Marek Procházka

Metalation of 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)porphyrin in silver colloids studied via time dependence of surface‐enhanced resonance Raman spectra

In SERS-active systems, when a free base porphyrin is adsorbed at a roughened metal surface, the metal ion may be incorporated into the porphyrin core. We have investigated the metalation kinetics of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP), reflected in the time evolution of its SERRS spectra. To establish proper metalation Raman markers, resonance Raman spectra of the free base and chemically Ag metalated TMPyP forms were measured under different conditions. The increase in intensity of the 395 cm-1 line, the decrease in intensity of the 329 cm-1 line, the reduction of the 1337+1360 cm-1 doublet to one strong line at 1340 cm-1 and the vanishing of the 1140 cm-1 medium line (the last exceptionally for 514.5 nm excitation) were found to be suitable markers for quantitative analysis. All other spectral changes related to metalation may coincide with effects caused by other variations of the porphyrin state. Time evolution of the porphyrin metalation was studied in various Ag colloid systems, with or without phosphate anions, citrate and/or Triton X-100. Time-dependent SERRS spectra of TMPyP were recorded within periods from minutes to several hours. Factor analysis of the SERRS spectra proved that the spectral changes were induced by only one phenomenon (metalation). The SERRS spectra were decomposed into the spectrum of the free base TMPyP and that of its Ag metalated form, and the metalation kinetics were determined by means of the time dependence of the metalated form portion in the SERRS spectrum. The results show a remarkable reliance on the state of the metal surface.

Laser ablation: Preparation of “chemically pure” Ag colloids for surface-enhanced Raman scattering spectroscopy

“Chemically pure” Ag colloids as active surfaces for surface-enhanced Raman scattering (SERS) spectroscopy were prepared by laser ablation of an Ag foil in pure water, in the presence of Cl− anions, and in the presence of an adsorbate. SERS-activity of the ablated colloids was proved using 2,2′-bipyridine [bpy] and phtalazine [pht] as adsorbates. Moreover, a SERS-active Ag colloid/adsorbate system was prepared by laser ablation of Ag foil immersed in an aqueous solution of pht. SERS spectra of pht obtained from this system are identical with those of pht added to Ag colloid ablated in pure water. The possibility of preparing a SERS-active system by laser ablation of Ag in the presence of an adsorbate was thus demonstrated. Furthermore, Ag colloid-bpy films were prepared from the laser ablated colloids and their SERS activity proved by obtaining a good quality SERS spectra of bpy.

Testing anionic spacers by SERRS (surface-enhanced resonance Raman scattering) of a cationic free-base porphyrin in systems with laser-ablated Ag colloids

Abstract Thiopheneacetic acid and several thiol-based anionic species were tested as prospective spacers between the surface of Ag colloidal particles (prepared by laser ablation) and a chromophoric cationic adsorbate. Time-evolution of the SERRS signal of a cationic free base porphyrin, 5,10,15,20-tetrakis(1-methyl-4-pyridiniumyl)porphine (H 2 TMPyP) attached to the surface of laser-ablated Ag colloidal particles modified by adsorption of either 3-thiopheneacetic acid or a thiol-based anionic species was measured on 2 h time-scale and analyzed. While H 2 TMPyP adsorbed on bare surfaces of laser-ablated Ag colloidal particles is rapidly converted into AgTMPyP surface complex (spectrally identical with its synthetic analogue), denaturation of the native structure of the porphyrin by formation of the same AgTMPyP surface species was not observed upon adsorption on the modified colloidal surfaces. The native structure of H 2 TMPyP was fully preserved upon adsorption on Ag colloid modified by 3-thiopheneacetic acid and good quality SERRS spectra of H 2 TMPyP were obtained from Ag colloid/3-thiopheneacetic acid/H 2 TMPyP system. By contrast, none of the thiol-based spacers enabled to obtain SERRS spectrum of unperturbed H 2 TMPyP. Modification of Ag colloid by 3-mercaptopropionic acid, 2-mercaptoethanesulfonic acid, 2-mercaptoethanesulfonate and 3-mercaptopropanesulfonate did not prevent metalation of the porphyrin, however, it affected the structure of the resulting AgTMPyP surface complex, as witnessed by the difference of the characteristic marker bands (384, 1005, 1366 and 1566 cm −1 ) from those of synthetically prepared AgTMPyP. Modification of the colloid by mercaptoethanol prevents porphyrin metalation, however, it induces another kind of perturbation of the native structure of H 2 TMPyP.

SERS Microspectroscopy of Biomolecules on Dried Ag Colloidal Drops

We report the application of dried Ag hydroxylamine-reduced colloidal drops to surface-enhanced (resonance) Raman scattering (SE(R)RS) study of biomolecules using Raman microspectroscopy. 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP), amino acid tryptophan, and phospholipid 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) served as testing biomolecules. Ag colloid/biomolecule drop dried on glass support forms a ring in the edge part of the drop in which almost all nanoparticles are clustered. This specific drying process promotes adsorption of the studied biomolecules in highly enhancing sites (“hot spots”) as well as concentrates them in the ring. We were able to obtain SE(R)RS spectra from the ring that cannot be acquired directly from Ag colloidal solutions (SERRS spectrum of 1×10−10 M TMPyP by 1 s accumulation time, SERS spectrum of 2×10−7 M DSPC). Despite the spectral irreproducibility and problems with spurious bands in some cases, SERS microspectroscopy of studied biomolecules using dried Ag colloid/adsorbate systems improves SERS applicability and sensitivity in comparison to measurements directly from Ag colloidal solution.

Metallation kinetics of a free base porphyrin in surface-enhanced resonance Raman scattering active Ag colloid system as a probe of porphyrin–nucleic acids interaction

Abstract Complexes of the cationic free base 5,10,15,20-tetrakis (1-methyl-4-pyridyl) porphyrin with DNA, double-stranded poly(dA-dT) and poly(dG-dC) polynucleotides have been studied by using surface-enhanced resonance Raman scattering spectroscopy (SERRS). SERRS spectra of these complexes have been recorded during time-scale varying from minutes to days, and the differences in the course of the porphyrin metallation, indicating different accessibility of the metal surface for the porphyrin core in the case of particular complexes, have been monitored. The results obtained for the three studied systems are in very good agreement with the expected dominant types of the porphyrin interaction with the nucleic acids, i.e., intercalation in the case of poly(dG-dC) and external binding in the case of poly(dA-dT).

METALATION OF POSITIVELY CHARGED WATER SOLUBLE MESOPORPHYRINS STUDIED VIA TIME-RESOLVED SERRS SPECTROSCOPY

Abstract Time-resolved SERRS spectra of 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]21 H ,23 H -porphine (TMAP) were recorded (using a multichannel Raman spectrometer) in various SERS-active Ag colloid/porphyrin systems. Data treatment based on a factor analysis was used to decompose all the SERRS spectra into two main components: SERRS spectrum of the free base TMAP and that of its Ag metalated form. The metalation kinetics obtained in this way was found to be highly dependent on the presence of phosphate anions, citrate and/or Triton X-100 in the colloidal system. The results are analogous to those previously obtained for 5,10,15,20-tetrakis(1-methyl-4-pyridyl)21 H ,23 H -porphine, a porphyrin with a substantially stronger tendency towards metalation.

Colloidal systems of silver nanoparticles and high-regioregular cationic polythiophene with ionic-liquid-like pendant groups: Optical properties and SERS.

We report tuning of structure dependent optical properties of colloidal systems of borate-stabilized silver nanoparticles (Ag NPs) and polythiophene-based cationic polyelectrolyte with ionic-liquid like side groups: poly{3-[6-(1-methylimidazolium-3-yl)hexyl]thiophene-2,5-diyl bromide} (PMHT-Br) towards obtaining local electromagnetic field enhancement effects. Surface-enhanced Raman scattering (SERS) studies showed that the strong electromagnetic field enhancement is related to the formation of aggregates of Ag NPs achieved at the components ratio providing the charge balance between Ag NPs and cationic polythiophene, at which Ag NPs are nearly single-polymer-layer coated, their zeta potential is close to zero and they easily form aggregates in which the mean inter-particle distance enables the occurrence of desired plasmonic effects. Fluorescence quenching is efficient only in the systems with low concentrations of PMHT-Br, in which almost all polymer chains directly interact with the Ag NPs surface.

Surface-enhanced resonance Raman spectroscopy of porphyrin and metalloporphyrin species in systems with Ag nanoparticles and their assemblies.

The advantages of systems with Ag nanoparticles and their assemblies for surface-enhanced resonance Raman scattering (SERRS) spectral investigation, detection and determination of porphyrin species are demonstrated. SERRS spectral detection limits of the testing porphyrin species (including porphyrin aggregates) in these systems are shown to be, on average, 10(2)-10(3) lower than detection limits by resonance Raman scattering (RRS). Systems with Ag nanoparticles modified by anionic organosulfur spacers enable us to obtain SERRS spectra of unperturbed cationic porphyrin species. In the case of thiopheneacetate-modified Ag particles prepared by laser ablation, no negative effect of the spacer on the spectral detection limit of the porphyrin was observed. Systems with isolated Ag nanoparticles allow for obtaining SERRS spectra of porphyrin species upon excitation into the Soret electronic absorption band which leads to at least a 10-fold decrease in the detection limit.

Drop coating deposition Raman spectroscopy of liposomes: role of cholesterol.

Drop coating deposition Raman (DCDR) spectroscopy was used to study liposomes (DPPC and asolectin) with growing proportion of cholesterol. Deposited samples of both liposomes on special hydrophobic surface formed a dried drop with a circular shape with a ring of concentrated liposomes at the outer edge. The presence of cholesterol in liposome causes a diminishing of the drop size and an increasing in diameter of the ring, but DPPC with 20% of cholesterol forms the compact drop without the ring. Raman spectra contain characteristics of both lipids and cholesterol, liposomes do not change their initial phase state after drying. Spectral mapping shows that maximum Raman intensity originated from the inner part of the ring. Our results suggest that DCDR spectroscopy can be used for studying lipids containing cholesterol in situ.

Concentration dependent behavior of the free base porphyrins in Ag colloid/porphyrin SERS-active system studied via the metalation kinetics

Abstract Metalation of 5,10,15,20-tetrakis(1-methyl-4-pyridyl) porphyrin (TMPyP), adsorbed on laser-ablated Ag colloid was investigated as a function of the porphyrin concentration. Factor analysis and further treatment of the results provided parameters of the metalation kinetics. High sensitivity to the concentration of the TMPyP molecules was demonstrated when qualitative differences were obtained for the concentrations below and above the covering limit.