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High-Sensitivity IR Spectroscopy


New biological drugs such as peptide drugs and vaccines are emerging to fill pharmaceutical voids.  They are typically prepared in water-based buffers at lower concentrations (0.1 mg/mL to 10 mg/mL) with less structural stability as compared to other biologicals (e.g., monoclonal antibodies).  However, water interference prevents commonly used infrared (IR) spectroscopy-based characterization methods from working at these low concentrations.  We are developing a new IR-based approach that overcomes this problem to quantify these drugs in their final preparations.


Infrared (IR) absorption spectroscopy has been used widely as a non-invasive, label-free characterization method for chemical identification and structure of biomolecules. Fourier-transform IR (FT-IR) technology is commonly used to characterize proteins and other biological molecules produced during biopharmaceutical processes. FT-IR is advantageous because it does not require additional sample preparation steps, such as buffer exchange and dilution, which are needed for other techniques like far-ultraviolet (UV) circular dichroism (CD) spectroscopy.

Extensive studies on IR spectroscopy of proteins have shown that the amide bands can be used to semi-quantitatively characterize the secondary structure (e.g., a-helix and b-sheet) of the protein backbone conformation. However, the interference by strong water absorption keeps FT-IR from characterizing low concentration samples of <10 mg/mL and prevents the usage of a long-pathlength optical cell. Non-invasive optical characterization of low-concentration protein samples is critical for new types of drugs, such as peptide drugs (typically 1 mg/mL) and vaccines (0.1 mg/mL to 10 mg/mL).

Recently, we have developed a new mid-IR absorption spectroscopy using a quantum cascade laser (QCL) technology that can detect the amide I band of a protein solution with 100 times better chemical sensitivity compared to traditional mid-IR. The technology was recently awarded a patent [1].

Figure 1
Figure 1. Comparison of conventional and spectrum-engineered IR approaches. The displayed IR spectra were acquired from a bovine serum albumin (BSA, 10 mg/mL) solution with the pathlength of 25 mm using a home-built QCL-IR spectroscopy system [1].


[1] Y. J. Lee, Spectrum Adjuster and Producing a Pure Analyte Spectrum. US Patent Appl. No. 16,164,859. (2018).

Created May 15, 2019