A new cysteine-based methacrylic monomer (CysMA) was conveniently synthesized via selective thia-Michael addition of a commercially available methacrylate-acrylate precursor in aqueous solution without recourse to protecting group chemistry. Poly(cysteine methacrylate) (PCysMA) brushes were grown from the surface of silicon wafers by atom-transfer radical polymerization. Brush thicknesses of ca. 27 nm were achieved within 270 min at 20 °C. Each CysMA residue comprises a primary amine and a carboxylic acid. Surface zeta potential and atomic force microscopy (AFM) studies of the pH-responsive PCysMA brushes confirm that they are highly extended either below pH 2 or above pH 9.5, since they possess either cationic or anionic character, respectively. At intermediate pH, PCysMA brushes are zwitterionic. At physiological pH, they exhibit excellent resistance to biofouling and negligible cytotoxicity. PCysMA brushes undergo photodegradation: AFM topographical imaging indicates significant mass loss from the brush layer, while XPS studies confirm that exposure to UV radiation produces surface aldehyde sites that can be subsequently derivatized with amines. UV exposure using a photomask yielded sharp, well-defined micropatterned PCysMA brushes functionalized with aldehyde groups that enable conjugation to green fluorescent protein (GFP). Nanopatterned PCysMA brushes were obtained using interference lithography, and confocal microscopy again confirmed the selective conjugation of GFP. Finally, PCysMA undergoes complex base-catalyzed degradation in alkaline solution, leading to the elimination of several small molecules. However, good long-term chemical stability was observed when PCysMA brushes were immersed in aqueous solution at physiological pH.

Single-atom catalysts (SACs) are becoming a hot research topic owing to their unique characteristics of maximum specific activity and atomic utilization. Herein, we proposed a new single atom nanozyme (SAN) based on single Fe atoms anchor on N-doped carbons supported on carbon nanotube (CNT/FeNC). The CNT/FeNC with robust atomic Fe-N x moieties has been synthesised, showing superior peroxidase-like activity. Furthermore, the CNT/FeNC was used as the signal element in a series of paper-based bioassays for ultrasensitive detection of H 2 O 2 , glucose, and ascorbic acid. The SAN provides a new type of signal element for developing various biosensing techniques.

This paper describes detailed studies on the controlled synthesis of poly[2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium hydroxide (polyMEDSAH) from initiator-modified gold surfaces and the properties of these brushes as a function of grafting density and thickness. Improved control over polymerization was achieved by preforming the catalytically active complex to ensure that the monomers did not coordinate to the catalyst. We observed an intriguing transition thickness (h crit ) in which the polyMEDSAH brushes switched from hydrophilic to hydrophobic due to the strong inter-and intrachain associations. We studied this transition as a function of the rate of polymerization and grafting density and found that both factors strongly influence the value of h crit . Faster grown polyMEDSAH brushes have higher h crit values, and brushes grown from higher grafting density have higher h crit value. These observations suggest that the h crit is governed by the density of the brushes, the polymer chain length, and the degree of alignment. Furthermore, the inter-or intrachain associations can be reversed by increasing the temperature, leading to a hydrophobic to hydrophilic switch, where the magnitude of the switching is governed by the grafting density.

This article describes the aqueous atom transfer radical polymerization synthesis of poly(3-sulfopropylmethacrylate) brushes onto gold and Si/SiO2 surfaces in a controlled manner. The effect of Cu(I)/Cu(II) ratio was examined, and a quartz crystal microbalance was used to study the kinetics of the brush synthesis. The synthesized brushes displayed a thickness from a few nanometers to several hundred nanometers and were characterized using atomic force microscopy, ellipsometry, Fourier transform infrared spectroscopy (FTIR), contact angle measurements, and X-ray photoelectron spectroscopy (XPS). The as-synthesized sulfonate brushes had very good ion-exchange properties for the ions tested in this study, i.e., Na+, K+, Cu2+, and Ag+. FTIR and XPS show that the metal ions are coordinating to sulfonate moieties inside the brushes. The brushes were easily loaded with silver ions, and the effect of silver ion concentration on silver loading of the brush was examined. The silver-loaded brushes were shown to be antibacterial toward both gram negative and gram positive bacteria. The silver leaching was studied through leaching experiments into water, NaNO3, and NaCl (physiological medium). The results from these leaching experiments are compared and discussed in the article.