Drastically Different Porphyrin Adsorption and Metalation Processes in Chemically Prepared and Laser-Ablated SERS-Active Silver Colloidal Substrates

Abstract

Processes of adsorption and metalation of a cationic water-soluble free base porphyrin, i.e., 5,10,15,20-tetrakis-(1-methyl-4-pyridyl)porphyrin (TMPyP) on Ag colloids have been monitored by surface enhanced resonance Raman spectroscopy (SERRS) as a function of time and porphyrin concentrations. Ag colloids employed were prepared either by laser ablation or by chemical reduction (by sodium borohydride and citrate) of Ag salts. SERRS intensities of TMPyP depend on the morphology of the colloidal aggregates in each system; aggregation, in turn, is governed by a balance between the so-called "diffusion limited aggregation" and "contact limited aggregation" processes, strongly influenced by the TMPyP concentration and the initial state of the colloidal particles (i.e. the residuals ions stuck at the substrate surface). The time evolution of the overall SERRS intensities is thus a function of the colloid preparation procedure. On the other hand, the kinetics of metalation reflects primarily the accessibility of the substrate surface for porphyrin adsorption. Consequently, it is highly sensitive to porphyrin concentration, the covering of the colloid surface by porphyrin molecules being the main qualitative limiting factor. Moreover, the process of metalation is controlled by residual ions at the substrate surface and therefore completely different for laser-ablated and chemically prepared Ag colloids. In the former, the amount of the metalated species is only limited by the adsorbate concentration while in the latter it is also mediated by the removal of residual ions from the colloidal surface by porphyrin molecules.

Raman Spectroscopy of Proteins and Nucleoproteins

“…Fitting of a theoretical model leads to additional data reduction [elimination of the spectral components S j (ν)]. In effect, the model is applied only to the relevant columns of the matrix V ij multiplied by their corresponding singular values W j (Prochazka et al, ; Hanus et al, ,b, ; Nemecek et al, ). Coefficients of the matrix ρ nj that are fitted along with parameters of the model can be used to construct Raman spectra of the individual spectral species Z n (ν).…”

Spacer‐free SERRS spectra of unperturbed porphyrin detected at 100 fM concentration in Ag hydrosols prepared by modified Tollens method

“…Figures (A) and (B) show that free base TMPyP SERRS signal (as determined on the basis of band assignments in) has been detected in concentrations varying from 1 × 10 –6 to 1 × 10 –13 M in the final system (for experimental details see supporting information). Such a broad range of TMPyP concentrations is intentionally presented because it is well‐known that TMPyP metalation is easier and faster below its concentration of monolayer coverage . The monolayer coverage TMPyP concentration in a particular system strongly depends on the size and type of Ag nanoparticles .…”

“…For the sake of an unambiguous determination of a porphyrin type in an investigated system, a selective method has to be chosen. Surface‐enhanced resonance Raman scattering (SERRS) spectroscopy is an efficient tool for fulfilling both requirements at once as it has been clearly demonstrated in the literature already . The metalation of a free base porphyrin molecule, i.e.…”

“…Taking into account the results of Procházka et al . the TMPyP metalation process can be controlled by the presence of ions at the Ag nanoparticle surface.…”

Binding of Platinum Complexes to DNA Monitored by Raman Spectroscopy

“…Time evolutions of the changes in the Raman spectra after addition of cisplatin were analyzed using advanced multivariate statistical methods [3,4] to reveal minimal number of spectroscopically distinguishable species present in the mixture. Time evolutions of the changes in the Raman spectra after addition of cisplatin were analyzed using advanced multivariate statistical methods [3,4] to reveal minimal number of spectroscopically distinguishable species present in the mixture.…”