Sensing of mercury and silver ions using branched Au nanoparticles prepared by hyperbranched polyethylenimine fabricated and capped AuNPs seeds

Branched AuNPs usually have two or more local surface plasmon resonance (LSPR) absorption bands due to their structural anisotropy, and the LSPR performance is more sensitive to the changes of environmental refractive index than that of spherical AuNPs. The design and preparation of branched AuNPs as colorimetric probes is expected to improve the selectivity and sensitivity of detection of targets. In this paper, branched AuNPs were innovatively synthesized via hyperbranched polyethylenimine (HPEI) fabricated and capped AuNPs as seeds and cetyltrimethylammonium bromide (CTAB) as template agent. The branched AuNPs were characterized by TEM, DLS, zeta potentials and UV-vis spectra. Using the branched AuNPs as a colorimetric probe, the detection system for Hg²⁺and Ag⁺showed bright color changes from blue to orange and blue to green based on the morphological evolution of branched AuNPs. The branched AuNPs could selectively detect Hg²⁺and Ag⁺at concentrations as low as 77 and 140 nM, respectively. Moreover, this unusual colorimetric method has been successfully used in real water samples and has great potential as a simple, rapid, sensitive and selective method for the detection of Hg²⁺and Ag⁺.

Laccase-immobilized dendritic nanofibrous membranes as a novel approach towards the removal of bisphenol A

Laccase enzymes from Rhus vernificera were covalently bound on hyperbranched polyethyleneimine/polyethersulfone (HPEI/PES) electrospun nanofibrous membranes and used for the removal of bisphenol A (BPA) from water. The laccase enzyme was anchored on the dendritic membranes through the abundant peripheral amine groups on the HPEI using glutaraldehyde as a crosslinker. The membranes were characterized with attenuated total reflectance-Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) and ultraviolet-visible spectroscopy and correlative light and electron microscopy (CLEM). Furthermore, contact-angle analyses, pure water flux measurements and rejection analyses were carried out. CLEM showed that the enzymes were uniformly dispersed on the nanofibres while SEM analysis revealed that the nanofibres had an average diameter of 354 ± 37 nm. EDS showed the presence of Cu, which is the active entity in laccase enzymes. The laccase-modified membranes were hydrophilic (50°-53° contact angle) and exhibited high BPA rejection of 89.6% as compared to the 52.4% demonstrated by pristine PES. The laccase-modified membranes also maintained a constant permeate flux (7.07 ± 5.54 L/m² h) throughout the filtration process. Recyclability studies indicated that the membranes still maintained a high BPA removal of up to 79% even after four filtration cycles.