The plasmonic properties of Au nanoparticles (AuNP), which allow the observation of enhanced spectroscopic effects, are strongly affected by the aggregation and precipitation caused by the strong interactions between nanoparticles. To avoid AuNP aggregation and precipitation, the present study proposes coating with MnO2, forming AuNP@MnO2 core-shell structures. The MnO2 layers presented 1-10 nm thickness so that highly surface-enhanced fluorescence was obtained with maximum intensity given by 5 nm thick MnO2. The decrease in Raman intensity could be controlled, despite the inherent reduction in surface-enhanced Raman scattering (SERS) intensity with increasing adsorbate-surface distance. The decrease in Raman intensity was compensated by increasing AuNP stability caused by the MnO2 shell.

There is still a significant need for low cost, fast and trustworthy diagnostic devices based on biosensors, which may impact positively for applications in developing countries. Localized surface plasmon resonance (LSPR) based biosensors have been taken as powerful alternative to deal with the above limitations. The local electromagnetic field enhancement caused by the LSPR in metallic nanomaterials allows the emergence of the surface enhanced Raman scattering (SERS) effect, which have recently been applied as biosensing platforms. In the present report, gold nanorods (AuNRs) were synthesized and modified with a sandwich immunoassay to detect bovine serum albumin antibody (anti-BSA). The sensitivity of the platform was evaluated by the extrinsic SERS signal from AuNRs in solution phase with added Nile blue as reporter molecule (AN-S-AuNRs), which was subsequently modified with bovine serum albumin (BSA); the assay consisted on capturing BSA modified AN-S-AuNRs by anti-BSA molecules immobilized on AuNRs on glass slides (AuNRs-chip). SERS mapping evidenced the analyte detection based on the substantial increase in the positive events with SERS signal of the reporter molecule in the presence of anti-BSA compared to the assay in the absence of the antibody. The present study may potentially guide the construction of efficient SERS immunosensors.

One of the goals of this manuscript is to celebrate the forty years of the SBQ (Sociedade Brasileira de Química). We believe using historical analysis could benefit our researchers to overcome the challenges ahead, look into the future, to the scientific progress and the way science increases its problem-solving ability. There are several topics covered by the challenges in Physical Chemistry: nanoscience and nanotechnology, single molecule studies, gas phase photochemistry and photophysics, molecular structure, spectroscopy, reaction dynamics, interfacial phenomena, energy, and so on. However, the critical challenge for our Division still is to create a desired link between experimental approaches and theoretical knowledge.

Complexos do tipo trans-[Ru(L)(NH3)4(L’)](PF6)n, onde L = 4-cianopiridina (CNpy), NCS-, CN-, e L’ = CNpy, 1,4-ditiano (1,4-dt), 4-mercaptopiridina (pyS) e tionicotinamida (tna), foram sintetizados e caracterizados. SAMs sobre ouro formadas com os complexos que contêm ligantes sulfurados foram estudadas por desorção redutiva e espectroscopia SERS. Dependendo da natureza do ligante L’, a capacidade retiradora do ligante CNpy mostrou ser forte o suficiente para oxidar parcialmente o átomo de rutênio e, em consequência, deslocalizar densidade eletrônica s do ligante localizado em posição trans. Os resultados de desorção redutiva mostraram que a estabilidade das SAMs formadas está diretamente relacionada a este efeito.

Trans-[Ru(L)(NH3)4(L’)](PF6)n type complexes, where L = 4-cyanopyridine (CNpy), NCS-, CN-, and L’ = CNpy, 1,4-dithiane (1,4-dt), 4-mercaptopyridine (pyS) and thionicotinamide (tna), were synthesized and characterized. SAMs on gold of the complexes containing sulfur were studied by reductive desorption and SERS spectroscopy. Depending on the nature of L’, the withdrawing capability of the CNpy ligand is strong enough to partially oxidize the ruthenium atom and, as a consequence, delocalize the s electronic density from the trans located ligand. The reductive desorption results showed that the stability of the SAMs is directly related to this effect.

O processo redox da metaloproteína cyt c foi observado através da utilização de eletrodos de ouro modificados com os complexos [Ru(CNPy)(NH3)4(1,4-dt)]2+ e [Ru(CNPy)(NH3)4(pyS)]2+ , onde CNPy = 4-cianopiridina, pyS = 4-mercaptopiridina e 1,4-dt = ditiano. Os valores dos potenciais redox observados indicam a forma in natura da proteína. A forma dos voltamogramas, todavia, é dependente da conformação do complexo modificador sobre a superfície que, por sua vez, foi determinada por SERS. Os potenciais de dessorção redutiva, observados em -0,52 e -0,64 V vs Ag|AgCl|Cl- para os complexos [Ru(CNPy)(NH3)4(1,4-dt)]2+ e [Ru(CNPy)(NH3)4(pyS)]2+ , respectivamente, são indicativos do tipo de ligação com a superfície e da capacidade pi retiradora do ligante CNpy.

The redox process of the cyt c metalloprotein was assessed by the cationic SAMs formed with [Ru(CNPy)(NH3)4(1,4-dt)]2+ and [Ru(CNPy)(NH3)4(pyS)]2+ complexes on gold, where CNPy = 4-cyanopyridine, pyS = 4-mercaptopyridine and 1,4-dt = dithiane. The observed cyt c redox potentials are indicative of the native protein form. The voltammograms, however, were observed to be affected by the conformation of the modifiers, determined by SERS spectroscopy. The [Ru(CNPy)(NH3)4(pyS)]2+ complex, which exhibits trans conformation on the surface, presented a well-defined voltammogram. On the other hand, the gauche conformation of the [Ru(CNPy)(NH3)4(1,4-dt)]2+ SAM seems to make the assessment of the cyt c hET reaction difficult. The reductive desorption potentials, at -0.52 and -0.64 V vs Ag|AgCl|Cl- for the [Ru(CNPy)(NH3)4(1,4-dt)]2+ and [Ru(CNPy)(NH3)4(pyS)]2+ SAMs, respectively, are indicative of the bonding mode with the surface and the pi withdrawing capability of the CNpy ligand.