Abstract:
The invention provides a dual cell holder system that allows for the identical match of temperature conditions for both sample and reference simultaneously by providing two cells and a dual cell holder. The system is heated by a heating element and cooled by a Peltier, thus eliminating a significant source of humidity and the potential for leak from a water-cooling device or any of its hoses.

Description:
BACKGROUND OF THE INVENTION 
     The protein aggregation phenomena are prevalent throughout the industrial bioprocess. Proteins are expensive to express, isolate and purify due to their complex physical-chemical characteristics. Aggregation is considered a primary mode of protein degradation, often leading to immunogenicity in patients and a loss of efficacy. That is why the detection and determination of protein aggregates is a key point in the biopharmaceutical industry, as well as, in scientific research. The formation of protein aggregates is critical in industrial applications, because they can highly affect the production of protein therapeutics (i.e., biologics or biosimilars) effectively lowering the production yields. 
     U.S. Pat. No. 8,268,628 by Pastrana et al., teaches a method for determining the mechanism of aggregation and the amount of aggregation in protein, peptide or peptoid formulation, in solution or lyophilized state without the use of probes or additives by performing a novel FT-IR and 2DCOS analysis. FT-IR spectroscopy allows for a high degree of flexibility and speed in the determination of protein aggregates, with limited manipulation and without the use of exogenous probes. According to the &#39;628 method, a sample is heated and left to equilibrate followed by spectral acquisition at the desired temperature and by following the method described by the &#39;628 patent the determination of protein, peptide and peptoid, stability, aggregation and viability can be performed. The method has been applied to the study of lipids, membrane proteins, hydrophilic proteins, peptides and peptoids as a single component or in binary or ternary mixtures with other peptides, or lipid mixtures. When studying two protein components in a mixture or complex, one of the components must be isotopically labeled to allow for the simultaneous detection of each component. The flexibility of sample preparation, its potential for automation and data analysis are key elements of value for pharmaceutical protein formulation as illustrated in  FIG. 11 . 
     More specifically, the method described in the &#39;628 patent uses FT-IR spectroscopy combined with the two-dimensional correlation analysis (2DCOS) which allows for the determination of the presence of aggregates, the determination of the mechanism of aggregation, allowing for correction in the pipeline manufacturing process of the protein to once again generate viable protein. In addition, the thermal transition of the protein can also be determined and a 2DCOS plot generated to compare with the established viable protein, allowing for quality control, stability and viability of the desired protein product. The ease of sample preparation and data analysis allows for the automation of this method. 
     However, FT-IR accessories for thermal dependence studies where both reference and sample are under identical temperature conditions are not commercially available. Normally, a user would have to perform the analysis of the reference then the sample and at times also collect water vapor spectra and perform tedious data manipulation. 
     Thus, there is a long felt need in the art for an FT-IR accessory suitable for thermal dependence studies where both reference and sample are maintained under identical temperature conditions. 
     SUMMARY OF THE INVENTION 
     The invention provides a dual cell holder system that allows for the identical match of temperature conditions for both sample and reference. 
     According to an aspect of the invention, a dual cell holder system allows for the identical match of temperature conditions for both sample and reference for a stepwise shuttling between reference and sample during spectral data acquisition. 
     According to another aspect of the invention, a dual cell holder enhances the capability of: matching the desired temperature conditions for sample and reference, the instrument response, the detector response, and humidity conditions resulting in a significant improvement in the acquired spectral data quality with minimal data manipulation and baseline correction. 
     According to still another aspect of the invention, the time required for data analysis is dramatically reduced. 
     According to one aspect of the invention, the time saved in data manipulation can be invested in increased data acquisition times to enhance S/N ratio by increasing the number of scans. 
     According to another aspect of the invention, the device is heated by a heating element and cooled by a Peltier, thus eliminating a significant source of humidity (i.e., water bath) and the potential for leak from the water-cooling device or any of its hoses. 
     According to still another aspect of the invention, an interface is provided to allow for programming the method so as to run fully automated without the need of a user. 
     According to yet another aspect of the invention, the dual cell holder system is not limited to analyzing proteins, peptides or peptoids as described for example in the &#39;628 patent mentioned above, but may be used to analyze any liquid sample, lipid, or polymers during a thermal perturbation. 
     According to one aspect of the invention, the dual cell holder can be applied to the study of substances (organic or inorganic), materials or reagents, and liquids in general. 
     According to another aspect of the invention, the dual cell holder can be used in spectrophotometers where a shuttle or automated method of sampling is used. 
     According to still another aspect of the invention, the use of the dual cell holder is not limited to the infrared range, but can also be used in UV and visible range, circular dichroism (CD), vibrational circular dichroism, and Raman spectroscopies for the characterization of different materials and substances or excipients. 
     According to yet another aspect of the invention, the device for the FT-IR accessory is a self-contained demountable cell with a fixed path length that will not leak 
     According to one aspect of the invention, the dual cell holder is easily used with several thermal couples for accurate temperature reading, a single heating element and Peltier cooling system. 
     According to another aspect of the invention, the dual cell holder allows the sample and the reference to have similar temperature gradient and temperature equilibrium conditions making it ideal for protein analysis. 
     According to still another aspect of the invention, the samples that may be analyzed are not limited to proteins. Other excipients, such as liquids, organics or inorganic materials or reagents can also be analyzed within the temperature range limitations of the device of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention, in which: 
         FIG. 1  shows a front view of the dual cell holder, according to the present invention. 
         FIG. 2A  shows a top perspective view of a bottom part of the dual cell holder, according to the present invention. 
         FIG. 2B  shows a bottom perspective view of a bottom part of the dual cell holder, according to the present invention. 
         FIG. 3A  shows a top view of a bottom part of the dual cell holder, according to the present invention. 
         FIG. 3B  shows a front view of a bottom part of the dual cell holder, according to the present invention. 
         FIG. 3C  shows a bottom view of a bottom part of the dual cell holder, according to the present invention. 
         FIG. 4A  shows a top perspective view of a top part of the dual cell holder, according to the present invention. 
         FIG. 4B  shows a bottom perspective view of a top part of the dual cell holder, according to the present invention. 
         FIG. 5A  shows a top view of a top part of the dual cell holder, according to the present invention. 
         FIG. 5B  shows a front view of a top part of the dual cell holder, according to the present invention. 
         FIG. 5C  shows a bottom view of a top part of the dual cell holder, according to the present invention. 
         FIG. 6A  shows a cross-sectional view of a top part of a cell, according to the present invention. 
         FIG. 6B  shows a cross-sectional view of a bottom part of a cell, according to the present invention. 
         FIG. 6C  shows another view of a top part of a cell, according to the present invention. 
         FIG. 6D  shows another view of a bottom part of a cell, according to the present invention. 
         FIG. 7  shows a window, according to the present invention. 
         FIG. 8  shows another window with the sample, according to the present invention. 
         FIG. 9  shows a cross-sectional view of the cell enclosing the sample, according to the present invention. 
         FIG. 10  shows an exploded perspective view of the dual cell holder system, according to the present invention. 
         FIG. 11  illustrates the phases of a protein bioprocess. 
     
    
    
     Throughout the figures, the same reference numbers and characters, unless otherwise stated, are used to denote like elements, components, portions or features of the illustrated embodiments. The subject invention will be described in detail in conjunction with the accompanying figures, in view of the illustrative embodiments. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The dual cell holder system of the present invention comprises a substantially symmetrical dual cell holder  1  having two interlocking parts, top part  3  and a bottom part  2  as shown in  FIG. 1 . As can be seen, the dual cell holder  1  is designed to provide separate areas for positioning within both a sample and a reference at the appropriate distance from each other as required by a spectrometer. The shape and configuration of the dual cell holder  1  allows for the use of both active cooling and heating components. 
     The bottom part  2  of the dual cell holder  1  is further illustrated in  FIGS. 2A, 2B, 3A, 3B and 3C . The bottom part  2  is divided into two separate portions each one having a separate recessed receiving area  2   h  configured to receive the cell having either the reference or the sample. A solid middle section having a top surface  2   a  is provided to separate both receiving areas  2   h . Each receiving area of the bottom part  2  is provided with front and back openings configured in the preferred embodiment as semi-circular openings  2   g  coaxially aligned with its respective receiving area  2   h . As will be explained later in detail, these openings  2   g  are provided to allow an IR beam to have unobstructed access to the windows containing the reference and sample enclosed within the respective cells which in turn, are positioned inside the receiving areas  2   h . Guiding elements  2   m  are provided on the lateral sides of a back surface  2   c  so that when interlocked with the top part  3  the dual cell holder  1  is easily mounted on an existing sample shuttle of an FT-IR sample compartment. An opening  2   i  are provided on each side  2   e  and  2   f  of the bottom part as shown in  FIGS. 2A and 3A . These openings  2   i  are provided to allow unobstructed insertion of a temperature sensor such as a thermocouple that will contact the sample and reference for accurate temperature measurements. A bottom surface  2   b  of the bottom part  2  is provided with a recessed portion  2   l  configured to receive a cooling element for cooling the dual cell holder  1 . In a preferred embodiment of the invention, the cooling element is a Peltier element having a shape configured to match and to snuggly fit inside said recessed portion  2   l . A pass-through aligning opening is also provided on each side of the bottom part  2 , wherein one end  2   j  of the pass-through opening is located on the top surface  2   a  and the other end  2   k  of said pass-through opening is located on the bottom surface  2   b . These pass-through aligning openings are provided to receive a set of screws  10  that will provide proper alignment when the bottom part  2  is interlocked with the top part  3  the dual cell holder  1 . Also, the set of screws  10  can be used to fasten or clamp the top and bottom part together by means of nuts  9  as shown in  FIG. 10 . 
     The top part  3  of the dual cell holder  1  is further illustrated in  FIGS. 4A, 4B, 5A, 5B and 5C . As will be evident the configuration of the top part  3  is similar and symmetrical to the configuration of the bottom part  2  with the exception of some elements or portions that will be explained in detail below. The top part  3  is also divided into two separate portions each one having a separate recessed receiving area  3   h  configured to receive the cell having either the reference or the sample. A solid middle section having a top surface  3   a  is provided to separate both receiving areas  3   h . Each receiving area of the top part  3  is provided with front and back openings configured in the preferred embodiment as semi-circular openings  3   g  coaxially aligned with its respective receiving area  3   h . These openings  3   g  are provided to allow an IR beam to have unobstructed access to the windows containing the reference and sample enclosed within the respective cells which in turn, are positioned inside the receiving areas  3   h . Guiding elements  3   m  are provided on the lateral sides of a back surface  3   c  so that when interlocked with the bottom part  2  the dual cell holder  1  is easily mounted on an existing sample shuttle of an FT-IR sample compartment. An opening  3   i  are provided on each side  3   e  and  3   f  of the top part  3  as shown in  FIGS. 4A and 5A . These openings  3   i  are provided to allow unobstructed insertion of a temperature sensor such as a thermocouple that will contact the sample and reference for accurate temperature measurements. A bottom surface  3   b  of the top part  3  is also provided with a recessed portion  3   l  configured to receive a cooling element for cooling the dual cell holder  1 . A pass-through opening  3   n  passing through said top part  3  from a front surface  3   d  to a back surface  3   c  is provided to receive a heating element for heating the dual cell holder  1 . A pass-through aligning opening is also provided on each side of the top part  3 , wherein one end  3   k  of the pass-through aligning opening is located on the top surface  3   a  and the other end  3   k  of said pass-through aligning opening is located on the bottom surface  3   b . These pass-through aligning openings are provided to receive a set of screws  10  that will provide proper alignment when the bottom part  2  is interlocked with the top part  3  of the dual cell holder  1  as shown in  FIG. 10 . 
     The cell according to the invention is further illustrated in  FIGS. 6A, 6B, 6C, and 6D . The cell of the invention comprises a pair of interlocking circular parts  4  and  5  configured to form a chamber that securely encases a set of optically transparent windows allowing for the spectroscopic analysis of the desired sample and reference. A part  4  comprises a lid configured to be cover a part  5  comprising a housing configured to receive the set of windows containing the sample or reference. A mating threaded mechanism is provided on both parts  4  and  5  to selectively close and tighten the cell of the invention. A pair of coaxially aligned port openings  4   g  are provided around the periphery of said part  4  providing unobstructed access to an interior area  4   e  of said part  4 . A pair of coaxially aligned port openings  5   g  are also provided around the periphery of said part  5  providing unobstructed access to an interior area  5   e  of said part  5 . In operation, part  4  is positioned on top of said part  5  serving as a lid that is tighten until the set of port openings  4   g  are coaxially aligned with the set of port openings  5   g  of the part  5  so a temperature sensor is inserted into an interior area defined by the interior areas  4   e  and  5   e  for contacting the set of windows containing the sample or reference for measurement purposes. The part  4  further comprises a round opening  4   b  centrally positioned on a top surface  4   a  of the part  4 . The part  5  further comprises a round opening  5   b  centrally positioned on a bottom surface  5   a  of the part  5 . In operation, part  4  is positioned on top of said part  5  so that the round opening  4   b  is coaxially aligned with the round opening  5   b  of said part  5  to allow an IR beam to have unobstructed access to the windows containing the reference and sample enclosed within the respective cells. 
       FIGS. 7 and 8  illustrates the set of windows according to the present invention. A first window comprises an optically transparent window  6   a  and a second window comprises an optically transparent window  7   a  having a receiving portion  7   b  containing the sample or reference. 
       FIGS. 9 and 10  illustrates the complete cell containing the reference/sample and the dual cell holder of the invention in conjunction with said cell, respectively. The set of windows containing the sample/reference is positioned inside the part  5 , wherein a spacer  8  is also provide to ensure proper distance, alignment and securely position said windows within the cell. If needed a second spacer  8  could be provided or alternatively no spacer could be used. As can be seen, openings  4   g  and  5   g  are coaxially aligned to allow unobstructed access and contact with said windows  6  and  7 . 
     In operation, once the reference and sample cells are prepared as illustrated in  FIG. 9  each cell is inserted into the respective receiving areas  2   h  of the bottom part  2 . A retaining portion  2   n  is provided on each receiving area  2   h  so that a retaining tab  5   c  located on the bottom surface  5   a  of the cell is inserted and received inside said retaining portion  2   n  allowing said cell to be inserted in a single direction with respect to said receiving areas  2   h . Screws  10  are inserted into the aligning pass-through openings and are secured with nuts to maintain the parts  4  and  5  aligned during the installation process. Once the cells are positioned within the receiving areas, the cells are moved to ensure that the openings  4   g  and  5   g  are also coaxially aligned with openings  2   i  and  3   i  to allow insertion of a temperature sensor as previously explained. After all the openings are coaxially aligned the interlocking parts  4  and  5  are secured by the set of screws  10  and nuts  9  so that the dual cell holder is mounted into the machine by means of the guiding elements  2   m  and  3   m . The Peltier element is positioned in contact with the recessed portion  2   l  or  3   l  and the heating element is inserted into the pass-through opening  3   n.    
     The dual cell holder system of the present invention comprises two cells and a dual cell holder that are made of materials such as Aluminum or anodized Aluminum that effectively allow heat transfer to and from the sample and reference inside the cells. The cell of the invention comprises two interlocking parts containing a center hole with a preferred width of 2.5 cm to allow for the IR beam to access said sample and reference. 
     In order to provide an identical match of temperature conditions for both sample and reference for analysis the dual cell holder system of the present invention is used with additional components. An Ambient Temperature Controller is used to provide feedback about ambient temperature. A Contact Temperature Sensor is used to provide feedback about the cell holder temperature. A Heater element is used to apply heat energy to the cell holder. A Heater control circuit provides the required signals and power to the Heater element. A Thermoelectric element is used to remove heat energy from the cell holder. A Thermoelectric circuit is used to provide the required signals and power to the thermoelectric element. A Temperature Controller is provided to manage the thermoelectric control circuit and the heater element control circuit. The Controller takes decisions based on mathematical models to provide temperature control. A Communications System provides communication between the Temperature Controller and the Test System. It also keeps the synchronization of the operation between the systems. A Security System verifies operation parameters and interrupts power to the system in case the operation parameters turn dangerous. 
     In accordance with a method for accurate temperature control and sensing, the Temperature Controller receives the parameters of operation from the Communications System and saves it to an internal memory. The Temperature Controller loads any previously used operating corrections and sends a ready signal to the Communications System which in turns sends a start signal to the Temperature controller. The Temperature Controller starts a temperature feedback monitoring process where the current temperature is read and compared with a target temperature. A selection between a heating and cooling operation as well as the intensity of the operation is determined based on the comparison. The previous step is repeated periodically until a target temperature is reached. After completing a configurable stabilization period a ready signal is sent to the Communications Controller. This whole process is repeated until the test recipe is done and the Communication System sends an experiment done signal. Afterwards, the Temperature Controller verifies the temperature of the cell holder and applies any correction necessary for safe handling of the cell holder. The device of the present invention may be used for both qualitative and quantitative determination of the desired sample. The device allows for the use of different windows and path lengths enclosed in a cell. The device allows for accurate temperature control of both sample and reference simultaneously. 
     Although the present invention has been described herein with reference to the foregoing exemplary embodiment, this embodiment does not serve to limit the scope of the present invention. Accordingly, those skilled in the art to which the present invention pertains will appreciate that various modifications are possible, without departing from the technical spirit of the present invention.