The temperature ramps applied throughout the experiment validating the reversibility of the behavior described above are shown in Fig. and the corresponding regions of SERS spectra obtained for thus prepared samples are presented in Fig. . It can be seen that the spectra obtained for samples with a temperature change occurring between addition of cysteine aliquots (two middle curves in Fig. ) resemble the spectrum of the sample thermostated continuously at a lower temperature of 40 °C (bottom spectrum in Fig ). This is a strong indication that the SERS spectral profile (and by extension: the composition of the surface monolayer) is determined by the temperature at which the second cysteine aliquot was added. These observations along with the results of the two-step adsorption experiments at various temperatures suggest that the cysteine layer on AgNPs may, at a temperature higher than 25 °C, undergo a phase transition to a state in which a rapid exchange with the solution can occur. Such a phase transition seems to be reversible, since the SERS spectrum obtained for the cooled sample resembles that of the sample prepared at a lower temperature (see Fig. ). In addition, a phase transition is a more likely explanation for the observed behavior than overcoming the kinetic barrier of the exchange by increasing the temperature, as the relative temperature rise required here in order to elicit the exchange is smaller than 12% in the Kelvin scale. This relatively minor increase is unlikely to be the sole reason for the observed abrupt activation of the monolayer for the exchange between the surface and the solution, especially as the thiolate monolayers tend not to desorb at that temperature range 103 . Reported experiments performed for cysteine adsorbed in ultrahigh vacuum (UHV) on Au crystalline surfaces showed that such layers are stable up to at least 80 °C104,105 . Desorption of cysteine multilayers from Ag(111) obtained in UHV was observed at 60 °C, however, the first monolayer was stable up to 120 °C106 . Cysteine adsorbed from the solution onto planar gold had negligible desorption at room temperature as well 107 . Computational simulations showed comparable results, as cysteine adsorbed on Au(111), according to DFT, did not desorb upon heating up to 400 K, although it became more mobile 108 . Although some desorption of glutathione from the surface of AgNPs was observed already at the room temperature, it occurred at a timescale of hours rather than minutes 109 .