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Boron-doped diamond (BDD) has been modified with bare gold nanoparticles (AuNPs) for the investigation of bovine serum albumin (BSA) protein films. First, the BDD electrode was amino- terminated via silanization with (3-aminopropyl)triethoxysilane (APTES). Then, the AuNPs were synthesized using a stainless steel-assisted method, and immobilized at the APTES-modified BDD surface (BDD/APTES/AuNPs). The resulting morphology of both modification steps was characterized using atomic force microscopy (AFM). Besides, the synthesis of AuNPs was in-situ monitored via infrared attenuated total reflection (IR-ATR) spectroscopy using a combined IR-ATR-EC-AFM system taking advantage of surface enhanced IR absorption (SEIRA) effects induced by the AuNPs. The modified conductive IR-ATR BDD waveguide was employed to investigate spectroelectrochemically films of globular and fibrilized BSA, which were deposited onto the AuNPs-modified surface. SEIRA spectroscopy enabled the discrimination between globular and fibril aggregates of BSA via curve fitting of amide I band revealing a major contributions of crossed b-sheet structures within the fibril aggregates. Finally, preliminary square-wave voltammetry experiments showed that the spectroelectrochemical setup has potential for in-situ electrochemical characterization of such protein films., acceptedVersion

Diamond has excellent optical properties including broadband transmissivity, low self- absorption and a high refractive index, which have prompted its use in 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 -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., submittedVersion