Effect of surface ligand and temperature on lipid vesicle-gold

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Effect of surface ligand and temperature on lipid vesiclegold nanoparticle interaction: a spectroscopic investigation NISHU KANWA, Ananya Patnaik, soumya kanti De, Mirajuddin Ahamed, and Anjan Chakraborty Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b03673 • Publication Date (Web): 02 Jan 2019 Downloaded from http://pubs.acs.org on January 3, 2019

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Effect of surface ligand and temperature on lipid vesicle-gold nanoparticle interaction: a spectroscopic investigation

Nishu Kanwa, Ananya Patnaik, Soumya Kanti De, Mirajuddin Ahamed and Anjan Chakraborty* Discipline of Chemistry Indian Institute of Technology Indore, Indore, Madhya Pradesh, India, 453552.

Authors for correspondence Email: [email protected]

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Abstract: We herein investigate the interactions of differently functionalized anionic and cationic gold nanoparticles (AuNPs) with zwitterionic phosphocholine (PC) as well as inverse phosphocholine (iPC) lipid bilayers via spectroscopic measures. In this study, we used PC lipids with varying phase transition temperatures, i.e. DMPC (Tm = 24 °C), DOPC (Tm = -20 °C) and iPC lipid DOCP (Tm = -20 °C) to study their interactions with AuNPs functionalized with anionic ligands citrate, 3-mercaptopropionic acid (MPA), glutathione (GSH); and cationic ligand cysteamine. We studied the interactions by steady state and time resolved spectroscopic studies using membrane-sensitive probes PRODAN and ANS, as well as by CLSM imaging and DLS measurements. We observe that AuNPs bring in stability to the lipid vesicle, and the extent of interaction differs with the different surface ligands on the AuNPs. We observe that cit-AuNPs effectively increases the phase transition temperature of the vesicles by interacting with it. Our study reveals that the extent of interaction depends on the bulkiness of the ligands attached to the AuNPs. The bulkier ligands exert less Van der Waals force resulting in a weaker interaction. Moreover, we find that the interactions are more strongly pronounced when the vesicles are near the phase transition temperature of the lipid. The confocal laser scanning microscopy (CLSM) imaging and dynamic light scattering (DLS) measurements demonstrate the surface modifications in the vesicles as a result of these interactions.


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Introduction: Lipid bilayer membranes have been a subject of great interest in the recent past owing to their sensitivity in terms of phase transition temperature, hydration and dehydration upon interaction with several nanoparticles, polymers and metal ions etc.

1-8

The changes in the

phase transition temperature of the bilayer induced due to such interactions greatly affect the membrane polarity, fluidity, order and surrounding water content.1-12 For example, the introduction of guest molecules such as cholesterol and proteins strongly modifies the membrane properties and brings in stability and order.7-12 Furthermore, interactions between lipid bilayers and metal nanoparticles are also an emerging area of research these days as they usually result into distinctly biocompatible systems.13-18 These systems have immense applications in various fields like imaging, drug delivery, separation and biosensing.16-20 The interaction of nanoparticles with zwitterionic lipid bilayers is widely discussed in literature,3,4,13-26 some of them efficiently provide stability to the membrane.21-24 Amongst the variety of these materials, gold nanoparticles are of great significance. The surface chemistry of gold nanoparticles can be easily controlled by various capping agents, majorly with thiol ligands.27-30 They are also known to exhibit a strong Van der Waals interaction giving rise to a strong physisorption and low colloidal stability. 31 The colloidal solution containing gold nanoparticles show interparticle distance-dependent color due to localized surface plasmon resonance coupling, which makes them easy to monitor visually.3233

It is well known that various functionalized gold nanoparticles have a strong tendency to

interact with lipid bilayer membranes. 34-43 The bilayer membranes remain more intact and lose their tendency to fuse with one another when coated with nanoparticles with a high charge density on the surface of the bilayer, even when the nanoparticles adsorb to the liposome surface to 25% surface coverage.23 This technique to stabilize the otherwise transient liposomes renders them useful for several applications which are predominantly an expanding area of research.44-48 Considering the biocompatible nature and a vast range of applications of liposome-gold nanoparticle assemblies, their mode of interaction remains an area of interest. Although numerous studies have been conducted to study the interactions of lipid bilayers and gold nanoparticles,1-4,15,18,

34-43

the literature lacks spectroscopic investigations regarding these

interactions. Moreover, a few questions remain unanswered. While the anionic nanoparticles are reported to increase the phase transition temperature or induce gelation in the lipid bilayer, the same for cationic nanoparticles are not reported. The interaction of nanoparticles with change in fluidity, i.e. liquid crystalline and gel phase of bilayer has not been investigated. The interactions 3 ACS Paragon Plus Environment

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of gold nanoparticles with the PC head group are explored,1-4,15, 34-36, 38-39 however the same interactions with the inverse PC head groups are not reported. The spectroscopic evidence for this interaction and its consequence on the encapsulated drug molecules are not reported elsewhere. In this context, fluorescent molecular probes are of immense significance to monitor the changes in the fluorescent parameters of the lipid bilayer membrane. Several fluorescent probes which are particularly sensitive to membrane polarity can reveal changes in terms of emission wavelength and intensity as well as lifetime decay and anisotropy.49-58 Amongst the spectral sensitive probes, PRODAN (6-Propionyl-2-Dimethylaminonaphthalene) and ANS (8-anilino-1 naphthalenesulphonate) are particularly interesting because both these fluorescent probes are sensitive towards the dielectric constant and polarity of the surrounding media. The photophysical behavior of PRODAN and ANS in aqueous and membrane media have been well studied in literature.49-58 A significant red shift of the PRODAN emission is observed with increasing solvent polarity, owing to dipolar relaxation phenomenon.50-51 However, in case of ANS, the charge transfer (CT) state in a polar medium decays to the ground state via electron transfer process resulting in quenched fluorescence. The intense blue fluorescence in hydrophobic environment is mostly due to the restricted rotational motion of the phenylamino group of ANS.49 In view of the above discussion, we explored the sensitivity of membrane probes, PRODAN and ANS towards changes in the surface properties of the zwitterionic phosphocholine (PC) and inverse phosphocholine (iPC) zwitterionic lipids with anionic and cationic gold nanoparticles functionalized with ligands of varying bulkiness. We particularly tried to address the following points: (i) how the charge and bulkiness of the surface ligands attached to gold nanoparticles affect the strength of interaction; (ii) if the experimental results obtained from spectroscopic measurements can be explained under the framework of the existing theory, i.e. if the binding mechanism of lipid vesicles and nanoparticles is at par with the theoretical interpretations and literature studies; (iii) how the interaction between the lipid vesicles and AuNPs takes place particularly at the phase transition temperature, and what is the effect of experimental temperature and phase state of the lipid vesicles on these interactions; (iv) how the packing of the lipid membrane, i.e. fluidity of the membrane alters the strength of interaction, and (v) how the packing of the lipid bilayer membrane changes as a consequence of interaction with the gold 4 ACS Paragon Plus Environment

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nanoparticles. Keeping these points in mind, we used PC lipids DMPC (1,2-dimyristoyl-snglycero-3-phosphocholine, Tm = 24 °C), DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine, Tm = -20 °C) and iPC lipid DOCP (2-((2,3-bis(oleoyloxy)propyl)dimethylammonio)ethyl hydrogen phosphate, Tm = -20 °C). We studied the interactions of these lipid vesicles with anionic gold nanoparticles functionalized with citrate (cit-AuNPs), mercaptopropionic acid (MPA-AuNPs) and glutathione (GSH-AuNPs); and cationic AuNPs functionalized with cysteamine (cysAuNPs). We varied the experimental temperature above and below the phase transition temperature of the lipids, i.e. when the bilayer is present in liquid crystalline (Lα) and gel (Lβ) phase respectively. These membrane probes (PRODAN and ANS) are distinctly capable of detecting specific changes in terms of the packing, fluidity and order of the DMPC membrane upon undergoing interactions with the AuNPs at its surface. For this, we exploited steady state fluorescence and time resolved spectroscopic techniques to unravel the different modes of interaction, and observed how the degree of interaction changes with bulkiness of the surface ligands used to functionalize AuNPs. We also conducted dynamic light scattering (DLS) and confocal laser scanning microscopy (CLSM) measurement to further investigate the modifications in the surface of the bilayer as a consequence of these interactions.


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Scheme 1: Representative image showing the interaction of differently functionalized gold nanoparticles with lipid vesicles. Cit-AuNPs stabilize the bilayer to a higher extent and raise the phase transition temperature of the lipid. MPA and GSH-AuNPs adsorb on the bilayer surface less strongly due to their bulky structures. Figure not to scale. Materials and Methods: Materials:

Phospholipids (DMPC and DOPC), inverse phospholipid (DOCP), HAuCl4,

PRODAN, ANS, 3-mercaptopropionic acid, trisodium citrate and cysteamine were purchased from Sigma-Aldrich. Glutathione and sodium borohydride were purchased from Sisco research laboratories (SRL). Phosphate buffer salts were purchased from Merck. All materials were used as received. In all cases, we used Milli-Q water to prepare the solutions.


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Preparation of lipid vesicles: Lipid vesicles were prepared in phosphate buffer saline (PBS, pH = 7.4, I = 0.025 M) by dissolving the lipid in ethanol (0.01% of the hydrating solution) and injecting in a preheated PRODAN or ANS solution above the phase transition of the specific lipid. The solution was stirred at this temperature for nearly an hour, and cooled down to room temperature before performing any further studies. The total concentration of the lipid was fixed at 0.6 mM, while that of PRODAN and ANS was fixed at 2 µM and 4 µM, respectively for all of the experiments. For confocal imaging, the vesicles were prepared by thin film hydration method to yield vesicles of ~ 500-700 nm size and stained with ~ 20 nM Rhodamine-B dye for atleast 2 hours. Synthesis of citrate-capped gold nanoparticles: Citrate-capped AuNPs were synthesized following the classical citrate reduction of HAuCl4, using a previously described protocol with slight modification.28 All glasswares used for the synthesis were cleaned in freshly prepared aqua regia solution, rinsed with Milli-Q water and dried in oven. Further, trisodium citrate solution (38.8 mM, 10 mL) was rapidly injected to a boiling HAuCI4 solution (1.0 mM, 100 mL) under vigorous stirring. The resulting wine-red colored colloidal solution was boiled for 30 minutes, cooled down to room temperature and stored at 4 °C for further use. The obtained citrate-capped AuNPs had a concentration of 13.4 nM. Functionalization of gold nanoparticles: Citrate capped AuNPs were functionalized with MPA and GSH following a previously described protocol with slight modification.59 Briefly, MPA (25 mM, 10 µL) or GSH (25 mM, 10 µL) was added to citrate-capped AuNPs (13.4 nM, 746 µL) and incubated overnight, and stored at 4 °C for further use. The final concentration of obtained MPA or GSH functionalized AuNPs is ~ 13.27 nM. Freshly prepared AuNP solutions were used for each experiment. Synthesis of cationic gold nanoparticles: Cysteamine functionalized gold nanoparticles (cysAuNPs) were synthesized following a previously described protocol with slight modification.60 Briefly, 1.2 mL of 213 mM cysteamine and 1.42 mM HAuCl4 were mixed, and then the mixture was blended under ambient temperature for 20 min. Subsequently, 30 mL of 10 mM NaBH4 was added to the above solution, the mixture was stirred for another 25 minutes at room temperature in the dark and stored at 4 °C for further use.


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Synthesis of supported lipid bilayer (SLB): SLB was synthesized on a well-cleaned glass support as reported previously.61-62 Specifically, planar glass slides were cleaned by washing in 0.1% sodium dodecyl sulfate (SDS), deionized water followed by piranha cleaning. After cleaning, SUVs were deposited on the glass slide using standard liposome deposition technique. This involves making hydration of thin lipid films. Lipid vesicles were extruded through a 100 nm filter and then incubated for 1 hour at 40 °C (above the phase transition temperature of the lipid). After incubation, SLBs were washed in petri dishes with buffer at least 3 times to remove the vesicles in excess. Instrumentation: The HR-TEM study to reveal the morphology of the as-synthesized citratecapped AuNPs was conducted using Tecnai T20 transmission electron microscope with an operating voltage of 200 keV. Absorption spectra of the AuNPs were recorded using a Varian UV-Vis spectrophotometer (Carry 100 Bio) in a quartz cuvette (10 × 10 mm). Zeta potential measurements of the AuNPs were performed on a NanoPlus zeta/particle size analyzer (NanoPlus-3 model). Steady-state fluorescence spectra were recorded using a Fluoromax-4p spectrofluorometer from Horiba JobinYvon (model: FM-100). All fluorescence emission spectra were analyzed using OriginPro 8.1 software. The area fraction curve was plotted by deconvolution of the spectra into two peaks at 435 nm and 500 nm, and plotting the fraction (A435nm/A490 nm) v/s experimental temperature using Origin 8.1. The lipid vesicle −nanoparticle interaction was studied by varying the concentration of gold nanoparticles in a fixed concentration of lipid and PRODAN or ANS. Briefly, we prepared a set of solutions in different volumetric flasks that contained 2 μM PRODAN, 0.6 mM lipid, 4 μM ANS and different concentrations of AuNPs. The samples were excited at 375 nm. The fluorescence spectra were corrected for the spectral sensitivity of the instrument. The excitation and emission slits were 2 nm each for all of the PRODAN and ANS emission measurements. Throughout all of the titration experiments, we maintained pH = 7.4, I = 0.025 M, and the desired experimental temperature. For time-correlated single-photon counting (TCSPC), we used a picosecond TCSPC machine from Horiba (Fluorocube- 01-NL). The samples were excited at 375 nm using a picosecond diode laser (model: Pico Brite-375L), and the decays were collected at 440 and 500 nm. We used a filter on the emission side to eliminate the scattered light. The signals were collected at magic 8 ACS Paragon Plus Environment

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angle (54.75°) polarization using a photomultiplier tube (TBX-07C) as the detector. The full width at half-maximum (fwhm) of the instrument response function of our setup was ∼140 ps. The data analysis was performed using IBH DAS version 6 decay analysis software. Throughout all of the titration experiments, we maintained pH = 7.4, I = 0.025 M, and the desired experimental temperature. The decays were fitted with a multiexponential function: −t

D(t) = ∑ni=1 ai exp( τ )

(1)

i

Here D(t) denotes normalized fluorescence decay and 𝑎𝑖 is the normalized amplitude of decay components τi, respectively. The average lifetime was obtained from the equation: 〈𝜏〉 = ∑𝑛𝑖=1 𝑎𝑖 𝜏𝑖

(2)

The quality of the fit was judged by reduced chi square (χ2) values and corresponding residual distribution. The acceptable fit has a χ2 near unity. For the confocal imaging of samples, we used a confocal microscope from OLYMPUS, model no. IX-83. A Multiline Ar laser (gas laser) with an excitation wavelength of 488 nm was used. The observation mode was LSM (laser scanning microscopy), the scan mode was XY, and the scan direction was one way. The liquid samples were dropped on glass slides, spin coated and fixed with coverslips before imaging. DLS measurements of the lipid vesicle-AuNP assemblies were performed on a NanoPlus zeta/particle size analyzer (NanoPlus-3 model).


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Results and Discussion: (I)

Characterization of differently functionalized gold nanoparticles:

Three types of differently functionalized anionic gold nanoparticles were synthesized using surface ligands namely 1) citrate, 2) MPA, 3) GSH; and cationic AuNPs functionalized with cysteamine (Figure 1a). Anionic nanoparticles were obtained by the simple ligand exchange of citrate capped AuNPs with MPA and GSH respectively, and thus possess an identical core diameter. AuNPs were characterized by TEM, which reveals a narrow distribution of the diameter (12-14 nm), as shown in Figure 1b-c. The citrate group bound to AuNPs can be easily replaced by thiol-bearing ligands

27-28,59,63

and UV-Vis absorption spectra reveal that the

nanoparticle monodispersity is maintained after the ligand exchange. Pure citrate-stabilized gold nanoparticles display a surface plasmon resonance (SPR) band at 521 nm, which is a characteristic of isolated spherical gold nanoparticles.29-30,64-65 A similar plasmon band is obtained for MPA-AuNP and GSH-AuNP, without any shift in the SPR wavelength. This indicates that the AuNPs remain unaggregated and are highly stable (Figure 1d). Zeta potential measurements reveal that all the synthesized nanoparticles are negatively charged (Figure 1e) and the high surface potential prevents the AuNPs from undergoing any aggregation. Further, cationic AuNPs were synthesized using cysteamine. These AuNPs also show an SPR at 520 nm (Figure 1d), and indicated a size of 10-15 nm. Zeta potential measurements reveal the formation of positively charged AuNPs (Figure 1e). All these nanoparticles obtained are water-soluble and stable in aqueous solutions with no aggregation observed for a period of one month when stored at 4 °C.


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Figure 1: Characterization of as-synthesized AuNPs. Chemical structures of the surface ligands used to functionalize AuNPs (a); representative TEM images of citrate AuNPs (b and c); UV-Vis spectra (d); and zeta potential measurements of citrate, MPA, GSH and cysteamine functionalized AuNPs (e). (II)

Probing the interactions of gold nanoparticles with lipid vesicles using PRODAN:

The choice of PRODAN as a spectral probe lies in the fact that the spectral bands can be distinctly assigned as a factor of the polarity of the medium. PRODAN shows an emission at 527 nm in aqueous medium which is assigned to charge transfer (CT) state. There are some reports where this state has been assigned as a twisted intramolecular charge transfer (TICT) state. 66-68 However in the presence of less polar medium like lipid bilayer, another emission band arises at around 435-440 nm assigned to locally excited (LE) state. The LE band indicates that PRODAN is partitioned in lipid bilayer.66 This interesting feature of PRODAN makes the spectral studies simpler to analyze. Here we used DMPC, which has a phase transition temperature of 24 °C, to study the interaction with differently functionalized gold nanoparticles. It is revealed from Figure 2 that the emission spectra of PRODAN shifted to a shorter wavelength upon interaction of the lipid vesicle with all three anionic nanoparticles. We discard the possibility of aggregation 11 ACS Paragon Plus Environment

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of the AuNPs on the lipid surface. The UV-Visible spectra indicate that the adsorption of AuNPs on the vesicles takes place without any abnormal broadening or peak shift with an increase in concentration (Supporting Information Figure 1). The observed blue shift in the emission spectra bears the signature of the dehydration of the lipid bilayer.5, 66 The lipid undergoes a fluidto-gel phase (Lα to Lβ) transition due to the adsorption of nanoparticles on the bilayer surface. This transition, however, takes place locally at the point of contact of the nanoparticles. Initially, the headgroup of the zwitterionic lipid is roughly parallel to the bilayer surface. However, upon addition of the nanoparticles, the headgroup tends to tilt so as to favor the interactions with the negatively charged AuNPs via the positively charged choline group.59 It has been reported that P-N (Phosphorous-Nitrogen) dipole in zwitterionic phosphatidylcholine (PC) is usually tilted to an angle of about 30 degree in the Lβ phase from the parallel position (0~3 degree) in the fluid (Lα) phase.69 It has also been reported that the adsorption of the anionic AuNPs on the zwitterionic lipid bilayer makes it much stiffer, since the in-plane elasticity of the lipid bilayer reduces remarkably.70 However, the nature of the interaction depends on the surface charge of the nanoparticles, and anionic AuNPs interact only on the surface of the membrane resulting into dehydration, rather than penetrating into the bilayer membrane.71


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Figure 2: Normalized emission spectra of PRODAN in DMPC solution as a function of AuNP concentration (0 to 5.4 nM) for (a) citrate AuNPs, (b) MPA AuNPs, and (c) GSH AuNPs at 25 °C; and their corresponding area fraction versus concentration of AuNPs plots at 440 (blue emission) and 490 nm (red emission) shown in the insets. Representative time-resolved decay curves of PRODAN in DMPC−AuNPs (d-f) solutions at 440 nm at 25 °C (anisotropy decays for adsorption of cit-AuNPs are shown in the inset). Interestingly, a maximum blue shift in the emission spectra was observed for cit-capped AuNPs, followed by MPA-functionalized AuNPs and least in GSH-functionalized AuNPs. This observation is more clearly evident from the area fraction plot (inset of Figure 2a-c), which reveals that the band corresponding to LE state increases inordinately for cit-capped AuNPs. The blue shift in the emission spectra indicates that the LE state of PRODAN is more pronounced in case of the lipid vesicle interacting with citrate-capped AuNPs, than MPA and GSHfunctionalized AuNPs. This also indicates that lipid vesicle upon interaction with cit-AuNPs is least hydrated at room temperature (25 °C). It is reported that chemisorption does not take place in the present case as chemical reaction does not takes place between lipid head groups and ligands or nanoparticles.59 The AuNPs undergo a physiadsorption on the surface of the lipid vesicles that exert strong Van der Waals force. It is evident that the adsorption efficiency for all the three anionic AuNPs differs from one another. The citrate-capped AuNPs distinctly affect the bilayer packing by exerting a relatively stronger Van der Waals force in order to bring it to a stronger gel (Lβ) phase. MPA-capped AuNPs can still be efficiently absorbed owing to the small size of the ligand (~0.3 nm). Since MPA is relatively shorter thiolated carboxyl molecule, the capping of AuNPs with MPA results into stronger adsorption on the surface of the lipid vesicle as compared to the more bulky GSH group, which rather reduces the adsorption efficiency. These surface ligands separate the AuNP core from the bilayer surface, which results into a decrease in the Van der Waals force between the bilayer surface and the AuNP core. 59 It is also evident from the zeta potential measurements that all the three differently functionalized AuNPs are negatively charged, which results into electrostatic interactions to nearly similar extent. However, the bulkiness of the ligands plays a major role in deciding the AuNP core distance from the bilayer headgroup. The increasing bulkiness of the ligands causes steric hindrance which reduces the interaction between lipid vesicles and incoming nanoparticles. In view of the fact that van der Waals forces are short ranged interactions, any surface ligand that leads to even 13 ACS Paragon Plus Environment

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a small separation from the AuNP core is efficient enough to affect the adsorption strength. This effect has also been represented by a pictorial representation in Scheme 1. It has been reported that the bulkiness of the surface ligands, rather than their structure, plays a more significant role in the interaction of AuNPs with the lipid bilayer.63 Our results are in good agreement with Liu et al.59 To further establish these results, we conducted lifetime and anisotropy decay measurements of PRODAN in presence of DMPC, upon addition of various AuNPs. We collected decays at 440 nm to monitor the influence of the nanoparticles on the gelation of the lipid vesicles. Table S1 (Supporting Information) reveals that the observed lifetimes are biexponential, with a shorter component (τ1) at around 1 ns and the longer component (τ2) varying from 3 to 5 ns. Interestingly, we observe that τ2 is the longest in the case of lipid vesicle bearing citrate-capped AuNPs, followed by MPA-AuNPs and GSH-AuNPs. The longer component τ2 increases from 3.83 ns to 5.15 ns upon addition of cit-AuNPs to DMPC bilayer, while the amplitude (a1 and a2) remains almost the same. The increase in the longer component indicates that the adsorption of cit-AuNPs on the DMPC bilayer surface results into its stabilization.66 The fact clearly indicates that cit-capped AuNPs tend to bring DMPC in the gel (Lβ ) phase more effectively, and offers a less hydrated environment to PRODAN due to increased rigidity as compared to MPA and GSHfunctionalized AuNPs. Furthermore, anisotropy measurements reveal that the rotational relaxation in DMPC bilayer upon adsorption of cit-AuNPs on the surface of the bilayer becomes significantly slower as shown in Figure 2d (inset). However, we did not observe any significant changes in anisotropy decay upon addition of MPA or GSH-AuNPs to the DMPC bilayer (Supporting Information Figure 2). This observation further validates the fact that citrate AuNPs tend to bring more stability to the lipid vesicle as compared to MPA-AuNPs and GSH-AuNPs. This is because citAuNPs experience no hindrance from any bulky groups upon interaction, as opposed to MPA and GSH-functionalized AuNPs. Cit-AuNPs replaces the water molecules from the DMPC bilayer headgroup, which dehydrates the bilayer and causes shrinkage of the lipid bilayer. We also performed a control experiment with aqueous PRODAN in order to further confirm that the subsequent effects are brought by the adsorption of the AuNPs on the bilayer surface. The results reveal that there appears no peak shift in the emission spectra upon addition of the AuNPs to 14 ACS Paragon Plus Environment

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aqueous PRODAN and no changes in the lifetime measurements (Supporting Information Figure 3). The pronounced effect observed for cit-AuNPs as compared to AuNPs functionalized with more bulky surface ligands can be explained by the interaction energy model using Derjaguin-LandauVerwey-Overbeek (DLVO) theory, which considers contributions from electrostatic as well as Van der Waals forces. Supporting Information Figure 4 reveals the total potential as a function of their distance from the bilayer surface for different surface ligands. The interaction energy between the AuNPs and lipid bilayers is evaluated by equation 3: Vt (h) = VEDL (h) + V VDW (h)

(3)

Where Vt is the total interaction energy as a function of separation distance h (nm), which is the sum of electrical double layer (VEDL) and Van der Waals interaction energy (V VDW). Since the size of the vesicles is very large as compared to the nanoparticles, their interaction can be modeled by considering the surface as planar at the site of interaction. The electrical double layer (VEDL) potential can be calculated from equation 4: 𝑘 𝑇

𝐵 VEDL (h) = 64𝜋𝜀o𝜀 r𝑎p2( 𝑧𝑒 )2 𝜏𝑙𝑖𝑝 𝜏𝐴𝑢𝑁𝑃 exp(−𝑘ℎ)

(4)

Where ap denotes the nanoparticle radius, and lip and AuNP denotes the dimensionless surface potential for lipid vesicles and AuNPs respectively. Further, the van der Waals interaction energy (V VDW) can be calculated from equation 5: 𝑉𝑉𝐷𝑊 (ℎ) = -

𝐴𝐺𝑊𝐿 𝑎𝑝

6ℎ(1+

(5)

14ℎ ) 𝜆

Where AGWL indicates the Hamaker constant for the lipid bilayer to AuNP interaction in water. The parameters used for the calculation of equations 4 and 5 are summarized in Table S2 (Supporting Information). The maximum energy barrier is observed for AuNPs with the bulkiest surface ligand (GSH). However, for small cit-AuNPs, the potential energy is the least indicating a stronger interaction with the bilayer surface. We infer that smaller AuNPs distribute most on the surface of the bilayer and they accumulate to the bilayer surface at a higher rate because small-sized AuNPs have a higher number density than the larger ones.72


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It has been previously reported66 that the maximum induced gelation in a lipid bilayer takes place near the phase transition temperature of the lipid. In this context, temperature dependent studies to observe the changes in the phase transition temperature upon addition of various AuNPs may be crucial. We exploited the sensitivity of PRODAN towards the temperature-induced phase transition for DMPC bilayer using temperature dependent emission intensity. We observed that the fluorescence intensity of PRODAN corresponding to the LE state (435 nm) decreases and that of the TICT state (490 nm) increases with a rise in temperature, indicating that the bilayer membranes change their phase from a highly ordered and compact Lβ phase to fluidic Lα phase (Supporting Information Figure 5).We analyzed the alterations in the emission spectra of PRODAN and an area fraction curve was plotted versus temperature. The decrease in fluorescence area at blue end is sigmoidal with a maximum change at the phase transition temperature of the bilayer as shown in Figure 3a. This is more clearly notable in the derivative plot of fluorescence emission intensity (dA/dT) with varying temperature, as shown in Figure 3b. It is revealed that the phase transition temperature of the DMPC bilayer is observed at 23 °C, however, the addition of cit-AuNPs to the lipid vesicle results into further stabilization of the vesicle, which results in an increase in the phase transition from 23 °C to 25 °C. Moreover, corresponding to the addition of MPA and GSH-AuNPs, phase transition temperature of DMPC bilayer did not show any effective changes (data not shown). The electrostatic forces between the nanoparticles and the bilayer head group makes the otherwise loosely packed lipid molecules to tightly pack around the AuNP binding sites. The adsorption of negatively charged AuNPs is known to stiffen the phosphatidylcholine (PC) lipid bilayer and restructure the bound lipid molecules into a raft-like phase.73-74 This results in the stitching of the bilayer, making it more stable which results into an increase in the phase transition temperature of the bilayer.


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Figure 3: Plots of temperature-induced variation in the steady-state fluorescence spectra of PRODAN in DMPC vesicles; where a) Area fraction (A435 nm/A490 nm) v/s temperature plot for DMPC-PRODAN in the presence and absence of Cit-AuNPs (from 10 °C to 45 °C) and b) First derivative of area (dA/dT) v/s temperature plot. Here, [DMPC] = 0.6 mM, [PRODAN] = 2 μM and [AuNP] = 5.4 nM. Since DMPC is present in nearly Lα phase at 25 °C, changes corresponding to phase transition are more pronounced at this temperature. However, below this temperature when the bilayer is present in a more rigid Lβ phase, we presume that only trivial changes might be observed. We performed the experiment at 15 °C to know the fate of the nanoparticle interaction with the lipid vesicles. From Figure 4a-c, we observe that no peak shift in the emission spectra appears while the peak corresponding to ~490 nm (CT state) decreases upon addition of all the three anionic AuNPs, which is also evident from the area fraction plot (Supporting Information Figure 6). The lifetime decay at 440 nm increases moderately for all the three AuNPs (inset of Figure 4a-c, data compiled in Supporting Information Table S1). Therefore, at lower temperatures, the differently functionalized AuNPs are adsorbed to nearly a similar extent on the surface of the lipid vesicle. Since DMPC is already in Lβ phase at 15 °C, it is more rigid at this temperature. As a result, there is a moderate effect in terms of instantaneous adsorption and gelation for all the AuNPs. Interestingly, it is revealed that maximum gelation is observed in the case of DMPC bilayers at 25 °C, than below or above the phase transition temperatures. We explain this observation by the fact that near the phase transition temperature of the lipid (T = 25 °C), DMPC 17 ACS Paragon Plus Environment

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remains in a nearly Lα phase; thus, even a little increase in the phase transition temperature drastically alters DMPC from a nearly Lα phase to a more compact Lβ phase.

Figure 4: Normalized emission spectra for the addition of AuNPs in different concentrations (0 to 5.4 nM) to DMPC−PRODAN solution for (a) citrate AuNPs, (b) MPA AuNPs, and (c) GSH AuNPs at 15 °C and (d-f) at 35 °C (inset shows corresponding time resolved decay curves at 440 nm).

Further, since the lipid vesicle surface does not display significant changes upon interaction with AuNPs at 15 °C, we performed the experiment far above the phase transition of the lipid, i.e. at 35 °C when the bilayer is present in Lα phase. At a temperature above the phase transition temperature (i.e. 35 °C), we observe that a small blue shift takes place upon addition of AuNPs on the bilayer surface, indicating gelation, and the intensity corresponding to LE state increases (Figure 4d-f). This is more clearly notable in area fraction plots (Supporting Information Figure 7). However, there is apparently no change in the lifetime decay at 440 nm (inset of Figure 4d-f). This can be explained in the light of the fact that since DMPC remains in Lα phase at 35 °C, it is not capable of holding more nanoparticles as compared to DMPC in Lβ or nearly Lα phase. The higher increment in lifetime decay at lower temperature stems from the fact that 18 ACS Paragon Plus Environment

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DMPC being in Lβ phase or nearly Lα phase occupies less area per lipid molecule, allowing it to capture more number of nanoparticles. Since the experimental temperature is far above the phase transition temperature of DMPC, it remains in Lα state and any change, howsoever small, that occurs upon the addition of AuNPs cannot change the phase state of the lipid vesicle. It is therefore, not possible to detect the small change that appears in the steady state, by lifetime measurements at 440 nm. We further performed the experiment with liposomes synthesized from lipid with low phase transition temperature, i.e. DOPC (Tm = -20 °C) at an experimental temperature 25 °C when the bilayer is present in Lα phase. We observe that there appears a blue shift in the emission spectra to nearly a similar extent, also clearly depicted by the area fraction plots (as shown in the inset of Figure 5). The lifetime decay however did not reveal any significant changes at 440 nm (data summarized in Supporting Information Table S1). The results are in agreement with those obtained for DMPC liposomes at 35 °C. Thus, we can infer from these data that when the bilayer is present in the LC phase, the peak shift (or gelation) is not that much pronounced as near the phase transition temperature of the lipid. This holds true in our experiment for zwitterionic PC lipids with varying phase transition temperatures.


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Figure 5: Normalized emission spectra for the addition of AuNPs in different concentrations (0 to 5.4 nM) to DOPC−PRODAN solution for (a) citrate AuNPs, (b) MPA AuNPs, and (c) GSH AuNPs (inset shows area fraction plots); and corresponding timeresolved decay curves of PRODAN in DOPC−AuNPs solutions at 440 nm (d-f) at 25 °C.

Since we already studied the effect of functionalized AuNPs on phosphocholine lipid vesicle (DMPC and DOPC), we further studied their effect on lipid vesicle with inverse phosphocholine (iPC) lipid DOCP at 25 °C. We observed that (Figure 6) there appears a blue shift after the addition of AuNPs to the DOCP vesicles. This blue spectral shift is obtained for all anionic functionalized AuNPs, indicating gelation taking place in all the cases. This is also evident from the area fraction plots (Figure 6a-c inset). Moreover, the lifetime decay increases marginally for the addition of AuNPs to DOCP, indicating that the iPC lipid vesicles are also stabilized to a small extent upon interaction with AuNPs. Thus, it is notable that the observation holds true even for iPC lipids that the gelation of the bilayer takes places to a small extent when the bilayer is present below the phase transition temperature of the lipid.

Figure 6: Normalized emission spectra for the addition of AuNPs in different concentrations (0 to 5.4 nM) to iPC DOCP−PRODAN solution for (a) citrate AuNPs, (b)


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MPA AuNPs, and (c) GSH AuNPs (inset shows area fraction plots); and corresponding time-resolved decay curves of PRODAN in DOCP−AuNPs solutions at 440 nm (d-f) at 25 °C.

Until now, we focused primarily on anionic AuNPs, but we further explored the effects caused by cationic AuNPs on lipid vesicle. We used cysteamine AuNPs (cys-AuNP) to study the interaction with DMPC bilayer at 25 °C. We observed that even for cationic AuNP, there is a blue spectral shift, indicating gelation of the bilayer. However, it is interesting to note that the gelation effect is minimum for cationic AuNPs, indicating that the binding is much weaker on the bilayer surface. The results are also supported by a slight increase in lifetime decay at 440 nm (Supporting Information Figure 8). Geiger et al 75 demonstrated that lipid bilayers interact with both positively and negatively charged AuNPs without structurally affecting the vesicles. Granick et al4 also illustrated that since the phospholipid zwitterionic headgroup terminates with positive charge, lipids beneath an adsorbed nanoparticle bind more weakly when the nanoparticle charge is cationic. We also performed a control experiment of the spectroscopic study with the surface ligands to further ensure that the effects are caused by the functionalized AuNPs and not the ligands alone. We observed no changes in the steady state spectra upon addition of surface ligands to liposome-PRODAN solutions (Supporting Information Figure 9), indicating that the effects in the bilayer are caused by the functionalized AuNPs. Summarizing the above stated results, the lipid vesicle is brought to gelation and stabilized to a different extent at different temperatures. This holds true for both anionic as well as cationic AuNPs in our experiments for zwitterionic phosphocholine lipids and inverse phosphocholine lipids. There is a scope for gelation, howsoever small, at all the experimental temperatures but the maximum extent of gelation is brought at a temperature just above the phase transition of the lipid. Supporting Information Figure 10 represents the extent to gelation brought to the bilayer by the addition of cit-AuNPs when the bilayer is present in different phases, i.e. Lβ (15 °C), Lα (35 °C) and just above the phase transition of the temperature in nearly Lα state (25 °C). A maximum blue shift is revealed, corresponding to a higher population of the LE state of PRODAN in the Lβ phase, followed by huge increment in the lifetime at this temperature and vice versa.


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(III)

Probing the interactions of gold nanoparticles with lipid vesicle using ANS:

It is well known that ANS exhibits an emission spectra at 520 nm in the aqueous phase. However, in a less polar medium, i.e. lipid bilayers, it shows a remarkable blue shift in the emission spectra and a peak appears at 475-480 nm, followed by a huge increment (~80 times) in the fluorescence intensity. Thus, we chose ANS as a spectral probe in this study owing to its unique and appealing property of exhibiting a huge spectral shift as a function of the polarity of the medium. Figure 7 reveals the fate of ANS-bound DMPC upon addition of various anionic AuNPs. It is clearly evident that the emission spectra of ANS present in the bilayer shows a blue shift upon interaction with AuNPs. It is well known that the ANS moiety binds non-covalently to the lipid headgroup in the interfacial polar region and the hydrocarbon core of the phospholipid bilayer. The aniline group of ANS incorporates into the hydrocarbon layer, whereas naphthalene and sulfonate group reside in the polar headgroup regions. ANS lies near the hydrophilic interfacial region of the lipid bilayer being a charged species.49,54-55 The shifting of the emission spectra of ANS upon addition of AuNPs to the lipid vesicle indicates stabilization of the bilayer. Since the experiment was performed at 25 °C, DMPC remains in nearly Lα state, thus even a little change in the emission spectra can be easily detected. Interestingly, we observe from Figure 7 (a-c) that in the emission spectra of ANS, a peak at around 520-530 nm starts to emerge after the addition of AuNPs. This peak corresponds to the partitioning of ANS in the aqueous medium. We reason that since ANS is loosely bound to the bilayer and highly sensitive to membrane polarity, the addition of AuNPs results in the leakage of free ANS in the aqueous medium, and the peak corresponding to the partitioning of ANS in aqueous medium appears at a higher wavelength.


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Figure 7: Normalized emission spectra for the addition of AuNPs in different concentrations (0 to 5.4 nM) to DMPC−ANS solution for (a) citrate AuNPs, (b) MPA AuNPs, and (c) GSH AuNPs, and corresponding time-resolved decay curves of ANS in DMPC−AuNPs solutions at 480 nm (d-f) at 25 °C.

For further insight, we conducted the liftime measurements of ANS in the presence of DMPC, upon addition of various anionic AuNPs, and collected the decay at 480 nm as shown in Figure 7 (d-e). It is evident from lifetime decay parameters (Supporting Information Table S3) that the lifetime at 480 nm increases upon addition of all the AuNPs. The decay parameters of ANS in DMPC are biexponential in nature. This indicates that ANS is heterogeneously distributed, although it resides mostly in the interfacial region of the bilayer. This is probably due to different modes of interaction of ANS with the lipid headgroups. Our results are in agreement with Misra et al.42 From the results summarized in Table S3 (Supporting Information), we observe that the longer component τ2 increases from 7.30 ns to 8.83 ns for Cit-AuNPs, and upto 8.84 ns and 8.82 ns for MPA and GSH-AuNPs, respectively. We reason that upon addition of AuNPs to the lipid vesicle, it is stabilized and becomes more rigid, which results in the increase in the lifetime decay parameters. We performed the similar experiments with ANS for the bilayer in Lβ (15 °C) and in Lα phase (35 °C), the results are shown in the Supporting Information Figure 11-12. 23 ACS Paragon Plus Environment

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(IV)

Confocal imaging, size and curvature effects of the bilayer upon interaction of gold nanoparticles with lipid bilayer:

We performed the confocal laser scanning microsopy (CLSM) imaging for the DMPC lipid vesicles, and that of the vesicles upon interaction with AuNPs. As shown in the Figure 8, we observe that the surface of the bilayer is unmodified initially. However, upon addition of AuNPs, the surface of the vesicles undergoes membrane alterations. This also leads to transient leakage of the dye. The results are in agreement with Berti et al.73 It has been reported that a consequence induced by AuNPs adsorbed on the bilayer surface is the membrane pore formation, which arises as a result of altered lipid packing. The pores are ruptures resulting from the lateral pressure induced by multiple AuNP adsorptions, rather than from the insertion of AuNPs. A hole is transiently formed before AuNP entry and closed after AuNP translocation.74 This effect is clearly evident from the CLSM images.

Figure 8: AuNP-DMPC bilayer interaction from Confocal Laser Scanning Microscopy (CLSM). Confocal, bright field and merged images for blank DMPC bilayers (a-c); and for DMPC-AuNP systems (d-f). Arrows in the DMPC-AuNP indicate the surface alterations 24 ACS Paragon Plus Environment

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caused due to AuNP adsorption on the surface of the bilayer. Bars in the images indicate 1 µm size.

For further understanding, we analyzed the hydrodynamic size distribution curves of the vesicles, and the vesicle-AuNP assemblies. For DMPC vesicles, the average diameter was found to be 135.6 nm (PDI = 0.249), whereas upon addition of AuNPs, the size decreased to 66.2 nm (PDI = 0.271 nm) for cit-AuNPs, 64.8 nm (PDI = 0.391) for MPA AuNPs and 60.2 nm (PDI = 0.438) for GSH- AuNPs (Supporting Information Figure 13). This decrement in size upon AuNP addition can be explained in the light of the formation of more stiff, rigid and discrete structures upon addition of AuNPs, than otherwise transient structures of lipid vesicles. It has been reported that the interaction of such nanoparticles with liposome surface tends to restructure the membrane into structurally stiffened nanoscale domains. 73 In the present report, we performed the experiment using lipid vesicles, but there are several studies which report nanoparticle interaction using supported lipid bilayers (SLBs).75-79 To further analyze these effects, we performed the confocal imaging experiment using SLB composed of DMPC lipid (Supporting Information Figure 14). It is depicted that a continuous membrane is observed at lower magnification, which upon further magnification reveals spherical vesicle formation. However, upon addition of AuNPs, these spherical vesicles exhibit distorted structures and a transient leakage of the dye is observed, as obtained in our earlier experiment with lipid vesicles. It has been reported 76 that the increase in binding efficiency with increase in nanoparticle size is indeed an effect of the nanoparticle curvature, as it largely influences the number of bonds formed between nanoparticles and bilayer head group, owing to a larger contact area in case of larger NPs. The report used SLBs and AuNPs to illustrate that the binding affinity of NPs with bilayer membrane is strongly dependent on weak, colloidal interactions between the membrane and the NPs. Further, it is concluded that the probability of bond formation between bilayer surface and NP increases with the NP size, due to their larger residence time near the bilayer surface owing to a larger Van der Waals interaction. The interaction is therefore largely dependent on the size of the nanoparticles. Further, the interaction of positively and negatively charged AuNPs with DOPC supported bilayers has been discussed in detail by Geiger et. al.

75

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without distorting the structure of the vesicles and the interaction strength per particle is independent of ionic strength and particle coating. The study also reveals that the interaction of these nanoparticles takes place for both SLBs and lipid vesicles. It is also reported

77

that the

interaction of lipid bilayer and nanoparticles depends on a number of factors, such as particle concentration, bilayer composition and charge amongst various other factors. The report concludes that cationic nanoparticles electrostatically interact with SLB and tend to rupture the lipid bilayers by forming pores on the bilayer surface, as opposed to anionic nanoparticles.

Conclusions: In summary, we studied the interaction of lipid vesicles (PC and iPC lipids) with anionic and cationic AuNPs and draw the following conclusions: 1) Lipid vesicles interact with the AuNPs to a maximum extent at a temperature near the phase transition temperature of the lipid and the gelation effect is not that effectively pronounced when the vesicles are present in Lα or Lβ phase. This holds true for both PC lipids as well as iPC lipids. 2) Extent of gelation of the lipid vesicles varies with the bulkiness of the surface ligands and the vesicles experience a minimum gelation when the ligand is bulky. While cit-capped AuNPs interact the strongest and effectively raise the phase transition temperature of the lipid vesicles, more bulky groups MPA and GSH distant AuNP core from the bilayer surface, so that the interactions are comparatively weaker. 3) Both anionic as well as cationic AuNPs tend to bring gelation and stability to the lipid vesicles. However, cationic AuNPs bind weakly as compared to their anionic counterparts on the vesicle surface. 4) The CLSM imaging and DLS measurements further demonstrate the surface modification due to these interactions on the lipid vesicles. These surface interactions between bilayer-AuNPs are found to effectively stabilize the bilayer resulting into biocompatible systems and can be used for a variety of bioinspired applications such as imaging, drug delivery and biosensing etc.


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Acknowledgment: The authors thank IIT Indore for providing the infrastructure, experimental facilities and financial support. The authors would like to thank Sophisticated Instrumentation Centre (SIC), IIT Indore for providing the instrumental facility.

References: (1) Thamphiwatana, S.; Fu, V.; Zhu, J.; Lu, D.; Gao, W.; Zhang, L. Nanoparticle-Stabilized Liposomes for pH-Responsive Gastric Drug Delivery. Langmuir 2013, 29, 12228−12233. (2) Adhikari, C.; Das, A.; Chakraborty, A. Controlled Release of a Sparingly Water-Soluble Anticancer

Drug

through

pH-Responsive

Functionalized

Gold-Nanoparticle-Decorated

Liposomes. ChemPhysChem 2015, 16, 866−871. (3) Pornpattananangkul, D.; Olson, S.; Aryal, S.; Sartor, M.; Huang, C.-M.; Vecchio, K.; Zhang, L. Stimuli-Responsive Liposome Fusion Mediated by Gold Nanoparticles. ACS Nano 2010, 4, 1935−1942. (4) Yu, Y.; Anthony, S. M.; Zhang, L.; Bae, S. C.; Granick, S. Cationic Nanoparticles Stabilize Zwitterionic Liposomes Better than Anionic Ones. J. Phys. Chem. C 2007, 111, 8233-8236. (5) De, S. K.; Kanwa, N.; Ahamed, M.; Chakraborty, A. Spectroscopic Evidence for Hydration and Dehydration of Lipid Bilayers upon Interaction with Metal Ions: A New Physical Insight.

Phys. Chem. Chem. Phys. 2018, 20, 14796-14807. (6) Binder, H.; Zschörnig, O. The Effect of Metal Cations on the Phase Behavior and Hydration Characteristics of Phospholipid Membranes. Chemistry and physics of lipids 2002, 115, 39–61. (7) Hong, H.; Tamm, L. K. Elastic Coupling of Integral Membrane Protein Stability to Lipid Bilayer Forces. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 4065–4070. (8) Vafaei, S.; Tabaei, S. R.; Cho, N.-J. Optimizing the Performance of Supported Lipid Bilayers as Cell Culture Platforms Based on Extracellular Matrix Functionalization. ACS Omega 2017, 2, 2395−2404.


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(9) Sankaram. M. B.; Thompson, T. E. Cholesterol-Induced Fluid-Phase Immiscibility in Membranes. Proc. Natl. Acad. Sci. U.S.A. 1991, 88, 8686-8690. (10) de Almeida, R. F. M.; Fedorov, A.; Prieto, M. Sphingomyelin / Phosphatidylcholine / Cholesterol Phase Diagram: Boundaries and Composition of Lipid Rafts. Biophys. J. 2003, 85, 2406–2416. (11) Raffy, S.; JTeissi, J. Control of Lipid Membrane Stability by Cholesterol Content. Biophys. J.1999, 76, 2072–2080. (12) Róg, T.; Pasenkiewicz-Gierula, M.; Vattulainen, L.; Karttunen, M. Ordering Effects of Cholesterol and its Analogues. Biochim. Biophys. Acta, Biomembr. 2009, 1788, 97–121. (13) Al-Jamal, W. T.; Kostarelos, K. Liposome-Nanoparticle Hybrids for Multimodal Diagnostic and Therapeutic Applications. Nanomedicine 2007, 2, 85-98. (14) Preiss, M. R.; Bothun, G. D. Stimuli-Responsive Liposome Nanoparticle Assemblies. Expert Opin. Drug Delivery 2011, 8, 1025-1040. (15) Paasonen, L.; Sipila, T.; Subrizi, A.; Laurinmaki, P.; Butcher, S. J.; Rappolt, M.; Yaghmur, A.; Urtti, A.; Yliperttula, M. Gold-Embedded Photosensitive Liposomes for Drug Delivery: Triggering Mechanism and Intracellular Release. J. Control. Release 2010, 147, 136-143. (16) Liu, J.; Jiang, X.; Ashley, C.; Brinker, C. J. Electrostatically Mediated Liposome Fusion and Lipid Exchange with a Nanoparticle Supported Bilayer for Control of Surface Charge, Drug Containment, and Delivery. J. Am. Chem. Soc. 2009, 131, 7567-7569. (17) Roiter, Y.; Ornatska, M.; Rammohan, A. R.; Balakrishnan, J.; Heine, D. R. ; Minko, S. Interaction of Nanoparticles with Lipid Membrane. Nano Lett. 2008, 8, 941-944. (18) Abraham, S.; Narine, S. S. A Facile Synthesis of Lipid Stabilized Gold Nanoparticles: A Step towards Biodegradable Biosensors. J. Nanosci. Nanotechnol. 2011, 11, 7027-32. (19) Huang, H.-C.; Chang, P.-Y.; Chang, K.; Chen, C.-Y.; Lin, C.-W.; Chen, J.-H.; Mou, C.-Y.; Chang, Z.-F.; Chang, F.-H. Formulation of Novel Lipid-Coated Magnetic Nanoparticles as the Probe for In Vivo Imaging. J. Biomed. Sci. 2009, 16, 86. 28 ACS Paragon Plus Environment

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(20) Castellana, E. T.; Gamez, R. C.; Russell, D. H. Label-Free Biosensing with LipidFunctionalized Gold Nanorods. J. Am. Chem. Soc. 2011, 133, 4182-4185. (21) Wang, B.; Zhang, L.; Bae, S. C.; Granick, S. Nanoparticle-Induced Surface Reconstruction of Phospholipid Membranes. Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 18171-18175. (22) Wang, F.; Liu, J. A Stable Lipid/TiO2 Interface with Headgroup Inversed Phosphocholine and a Comparison with SiO2. J. Am. Chem. Soc. 2015, 137, 11736-11742. (23) Zhang, L.; Granick, S. How to Stabilize Phospholipid Liposome (Using Nanoparticles). Nano Lett. 2006, 6, 694-698. (24) Tan, S.; Li, X.; Guo, Y.; Zhang, Z. Lipid-Enveloped Hybrid Nanoparticles for Drug Delivery. Nanoscale 2013, 5, 860-872. (25): Liu, J. Interfacing Zwitterionic Liposomes with Inorganic Nanomaterials: Surface Forces, Membrane Integrity, and Applications. Langmuir 2016, 32, 4393−4404 (26): Liu, X.; Li, X.; Xu, W.; Zhang, X.; Huang, Z.; Wang, F.; Liu, J. Sub-Angstrom Gold Nanoparticle/Liposome Interfaces Controlled by Halides. Langmuir 2018, 34, 6628−6635. (27) Gao, J.; Huang, X.; Liu, H.; Zan, F.; Ren, J. Colloidal Stability of Gold Nanoparticles Modified with Thiol Compounds: Bioconjugation and Application in Cancer Cell Imaging. Langmuir 2012, 28, 4464-4471. (28) Zhao, J.; Wu, Y.; Tao, H.; Chen, H.; Yang, W.; Qiu, S. Colorimetric Detection of Streptomycin in Milk Based on Peroxidase-Mimicking Catalytic Activity of Gold Nanoparticles. RSC Adv. 2017, 7, 38471-38478. (29) Piella, J.; Bastús, N. G.; Puntes. V. Size-Controlled Synthesis of Sub-10-nanometer CitrateStabilized Gold Nanoparticles and Related Optical Properties. Chem. Mater. 2016, 28, 10661075. (30) Maguraa, J.; Zelěnákováb, A.; Zelěnáka, V.; M. Kǎnuchovác, V. Thiol-Modified Gold Nanoparticles Deposited on Silica Support Using Dip Coating. Appl. Surf. Sci. 2014, 315, 392– 399. 29 ACS Paragon Plus Environment

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(31) Rance, G. A.; Marsh, D. H.; Bourne, S. J.; Reade, T. J.; Khlobystov, A. N. van der Waals Interactions between Nanotubes and Nanoparticles for Controlled Assembly of Composite Nanostructures. ACS Nano 2010, 4, 4920-4928. (32) Mustafa, D. E.; Yang, T.; Xuan, Z.; Chen, S.; Tu, H.; Zhang, A. Surface Plasmon Coupling Effect of Gold Nanoparticles with Different Shape and Size on Conventional Surface Plasmon Resonance Signal. Plasmonics 2010, 5, 221-231. (33) Wang, X.; Gogol, P.; Cambril, E.; Palpant, B. Near- and Far-Field Effects on the Plasmon Coupling in Gold Nanoparticle Arrays. J. Phys. Chem. C 2012, 116, 24741-24747. (34) Wang, F.; Curry, D. E.; Liu, J. Driving Adsorbed Gold Nanoparticle Assembly by Merging Lipid Gel/Fluid Interfaces. Langmuir 2015, 31, 13271-13274. (35) Preiss, M. R.; Hart, A.; Kitchens, C.; Bothun, G. D. Hydrophobic Nanoparticles Modify the Thermal Release Behavior of Liposomes. J. Phys. Chem. B 2017, 121, 5040-5047. (36) Moghadam, B. Y.; Hou, W. -C.; Corredor, C.; Westerhoff, P.; Posner, J. D. The Role of Nanoparticle Surface Functionality in the Disruption of Model Cell Membranes. Langmuir 2012 28, 16318-16326. (37) Salassi, S.; Simonelli, F.; Bochicchio, D.; Ferrando , R.; Rossi, G. Au Nanoparticles in Lipid Bilayers: A Comparison between Atomistic and Coarse-Grained Models. J. Phys. Chem. C 2017, 121, 10927-10935. (38) Toledo-Fuentes, X.; Lis, D.; Cecchet, F. Structural Changes to Lipid Bilayers and Their Surrounding Water upon Interaction with Functionalized Gold Nanoparticles. J. Phys. Chem. C 2016, 120, 21399-21409. (39) Sakaguchi, N.; Kimura, Y.; Hirano-Iwata, A.; Ogino, T. Fabrication of Au-NanoparticleEmbedded Lipid Bilayer Membranes Supported on Solid Substrates. J. Phys. Chem. B 2017, 121, 4474-4481. (40) Guo, Y.; Terazzi, E.; Seemann, R.; Fleury, J. B.; Baulin, V. A. Direct Proof of Spontaneous Translocation of Lipid-Covered Hydrophobic Nanoparticles through a Phospholipid Bilayer. Sci. Adv. 2016, 2. 30 ACS Paragon Plus Environment

Page 30 of 36

Page 31 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(41) Dichello, G. A.; Fukuda, T.; Maekawa, T.; Whitby, R. L. D.; Mikhalovsky, S. V.; Alavijeh, M.; Pannala, A. S.; Sarker, D. K. Preparation of Liposomes Containing Small Gold Nanoparticles using Electrostatic Interactions. Eur. J Pharm. Sci. 2017, 105, 55-63. (42) Hamilton, D. J.; Coffman, M. D.; Knight, J. D.; Reed, S. M. Lipid-Coated Gold Nanoparticles and FRET Allow Sensitive Monitoring of Liposome Clustering Mediated by the Synaptotagmin-7 C2A Domain. Langmuir 2017, 33, 9222-9230. (43) Rossi, G. Monticelli, L. Gold Nanoparticles in Model Biological Membranes: A Computational Perspective. Biochim. Biophys. Acta. Biomembr. 2016, 1858, 2380-2389. (44) Pastoriza-Santos, I.; Kinnear, C.; Pérez-Juste, J.; Mulvaney, P.; Liz-Marzán, L. M. Plasmonic polymer nanocomposites. Nat. Rev. Mater. 2018, 3, 375–391. (45) Zhang, S.; Geryak, R.; Geldmeier, J.; Kim, S.; Tsukruk, V. V. Synthesis, Assembly, and Applications of Hybrid Nanostructures for Biosensing. Chem. Rev. 2017, 117, 12942–13038. (46) Rahim, F. A.; Dong-Hwan, K. Nanoparticle polymer composites on solid substrates for plasmonic sensing applications. Nano Today 2016, 11, 415-434. (47) Baffou, G.; Quidant, R. Nanoplasmonics for chemistry. Chem. Soc. Rev. 2014, 43, 38983907. (48) Sepúlveda, B.; Angelomé, P. C.; Lechuga, L. M.; Liz-Marzán, L. M. LSPR-based nanobiosensors. Nano Today 2009, 4, 244-251. (49)

Mohapatra,

M.;

Mishra,

A.

K.

Photophysical

Behavior

of

8‑ Anilino-1-

Naphthalenesulfonate in Vesicles of Pulmonary Surfactant Dipalmitoylphosphatidylcholine (DPPC) and Its Sensitivity toward the Bile Salt−Vesicle Interaction. Langmuir 2013, 29, 1139611404. (50) Parasassi, T.; Krasnowska, E. K.; Bagatolli, L.; Gratton, E. Laurdan and Prodan as PolaritySensitive Fluorescent Membrane Probes. J. Fluoresc. 1998, 8, 365−373. (51) Krasnowska, E. K.; Gratton, E.; Parasassi. T. Prodan as a Membrane Surface Fluorescence Probe: Partitioning between Water and Phospholipid Phases. Biophy. J. 1998, 74, 1984-1993. 31 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(52) Wilson-Ashworth, H. A.; Bahm, Q.; Erickson, J.; Shinkle, A.; Vu, M. P.; Woodbury, D.; Bell, J. D. Differential Detection of Phospholipid Fluidity, Order, and Spacing by Fluorescence Spectroscopy of Bis-pyrene, Prodan, Nystatin, and Merocyanine 540. Biophys. J. 2006, 91, 4091-4101. (53) Novaira, M.; Biasutti, M. A.; Silber, J. J.; Correa, N. M. New Insights on the Photophysical Behavior of PRODAN in Anionic and Cationic Reverse Micelles: From which State or States does it Emit? J. Phys. Chem. B 2007, 111, 748-759. (54) Gutowicz, J.; Krawczyk, A. Effect of 1-Anilinonaphthalene-8-Sulphonate on Phase Transition Temperature of Dipalmitoylphosphatidylcholine Liposomes. Chem. Phys. Lipids 1986, 39, 357-364. (55) Lesslauer, W.; Cain, J. E.; Blasie, J. K. X-ray Diffraction Studies of Lecithin Bimolecular Leaflets with Incorporated Fluorescent Probes. Proc. Natl. Acad. Sci. U.S.A. 1972, 69, 14991503. (56) Lesslauer, W.; Cain, J.; Blasie, J. K. On the Location of 1-Anilino-8-Naphthalene-Sulfonate in Lipid Model Systems: An X-Ray Diffraction Study. Biochim. Biophys. Acta, Biomembr. 1971, 241, 547-566. (57) Gulik-Krzywicki, T.; Shechter, E.; Iwatsubo, M.; Ranck, J.L.; Luzzati, V. Correlations between Structure and Spectroscopic Properties in Membrane Model Systems Trytophan and IAnilino-8-Naphtalene Sulfonate Fluorescence in Protein-Lipid-Water Phases. Biochim. Biophys. Acta, Biomembr. 1970, 219, 1-10. (58)

Kosower, E. M.; Kanety, H. Intramolecular Donor-Acceptor Systems. 10. Multiple

Fluorescences from 8-(Phenylamino) 1- Naphthalenesulfonates. J. Am. Chem. Soc. 1983, 105, 6236-6243. (59) Wang, F.; Liu, J. Self-Healable and Reversible Liposome Leakage by Citrate-Capped Gold Nanoparticles: Probing the Initial Adsorption/Desorption Induced Lipid Phase Transition. Nanoscale, 2015, 7, 15599-15604.


Page 32 of 36

Page 33 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(60) Zhao, J.; Wu, Y.; Tao, H.; Chen, H.; Yang, W.; Qiu, S. Colorimetric Detection of Streptomycin in Milk Based on Peroxidase-Mimicking Catalytic Activity of Gold Nanoparticles. RSC Adv., 2017, 7, 38471–38478. (61) Cremer, P.S.; Boxer, S.G. Formation and Spreading of Lipid Bilayers on Planar Glass Supports. J. Phys. Chem. B 1999, 103, 2554-2559. (62) Cheney, P. P.; Weisgerber, A. W.; Feuerbach, A. M.; Knowles, M. K. Single Lipid Molecule Dynamics on Supported Lipid Bilayers with Membrane Curvature. Membranes 2017, 7, 15. (63) Gao, J.; Zhang, O.; Ren, J.; Wu, C.; Zhao, Y. Aromaticity/Bulkiness of Surface Ligands to Promote the Interaction of Anionic Amphiphilic Gold Nanoparticles with Lipid Bilayers. Langmuir 2016, 32, 1601-1610. (64) Sen, T.; Patra, A. Formation of Self-Assembled Au Nanoparticles and the Study of Their Optical Properties by Steady-State and Time-Resolved Spectroscopies. J. Phys. Chem. C 2009, 113, 13125-13132. (65) Bastus, N. G.; Comenge, J.; Puntes, V. Kinetically Controlled Seeded Growth Synthesis of Citrate-Stabilized Gold Nanoparticles of up to 200 nm: Size Focusing versus Ostwald Ripening. Langmuir 2011, 27, 11098-11105. (66) Kanwa, N.; De, S. K.; Adhikari, C.; Chakraborty, A. Spectroscopic Study of the Interaction of Carboxyl-Modified Gold Nanoparticles with Liposomes of Different Chain Lengths and Controlled Drug Release by Layer-by-Layer Technology. J. Phys. Chem. B 2017, 121, 11333−11343. (67) Novaira, M.; Biasutti, M. A.; Silber, J. J.; Correa, N. M. New Insights on the Photophysical Behavior of PRODAN in Anionic and Cationic Reverse Micelles: From Which State or States Does It Emit? J. Phys. Chem. B 2007, 111, 748−759. (68) Thakur, R.; Das, A.; Chakraborty, A. Interaction of Human Serum Albumin with Liposomes of Saturated and Unsaturated Lipids with Different Phase Transition Temperatures: A Spectroscopic Investigation by Membrane Probe PRODAN. RSC Adv. 2014, 4, 14335−14347. 33 ACS Paragon Plus Environment

Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(69) Zhang, L.; Spurlin, T. A.; Gewirth, A. A.; Granick, S. Electrostatic Stitching in Gel-Phase Supported Phospholipid Bilayers. J. Phys. Chem. B 2006, 110, 33-35. (70) Torranoa, A. A.; Pereiraa, Â. S.; Oliveira, O. N. Jr.; Barros-Timmonsa, A. Probing the Interaction of Oppositely Charged Gold Nanoparticles with DPPG and DPPC Langmuir Monolayers as Cell Membrane Models. Colloids Surf. B 2013, 108, 120-126. (71) Tatur, S.; Maccarini, M.; Barker, R.; Nelson, A.; Fragneto, G. Effect of Functionalized Gold Nanoparticles on Floating Lipid Bilayers. Langmuir 2013, 29, 6606-6614. (72) Hou, W-C; Moghadam, B. Y.; Corredor, C.; Westerhoff, P.; Posner, J. D. Distribution of Functionalized Gold Nanoparticles between Water and Lipid Bilayers as Model Cell Membranes. Environ. Sci. Technol. 2012, 46, 3, 1869-1876. (73) Montis, C.; Maiolo, D.; Alessandri, I.; Bergese, P.; Berti., D. Interaction of Nanoparticles with Lipid Membranes: A Multiscale Perspective. Nanoscale 2014, 6, 6452-6457. (74) Bhat, A.; Edwards, L. W.; Fu, X.; Badman, D. L.; Huo, S.; Jin, A. J. Lu, Q. Effects of Gold Nanoparticles on Lipid Packing and Membrane Pore Formation. Appl. Phys. Lett. 2016, 109, 263106 (1-5). (75) Troiano, J. M.; Olenick, L. L.; Kuech, T. R.; Melby, E. S.; Hu, D.; Lohse, S. E.; Mensch, A. C.; Dogangun, M.; Vartanian, A. M; Torelli, M. D.; Ehimiaghe, E.; Walter, S. R.; Fu, L.; Anderton, C. R.; Zhu, Z.; Wang, H.; Orr, G.; Murphy, C. J.; Hamers, R. J.; Pedersen, J. A.; Geiger, F. M. Direct Probes of 4 nm Diameter Gold Nanoparticles Interacting with Supported Lipid Bilayers. J. Phys. Chem. C 2015, 119, 534−546. (76) Lundgren, A.; Agnarsson, B.; Zirbs, R.; Zhdanov, V. P.; Reimhult, E.; Höök, F. Nonspecific Colloidal-Type Interaction Explains Size-Dependent Specific Binding of Membrane-Targeted Nanoparticles. ACS Nano 2016, 10, 9974−9982. (77) Lu, B.; Smith, T.; Schmidt, J. J. Nanoparticle–lipid bilayer interactions studied with lipid bilayer arrays. Nanoscale 2015, 7, 7858–7866.


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Langmuir

(78) Ferhan, A. R.; Ma, G. J.; Jackman, J. A.; Sut, T. N.; Park, J. H.; Cho, N-J. Probing the Interaction of Dielectric Nanoparticles with Supported Lipid Membrane Coatings on Nanoplasmonic Arrays. Sensors 2017, 17, 1484. (79) Farnoud, A. M.; Nazemidashtarjandi, S. Emerging investigator series: interactions of engineered nanomaterials with the cell plasma membrane; what have we learned from membrane models? Environ. Sci.: Nano 2019, Advance Article, DOI:10.1039/C8EN00514A.


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Effect of surface ligand and temperature on lipid vesicle-gold

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