Porphyrin-based sensor nanoarchitectonics in diverse physical detection modes

Porphyrins and related families of molecules are important organic modules as has been reflected in the award of the Nobel Prizes in Chemistry in 1915, 1930, 1961, 1962, 1965, and 1988 for work on porphyrin-related biological functionalities. The porphyrin core can be synthetically modified by introduction of various functional groups and other elements, allowing creation of numerous types of porphyrin derivatives. This feature makes porphyrins extremely useful molecules especially in combination with their other interesting photonic, electronic and magnetic properties, which in turn is reflected in their diverse signal input-output functionalities based on interactions with other molecules and external stimuli. Therefore, porphyrins and related macrocycles play a preeminent role in sensing applications involving chromophores. In this review, we discuss recent developments in porphyrin-based sensing applications in conjunction with the new advanced concept of nanoarchitectonics, which creates functional nanostructures based on a profound understanding of mutual interactions between the individual nanostructures and their arbitrary arrangements. Following a brief explanation of the basics of porphyrin chemistry and physics, recent examples in the corresponding fields are discussed according to a classification based on physical modes of detection including optical detection (absorption/photoluminescence spectroscopy and energy and electron transfer processes), other spectral modes (circular dichroism, plasmon and nuclear magnetic resonance), electronic and electrochemical modes, and other sensing modes.

A Simple and Sensitive Colorimetric Detection of Silver Ions Based on Cationic Polymer-Directed AuNPs Aggregation

This paper describes a simple and sensitive colorimetric sensor employing single-stranded DNA (ssDNA) ligand, cationic polymer, and gold nanoparticles (AuNPs) to detect silver ions. The positively charged polymer can electrostatically interact with ssDNA and destroy the charge balance leading to induction of AuNP aggregation. Silver ions (Ag+) can bind to cytosine (C)-rich nucleic acids to form the C-Ag+-C hair-pin structure, which can prevent its interaction with polymers. The resulting cationic polymer could aggregate AuNPs causing a remarkable change in colour. The concentration of Ag+ can be determined visually. This sensing platform exhibits high sensitivity and selectivity towards Ag+ versus other metal ions, with a detection limit of 48.6 nM. The assay did not require any labelling or modifying steps. This method is simple, effective, and convenient and can in principle be used to detect other metal ions or small molecules.