Patent Application
20240290599
The present invention relates to systems and methods for sampling, in particular to systems and methods wherein the sampling is based on ultrasound assisted removal of material from the sample for feeding the material to a detecting means. The invention relates also a detecting means comprising the system.
Analysis of samples via mass spectrometry (MS) rely on desorption and ionization methods including matrix-assisted laser desorption ionization (MALDI), desorption electrospray ionization (DESI), laser ablation electrospray ionization (LAESI) and secondary ion mass spectrometry (SIMS). Each method performs at best with certain types of analytes and are used for different applications, although there is no universal ionization method that fits for all analytical purposes. Each of the method works either in ambient or in vacuum conditions but none of the current desorption methods operates well with sample immersion. Since biological samples e.g., cell cultures and tissue sections are often stored at liquid medium their mass spectrometric analysis may be laborious. Accordingly, there is still a need for further systems and methods for sampling.
The present invention is based on the observation that at least some of the problems related to sampling material from samples immersed in a fluid can be avoided or at least alleviated by creating controlled focused cavitation at predetermined positions within a sample. According to the present invention cavitation created by high-intensity focused ultrasound waves (HIFU) removes material from interface between the sample and the immersion fluid. The combination of acoustic streaming and flow field induced by transport of fluid into a feeding means such as a sampling capillary close to the ultrasound focus allows capturing removed material and transporting it for further analysis.
Accordingly, it is an object of the present invention to provide a system for sampling material to a detecting means, the system comprising
It is also an object of the present invention to provide a detecting means comprising system of claim 1.
It is still an object of the present invention to provide a method for feeding material from a sample to a detecting means using the system of claim 1.
Further objects of the present invention are described in the accompanying dependent claims.
Exemplifying and non-limiting embodiments of the invention, both as to constructions and to methods of operation, together with additional objects and advantages thereof, are best understood from the following description of specific exemplifying embodiments when read in connection with the accompanying drawings.
The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of un-recited features. The features recited in the accompanied depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e., a singular form, throughout this document does not exclude a plurality.
According to one aspect the present invention concerns a sampling system for transporting material removed from a sample to a detecting means. An exemplary system 100 is shown in
The transducer is configured to emit focused ultrasound waves towards a target on interface 103a between the sample and the fluid. An exemplary transducer suitable for the system is a focused piezoelectric transducer. An exemplary operating frequency is 12 MHz. The intensity of the ultrasound at the target is preferably at least 1 W/cm2 to allow removing material from the sample and for producing an acoustic stream in the fluid. An acoustic stream is a steady flow in a fluid driven by the absorption of high amplitude acoustic oscillations.
The feeding means shown in the figure comprises a first end 105a configured to be positioned between the transducer and the interface, a second end 105b configured to be connected to the detecting means 106, and a fluid transporting means 107 between the first end and the second end. An exemplary fluid transporting means is a pump.
The first end should be in close proximity to the interface when the system is in operation. The distance h between the interface 103a and the first end 105a is preferably 1.5-5 mm. An exemplary distance is 2 mm. This warrants effective transportation of the material from the fluid to the detecting means. A typical first end comprises a capillary tube. If the distance is too short, the ultrasound beam is distorted by the capillary and the cavitation threshold is not exceed at the focal point. If the distance is too long, the sampling flow volume rate should be increased to effectively collect removed material. Problems might also arise due to increased sample volume i.e., sensitivity might decrease.
According to a preferable embodiment the system also comprises means 108 for adjusting the distance h between the interface 103a and the first end 105a. An exemplary means 108 comprises manual micro-meter screws.
When the system is in operation, the sample is immersed in the fluid, and the transducer emits high intensity focused ultrasound (HIFU) waves 109 towards a target on interface between the sample and the fluid. The HIFU induced cavitation erosion removes material from the sample at the target. Acoustic streaming induced by the focused ultrasound beam near acoustic hard boundary causes the removed material to move away from the interface, i.e., along the y-direction of the coordinate system 199. An exemplary removed material particle is illustrated in the figure by a star marked by a reference number 110.
The transducer needs to operate at an intensity at the focal spot which is preferably higher than 1 W/cm2, more preferably 10 W/cm2 or higher. The frequency of the transducer should be at least 20 kHz, preferably between 1 MHz and 15 MHz. Higher frequencies, up to 1 GHz can be used. Higher frequency provides a smaller focal spot for more localized sampling. For example, for a 12 MHz transducer with a numerical aperture of 0.85, the cavitation erosion pit radii ranges from 20 μm to 200 μm depending on the sample and ultrasound parameters. Increasing the frequency increases the cavitation pressure threshold so higher frequencies require tighter focusing and/or higher driving voltage of the piezo.
Breaking the sample cohesion, e.g., aluminum surface, requires higher acoustic pressure amplitude and higher total energy than breaking down adhesion of the sample, e.g., a thin film on a hard substrate. For aluminum in water the pressure amplitude at the focus should exceed 10 MPa, preferably higher, such as 20-25 MPa. The cavitation probability increases as the amplitude increases so higher amplitudes provide higher erosion/extraction efficiency. As the amplitude gets higher the erosion area increases as the part of the field that exceeds cavitation threshold increases. Accordingly, the spatial resolution of the method depends on the amplitude. The cavitation threshold is function of frequency i.e., the higher frequency the higher is the cavitation threshold. For breaking the adhesion, 15 MPa suffices and tuning the amplitude allows tuning the extraction area. The cycle count of the ultrasonic bursts should be preferably between 20 and 80 or more to provide high enough cavitation probability. The pulse repetition frequency (PRF) should be tuned in such a manner that the transducer does not overheat. For example, for a water-immersed 12 MHz single-element piezoceramic, maximum of 50 W-100 W of forward electric power is suitable.
The target can be of any geometric shape. A particular target is a point on the interface. Another target is a line on the interface.
According to a particular embodiment the system comprises means 111 for moving the focal point of the ultrasound waves. This can be done e.g., by moving the transducer or by moving the housing. According to an exemplary embodiment the system comprises means 112 configured to move the transducer in x,y,z-directions of the coordinate system 199 e.g., by translation stages controlled with manual micro-meter screws. This allows positioning the interface at the focal point of the ultrasound waves. According to another embodiment the transducer is a phased 25 array transducer that is configured to tune the focal distance. The focal point adjustment can be assisted by placing a hydrophone or the like in the housing.
According to another embodiment the moving of the focal point of the ultrasound waves is done by a means 113 configured to move the housing in x,y,z-directions, at least in x,z-directions of the coordinate system 199. The movement can be performed by placing the housing onto a CNC-router table operated by a microcontroller.
According to a particular embodiment the system comprises means 114, such as a computer program to assist with selecting the target based on an ultrasound image. According to an exemplary embodiment the program determines areas of the sample surface that are harder than a predetermined hardness level and instructs the means 111 to move the focal point by moving the transducer above those areas one by one. Then, the HIFU induced cavitation erosion removes material from the selected sites, and the system feeds the removed material to the detecting means for analysis. This approach may be used to find abnormalities such as cancers in biological samples. According to another preferable embodiment the means 114 is also configured to instruct the means 108 to adjust the distance h between the interface and the first end and/or to instruct moving the holding means.
According to one embodiment the image is an image imputed to the computer program. According to another embodiment the system comprises imaging means 115 such as a second transducer configured to produce the image which is then transferred to the computer program. According to another embodiment the transducer 104 is configured to produce the ultrasound image. Ultrasound imaging is well known in the art.
According to still another embodiment the system comprises means 116 for controlling properties of the fluid. Exemplary properties are pH of the fluid, temperature of the fluid, water content of a non-aqueous fluid, relative humidity of a gaseous fluid, velocity of the fluid.
According to another embodiment the present invention concerns a detecting means 106 comprising the sampling system described above. The detecting means is preferably selected from mass spectrometer, Raman spectrometer, NMR spectrometer, IR spectrometer, UV spectrophotometer, scanning electron microscope, atomic force microscope, quartz crystal balance, dynamic light scattering meter, high pressure liquid chromatograph, x-ray diffractometer, activity assay means, immunoassay means, preferably mass spectrometer, and Raman spectrometer.
According to a particular embodiment the detecting means comprises two or more spectrometers. According to an exemplary embodiment the sampling system is connected to a mass spectrometer via a Raman spectrometer.
According to a preferable embodiment the detecting means is an electrospray ionization (ESI) mass spectrometer. ESI is a versatile soft ionization method suitable for many kinds of analytes and can easily be coupled with other separation methods e.g., liquid chromatography (LC) increasing the analytical performance. Different techniques have also developed further from the basis of spraying the solvent with or without analyte at the ion source as in DESI. ESI suits also for wide range of analytes, and it generates either positive or negative polarity of ions. In comparison to other techniques like SIMS or MALDI, ESI stands for more gentle type of ionization method. Generation of unfragmented ions would be considered as an advantage in respect to MS data interpretation of complex samples such as biological samples.
The system 200 comprises preferably also one or more of
According to another aspect the present invention concerns a method for feeding material from a sample to a detecting means using the sampling system described above. The method comprises the following steps:
According to a particular embodiment the method the step iv) comprises feeding at least part of the fluid comprising the removed material to the detecting means.
Particular samples suitable for the method are those which should be preserved and analysed while immersed into a fluid. Exemplary samples are biological samples such as cell cultures, tissue sections, forensic samples, plants, and materials comprising active pharmaceutical ingredients. Further exemplary samples are organic or inorganic solid or semisolid materials that do not dissolve into the immersion fluid, paints, polymers, gel-like materials, and metals.
According to a particular embodiment the sample comprises material rich in rare and precious metals (RPM), such as gold.
High-intensity focused-ultrasound-induced (HIFU) inertial cavitation can be used to erode surfaces such as surfaces of PCBs. With a MHz transducer, both imaging to determine ROIs and extracting RPMs is possible.
Exemplary immersion fluids are water, buffer solutions such as PBS, and alcohols such as ethanol and methanol, acetonitrile, and their mixtures. Naturally, desalting, or other purification methods may be is needed prior detection.
According to another embodiment the fluid is gas, in particular moist gas.
According to the method a target on the interface sample is subjected to high intensity focused ultrasound. When the sample is solid, the interface is the surface of the sample. The intensity of the ultrasound should be high enough to remove material from the sample.
The distance d between the transducer and the interface is adjusted, if needed by moving the transducer along the +/−y-direction of the coordinate system 199 until the focal point is at the desired position. The energy density of the ultrasound waves should be high enough to remove material from the surface, but low enough to prevent decomposition of the material. Exemplary ultrasonic excitation parameters are piezo voltage amplitude, cycle count in a burst, total amount of bursts and pulse repetition frequency. Exemplary parameters for the method are listed below.
According to another embodiment the method comprises imaging the sample prior to the step ii) and selecting the target point based on the image.
The setup consists of an acoustic excitation part and a liquid handling part. A signal generator (Tektronix AFG31052, UK) was used to generate sinusoidal electric signal, which was amplified with RF power amplifier (Amplifier Research 500A100A, USA). A custom-made transducer (3D-printed) with a concave piezo-electric crystal converted the electric signal into mechanical pressure waves propagating through the immersion bath. The electric signal consists of bursts of a sine wave at f=7.0 MHz and PRF=500 Hz. Ultrasound echoes reflected from the sample surface was recorded with an oscilloscope (Picoscope 5203, UK) using a 100×-probe for aligning (adjusting the focal distance precisely) with low intensity ultrasound excitation amplitude which is suitable e.g., for imaging modality. A coded excitation signal (frequency modulated chirp sine wave, f=6-8 MHz) was used for cross-correlating the emitted electric signal with the acoustic echo signal resulting in a cross-correlogram, from which the time-of-flight (TOF) of the propagation path was acquired. The transducer was moved along the x,y,z-directions by translation stages controlled with manual micro-metre screws. Milli-Q (Merck Millipore, France) purified water was used as immersion fluid.
Sampling of immersed fluid was performed in a syringe-free manner with a fluid handling pump (VICI® M6, Switzerland). Material for the sampling capillaries was Peek 1/16″ (ID of 50 μm). Finger-tight capillary connections (VICI®, Switzerland) were used between the connections. Each sample (sample volume of 200 μl) was withdrawn into a sampling loop before the pump A-channel, which was then emptied into a 500 μl Eppendorf tube by changing the pumping direction and by withdrawing Milli-Q water into the pump's B-channel. The liquid handling pump was controlled by motion control unit (M-Force) from Schneider Electric®. The M-force unit has i/o pins, which were utilized for trigger-functions of programmed (using its own programming language Mcode) pumping actions (infusion and withdrawal at the specific volume rate and volume). When some i/o pin was pulled to ground it triggered the pre-programmed pumping action. The volume rate of sampling was set to 5000 μl/min, which provided good consistency in results of sampling. After each sonicated sample, the sampling capillary line was flushed with 3 ml of MeOH and 3 ml of Milli-Q preventing carry-over effects (solvents are withdrawn through the B-channel into waste).
For chemical analysis of the samples Agilent® Ion Trap (6330) with electrospray ionization (ESI) source at positive polarity was used. Samples were introduced by direct infusion using a syringe pump (Harvard apparatus, PHD 2000) at a flow rate of 20 μl/min. Source parameters were as following: dry gas temperature 325° C., nebulizer pressure 15.0 psi and dry gas flow rate 5 l/min. Acquisition parameters of ion optics and trap are displayed in Table T2. Data was captured by averaging five spectra and using a rolling average of two. The m/z-range of acquiring data was set to start from m/z=50 to m/z=1000.
The following chemicals were used methanol (LC-MS Chromasolv®, Honeywell, Germany) and formic acid (98-100% for analysis EMSURE®, Merck KGaA, Germany) in the MS analysis. Marker was Sakura 130, black, Japan. The pre-tests black marker tip was dipped into 100% MeOH and diluted (1/100) into 20%, 40%, 60%, 80% and 100% MeOH (with 0.1% formic acid FA). As the MeOH concentration rises from 20% to 60% higher m/z (especially m/z=530) becomes more abundant, which rises from the improved solubility of the marker molecules to higher solvent content. The higher the MeOH concentration was the higher also becomes the abundance of non-relevant background ion peaks (contaminants e.g., from the ion source and capillaries). Therefore, a suitable solvent for this marker analyses was chosen to be the 60% MeOH+0.1% FA (acid for ionization efficiency).
During the sampling process the sampling capillary wash flushed after each HIFU excitation with three ml of 100% MeOH and three ml of Milli-Q water to prevent contamination of adjacent samples. Also, at least one ml of sampling fluid from the immersion bath was withdrawn through the sampling loop to secure the background stability (sampling loop contains a fully representative liquid background before each sample).
The sampling loop (200 μl) was emptied into a 500 μl Eppendorf tube. Immediately, a solvent plus acid mixture (300 μl, containing 100% MeOH+0.17% FA) was added into the Eppendorf for dissolving captured particles and the cap was closed. Tubes were labelled and stored at refrigerator (−18° C.) until they were analyzed by MS.
Data processing was performed with MATLAB® 2020b after the raw data (x,y) was exported using the Agilent Data Analysis for 6300 series Ion Trap LC/MS version 3.4 software. Generally, m/z spectra display only the raw data without any signal processing, but a simple background subtraction was performed to enhance the peaks arising from the marker for the sample taken during the HIFU excitation, from which the previously sampled (SN, foc. (focused)) mass spectrum was subtracted. If the subtracted signal intensity was negative, it was recorded as zero.
The HIFU generated desorption process was demonstrated by using a marker ink on top of an aluminium surface.
Chemical analysis of ultrasound desorbed surface material was performed by mass spectrometry using electrospray ionization. Liquid samples taken during and after HIFU excitation were analysed. Several adjacent samples were taken within the same samples and the abundance of two m/z peaks (530, 439) corresponding to a marker (Sakura 130) were determined.
The abundance levels of the two marker ions are presented in
Removal of Sharpie Fine Point Permanent Marker from a Sample Surface
Sharpie fine point marker (colour back or blue) was applied on top of a microscopy cover slide. The marked was allowed to dry and the slide was immersed into a water bath. A plurality of spots (spacing 1 mm) were removed by focusing HIFU to the slide surface using different US intensities. The distance h between the sample surface (here: interface between the sample and the fluid) and sampling capillary was adjusted to 2 mm. The samples were withdrawn (aspiration of pump) with 5 ml/min during the HIFU excitation. Sample volume was 200 μL. Samples were infused from the sampling capillary into an Eppendorf tube, diluted with HPLC/MS solvent (CH3CN:H2O; 1:1 (v/v)+0.1% by vol formic acid) and analysed by mass spectrometry.
The specific examples provided in the description above should not be construed as limiting the scope and/or the applicability of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20215787 | Jul 2021 | FI | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FI2022/050470 | 6/27/2022 | WO |
