Abstract
Diamond has excellent optical properties including broadband transmissivity, low self‐absorption, and a high refractive index, which have prompted its use for optical sensing applications. Thin‐film diamond strip waveguides (DSWGs) combined with tunable quantum cascade lasers (tQCLs) providing an emission wavelength range of 5.78–6.35 μm (1735–1570 cm−1) have been used to obtain mid‐infrared (MIR) spectra of proteins, thereby enabling the analysis of their secondary structure via the amide I band. Three different proteins were analyzed, namely bovine serum albumin (BSA), myoglobin, and γ‐globulin. The secondary structure of BSA and myoglobin has a major contribution of α‐helices, whereas γ‐globulins are rich in β‐sheet structures, which is reflected in the amide I band. A comparison of the spectra obtained via the combination of the tQCL and DSWG with spectra obtained using conventional Fourier transform infrared (FTIR) spectroscopy and a commercial diamond attenuated total reflection (ATR) element has been performed. It is shown that the main features evident in FTIR‐ATR spectra are also obtained using tQCL‐DSWG sensors.
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