JP2000275162A - Cantilever for afm made of functional organic macromolecular gel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve change in physical properties corresponding to the surface environment of a sample and the transfer of a substance by connecting an organic macromolecular gel to the cantilever probe of an atomic force micro scope (ATM). SOLUTION: The outer surface of a cantilever probe T for ATM in a shape being used conventionally is covered with gel G, or the inside of the probe T is filled with the gel G for formation so that a tip part can be exposed, and a functional organic gel is allowed to exist at the tip of the probe T that approaches or touches the sample. The organic macromolecular gel may cause volume phase transformation (swelling, shrinkage) by external stimulus, namely pH change, temperature change, light emission, electric field, strength of compositions and ions in a solution, or the like. The organic macromolecular gel is represented by acrylamide gel, acrylamide derivative gel, and the like, and acrylamide/acryl acid copolymer gel are especially preferable. In this sort of cantilever for AFM, the characteristics (hardness, size, and the like of probe) change according to the surface environment of the sample for imaging corresponding to environment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an atomic force microscopy (AFM) cantilever, and more particularly to a new type of AFM which is completely different from a conventional type in which a functional gel is bonded to a probe. About the cantilever.

[0002]

2. Description of the Related Art As is well known, an atomic force microscope (AFM) is provided with a needle-like projection (tip) at the tip of an extremely soft spring called a cantilever, and this tip is brought close to a sample. The ability to measure the weak force (atomic force) generated between the sample surface and the probe through the cantilever strain when observing the solid surface of the sample on a nanometer scale. It is used as a device that can

[0003] Heretofore, AFM has been studied and developed with the main purpose of viewing (imaging) a solid surface with as high a resolution as possible. Therefore, the tip of a cantilever is made as rigid as possible. It has been devised to be small and sharp so that the surface image is reflected.
However, in applications to organic chemistry and bio-related fields, a flexible, fragile and elastic sample is often used as a subject, and high-resolution imaging is often not the primary purpose. In such a case, a probe exclusively oriented to stiffening or sharpening is not necessarily optimal so as to be suitable for measurement under a specific environmental condition without transferring a substance.

[0004] The influence on the soft sample surface is small, and the characteristics change according to the surface environment of the sample. Furthermore, if a cantilever probe for AFM that can transfer a substance can be obtained, if only imaging is performed, However, it is expected that various kinds of information on the sample surface will be acquired to further enhance the usefulness of the AFM. However, there is no technology embodying such a cantilever probe for the AFM.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cantilever probe for an AFM that changes its characteristics in accordance with the surface environment of a sample and enables the transfer of a substance, thereby achieving an AFM-based probe. It is to provide a new measurement technique.

[0006]

Means for Solving the Problems The present inventors have focused on organic polymer gels that exhibit various functions by undergoing a volume phase transition (swelling / shrinking) in response to an external stimulus. The present invention has been established by establishing a technique capable of bonding to the probe surface of an AFM cantilever.

Thus, the present invention first provides an AFM cantilever characterized in that an organic polymer gel is bonded to a probe of an atomic force microscope (AFM) cantilever. In one preferred embodiment of the cantilever for AFM of the present invention, the organic polymer gel comprises an acrylamide / acrylic acid copolymer gel.

The present invention further relates to a method for preparing the above-mentioned AFM cantilever, which comprises the following steps: (1) a functional group chemically bonding to a material constituting the cantilever and a monomer forming a desired organic polymer gel to a chemical bond; The probe of the cantilever is coated with a coupling agent having a functional group to be formed, and then (2) the probe after coating the coupling agent is immersed in a polymerization solution containing a monomer for forming the organic polymer gel. And causing the probe to form a thin layer of an organic polymer gel by removing the probe immediately before the gel is formed in the solution.

In a preferred embodiment of the cantilever for AFM, when the organic polymer gel comprises an acrylamide / acrylic acid copolymer gel, in the method of the present invention, the cantilever is composed of silicon nitride or silicon, and the coupling agent is an alkyl chain. Is a silane coupling agent having a vinyl group at the end of the silane coupling agent.The probe after coating with the silane coupling agent is immersed in a copolymer solution containing an acrylamide monomer, an acrylic acid monomer and a cross-linking agent, and the polymerization is performed. A thin layer of acrylamide / acrylic acid copolymer gel is formed on the surface.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cantilever for AFM of the present invention has a novel structure in which an organic polymer gel is bonded to a probe. As used herein, the term "probe" refers to a needle-shaped protrusion approaching or abutting on the sample surface, as can be understood from the description of the AFM described above. Refers to a spring-like portion that is distorted in response to an atomic force and includes a probe.

However, the cantilever for AFM of the present invention is not limited to a shape generally used for AFM, but also to a scanning probe microscope other than AFM.
robe microscopy (SPM) also refers to one that adopts a shape similar to the probe used in SPM. FIG. 1 shows a typical shape of such an AFM cantilever of the present invention.

FIG. 1A shows a typical shape conventionally used as an AFM cantilever, wherein the outer surface of a probe (T) of the cantilever is covered with a gel (G). On the other hand, FIG. 1 (b) shows an internal type, that is, a shape in which the inside of the probe (T) is filled with the gel (G) so that the tip is exposed. As can be understood from the figure, the embodiment shown in FIG. 1B is similar to the probe used in the near-field light microscope (in the near-field light microscope, the portion corresponding to the inside filled with the gel is shown). Optical fiber is provided).

As shown in FIGS. 1A and 1B,
The AFM cantilever of the present invention only needs to be configured so that at least a functional organic gel as described below exists at the tip of the probe that approaches or contacts the sample.

As described above, the organic polymer gel attached to the tip of the probe of the cantilever for AFM according to the present invention is not particularly limited.
Basically, any gel can be used as long as it causes a volume phase transition (swelling / shrinking) due to change, temperature change, light irradiation, electric field, composition in the solution, ionic strength, and the like.

Typical examples of such an organic polymer gel include acrylamide gel, acrylamide derivative gel (eg, isopropylacrylamide gel, acryloylpiperidine gel), or acrylamide or a derivative thereof, and acrylic acid, vinyl acetic acid or allyl acetic acid. And a copolymer gel of One of the particularly preferred gels
An example is an acrylamide / acrylic acid copolymer gel, which is known to undergo a volume phase transition depending on pH, temperature, electric field, and the like. As the organic polymer gel, in addition to the acrylic gel as described above, a gel made of a synthetic polymer such as a styrene derivative gel, and a gel derived from a natural polymer such as a gelatin gel, an agarose gel, and a DNA gel. Can be used.

The present invention also provides a method for binding a functional organic gel as described above to an AFM cantilever. That is, in the method of the present invention, first, by immersing the cantilever in a solution of the coupling agent,
The cantilever probe is coated with the coupling agent. Here, when the cantilever has a shape as shown in FIG. 1A, only the probe of the cantilever may be immersed in the coupling agent solution, but the shape as shown in FIG. In this case, the entire cantilever is immersed in the coupling agent solution so that the inner cavity surface is covered with the coupling agent.

As the coupling agent, one having a functional group chemically bonding to a material (surface) constituting the cantilever and a functional group chemically bonding to a monomer constituting a desired organic polymer gel is used. Such a coupling agent cantilever cantilever from many coupling agents such as silane, titanate, and chromium, which are conventionally used for improving the performance of a composite material combining an inorganic material and an organic polymer material. It can be selected according to the constituent material and the type of desired functional gel.

Preferred coupling agents are silane coupling agents, and depending on the material of the cantilever (ceramics (including glass and silica), silicon and metal), a reactive group (for example, a halogen group, Alkoxyl groups, etc., which are hydrolyzed to silanol groups and react with the surface of the inorganic substance), and the functional groups (vinyl group, epoxy group, amino group, mercapto group, etc.) that form the desired polymer gel and chemically bond. Use what you have. For example, when a thin layer of an acrylamide / acrylic acid copolymer gel is bonded to a cantilever composed of silicon (Si) or silicon nitride (Si ₃ N ₄ ), which is the most common, a vinyl is added to the end of the alkyl chain. Group-containing silane coupling agents (for example, allyltrichlorosilane, 7
-Octenyltrichlorosilane) is preferred.

In the method of the present invention, the cantilever (cantilever probe) coated with the coupling agent as described above is then immersed in a polymerization solution containing a monomer for forming an organic polymer gel. The polymerization is performed to form a thin layer of the organic polymer gel on the cantilever (cantilever probe).

As described above, in order to reliably form a thin layer of a functional organic polymer gel on a cantilever according to the method of the present invention, the reaction products and reaction conditions for the polymerization reaction are selected as described below. There are a few things to keep in mind.

First, it should be noted that, in the coupling agent that coats (modifies) the surface of the cantilever, the functional group that reacts with the monomer constituting the organic polymer gel to form a chemical bond has a relatively low reactivity. It is to make it low. If a highly reactive functional group is used, excessive crosslinking will be formed in the subsequent polymerization step (gel formation step), and the gel will not be a gel but a cured polymer. Therefore, for example, as described above, the surface of the cantilever is modified using a silane coupling agent having a vinyl group having a low reactivity at the terminal of the alkyl chain.

Next, a cantilever modified with a coupling agent is converted into a monomer and other compounds (crosslinking agent, polymerization initiator, etc.) for forming a desired organic polymer gel.
And the polymerization is started under conditions for synthesizing a normal gel. At this time, as the monomer, one having a higher concentration near the surface of the cantilever modified with the coupling agent, that is, a monomer having a stronger interaction (attraction) with the cantilever surface than the solvent, or a cantilever due to the entropy of the solvent. Use what is adsorbed on the surface. For example, a monomer having an acrylic group in water (and a crosslinking agent) is used for the surface of the cantilever covered with a vinyl group.

Thus, the bulk (polymerization reaction solution)
If the cantilever is removed from the reaction solution before reaching the gel point, the solution is not gelled, but the gelation is progressing faster because the concentration of the monomer is higher on the surface of the cantilever than in the bulk, A cantilever (cantilever probe) to which a thin layer (film) of an organic polymer gel is grafted can be prepared. The thickness of the organic polymer gel film is generally in the range of several nanometers to several hundred nanometers, and this film thickness is such that the closer the cantilever is removed from the polymerization reaction solution, the closer to the gel point of the bulk. It gets thicker. Further, the thickness of the gel can be controlled not only by adjusting the reaction time as described above, but also by changing the monomer concentration, the cross-linking agent concentration, and the initiator concentration.

The cantilever for AFM of the present invention, which has been prepared as described above and is bound with a gel that undergoes a phase transition in response to an external stimulus, has properties, for example, depending on the external stimulus, that is, the surface environment of the sample. Since the hardness and size (volume) of the probe change, imaging according to such an environment becomes possible. For example, for a sample for which an AFM image cannot be obtained, imaging can be performed by changing the pH of the sample surface.

Furthermore, a specific environment (for example,
It is also possible to make the AFM cantilevers move according to pH, temperature, composition, etc., so that information on their environment on the sample surface can be obtained.

The AFM cantilever of the present invention, in which a functional gel film (thin layer) is bonded to the tip of the probe and the above operation is performed through its volume phase transition (swelling / shrinking), While holding solvents and solute molecules such as water in the membrane of the membrane, transferring the water and other molecules to and from the probe on the nanoscale, and moving from one point on the surface to a different location Material transfer, and further, material transfer from the outside to the sample surface is realized. Therefore, if the cantilever of the present invention is used, it goes beyond mere imaging.
A new AFM measurement technique is expected that enables observation of the surface state and analysis of physical properties of the surface in consideration of material transfer according to environmental changes. Chemical modification of the outer surface of an AFM cantilever probe to cover the probe with a film that exposes specific chemical sites to the surface has traditionally been performed, but these are non-crosslinked, small molecules. It is a membrane, not a gel. Therefore, a solvent or a solute molecule cannot be held in these films, and a substance exchange with the outside cannot be performed.

In the AFM measurement using the cantilever (cantilever probe) of the present invention, the SPM including the AFM is used.
Hardware and software that have been conventionally used in the field can be used as they are.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to further clarify the features of the present invention,
Although an example is shown, the present invention is limited by this example.
Not something.Example 1: Characteristic test of pH-responsive gel probe for AFM  Silicon nitride (Si) as shown in FIG.₃N₄) Made
AFM cantilever tip with low reactivity vinyl group
Modified (coated) with the silane coupling agent. sand
That is, under a nitrogen atmosphere, the probe is
Toluene or 7-octenyltrichlorosilane
Immersion solution (1 mM) for 30 minutes.

Next, this cantilever surface-modified with a silane coupling agent was treated with acrylamide (0.185 M), acrylic acid (0.185 M) and bisacrylamide (2.28 m
M: crosslinker) and a copolymer solution consisting of ammonium persulfate / TEMED (14.7 / 44.7 mM: initiator) to form an acrylamide / acrylic acid copolymer gel. When immersed in the polymerization solution for 60 minutes, the bulk (polymerization solution body) had not yet reached the gel point, but the cantilever was taken out of the solution, and immediately after washing, the AFM experiment was performed. It is confirmed by AFM that the film thickness of the acrylamide / acrylic acid copolymer gel formed under these polymerization conditions when dried is about 6 nm.

The AFM experiment was performed in water (about 10 mM) at room temperature.
Na ⁺ ) glass surface (hydrophobic surface) while changing the pH. The spring constant of the AFM cantilever is
0.032 N / m, and the lifting speed of the cantilever tip was 500 nm / sec.

FIG. 2 shows the force / distance relationship between the probe and the surface of the hydrophobic glass in water when the pH value is changed while the position of the probe is fixed. pH 7
In, the repulsive force gradually increases as the distance approaches, but the suction force is independent of the distance over a wide range, indicating that the gel on the probe is in a swelling state and hydrophilic. [(A) of FIG. 2]. On the other hand, when the pH is lowered to 2, the range in which the repulsive force is present decreases, whereas a strong suction force is observed at a certain distance, indicating that the gel layer contracts and becomes hydrophobic [FIG. (B)]. In fact, it has been observed that bulk acrylamide / acrylic acid copolymer gels also shrink at pH 2 or lower and swell at pH 3 or higher.

FIG. 3 shows the results of an attempt to image the glass surface by changing the pH. At pH 6, even with a gel probe that swells thickly and adheres to the sample surface and an image cannot be obtained (A in FIG. 3), when the pH was reduced to 2 or less, reproducible imaging was possible with a resolution of several tens of nanometers ( FIG. 3B). As described above, it was confirmed that the polymer gel layer of the acrylamide / acrylic acid copolymer functions as a pH-responsive cantilever probe for AFM.

[Brief description of the drawings]

FIG. 1 shows a typical shape of a cantilever for AFM of the present invention, wherein (a) shows a form in which the surface of a cantilever probe generally used in AMF is coated with a gel; And (b) shows a type in which the gel is filled in the inner cavity of the probe and the gel is exposed at the tip.

FIG. 2 shows an example of a force curve when an AFM measurement is performed using the AFM cantilever of the present invention to which an organic polymer gel is bound.

FIG. 3 is a micrograph showing a structure of a ceramic material (glass) when imaging is performed by an AFM having a cantilever of the present invention to which an organic polymer gel is bonded.
The scale bar in the figure is 200 nm.

Claims (4)

[Claims] 1. A cantilever for an AFM, wherein an organic polymer gel is bonded to a probe of the cantilever of an atomic force microscope (AFM). 2. The cantilever for AFM according to claim 1, wherein the organic polymer gel comprises an acrylamide / acrylic acid copolymer gel that swells and shrinks according to pH. 3. A method for preparing the cantilever for AFM according to claim 1, wherein (1) chemically bonding with a functional group chemically bonding with a material forming the cantilever and a monomer forming a desired organic polymer gel. The probe of the cantilever is coated with a coupling agent having a functional group, and then (2) the probe after coating the coupling agent is immersed in a polymerization solution containing a monomer for forming the organic polymer gel. A method of forming a thin layer of an organic polymer gel on the probe by removing the probe immediately before the gel is formed in the solution. 4. The method for preparing the cantilever for AFM according to claim 2, wherein the cantilever is composed of silicon nitride or silicon, and the coupling agent has a vinyl group at a terminal of the alkyl chain. A silane coupling agent, a probe coated with a silane coupling agent is immersed in a copolymer solution containing an acrylamide monomer, an acrylic acid monomer and a cross-linking agent to cause polymerization. A method comprising forming a thin layer of a polymer gel.