iBB

Many metal nanoparticles exhibit plasmonic properties that can be explored in different applications. The synthesis of these nanoparticles often leads to a heterogeneous mixture in terms of sizes and shapes that needs to be fractionated to yield samples with narrow plasmon resonances. A simple method based on sucrose density gradient centrifugation has been proposed by BERG-iBB researchers and colleagues from Centro de Química Estrutural and Universidade de Aveiro for the fractionation of colloidal silver nanotriangles. The method affords particle fractions with surface plasmon resonances spanning from red to infrared spectral ranges that could be used to tune optical properties for plasmonic applications. The work is part of the PhD thesis of Rui Oliveira Silva and was published in Nanomaterials.

Porphyrins are typically weak emitters, which presents challenges to their optical detection by single-molecule fluorescence microscopy. A recent collaboration between BERG-iBB, Centro de Química Estrutural and Universidade Nova explores the enhancement effect of gold nanodimer antennas on the fluorescence of porphyrins in order to enable their single-molecule optical detection. Four meso-substituted free-base porphyrins were evaluated: two cationic, one neutral, and one anionic porphyrin. The gold nanodimer antennas are able to enhance the emission from these porphyrins by a factor of 10^5–10^6 increase in the maximum detected photon rates. This extreme enhancement is due to the combination of an antenna effect on the excitation rate that is estimated to be above 10^4-fold and an emission efficiency that corresponds to an increase of 2–10 times in the porphyrin’s fluorescence quantum yield. The work was published in the Journal of Physical Chemistry Letters, and is co-authored by David Botequim, Miguel Prazeres (BERG) and Pedro Paulo (CQE).