Mid-infrared enhanced spectrochemical detection using azide vibrational probes

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Biophysics

Background:

• Trace element analysis in complex matrices is vital but challenged by background interference and low detection limits.
• Surface Enhanced Infrared Absorption (SEIRA) spectroscopy offers label-free detection of analytes via bioreceptor interactions.
• Existing SEIRA methods require improvement for enhanced sensitivity and specificity in complex samples.

Purpose of the Study:

• To develop and demonstrate an advanced mid-infrared SEIRA spectroscopy method for sensitive trace element detection.
• To utilize a pixeled SEIRA substrate with a specific infrared-active vibrational probe for improved signal-to-noise ratio.
• To validate the method's efficacy using a model system of an antibody fragment and its antigen.

Main Methods:

• Development of a pixeled SEIRA substrate for enhanced signal transduction.
• Site-specific labeling of a model bioreceptor (trastuzumab Fab') with a small azide moiety (azidoacetic acid) as a vibrational tag.
• Application of mid-infrared SEIRA spectroscopy to monitor bioreceptor immobilization and detect the target analyte (Her2 antigen).

Main Results:

• The azide tag's spectral signature (around 2100 cm^-1) is located in a cell- and protein-silent spectral window.
• The small size of the azide tag minimally impacts the bioreceptor's structure and biological function.
• The developed method achieved detection of Her2 antigen at concentrations as low as 83 amol within a 100 μm² area.

Conclusions:

• The advanced mid-infrared SEIRA spectroscopy method, utilizing a pixeled substrate and azide vibrational probe, significantly enhances sensitivity for trace analyte detection.
• This technique provides a label-free, highly sensitive platform for analyzing soluble analytes in complex biological and chemical matrices.
• The method holds promise for applications in diagnostics, drug development, and environmental monitoring where ultralow concentration detection is critical.