Femtosecond Time Resolution Optical Response Single-Molecule Signal Detection Method and Device

Abstract

The present invention relates to the technical field of signal testing, and particularly to a femtosecond-level time-resolution optical response single-molecule signal detection method and device, which includes the following steps: The pump pulse optical path is incident into the guiding optical fiber through a series of mirrors, a broadband optical parametric amplifier, a first aperture, a chopper, a first attenuation sheet, and a second beam combining / splitting sheet; The probe light optical path is incident into the guiding optical fiber through a time delay device, a series of mirrors, a second aperture, a white light generation module, and a second beam combining / splitting sheet; The two beams of light enter the multifunctional sample rod, and after passing through a polarizer, they are irradiated onto a graphene single-molecule device connected with a single light-responsive molecule; The single light-responsive molecule is excited after being irradiated by the pump pulse optical path, and then is detected through the probe light optical path. The method and device provided by the present invention can achieve the detection of weak signals of single light-responsive molecules with femtosecond-level time resolution, and can improve the signal-to-noise ratio of the electrical signals measured by the comprehensive physical property measurement system.

Description

Technical Field

[0001] The present invention relates to the technical field of signal testing, and particularly to a femtosecond time-resolution optical response single-molecule signal detection method and device. Background Art

[0002] Studying individual molecules can provide researchers with unprecedented resolution to observe and detect molecular behavior. Traditional chemical research is usually at the ensemble level, that is, measuring the average behavior of a large number of molecular populations, which often masks the unique properties of individual molecules. When the spatial scale is refined to the scale of individual molecules, researchers can directly observe the physical and chemical properties of individual molecules, which helps to reveal the essence of processes such as intermolecular interactions, reaction kinetics, conformational changes, and electron transfer.

[0003] Studying individual molecules requires the use of single-molecule electrical devices. Currently, a commonly used single-molecule electrical device is to connect a single molecule with amino groups at both ends through chemical design to a graphene electrode through an amide covalent bond, thereby constructing a stable graphene-molecule-graphene single-molecule junction. Since the signal of a single molecule is very weak and is easily interfered by environmental noise, the signal testing conditions for single molecules are very strict. Among them, the Physical Property Measurement System (PPMS) can provide an electrical testing environment of ultra-low temperature and strong magnetic field, so it is often necessary to use PPMS for testing in the research of single-molecule electronics and has important application value.

[0004] PPMS is developed by Quantum Design Company in the United States and is widely used in the fields of materials science, condensed matter physics, and nanotechnology. The main composition of PPMS is to integrate a variety of physical property measurement means such as fully automatic thermal, electrical, and magnetic on a finely controlled ultra-low temperature and strong magnetic field platform. In addition, PPMS also provides some extended function options to meet the different research needs of researchers. This highly integrated testing instrument has been recognized by scientists around the world in the past ten years, so in the field of single-molecule electronics, PPMS has become a research tool.

[0005] However, due to the limitation of the instrument response time resolution in electrical testing, the test on PPMS only meets the nanosecond time scale. However, for a single molecule, the time scale of multiple processes such as molecular configuration changes, electron transfer, and energy level transitions usually occurs on the picosecond or even femtosecond scale, so the existing PPMS testing technology cannot test the above processes of a single molecule. In addition, since the photoinduced current generated by a single photoresponsive molecule when excited by light is usually in the order of several picoamperes, it is a weak signal, and the noise in conventional testing is at the nanoampere level, which will completely submerge the photoresponsive signal, it is difficult to test the photoinduced current generated by a single photoresponsive molecule. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method and device for detecting light-responsive single-molecule signals with femtosecond time resolution, which can realize the detection of weak signals of single light-responsive molecules with femtosecond time resolution.

[0007] The present invention is achieved through the following technical solutions:

[0008] The method for detecting single-molecule signals with light response at a femtosecond time resolution comprises the following steps:

[0009] S1: The laser emitted from the femtosecond laser is reflected by the first reflector to the first beam combiner and splitter. 50% of the light is transmitted to form the pump pulse optical path, and 50% of the light is reflected to form the detection light path.

[0010] S2: The pump pulse light path is reflected by the second reflector to the broadband optical parametric amplifier, then reflected by the third reflector to enter the first aperture for beam positioning, then emitted to the tunable first attenuator after passing through the chopper with a fixed frequency, and then emitted into the introduction optical fiber through the fourth reflector and the second beam combining and splitting plate respectively;

[0011] S3: The detection light is reflected in the time delay device to achieve femtosecond delay, and then reflected by the fifth and sixth reflectors to enter the second aperture for beam positioning, and then passes through the white light generation module to generate continuous detection white light, and then passes through the seventh reflector and the second beam combiner and splitter to be injected into the introduction optical fiber;

[0012] S4: The pump pulse optical path and the detection light optical path enter the multifunctional sample rod placed in the test cavity of the comprehensive physical property measurement system, and are polarized by the polarizer in the multifunctional sample rod to generate left-handed or right-handed circularly polarized light, which is then irradiated onto the graphene single-molecule device connected to a single photoresponsive molecule to be detected and placed on the sample carrier of the multifunctional sample rod. The graphene single-molecule device connected to a single photoresponsive molecule to be detected is connected to the electrode column of the sample carrier through a copper wire and a conductive silver glue;

[0013] S5: After being irradiated by the pump pulse optical path, a single photo-responsive molecule is excited, then detected through the probe light optical path, and reflected by the signal acquisition unit and displayed on the computer.

[0014] Optimally, the femtosecond laser is a titanium-sapphire femtosecond laser.

[0015] Optimally, the white light generation module includes a first convex lens, a tunable second attenuation sheet, a Yag white light crystal, a second convex lens, and a filter arranged in sequence.

[0016] Furthermore, the multi-functional sample rod includes a sample rod main body, an input optical fiber interface, a fixture, a polarizer, a sample stage, and a twisted wire. The input optical fiber interface is fixedly installed at the top of the sample rod main body and connected to the input optical fiber. The fixture is fixedly installed inside the sample rod main body and below the input optical fiber interface. The polarizer is installed on the fixture. The sample stage is installed inside the sample rod main body and below the fixture. The graphene single-molecule device connected with a single photo-responsive molecule to be detected is fixedly placed on the sample stage. The twisted wire is connected to the gold electrode of the graphene single-molecule device connected with a single photo-responsive molecule to be detected and the signal acquisition unit.

[0017] Optimally, the twisted wire is a twisted pair.

[0018] Furthermore, the signal acquisition unit includes a preamplifier and a lock-in amplifier. The preamplifier is used to amplify the detection information transmitted by the twisted wire and then transmit it to the lock-in amplifier. The lock-in amplifier is used to extract the components with the same frequency as the reference signal and phase correlation and transmit them to the computer.

[0019] Furthermore, the method for the lock-in amplifier to extract the components with the same frequency as the reference signal and phase correlation is as follows:

[0020] D1: The lock-in amplifier represents the input signal as an AC signal superimposed on a DC bias according to Equation (1):

[0021] (1);

[0022] Where: represents the input signal of the lock-in amplifier, represents the average current generated by the graphene single-molecule device connected with a single photo-responsive molecule to be detected, represents the photocurrent generated by the graphene single-molecule device connected with a single photo-responsive molecule to be detected, represents the reference frequency generated by the lock-in amplifier, equal to the chopper frequency, represents time, represents the initial phase of the lock-in amplifier, represents random noise;

[0023] D2: The lock-in amplifier synchronously multiplies and integrates the input signal with the reference signal, and extracts the signal component in phase with the reference frequency according to Equation (2):

[0024] (2);

[0025] Where: represents the extracted signal component in phase with the reference frequency, represents the integration time period;

[0026] D3: The extracted signal component in phase with the reference frequency is obtained through sum-to-product calculation to get (3):

[0027] (3);

[0028] D4: Fix the initial phase of the lock-in amplifier, lock the optoelectronic signal submerged in noise at the reference frequency, amplify it, and then transmit it to the computer for reading out.

[0029] Optimized, in step D4, the initial phase of the lock-in amplifier is fixed at 0.

[0030] Optimized, in step S3, the wavelength range of the continuous detection white light generated by the white light generation module is 500 nm - 950 nm.

[0031] A femtosecond time-resolution optical response single-molecule signal detection device, which is used to perform the femtosecond time-resolution optical response single-molecule signal detection method described in any one of the above, includes a femtosecond laser, a first mirror, a first beam combining and splitting plate, a pump pulse optical path, a probe light optical path, a second beam combining and splitting plate, an input optical fiber, a comprehensive physical property measurement system, a multi-functional sample rod, a signal acquisition unit and a computer. The femtosecond laser, the first mirror and the first beam combining and splitting plate are sequentially coupled. The pump pulse optical path includes a second mirror, a broadband optical parametric amplifier, a third mirror, a first aperture, a chopper with a fixed frequency, a tunable first attenuator and a fourth mirror, which are sequentially coupled. The probe light optical path includes a time delay device, a fifth mirror, a sixth mirror, a second aperture, a white light generation module and a seventh mirror, which are sequentially coupled. The white light generation module includes a first convex lens, a tunable second attenuator, a Yag white light crystal, a second convex lens and a filter, which are sequentially coupled. The pump pulse optical path and the probe light optical path are combined by the second beam combining and splitting plate and then enter the input optical fiber. The multi-functional sample rod is placed in the test cavity of the comprehensive physical property measurement system. The multi-functional sample rod includes a sample rod main body, an input optical fiber interface, a clamp, a polarizer, a sample stage and a twisted pair. The input optical fiber interface is fixedly installed at the top of the sample rod main body and is connected to the input optical fiber. The clamp is fixedly installed in the sample rod main body and is located below the input optical fiber interface. The polarizer is installed on the clamp. The sample stage is installed in the sample rod main body and is located below the clamp. A graphene single-molecule device connected with a single light-responsive molecule to be detected is fixedly placed on the sample stage and is connected to the sample stage electrode post through a copper wire and conductive silver glue. The twisted pair is connected to the gold electrode of the graphene single-molecule device connected with a single light-responsive molecule to be detected and the signal acquisition unit. The signal acquisition unit includes a preamplifier and a lock-in amplifier connected to each other. The current amplifier is connected to the twisted pair, and the lock-in amplifier is connected to the computer.

[0032] Advantages of the invention:

[0033] The femtosecond time-resolution optical response single-molecule signal detection method and device provided by the present invention have the following advantages:

[0034] 1. The detection device composed of a combination of a comprehensive physical property measurement system and a femtosecond laser combines the advantages of optical and electrical detection technologies. It can not only regulate a single molecule by multimodal means such as optical field and electric field, but also improve the time resolution to the femtosecond level. It can monitor the femtosecond optical response kinetic process of a single molecule, and the time delay device can be used to tune the optical path in the input optical path, so as to flexibly detect the optical response process at different time scales;

[0035] 2. Modulate the pump pulse frequency using a chopper, output the chopper frequency through a lock-in amplifier as the reference frequency, and combine the phase-sensitive detection of the lock-in amplifier to enable the detection of weak signals from single photo-responsive molecules;

[0036] 3. By independently designing a multi-functional sample rod, a fixture is machined above the sample stage of the multi-functional sample rod, and a polarizer is installed. It can be simply and quickly used to switch femtosecond-level ultrafast optical pulses of different polarization modes, thereby converting the imported linearly polarized ultrafast laser into left-handed or right-handed circularly polarized light, enabling photo-response research related to single-molecule chiral spin;

[0037] 4. The current transmission selects twisted pair wires to reduce the noise of the electrical signals measured by the comprehensive physical property measurement system from the original nanoampere level noise to the picopicoampere level, improving the signal-to-noise ratio. Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the process of the present invention.

[0039] Figure 2 It is a schematic diagram of the device of the present invention.

[0040] Figure 3 It is a schematic diagram of the assembly structure of the multi-functional sample rod of the present invention.

[0041] Figure 4 It is a partially enlarged schematic diagram of part B of the multi-functional sample rod of the present invention.

[0042] Figure 5 It is a comparison diagram of the electrical test background noise of the multi-functional sample rod of the present invention.

[0043] Figure 6 It is the current-voltage image of the graphene single-molecule device connected with a single photo-responsive molecule of the present invention when no femtosecond laser is applied.

[0044] Figure 7 It is the current-voltage image of the graphene single-molecule device connected with a single photo-responsive molecule of the present invention when a femtosecond laser irradiation is applied and the time delay line is 100 femtoseconds.

[0045] In the figure: 1. femtosecond laser; 2. first reflector; 3. first beam combining and splitting plate; 4. second reflector; 5. broadband optical parametric amplifier; 6. third reflector; 7. first aperture; 8. chopper with a fixed frequency; 9. tunable first attenuator; 10. fourth reflector; 11. time delay device; 12. computer; 13. fifth reflector; 14. sixth reflector; 15. second aperture; 16. first convex lens; 17. tunable second attenuator; 18. Yag white light crystal; 19. second convex lens; 20. filter; 21. seventh reflector; 22. second beam combining and splitting plate; 23. input optical fiber; 24. multifunctional sample rod; 24-1. input optical fiber interface; 24-2. sample rod main body; 24-3. twisted pair; 24-4. polarizer; 24-5. fixture; 24-6. sample stage; 25. comprehensive physical property measurement system; 26. preamplifier; 27. lock-in amplifier. Detailed implementation mode

[0046] A femtosecond time-resolution optical response single-molecule signal detection method, which includes the following steps, and its flowchart is as Figure 1 shown:

[0047] S1: The laser emitted from the femtosecond laser is reflected by the first reflector onto the first beam combining and splitting plate. 50% of the light is transmitted to form a pump pulse optical path, and 50% of the light is reflected to form a probe light optical path;

[0048] Specifically, the femtosecond laser can preferably be a titanium sapphire femtosecond laser. Further, the titanium sapphire femtosecond laser can preferably be the PHAROS series titanium sapphire femtosecond laser produced by Light Conversion Company, which has millijoule-level high pulse energy and high average power, the generated laser wavelength is 1030 nanometers, the laser repetition frequency is usually 100 kilohertz, and the laser pulse width can be less than 100 femtoseconds.

[0049] S2: The pump pulse optical path is reflected by the second reflector into the broadband optical parametric amplifier, and then reflected by the third reflector and enters the first aperture for beam positioning, and then passes through the chopper with a fixed frequency and then exits to the tunable first attenuator, and then is respectively incident into the input optical fiber through the fourth reflector and the second beam combining and splitting plate;

[0050] Specifically, the broadband optical parametric amplifier can preferably be the ORPHEUS series collinear optical parametric amplifier produced by Light Conversion Company, which is used to convert the generated femtosecond laser into pump pulses of other wavelengths and has a tunable function.

[0051] The femtosecond laser at 1030 nm output by the titanium sapphire femtosecond laser passes through the first beam combining and splitting prism and the second reflector, and then enters the broadband optical parametric amplifier, where it can be frequency-doubled to obtain pump pulses in the range of 325 nm to 1000 nm.

[0052] The chopper can preferably be a chopper manufactured by THORLABS, which can block the pulsed light at intervals of the ultrafast laser with a repetition frequency of 100 kHz, and the final frequency is the frequency set by the chopper, forming pump-probe with respect to the probe light.

[0053] S3: The optical path of the probe light is reflected into the time delay unit to achieve femtosecond-level delay, and then reflected by the fifth reflector and the sixth reflector and enters the second aperture for beam positioning, and then passes through the white light generation module to generate continuous probe white light, and then passes through the seventh reflector and the second beam combining and splitting prism and is injected into the fiber optic cable;

[0054] The time delay unit here can preferably be a time delay unit manufactured by THORLABS, which consists of a high-precision motor platform and multiple internal reflectors in the platform. The femtosecond light output by the titanium sapphire femtosecond laser is reflected multiple times by the time delay unit for optical path setting. The moving range of the high-precision motor platform is 0 to 300 nm, and the femtosecond laser can be reflected repeatedly 8 times within the high-precision motor platform. According to the speed of light being 3×10^8 m / s, the delay time of the time delay unit for the probe light is 0 to 8 nanoseconds.

[0055] Since the time delay unit can achieve femtosecond-level optical path delay through the high-precision motor platform, so that the interval between the pump pulse and the probe pulse reaches the femtosecond level, it is possible to improve the time resolution of the test to the femtosecond level at most. And the tunability of the time delay unit can make the interval between the pump pulse and the probe pulse reach up to 8 nanoseconds at most, so as to be able to detect the optical response dynamics processes on different time scales.

[0056] Optimally, the white light generation module includes a first convex lens, a tunable second attenuation sheet, a Yag white light crystal, a second convex lens, and a filter arranged in sequence.

[0057] The Yag white light crystal here has a thickness of about 13 mm and can convert the incident femtosecond laser at 1030 nm into probe white light, and the specific wavelength range is 500 nm to 950 nm.

[0058] S4: The pump pulse optical path and the probe light optical path enter a multi-functional sample rod placed in the test cavity of the comprehensive physical property measurement system. After passing through a polarizer in the multi-functional sample rod to generate left-handed or right-handed circularly polarized light, the light is irradiated onto a graphene single-molecule device connected with a single photo-responsive molecule and placed on the sample stage of the multi-functional sample rod for detection. The graphene single-molecule device connected with a single photo-responsive molecule to be detected is connected to the electrode post of the sample stage through a copper wire and conductive silver glue.

[0059] The multi-functional sample rod is placed in the test cavity of the comprehensive physical property measurement system, and the pump pulse optical path and the probe light optical path enter the multi-functional sample rod. The comprehensive physical property measurement system can provide an ultra-low temperature and strong magnetic field experimental environment required for single-molecule testing, equipped with a dilution refrigerator, with a minimum temperature of about 50 millikelvin and a maximum magnetic field of up to ±9 tesla.

[0060] Specifically, the multi-functional sample rod includes a sample rod main body, an imported optical fiber interface, a fixture, a polarizer, a sample stage, and a twisted pair. The imported optical fiber interface is fixedly installed at the top of the sample rod main body and connected to the imported optical fiber. The fixture is fixedly installed inside the sample rod main body and below the imported optical fiber interface. The polarizer is installed on the fixture. The sample stage is installed inside the sample rod main body and below the fixture. The graphene single-molecule device connected with a single photo-responsive molecule to be detected is fixedly placed on the sample stage. The twisted pair is connected to the gold electrode of the graphene single-molecule device connected with a single photo-responsive molecule to be detected and the signal acquisition unit.

[0061] Installing a polarizer required for the experiment on the fixture can change the polarization state of the femtosecond laser into left-handed circularly polarized light or right-handed circularly polarized light, thereby realizing the photo-responsive kinetic process related to the chirality spin of a single molecule to meet the experimental requirements of different polarized lights.

[0062] Optimally, the twisted pair is a double twisted pair, which can reduce the noise of external interference.

[0063] The comparison diagram of the electrical test background noise of the multi-functional sample rod is as Figure 5 shown. Among them, a is the electrical test background noise diagram of the multi-functional sample rod when using a coaxial cable, and b is the electrical test background noise diagram of the multi-functional sample rod when using a double twisted pair. By comparison, it is obtained that the background noise during the current test using the double twisted pair is reduced from the nanoampere level to the picometer level. Thus, the signal-to-noise ratio is effectively improved in the test of the weak signal of a single photo-responsive molecule.

[0064] S5: After being irradiated by the pump pulse optical path, a single photo-responsive molecule is excited, and then detected through the probe light optical path and reflected by the signal acquisition unit and displayed on the computer.

[0065] By adjusting the time delay device and combining with the experimental environment of the comprehensive physical property measurement system itself, it is possible to achieve the measurement of a single photo-responsive molecule with femtosecond resolution.

[0066] Specifically, the femtosecond laser after passing through the polarizer irradiates the graphene single-molecule device connected with a single photo-responsive molecule on the sample stage. Under the excitation of the pump pulse, the photo-responsive molecule will be excited to the excited state. Then, after a certain time delay, the probe pulse irradiates the photo-responsive molecule for detection. This time delay is determined by the time delay device and can achieve the femtosecond level. Therefore, the time resolution of the photo-response dynamics of a single photo-responsive molecule can reach the femtosecond level. Then, the single photo-responsive molecule generates a corresponding photo-response, such as the photocurrent phenomenon, etc. The signal is transmitted to the signal acquisition unit through the multi-functional sample rod, and the detection signal is collected.

[0067] Furthermore, the signal acquisition unit includes a pre-amplifier and a lock-in amplifier. The pre-amplifier is used to amplify the detection information transmitted by the twisted wire and then transmit it to the lock-in amplifier. The lock-in amplifier is used to extract the components with the same frequency as the reference signal and having a phase correlation and transmit them to the computer.

[0068] Since the pump pulse optical path is equivalent to passing through a chopper with a fixed frequency modulated by the lock-in amplifier, the pump pulse excites the single photo-responsive molecule at this fixed frequency.

[0069] When the pump pulse is present, the single photo-responsive molecule is excited, and an electrical signal with a photo-response process can be obtained under the action of the probe pulse; when the pump pulse is blocked, the single photo-responsive molecule is not excited, and an electrical signal without a photo-response process is obtained. The lock-in amplifier, relying on the phase-sensitive detection technology, only extracts the components with the same frequency as the reference signal and having a phase correlation, and other noise signals not at this frequency will be greatly suppressed.

[0070] Specifically, the method for the lock-in amplifier to extract the components with the same frequency as the reference signal and having a phase correlation is as follows:

[0071] D1: The lock-in amplifier represents the input signal as an AC signal superimposed on a DC bias according to Equation (1):

[0072] (1);

[0073] Where: represents the input signal of the lock-in amplifier, represents the average current generated by the graphene single-molecule device connected with a single photo-responsive molecule to be detected, , is the current signal when the pump pulse is present, is the current signal when the pump pulse is blocked, Represents the photocurrent generated by a graphene single-molecule device connected to a single light-responsive molecule to be detected, , Represents the reference frequency generated by the lock-in amplifier, equal to the chopper frequency, Represents time, Represents the initial phase of the lock-in amplifier, Represents random noise, which includes noise components such as thermal noise and electromagnetic interference that are not related to the reference frequency;

[0074] Since the pump pulse is periodically turned on and off, in the long run is a DC component, and the lock-in amplifier modulates the pump light at frequency Therefore, an AC component of the same frequency will appear in the current signal. Here, the weak is the useful signal that is expected to be extracted by the lock-in amplifier;

[0075] And the random noise is not of the same frequency as, so it can be effectively suppressed in lock-in detection.

[0076] D2: The lock-in amplifier synchronously multiplies and integrates the input signal with the reference signal, and extracts the signal component in phase with the reference frequency according to Equation (2):

[0077] (2);

[0078] Where: Represents the signal component extracted in phase with the reference frequency, Represents the integration time period;

[0079] D3: The signal component extracted in phase with the reference frequency is calculated by sum-to-product to obtain (3):

[0080] (3);

[0081] D4: Fix the initial phase of the lock-in amplifier, lock the optoelectronic signal submerged in noise at the reference frequency, amplify it, and then transfer it to the computer for reading, so as to maximize the extraction of useful signals , and the weak optoelectronic signal originally submerged in noise is locked, amplified, and read at the reference frequency.

[0082] Optimized, in step D4, the initial phase of the lock-in amplifier is fixed at 0.

[0083] Specifically, the synthetic route structural formula of a single light-responsive molecule A is as follows:

[0084]

[0085] Specific synthesis method:

[0086] In a nitrogen atmosphere, (102 mg, 0.43 mmol) was added to a benzene solution (10 mL) of A-Boc-OF (32 mg, 0.023 mmol). After the mixed system was stirred at room temperature for 6.5 h, the insoluble substances were removed by suction filtration under reduced pressure. The obtained filtrate was concentrated and purified by column chromatography to obtain A-Boc.

[0087] 1 H NMR (400 MHz, Chloroform- d ) δ 8.15 (d, J = 7.0 Hz, 2H), 8.06 (d, J = 7.0 Hz, 2H), 7.17 – 7.68 (m, 4H), 7.67 – 7.62 (m, 10H), 7.52 (d, J = 1.7 Hz, 2H), 7.51 (d, J = 1.6 Hz, 2H), 7.48 (td, J = 6.8, 1.3 Hz, 2H), 7.42 (s, 2H), 7.37 (s, 2H), 7.25 – 7.21 (m, 4H), 5.21 (t, J = 4.9 Hz, 2H), 3.18 (td, J = 5.7, 4.9 Hz, 4H), 2.66 (tt, J = 7.7, 1.0 Hz, 4H), 1.80 (tt, J = 7.9, 5.6 Hz, 4H), 1.41 (s, 18H), 1.26 (s, 36H).

[0088] 13 C NMR (100 MHz, Chloroform- d) δ 187.35, 156.50, 149.43, 148.12, 146.06, 142.44, 139.73, 138.92, 135.19, 134.28, 132.52, 129.39, 129.14, 127.66, 127.64, 126.43, 126.30, 125.60, 124.73, 124.49, 124.42, 123.61, 123.56, 122.43, 79.55, 60.38, 40.22, 34.63, 33.59, 29.66, 29.29, 28.30。

[0089] In a nitrogen atmosphere, trifluoroacetic acid (22 μL, 0.29 mmol) was added to a dichloromethane solution (10 mL) of A-Boc (20 mg, 0.014 mmol). The mixed system was stirred at room temperature and monitored by thin-layer chromatography until the reaction was complete. Extraction was carried out using dichloromethane and sodium bicarbonate solution, the organic phases were combined and concentrated, and recrystallization with petroleum ether gave the single photoreactive molecule A.

[0090] 1 H NMR (400 MHz, Chloroform- d ) δ 8.15 (d, J = 7.0 Hz, 2H), 8.06 (d, J = 7.0 Hz, 2H), 7.17 – 7.68 (m, 4H), 7.67 – 7.62 (m, 10H), 7.52 (d, J = 1.7 Hz, 2H), 7.51 (d, J = 1.6 Hz, 2H), 7.48 (td, J = 6.8, 1.3 Hz, 2H), 7.42 (s, 2H), 7.37 (s, 2H), 7.25 – 7.21 (m, 4H), 2.77 (tt, J = 6.3, 5.4 Hz, 4H), 2.65 (tt, J = 7.7, 1.0 Hz, 4H), 1.76 (tt, J = 7.5, 5.4 Hz, 4H), 1.59 (d, J = 12.6 Hz, 4H), 1.26 (s, 36H).

[0091] 1313C NMR (100 MHz, Chloroform- d ) δ 193.44, 193.36, 148.32, 148.29,146.18, 146.13, 146.08, 146.04, 144.46, 144.44, 141.75, 141.74, 140.15,140.14, 138.75, 138.73, 137.69, 137.65, 134.38, 134.33, 134.08, 134.02,132.06, 132.01, 129.34, 129.30, 129.26, 129.22, 128.86, 128.84, 128.82,128.80, 128.19, 128.17, 128.15, 128.12, 127.44, 127.39, 127.34, 127.29,126.50, 126.47, 126.45, 126.43, 125.69, 125.67, 125.52, 125.49, 124.30,124.28, 123.96, 123.89, 123.80, 123.73, 122.60, 122.58, 65.69, 65.65, 41.73,41.70, 34.66, 33.91, 33.10, 33.06, 29.34, 29.32, 29.30。

[0092] The structural formula of a single photo-responsive molecule A is as follows:

[0093]

[0094] The synthetic route structural formula of A-Boc-OF is as follows:

[0095]

[0096] Under a nitrogen atmosphere, I (161 mg, 0.2 mmol), II 3',5'-di-tert-butyl-4'-hydroxy-[1,1'-biphenyl]-2-carbaldehyde (155 mg, 0.5 mmol), and an acetic acid solution (3 mL) of ammonium acetate (869 mg, 11.3 mmol) were stirred at 110 °C for 2 days. The reaction mixture was cooled to room temperature and the mixture was neutralized with ammonia water. The precipitate was filtered and washed with hexane to obtain A-Boc-OF (a mixture of structural isomers).

[0097] 1 1H NMR (400 MHz, Chloroform-d ) δ 8.08 (dd, J J = 8.2, 1.3 Hz, 2H), 7.73 –7.62 (m, 14H), 7.58 (td, J J = 8.0, 1.3 Hz, 2H), 7.54 – 7.48 (m, 6H), 7.29 – 7.19(m, 8H), 5.74 (s, 2H), 5.21 (t, J J = 4.9 Hz, 2H), 3.18 (td, J J = 5.7, 4.9 Hz, 4H),2.66 (tt, J J = 7.7, 1.0 Hz, 4H), 1.80 (tt, J J = 7.9, 5.6 Hz, 4H), 1.41 (s, 56H).

[0098] 13 C NMR (100 MHz, Chloroform- d ) δ 156.50, 154.56, 149.76, 142.44,140.01, 139.94, 138.92, 138.69, 137.70, 137.53, 130.90, 130.85, 130.25,129.69, 129.39, 128.73, 128.46, 128.26, 127.64, 127.21, 127.12, 125.87,125.43, 79.55, 40.22, 34.74, 33.59, 30.29, 29.66, 28.30.

[0099] The synthetic route structural formula of I is as follows:

[0100]

[0101] Under a nitrogen atmosphere, 2,2′-(1,4-phenylene)bis(1-(4-bromophenyl))ethane-1,2-dione (500 mg, 1 mmol), 4-tert-butylcarbamate phenylboronic acid pinacol ester (902 mg, 2.5 mmol), Pd(dppf)Cl 2 (36mg, 0.05 mmol), 1 mL of a supersaturated solution of potassium carbonate, and 10 mL of a tetrahydrofuran solution were reacted overnight at 80 °C. After cooling to room temperature, extraction was carried out using dichloromethane, the organic phases were combined, concentrated, and purified by column chromatography to obtain the above I.

[0102] 1 H NMR (400 MHz, Chloroform- d ) δ 8.06 (s, 4H), 7.99 – 7.90 (m, 8H), 7.53 – 7.50 (m, 4H), 7.23 (dt, J J = 8.2, 1.0 Hz, 4H), 5.21 (t, J J = 4.9 Hz, 2H), 3.18 (td, J J = 5.7, 4.9 Hz, 4H), 2.66 (tt, J J = 7.7, 1.0 Hz, 4H), 1.80 (tt, J J = 7.9, 5.6 Hz, 4H), 1.41 (s, 18H).

[0103] 13 C NMR (100 MHz, Chloroform- d ) δ 193.28, 193.19, 193.12, 193.03, 156.43, 156.39, 144.47, 144.46, 142.20, 142.19, 138.94, 138.92, 135.73, 135.67, 134.03, 133.97, 130.56, 130.54, 130.53, 130.51, 130.06, 130.04, 130.03, 130.01, 129.34, 129.30, 129.26, 129.22, 128.71, 128.66, 128.62, 128.58, 127.44, 127.39, 127.34, 127.29, 79.58, 79.54, 40.40, 40.36, 33.59, 30.02, 29.99, 28.32, 28.31.

[0104] Then, a graphene nano-gap point electrode array is prepared, and the specific steps are as follows: A single-layer graphene is obtained on a copper sheet by chemical vapor deposition, and then polymethyl methacrylate (PMMA) is spin-coated on the single-layer graphene at a rotation speed of 4000 r / min. After the obtained PMMA-graphene-copper is placed in a ferric chloride solution for 4 hours, it is wet-transferred to a clean 1 cm × 1 cm silicon wafer to obtain a PMMA-graphene-silicon wafer. Then, the PMMA-graphene-silicon wafer is placed in boiling acetone to remove the PMMA on the surface layer of the graphene, and a graphene thin film attached to the silicon wafer is obtained. Then, a photoresist is spin-coated on the silicon wafer with the graphene thin film attached at a rotation speed of 4000 r / min, and stripes are lithographed through an ultraviolet lithography machine. After being fully immersed in a developer for 5 seconds, it is taken out and dried, and a silicon wafer with photoresist only above the middle graphene stripe and no photoresist in other places is obtained. Then, it is placed in an oxygen plasma etching machine for etching to obtain a silicon wafer with graphene stripes attached. After removing the glue with acetone, the process of spin-coating the photoresist is repeated again. Electrodes are lithographed through an ultraviolet lithography machine. After development, a gold thin film is evaporated by a thermal resistance evaporation coater. After removing the glue with acetone, a gold electrode-graphene stripe-silicon wafer is obtained.

[0105] Further, an electron beam exposure machine is used to etch dotted lines on the above-mentioned gold electrode-graphene stripe-silicon wafer. Each dotted line is 150 nanometers long and the interval is 36 nanometers. After development, it is placed in an oxygen plasma etching machine for etching to obtain a graphene nano-gap point electrode array.

[0106] A single light-responsive molecule A is connected to the prepared graphene nano-gap point electrode array through a stable amide bond to obtain a graphene single-molecule device of a single light-responsive molecule A. The specific process is as follows: The graphene nano-gap point electrode array is placed in a two-necked flask, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and molecule A are added to the flask. After the two-necked flask is sealed, the operation of pumping and releasing gas is carried out multiple times to make the sealed two-necked flask in a nitrogen environment. 10 mL of anhydrous pyridine is taken with a syringe and injected into the above two-necked flask, and the reaction is carried out at room temperature for 48 hours to obtain a graphene single-molecule device connected with a single light-responsive molecule.

[0107] Then, an Agilent B1500A semiconductor parameter analyzer and a probe station can be used for testing. The gold electrodes of the graphene single-molecule device connected with a single light-responsive molecule are connected to the sample stage electrode posts through copper wires and conductive adhesives. The multi-functional sample rod is placed in the test cavity of the comprehensive physical property measurement system. The current-voltage image of the graphene single-molecule device connected with a single light-responsive molecule without applying a femtosecond laser is Figure 6 , and in the figure, the current value changes significantly with the change of voltage, proving the effective connection of a single light-responsive molecule.

[0108] Finally, turn on the switches of each instrument. Set the time delay to 100 femtoseconds, and set the chopper frequency to output 1 kHz through the lock-in amplifier. Set the temperature of the comprehensive physical property measurement system to 2 Kelvin. Test the current-voltage image of the graphene single-molecule device connected with a single light-responsive molecule under the condition that a femtosecond laser is irradiated and the time delay line is 100 femtoseconds as shown in Figure 7 shown.

[0109] Compare Figure 6 with Figure 7 and find that the current value of the graphene single-molecule device connected with a single A molecule is significantly increased under the condition that a femtosecond laser is irradiated and the time delay line is 100 femtoseconds at the same voltage, indicating that this method can achieve the detection of single-molecule light-responsive signals with femtosecond-level resolution.

[0110] In addition, when testing the current signal over time, the lock-in amplifier continuously extracts the modulation component at the 1 kHz reference frequency through phase-sensitive detection, and the noise that is not in the same frequency and phase as this frequency will be suppressed, so as to achieve the detection of weak single-molecule light-responsive signals. Change the setting of the time delay and repeat the above test to obtain the time-resolved light-responsive kinetic curve and achieve the detection of weak single-molecule light-responsive signals with femtosecond-level resolution.

[0111] The femtosecond-level time-resolution single-molecule light-responsive signal detection device is used to perform the femtosecond-level time-resolution single-molecule light-responsive signal detection method described in any one of the above. The device diagram is as shown in Figure 2 shown, which includes a femtosecond laser 1, a first mirror 2, a first beam combiner / splitter 3, a pump pulse optical path, a probe light optical path, a second beam combiner / splitter 22, an input optical fiber 23, a comprehensive physical property measurement system 25, a multi-functional sample rod 24, a signal acquisition unit and a computer 12. The femtosecond laser, the first mirror, and the first beam combiner / splitter are sequentially coupled. The pump pulse optical path includes a second mirror 4, a broadband optical parametric amplifier 5, a third mirror 6, a first aperture 7, a chopper 8 with a fixed frequency, a tunable first attenuator 9, and a fourth mirror 10 that are sequentially coupled. The probe light optical path includes a time delay 11, a fifth mirror 13, a sixth mirror 14, a second aperture 15, a white light generation module, and a seventh mirror 21. The white light generation module includes a first convex lens 16, a tunable second attenuator 17, a Yag white light crystal 18, a second convex lens 19, and a filter 20 that are sequentially coupled. The pump pulse optical path and the probe light optical path are combined by the second beam combiner / splitter and then enter the input optical fiber. The multi-functional sample rod is placed in the test cavity of the comprehensive physical property measurement system. The structural schematic diagram of the multi-functional sample rod is as shown in Figure 3 、 Figure 4As shown in the figure, the multifunctional sample rod includes a sample rod main body 24-2, an input optical fiber interface 24-1, a fixture 24-5, a polarizer 24-4, a sample stage 24-6, and a twisted pair 24-3. The input optical fiber interface is fixedly installed at the top of the sample rod main body and connected to the input optical fiber. The fixture is fixedly installed inside the sample rod main body and is located below the input optical fiber interface. The polarizer is installed on the fixture. The sample stage is installed inside the sample rod main body and is located below the fixture. The graphene single-molecule device connected with a single light-responsive molecule to be detected is fixedly placed on the sample stage and connected to the sample stage electrode post through a copper wire and conductive silver paste. The twisted pair is communicated with the gold electrode of the graphene single-molecule device connected with a single light-responsive molecule to be detected and the signal acquisition unit. The signal acquisition unit includes a preamplifier 26 and a lock-in amplifier 27 which are connected to each other. The preamplifier is communicated with the twisted pair, and the lock-in amplifier is communicated with the computer.

[0112] The detection device formed by combining the comprehensive physical property measurement system and femtosecond laser in the present invention combines the advantages of optical and electrical detection technologies, and can realize the regulation of a single molecule by multimodal means such as light field and electric field, improve the time resolution to the femtosecond level, and monitor the femtosecond-level light response dynamics process of a single molecule.

[0113] Moreover, the chopper is used to modulate the pump pulse frequency, the output of the chopper frequency is used as the reference frequency by the lock-in amplifier, and the weak signal detection of a single light-responsive molecule is realized by combining the phase-sensitive detection of the lock-in amplifier. And by independently designing a multifunctional sample rod and installing a polarizer inside the multifunctional sample rod, the femtosecond-level ultrafast optical pulse with different polarization modes can be switched, so as to convert the imported linearly polarized ultrafast laser into left-handed or right-handed circularly polarized light, and the light response research related to single-molecule chiral spin can be carried out. At the same time, the twisted pair is selected for current transmission to reduce the noise of the electrical signal measured by the comprehensive physical property measurement system from the original nanoampere level noise to the picopicoampere level, improving the signal-to-noise ratio.

[0114] In summary, the femtosecond-level time resolution light response single-molecule signal detection method and device provided by the present invention can realize the detection of weak signals of a single light-responsive molecule with femtosecond-level time resolution, and can improve the signal-to-noise ratio of the electrical signal measured by the comprehensive physical property measurement system.

[0115] The above description is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for detecting single-molecule signals with light response at a femtosecond time resolution, characterized in that: The steps include: S1: The laser emitted from the femtosecond laser is reflected by the first reflector to the first beam combiner and splitter. 50% of the light is transmitted to form the pump pulse optical path, and 50% of the light is reflected to form the detection light path. S2: The pump pulse light path is reflected by the second reflector to the broadband optical parametric amplifier, then reflected by the third reflector to enter the first aperture for beam positioning, then emitted to the tunable first attenuator after passing through the chopper with a fixed frequency, and then emitted into the introduction optical fiber through the fourth reflector and the second beam combining and splitting plate respectively; S3: The detection light is reflected in the time delay device to achieve femtosecond delay, and then reflected by the fifth and sixth reflectors to enter the second aperture for beam positioning, and then passes through the white light generation module to generate continuous detection white light, and then passes through the seventh reflector and the second beam combiner and splitter to be injected into the introduction optical fiber; S4: The pump pulse optical path and the detection light optical path enter the multifunctional sample rod placed in the test cavity of the comprehensive physical property measurement system, and the left-handed or right-handed circularly polarized light is polarized by the polarizer in the multifunctional sample rod and then irradiated onto the graphene single-molecule device connected to a single photoresponsive molecule to be detected and placed on the sample carrier of the multifunctional sample rod. The graphene single-molecule device connected to a single photoresponsive molecule to be detected is connected to the electrode column of the sample carrier through a copper wire and a conductive silver glue. The multifunctional sample rod comprises a sample rod body, an introduction optical fiber interface, a clamp, a polarizer, a sample carrier and a twisted wire. The introduction optical fiber interface is fixedly mounted on the top of the sample rod body and connected to the introduction optical fiber. The clamp is fixedly mounted in the sample rod body and located below the introduction optical fiber interface. The polarizer is mounted on the clamp. The sample carrier is mounted in the sample rod body and located below the clamp. The graphene single-molecule device connected to a single photoresponsive molecule to be detected is fixedly placed on the sample carrier. The twisted wire is connected to the gold electrode of the graphene single-molecule device connected to a single photoresponsive molecule to be detected and a signal acquisition unit. The preparation method of the graphene single-molecule device connected with a single photoresponsive molecule is as follows: Under nitrogen atmosphere, 161 mg, 0.2 mmol of Ⅰ, 155 mg, 0.5 mmol of Ⅱ 3',5'-di-tert-butyl-4'-hydroxy-[1,1'-biphenyl]-2-carboxaldehyde, 869 mg, 3 mL, 11.3 mmol of ammonium acetate in acetic acid solution were stirred at 110°C for 2 days. The reaction mixture was cooled to room temperature and neutralized with ammonia water. The precipitate was filtered and washed with hexane to obtain A-Boc-OF. The synthetic route structure of A-Boc-OF is as follows: Under nitrogen atmosphere, 102 mg, 0.43 mmol Add to 32 mg, 0.023 mmol A-Boc-OF in 10 ml benzene solution, stir the mixture at room temperature for 6.5 h, remove the insoluble matter by vacuum filtration, concentrate the filtrate and purify by column chromatography to obtain A-Boc; Under nitrogen atmosphere, 22 μl, 0.29 mmol of trifluoroacetic acid was added to 20 mg, 0.014 mmol of A-Boc in 10 ml of dichloromethane solution. The mixed system was stirred at room temperature and monitored by thin layer chromatography until the reaction was completed. Dichloromethane and sodium bicarbonate solution were used for extraction. The organic phases were combined and concentrated, and recrystallized from petroleum ether to obtain a single photoresponsive molecule A. The synthetic structure of a single photoresponsive molecule A is as follows: A single layer of graphene was obtained on a copper sheet by chemical vapor deposition, and then polymethyl methacrylate was spin-coated on the single layer of graphene at a speed of 4000 r / min. The obtained polymethyl methacrylate-graphene-copper was placed in a ferric chloride solution for 4 hours, and then transferred to a clean 1 cm × 1 cm silicon wafer by a wet method to obtain polymethyl methacrylate-graphene-silicon wafer. The polymethyl methacrylate-graphene-silicon wafer was then placed in boiling acetone to remove the polymethyl methacrylate on the surface of the graphene to obtain a graphene film attached to the silicon wafer. The silicon wafer with the graphene film attached was then heated at 4000 r / min. Spin-coat the photoresist at a speed of 1000 r / min, photolithograph the strips with an ultraviolet photolithography machine, soak the strips in a developer for 5 seconds, take them out and blow dry them, and obtain a silicon wafer with photoresist only on the graphene strip in the middle and no photoresist on other places, and then place them in an oxygen plasma etcher for etching to obtain a silicon wafer with graphene strips attached, and repeatedly spin-coat the photoresist after removing the glue with acetone, photolithograph the electrodes with an ultraviolet photolithography machine, and after development, use a thermal resistance evaporation coating machine to evaporate a layer of gold film, and after removing the glue with acetone, obtain a gold electrode-graphene strip-silicon wafer; An electron beam lithography machine is used to etch dotted lines on the gold electrode-graphene strip-silicon wafer, each dotted line is 150 nanometers long and 36 nanometers apart, and after development, the dotted lines are placed in an oxygen plasma etcher for etching to obtain a graphene nano-gap dot electrode array; Connecting a single photoresponsive molecule A to the prepared graphene nanogap dot electrode array via a stable amide bond to obtain a graphene single-molecule device of the single photoresponsive molecule A; S5: A single photoresponsive molecule is excited after being irradiated by the pump pulse optical path, and then detected by the detection light optical path, and reflected by the signal acquisition unit and displayed on the computer. The signal acquisition unit includes a pre-current amplifier and a phase-locked amplifier. The pre-current amplifier is used to amplify the detection information transmitted by the twisted wire and transmit it to the phase-locked amplifier. The phase-locked amplifier is used to extract the components with the same frequency and phase correlation as the reference signal and transmit them to the computer.

2. The method for detecting single-molecule signals with light response at a femtosecond time resolution according to claim 1, characterized in that: The femtosecond laser is a titanium sapphire femtosecond laser.

3. The method for detecting single-molecule signals with light response at a femtosecond time resolution according to claim 1, characterized in that: The white light generation module comprises a first convex lens, a tunable second attenuation plate, a Yag white light crystal, a second convex lens and a filter which are arranged in sequence.

4. The method for detecting single-molecule signals with light response at a femtosecond time resolution according to claim 1, characterized in that: The twisted wire is a twisted pair wire.

5. The method for detecting single-molecule signals with light response at a femtosecond time resolution according to claim 1, characterized in that: The method of extracting the component with the same frequency and phase correlation with the reference signal by the lock-in amplifier is as follows: D1: The lock-in amplifier expresses the input signal as an AC signal superimposed on a DC bias according to equation (1): （1）； in: represents the lock-in amplifier input signal, represents the average current generated by the graphene single-molecule device connected to a single photoresponsive molecule to be detected, represents the photocurrent generated by the graphene single-molecule device connected to a single photoresponsive molecule to be detected, represents the reference frequency generated by the lock-in amplifier, Indicates time, represents the initial phase of the lock-in amplifier, represents random noise; D2: The phase-locked amplifier multiplies the input signal and the reference signal synchronously and integrates them, and extracts the signal component that is in phase with the reference frequency according to equation (2): （2）； in: represents the extracted signal component that is in phase with the reference frequency, represents the integration time period; D3: The extracted signal that is in phase with the reference frequency is obtained by sum-difference product calculation (3): （3）； D4: Fix the initial phase of the phase-locked amplifier, lock the photoelectric signal submerged in the noise at the reference frequency, amplify it, and then transmit it to the computer for reading.

6. The method for detecting single-molecule signals with light response at a femtosecond time resolution according to claim 5, characterized in that: In step D4, the initial phase of the lock-in amplifier is fixed to 0.

7. The method for detecting single-molecule signals with light response at a femtosecond time resolution according to claim 1, characterized in that: The wavelength range of the continuous detection white light generated by the white light generation module in step S3 is 500 nanometers to 950 nanometers.

8. A device for detecting single-molecule signals with a time resolution of femtoseconds, for performing a method for detecting single-molecule signals with a time resolution of femtoseconds as claimed in any one of claims 1 to 7, characterized in that: The invention comprises a femtosecond laser, a first reflector, a first beam-combining and beam-splitting plate, a pump pulse optical path, a detection light optical path, a second beam-combining and beam-splitting plate, an introduction optical fiber, a comprehensive physical property measurement system, a multifunctional sample rod, a signal acquisition unit and a computer. The femtosecond laser, the first reflector and the first beam-combining and beam-splitting plate are coupled in sequence. The pump pulse optical path comprises a second reflector, a broadband optical parametric amplifier, a third reflector, a first aperture, a chopper with a fixed frequency, a tunable first attenuation plate and a fourth reflector coupled in sequence. The detection light optical path comprises a time delay device, a fifth reflector, a sixth reflector, a second aperture, a white light generating module and a seventh reflector coupled in sequence. The white light generating module comprises a first convex lens, a tunable second attenuation plate, a Yag white light crystal, a second convex lens and a filter coupled in sequence. The pump pulse optical path and the detection light optical path are combined by the second beam-combining and beam-splitting plate and then enter the introduction optical fiber. The multifunctional sample rod comprises a first convex lens, a second convex lens and a filter coupled in sequence. The multifunctional sample rod is placed in a test cavity of a comprehensive physical property measurement system. The multifunctional sample rod comprises a sample rod body, an introduction optical fiber interface, a fixture, a polarizer, a sample carrier and a twisted pair. The introduction optical fiber interface is fixedly installed on the top of the sample rod body and connected to the introduction optical fiber. The fixture is fixedly installed in the sample rod body and located below the introduction optical fiber interface. The polarizer is installed on the fixture. The sample carrier is installed in the sample rod body and located below the fixture. A graphene single-molecule device connected to a single light-responsive molecule to be detected is fixedly placed on the sample carrier and connected to the sample carrier electrode column through a copper wire and a conductive silver glue. The twisted wire is connected to a gold electrode of the graphene single-molecule device connected to a single light-responsive molecule to be detected and a signal acquisition unit. The signal acquisition unit comprises a pre-current amplifier and a phase-locked amplifier connected to each other. The current amplifier is connected to the twisted pair, and the phase-locked amplifier is connected to a computer.

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