DE102010050595A1 - Method for detecting organic matter e.g. lactose using terahertz spectroscopy, involves detecting radiation beam transmitted through sample and/or reflected from sample, and analyzing detected radiation for identifying organic matter - Google Patents

Abstract

The method (100) involves suspending organic matter (105) in a medium and drying the organic matter (106) to form a sample. The sample is irradiated (110) with light or an exposure beam e.g. time domain-pulsed exposure beam and continuous frequency domain radiation, of electromagnetic radiation in a drying box, where the exposure beam comprises frequencies in a range of about 100 GHz to 2 THz. The radiation beam transmitted through the sample and/or reflected from the sample are detected (112). The detected radiation is analyzed (114) for identifying the organic matter. The medium is selected from a group consisting of agar, guar gum, gellan gum, carrageenan, xantham gum, fibrous sodium pectate, acrylamide and other agar substitutes.

Description

BACKGROUND OF THE INVENTION

Field of the invention

The invention relates generally to methods of detecting organic matter, and more particularly to a method of detecting organic material using terahertz spectroscopy.

Description of related art

Terahertz (THz) spectroscopy can be split into two basic techniques: the time domain and the frequency domain. Time domain systems use optical pulses from a mode locked laser to generate THz pulses through a demodulation process in a photoconductive (ie, "Auston") switch (PCS = Conductive Switch). The THz pulse is passed through a sample of interest before being focused on a second PCS (the detector) which is operated by a delayed optical pulse from the same mode-locked laser. The delay of this optical detector pulse is changed; and the detector PCS photocurrent is measured as a function of the delay to obtain a THz autocorrelation function. Normalization and Fourier transform are applied to this autocorrelation to produce frequency dependent transmission through the sample of interest. As in Fourier transform spectroscopy, the spectral resolution is determined primarily by the length of the delay line, which can be very difficult to increase beyond 1 cm, giving a typical resolution of 1 cm ^-1 or 30 GHz.

On the other hand, in frequency-domain technique, continuous wave THz radiation is produced by photomixing, in the combined output of two single-frequency lasers in a personal computer. The wavelength of the one (or both) laser is tuned to change the THz output frequency. In most spectroscopic applications of photo-mixing, the THz output beam from the PC is coupled to a sensitive broadband thermodetector (eg, LHe bolometer or Golay cell), making the overall signal processing incoherent and phase insensitive. Coherent (homodyne) detection can be achieved at room temperature by mixing the same optical radiation from the lasers in a detector PC where the THz signal is also incident or incident. This provides greater sensitivity and faster data acquisition than the incoherent technique and preserves the phase information.

SUMMARY OF THE INVENTION

In the present application, methods for detecting organic material using terahertz spectroscopy are disclosed. According to some examples, the methods include suspending organic material in a medium to form a sample, irradiating the sample with an illumination beam of electromagnetic radiation, the illumination beam having a plurality of frequencies in the range of about 100 GHz to about 2 THz Detecting the radiation reflected by and / or from the sample, and analyzing the detected radiation to identify the organic material, wherein the medium is selected from the group consisting of: agar, guar gum, gellan gum, carrageenan, xantham gum, fibrous sodium pectate and other agar -Substitute. Preferably, the medium is agar.

Preferably, the plurality of frequencies is in the range of about 400 GHz to about 700 GHz. In another embodiment, the plurality of frequencies is in the range of about 500 GHz to about 800 GHz. The method may further comprise applying electrical poles to the sample in a dry box.

In one embodiment, the organic material is a carbohydrate. The organic material may be a monosaccharide or a disaccharide. The organic material may be a disaccharide selected from the group consisting of sucrose, lactulose, lactose, maltose, trehalose, cellobiose and mixtures thereof. Preferably, the organic material is lactose.

The method may further comprise performing a baseline comparison with a central sample without the organic material including irradiating the central sample with the exposure beam; Detecting the radiation transmitted through the medium or medium sample and / or the radiation reflected from the medium sample; and, comparing the detected radiation of the medium sample with the detected radiation of the sample. The method may further include performing a baseline comparison with air, including irradiating the air with the illumination beam; detecting the radiation transmitted through the air and / or the radiation reflected by the air; and comparing the detected radiation of the air with the detected radiation of the sample.

The method may further comprise using a weighted average sample by irradiating and detecting the radiation from the sample more than once.

In one embodiment, the exposure beam is a time-domain pulsed exposure. In another embodiment, the illumination beam is a frequency domain continuous exposure.

The method may further include: generating a composite laser beam in an integrated laser module; and applying the composite laser beam to a first photoconductive switch activated by the composite laser beam to form the exposure beam as an optically generated exposure beam. The method may include applying the composite laser beam to a detector positioned to detect the radiation transmitted through the sample and / or reflected from the sample, the detector having a second photoconductive switch activated by the composite optical beam. The method may include generating the composite laser beam from first and second lasers at different frequencies, each modulated with a different low frequency identification tone.

BRIEF DESCRIPTION OF THE DRAWINGS

1 Fig. 10 illustrates a method for detecting organic materials using THz spectroscopy;

2 is a block diagram of a THz spectrometer used to implement the method of the 1 can be used and which is able to achieve the desired detection levels at low tetrahedral frequencies;

3 is a graph which characterizes a THz spectrometer and configured as shown in FIG 2 is shown;

4 Figure 13 is a plot of the THz spectrum (power versus wavelength) for lactose powder alone; and

5 is a plot of the THz spectrum (power versus wavelength) for air, agar and agar with lactose in an exemplary application of the THz spectrometer 3 ,

DETAILED DESCRIPTION

In the following, methods for detecting organic material using THz spectroscopy wherein the organic material is suspended in a medium will be described. The medium may be selected from the group consisting of: agar, guar gum, gellan gum, carrageenan, xantham gum, fibrous sodium pectate, and other agar substitutes. Preferably, the medium is agar. The medium may be a film or layer forming polysaccharide. Preferably, the medium is agar.

Agar has been used in microbiology to provide a solid surface containing a medium for the growth of bacteria. Agar is a heterogeneous mixture of two classes of polysaccharide: agarose and agaropectin, which share the same galatose-based backbone. The neutral charge and the low level of chemical complexity of agarose make it less likely to interact with biomolecules.

Suspending the organic material to be detected in agar stabilizes the organic material for effective THz spectroscopy. Although not determined by theory, it is believed that the agar allows detection of intramolecular vibrational modes and intermolecular vibrational modes.

Using this method, many types of organic material can be analyzed. Organic material is any chemical compound that contains carbon. Organic compounds can be either natural or synthetic compounds. Natural compounds are those produced by plants or animals, such as sugars or simple carbohydrates.

The organic material is preferably a carbohydrate. Carbohydrates are simple organic compounds that are aldehydes or ketones. Carbohydrates have four chemical moieties: monosaccharides, disaccharides, oligosaccharides and polysaccharides. The basic carbohydrate units are monosaccharides such as glucose, galactose and fructose. Common disaccharides formed from two monosaccharides include sucrose, lactulose, lactose, maltose, trehalose and cellobiose. An oligosaccharide is a polymer formed from a small number of monosaccharides. Polysaccharides are polymeric carbohydrate structures formed by repeating units of either monosaccharides or disaccharides joined together by glycoside linkages. Some common polysaccharides include: starches, glycogen, cellulose and chitin.

Preferably, the organic material is a carbohydrate, preferably a monosaccharide or a disaccharide, and most preferably a disaccharide. In preferred embodiments, the organic material may be a disaccharide selected from the group consisting of sucrose, lactose, lactose, maltose, trehalose, zellobiose, and mixtures thereof.

The sample, d. H. the medium with the organic material can be dried. The drying process preferably removes most of the water from the sample. The drying process may include, for example, chemical drying, application of a vacuum, ambient drying or application of heat. In a preferred embodiment, the drying process removes substantially all of the water from the sample.

1 illustrates an exemplary method 100 for detecting organic material using THz spectroscopy by suspending the material in agar. Although the example relating to the suspension in arga is described, it will be appreciated that any type of suitable medium can be used. At the block 102 Agar is prepared. For example, a certain amount of agar is added to the water, boiled and allowed to cool. At the block 104 Before the agar is completely cooled, the organic material is dissolved or suspended in the agar and mixed to ensure uniformity. At the optional block 105 After the organic material is dissolved or suspended in the agar, the not yet settled agar may be subjected to an electric pole process with the organic material.

Common poling processes include, for example, contact poles and coronapoles. For example, in the case of contact poling, the sample is arranged between two electrodes which apply the poling electric field. The sample may be contained within a housing during drying, but is otherwise not limited thereto. In coronapole, a large electric field is applied between a needle placed above the sample and a ground plate on the other side of the sample. The large electric field creates a corona discharge between the needle and the sample. Ions build up on the surface of the sample and generate a very strong electric field on the sample, which polishes the organic material in the sample.

In general, poling may be achieved at or below room temperatures, or in some cases at a temperature above room temperature. By way of example only, it should not be noted that pole fields may be approximately 40 to 150 V / micron.

The poling technique and parameters used in aligning the dipoles of the organic material in the arga can be adjusted to the particular temperature desired for drying. For a dried sample, poling can be carried out by gradually raising the temperature of the sample during poling and, in some instances, simultaneously raising the poling field.

The poling process aligns the poles of the molecules in the organic material, and as the medium settles and dries, the molecules are locked and held in the aligned position. By controlling the applied electric field, the sample can be controlled or controlled to affect the resulting terahertz beam transmitted waveform. In this way, electrical poling can be used to improve the THz spectroscopic analysis by controlling the terahertz waveform and the overall process efficiency.

Electrical poling is preferably used during setting and drying of the agar. The electrical poling may be applied in a continuous or pulsed manner, and may be applied during a selective portion of the agar drying step.

In a further embodiment, the method 100 an electrophoresis process. For example, the organic material may be placed in or on the medium once the medium has cooled and settled. An electric field can be applied and the organic material migrates or migrates through the medium. The medium can then be dried, which fixes or locks the aligned organic material in the medium. If the organic material is not uniform, the electrophoresis process may separate the components of the organic material within the medium in size or charge.

Referring again to 1 you realize that at the block 106 the agar is dried with the suspended organic material to form a sample. The agar settles at room temperature. Optional dry processes such as the application of heat or electrohydrodynamic drying can improve drying and finally THz analysis. At the block 108 the sample is fed to the THz spectroscopy system. This sample can be taken from a larger production volume and will be on the THz system may be delivered via a delivery mechanism such as a vial, petri dish, glass plate, etc. The sample may be provided by manual or automated means, and may be continuously fed or periodically taken, for example, in a batch manner. In a continuous mode of operation, the samples may continuously pass the detector, with the detector irradiating the passing samples. At the block 108 Optionally, the sample can be delivered to a dry box to minimize the detection of water vapor transients.

At the block 110 The THz radiation generated by the spectroscopy system is used around the sample from the block 106 spectrally examined. The device detects the through the sample at the block 112 transmitted and / or reflected radiation, wherein a THz sequence detector collects the transmitted and / or reflected radiation and converts the corresponding data. The detector may be of a different type, including a scanning THz detector or array traditionally used for THz imaging. Preferably, the detector is an intensity detector.

At the block 114 the detected radiation is analyzed to determine the absorbance and thus the chemical content of the sample, in particular whether the sample contains any contaminant from a number of identifiable impurities. Various analysis methods can be used at the block 114 including the comparison of the detected radiation values from the block 112 with known radiation profiles of the organic material or the base lining of the detected radiation values compared to a pure sample (without organic material) of the Argas. For the former case, the detected radiation may be compared to a known library of organic material (stored, for example, in a look-up table or other data memory) for determining which organic material is present in the sample. In the latter case, obtaining a characteristic absorption spectrum of the pure argon may be provided as a baseline. Then, the baseline can be subtracted from the pure Arga from the detected radiation from the sample to determine which organic material is present. In some examples, the block may also determine a quality or safety factor that analyzes the quality of the detected radiation data and provides a separate indication of tactile data accuracy that may vary depending on the noise in the detection radiation signal, intensity variations across the spectral range, and other operating conditions.

Since in the preferred examples the method 100 is not destructive, the same sample can be tested countless times by analyzing the analysis block 114 can perform the detected radiation data through multiple tests of the same sample or through multiple tests taken on different samples of the same production volume. The averaging of the data helps to reduce the noise. More Robust Analysis Techniques Including Partial Least Squares (PLS) Models of Maurer et al, J. Agric. Food Chem. 57: 3974-3980 (2009) can be modified to develop correlation models between the THz spectroscopy data and the type of organic material.

The by block 110 The generated THz beam comprises a plurality of frequencies in the range of about 100 GHz to about 2 THz and preferably in the range of about 400 GHz to about 700 GHz or in the range of about 500 GHz to about 800 GHz. An example of a THz beam generator and spectroscopy system will now be described.

A simplified block diagram of 2 illustrates the integration of the dual laser module 205 in a spectrometer system 200 to implement the process 100 , In general, the following applies: the spectrometer system 200 can be reflection or transmission through the sample 204 use, by appropriate arrangement of a THz source header 206 and a THz detector head 208 , Furthermore, the system includes 200 a computer 210 comprising, for example, a processor and other electronic circuitry for determining the identity or composition of the target and / or printing or displaying the results so that the information is readily available to the user.

In the illustrated duel laser module configuration is a primary laser beam 212 with a window 214 in the appropriately positioned source header 206 coupled and then the coupling is done with a lens 216 that the beam 212 focused on one point, approximately 10 microns in diameter on the surface of a PCS 218 , The optical frequency signal directed to the surface of the PCS semiconductor device generates THz radiation from the PCS 218 in the frequency range from 100 GHz to over 2 THz, in accordance with the offset frequency between the lasers in the dual laser module 205 , The from the PCS device 218 emitted THz radiation is collimated and collected by a silicon lens 220 , attached to the source head 206 , The Lens 220 is preferably a hemispherical structure, approximately 1 cm in diameter. Additional (not shown) Lenses consisting of Teflon can be downstream of the lens 220 may be arranged to collimate the RF, ie high frequency, beams in the THz output beam. Beamforming mirrors may also be used instead of or in addition to the silicon lens. The sample 204 absorbs and transmits a portion of the radiation, and in the illustrated embodiment, a portion of the radiation is also reflected back toward the source or user.

A secondary beam 220 from the dual laser module 205 is on the detector head 208 directed. The secondary beam 220 is for example with a window 224 coupled, and then with a lens 226 coupled the beam to a point of approximately 10 micro diameter on the surface of a PCS 228 focused. A silicon lens 230 collects the transmitted or reflected radiation from the sample 204 that then through the PCS 228 is detected and by the computer 210 is processed.

The 2 Thus, FIG. 1 shows an example of a THz spectroscopy system that may be used, as in the example process of FIG 1 was discussed. Generally speaking, this system is implemented using two ErAs: GaAs PCSs in an extremely compact configuration using all of the solid state components and no moving parts. The system uses a single integration package of two 783 nm DFB laser diodes with a high-resolution wavelength discriminator. Digital signal processing electronics can provide precise frequency control and yield with approximately 200 MHz accuracy of the THz signal frequency. Continuous frequency sweep was demonstrated and a better than 500 MHz resolution of 100 GHz to 1.85 THz was achieved, giving better resolution spectral data for analysis. The coherent detection sensitivity is in good agreement with the previous theoretical predictions and gives a signal-to-noise ratio of 90 dB / Hz at 100 GHz and 60 dB / Hz at 1 THz through a path length in air of one foot. Spectrometer frequency resolution and dynamic range are suitable applications and include the analysis of chemical, biological and explosive materials in solid phase and gas phase at atmospheric pressure.

The design uses highly compact photonic integration techniques, electronic differential chopping and coherent room temperature THz detection. The highly integrated photonic device using semiconductor diode lasers does not use moving parts and is inherently insensitive and well suited for outdoor applications. The coherent (homodyne) detection method provides excellent SNR in accordance with the theory and has much faster data acquisition times and no cryogenic cooling as required by liquid helium-based bolometers in more conventional (incoherent) THz photomix spectrometers.

Although a frequency domain THz spectroscopy system has been described, other THz spectroscopy systems can instead be used for organic material detection. These include time-domain THz spectroscopy systems for, for example, those using a mode locking laser (eg, Ti: sapphire laser or Soldid statelaser) capable of generating a sequence of femtosecond pulses focused on appropriate semiconductor material to form THz To generate radiation. The THz signals generated by the optical pulses typically have peaks in the range of 0.5-2 THz and have average power levels in the microwatt range and peak energy of about one femtojoule. In some examples, the mode-locked pulsed laser beam may be split and synchronized through an optical scan delay line and cause a THz generator material (emitter) to be struck and a detector of known phase coherency is provided. By sampling a delay line or conduction, gating, or keys, the THz signals incident on the detector, a time dependent waveform is generated in proportion to the THz field amplitude. Once generated, the THz radiation is put to the test 204 which is to be analyzed, and the detector or detector array is used to collect the signal propagated through or reflected from the object. Such measurements are made in the time domain by collecting the timed train of pulses and then processing by a Fourier transform to recover the frequency domain spectral information.

In any type of system, THz spectroscopy is capable of a specific location on the sample 204 or it can be designed as a scanning system which scans every dot or "pixel" on a sample 205 scans either in one focal plane or in consecutive focal planes at different areas. This may be particularly useful for the detection of organic material in the event that the organic material was not homogeneously incorporated, since the THz from the system 200 can be focused or scanned over specific points of the targeted analysis.

This method can be used to identify unknown organic Material with a unique THz spectrum that can be identified using the disclosed methods. Further, if the organic material and its unique THz spectrum are known, then this method can enable the detection of impurities in this known organic material. The use of the medium to suspend the organic material allows the stabilization of the material including the contaminant. The electrical poling can improve the analysis of the organic material.

This method also allows the testing of liquids and powders that may be dissolved in the medium. Liquid samples are problematic in THz spectroscopy because of the high concentration of water which has high absorption across the THz spectrum. For example, liquid water of 1 mm thickness normally completely attenuates the radiation in the THz frequency range. Agar, surprisingly, contributes very little to signal reduction and therefore provides an effective medium for testing organic material.

EXAMPLES

The THz spectrometer was used to study a low frequency vibrational mode in lactose monohydrate in both a pure powder form and in a "dissolved" form suspended in an agar matrix.

The THz spectrometer characterization

Using a THz spectrometer like the one detailed in 2 As shown, the signal-to-noise ratio ("SNR") has been measured, and this is in 3 shown. The lower curve 301 is the power spectrum with the blocked THz beam. The upper curve 302 Figure 12 shows the detected power spectrum for a 30 centimeter (cm) path length in air with a 1 GHz frequency resolution and 1 second integration time. The signal 302 is with (black) and without (gray) with a 25-point smoothing function as it is applied. The rapid change in un-smoothed signal power, depending on the frequency, is expected and is due to an interferometric effect caused by significantly different lengths of the laser-to-photo mixer arms of the spectrometer.

Smoothing removes this interferometric effect but also eliminates the phase information contained therein. The signal-to-noise ratio of about 80 dB / Hz obtained at 200 GHz is consistent with the theoretical prediction. The SNR improvement is primarily due to the improved optical beam collimation and the integrated laser arrangement and improved optical and THz coupling of the present instrument. The dashed vertical lines indicate the frequencies of the strongest water vapor absorptions.

Comparative Examples

A lactose monohydrate sample was placed in the center of a large metal bowl provided with a transparent plastic adhesive tape on the back. After the powder was distributed in the bowl, the clear plastic adhesive tape was placed over the sample to hold it in place and set the sample thickness to 3 mm. The frequency domain THz spectrometer, as detailed in 2 was then used to measure the lowest frequency absorption feature in the lactose monohydrate powder. The THz spectrum was generated with a resolution of 500 MHz and 1 second integration time. The five decade dynamic range of the THz spectrometer at these frequencies is clear and makes it possible to easily determine the full width half maximum of the absorption feature, which accounts for approximately 25 GHz and roughly 535 GHz, as in FIG 4 shown, occurs. Although the weak 620 GHz water vapor transfer is present, the much stronger 557 GHz transition is masked by the broad lactose monohydrate transition.

example 1

A mixture of 2 grams of organic grade agar was boiled briefly in 40 ml of water to provide crosslinking and then dried under a low speed fan. Such a technique produced an agar layer or agar film of approximately 0.5 mm thickness after drying. For the sample containing lactose, 2 g of biological grade arga was boiled briefly in 40 ml of water, whereupon cooling was allowed. Before the agar was completely cooled, 4 grams of lactose monohydrate was added to the mixture and mixed. 5 illustrates a comparison between a single background scan of air 503 , a scan of the pure agar layer 502 , and a sample of the agar layer of the lactose monohydrate 501 contains. The THz spectrum was generated with a 500 MHz resolution and 1 second integration time.

There is a relatively low loss of 7 dB for the dried agar matrix. In comparison, this means that a 1 mm thick sample of liquid-phase water would normally completely attenuate the radiation in this frequency range. It is clear that the bulk of the Removed water from the arga and it is believed that the current 7 dB damping is due to still existing water. The sample containing lactose monohydrate shows 15 to 20 dB loss. This loss can be minimized with improved drying techniques. Since the measurements were done in the surrounding neighborhood, the typical 557 and 752 GHz water vapor transitions are present on all curves. The agar sample 502 also shows the features at 605 and 676 GHz. The agar and lactose sample 501 seems to have a narrow feature at 571 GHz and a wider feature centered at 670 GHz. The waterline at 557 GHz also appears slightly broadened in the arga and lactose samples 501 , Although not bound by theory, it is believed that this is due to the presence of an unresolved lactose monohydrate trait. These features of the sample, which include agar and lactose, allow analysis of the entire THz spectrum compared to the lactose powder present in the example above alone.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Maurer et al, J. Agric. Food Chem. 57: 3974-3980 (2009) [0033]

Claims (18)

A method of detecting organic material using tetrahertz spectroscopy, the method comprising: Suspending organic material in a medium to form a sample; Irradiating the sample with an illuminating or exposing beam of electromagnetic radiation, the exposing beam having a plurality of frequencies in the range of about 100 GHz to about 2 THz; Detecting the radiation transmitted through the sample and / or the radiation reflected by the sample; and Analyzing the detected radiation to identify the organic material, wherein the medium is selected from the group consisting of agar, guar gum, gellan gum, carrageenan, xantham gum, fibrous sodium pectate, acrylamide and other agar substitutes. The method of claim 1, wherein the medium is agar. The method of claim 1, further comprising applying electrical poling to the sample. The method of claim 1, wherein the sample is irradiated in a dry box. The method of claim 1, wherein the plurality of frequencies is in the range of about 400 GHz to about 700 GHz. The method of claim 1, wherein the plurality of frequencies is in the range of about 500 GHz to about 800 GHz. The method of claim 1, wherein the organic material is a carbohydrate. The method of claim 1, wherein the organic material is a monosaccharide or a disaccharide. The method of claim 1, wherein the organic material is a disaccharide selected from the group consisting of sucrose, lactulose, lactose, maltose, trehalose, cellobiose and mixtures thereof. The method of claim 1, wherein the organic material is lactose. The method of claim 1, further comprising: Perform a baseline comparison against a media sample without organic material, providing: Irradiating the medium sample with the exposure beam; Detecting the radiation reflected by the medium sample and / or by the medium sample; and Comparing the detected radiation of the medium sample with the detected radiation of the sample. The method of claim 11, wherein a baseline comparison is performed with air, wherein: Irradiation of the air with the exposure beam; Detecting the radiation transmitted through the air and / or reflected from the air; and Comparing the detected radiation of the air with the detected radiation of the sample. The method of claim 1, further comprising performing a weighted average sample by irradiating and detecting the radiation from the sample more than once. The method of claim 1, wherein the exposure beam is a time-domain pulsed exposure. The method of claim 1, wherein the exposure beam is continuous frequency domain radiation. The method of claim 1, further comprising: Generating a composite laser beam in an integrated laser module; and Applying the composite laser beam to a first photoconductive switch activated by the composite laser beam to form the exposure beam as an optically generated exposure beam. The method of claim 16, further comprising: Applying the composite laser beam to a detector positioned to detect the radiation transmitted through or reflected from the sample, the detector having a second photo-conductive switch activated by the composite optical beam. The method of claim 16, further comprising: Generating the composite laser beam from first and second lasers at different frequencies, each modeled with a different low frequency identification tone.

Images