity and robust emission even after the excitation has ceased. PLNPs have been widely used across various domains, including information displays, data encryption, biological imaging, and artistic decoration with sustained and vivid luminosity, providing boundless possibilities for a variety of innovative technology and artistic projects. This protocol focuses on an experimental procedure for the hydrothermal synthesis of PLNPs. The successful synthesis of enduring luminescent nanomaterials with Mn2+ or Cr3+ serving as a luminescent center in Zn2GeO4: Mn (ZGO: Mn) or ZnGa2O4: Cr highlights the universality of this synthetic method. On the other hand, the optical properties of ZGO: Mn can be changed by adjusting the pH of precursor solutions, demonstrating the tunability of the protocol. When charged with ultraviolet (UV) at a wavelength of 365 nm for 3 min and then stopped, PLNPs exhibit the remarkable capacity to generate afterglow efficiently and consistently, which makes them ideal for making two-dimensional rewritable displays and three-dimensional transparent, luminous artworks. This protocol outlined in this paper provides a feasible method for the synthesis of persistent luminescent nanoparticles for further illumination and imaging applications, opening up novel prospects for the fields of science and art.

Author Spotlight: Advancing Bioimaging and Therapy with Functional Nanomaterials

A protocol is presented for the synthesis of persistent luminescent nanomaterials (PLNPs) and their potential applications in rewritable displays and artistic processing utilizing the afterglow effect under ultraviolet light (365 nm) irradiation.

Persistent luminescent nanoparticles (PLNPs) possess the capabilities to maintain extended longevity and robust emission even after the excitation has ...

Vapor Phase Deposition of Electroactive Poly(3,4-ethylenedioxythiophene) onto Electrospun Commodity Polymer Nanofibers

This study investigates the preparation of polyacrylonitrile (PAN) nanofibers through electrospinning to create highly porous and strong materials for applications in water purification, electrocatalysis, and biomedicine. The uniformly white PAN nanofiber mats were cut into 2 cm x 2 cm coupons to ensure consistency. After electrospinning, these nanofibers were coated with an electroactive polymer (EAP) using chemical vapor deposition, with iron (III) chloride (FeCl3) serving as an oxidant for polymerizing 3,4-ethylenedioxythiophene (EDOT) into poly(3,4-ethylenedioxythiophene) (PEDOT). The study examined the impact of different FeCl3 concentrations on PEDOT deposition on the PAN coupons. PEDOT deposition led to an increase in coupon weight. Scanning electron microscopy (SEM) revealed increases in the diameter of the nanofibers treated with increasing FeCl3 oxidant concentration, although higher FeCl3&#160;concentrations caused inter-fiber bridging, implying a concomitant decrease in inter-fiber spacing. Energy dispersive X-ray spectroscopy (EDS) was used to confirm the presence of Fe, Cl, and S in the nanofibers, with sulfur content rising with FeCl3&#160;concentration used, suggesting increased PEDOT deposition efficiency with increasing oxidant concentration. Mechanical testing showed that PEDOT-coated PAN fibers had improved tensile strength and toughness in the hydrated state compared to pure PAN nanofibers. These results highlight the crucial role of FeCl3&#160;concentration in influencing the morphology and properties of PAN-PEDOT composites, enhancing their suitability for applications such as water purification, tissue engineering, biosensing, catalysis, and energy storage.

This paper describes a simple technique for coating electrospun PAN nanofibers with electroactive polymers using vapor deposition. The effects of the oxidant FeCl&#8323; on the deposition of poly(3,4-ethylenedioxythiophene) coatings on PAN were investigated to understand and optimize polymer growth, fiber diameter, and overall mechanical strength of the nanofiber mats.

This study investigates the preparation of polyacrylonitrile (PAN) nanofibers through electrospinning to create highly porous and strong materials for ...

Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

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