CN109799205B

CN109799205B - Infrared molecular fingerprint sensor with planar thin film structure and preparation method thereof

Info

Publication number: CN109799205B
Application number: CN201910127577.1A
Authority: CN
Inventors: 刘志军; 郭世兴; 何德
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2019-02-20
Filing date: 2019-02-20
Publication date: 2021-11-09
Anticipated expiration: 2039-02-20
Also published as: CN109799205A

Abstract

The invention discloses an infrared molecular fingerprint sensor with a planar thin film structure and a preparation method thereof, wherein the infrared molecular fingerprint sensor comprises a double-layer film planar structure sensor and a single-layer film planar structure sensor, and the double-layer film planar structure sensor is composed of two layers of films, namely copper (Cu) and zinc selenide (ZnSe), on a silicon (Si) substrate; the single-layer film planar structure sensor is composed of a gold film on a silicon (Si) substrate. The sensor is based on the principles of film optical cavity resonance and interface field enhancement, consists of planar multilayer metal and a dielectric film, does not need a graphical processing process, and has the advantages of simple processing, low cost, high yield, large effective detection area, monomolecular layer detection sensitivity and the like.

Description

Infrared molecular fingerprint sensor with planar thin film structure and preparation method thereof

Technical Field

The invention belongs to the technical field of optical molecular sensors, and particularly relates to an infrared molecular fingerprint sensor with a planar film structure and a preparation method thereof.

Background

The optical molecular detection technology can carry out quantitative detection and analysis on trace substances such as protein, ribose and nucleic acid, is very important for people to know the vital problems such as gene structure, gene expression and regulation, and has wide application prospect in the fields of pharmaceutical development, food safety, environmental engineering, drug formulation, disease monitoring and the like. Given that organic and biological molecules are closely related to human life, environment and disease, the innovation and application progress of molecular detection technology is directly related to human health and production mode, especially the level of new detection, diagnosis and treatment instruments.

Common optical molecular sensors can be roughly divided into two types according to different working principles, one type of optical molecular sensor depends on target molecules to be adsorbed on the surface of the sensor, so that the refractive index of the surface of the sensor is changed, the absorption wavelength of the sensor is moved, and the detection of the target molecules is completed, the sensor can only detect the refractive index change caused by molecular mass, but cannot distinguish the chemical structure characteristics in the molecules, and the optical molecular sensor is limited in a plurality of important applications; the other method is that according to the characteristic that molecules have specific 'absorption fingerprints' in the middle infrared band, the micro structure on the surface of the sensor is used for enhancing the optical field near the target molecules to cause the vibration enhancement of chemical bonds in the target molecules, thereby completing the specific identification and detection of the target molecules and obtaining the characteristic information of the chemical bonds in the molecules. In such a sensor based on fingerprint absorption, it is a common technique to make microstructures with different shapes on the sensor surface by using a micro-machining method to obtain a localized enhanced optical field, so as to enhance the vibration of chemical bonds in target molecules adsorbed on the surface of a detector. Representative work that has been reported specifically includes: neubrech et al propose to use rod-like nano-antennas to accomplish high sensitivity detection of 1-octadecanethiol, [ resistant plasma and biological coupling in a labeled nano-antenna for detecting, PHYSICAL REVIEW LETTERS 101(15) ], 157403(2008), ] 2009 e.cubukcu et al also achieve effective detection of target molecules using a Resonant ring antenna fabricated by microfabrication process, [ spring resonator sensors for detecting of single molecular molecules, APPLIED PHYSICS LETTERS 95(4) (043113) (2009) ].

In the prior art, the molecular fingerprint sensor generally consists of a patterned metal or medium structure with a micro-nano structure, the preparation process of the molecular fingerprint sensor needs to use a thin film patterning processing method such as photoetching or electron beam etching, the manufacturing process is complex, the cost is high, and meanwhile, the repeatability and controllability of the device limit the practical large-scale application.

Disclosure of Invention

The invention aims to provide a molecular fingerprint sensor without a graphical planar film structure and a preparation method thereof, the sensor is based on the principles of film optical cavity resonance and interface field enhancement, consists of planar multilayer metal and a dielectric film, does not need a graphical processing process, and has the advantages of simple processing, low cost, high yield, large effective detection area, monomolecular layer detection sensitivity and the like.

In order to achieve the technical purpose, the invention is specifically realized by the following technical scheme:

an infrared molecular fingerprint sensor with a planar thin film structure comprises a double-layer film planar structure sensor and a single-layer film planar structure sensor, wherein the double-layer film planar structure sensor is composed of two layers of films, namely copper (Cu) and zinc selenide (ZnSe), on a silicon (Si) substrate; the single-layer film planar structure sensor is composed of a gold film on a silicon (Si) substrate.

The double-layer film planar structure sensor ensures that the maximum value of the generated Fabry-Perot resonance field is positioned on the surface of ZnSe by setting the thickness of the ZnSe dielectric layer to be a quarter wavelength, thereby completing the effective detection of target molecules.

The single-layer film plane structure sensor is based on the discontinuous boundary condition of an optical field on the surface of gold, and the superposition of an incident electric field and a reflected electric field on the surface of gold enhances the electric field, so that the effective detection of molecules to be detected is realized.

In another aspect of the present invention, there is provided a method for preparing the above molecular fingerprint sensor, comprising the steps of:

1) preparing a single-layer gold film with the thickness of more than 100nm or a copper/quarter-wavelength thick ZnSe two-layer film with the thickness of more than 100nm on a silicon wafer (or any other material substrate) by using an electron beam vacuum coating technology;

2) placing the prepared film sample in a molecular solution to be detected for soaking for 24 hours;

3) and respectively washing the soaked film sample with ethanol and deionized water, and then drying with nitrogen to complete the adsorption self-assembly of the molecules to be detected on the surface of the sensor.

Furthermore, for a typical detection object, namely the octadecanethiol ODT organic molecule, the solvent in the solution is ethanol, and the ODT concentration ratio is 1 mM/L.

Furthermore, for bovine serum albumin BSA molecules, the solvent in the solution is phosphate buffered saline, and the concentration ratio of BSA is 1 mg/ml.

The invention has the beneficial effects that:

the infrared molecular fingerprint sensor molecule detection is based on a new principle of film cavity resonance and film interface light field discontinuity, is different from a localized light field resonance mechanism of a conventional micro-nano structure sensor, and a device is composed of a non-patterned multilayer film.

Drawings

FIG. 1 is a schematic diagram of a two-layer membrane planar structured molecular sensor;

FIG. 2 is a graph of field enhancement factor as a function of angle of incidence for a two-layer membrane planar structured molecular sensor;

FIG. 3 is a schematic diagram of a monolayer film planar structured molecular sensor;

FIG. 4 is a plot of field enhancement factor as a function of angle of incidence for a monolayer film planar structured molecular sensor;

FIG. 5 is a schematic diagram of an ODT molecular sensor based on a two-layer membrane structure;

FIG. 6 is a reflection spectrum at different angles of incidence for s-polarization;

FIG. 7 is a schematic diagram of a BSA molecular sensor based on a monolayer film structure;

FIG. 8 is a reflection spectrum for p-polarization at different angles of incidence.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to specific embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Based on a planar thin film structure, the invention designs a non-graphical high-sensitivity molecular sensor. The specific design scheme is shown in figures 1-4. Fig. 1 is a two-layer film planar structure sensor, the structure is composed of two layers of films of copper (Cu) and zinc selenide (ZnSe) on a silicon (Si) substrate, and the maximum value of the fabry-perot resonance field generated is ensured to be located on the surface of ZnSe by setting the thickness of the ZnSe dielectric layer to a quarter wavelength, so as to accomplish effective detection of target molecules. Fig. 2 is a relationship of theoretically calculated electric field enhancement factors of the ZnSe surface with the change of the incident angle in different polarization directions (s-polarization and p-polarization), and it can be seen that when s-polarized light is incident, the optical field is effectively enhanced, the field enhancement factor is maintained at 1.87, and the field enhancement based on the thin film optical cavity resonance principle constitutes a physical mechanism of the molecular sensing of the present invention.

Based on the similar field enhancement principle, fig. 3 is a single-layer film planar structure molecular sensor design with a simpler structure, the structure is composed of a gold film on a silicon (Si) substrate, and the electric field is enhanced by superposition of an incident electric field and a reflected electric field of the gold surface based on the discontinuous boundary condition of an optical field on the gold surface, so as to realize effective detection of molecules to be detected. Fig. 4 is a rule that the electric field enhancement factor of the Au thin film surface changes with the incident angle when light with different polarizations (s-polarization and p-polarization) is incident, and for p-polarization, the electric field enhancement factor becomes larger with the increase of the incident angle, and the electric field enhancement factor can reach 1.94 at most, which indicates that the field enhancement based on the interface discontinuity is also suitable for molecular detection.

In a typical embodiment of the present invention, as shown in FIG. 5, the target detection molecule is Octadecanethiol (ODT). The molecular sensor consists of two layers of films of copper with the thickness larger than 100nm and ZnSe with the thickness of 362nm on a silicon substrate, wherein the thickness of the ZnSe meets the condition of quarter wavelength, and the resonance optical field frequency of the film is ensured to coincide with the fingerprint absorption wavelengths (at 2850cm-1 and 2918 cm-1) of the molecular ODT to be detected. The sensor is prepared by a conventional electron beam evaporation film coating technology. The monolayer ODT molecule to be detected is adsorbed on the surface of ZnSe by a self-assembly method. FIG. 6 shows the reflection spectrum of the sensor under different incident angles under s-polarization, and it can be clearly seen that there are distinct absorption peaks at 2850cm-1 and 2918cm-1, which correspond to the symmetric and anti-symmetric resonance modes of CH2 in ODT molecule, respectively, to realize the detection of single-layer ODT molecule. The absorption peaks of ODT molecules increase along with the increase of the incident angle, and at an angle of 75 degrees, the depths of the two absorption peaks are as high as 5.07 percent and 8.54 percent, which is equivalent to the detection signal of a molecular sensor based on a micro-nano structure.

In another exemplary embodiment of the present invention, as shown in FIG. 7, the target probe molecule is Bovine Serum Albumin (BSA). The molecular sensor consists of a 180nm gold monolayer on a silicon substrate. Also, the sensor is prepared by conventional electron beam coating techniques. The monolayer Bovine Serum Albumin (BSA) molecules are adsorbed on the surface of the gold film through a self-assembly process in the solution. Fig. 8 is an infrared reflection spectrum of the device. Two absorption peaks can be clearly seen at 1546cm-1 and 1664cm-1, which respectively correspond to the characteristic absorption of Amide II and Amide I functional groups of BSA protein molecules, and realize the fingerprint detection of BSA molecules. When the angle is increased, the absorption peaks at the two positions become larger, and at an angle of 80 degrees, the depths of the absorption peaks at the two positions reach 1.14 percent and 0.5 percent, so that the effective detection of the monomolecular layer BSA is realized.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. The infrared molecular fingerprint sensor with the planar thin film structure is characterized in that the infrared molecular fingerprint sensor is a single-layer film planar structure sensor, the single-layer film planar structure sensor is formed by a gold film on a silicon substrate, and based on the discontinuous boundary condition of an optical field on the surface of gold, the superposition of an incident electric field and a reflected electric field on the surface of gold enhances the electric field so as to realize the effective detection of bovine serum albumin BSA molecules;

the single-layer film planar structure sensor is prepared by the following method:

preparing a 180nm single-layer gold film on a silicon wafer by using an electron beam vacuum coating technology; placing the prepared film sample in bovine serum albumin BSA molecular solution for soaking for 24 hours; washing the soaked film sample with ethanol and deionized water respectively, and then drying the film sample by using nitrogen to complete the adsorption self-assembly of bovine serum albumin BSA molecules on the surface of the sensor;

the solvent in the bovine serum albumin BSA molecular solution is phosphate buffered saline, and the concentration ratio of BSA is 1 mg/ml.