Detection of Zn2+, Cd2+, Hg2+, and Pb2+ ions through label-free poly-L-glutamic acid

Synthesis and fluorescent property of carboxymethyl chitosan with different degrees of carboxymethylation and its application for fluorescence turn-on detection of Cd(II) ion

Recently, carboxymethyl chitosan (CMCS) has proved to be an intrinsically fluorescent material with aggregation-induced emission characteristic. In order to elucidate the influence of CMCS's chemical structure and solution behavior on its fluorescent intensity, two series of CMCS with different degrees of carboxymethylation (DCM) are synthesized by adjusting the mass ratio of monochloroacetic acid and sodium hydroxide to chitosan at various reaction temperature and time, and then characterized using Fourier-transform infrared spectroscopy and nuclear magnetic resonance. Their solution behaviors at different pH values are studied via zeta potential and ultraviolet-visible measurements. The data reveal that the isoelectronic point (IEP) of a CMCS decreases with increasing DCM, and all the CMCSs have good water solubility at pH range below their IEPs. Fluorescence spectra indicate that a CMCS shows the highest fluorescent intensity in a slightly acidic environment next to its IEP, and the photoluminescence of a CMCS solution increases significantly after heat treatment above T = 70 °C. Furthermore, we compare for the first time the use of heated CMCS solutions for the fluorescence turn-on detection of cadmium ion in pure and tap water, respectively. The limit of detection is found to be ca. 1 μM for the Cd2+ in pure water.

A fluorescent turn-on sensor for mercury (II) ions in near neutral poly(metharylic acid) solution

The conformational change of poly (methacrylic acid) (PMAA) at various pH values is well studied; however, the application of PMAA in the field of analytical chemistry has been very limited. This investigation takes advantage of the conformational change of PMAA at various pH levels and the conformational change induced by metal ions. By adjusting the pH, thiophene-phenylanilide-acridinium molecules can serve as turn-on sensors for Hg²⁺ ions. In pH 7.4 buffer with PMAA molecules, the sensor is selectively turned on by Hg²⁺ ions to display strong charge shift state (CSH) emission at 560 nm. The intensity shows linear response to the concentration of Hg²⁺ ions between 0.020 mM and 0.151 mM with a detection limit in nanomolar range. The photophysical properties of sensor molecules in PMAA/mercury (II) mixture at near neutral pH are comparable to those in PMAA solution in acidic condition without mercury (II) ions. The effect of pH, temperature, polymer size, and polymer concentration on emission intensity were investigated. The sensor showed excellent percent recovery (98.4 % to 103 %) of spiked mercury (II) ions in real water samples. The sensing mechanism is likely through intrachain and interchain coordination of mercury (II) ions with the carboxyl groups on the side chain of PMAA to induce an extended coil conformation of PMAA. Calculations support the conclusion that the size and geometry of the binding sites formed inside PMAA are suitable to incorporate sensor molecules and enhance the charge shift state emission of sensor molecules.

Peptide-Based Sensing, Logic Computing, and Information Security on the Antimonene Platform

Peptides have higher information density than DNA and equivalent molecular recognition ability and durability. However, there are currently no reports on the comprehensive use of peptides' recognition ability and structural diversity for sensing, logic computing, information coding, and protection. Herein, we, for the first time, demonstrate peptide-based sensing, logic computing, and information security on the antimonene platform. The molecular recognition capability and structural diversity (amino acid sequence) of peptides (Pb²⁺-binding peptide DHHTQQHD as a model) adsorbed on the antimonene universal fluorescence quenching platform were comprehensively utilized to sense targets (Pb²⁺) and give a response (fluorescence turn-on) and then to encode, encrypt, and hide information. Fluorescently labeled peptides used as the recognition probe and the information carrier were quenched and hidden by the large-plane two-dimensional material antimonene and specifically bound by Pb²⁺ as the stego key, resulting in fluorescence recovery. The above interaction and signal change can be considered as a peptide-based sensing and steganographic process to further implement quantitative detection of Pb²⁺, complex logic operation, information coding, encrypting, and hiding using a peptide sequence and the binary conversion of its selectivity. This research provides a basic paradigm for the construction of a molecular sensing and informatization platform and will inspire the development of biopolymer-based molecular information technology (processing, communication, control, security).

Harnessing Peptides against lead pollution and poisoning: Achievements and prospects

Among the broad applicability of peptides in numerous aspects of life and technologies, their interactions with lead (Pb), one of the most harmful substances to the environment and health, are constantly explored. So far, peptides were developed for environmental remediation of Pb-contaminations by various strategies such as hydrogelation and surface display. They were also designed for Pb detection and sensing by electrochemical and fluorescent methods and for modeling natural proteins that involve in mechanisms by which Pb is toxic. This review aims at summarizing selected examples of these applications, manifesting the enormous potential of peptides in the combat against Pb pollution. Nevertheless, the absence of new medicinal treatments against Pb poisoning that are based on peptides is noticeable. An overview of previous achievements utilizing Pb-peptide interactions towards various goals is presented and can be therefore leveraged to construct a useful toolbox for the design of smart peptides as next-generation therapeutics against Pb.

Glutathione-capped Syzygium cumini carbon dot-amalgamated agarose hydrogel film for naked-eye detection of heavy metal ions

Development of a facile and sensitive analytical tool for the detection of heavy metal ions is still a challenging task because of interference from other chemical species. In this work, glutathione (GSH)-capped Syzygium cumini carbon dots (CDs) have been integrated with agarose hydrogel film and used as an amalgamated solid probe for sensing of different metal ions (Pb2+, Fe3+, and Mn2+). The synthesis of a solid sensing platform is based on the electrostatic interactions between GSH-capped Syzygium cumini CDs and agarose hydrogel. The developed hydrogel-based solid probe exhibited good linearities with the concentration ranges of metal ions from 0.005 to 0.075, 0.0075 to 0.1, and 0.0075 to 0.1 mM with detection limits of 1.3, 2.5, and 2.1 μM for Pb2+, Fe3+, and Mn2+ ions, respectively.