We present a procedure for the synthesis and purification of p-phenylenediamine-based carbon dots that can be used for the recognition of Fe(III) ions. Carbon dots have an approximately spherical shape with an average size of 10 nm and are composed of a carbonaceous core surrounded by functional groups attached to it, both of which are responsible for their dual fluorescence properties. The emission bands have a different behavior, with a blue band dependent and a red emission independent of the excitation wavelength, respectively. Red emission is appropriate for the detection of ions and other molecules in biological environments because this high wavelength prevents the occurrence of processes such as resonance energy transfer and internal filter effects. In particular, the presence of Fe(III) ions produces an important quenching phenomenon that can be applied to the fabrication of a sensor. The platform is very sensitive, with a detection limit of 0.85 µM, which is within the lowest values reported for this ion, and a high selectivity that is believed to be due to the formation of a specific complex in the ground state through specific interactions of Fe (III) ions with pyridinic and amino groups on the surface of the nanomaterials.

The immobilization of biocatalysts on inorganic supports allows the development of bio-nanohybrid materials with defined functional properties. Gold nanomaterials (AuNMs) are the main players in this field, due to their fascinating shape-dependent properties that account for their versatility. Even though incredible progress has been made in the preparation of AuNMs, few studies have been carried out to analyze the impact of particle morphology on the behavior of immobilized biocatalysts. Herein, the artificial peroxidase Fe(III)-Mimochrome VI*a (FeMC6*a) was conjugated to two different anisotropic gold nanomaterials, nanorods (AuNRs) and triangular nanoprisms (AuNTs), to investigate how the properties of the nanosupport can affect the functional behavior of FeMC6*a. The conjugation of FeMC6*a to AuNMs was performed by a click-chemistry approach, using FeMC6*a modified with pegylated aza-dibenzocyclooctyne (FeMC6*a-PEG₄@DBCO), which was allowed to react with azide-functionalized AuNRs and AuNTs, synthesized from citrate-capped AuNMs. To this end, a literature protocol for depleting CTAB from AuNRs was herein reported for the first time to prepare citrate-AuNTs. The overall results suggest that the nanomaterial shape influences the nanoconjugate functional properties. Besides giving new insights into the effect of the surfaces on the artificial peroxidase properties, these results open up the way for creating novel nanostructures with potential applications in the field of sensing devices.

In this work, the methoxy terminated oligo- and polyethylene glycol of different chain lengths (EGn, n = 7, 18, 45 and 136) is grafted on AuNP surfaces under conditions where they attain maximum grafting densities. These EGn–AuNPs gain stability relative to the pristine c-AuNPs in aqueous solutions and in a wide temperature interval and they form stable suspensions in solutions of high NaCl concentrations. To show the thermoresponsive properties of these EGn–AuNPs, temperature titration experiments are carried out in the presence of increasing amounts of salts. The concentrations of NaCl are chosen by checking the stability of EGn–AuNPs at room temperature and choosing the highest concentrations that allow them to form stable suspensions. The analysis of the temperature titration experiments monitored by UV-visible spectroscopy and dynamic light scattering allows us to establish the existence of transitions from individual to assembled nanoparticles, the reversibility of the temperature transitions and hysteretic behaviour in these systems. While EG7–AuNPs only show reversible temperature transitions in the presence of 5 mM NaCl, EG18–AuNPs do up to 1 M NaCl, becoming only partially reversible in 2 M NaCl. The titrations of EG45–AuNPs in 3 and 5 M NaCl show irreversible temperature transitions. Finally, EG136–AuNPs present a complex and interesting behaviour with two temperature transitions, the first one showing hysteresis and the second being reversible.

Research into the use of nanoparticles to enhance the delivery and efficacy of polyphenols is a topic of growing interest in the fields of nanotechnology, pharmacology and food science. Nanoparticles, due to their small size and high surface area, can improve the stability, solubility and bioavailability of polyphenols. Combining polyphenols with other bioactive compounds within nanoparticles can create synergistic effects, enhancing their overall therapeutic potential. In this work, we present a new polyethylene glycol (PEG) capping ligand modified with caffeic acid (CA), HS‐PEG‐CA and two types of gold nanoparticles: (i) coated with a PEG‐thiol derivative functionalized with CA (HS‐PEG‐CA) (homofuncionalized NP) and (ii) HS‐PEG‐CA cationic carbosilane dendrons with antibacterial properties (heterofuncionalized NP). The antioxidant capacity of the CA, in three systems, has been studied by different techniques such as FRAP, DDPH and cyclic voltammetry, demonstrating that it is preserved when it is supported on the NP and increases when it is part of the PEG ligand. In addition, heterofuntionalized NP showed activity against S. aureus and HS‐PEG2K‐CA ligand can effectively anchor to gold substrates.