We attempt to predict the water contact angle (WCA) of self-assembled monolayers (SAMs) and protein adsorption on the SAMs from the chemical structures of molecules constituting the SAMs using machine learning with an artificial neural network (ANN) model. After training the ANN with data of 145 SAMs, the ANN became capable of predicting the WCA and protein adsorption accurately. The analysis of the trained ANN quantitatively revealed the importance of each structural parameter for the WCA and protein adsorption, providing essential and quantitative information for material design. We found that the degree of importance agrees well with our general perception on the physicochemical properties of SAMs. We also present the prediction of the WCA and protein adsorption of hypothetical SAMs and discuss the possibility of our approach for the material screening and design of SAMs with desired functions. On the basis of these results, we also discuss the limitation of this approach and prospects.

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We report a method to establish experimental conditions for tip-enhanced Raman spectroscopy (TERS) with low thermal and mechanical damage to samples. In this method, we monitor the thermal desorption of thiol molecules from a gold-coated probe of an atomic force microscope (AFM) via TERS spectra. Temperatures for desorption of thiol molecules (60-100 °C) from gold surfaces cover the temperature range for degradation of heat-sensitive biomaterials (e.g. proteins). By monitoring the desorption of the thiols on the probe, we can estimate the power of an excitation laser for the samples to reach their critical temperatures for thermal degradation. Furthermore, we also found that an active oscillation of AFM cantilevers significantly promotes the heat transfer from the probe to the surrounding medium. This enables us to employ a higher power density of the excitation laser, resulting in a stronger Raman signal compared with the signal obtained with a contact mode. We propose that this combinatory method is effective in acquiring strong TERS signals while suppressing thermal and mechanical damage to soft and heat-sensitive samples.

We report that the thermal stability of self-assembled monolayers (SAMs) of two isocyanide derivatives (1pentyl isocyanide and benzyl isocyanide) on a gold surface was drastically improved by their preparation at high temperature (373 K). In the case of conventionally prepared isocyanide SAMs, thermal desorption spectroscopy revealed that the isocyanides changed their adsorption states with corresponding increase in binding energy. The results of surface-enhanced Raman scattering spectroscopy measurements also clearly indicated the change in adsorption states at 373 K during heating. Theoretical calculations using density functional theory revealed that there are two stable adsorption states (atop and adatom configurations) and that the calculated vibrational energies are in good agreement with those observed in Raman spectra.

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Bacterial adhesion on material surfaces is a significant problem in many areas, especially on medical devices. Upon colonizing a surface, bacteria tend to form biofilms and become difficult to eradicate. A multistep process is involved in bacterial biofilm formation, including primary adhesion to material surface and accumulation of bacterial cells. Controlling the primary adhesion of bacteria is an efficient way to manage biofilms. This study focused on the primary adhesion of bacteria on a copolymer thin-film composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), 3-methacryloxypropyl trimethoxysilane (MPTMSi), and 3-(methacryloyloxy) propyl-tris(trimethylsilyloxy) silane (MPTSSi), which has antibiofouling and thickness and stiffness tunable properties. We modulated the thickness (5−90 nm) and stiffness of the thin-film via changing the polymer concentration in the coating solution (dip coating). All polymer thin-films inhibited Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa primary adhesions. Interestingly, S. aureus adhesion was affected by the thickness and/or stiffness of the thin-film. We conclude that the mechanical property of the thin-film is one of the influential factors determining bacterial adhesion. These findings would be of significance in designing antibacterial materials.