CN114235708A - Terahertz photoacoustic detection device and method - Google Patents
Terahertz photoacoustic detection device and method Download PDFInfo
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Abstract
The embodiment of the invention discloses a terahertz photoacoustic detection device and method. The terahertz photoacoustic detection device comprises a light source module, an ultrasonic detection module, a processing module and a temperature control module, wherein the light source module is used for emitting a terahertz light beam with tunable wavelength, the terahertz light beam is incident to a sample to be detected, and a photoacoustic signal is formed after the terahertz light beam passes through the sample to be detected; the temperature control module is used for adjusting the temperature of a sample to be measured; the ultrasonic detection module is used for detecting photoacoustic signals and converting the photoacoustic signals into electric signals; the processing module is connected with the ultrasonic detection module and used for acquiring the absorption spectrum in the sample to be detected according to the electric signal so as to realize the fusion of the terahertz technology and the photoacoustic technology, acquire the terahertz characteristic absorption information of the target detection object in the sample to be detected, and expand the further application of terahertz radiation in life science.
Description
Technical Field
The embodiment of the invention relates to the technical field of terahertz, in particular to a terahertz photoacoustic detection device and method.
Background
Terahertz (THz) waves refer to electromagnetic waves having a frequency in the range of 0.1THz to 10THz, which are located between the microwave and infrared regions. The terahertz light beam has the advantages of low photon energy, rich absorption spectrum, good penetrability and the like, and has a huge application prospect in a plurality of important fields such as physics, chemistry, electronic information, life science, material science, communication radar, national safety and the like.
The terahertz radiation has very low photon energy (about meV magnitude) and cannot cause ionization damage, the terahertz spectrum of the substance contains rich physical and chemical information, and the research on the spectrum of the substance in the wave band has important significance for the exploration of the characteristics of the substance.
However, the existing terahertz biological detection uses the terahertz reflection spectrum and the attenuated total reflection spectrum technology, and most of the existing terahertz biological detection needs to perform complex pretreatment on a sample or directly detect an extremely thin (200 μm) water-rich sample, which is difficult to obtain the internal information of the sample, and a strong absorption signal of water often submerges a weak signal emitted by a target biomolecule, thereby greatly limiting the further application of terahertz radiation in life science.
Disclosure of Invention
The embodiment of the invention provides a terahertz photoacoustic detection device and method, which are used for realizing the fusion of a terahertz technology and a photoacoustic technology, acquiring terahertz characteristic absorption information of a target detection object in a sample to be detected, and expanding the further application of terahertz radiation in life science.
In a first aspect, an embodiment of the present invention provides a terahertz photoacoustic detection apparatus, including a light source module, an ultrasonic detection module, a processing module, and a temperature control module;
the light source module is used for outputting a terahertz light beam with tunable wavelength, the terahertz light beam is incident to a sample to be detected, and forms a photoacoustic signal after passing through the sample to be detected;
the temperature control module is used for adjusting the temperature of the sample to be detected;
the ultrasonic detection module is used for receiving the photoacoustic signal and converting the photoacoustic signal into an electric signal;
the processing module is connected with the ultrasonic detection module and used for acquiring the absorption spectrum in the sample to be detected according to the electric signal.
Optionally, the light source module includes a first pulse laser, a mirror group, a grating, a half-wave plate, a converging lens, a first nonlinear crystal, and a plurality of filters; pulse laser output by the first pulse laser sequentially passes through the reflector group, the grating, the half-wave plate and the converging lens and then is focused on the first nonlinear crystal to excite a terahertz light beam; the plurality of filters are used for transmitting terahertz light beams with different wavelengths, so that the light source module outputs terahertz light beams with tunable wavelengths.
Optionally, the terahertz photoacoustic detection device further includes a parabolic mirror set, and the parabolic mirror set is used for focusing the terahertz light beam output by the light source module to the sample to be detected.
Optionally, the light source module further includes a pump light filter, where the pump light filter is located at an output end of the first nonlinear crystal, and is configured to block the pulse laser output by the first pulse laser and transmit the terahertz light beam output by the first nonlinear crystal.
Optionally, the first nonlinear crystal includes a lithium niobate crystal.
Optionally, the light source module includes a second pulse laser, a telescope group, an iris diaphragm, a first parallel plane mirror, a second nonlinear crystal, a second parallel plane mirror, and a rotating stage; pulse laser output by the second pulse laser sequentially passes through the telescope group and the iris diaphragm and is incident into an optical parametric oscillation cavity formed by the first parallel plane mirror, the second nonlinear crystal and the second parallel plane mirror, and the rotating platform is used for driving the second nonlinear crystal to rotate so as to output a terahertz light beam with tunable wavelength.
Optionally, the second nonlinear crystal comprises a near stoichiometric lithium niobate crystal.
Optionally, the light source module further includes a third pulse laser, where the third pulse laser is configured to emit an ultraviolet pulse laser, and the ultraviolet pulse laser and the terahertz light beam are incident to the sample to be measured together.
Optionally, the terahertz photoacoustic detection apparatus further includes a scanning translation stage, where the scanning translation stage is configured to drive the sample to be detected to perform point-by-point two-dimensional scanning;
the processing module is used for acquiring the photoacoustic imaging of the sample to be detected according to the point-by-point two-dimensional scanning information of the sample to be detected.
Optionally, the temperature control module is configured to adjust a temperature of the sample to be measured.
In a second aspect, an embodiment of the present invention further provides a terahertz photoacoustic detection method, which is performed by the above-mentioned terahertz photoacoustic detection apparatus, and includes:
the terahertz light source module outputs a terahertz light beam with tunable wavelength, the terahertz light beam is incident to a sample to be detected, and a photoacoustic signal is formed after the terahertz light beam passes through the sample to be detected;
the ultrasonic detection module receives the photoacoustic signal and converts the photoacoustic signal into an electric signal;
the processing module acquires an absorption spectrum in the sample to be detected according to the electric signal;
the temperature control module adjusts the temperature of the sample to be detected, and the light source module tunes the wavelength of the terahertz light beam to realize multispectral absorption spectrum detection of the sample to be detected at different temperatures.
Optionally, the photoacoustic detection apparatus further includes a scanning translation stage, where the scanning translation stage is configured to drive the sample to be detected to perform point-by-point two-dimensional scanning;
and the processing module acquires the photoacoustic imaging of the sample to be detected according to the point-by-point two-dimensional scanning information of the sample to be detected.
The terahertz photoacoustic detection device provided by the embodiment of the invention comprises a light source module, an ultrasonic detection module, a processing module and a temperature control module, wherein a terahertz light beam with tunable wavelength is output by the light source module, is incident to a sample to be detected and forms a photoacoustic signal after passing through the sample to be detected, and the photoacoustic signal is detected and converted into a sound signal, so that the cost is reduced; the temperature of the sample to be detected is adjusted through the temperature control module, so that the detection sensitivity can be adjusted; receiving a photoacoustic signal through an ultrasonic detection module, and converting the photoacoustic signal into an electric signal; and acquiring the absorption spectrum in the sample to be detected through the processing module according to the electric signal. The terahertz characteristic absorption device has the advantages that the terahertz technology and the photoacoustic technology are fused, terahertz characteristic absorption information of a target detection object in a sample to be detected is obtained, further application of terahertz radiation in life science is expanded, and the terahertz characteristic absorption device has the advantages of being simple in structure, convenient to operate and low in cost.
Drawings
Fig. 1 is a schematic structural diagram of a terahertz photoacoustic detection apparatus provided by an embodiment of the present invention;
fig. 2 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention;
fig. 3 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention;
fig. 4 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention;
fig. 5 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention;
fig. 6 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention;
fig. 7 is a schematic flow chart of a terahertz photoacoustic detection method provided by an embodiment of the present invention;
fig. 8 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention;
fig. 9 is a flowchart of another terahertz photoacoustic detection method provided by the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
At present, the following characteristics of terahertz waves enable the terahertz waves to have great advantages in the field of biomedicine: 1. the terahertz radiation photon energy is very low (1THz is about 4.1meV), and compared with the current clinical commonly used X-ray (-keV), the terahertz radiation energy is reduced by several orders of magnitude, and the ionization damage can not be caused, so that the terahertz radiation photon energy can be more safely applied to in-vivo detection; 2. group vibrations and phase changes within many biological macromolecules, and the vibrational frequencies of interactions between biomolecules and the surrounding medium are mostly in the terahertz range; 3. polar molecules, particularly water molecules, have strong absorbability to terahertz waves, and the characteristic can be utilized to carry out related research on the water content of biological tissues. Due to these advantages, terahertz spectroscopy and imaging have been developed as a very potential technical means for detecting biomolecules such as proteins, DNA, RNA, sugars, etc. in vitro and in vivo, and can also be used to analyze structural dynamics of water and ionic hydration or to differentiate between tumors and healthy tissue based on water content.
Although the high absorption rate of terahertz radiation by water is advantageous in biomedicine, tumor cells and normal cells can be distinguished according to different water contents, and the structure dynamics of water and biomolecules are researched, the strong absorption of water still limits the application of terahertz technology to water-rich samples such as aqueous solutions and biological tissues considering that the biological activity of many biological samples can be maintained in water environment. Conventional terahertz biological analysis all uses terahertz reflection spectroscopy and attenuated total reflection spectroscopy, and most samples need to be subjected to complex pretreatment or directly detected to ultra-thin (200 μm) water-rich samples, so that the internal information of the samples is difficult to obtain, and weak signals emitted by target biomolecules are often submerged by strong absorption signals of water, thereby greatly limiting further application of terahertz radiation in life science. There are also some research teams constantly exploring attempts to enhance the required signal by increasing the intensity of the terahertz radiation or increasing the sensitivity of the terahertz detector. However, in the long term, these solutions may be unsatisfactory because the water background exponentially attenuates the target signal, the ultra-intense radiation poses a health risk, and the price of the ultra-sensitive detector may be prohibitive.
Fig. 1 is a schematic structural diagram of a terahertz photoacoustic detection apparatus according to an embodiment of the present invention. Referring to fig. 1, a terahertz photoacoustic detection apparatus 100 provided in this embodiment includes a light source module 101, an ultrasonic detection module 102, a processing module 103, and a temperature control module 104, where the light source module 101 is configured to output a terahertz light beam with a tunable wavelength, and the terahertz light beam is incident on a sample 105 to be measured and forms a photoacoustic signal after passing through the sample 105 to be measured; the temperature control module 104 is used for adjusting the temperature of the sample 105 to be measured; the ultrasonic detection module 102 is configured to receive a photoacoustic signal and convert the photoacoustic signal into an electrical signal; the processing module 103 is connected with the ultrasonic detection module 102, and the processing module 103 is used for acquiring an absorption spectrum in the sample 105 to be detected according to the electric signal.
The photoacoustic technique is a technique for irradiating a biological tissue with a photoacoustic effect, i.e., a short pulse laser as an excitation source, and detecting the generated ultrasonic wave by radiating the ultrasonic wave while thermally insulating the optical absorption region inside the tissue if the duration of the laser pulse is much shorter than the thermal conduction time of the optical absorption region inside the tissue. Photoacoustic imaging, a new method of imaging biological tissue, combines the advantages of both optical and ultrasound imaging. Due to the fact that different biological tissues have different optical absorption coefficients for laser with specific wavelength, photoacoustic imaging can achieve high imaging contrast; by using ultrasonic wave as information carrier, the photoacoustic imaging can achieve higher imaging resolution and deeper imaging depth, which can not be achieved by pure optical or acoustic imaging at the same time. At present, experiments prove that the pulse terahertz radiation can generate ultrasonic waves through the thermal expansion of a terahertz absorption material, wherein the change of an ultrasonic signal reflects the change of a terahertz signal, and the detection of the terahertz waves is realized.
It can be understood that, after the terahertz light beams with tunable wavelengths are output by the light source module 101, and after the terahertz light beams with different wavelengths are incident on the sample 105 to be detected, and the temperature control module 104 controls the temperature of the sample 105 to be detected to be the same, the terahertz photoacoustic detection apparatus 100 can obtain the multi-wavelength absorption spectrum of the sample 105 to be detected under the terahertz light beams with different wavelengths.
In addition, when the wavelength of the terahertz light beam output by the light source module 101 is kept unchanged, the temperature control module 104 controls the temperature of the sample 105 to be detected to change, the temperature adjustment range of the temperature control module 104 can be adjusted to 0-40 ℃, so that the sensitivity adjustment of terahertz photoacoustic detection is realized, and the terahertz photoacoustic detection device 100 can acquire the absorption spectra of the sample 105 to be detected at different temperatures under the same wavelength of terahertz light beam. Wherein the sample 105 to be tested can be a water-rich sample.
Therefore, the terahertz photoacoustic detection device 100 can be used for acquiring the absorption spectrum of the sample 105 to be detected under terahertz light beams with different temperatures or different wavelengths, and the terahertz photoacoustic detection device 100 has the advantages of simple structure and low cost.
The detected terahertz photoacoustic signals are all based on an initial sound pressure formula:
in the formula, Γ is defined as a green parameter (dimensionless) representing the dissonance of the absorbing material, depending only on the material properties; beta is related to the thermal coefficient of volume expansion of the material; vs is the speed of sound; cp is the material specific heat capacity; mu.saRepresenting the light absorption coefficient, by the characteristics of the materialDetermined by the wavelength of the electromagnetic wave; etathThe percentage of absorbed energy converted into heat is related to the characteristics of the terahertz wave band material, and is generally regarded as 1, and F is the power of the light source. For the matter with unknown absorption, detecting to obtain a terahertz photoacoustic signal P0The absorption spectrum mu can be obtaineda(λ); for substances with known terahertz absorption spectrum, through detected terahertz photoacoustic signal P0And calculating the concentration of the substance inversely according to the Lambert-beer law.
For example, when detecting an unknown substance (such as a mixed solution of several solutions), the terahertz photoacoustic signal is P0Then, the absorption spectrum mu of the unknown substance can be obtained based on the initial sound pressure formulaa(λ), however, the individual absorption spectra of each of the several solutions are known in advance, and the composition and relative content of the several solutions in the unknown substance can be solved back according to the lambert-beer law.
According to the technical scheme of the embodiment of the invention, the light source module is used for outputting the terahertz light beam with tunable wavelength, the terahertz light beam is incident to the sample to be detected, and forms a photoacoustic signal after passing through the sample to be detected, and the photoacoustic signal is detected and converted into a sound signal, so that the cost is reduced; the temperature of the sample to be detected is adjusted through the temperature control module, so that the detection sensitivity can be adjusted; receiving a photoacoustic signal through an ultrasonic detection module, and converting the photoacoustic signal into an electric signal; and acquiring the absorption spectrum in the sample to be detected through the processing module according to the electric signal. The terahertz characteristic absorption device has the advantages that the terahertz technology and the photoacoustic technology are fused, terahertz characteristic absorption information of a target detection object in a sample to be detected is obtained, further application of terahertz radiation in life science is expanded, and the terahertz characteristic absorption device has the advantages of being simple in structure, convenient to operate and low in cost.
Fig. 2 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention. Referring to fig. 2, the light source module 101 includes a first pulse laser 106, a mirror group 200, a grating 110, a half-wave plate 111, a converging lens 112, a first nonlinear crystal 113, and a plurality of filters 124 (only one filter is exemplarily shown in fig. 2); pulse laser output by the first pulse laser 106 sequentially passes through the reflector group 200, the grating 110, the half-wave plate 111 and the converging lens 112 and then is focused on the first nonlinear crystal 113 to excite a terahertz light beam; the plurality of filters 124 are configured to transmit terahertz light beams with different wavelengths, so that the light source module 101 outputs a terahertz light beam with a tunable wavelength.
The first pulse laser 106 can be a Legend Elite series titanium sapphire femtosecond pulse regenerative amplification laser, a power Evolution-HE laser is adopted as a standard pumping light source of the laser, a Vitara oscillator is adopted as a seed light source, two-stage amplification is carried out on the seed light, the single pulse energy output can reach 8mJ at most, the pulse width is 40fs, the repetition frequency is 1kHz, the central wavelength is 800nm, and the spectrum width is 30 nm. For example, in the present embodiment, the mirror group 200 includes the first mirror 107, the second mirror 108, and the third mirror 109, and in other embodiments, the number of mirrors in the mirror group 200 may be increased or decreased according to actual requirements, and only the laser beam emitted by the first pulse laser 106 needs to be reflected to the grating 110.
Optionally, first nonlinear crystal 113 comprises a lithium niobate crystal. In the embodiment, the terahertz radiation has the repetition frequency of 1kHz, the sub-picosecond pulse width and the pulse energy of 0.23mJ/cm2The spectral range is 0.2-1.5 THz. The terahertz light beam excited by the lithium niobate crystal is emitted out in a way that the terahertz light beam excited by the lithium niobate crystal is vertical to the surface of the crystal at a smaller emission angle, and the terahertz light beam is approximately regarded as a point source with a smaller divergence angle.
The plurality of filters 124 may be a plurality of filters, and when the first nonlinear crystal 113 is excited to form the terahertz light beam, the terahertz light beam passes through different filters 124, so as to filter the terahertz light beam with the wavelength which cannot pass through the filters 124, and pass through the terahertz light beam with the same wavelength as the filters 124. According to requirements, selection can be performed among the plurality of filters 124, so that the wavelength of the terahertz light beam can be tunable.
The processing module 103 may include a data acquisition card, the data acquisition card may be an acquisition device such as an oscilloscope, the processing module 103 is connected to the ultrasonic detection module 102 for acquiring an electrical signal, and fig. 2 also shows that the processing module 103 is connected to the first pulse laser 106 for signal synchronization and other functions.
Optionally, with continued reference to fig. 2, the terahertz photoacoustic detection apparatus 100 further includes a parabolic mirror 300, where the parabolic mirror 300 is configured to focus the terahertz light beam output by the light source module 101 to the sample 105 to be detected.
The parabolic mirror 300 may include a first parabolic mirror 114 and a second parabolic mirror 115, the plurality of filters 124 are located between the first parabolic mirror 114 and the second parabolic mirror 115, the terahertz light beam excited by the first nonlinear crystal 113 is collimated by the first parabolic mirror 114, then enters the filters 124, passes through the filters 124, enters the second parabolic mirror 115, and is focused by the second parabolic mirror 115 and enters the sample 105 to be measured.
In this embodiment, the first parabolic mirror PM1 is 101.6mm, the second parabolic mirror PM2 is 50.8mm, and the two parabolic mirrors are placed in a confocal manner, which has the advantage that no aberration and filtering is generated, and the terahertz light beam is compressed to be one half of the surface output of the first nonlinear crystal 113 at the back focal point of the second parabolic mirror 115, which is about 1.5 mm. In other embodiments, other numbers of parabolic mirrors may be used, or other focusing mirror groups may be used to realize the focusing of the terahertz light beam, which is not limited in the embodiments of the present invention.
Fig. 3 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention. Referring to fig. 3, the light source module 101 further includes a pump light filter 400, where the pump light filter 400 is located at the output end of the first nonlinear crystal 113, and is used for blocking the pulse laser output by the first pulse laser 106 and transmitting the terahertz light beam output by the first nonlinear crystal 113. The pump light filter 400 may be a silicon wafer. By adding the silicon wafer, the terahertz light beam output by the first nonlinear crystal 113 does not include the pump laser output by the first pulse laser 106, so that fewer impurity light beams are contained in the terahertz light beam, and the final spectrum acquisition precision is higher.
Fig. 4 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention. Referring to fig. 4, the light source module 101 further includes a third pulse laser 116, where the third pulse laser 116 is configured to emit an ultraviolet pulse laser, and the ultraviolet pulse laser and the terahertz light beam are incident to the sample 105 to be measured together.
In this embodiment, the third pulse laser 116 outputs a center wavelength of 266nm, a frequency of 1Hz-1kHz, an average power of 93.4mW/1kHz, and a pulse width of 4.6ns/1 kHz.
The sample 105 to be detected has a special absorption spectrum in the terahertz waveband; exciting a sample to be detected 105 by utilizing a terahertz pulse beam; the temperature of the sample to be measured 105 rises; then, exciting the sample 105 to be tested by utilizing ultraviolet pulse laser within thermal diffusion constraint time (100-; collecting photoacoustic signals generated by ultraviolet pulses; therefore, the sample absorption characteristic of the terahertz waveband is utilized, and the photoacoustic signal is enhanced; meanwhile, the resolution (266 nm) of the focused ultraviolet pulse laser is utilized, and high-resolution photoacoustic imaging which cannot be achieved by the pure terahertz pulse laser is facilitated. Further, after the third pulse laser 116 is added, the absorption spectrum of the sample 105 to be measured finally obtained is more accurate.
Fig. 5 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention. Referring to fig. 5, the light source module 101 includes a second pulse laser 106', a telescope group 117, an iris 118, a first parallel flat mirror 119, a second nonlinear crystal 120, a second parallel flat mirror 121, and a rotation stage (not shown in fig. 5); the pulse laser output by the second pulse laser 106' sequentially passes through the telescope group 117 and the iris 118 and is incident into an optical parametric oscillation cavity formed by a first parallel plane mirror 119, a second nonlinear crystal 120 and a second parallel plane mirror 121, and the rotary table is used for driving the second nonlinear crystal 120 to rotate so as to output a terahertz light beam with tunable wavelength.
Optionally, the second nonlinear crystal 120 comprises a near stoichiometric lithium niobate crystal. The light source module 101 is used for generating a terahertz strong field system (the terahertz radiation repetition frequency is 10Hz, and the continuous tuning output range is 1.16THz-4.64 THz). In addition, the light source module 101 may also adopt a terahertz strong field system based on other generation mechanisms, such as organic crystal optical rectification, infrared laser difference frequency, laser-driven solid plasma, and the like, which may be selected according to actual situations in specific implementation.
The first parallel flat mirror 119 and the second parallel flat mirror 121 are stokes mirror mirrors, the first parallel flat mirror 119 and the second parallel flat mirror 121 are formed by flat mirrors with high transmittance and high reflectivity, the plated film is high-transmittance and high-reflectivity, the first parallel flat mirror 119 and the second parallel flat mirror 121 are parallel to the side face of the nonlinear crystal 120, the base angle of the nonlinear crystal 120 is 65 degrees, the base angle is an isosceles trapezoid, and the base angle is formed by near stoichiometric lithium niobate crystals. The first parallel flat mirror 119, the second parallel flat mirror 121 and the nonlinear crystal 120 form an optical parametric oscillation cavity, and pulse laser light output by the second pulse laser 106' generates stokes light and terahertz light based on the stimulated electromagnetic coupling scattering effect. The terahertz light generated by the method has good stability.
Fig. 6 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention. Referring to fig. 6, the light source module 101 further includes a third pulse laser 116, where the third pulse laser 116 is configured to emit an ultraviolet pulse laser, and the ultraviolet pulse laser and the terahertz light beam are incident to the sample 105 to be measured together. Among other things, this embodiment is beneficial for improving the final spectral accuracy.
It is understood that in the light source module 101 shown in fig. 5 and 6, a pump light filter 400 (not shown in fig. 5 and 6) may also be added at the output end of the second nonlinear crystal 120 to filter the laser beam emitted from the second pulse laser 106'.
Fig. 7 is a schematic flow chart of a terahertz photoacoustic detection method provided by an embodiment of the present invention. Referring to fig. 7, the detection method may be performed by any one of the terahertz photoacoustic detection apparatuses provided by the above embodiments, including:
s101, a light source module outputs a terahertz light beam with tunable wavelength, the terahertz light beam is incident to a sample to be detected, and a photoacoustic signal is formed after the terahertz light beam passes through the sample to be detected;
s102, the ultrasonic detection module receives the photoacoustic signal and converts the photoacoustic signal into an electric signal;
s103, the processing module obtains an absorption spectrum in the sample to be detected according to the electric signal;
the temperature control module adjusts the temperature of the sample to be detected, and the light source module tunes the wavelength of the terahertz light beam to realize multispectral absorption spectrum detection of the sample to be detected at different temperatures.
Specifically, the sample to be detected may be a water-rich sample, the water-rich sample is a water-rich biological sample, and the water-rich biological sample contains biomolecule information, where the biomolecule information may be at least one of biomolecule information such as protein molecules, DNA molecules, and sugar molecules.
Based on an initial sound pressure formula, for unknown substances, the terahertz irradiation wavelength is changed, and firstly, the light source power P at different wavelengths is measureda(λ1)、Pa(λ2)、…、Pa(λn) (ii) a Putting a sample to be detected, detecting photoacoustic signals of the sample to be detected, and obtaining photoacoustic signals respectively P based on terahertz when different wavelengths are detected0(λ1)、P0(λ2)、…、P0(λn). Then using the result for normalization, P0(λn)/Pa(λn) The ratio of the absorption coefficient to the absorption coefficient of the sample to be measured can be obtained, namely the absorption spectrum mu of the sample to be measured is obtaineda(λ)。
Wherein, the preparation process of the sample to be detected is as follows: the terahertz photoacoustic detection device comprises a micro-fluidic chip, a peristaltic pump, a silica gel hose and a sample holder, wherein the micro-fluidic chip is connected with the peristaltic pump through the silica gel hose, a sample to be detected is conveyed to the micro-fluidic chip through the silica gel hose by the peristaltic pump, the micro-fluidic chip is fixed in the center of a small hole of the sample holder, and the small hole of the sample holder is used for light beams emitted by a light source module.
First, a first sample solution to be tested is injected into the customized microfluidic chip through a needle tube, and bubbles are avoided in the process. And then the temperature control module and the microfluidic chip are tightly combined. And finally, connecting the peristaltic pump with the microfluidic chip through a silica gel hose.
The device adjusting process comprises the following steps: and placing a sample frame with a small hole, wherein the size of the small hole is slightly smaller than that of the terahertz light spot, adjusting the relative position of the small hole and the ultrasonic detection module, and adjusting the detection light path signal to the optimal state. Then, fixing the micro-fluidic chip sealed with liquid in the center of the small hole, pasting metal glue on the detection surface of the chip, and smearing an ultrasonic coupling agent to connect an ultrasonic detection module (an ultrasonic probe) and a processing module (an amplifier and an oscilloscope). And after the completion, opening the oscilloscope, adjusting the relative position of the ultrasonic detection module and the sample to be detected, and fixing the ultrasonic detection module after the oscilloscope displays the optimal and stable waveform.
The measurement process comprises the following steps: observing the waveform of the oscilloscope, and storing the terahertz photoacoustic signals of the sample to be detected under the first group of filters at normal temperature; then changing the temperature of the sample to be detected, and storing the terahertz photoacoustic spectrum of the sample to be detected under the terahertz photoacoustic of the waveband at different temperatures; then, the process is repeated by rotating the second set of filters, and the photoacoustic signal … … at different temperatures in this band is recorded and the measurement process is repeated until the last set of filters. And replacing the next sample to be measured by the peristaltic pump, and repeating the measuring process. And further obtaining terahertz photoacoustic signals of the sample to be detected at different temperatures under different wavebands, and obtaining terahertz photoacoustic spectra of the sample to be detected at different temperatures under different wavebands through normalization processing.
Fig. 8 is a schematic structural diagram of another terahertz photoacoustic detection apparatus provided by an embodiment of the present invention. Referring to fig. 8, the terahertz photoacoustic detection apparatus 100 provided by this embodiment further includes a scanning translation stage 122, where the scanning translation stage 122 is configured to drive the sample 105 to be detected to perform point-by-point two-dimensional scanning; the processing module 103 is configured to obtain photoacoustic imaging of the sample 105 according to the point-by-point two-dimensional scanning information of the sample 105.
It can be understood that strong absorption of water seriously limits the application of the terahertz technology to information extraction of other target biomolecules in water-rich samples such as aqueous solutions and biological tissues, and the terahertz photoacoustic signal of water is inhibited to realize high-sensitivity detection of other target molecules in aqueous solutions and extract effective absorption information of target substances; the photoacoustic spectrum of the biological tissue is detected, and the detected energy is the energy generated by the non-radiative excitation of the light energy absorbed by the biological tissue, namely, the absorption is directly detected, and the spectral characteristics of the biological tissue can be reflected.
In addition, on the basis of the previous embodiment, namely after the terahertz photoacoustic spectrum of the sample to be detected is obtained, it can be determined under which frequency band and at which temperature the absorption of the biomolecule in the sample to be detected is obvious, and then the sample to be detected can be irradiated by the terahertz light of the frequency band, and the temperature of the sample to be detected is adjusted under the temperature, so that clear photoacoustic imaging of the solute in the sample to be detected can be obtained, wherein the terahertz light beam is used as a light source to excite the sample to generate photoacoustic signals, and the imaging resolution of about 100 μm can be realized.
Fig. 9 is a flowchart of another terahertz photoacoustic detection method provided by the embodiment of the present invention. Referring to fig. 9, the method is applied to the terahertz photoacoustic detection apparatus shown in fig. 8, and includes:
s201, a scanning translation table drives a sample to be detected to perform point-by-point two-dimensional scanning;
s202, the processing module obtains photoacoustic imaging of the sample to be detected according to point-by-point two-dimensional scanning information of the sample to be detected.
The working principle of the photoacoustic imaging embodiment is described in detail below.
Referring to fig. 8, the apparatus 100 further includes a frame 123 for fixing a sample to be measured, the frame 123 is fixed on the scanning translation stage 122, a through hole is formed in the bottom of the frame 123 and is used for placing an optical filter (which may be a silicon wafer), the sample 105 to be measured is placed above the optical filter, and two sets of adjustable pressing compression springs are further arranged on the frame 123 and are used for fixing the sample 105 to be measured; the scanning translation stage 122 drives the sample 105 to be measured to move, so that the light beam emitted by the light source module 101 scans the sample 105 to be measured two-dimensionally point by point; the temperature control module 104 is located on a sample 105 to be measured.
In this embodiment, the terahertz photoacoustic detection apparatus 100 is of a transmissive structure, that is, a light beam emitted from the light source module 101 is emitted into the sample 105 to be detected from bottom to top, and the ultrasonic detection module 102 receives an ultrasonic signal of the sample 105 to be detected above the sample 105 to be detected. Bear thin, thick slice form sample 105 that awaits measuring in the frame 123, and easily fix and take out, can guarantee the packing into of couplants such as water, and the sample 105 that awaits measuring of infiltration to interference light intensity is avoided, whole frame can rise, cooling control and keep low vibrations. In this example, the frame 123 is made of a light cold-conducting aluminum material, a hole is formed in the aluminum material, and a filter with a corresponding wave band is placed in the hole, so that the sample 105 to be measured can be directly placed while light is transmitted. Two sets of adjustable pressing compression springs are arranged in the frame 123, so that different samples can be fixed by different degrees of tightness, the sample 105 to be measured can be taken out after measurement is finished, a layer of ultrasonic transparent preservative film can be wrapped on the upper surface of the sample 105 to be measured and filled with liquid in order to prevent a coupling agent from permeating between the sample 105 to be measured and light, and the coupling of the ultrasonic detection module 102 and the sample 105 to be measured is ensured.
The scanning translation stage 122 drives the frame 123 to perform point-by-point scanning in a raster scan manner. The two-dimensional scanning translation stage adopts an L509 linear translation stage of PI company, and the acquisition card adopts GaGeRazor14 (sampling frequency 200MHz, 14-bit conversion precision). The program control of the imaging scan is written in Labview. The system scan mode can be divided into a slow scan mode and a fast scan mode. In slow-scan mode, the scan stage 122 moves in fixed steps (e.g., 50 μm), and the post-processing module 103 starts each step, repeatedly acquires n a lines, averages the acquired n a lines, and then steps to the next position until the entire scan range is completely acquired. The slow-scan signal is generally stable and has a high signal-to-noise ratio. In the fast scanning mode, the two-axis translation stage respectively works in a fast axis mode and a slow axis mode, the fast axis translation stage continuously and uninterruptedly moves (for example, moves from 0mm to 10 mm), in the process of fast axis movement, the processing module 103 collects photoacoustic signals at equal time intervals under external triggering of the laser, and meanwhile, the Labview accesses the position information of the translation stage in real time. When the fast axis movement is finished, the slow axis moves in steps (for example, 50 μm), and the fast axis moves continuously. The above processes are repeated continuously to achieve the purpose of fast scanning, and the fast scanning mode has fast scanning speed.
Specifically, the slow-scan mode procedure is as follows:
step 1: the scanning translation stage moves to (x, y);
step 2: the light source module excites light and emits light, and the circuit triggers the processing module. Irradiating a sample to be detected by a terahertz light beam to generate a photoacoustic signal, receiving the photoacoustic signal by an ultrasonic detection module, and acquiring and converting the photoacoustic signal into a digital signal which is marked as a string of Aline (x, y);
step 3: adding a time window to the string of Aline photoacoustic signals, and calculating a peak-to-peak value Vpp in the window as intensity I (x, y);
step 4: the scan translation stage moves to the next position (x, y) at Step intervals of 50 μm, back to Step2, until the entire rectangular area is scanned, entering Step 5;
step 5: and (c) forming the I (x, y) into an n x n image, wherein n x n represents the number of scanning sites.
Specifically, the fast scan mode process is as follows:
step 1: the scanning translation stage moves to the starting point (x)0，y0)；
Step 2: setting the speed and the moving terminal (X) of the X-scan translation stage (fast scan axis)1，y0) Turning on the laser, emitting light, starting the scanning translation stage to move, and starting the processing module; wherein the processing module comprises an acquisition card (indicated by reference numeral 126 in FIG. 8) and an amplifier (indicated by reference numeral 125 in FIG. 8);
step 3: and the processing module collects 1K alines and specific coordinates (xi, yi) corresponding to the alines for 1s in the process that the X scanning translation stage moves to the end point under the pulse repetition frequency of 1KHZ of the laser until the X scanning translation stage stops moving.
Step 4: the Y scan stage moves 50 μm and returns to Step 2. (the end point set at this time corresponds to the X-scan translation stage moving back). Until the Y scanning translation stage moves to the set target position, entering Step 5;
step 5: calculating peak-to-peak value Vpp of the collected Aline, and corresponding to the position coordinates thereof to obtain a data set (x)i，yiVpp) (note that unlike slow scan, each point (x) of fast scan isi，yi) Not equally spaced) to obtain the final interpolated image.
And finally, acquiring the image of the biomolecules in the water-rich biological sample by adopting a linear interpolation and maximum amplitude projection algorithm, wherein the calculation function is an edge diffusion function and a line diffusion function. Because the acquired signal contains high-frequency noise, a butterworth filter is generally adopted to perform band-pass filtering on the signal, and the frequency characteristic of the ultrasonic detection module 102 is used as a parameter of the filter to filter the high-frequency noise. And constructing a reconstruction grid, and performing linear interpolation by using the peak-to-peak value (Vpp) of the electric signal and the corresponding position (x, y) to obtain a maximum amplitude projection diagram. Due to the use of 4 ℃ silencing control, the obtained imaging graph is a water-independent terahertz-based photoacoustic imaging graph.
According to an embodiment of the present invention, the temperature control module 104 is used to adjust the temperature of the sample 105 to be measured, for example, the temperature of water can be controlled at 4 ℃.
As the elastic coefficient of water is 0 at 4 ℃, the phenomenon of noise reduction is caused, namely, no photoacoustic signal appears after pulse laser energy is absorbed. Therefore, the temperature control module 104 is added into the frame 123 and kept at 4 ℃, which is beneficial to silencing water in the sample 105 to be detected, so that the signal-to-noise ratio of photoacoustic signals of other important biomolecules is increased, and the problem of measuring non-water molecules by terahertz is solved. Referring to fig. 8, the temperature control module 104 includes a temperature sensor 1041, a temperature control plate 1042 and a temperature controller 1043, the temperature control plate 1042 adopts a TEC12706, the temperature sensor 1041 adopts a film probe, the control algorithm adopts a PID adjustment algorithm, and the control accuracy reaches 0.1 ℃. In order to ensure that the refrigerating effect of the temperature control piece and the cooling vibration during imaging are as small as possible, the temperature control piece is refrigerated in a circulating water cooling mode, and the heat is taken away by the hot end of the temperature control piece in a mode of being close to 0 vibration.
The temperature control module can be used for adjusting the temperature of a sample to be detected, for example, the temperature of the sample to be detected is controlled to be 4 ℃, the photoacoustic signal of water can be inhibited, and the ultraviolet light pulse laser can further eliminate the photoacoustic signal of water, so that the finally obtained photoacoustic image and photoacoustic spectrum of target detection molecules which are almost irrelevant to water molecules are obtained, the problem that weak signals sent by target biological molecules are often submerged by strong absorption signals of water is solved, and further application of terahertz radiation in life science is expanded.
In the terahertz photoacoustic detection apparatus provided by the embodiment of the present invention, the ultrasonic detection module 102 is a focused ultrasonic detector.
In summary, according to the terahertz photoacoustic detection method provided by the embodiment of the present invention, the device includes a light source module, an ultrasonic detection module, a processing module and a temperature control module, the light source module is configured to output a terahertz light beam with a tunable wavelength, the terahertz light beam is incident on a sample to be detected and forms a photoacoustic signal after passing through the sample to be detected, and the detection of the photoacoustic signal is converted into the detection of an acoustic signal by optical signal detection, so that the cost is reduced; the temperature control module is used for adjusting the temperature of the sample to be detected, and can realize the adjustment of detection sensitivity; the ultrasonic detection module is used for receiving the photoacoustic signal and converting the photoacoustic signal into an electric signal; the processing module is connected with the ultrasonic detection module and is used for acquiring the absorption spectrum in the sample to be detected according to the electric signal. The terahertz characteristic absorption information and the projection image of the target detection object in the water-rich sample are acquired by realizing the fusion of the terahertz technology and the photoacoustic technology, and the further application of terahertz radiation in life science is expanded.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (12)
1. A terahertz photoacoustic detection device is characterized by comprising a light source module, an ultrasonic detection module, a processing module and a temperature control module;
the light source module is used for outputting a terahertz light beam with tunable wavelength, the terahertz light beam is incident to a sample to be detected, and forms a photoacoustic signal after passing through the sample to be detected;
the temperature control module is used for adjusting the temperature of the sample to be detected;
the ultrasonic detection module is used for receiving the photoacoustic signal and converting the photoacoustic signal into an electric signal;
the processing module is connected with the ultrasonic detection module and used for acquiring the absorption spectrum in the sample to be detected according to the electric signal.
2. The terahertz photoacoustic detection apparatus of claim 1, wherein the light source module comprises a first pulse laser, a mirror group, a grating, a half wave plate, a condensing lens, a first nonlinear crystal, and a plurality of filters;
pulse laser output by the first pulse laser sequentially passes through the reflector group, the grating, the half-wave plate and the converging lens and then is focused on the first nonlinear crystal to excite a terahertz light beam;
the plurality of filters are used for transmitting terahertz light beams with different wavelengths, so that the light source module outputs terahertz light beams with tunable wavelengths.
3. The terahertz photoacoustic detection apparatus of claim 2, further comprising a parabolic mirror set for focusing the terahertz light beam output by the light source module onto the sample to be detected.
4. The terahertz photoacoustic detection apparatus of claim 2, wherein the light source module further comprises a pump light filter at the output end of the first nonlinear crystal, and the pump light filter is configured to block the pulse laser output by the first pulse laser and transmit the terahertz light beam output by the first nonlinear crystal.
5. The terahertz photoacoustic detection apparatus of claim 2, wherein the first nonlinear crystal comprises a lithium niobate crystal.
6. The terahertz photoacoustic detection apparatus of claim 1, wherein the light source module comprises a second pulse laser, a telescope group, an iris, a first parallel flat mirror, a second nonlinear crystal, a second parallel flat mirror, and a rotary stage;
pulse laser output by the second pulse laser sequentially passes through the telescope group and the iris diaphragm and is incident into an optical parametric oscillation cavity formed by the first parallel plane mirror, the second nonlinear crystal and the second parallel plane mirror, and the rotating platform is used for driving the second nonlinear crystal to rotate so as to output a terahertz light beam with tunable wavelength.
7. The terahertz photoacoustic detection apparatus of claim 6, wherein the second nonlinear crystal comprises a near-stoichiometric lithium niobate crystal.
8. The terahertz photoacoustic detection apparatus of claim 2 or 6, wherein the light source module further comprises a third pulse laser, and the third pulse laser is configured to emit an ultraviolet pulse laser, and the ultraviolet pulse laser and the terahertz light beam are incident on the sample to be detected together.
9. The terahertz photoacoustic detection apparatus according to claim 8, further comprising a scanning translation stage, wherein the scanning translation stage is configured to drive the sample to be detected to perform point-by-point two-dimensional scanning;
the processing module is used for acquiring the photoacoustic imaging of the sample to be detected according to the point-by-point two-dimensional scanning information of the sample to be detected.
10. The terahertz photoacoustic detection apparatus of claim 9, wherein the temperature control module is configured to adjust the temperature of the sample to be detected.
11. A terahertz photoacoustic detection method performed by the terahertz photoacoustic detection apparatus according to any one of claims 1 to 8, comprising:
the terahertz light source module outputs a terahertz light beam with tunable wavelength, the terahertz light beam is incident to a sample to be detected, and a photoacoustic signal is formed after the terahertz light beam passes through the sample to be detected;
the ultrasonic detection module receives the photoacoustic signal and converts the photoacoustic signal into an electric signal;
the processing module acquires an absorption spectrum in the sample to be detected according to the electric signal;
the temperature control module adjusts the temperature of the sample to be detected, and the light source module tunes the wavelength of the terahertz light beam to realize multispectral absorption spectrum detection of the sample to be detected at different temperatures.
12. The terahertz photoacoustic detection method according to claim 11, wherein the photoacoustic detection apparatus further comprises a scanning translation stage, and the scanning translation stage is configured to drive the sample to be detected to perform point-by-point two-dimensional scanning;
and the processing module acquires the photoacoustic imaging of the sample to be detected according to the point-by-point two-dimensional scanning information of the sample to be detected.
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