Pyranine-Modified Amphiphilic Polymer Conetworks as Fluorescent Ratiometric pH Sensors.

The fluorescent dye 8-hydroxypyrene-1,3,6-trisulfonate (pyranine) combines high photostability with ratiometric pH detection in the physiological range, making it a prime candidate for optical sensors in biomedical applications, such as pH-based chronic wound monitoring. However, pyranine's high water solubility and the difficulty of covalent attachment pose severe limitations in terms of leaching from sensor matrices. Herein, pyranine-modified nanophase-separated amphiphilic polymer conetworks (APCNs) are reported as fluorescent ratiometric pH sensors. The thin, freestanding APCN membranes composed of one hydrophilic and one hydrophobic polymer provide an optically transparent, flexible, and stable ideal matrix that enables contact between dye and aqueous environment. An active ester-based conjugation approach results in a highly homogeneous and stable pyranine modification of the APCN's hydrophilic phase. This concept effectively solves the leaching challenge for pyranine without compromising its functionality, which is demonstrated by ratiometric pH detection in the range of pH 5-9.

Controlled formation of chitosan particles by a clock reaction.

Clock reactions allow precise control of chemical composition in the time domain. Such nonlinear chemical systems have recently been introduced to mimic the self-assembly pathways common in living organisms. Here, we demonstrate the use of a clock reaction to trigger the formation of polymeric nanoparticles. By adjusting the delay of a formaldehyde clock reaction, we controlled the precipitation of chitosan to form particles with sizes tunable in a wide range (from about 200 to 600 nm diameter). The chemical structure of chitosan was not significantly perturbed by the clock reagents.

Sensor Based on Aptamer Folding to Detect Low-Molecular Weight Analytes.

Aptamers have emerged as promising biorecognition elements in the development of biosensors. The present work focuses on the application of quartz crystal microbalance with dissipation monitoring (QCM-D) for the enantioselective detection of a low molecular weight target molecule (less than 200 Da) by aptamer-based sensors. While QCM-D is a powerful technique for label-free, real-time characterization and quantification of molecular interactions at interfaces, the detection of small molecules interacting with immobilized receptors still remains a challenge. In the present study, we take advantage of the aptamer conformational changes upon the target binding that induces displacement of water acoustically coupled to the sensing layer. As a consequence, this phenomenon leads to a significant enhancement of the detection signal. The methodology is exemplified with the enantioselective recognition of a low molecular weight model compound, L-tyrosinamide (L-Tym). QCM-D monitoring of L-Tym interaction with the aptamer monolayer leads to an appreciable signal that can be further exploited for analytical purposes or thermodynamics studies. Furthermore, in situ combination of QCM-D with spectroscopic ellipsometry unambiguously demonstrates that the conformational change induces a nanometric decrease of the aptamer monolayer thickness. Since QCM-D is sensitive to the whole mass of the sensing layer including water that is acoustically coupled, a decrease in thickness of the highly hydrated aptamer layer induces a sizable release of water that can be easily detected by QCM-D.

Oscillating Reactions Meet Polymers at Interfaces.

Chemo-mechanical phenomena, including oscillations and peristaltic motions, are widespread in nature-just think of heartbeats-thanks to the ability of living organisms to convert directly chemical energy into mechanical work. Their imitation with artificial systems is still an open challenge. Chemical clocks and oscillators (such as the popular Belousov-Zhabotinsky (BZ) reaction) are reaction networks characterized by the emergence of peculiar spatiotemporal dynamics. Their application to polymers at interfaces (grafted chains, layer-by-layer assemblies, and polymer brushes) offers great opportunities for developing novel smart biomimetic materials. Despite the wide field of potential applications, limited research has been carried out so far. Here, we aim to showcase the state-of-the-art of this fascinating field of investigation, highlighting the potential for future developments and providing a personal outlook.

Scalable Biosynthesis of Melanin by the Basidiomycete Armillaria cepistipes.

Natural melanin features many interesting properties, including the ability to shield electromagnetic radiation, the ability to act as scavenger for radical and reactive oxygen species and the capacity to chelate different metal ions. For these reasons, melanin is becoming increasingly relevant for the development of functional materials with potential applications in cosmetics, drug delivery, and water purification. However, the extraction and purification of melanin from conventional sources (e.g., sepia ink, hair, and wool) is inefficient and not easily scalable, hence diverting its technological applications. Some fungal species, especially wood-decay basidiomycetes, can be regarded as promising sources of melanin. In the present study, we screened different fungi in regard to their melanin-biosynthesis abilities using l-tyrosine as a precursor, and we found that an Armillaria cepistipes strain (Empa 655) produced the highest yield of melanin (27.98 g L-1). Physicochemical characterization of the obtained fungal melanin revealed a typical eumelanin structure. The method for the biosynthesis of fungal melanin we propose is efficient, scalable, and sustainable and has the potential to provide support for further technological exploitation.

Preparation of a Sepia Melanin and Poly(ethylene-alt-maleic Anhydride) Hybrid Material as an Adsorbent for Water Purification.

Meeting the increasing demand of clean water requires the development of novel efficient adsorbent materials for the removal of organic pollutants. In this context the use of natural, renewable sources is of special relevance and sepia melanin, thanks to its ability to bind a variety of organic and inorganic species, has already attracted interest for water purification. Here we describe the synthesis of a material obtained by the combination of sepia melanin and poly(ethylene-alt-maleic anhydride) (P(E-alt-MA)). Compared to sepia melanin, the resulting hybrid displays a high and fast adsorption efficiency towards methylene blue (a common industrial dye) for a wide pH range (from pH 2 to 12) and under high ionic strength conditions. It is easily recovered after use and can be reused up to three times. Given the wide availability of sepia melanin and P(E-alt-MA), the synthesis of our hybrid is simple and affordable, making it suitable for industrial water purification purposes.