Determination of binding parameters between lysozyme and its aptamer by frontal analysis continuous microchip electrophoresis (FACMCE)

Swelling-Induced Information Camouflage and Optical Decryption on a Transparent Recoverable Hydrogel Surface

Information camouflage and decryption on hydrogels rely on chemical stimuli such as pH, ultraviolet light, and chemical reactions, in which the cyclability is limited. This work develops a simpler yet effective physical method that can achieve the information camouflage on hydrogels by water swelling and decrypt it under white light. The information camouflage and decryption can proceed with unlimited cycles. To successfully reach the information camouflage, the hydrogel is synthesized with the water swelling ratio in weight as high as 250, which is enabled by the strong electrostatic repulsion of cationic moieties inside the network. At such a high water-swollen state, the hydrogel is still robust and elastic, which provides a mechanical basis to maintain the stability of the camouflaged information. We write information on the hydrogel surface by laser cutting. Upon immersing the hydrogel in water, the high swelling results in huge expansion of the hydrogel, thus inducing the information camouflage. With exposure to white light, the information can be decrypted and becomes visible again. Our protocol utilizes a simple physical process to enable the camouflage and decryption of complex information, which might open an alternative pathway for the development of hydrogel materials in the application of informatics.

Out-of-Equilibrium Measurements of Kinetic Constants on a Biosensor

Conventional measurements of kinetic constants currently in use are performed at equilibrium and may require large volumes, especially at a low association rate constant k_on. If the measurements are made out of equilibrium, the values obtained may be biased by dilution of the sample with the flow of the running buffer. In some applications, the available sample volume can be very critical and requires the development of tools to measure kinetic constants with low volumes. In this paper, by combining an experimental, numerical and modeling approach, we propose a surface plasmon resonance-based method that relies on an out-of-equilibrium measurement using the effect of dilution by flow to its advantage. This new method should have a significant impact in biochemistry and medical research.

Smart Responsive Luminescent Aptamer-Functionalized Covalent Organic Framework Hydrogel for High-Resolution Visualization and Security Protection of Latent Fingerprints

Covalent organic frameworks (COFs) have been proposed as alternative candidates for "smart" materials due to their ordered π-columnar structures. However, it remains a challenge to develop external-stimuli-responsive luminescent COFs for confidential information protection. Here, we have designed and synthesized a water-dispersible and smart responsive luminescent carboxymethyl cellulose-COF hydrogel encapsulated 5-(dimethylamino)-N,N-bis (pyridin-2-ylmethyl) napthalene-1-sulfonamide, named CMC-COF-LZU1⊃DPYNS, for latent fingerprint imaging and encryption. We show that the fluorescence of CMC-COF-LZU1⊃DPYNS is reversibly switchable upon addition of Cu²⁺/H₂O. This effect endows potential applications of tunable luminescent COFs based hydrogel as an invisible security probe for imaging, recording, storage, and security of latent fingerprint information. It is shown that the latent fingerprint information incubated by the aptamer-functionalized CMC-COF-LZU1⊃DPYNS hydrogel is invisible in the presence of Cu²⁺, but three levels of fingerprint features with high-resolution patterns could be readable upon addition of H₂O under UV light. The design strategy provides a promising platform for the development of smart responsive luminescent COFs and their detection and protection of valuable latent fingerprint information.

Capillary electrophoresis-based approaches for the study of affinity interactions combined with various sensitive and nontraditional detection techniques

Nearly all processes in living organisms are controlled and regulated by the synergy of many biomolecule interactions involving proteins, peptides, nucleic acids, nucleotides, saccharides, and small molecular weight ligands. There is growing interest in understanding them, not only for the purposes of interactomics as an essential part of system biology, but also in their further elucidation in disease pathology, diagnostics, and treatment. The necessity of detailed investigation of these interactions leads to the requirement of laboratory methods characterized by high efficiency and sensitivity. As a result, many instrumental approaches differing in their fundamental principles have been developed, including those based on capillary electrophoresis. Although capillary electrophoresis offers numerous advantages for such studies, it still has one serious limitation, its poor concentration sensitivity with the most commonly used detection method-ultraviolet-visible spectrometry. However, coupling capillary electrophoresis with a more sensitive detector fulfils the above-mentioned requirement. In this review, capillary electrophoresis combined with fluorescence, mass spectrometry, and several nontraditional detection techniques in affinity interaction studies are summarized and discussed, together with the possibility of conducting these measurements in microchip format.

Sensitive assay of Escherichia coli in food samples by microchip capillary electrophoresis based on specific aptamer binding strategy

The rapid and cost-effective detection of bacteria is of great importance to ensuring food safety, preventing food poisoning. Herein, we developed a sensitive detection of Escherichia coli (E. coli) using bacteria-specific aptamer in conjunction with microchip capillary electrophoresis-coupled laser-induced fluorescence (MCE-LIF). Based on the differences between charge to mass ratios of free aptamer and bacteria-aptamer complex, which influence their electrophoretic mobilities, the separation of free aptamers and complex peaks by MCE could be achieved. Under optimal conditions, the sensitive detection of E. coli was achieved with a detection limit of 3.7 × 10² CFU mL^-1, at a fast response of 135 s and a short detection length of 2.3 cm. The spiked recovery experiment showed that E. coli could be recovered from spiked drinking water and milk samples with recovery rates of 94.7% and 92.8%, respectively. This work demonstrates that the established detection strategy can be a useful tool for the detection and/or monitoring of E. coli in food and environment.

Reversible Response of Luminescent Terbium(III)-Nanocellulose Hydrogels to Anions for Latent Fingerprint Detection and Encryption

Fingerprint fluorescence imaging has become one of the most prominent technologies in the field of forensic medicine, but it seldom considers the security protection of detection information, which is of great importance in modern society. Herein we demonstrate that luminescent Tb^III -carboxymethyl cellulose (CMC) complex binding aptamer hydrogels that are reversibly responsive to ClO^- /SCN^- can be used for the selective detection, protection, and storage of fingerprint information. The imaging information of the fingerprint can be quenched and recovered by ClO^- /SCN^- regulation, respectively, resulting in reversible on/off conversion of the luminescence signals for the encryption and decryption of multiple levels of information. The present study opens new avenues for multilevel imaging, data recording, and security protection of fingerprint information with tunable fluorescent hydrogels.

A sensitive assay based on specific aptamer binding for the detection of Salmonella enterica serovar Typhimurium in milk samples by microchip capillary electrophoresis

The detection of Salmonella enterica serovar Typhimurium (S. Typhimurium) is very important for the prevention of food poisoning and other infectious diseases. Here we reported a simple and sensitive strategy to test S. Typhimurium by microchip capillary electrophoresis couple with laser-induced fluorescence (MCE-LIF) based on the specific reaction between the bacterium and corresponding aptamers. Based on the differences in charge to mass ratio between bacteria-aptamer complexes and free aptamers, a separation of the complexes and free aptamers could be obtained by MCE. The optimal parameters of the specific reaction including fluorescent dye concentration, Mg²⁺ concentration, incubation time, and pH of incubation solution were carefully investigated. Meanwhile, a non-specific DNA was exploited as a contrast for the detection of S. Typhimurium. Under the optimal conditions, a rapid separation of the bacteria-aptamer complex and free aptamers was achieved within 135 s with a limit of detection (S/N = 3) of 3.37 × 10² CFU mL^-1. This method was applied for the detection of S. Typhimurium in fresh milk samples and a recovery rate of 95.8% was obtained. The experimental results indicated that the specific aptamers are of enough biostability and the established method could be used to analyze S. Typhimurium in foods.

Effect of dendrimer generation on the interactions between human serum albumin and dendrigraft polylysines

This work aims at studying the interaction between human serum albumin and different generations of dendrigraft poly-L-lysine (DGL) in physiological conditions. The binding constants and stoichiometry of the interaction were successfully determined using frontal analysis continuous capillary electrophoresis. The effect of generation on the interaction was evaluated for the five first generations of DGL. An increase of the binding constant accompanied with a decrease of the HSA:DGL (1:n) stoichiometry and a decrease of the cooperativity with dendrimer generation was observed. These findings were in good agreement with the increase of ligand (DGL) size, the increase of electrostatic ligand-ligand repulsion, and the localization of two negatively charged interaction sites on the HSA. The effect of the ligand topology (linear vs dendrigraft) on the HSA interaction revealed that linear poly(L-lysine) leads to much lower stoichiometry compared to DGL of similar molar mass due to much higher flexibility and contour length.

Near-infrared-light-mediated imaging of latent fingerprints based on molecular recognition

Photoluminescence is one of the most sensitive techniques for fingerprint detection, but it also suffers from background fluorescence and selectivity at the expense of generality. The method described herein integrates the advantages of near-infrared-light-mediated imaging and molecular recognition. In principle, upconversion nanoparticles (UCNPs) functionalized with a lysozyme-binding aptamer were used to detect fingerprints through recognizing lysozyme in the fingerprint ridges. UCNPs possess the ability to suppress background fluorescence and make it possible for fingerprint imaging on problematic surfaces. Lysozyme, a universal compound in fingerprints, was chosen as the target, thus simultaneously meeting the selectivity and generality criteria in photoluminescence approaches. Fingerprints on different surfaces and from different people were detected successfully. This strategy was used to detect fingerprints with cocaine powder by using UCNPs functionalized with a cocaine-binding aptamer.

Recent developments in capillary and microchip electroseparations of peptides (2011-2013)

The review presents a comprehensive survey of recent developments and applications of capillary and microchip electroseparation methods (zone electrophoresis, ITP, IEF, affinity electrophoresis, EKC, and electrochromatography) for analysis, isolation, purification, and physicochemical and biochemical characterization of peptides. Advances in the investigation of electromigration properties of peptides, in the methodology of their analysis, including sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, as well as in detection of peptides, are presented. New developments in particular CE and CEC modes are reported and several types of their applications to peptide analysis are described: conventional qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC techniques to provide relevant physicochemical characteristics of peptides are demonstrated.

Aptamer-conjugated nanoparticles: preservation of targeting functionality demonstrated by microchip electrophoresis in frontal mode

Aptamer-conjugated nanoparticles (Apt-NPs) are increasingly being developed for biomedical purposes and especially for diagnosis and therapy. However, there is no quantitative study of the targeting functionality of such grafted aptamers compared with free aptamers. Thus, we report the first determination of binding parameters for Apt-NP/target complexes, thanks to a continuous frontal analysis in a microchip electrophoresis format (named FACMCE), based on a methodology previously developed by our group. As a model system, the targeting ability of a lysozyme-binding aptamer conjugated to fluorescent maghemite nanoparticles was evaluated and showed evidence that the conjugation does not alter the affinity of this aptamer.

RNA aptamer evolution: two decades of SELEction

Aptamers are small non-coding RNAs capable of recognizing, with high specificity and affinity, a wide variety of molecules in a manner that resembles antibodies. This class of nucleic acids is the resulting product of applying a well-established screening method known as SELEX. First developed in 1990, the SELEX process has become a powerful tool to select structured oligonucleotides for the recognition of targets, starting with small molecules, going through protein complexes until whole cells. SELEX has also evolved along with new technologies positioning itself as an alternative in the design of a new class of therapeutic agents in modern molecular medicine. This review is an historical follow-up of SELEX method over the two decades since its first appearance.