MATERIAL COMPRISING OLIGOGLYCINE TECTOMERS AND NANOWIRES

Abstract

The invention relates to a material comprising oligoglycine tectomers and nanowires. This material is useful as an electrode, as a conductive and transparent hybrid material, and as a pH sensor, as well as in biomedical applications.

Claims

1. Material comprising oligoglycine tectomers and nanowires (NWs).

2. The material according to claim 1, wherein the NWs are silver nanowires (AgNWs).

3. The material according to claim 1, wherein the NWs are gold nanowires (AuNWs).

4. Material according to claim 1, wherein the oligoglycine tectomers are deposited on the NWs.

5. Method for obtaining the material as claimed in claim 1, comprising: i) the deposition, preferably by spray coating, of NWs on a substrate, preferably wherein the substrate is selected from glass, polyethylene terephthalate (PET) or polymethylmethacrylate (PMMA); and ii) The deposition of solutions of oligoglycine tectomers on the films of NWs resulting from step (i).

6. The method according to claim 5, wherein step (ii) is carried out by drop casting, dip coating, doctor blade or by spin coating.

7. An electrode or as a transparent conducting component comprising a material as claimed in claim 1.

8. An electrode as claimed in claim 7, for transparent electronic and optoelectronic devices, touch screens, solar cells, sensors and biosensors.

9. An electrode or transparent conducting compound according to claim 7, wherein the material has antimicrobial, antiviral, moisture barrier and protection properties, against high temperatures and self-cleaning agent anti-fouling properties.

10. An electrode or transparent conducting material according to claim 9, wherein the conducting material has properties for the protection against temperatures of up to 85 C.

11. The conducting hybrid material as claimed in claim 1, characterised by having transparency values above 90%.

12. A pH sensor comprising the material according to claim 1.

13. The material according to claim 1, when employed for loading drugs and fluorescent substances.

14. Device comprising the material according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0039] FIG. 1. Transmittance (at 550 nm) vs Rs of AgNW films of different densities. This figure includes a representative atomic force microscopy (AFM) 3D topography image of an AgNW film of intermediate density.

[0040] FIG. 2 Left: AFM topography image of individual layers of oligoglycine tectomers deposited on a glass substrate. Right: Height profile showing that individual tectomer layers are approximately 5.7 nm thick.

[0041] FIG. 3. The chemical structure of the biantennary oligoglycine, and the representation of its assembly in the form of tectomers deposited on a glass substrate.

[0042] FIG. 4 (a) Sheet resistance (Rs) as a function of time of an AgNW medium-density electrode on which a solution of 0.5 mg/mL biantennary oligoglycine has been deposited, left to dry at room temperature. A diagram of the system used to measure the current vs voltage curves is included. (b) Change of Rs (in %) as a function of the oligoglycine concentration in the original aqueous solution.

[0043] FIG. 5 3D representation of AFM topography images of low density AgNW film deposited on glass substrates, showing (a) tectomer aggregates and (b) an individual tectomer layer deposited on a low density AgNW conducting film. AFM topography images and contact angle measurements of water on intermediate density AgNW films covered with tectomer layers from solutions of oligoglycine at a concentration (c, f) 0.01 mg/ml, (d, g) 0.5 mg/ml and (e, h) 1 mg/ml.

[0044] FIG. 6 pH-dependent assembly and destruction tectomer layers in solution and on electrodes of AgNWs. Photograph of oligoglycine solutions at different pH values (b). Micrographs of transmission electron microscopy (TEM) of 1 mg/ml oligoglycine solution samples with at pH 2.2 (a) and pH 7.4 (c). AFM images that show how the topography of AgNW/tectomer hybrids deposited on glass substrates change when exposed to solutions of different pH values (d).

[0045] FIG. 7. Kinetics of bacteria growth (a) E. Coli and (b) salmonella on a glass substrate using as culture medium brain heart infusion (BHI broth), (.box-tangle-solidup.) without and (+) in the presence of AgNW/tectomer.

[0046] FIG. 8 Transmission electronic microscopy images (TEM) of AuNW/tectomer hybrids.

EXAMPLES

[0047] Below the invention will be illustrated by means of tests performed by the inventors, which highlights the effectiveness of the product of the invention.

Example 1

Preparation of the Material

[0048] For the fabrication of the material, AgNWs have been used, which have high transparency and electrical conductivity, and which have also proven to be exceptional materials for multiple applications ranging from capacitive touch sensors to multifunctional wearable sensors (see, for example, Advanced Functional Materials 2014, 24, 7580-7587; Nanoscale 2014, 6, 2345-2352; ACS Nano 2014, 8, 5154-5163). The AgNWs are deposited by spray coating on glass substrates, forming layers of different (and controlled) densities. AgNW deposition on substrates of polyethylene terephthalate (PET) and (poly(methyl methacrylate), PMMA) was also performed, which gives the material high transparency and flexibility.

[0049] Aqueous solutions of biantennary, triantennary and tetrantennary oligoglycine were used for the tectomer coatings. The deposition of the oligoglycine tectomers on the films of NWs was conducted by drop casting procedures, by immersion in oligoglycine tectomer solutions (dip coating), by dragging the dispersions on the substrates with a blade (doctor blade) or by centrifugation (spin coating).

[0050] Drop casting: The tectomer solutions were drop casted on AgNW film and left to dry at room temperature for 3 hours, or until the water had evaporated completely.

[0051] Dip coating: Solutions were deposited by dip coating of the substrate for 10 seconds, after which the substrate is removed from the solution at a speed of 1 mm/min. Once the process has been completed, the substrate with its coating is left dry in an upright position for 15 minutes.

[0052] Doctor blade: Is a suitable procedure for obtaining large tectomer coatings. 2 mL of tectomer solution were deposited at the end of a substrate and were then spread evenly over the substrate. In these experiments the blade height used was 50 micrometers; it can be adjusted in each case.

[0053] Spin-coating: the tectomer solutions were deposited on the spray coated AgNW films and spun at 2000 rpm for 10 seconds.

[0054] The density of AgNWs deposited by spray coating, and the concentration, volume and type of oligoglycine of the tectomer solutions define the composition of the coatings.

[0055] The fabrication of the material comprising AuNWs takes place by a procedure analogous to the above with the corresponding starting materials, i.e. with AuNWs instead of AgNWs.

Example 2

Transmittance (T) vs Sheet Resistance (Rs)

[0056] Thus, transmittance (T) vs Rs curves were obtained. The choice of the deposition system was justified by the fact that spray coating is industrially scalable and can produce films with high transparency on large substrates. Three types of AgNW electrodes, Rs=50 Ohm/sq, 1 kOhm/sq, and 1 MOhm/sq, were prepared depending on the density (high, intermediate and low, respectively) of AgNWs in the AgNW films.

[0057] As shown in FIG. 1, the transmittance is greater than 92% for low densities of AgNWs and gradually decreases as AgNWs are added. The AFM 3D topography image of the intermediate density AgNW film included in FIG. 1 provides values of Rs10 kOhm/sqr as well as transparency values of 91%, with 2-3 layers of AgNWs evenly distributed on the substrate.

Example 3

Morphology of Oligoglycine Tectomer Layers on Glass

[0058] AFM has been used to study the morphology of the oligoglycine tectomer layers deposited on a glass substrate (FIG. 2). AFM characterization shows that the oligoglycine molecules are assembled forming two-dimensional systems or platelets whose sizes are in the micrometer range (FIG. 2 left), each individual platelet being approximately 5.7 nm thick (FIG. 2 right). Each tectomer platelet consists of a coplanar stacking of biantennary oligoglycine molecules, facing each other such that its hydrophobic component is always exposed on the surface, as shown in the diagram of FIG. 3. Tectomer layers are atomically-smooth, highly uniform, and present no structural defects.

Example 4

Current and Voltage as a Function of Time

[0059] Oligoglycine solutions have been deposited on AgNWs, obtaining for each sample current vs voltage (I-V) curves as a function of time. I-V curves of the AgNW films and AgNWs/oligoglycine hybrid systems showed an excellent ohmic behaviour, regardless of the density of AgNWs and of concentration of oligoglycine used.

[0060] The diagram of the system used to make these measurements is shown in FIG. 4a. In films with an intermediate content in AgNWs there is a sharp decrease (between 50-70%) of the initial value of Rs when oligoglycine solutions of 0.5 and 1.0 mg/mL were deposited (FIG. 4.b). This decrease in the value of Rs is due to the action of the tectomer layers deposited. The concentration in oligoglycine increases during the water evaporation process of the solutions deposited, and the tectomer layers and aggregates mechanically press the AgNWs, increasing the contact between individual AgNWs, This increase in conductivity is achieved while maintaining at all times transparency of baseline electrodes (transparency values above 90% with transparency changes as low as 1% with respect of the starting AgNW electrodes have been measured in the AgNW/oligoglycine materials of this study). In this regard, tectomer layers would have a behaviour similar to that described for graphene, which similarly mechanically press the AgNWs on which they are deposited (see, for example, Advanced Functional Materials 2014, 24, 7580-7587; ACS Applied Materials & Interfaces 2013, 5, 11756-11761; Sci. Rep. 2013, 3, 1112).

[0061] The effective interaction between the oligoglycine and the AgNWs in these systems and that produces the synergistic effects described herein also entails significant changes observed by X-ray photoelectron spectroscopy (XPS) in the peaks corresponding to Ag3d, N1s and O1s as a result of the deposition of the tectomer solutions on electrodes of AgNWs. This interaction between the tectomers and the NWs can be modulated if the NWs are functionalized. For example, the electrostatic interactions between functional groups of functionalized NWs and protonated terminal amino groups of the tectomers change the degree of interaction between the two components and the structure of the hybrid material.

Example 5

Hydrophobicity

[0062] Due to the unique way in which the biantennary oligoglycine self-assembles in the form of tectomers in these experiments, its hydrophobic part is always exposed to the air. As a result, the water contact angle studies have been conducted to determine the hydrophobicity of tectomer-coated AgNW electrodes. These studies show a significant hydrophobicity increase (90) of the AgNW electrodes coated with tectomers from solutions of 0.5 and 1.0 mg/mL of biantennary oligoglycine (FIG. 5). This result indicates that the tectomer coatings act as an effective barrier to moisture, giving the system self-cleaning and anti-fouling functions. When the water drop is deposited on the AgNW electrode without tectomer coating, conversely, the water contact angle decreases from 33 to 11, which indicates that the water penetrates into the unprotected conducting AgNW film.

Example 6

AgNW/Oligoglycine Hybrids as pH Sensors

[0063] On the other hand, when the pH of an oligoglycine solution changes to acidic or basic regions, the oligoglycine assembly may take place or otherwise be destroyed (FIG. 6a-c), since the change in pH can make the terminal amino groups of the oligoglycine neutral or charged (Beilstein Journal of Organic Chemistry 2014, 10, 1372-1382). The self-assembling or destruction of the tectomer layers is completely reversible and can be carried out repeatedly. These pH-dependent structural changes of oligoglycine can be observed also in hybrid electrodes of AgNWs/oligoglycine (FIG. 6d) and can therefore be considered as pH sensors.

[0064] Oligoglycine coatings provide new biofuncionalidades to AgNW electrodes. As oligoglycines have the ability to physically or chemically immobilise viruses and bacteria (Russ J Bioorg Chem 2010, 36, 574-580), their hybridisation with AgNWs gives rise to new functionalities that make them useful as biomedical materials. In this regard, hybrids of AgNWs and two-dimensional peptide systems give rise to the formation of sophisticated nanostructures with smart response to the environment. In addition, the interaction of viruses and other analytes in these hybrid systems can be controlled through the functionalisation of terminal amino groups of oligoglycines, which makes them useful as biosensors or for the immobilisation of bacteria and viruses. The adhesion of viruses, bacteria, or other analytes to these films and electrodes of tectomer and AgNW hybrids can be removed by varying the pH of the environment, such that at low pH values the oligoglycine assemblies are destroyed, thus removing the materials attached to them.

Example 7

Use of Tectomer Coatings as Protection for AgNWs Under Extreme Environmental Conditions

[0065] The performance of the transparent AgNW electrodes largely depends on the degradation and deterioration of the AgNWs themselves (Small 2014, 10, 4171-4181). Under environmental conditions, AgNWs undergo oxidation and sulfurization processes, so that it is highly important to protect the AgNW electrodes against harsh environmental conditions, such as for example humidity, exposure to oxygen and ozone as well as other gaseous molecules containing sulphur. Accordingly, different coatings that protect the nanowires against deterioration in these conditions have been developed, either by coating the individual nanowires or systems consisting of a set of nanowires (ACS Appl. Mater. Interfaces 2012, 4, 6410-6414; Nanoscale 2014, 6, 4812-4818; ACS Appl. Mater. Interfaces 2015, 7, 23297-23304; J. Nanoparticle Res. 2012, 14, 1-9; Appl. Phys. Lett. 2011, 99, 183307). In this case, a tectomer solution was drop casted on AgNW films until they were fully covered, and left to dry at room temperature. AgNW electrodes with and without tectomer coating were exposed to high temperature (85 C) and high relative humidity (85%) atmosphere. After 2 hours of exposure to these extreme environmental conditions, sheet resistance of the AgNW electrodes was measured, noting that it increased only by 10-14% with tectomer coating, while a 200% increase in sheet resistance took place for the uncoated AgNW electrodes. Therefore, these results show that tectomer coatings provide protection to AgNW systems under harsh environmental conditions.

Example 8

AgNWs Coated with Tectomers Exhibit Antimicrobial Activity

[0066] Studies on the kinetics of E. coli and salmonella growth using as culture medium a brain-heart infusion (BHI broth), in AgNW/tectomer materials deposited on glass, show that bacterial growth is significantly inhibited in these compared with the substrate used without coating (FIG. 7). These results show that coatings with tectomers protect not only the AgNWs against deterioration produced by the environment (example 7), but it also preserves the antimicrobial activity of the AgNWs (Mater. Sci. Eng. C 2017, 70,1011-1017). The adhesive action of tectomers on bacteria (Colloids Surf. A 2014, 460, 130-136) and viruses (ChemBioChem 2003, 4, 147-154; Glycoconjugate J. 2004,1, 471-478), favours the contact with the AgNWs, and therefore their antimicrobial activity. Indeed, previous work has shown that tectomers can be loaded with drugs (ACS Appl. Mater. Interfaces, 2016, 8, 1913-1921), so the effectiveness of the antimicrobial activity of these materials can be increased, while preserving the properties of the AgNWs.

Example 9

Interaction of Tectomers with Gold Nanowires

[0067] AuNW/tectomer hybrids have been prepared. The AuNWs used had an average diameter of 30 nm and lengths of 4.5 m. TEM characterisation of the aqueous dispersions resulting from mixing 0.5 mg.Math.mL1 of biantennary oligoglycine and 0.05 mg.Math.mL1 of AuNWs is shown in FIG. 8, in which there is an extensive coating of AuNWs by the oligoglycine tectomers.

[0068] The functionalisation of AuNWs as a result of surface modification with tectomers is promising for applications in electronics, sensors, energy (solar cells) and biomedicine. Thus, AuNW/tectomer hybrids can combine the features of biomedical interest of both the AuNWs and the tectomers, which can be loaded with drugs and fluorescent substances (ACS Appl. Mater. Interfaces 2016, 8, 1913-1921).

[0069] In addition, the procedures described herein can be extended to functionalised nanowires, such as for example carboxylated nanowires.